TY - CONF
AB - Algorithms for discrete energy minimization play a fundamental role for low-level vision. Known techniques include graph cuts, belief propagation (BP) and recently introduced tree-reweighted message passing (TRW). So far, the standard benchmark for their comparison has been a 4-connected grid-graph arising in pixel-labelling stereo. This minimization problem, however, has been largely solved: recent work shows that for many scenes TRW finds the global optimum. Furthermore, it is known that a 4-connecled grid-graph is a poor stereo model since it does not take occlusions into account. We propose the problem of stereo with occlusions as a new test bed for minimization algorithms. This is a more challenging graph since it has much larger connectivity, and it also serves as a better stereo model. An attractive feature of this problem is that increased connectivity does not result in increased complexity of message passing algorithms. Indeed, one contribution of this paper is to show that sophisticated implementations of BP and TRW have the same time and memory complexity as that of 4-connecled grid-graph stereo. The main conclusion of our experimental study is that for our problem graph cut outperforms both TRW and BP considerably. TRW achieves consistently a lower energy than BP. However, as connectivity increases the speed of convergence of TRW becomes slower. Unlike 4-connected grids, the difference between the energy of the best optimization method and the lower bound of TRW appears significant. This shows the hardness of the problem and motivates future research.
AU - Vladimir Kolmogorov
AU - Rother, Carsten
ID - 3184
TI - Comparison of energy minimization algorithms for highly connected graphs
VL - 3952 LNCS
ER -
TY - JOUR
AB - This paper describes models and algorithms for the real-time segmentation of foreground from background layers in stereo video sequences. Automatic separation of layers from color/contrast or from stereo alone is known to be error-prone. Here, color, contrast, and stereo matching information are fused to infer layers accurately and efficiently. The first algorithm, Layered Dynamic Programming (LDP), solves stereo in an extended six-state space that represents both foreground/background layers and occluded regions. The stereo-match likelihood is then fused with a contrast-sensitive color model that is learned on-the-fly and stereo disparities are obtained by dynamic programming. The second algorithm, Layered Graph Cut (LGC), does not directly solve stereo. Instead, the stereo match likelihood is marginalized over disparities to evaluate foreground and background hypotheses and then fused with a contrast-sensitive color model like the one used in LDP. Segmentation is solved efficiently by ternary graph cut. Both algorithms are evaluated with respect to ground truth data and found to have similar performance, substantially better than either stereo or color/contrast alone. However, their characteristics with respect to computational efficiency are rather different. The algorithms are demonstrated in the application of background substitution and shown to give good quality composite video output.
AU - Vladimir Kolmogorov
AU - Criminisi, Antonio
AU - Blake, Andrew
AU - Cross, Geoffrey
AU - Rother, Carsten
ID - 3185
IS - 9
JF - IEEE Transactions on Pattern Analysis and Machine Intelligence
TI - Probabilistic fusion of stereo with color and contrast for bilayer segmentation
VL - 28
ER -
TY - CONF
AB - We introduce a new approach to modelling gradient flows of contours and surfaces. While standard variational methods (e.g. level sets) compute local interface motion in a differential fashion by estimating local contour velocity via energy derivatives, we propose to solve surface evolution PDEs by explicitly estimating integral motion of the whole surface. We formulate an optimization problem directly based on an integral characterization of gradient flow as an infinitesimal move of the (whole) surface giving the largest energy decrease among all moves of equal size. We show that this problem can be efficiently solved using recent advances in algorithms for global hypersurface optimization [4, 2, 11]. In particular, we employ the geo-cuts method [4] that uses ideas from integral geometry to represent continuous surfaces as cuts on discrete graphs. The resulting interface evolution algorithm is validated on some 2D and 3D examples similar to typical demonstrations of level-set methods. Our method can compute gradient flows of hypersurfaces with respect to a fairly general class of continuous functional and it is flexible with respect to distance metrics on the space of contours/surfaces. Preliminary tests for standard L2 distance metric demonstrate numerical stability, topological changes and an absence of any oscillatory motion.
AU - Boykov, Yuri
AU - Vladimir Kolmogorov
AU - Cremers, Daniel
AU - Delong, Andrew
ID - 3186
TI - An integral solution to surface evolution PDEs via geo cuts
VL - 3953
ER -
TY - CONF
AB - We introduce the term cosegmentation which denotes the task of segmenting simultaneously the common parts of an image pair. A generative model for cosegmentation is presented. Inference in the model leads to minimizing an energy with an MRF term encoding spatial coherency and a global constraint which attempts to match the appearance histograms of the common parts. This energy has not been proposed previously and its optimization is challenging and NP-hard. For this problem a novel optimization scheme which we call trust region graph cuts is presented. We demonstrate that this framework has the potential to improve a wide range of research: Object driven image retrieval, video tracking and segmentation, and interactive image editing. The power of the framework lies in its generality, the common part can be a rigid/non-rigid object (or scene), observed from different viewpoints or even similar objects of the same class.
AU - Rother, Carsten
AU - Vladimir Kolmogorov
AU - Minka, Thomas P
AU - Blake, Andrew
ID - 3188
TI - Cosegmentation of image pairs by histogram matching - Incorporating a global constraint into MRFs
ER -
TY - CONF
AB - This paper presents an algorithm capable of real-time separation of foreground from background in monocular video sequences. Automatic segmentation of layers from colour/contrast or from motion alone is known to be error-prone. Here motion, colour and contrast cues are probabilistically fused together with spatial and temporal priors to infer layers accurately and efficiently. Central to our algorithm is the fact that pixel velocities are not needed, thus removing the need for optical flow estimation, with its tendency to error and computational expense. Instead, an efficient motion vs non-motion classifier is trained to operate directly and jointly on intensity-change and contrast. Its output is then fused with colour information. The prior on segmentation is represented by a second order, temporal, Hidden Markov Model, together with a spatial MRF favouring coherence except where contrast is high. Finally, accurate layer segmentation and explicit occlusion detection are efficiently achieved by binary graph cut. The segmentation accuracy of the proposed algorithm is quantitatively evaluated with respect to existing ground-truth data and found to be comparable to the accuracy of a state of the art stereo segmentation algorithm. Fore-ground/background segmentation is demonstrated in the application of live background substitution and shown to generate convincingly good quality composite video.
AU - Criminisi, Antonio
AU - Cross, Geoffrey
AU - Blake, Andrew
AU - Vladimir Kolmogorov
ID - 3189
TI - Bilayer segmentation of live video
VL - 1
ER -
TY - JOUR
AB - Algorithms for discrete energy minimization are of fundamental importance in computer vision. In this paper, we focus on the recent technique proposed by Wainwright et al. (Nov. 2005)- tree-reweighted max-product message passing (TRW). It was inspired by the problem of maximizing a lower bound on the energy. However, the algorithm is not guaranteed to increase this bound - it may actually go down. In addition, TRW does not always converge. We develop a modification of this algorithm which we call sequential tree-reweighted message passing. Its main property is that the bound is guaranteed not to decrease. We also give a weak tree agreement condition which characterizes local maxima of the bound with respect to TRW algorithms. We prove that our algorithm has a limit point that achieves weak tree agreement. Finally, we show that, our algorithm requires half as much memory as traditional message passing approaches. Experimental results demonstrate that on certain synthetic and real problems, our algorithm outperforms both the ordinary belief propagation and tree-reweighted algorithm in (M. J. Wainwright, et al., Nov. 2005). In addition, on stereo problems with Potts interactions, we obtain a lower energy than graph cuts.
AU - Vladimir Kolmogorov
ID - 3190
IS - 10
JF - IEEE Transactions on Pattern Analysis and Machine Intelligence
TI - Convergent tree reweighted message passing for energy minimization
VL - 28
ER -
TY - CONF
AB - The Feistel-network is a popular structure underlying many block-ciphers where the cipher is constructed from many simpler rounds, each defined by some function which is derived from the secret key.
Luby and Rackoff showed that the three-round Feistel-network – each round instantiated with a pseudorandom function secure against adaptive chosen plaintext attacks (CPA) – is a CPA secure pseudorandom permutation, thus giving some confidence in the soundness of using a Feistel-network to design block-ciphers.
But the round functions used in actual block-ciphers are – for efficiency reasons – far from being pseudorandom. We investigate the security of the Feistel-network against CPA distinguishers when the only security guarantee we have for the round functions is that they are secure against non-adaptive chosen plaintext attacks (nCPA). We show that in the information-theoretic setting, four rounds with nCPA secure round functions are sufficient (and necessary) to get a CPA secure permutation. Unfortunately, this result does not translate into the more interesting pseudorandom setting. In fact, under the so-called Inverse Decisional Diffie-Hellman assumption the Feistel-network with four rounds, each instantiated with a nCPA secure pseudorandom function, is in general not a CPA secure pseudorandom permutation.
AU - Maurer, Ueli M
AU - Oswald, Yvonne A
AU - Krzysztof Pietrzak
AU - Sjödin, Johan
ID - 3214
TI - Luby Rackoff ciphers from weak round functions
VL - 4004
ER -
TY - CONF
AB - Most cryptographic primitives such as encryption, authentication or secret sharing require randomness. Usually one assumes that perfect randomness is available, but those primitives might also be realized under weaker assumptions. In this work we continue the study of building secure cryptographic primitives from imperfect random sources initiated by Dodis and Spencer (FOCS’02). Their main result shows that there exists a (high-entropy) source of randomness allowing for perfect encryption of a bit, and yet from which one cannot extract even a single weakly random bit, separating encryption from extraction. Our main result separates encryption from 2-out-2 secret sharing (both in the information-theoretic and in the computational settings): any source which can be used to achieve one-bit encryption also can be used for 2-out-2 secret sharing of one bit, but the converse is false, even for high-entropy sources. Therefore, possibility of extraction strictly implies encryption, which in turn strictly implies 2-out-2 secret sharing.
AU - Dodis, Yevgeniy
AU - Krzysztof Pietrzak
AU - Przydatek, Bartosz
ID - 3215
TI - Separating sources for encryption and secret sharing
VL - 3876
ER -
TY - CONF
AB - We prove a new upper bound on the advantage of any adversary for distinguishing the encrypted CBC-MAC (EMAC) based on random permutations from a random function. Our proof uses techniques recently introduced in [BPR05], which again were inspired by [DGH + 04].
The bound we prove is tight — in the sense that it matches the advantage of known attacks up to a constant factor — for a wide range of the parameters: let n denote the block-size, q the number of queries the adversary is allowed to make and ℓ an upper bound on the length (i.e. number of blocks) of the messages, then for ℓ ≤ 2 n/8 and q≥ł2 the advantage is in the order of q 2/2 n (and in particular independent of ℓ). This improves on the previous bound of q 2ℓΘ(1/ln ln ℓ)/2 n from [BPR05] and matches the trivial attack (which thus is basically optimal) where one simply asks random queries until a collision is found.
AU - Krzysztof Pietrzak
ID - 3216
TI - A tight bound for EMAC
VL - 4052
ER -
TY - CONF
AB - To prove that a secure key-agreement protocol exists one must at least show P ≠NP. Moreover any proof that the sequential composition of two non-adaptively secure pseudorandom functions is secure against at least two adaptive queries must falsify the decisional Diffie-Hellman assumption, a standard assumption from public-key cryptography. Hence proving any of this two seemingly unrelated statements would require a significant breakthrough. We show that at least one of the two statements is true.
To our knowledge this gives the first positive cryptographic result (namely that composition implies some weak adaptive security) which holds in Minicrypt, but not in Cryptomania, i.e. under the assumption that one-way functions exist, but public-key cryptography does not.
AU - Krzysztof Pietrzak
ID - 3217
TI - Composition implies adaptive security in minicrypt
VL - 4004
ER -
TY - CHAP
AU - Harald Janovjak
AU - Sawhney, Ravi K
AU - Stark, Martin
AU - Mueller, Daniel J
ID - 3404
T2 - Techniques in Microscopy for Biomedical Applications
TI - Atomic force microscopy
VL - 2
ER -
TY - JOUR
AB - Despite their crucial importance for cellular function, little is known about the folding mechanisms of membrane proteins. Recently details of the folding energy landscape were elucidated by atomic force microscope (AFM)-based single molecule force spectroscopy. Upon unfolding and extraction of individual membrane proteins energy barriers in structural elements such as loops and helices were mapped and quantified with the precision of a few amino acids.
Here we report on the next logical step: controlled refolding of single proteins into the membrane. First individual bacteriorhodopsin monomers were partially unfolded and extracted from the purple membrane by pulling at the C-terminal end with an AFM tip. Then by gradually lowering the tip, the protein was allowed to refold into the membrane while the folding force was recorded.
We discovered that upon refolding certain helices are pulled into the membraneagainst a sizable externalforce of several tens of picoNewton. From the mechanical work, which the helix performs on the AFM cantilever, we derive an upper limit for the Gibbs free folding energy. Subsequent unfolding allowed us to analyze the pattern of unfolding barriers and corroborate that the protein had refolded into the native state.
AU - Kessler, Max
AU - Gottschalk, Kay E
AU - Harald Janovjak
AU - Mueller, Daniel J
AU - Gaub, Hermann
ID - 3413
IS - 2
JF - Journal of Molecular Biology
TI - Bacteriorhodopsin folds into the membrane against an external force
VL - 357
ER -
TY - JOUR
AB - Mechanisms of folding and misfolding of membrane proteins are of interest in cell biology. Recently, we have established single-molecule force spectroscopy to observe directly the stepwise folding of the Na+/H+antiporter NhaA from Escherichia coli in vitro. Here, we improved this approach significantly to track the folding intermediates of asingle NhaA polypeptide forming structural segments such as the Na+-binding site, transmembrane α-helices, and helical pairs. The folding rates of structural segments ranged from 0.31 s−1 to 47 s−1, providing detailed insight into a distinct folding hierarchy of an unfolded polypeptide into the native membrane protein structure. In some cases, however, the folding chain formed stable and kinetically trapped non-native structures, which could be assigned to misfolding events of the antiporter.
AU - Kedrov, Alexej
AU - Harald Janovjak
AU - Ziegler, Christine
AU - Kühlbrandt, Werner
AU - Mueller, Daniel J
ID - 3414
IS - 1
JF - Journal of Molecular Biology
TI - Observing folding pathways and kinetics of a single sodium-proton antiporter from Escherichia coli
VL - 355
ER -
TY - GEN
AU - Harald Janovjak
AU - Kedrov, Alexej
AU - Cisneros, David
AU - Sapra, Tanuj K
AU - Struckmeier, Jens
AU - Mueller, Daniel J
ID - 3415
T2 - Neurobiology of Aging
TI - Imaging and detecting molecular interactions of single membrane proteins
VL - 27
ER -
TY - JOUR
AB - We demonstrate for different protein samples that three-dimensional HNCO and HNCA correlation spectra may be recorded in a few minutes acquisition time using the band-selective excitation short-transient sequences presented here. This opens new perspectives for the NMR structural investigation of unstable protein samples and real-time site-resolved studies of protein kinetics.
AU - Schanda, Paul
AU - Van Melckebeke, Hélène
AU - Brutscher, Bernhard
ID - 8488
IS - 28
JF - Journal of the American Chemical Society
KW - Colloid and Surface Chemistry
KW - Biochemistry
KW - General Chemistry
KW - Catalysis
SN - 0002-7863
TI - Speeding up three-dimensional protein NMR experiments to a few minutes
VL - 128
ER -
TY - JOUR
AB - Structure elucidation of proteins by either NMR or X‐ray crystallography often requires the screening of a large number of samples for promising protein constructs and optimum solution conditions. For large‐scale screening of protein samples in solution, robust methods are needed that allow a rapid assessment of the folding of a polypeptide under diverse sample conditions. Here we present HET‐SOFAST NMR, a highly sensitive new method for semi‐quantitative characterization of the structural compactness and heterogeneity of polypeptide chains in solution. On the basis of one‐dimensional 1H HET‐SOFAST NMR data, obtained on well‐folded, molten globular, partially‐ and completely unfolded proteins, we define empirical thresholds that can be used as quantitative benchmarks for protein compactness. For 15N‐enriched protein samples, two‐dimensional 1H‐15N HET‐SOFAST correlation spectra provide site‐specific information about the structural heterogeneity along the polypeptide chain.
AU - Schanda, Paul
AU - Forge, Vincent
AU - Brutscher, Bernhard
ID - 8489
IS - S1
JF - Magnetic Resonance in Chemistry
SN - 0749-1581
TI - HET-SOFAST NMR for fast detection of structural compactness and heterogeneity along polypeptide chains
VL - 44
ER -
TY - JOUR
AB - We demonstrate the feasibility of recording 1H–15N correlation spectra of proteins in only one second of acquisition time. The experiment combines recently proposed SOFAST-HMQC with Hadamard-type 15N frequency encoding. This allows site-resolved real-time NMR studies of kinetic processes in proteins with an increased time resolution. The sensitivity of the experiment is sufficient to be applicable to a wide range of molecular systems available at millimolar concentration on a high magnetic field spectrometer.
AU - Schanda, Paul
AU - Brutscher, Bernhard
ID - 8490
IS - 2
JF - Journal of Magnetic Resonance
KW - Nuclear and High Energy Physics
KW - Biophysics
KW - Biochemistry
KW - Condensed Matter Physics
SN - 1090-7807
TI - Hadamard frequency-encoded SOFAST-HMQC for ultrafast two-dimensional protein NMR
VL - 178
ER -
TY - JOUR
AU - Kaloshin, Vadim
AU - Saprykina, Maria
ID - 8513
IS - 2
JF - Discrete & Continuous Dynamical Systems - A
SN - 1553-5231
TI - Generic 3-dimensional volume-preserving diffeomorphisms with superexponential growth of number of periodic orbits
VL - 15
ER -
TY - JOUR
AB - We study the extent to which the Hausdorff dimension of a compact subset of an infinite-dimensional Banach space is affected by a typical mapping into a finite-dimensional space. It is possible that the dimension drops under all such mappings, but the amount by which it typically drops is controlled by the ‘thickness exponent’ of the set, which was defined by Hunt and Kaloshin (Nonlinearity12 (1999), 1263–1275). More precisely, let $X$ be a compact subset of a Banach space $B$ with thickness exponent $\tau$ and Hausdorff dimension $d$. Let $M$ be any subspace of the (locally) Lipschitz functions from $B$ to $\mathbb{R}^{m}$ that contains the space of bounded linear functions. We prove that for almost every (in the sense of prevalence) function $f \in M$, the Hausdorff dimension of $f(X)$ is at least $\min\{ m, d / (1 + \tau) \}$. We also prove an analogous result for a certain part of the dimension spectra of Borel probability measures supported on $X$. The factor $1 / (1 + \tau)$ can be improved to $1 / (1 + \tau / 2)$ if $B$ is a Hilbert space. Since dimension cannot increase under a (locally) Lipschitz function, these theorems become dimension preservation results when $\tau = 0$. We conjecture that many of the attractors associated with the evolution equations of mathematical physics have thickness exponent zero. We also discuss the sharpness of our results in the case $\tau > 0$.
AU - OTT, WILLIAM
AU - HUNT, BRIAN
AU - Kaloshin, Vadim
ID - 8514
IS - 3
JF - Ergodic Theory and Dynamical Systems
SN - 0143-3857
TI - The effect of projections on fractal sets and measures in Banach spaces
VL - 26
ER -
TY - CONF
AB - We consider the evolution of a set carried by a space periodic incompressible stochastic flow in a Euclidean space. We
report on three main results obtained in [8, 9, 10] concerning long time behaviour for a typical realization of the stochastic flow. First, at time t most of the particles are at a distance of order √t away from the origin. Moreover, we prove a Central Limit Theorem for the evolution of a measure carried by the flow, which holds for almost every realization of the flow. Second, we show the existence of a zero measure full Hausdorff dimension set of points, which
escape to infinity at a linear rate. Third, in the 2-dimensional case, we study the set of points visited by the original set by time t. Such a set, when scaled down by the factor of t, has a limiting non random shape.
AU - Kaloshin, Vadim
AU - DOLGOPYAT, D.
AU - KORALOV, L.
ID - 8515
SN - 9789812562012
T2 - XIVth International Congress on Mathematical Physics
TI - Long time behaviour of periodic stochastic flows
ER -
TY - JOUR
AB - Phylogenetic relationships between the extinct woolly mammoth (Mammuthus primigenius), and the Asian (Elephas maximus) and African savanna (Loxodonta africana) elephants remain unresolved. Here, we report the sequence of the complete mitochondrial genome (16,842 base pairs) of a woolly mammoth extracted from permafrost-preserved remains from the Pleistocene epoch - the oldest mitochondrial genome sequence determined to date. We demonstrate that well-preserved mitochondrial genome fragments, as long as ∼1,600-1700 base pairs, can be retrieved from pre-Holocene remains of an extinct species. Phylogenetic reconstruction of the Elephantinae clade suggests that M. primigenius and E. maximus are sister species that diverged soon after their common ancestor split from the L. africana lineage. Low nucleotide diversity found between independently determined mitochondrial genomic sequences of woolly mammoths separated geographically and in time suggests that north-eastern Siberia was occupied by a relatively homogeneous population of M. primigenius throughout the late Pleistocene.
AU - Rogaev, Evgeny I
AU - Moliaka, Yuri K
AU - Malyarchuk, Boris A
AU - Fyodor Kondrashov
AU - Derenko, Miroslava V
AU - Chumakov, Ilya M
AU - Grigorenko, Anastasia P
ID - 854
IS - 3
JF - PLoS Biology
TI - Complete mitochondrial genome and phylogeny of pleistocene mammoth Mammuthus primigenius
VL - 4
ER -
TY - CONF
AB - We summarize some current trends in embedded systems design and point out some of their characteristics, such as the chasm between analytical and computational models, and the gap between safety-critical and best-effort engineering practices. We call for a coherent scientific foundation for embedded systems design, and we discuss a few key demands on such a foundation: the need for encompassing several manifestations of heterogeneity, and the need for constructivity in design. We believe that the development of a satisfactory Embedded Systems Design Science provides a timely challenge and opportunity for reinvigorating computer science.
AU - Thomas Henzinger
AU - Sifakis, Joseph
ID - 4431
TI - The embedded systems design challenge
VL - 4085
ER -
TY - CONF
AB - We add freeze quantifiers to the game logic ATL in order to specify real-time objectives for games played on timed structures. We define the semantics of the resulting logic TATL by restricting the players to physically meaningful strategies, which do not prevent time from diverging. We show that TATL can be model checked over timed automaton games. We also specify timed optimization problems for physically meaningful strategies, and we show that for timed automaton games, the optimal answers can be approximated to within any degree of precision.
AU - Thomas Henzinger
AU - Prabhu, Vinayak S
ID - 4432
TI - Timed alternating-time temporal logic
VL - 4202
ER -
TY - CONF
AB - We present an assume-guarantee interface algebra for real-time components. In our formalism a component implements a set of task sequences that share a resource. A component interface consists of an arrival rate function and a latency for each task sequence, and a capacity function for the shared resource. The interface specifies that the component guarantees certain task latencies depending on assumptions about task arrival rates and allocated resource capacities. Our algebra defines compatibility and refinement relations on interfaces. Interface compatibility can be checked on partial designs, even when some component interfaces are yet unknown. In this case interface composition computes as new assumptions the weakest constraints on the unknown components that are necessary to satisfy the specified guarantees. Interface refinement is defined in a way that ensures that compatible interfaces can be refined and implemented independently. Our algebra thus formalizes an interface-based design methodology that supports both the incremental addition of new components and the independent stepwise refinement of existing components. We demonstrate the flexibility and efficiency of the framework through simulation experiments.
AU - Thomas Henzinger
AU - Matic, Slobodan
ID - 4436
TI - An interface algebra for real-time components
ER -
TY - CONF
AB - The synthesis of reactive systems requires the solution of two-player games on graphs with ω-regular objectives. When the objective is specified by a linear temporal logic formula or nondeterministic Büchi automaton, then previous algorithms for solving the game require the construction of an equivalent deterministic automaton. However, determinization for automata on infinite words is extremely complicated, and current implementations fail to produce deterministic automata even for relatively small inputs. We show how to construct, from a given nondeterministic Büchi automaton, an equivalent nondeterministic parity automaton that is good for solving games with objective . The main insight is that a nondeterministic automaton is good for solving games if it fairly simulates the equivalent deterministic automaton. In this way, we omit the determinization step in game solving and reactive synthesis. The fact that our automata are nondeterministic makes them surprisingly simple, amenable to symbolic implementation, and allows an incremental search for winning strategies.
AU - Thomas Henzinger
AU - Piterman, Nir
ID - 4437
TI - Solving games without determinization
VL - 4207
ER -
TY - JOUR
AB - One source of complexity in the μ-calculus is its ability to specify an unbounded number of switches between universal (AX) and existential (EX) branching modes. We therefore study the problems of satisfiability, validity, model checking, and implication for the universal and existential fragments of the μ-calculus, in which only one branching mode is allowed. The universal fragment is rich enough to express most specifications of interest, and therefore improved algorithms are of practical importance. We show that while the satisfiability and validity problems become indeed simpler for the existential and universal fragments, this is, unfortunately, not the case for model checking and implication. We also show the corresponding results for the alternation-free fragment of the μ-calculus, where no alternations between least and greatest fixed points are allowed. Our results imply that efforts to find a polynomial-time model-checking algorithm for the μ-calculus can be replaced by efforts to find such an algorithm for the universal or existential fragment.
AU - Thomas Henzinger
AU - Kupferman, Orna
AU - Majumdar, Ritankar S
ID - 4451
IS - 2
JF - Theoretical Computer Science
TI - On the universal and existential fragments of the mu-calculus
VL - 354
ER -
TY - CONF
AB - We consider the problem if a given program satisfies a specified safety property. Interesting programs have infinite state spaces, with inputs ranging over infinite domains, and for these programs the property checking problem is undecidable. Two broad approaches to property checking are testing and verification. Testing tries to find inputs and executions which demonstrate violations of the property. Verification tries to construct a formal proof which shows that all executions of the program satisfy the property. Testing works best when errors are easy to find, but it is often difficult to achieve sufficient coverage for correct programs. On the other hand, verification methods are most successful when proofs are easy to find, but they are often inefficient at discovering errors. We propose a new algorithm, Synergy, which combines testing and verification. Synergy unifies several ideas from the literature, including counterexample-guided model checking, directed testing, and partition refinement.This paper presents a description of the Synergy algorithm, its theoretical properties, a comparison with related algorithms, and a prototype implementation called Yogi.
AU - Gulavani, Bhargav S
AU - Thomas Henzinger
AU - Kannan, Yamini
AU - Nori, Aditya V
AU - Rajamani, Sriram K
ID - 4523
TI - Synergy: A new algorithm for property checking
ER -
TY - CONF
AB - We designed and implemented a new programming language called Hierarchical Timing Language (HTL) for hard realtime systems. Critical timing constraints are specified within the language,and ensured by the compiler. Programs in HTL are extensible in two dimensions without changing their timing behavior: new program modules can be added, and individual program tasks can be refined. The mechanism supporting time invariance under parallel composition is that different program modules communicate at specified instances of time. Time invariance under refinement is achieved by conservative scheduling of the top level. HTL is a coordination language, in that individual tasks can be implemented in "foreign" languages. As a case study, we present a distributed HTL implementation of an automotive steer-by-wire controller.
AU - Ghosal, Arkadeb
AU - Thomas Henzinger
AU - Iercan, Daniel
AU - Kirsch, Christoph M
AU - Sangiovanni-Vincentelli, Alberto
ID - 4526
TI - A hierarchical coordination language for interacting real-time tasks
ER -
TY - CONF
AB - Computational modeling of biological systems is becoming increasingly common as scientists attempt to understand biological phenomena in their full complexity. Here we distinguish between two types of biological models mathematical and computational - according to their different representations of biological phenomena and their diverse potential. We call the approach of constructing computational models of biological systems executable biology, as it focuses on the design of executable computer algorithms that mimic biological phenomena. We give an overview of the main modeling efforts in this direction, and discuss some of the new challenges that executable biology poses for computer science and biology. We argue that for executable biology to reach its full potential as a mainstream biological technique, formal and algorithmic approaches must be integrated into biological research, driving biology towards a more precise engineering discipline.
AU - Fisher, Jasmin
AU - Thomas Henzinger
ID - 4528
TI - Executable biology
ER -
TY - CONF
AB - A stochastic graph game is played by two players on a game graph with probabilistic transitions. We consider stochastic graph games with ω-regular winning conditions specified as parity objectives. These games lie in NP ∩ coNP. We present a strategy improvement algorithm for stochastic parity games; this is the first non-brute-force algorithm for solving these games. From the strategy improvement algorithm we obtain a randomized subexponential-time algorithm to solve such games.
AU - Krishnendu Chatterjee
AU - Thomas Henzinger
ID - 4538
TI - Strategy improvement and randomized subexponential algorithms for stochastic parity games
VL - 3884
ER -
TY - CONF
AB - Games on graphs with ω-regular objectives provide a model for the control and synthesis of reactive systems. Every ω-regular objective can be decomposed into a safety part and a liveness part. The liveness part ensures that something good happens “eventually.” Two main strengths of the classical, infinite-limit formulation of liveness are robustness (independence from the granularity of transitions) and simplicity (abstraction of complicated time bounds). However, the classical liveness formulation suffers from the drawback that the time until something good happens may be unbounded. A stronger formulation of liveness, so-called finitary liveness, overcomes this drawback, while still retaining robustness and simplicity. Finitary liveness requires that there exists an unknown, fixed bound b such that something good happens within b transitions. While for one-shot liveness (reachability) objectives, classical and finitary liveness coincide, for repeated liveness (Büchi) objectives, the finitary formulation is strictly stronger. In this work we study games with finitary parity and Streett (fairness) objectives. We prove the determinacy of these games, present algorithms for solving these games, and characterize the memory requirements of winning strategies. Our algorithms can be used, for example, for synthesizing controllers that do not let the response time of a system increase without bound.
AU - Krishnendu Chatterjee
AU - Thomas Henzinger
ID - 4539
TI - Finitary winning in omega-regular games
VL - 3920
ER -
TY - CONF
AB - We present a compositional theory of system verification, where specifications assign real-numbered costs to systems. These costs can express a wide variety of quantitative system properties, such as resource consumption, price, or a measure of how well a system satisfies its specification. The theory supports the composition of systems and specifications, and the hiding of variables. Boolean refinement relations are replaced by real-numbered distances between descriptions of a system at different levels of detail. We show that the classical Boolean rules for compositional reasoning have quantitative counterparts in our setting. While our general theory allows costs to be specified by arbitrary cost functions, we also consider a class of linear cost functions, which give rise to an instance of our framework where all operations are computable in polynomial time.
AU - Krishnendu Chatterjee
AU - de Alfaro, Luca
AU - Faella, Marco
AU - Thomas Henzinger
AU - Majumdar, Ritankar S
AU - Stoelinga, Mariëlle
ID - 4549
TI - Compositional quantitative reasoning
ER -
TY - JOUR
AB - In 2-player non-zero-sum games, Nash equilibria capture the options for rational behavior if each player attempts to maximize her payoff. In contrast to classical game theory, we consider lexicographic objectives: first, each player tries to maximize her own payoff, and then, the player tries to minimize the opponent's payoff. Such objectives arise naturally in the verification of systems with multiple components. There, instead of proving that each component satisfies its specification no matter how the other components behave, it sometimes suffices to prove that each component satisfies its specification provided that the other components satisfy their specifications. We say that a Nash equilibrium is secure if it is an equilibrium with respect to the lexicographic objectives of both players. We prove that in graph games with Borel winning conditions, which include the games that arise in verification, there may be several Nash equilibria, but there is always a unique maximal payoff profile of a secure equilibrium. We show how this equilibrium can be computed in the case of ω-regular winning conditions, and we characterize the memory requirements of strategies that achieve the equilibrium.
AU - Krishnendu Chatterjee
AU - Thomas Henzinger
AU - Jurdziński, Marcin
ID - 4550
IS - 1-2
JF - Theoretical Computer Science
TI - Games with secure equilibria
VL - 365
ER -
TY - CONF
AB - We consider Markov decision processes (MDPs) with multiple discounted reward objectives. Such MDPs occur in design problems where one wishes to simultaneously optimize several criteria, for example, latency and power. The possible trade-offs between the different objectives are characterized by the Pareto curve. We show that every Pareto-optimal point can be achieved by a memoryless strategy; however, unlike in the single-objective case, the memoryless strategy may require randomization. Moreover, we show that the Pareto curve can be approximated in polynomial time in the size of the MDP. Additionally, we study the problem if a given value vector is realizable by any strategy, and show that it can be decided in polynomial time; but the question whether it is realizable by a deterministic memoryless strategy is NP-complete. These results provide efficient algorithms for design exploration in MDP models with multiple objectives.
This research was supported in part by the AFOSR MURI grant F49620-00-1-0327, and the NSF grants CCR-0225610, CCR-0234690, and CCR-0427202.
AU - Krishnendu Chatterjee
AU - Majumdar, Ritankar S
AU - Thomas Henzinger
ID - 4551
TI - Markov decision processes with multiple objectives
VL - 3884
ER -
TY - CONF
AB - A concurrent reachability game is a two-player game played on a graph: at each state, the players simultaneously and independently select moves; the two moves determine jointly a probability distribution over the successor states. The objective for player 1 consists in reaching a set of target states; the objective for player 2 is to prevent this, so that the game is zero-sum. Our contributions are two-fold. First, we present a simple proof of the fact that in concurrent reachability games, for all epsilon > 0, memoryless epsilon-optimal strategies exist. A memoryless strategy is independent of the history of plays, and an epsilon-optimal strategy achieves the objective with probability within epsilon of the value of the game. In contrast to previous proofs of this fact, which rely on the limit behavior of discounted games using advanced Puisieux series analysis, our proof is elementary and combinatorial. Second, we present a strategy-improvement (a.k.a. policy-iteration) algorithm for concurrent games with reachability objectives.
AU - Krishnendu Chatterjee
AU - de Alfaro, Luca
AU - Thomas Henzinger
ID - 4552
TI - Strategy improvement for concurrent reachability games
ER -
TY - CONF
AB - Many software model checkers are based on predicate abstraction. If the verification goal depends on pointer structures, the approach does not work well, because it is difficult to find adequate predicate abstractions for the heap. In contrast, shape analysis, which uses graph-based heap abstractions, can provide a compact representation of recursive data structures. We integrate shape analysis into the software model checker Blast. Because shape analysis is expensive, we do not apply it globally. Instead, we ensure that, like predicates, shape graphs are computed and stored locally, only where necessary for proving the verification goal. To achieve this, we extend lazy abstraction refinement, which so far has been used only for predicate abstractions, to three-valued logical structures. This approach does not only increase the precision of model checking, but it also increases the efficiency of shape analysis. We implemented the technique by extending Blast with calls to Tvla.
AU - Beyer, Dirk
AU - Thomas Henzinger
AU - Théoduloz, Grégory
ID - 4574
TI - Lazy shape analysis
VL - 4144
ER -
TY - GEN
AB - Mitchison and Jozsa recently suggested that the "chained-Zeno" counterfactual computation protocol recently proposed by Hosten et al. is counterfactual for only one output of the computer. This claim was based on the existing abstract algebraic definition of counterfactual computation, and indeed according to this definition, their argument is correct. However, a more general definition (physically adequate) for counterfactual computation is implicitly assumed by Hosten et. al. Here we explain in detail why the protocol is counterfactual and how the "history tracking" method of the existing description inadequately represents the physics underlying the protocol. Consequently, we propose a modified definition of counterfactual computation. Finally, we comment on one of the most interesting aspects of the error-correcting protocol.
AU - Hosten, Onur
AU - Rakher, Matthew
AU - Barreiro, Julio
AU - Peters, Nicholas
AU - Kwiat, Paul
ID - 573
TI - Counterfactual computation revisited
ER -
TY - GEN
AB - Vaidman, in a recent article adopts the method of 'quantum weak measurements in pre- and postselected ensembles' to ascertain whether or not the chained-Zeno counterfactual computation scheme proposed by Hosten et al. is counterfactual; which has been the topic of a debate on the definition of counterfactuality. We disagree with his conclusion, which brings up some interesting aspects of quantum weak measurements and some concerns about the way they are interpreted.
AU - Hosten, Onur
AU - Kwiat, Paul
ID - 574
TI - Weak measurements and counterfactual computation
ER -
TY - CONF
AB - Visible light photon counters (VLPCs) and solid-state photomultipliers (SSPMs) are high-efficiency single-photon detectors which have multi-photon counting capability. While both the VLPCs and the SSPMs have inferred internal quantum efficiencies above 93%, the actual measured values for both the detectors were in fact limited to less than 88%, attributed to in-coupling losses. We are currently improving this overall detection efficiency via a) custom anti-reflection coating the detectors and the in-coupling fibers, b) implementing a novel cryogenic design to reduce transmission losses and, c) using low-noise electronics to obtain a better signal-to-noise ratio.
AU - Rangarajan, Radhika
AU - Altepeter, Joseph B
AU - Jeffrey, Evan R
AU - Stoutimore, Micah J
AU - Peters, Nicholas A
AU - Onur Hosten
AU - Kwiat, Paul G
ID - 577
TI - High-efficiency single-photon detectors
VL - 6372
ER -
TY - CONF
AB - A source of single photons allows secure quantum key distribution, in addition, to being a critical resource for linear optics quantum computing. We describe our progress on deterministically creating single photons from spontaneous parametric downconversion, an extension of the Pittman, Jacobs and Franson scheme [Phys. Rev A, v66, 042303 (2002)]. Their idea was to conditionally prepare single photons by measuring one member of a spontaneously emitted photon pair and storing the remaining conditionally prepared photon until a predetermined time, when it would be "deterministically" released from storage. Our approach attempts to improve upon this by recycling the pump pulse in order to decrease the possibility of multiple-pair generation, while maintaining a high probability of producing a single pair. Many of the challenges we discuss are central to other quantum information technologies, including the need for low-loss optical storage, switching and detection, and fast feed-forward control.
AU - Peters, Nicholas A
AU - Arnold, Keith J
AU - VanDevender, Aaron P
AU - Jeffrey, Evan R
AU - Rangarajan, Radhika
AU - Onur Hosten
AU - Barreiro, Julio T
AU - Altepeter, Joseph B
AU - Kwiat, Paul G
ID - 578
TI - Towards a quasi-deterministic single-photon source
VL - 6305
ER -
TY - JOUR
AB - The logic underlying the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to surprising effects. Counterfactual computation constitutes a striking example: the potential outcome of a quantum computation can be inferred, even if the computer is not run 1. Relying on similar arguments to interaction-free measurements 2 (or quantum interrogation3), counterfactual computation is accomplished by putting the computer in a superposition of 'running' and 'not running' states, and then interfering the two histories. Conditional on the as-yet-unknown outcome of the computation, it is sometimes possible to counterfactually infer information about the solution. Here we demonstrate counterfactual computation, implementing Grover's search algorithm with an all-optical approach4. It was believed that the overall probability of such counterfactual inference is intrinsically limited1,5, so that it could not perform better on average than random guesses. However, using a novel 'chained' version of the quantum Zeno effect6, we show how to boost the counterfactual inference probability to unity, thereby beating the random guessing limit. Our methods are general and apply to any physical system, as illustrated by a discussion of trapped-ion systems. Finally, we briefly show that, in certain circumstances, counterfactual computation can eliminate errors induced by decoherence.
AU - Onur Hosten
AU - Rakher, Matthew T
AU - Barreiro, Julio T
AU - Peters, Nicholas A
AU - Kwiat, Paul G
ID - 579
IS - 7079
JF - Nature
TI - Counterfactual quantum computation through quantum interrogation
VL - 439
ER -
TY - CONF
AB - Visible light photon counters (VLPCs) and solid-state photomultipliers (SSPMs) facilitate efficient single-photon detection. We are attempting to improve their efficiency, previously limited to < 88% by coupling losses, via anti-reflection coatings, better electronics and cryogenics.
AU - Rangarajan, Radhika
AU - Peters, Nicholas A
AU - Onur Hosten
AU - Altepeter, Joseph B
AU - Jeffrey, Evan R
AU - Kwiat, Paul G
ID - 583
TI - Improved single-photon detection
ER -
TY - CONF
AB - Often the properties of a single cell are considered as representative for a complete polymer electrolyte fuel cell stack or even a fuel cell system. In some cases this comes close, however, in many real cases differences on several scales become important. Cell interaction phenomena in fuel cell stacks that arise from inequalities between adjacent cells are investigated in detail experimentally. For that, a specialized 2-cell stack with advanced localized diagnostics was developed. The results show that inequalities propagate by electrical coupling, inhomogeneous cell polarization and inducing in-plane current in the common bipolar plate. The effects of the different loss-mechanisms are analyzed and quantified.
AU - Büchi, Felix N.
AU - Freunberger, Stefan Alexander
AU - Santis, Marco
ID - 7326
IS - 1
T2 - ECS Transactions
TI - What is learned beyond the scale of single cells?
VL - 3
ER -
TY - JOUR
AB - Propagation of performance changes to adjacent cells in polymer electrolyte fuel cell stacks is studied by means of voltage monitoring and local current density measurements in peripheral cells of the stack. A technical fuel cell stack has been modified by implementing two independent reactant and coolant supplies in order to deliberately change the performance of one cell (anomalous cell) and study the coupling phenomena to adjacent cells (coupling cells), while keeping the working conditions of the later cell-group unaltered.
Two anomalies are studied: (i) air starvation and (ii) thermal anomaly, in a single anomalous cell in the stack and their coupling to adjacent cells. The results have shown that anomalies inducing considerable changes in the local current density of the anomalous cell (such as air starvation) propagate to adjacent cells affecting their performance. The propagation of local current density changes takes place via the common bipolar plate due to its finite thickness and in-plane conductivity. Consequently, anomalies which do not strongly influence the local current density distribution (such as a thermal anomaly under the studied working conditions) do not propagate to adjacent cells.
AU - Santis, Marco
AU - Freunberger, Stefan Alexander
AU - Papra, Matthias
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7327
IS - 2
JF - Journal of Power Sources
SN - 0378-7753
TI - Experimental investigation of coupling phenomena in polymer electrolyte fuel cell stacks
VL - 161
ER -
TY - JOUR
AB - An experimental technique for measuring the current density distribution with a resolution smaller than the channel/rib scale of the flow field in polymer electrolyte fuel cells (PEFCs) is presented. The electron conductors in a plane perpendicular to the channel direction are considered as two-dimensional resistors. Hence, the current density is obtained from the solution of Laplace's equation with the potentials at current collector and reaction layer as boundary conditions. Using ohmic drop for calculating the local current, detailed knowledge of all resistances involved is of prime importance. In particular, the contact resistance between the gas diffusion layer (GDL) and flow field rib, as well as GDL bulk conductivity, are strongly dependent on clamping pressure. They represent a substantial amount of the total ohmic drop and therefore require careful consideration. The detailed experimental setup as well as the concise procedure for quantitative data evaluation is described. Finally, the method is applied successfully to a cell operated on pure oxygen and air up to high current densities. The results show that electrical and ionic resistances seem to govern the current distribution at low current regimes, whereas mass transport limitations locally hamper the current production at high loads.
AU - Freunberger, Stefan Alexander
AU - Reum, Mathias
AU - Evertz, Jörg
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7328
IS - 11
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - Measuring the current distribution in PEFCs with sub-millimeter resolution
VL - 153
ER -
TY - JOUR
AB - A novel measurement principle for measuring the current distribution in polymer electrolyte fuel cells (PEFCs) is introduced. It allows, in contrast to all other known techniques, for the first time for a resolution smaller than the channel/rib scale of the flow field in PEFCs. The current density is obtained by considering the electron conductors in the cell as a two-dimensional resistor with the voltage drop caused by the current. The method was applied to a cell operated on oxygen up to high current densities. The results show that the ohmic resistances govern the current distribution in the low current regime, whereas mass transport limitations hamper the current production under the land at high loads.
AU - Freunberger, Stefan Alexander
AU - Reum, Mathias
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7329
IS - 9
JF - Electrochemistry Communications
SN - 1388-2481
TI - Expanding current distribution measurement in PEFCs to sub-millimeter resolution
VL - 8
ER -
TY - JOUR
AB - Polymer electrolyte fuel cells (PE fuel cells) working with air at low stoichiometries (<2.0) and standard electrochemical components show a high degree of inhomogeneity in the current density distribution over the active area. An inhomogeneous current density distribution leads to a non-uniform utilization of the active area, which could negatively affect the time of life of the cells. Furthermore, it is also believed to lower cell performance. In this work, the homogenization of the current density, realized by means of tailored cathodes with along-the-air-channel redistributed catalyst loadings, is investigated. The air stoichiometry range for which a homogenization of the current density is achieved depends upon the gradient with which the catalyst is redistributed along the air channel. A gentle increasing catalyst loading profile homogenizes the current density at relatively higher air stoichiometries, while a steeper profile is suited better for lower air stoichiometries. The results show that a homogenization of the current density by means of redistributed catalyst loading has negative effects on cell performance. Model calculations corroborate the experimental findings on homogenization of the current density and deliver an explanation for the decrease in cell performance.
AU - Santis, M.
AU - Freunberger, Stefan Alexander
AU - Reiner, A.
AU - Büchi, F.N.
ID - 7330
IS - 25
JF - Electrochimica Acta
SN - 0013-4686
TI - Homogenization of the current density in polymer electrolyte fuel cells by in-plane cathode catalyst gradients
VL - 51
ER -
TY - JOUR
AB - A previously developed mathematical model for water management and current density distribution in a polymer electrolyte fuel cell (PEFCs) is employed to investigate the effects of cooling strategies on cell performance. The model describes a two-dimensional slice through the cell along the channels and through the entire cell sandwich including the coolant channels and the bipolar plate. Arbitrary flow arrangements of fuel, oxidant, and coolant stream directions can be described. Due to the serious impact of temperature on all processes in the PEFC, both the relative direction of the coolant stream to the gas streams and its mass flow turns out to significantly affect the cell performance. Besides influencing the electrochemical reaction and all kinds of mass transfer temperature, variations predominantly alter the local membrane hydration distribution and subseqently its conductivity.
AU - Freunberger, Stefan Alexander
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7331
IS - 5
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - In-plane effects in large-scale PEFCs: II. The influence of cooling strategy on cell performance
VL - 153
ER -
TY - JOUR
AB - A quasi-two-dimensional, along-the-channel mass and heat-transfer model for a proton exchange membrane fuel cell (PEFC) is described and validated against experimental current distribution data. The model is formulated in a dimensional manner, i.e., local transport phenomena are treated one-dimensional in through-plane direction and coupled in-plane by convective transport in the gas and coolant channels. Thus, a two-dimensional slice running through the repetitive unit of a cell from the anode channel via membrane-electrode assembly (MEA) and cathode channel to the coolant channel and from inlet to outlet is modeled. The aim of the work is to elucidate the influence of operating conditions such as feed gas humidities and stoichiometric ratios on the along-the-channel current density distribution and to identify the distinct underlying voltage loss mechanisms. Furthermore, a complicated technical flow field is modeled by a combination of co- and counterflow subdomains and compared with experimental current densities.
AU - Freunberger, Stefan Alexander
AU - Santis, Marco
AU - Schneider, Ingo A.
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7332
IS - 2
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - In-plane effects in large-scale PEMFCs
VL - 153
ER -
TY - JOUR
AB - Background: Cell-to-cell communication at the synapse involves synaptic transmission as well as signaling mediated by growth factors, which provide developmental and plasticity cues. There is evidence that a retrograde, presynaptic transforming growth factor-β (TGF-β) signaling event regulates synapse development and function in Drosophila. Results: Here we show that a postsynaptic TGF-β signaling event occurs during larval development. The type I receptor Thick veins (Tkv) and the R-Smad transcription factor Mothers-against-dpp (Mad) are localized postsynaptically in the muscle. Furthermore, Mad phosphorylation occurs in regions facing the presynaptic active zones of neurotransmitter release within the postsynaptic subsynaptic reticulum (SSR). In order to monitor in real time the levels of TGF-β signaling in the synapse during synaptic transmission, we have established a FRAP assay to measure Mad nuclear import/export in the muscle. We show that Mad nuclear trafficking depends on stimulation of the muscle. Conclusions: Our data suggest a mechanism linking synaptic transmission and postsynaptic TGF-β signaling that may coordinate nerve-muscle development and function.
AU - Dudu, Veronika
AU - Bittig, Thomas
AU - Entchev, Eugeni
AU - Kicheva, Anna
AU - Julicher, Frank
AU - González Gaitán, Marcos
ID - 1715
IS - 7
JF - Current Biology
TI - Postsynaptic mad signaling at the Drosophila neuromuscular junction
VL - 16
ER -
TY - JOUR
AB - SiGe islands grown by deposition of 10 monolayers of Ge on Si(0 0 1) at 740 °C were investigated by using a combination of selective wet chemical etching and atomic force microscopy. The used etchant, a solution consisting of ammonium hydroxide and hydrogen peroxide, shows a high selectivity of Ge over SixGe1-x and is characterized by relatively slow etching rates for Si-rich alloys. By performing successive etching experiments on the same sample area, we are able to gain a deeper insight into the lateral displacement the islands undergo during post growth annealing.
AU - Georgios Katsaros
AU - Rastelli, Armando
AU - Stoffel, Mathieu
AU - Isella, Giovanni
AU - Von Känel, Hans
AU - Bittner, Alexander M
AU - Tersoff, Jerry
AU - Denker, Ulrich
AU - Schmidt, Oliver G
AU - Costantini, Giovanni
AU - Kern, Klaus
ID - 1745
IS - 12
JF - Surface Science
TI - Investigating the lateral motion of SiGe islands by selective chemical etching
VL - 600
ER -
TY - JOUR
AB - A microscopic picture for the GaAs overgrowth of self-organized InAs/GaAs(001) quantum dots is developed. Scanning tunneling microscopy measurements reveal two capping regimes: the first being characterized by a dot shrinking and a backward pyramid-to-dome shape transition. This regime is governed by fast dynamics resulting in island morphologies close to thermodynamic equilibrium. The second regime is marked by a true overgrowth and is controlled by kinetically limited surface diffusion processes. A simple model is developed to describe the observed structural changes which are rationalized in terms of energetic minimization driven by lattice mismatch and alloying.
AU - Costantini, Giovanni
AU - Rastelli, Armando
AU - Manzano, Carlos
AU - Acosta-Diaz, P
AU - Songmuang, Rudeeson
AU - Georgios Katsaros
AU - Schmidt, Oliver G
AU - Kern, Klaus
ID - 1746
IS - 22
JF - Physical Review Letters
TI - Interplay between thermodynamics and kinetics in the capping of InAs/GaAs (001) quantum dots
VL - 96
ER -
TY - JOUR
AB - We report on recent advances in the understanding of surface processes occurring during growth and post-growth annealing of strained islands which may find application as self-assembled quantum dots. We investigate the model system SiGe/Si(0 0 1) by a new approach based on "reading the footprints" which islands leave on the substrate during their growth and evolution. Such footprints consist of trenches carved in the Si substrate. We distinguish between surface footprints and footprints buried below the islands. The former allow us to discriminate islands which are in the process of growing from those which are shrinking. Islands with steep morphologies grow at the expense of smaller and shallower islands, consistent with the kinetics of anomalous coarsening. While shrinking, islands change their shape according to thermodynamic predictions. Buried footprints are investigated by removing the SiGe epilayer by means of selective wet chemical etching. Their reading shows that: (i) during post-growth annealing islands move laterally because of surface-mediated Si-Ge intermixing; (ii) a tree-ring structure of trenches is created by dislocated islands during their "cyclic" growth. This allows us to distinguish coherent from dislocated islands and to establish whether the latter are the result of island coalescence.
AU - Rastelli, Armando
AU - Stoffel, Mathieu
AU - Georgios Katsaros
AU - Tersoff, Jerry
AU - Denker, Ulrich
AU - Merdzhanova, Tsvetelina
AU - Kar, Gouranga S
AU - Costantini, Giovanni
AU - Kern, Klaus
AU - Von Känel, Hans
AU - Schmidt, Oliver G
ID - 1747
IS - 12
JF - Microelectronics Journal
TI - Reading the footprints of strained islands
VL - 37
ER -
TY - JOUR
AB - The authors apply selective wet chemical etching and atomic force microscopy to reveal the three-dimensional shape of SiGeSi (001) islands after capping with Si. Although the "self-assembled quantum dots" remain practically unaffected by capping in the temperature range of 300-450 °C, significant morphological changes take place on the Si surface. At 450 °C, the morphology of the capping layer (Si matrix) evolves toward an intriguing semifacetted structure, which we call a "ziggurat," giving the misleading impression of a stepped SiGe island shape.
AU - Georgios Katsaros
AU - Rastelli, Armando
AU - Stoffel, Mathieu
AU - Costantini, Giovanni
AU - Schmidt, Oliver G
AU - Kern, Klaus
AU - Tersoff, Jerry
AU - Müller, Elisabeth
AU - Von Känel, Hans
ID - 1748
IS - 25
JF - Applied Physics Letters
TI - Evolution of buried semiconductor nanostructures and origin of stepped surface mounds during capping
VL - 89
ER -
TY - JOUR
AB - Drugs that block the entry of human immunodeficiency virus type 1 (HIV-1) into host cells abrogate the establishment of a productive infection and should ideally diminish the chances of HIV-1 developing resistance. This review will give an overview of the mechanism by which the envelope glycoprotein mediates HIV-1 entry and will summarize current drug developments.
AU - Sandra Siegert
AU - Schnierle, Peter
AU - Schnierle, Barbara S
ID - 1796
IS - 5
JF - Mini-Reviews in Medicinal Chemistry
TI - Novel anti-viral therapy: Drugs that block HIV entry at different target sites
VL - 6
ER -
TY - JOUR
AB - Respiratory complex I plays a central role in cellular energy production in bacteria and mitochondria. Its dysfunction is implicated in many human neurodegenerative diseases, as well as in aging. The crystal structure of the hydrophilic domain (peripheral arm) of complex I from Thermus thermophilus has been solved at 3.3 angstrom resolution. This subcomplex consists of eight subunits and contains all the redox centers of the enzyme, including nine iron-sulfur clusters. The primary electron acceptor, flavin-mononucleotide, is within electron transfer distance of cluster N3, leading to the main redox pathway, and of the distal cluster Nia, a possible antioxidant. The structure reveals new aspects of the mechanism and evolution of the enzyme. The terminal cluster N2 is coordinated, uniquely, by two consecutive cysteines. The novel subunit Nqo15 has a similar fold to the mitochondrial iron chaperone frataxin, and it may be involved in iron-sulfur cluster regeneration in the complex.
AU - Leonid Sazanov
AU - Hinchliffe, Philip
ID - 1961
IS - 5766
JF - Science
TI - Structure of the hydrophilic domain of respiratory complex I from Thermus thermophilus
VL - 311
ER -
TY - JOUR
AB - The hydrophilic domain (peripheral arm) of the proton-translocating NADH:quinone oxidoreductase (complex I) from the thermophilic organism Thermus thermophilus HB8 has been purified and characterized. The subcomplex is stable in sodium dodecyl sulfate up to 80 °C. Of nine iron-sulfur clusters, four to five (one or two binuclear and three tetranuclear) could be detected by EPR in the NADH-reduced enzyme. The preparation consists of eight different polypeptides. Seven of them have been positively identified by peptide mass mapping and N-terminal sequencing as known hydrophilic subunits of T. thermophilus complex I. The eighth polypeptide copurified with the subcomplex at all stages, is strongly associated with the other subunits, and is present in crystals of the subcomplex, used for X-ray data collection. Therefore, it has been identified as a novel complex I subunit and named Nqo15. It is encoded in a locus separate from the nqo operon, containing the 14 other known complex I genes. ORFs encoding Nqo15 homologues are present in the genomes of the closest relatives of T. thermophilus. Our data show that, contrary to previous assumptions, bacterial complex I can contain proteins in addition to a "core" complement of 14 subunits.
AU - Hinchliffe, Philip
AU - Carroll, Joe D
AU - Leonid Sazanov
ID - 1966
IS - 14
JF - Biochemistry
TI - Identification of a novel subunit of respiratory complex I from Thermus thermophilus
VL - 45
ER -
TY - JOUR
AU - Salecker, Iris
AU - Häusser, Michael
AU - de Bono, Mario
ID - 6151
IS - 6
JF - EMBO reports
SN - 1469-221X
TI - On the axonal road to circuit function and behaviour: Workshop on the assembly and function of neuronal circuits
VL - 7
ER -
TY - JOUR
AU - Rogers, Candida
AU - Persson, Annelie
AU - Cheung, Benny
AU - de Bono, Mario
ID - 6152
IS - 7
JF - Current Biology
SN - 0960-9822
TI - Behavioral motifs and neural pathways coordinating O2 responses and aggregation in C. elegans
VL - 16
ER -
TY - JOUR
AB - Background: The glyoxylate cycle is thought to be present in bacteria, protists, plants, fungi, and nematodes, but not in other Metazoa. However, activity of the glyoxylate cycle enzymes, malate synthase (MS) and isocitrate lyase (ICL), in animal tissues has been reported. In order to clarify the status of the MS and ICL genes in animals and get an insight into their evolution, we undertook a comparative-genomic study. Results: Using sequence similarity searches, we identified MS genes in arthropods, echinoderms, and vertebrates, including platypus and opossum, but not in the numerous sequenced genomes of placental mammals. The regions of the placental mammals' genomes expected to code for malate synthase, as determined by comparison of the gene orders in vertebrate genomes, show clear similarity to the opossum MS sequence but contain stop codons, indicating that the MS gene became a pseudogene in placental mammals. By contrast, the ICL gene is undetectable in animals other than the nematodes that possess a bifunctional, fused ICL-MS gene. Examination of phylogenetic trees of MS and ICL suggests multiple horizontal gene transfer events that probably went in both directions between several bacterial and eukaryotic lineages. The strongest evidence was obtained for the acquisition of the bifunctional ICL-MS gene from an as yet unknown bacterial source with the corresponding operonic organization by the common ancestor of the nematodes. Conclusion: The distribution of the MS and ICL genes in animals suggests that either they encode alternative enzymes of the glyoxylate cycle that are not orthologous to the known MS and ICL or the animal MS acquired a new function that remains to be characterized. Regardless of the ultimate solution to this conundrum, the genes for the glyoxylate cycle enzymes present a remarkable variety of evolutionary events including unusual horizontal gene transfer from bacteria to animals.
AU - Fyodor Kondrashov
AU - Koonin, Eugene V
AU - Morgunov, Igor G
AU - Finogenova, Tatiana V
AU - Kondrashova, Marie N
ID - 868
JF - Biology Direct
TI - Evolution of glyoxylate cycle enzymes in Metazoa Evidence of multiple horizontal transfer events and pseudogene formation
VL - 1
ER -
TY - JOUR
AB - The impact of synonymous nucleotide substitutions on fitness in mammals remains controversial. Despite some indications of selective constraint, synonymous sites are often assumed to be neutral, and the rate of their evolution is used as a proxy for mutation rate. We subdivide all sites into four classes in terms of the mutable CpG context, nonCpG, postC, preG, and postCpreG, and compare four-fold synonymous sites and intron sites residing outside transposable elements. The distribution of the rate of evolution across all synonymous sites is trimodal. Rate of evolution at nonCpG synonymous sites, not preceded by C and not followed by G, is ∼10% below that at such intron sites. In contrast, rate of evolution at postCpreG synonymous sites is ∼30% above that at such intron sites. Finally, synonymous and intron postC and preG sites evolve at similar rates. The relationship between the levels of polymorphism at the corresponding synonymous and intron sites is very similar to that between their rates of evolution. Within every class, synonymous sites are occupied by G or C much more often than intron sites, whose nucleotide composition is consistent with neutral mutation-drift equilibrium. These patterns suggest that synonymous sites are under weak selection in favor of G and C, with the average coefficient s∼0.25/Ne∼10-5, where Ne is the effective population size. Such selection decelerates evolution and reduces variability at sites with symmetric mutation, but has the opposite effects at sites where the favored nucleotides are more mutable. The amino-acid composition of proteins dictates that many synonymous sites are CpGprone, which causes them, on average, to evolve faster and to be more polymorphic than intron sites. An average genotype carries ∼107 suboptimal nucleotides at synonymous sites, implying synergistic epistasis in selection against them.
AU - Fyodor Kondrashov
AU - Ogurtsov, Aleksey Yu
AU - Kondrashov, Alexey S
ID - 869
IS - 4
JF - Journal of Theoretical Biology
TI - Selection in favor of nucleotides G and C diversifies evolution rates and levels of polymorphism at mammalian synonymous sites
VL - 240
ER -
TY - JOUR
AB - New genes commonly appear through complete or partial duplications of pre-existing genes. Duplications of long DNA segments are constantly produced by rare mutations, may become fixed in a population by selection or random drift, and are subject to divergent evolution of the paralogous sequences after fixation, although gene conversion can impede this process. New data shed some light on each of these processes. Mutations which involve duplications can occur through at least two different mechanisms, backward strand slippage during DNA replication and unequal crossing-over. The background rate of duplication of a complete gene in humans is 10-9-10-10 per generation, although many genes located within hot-spots of large-scale mutation are duplicated much more often. Many gene duplications affect fitness strongly, and are responsible, through gene dosage effects, for a number of genetic diseases. However, high levels of intrapopulation polymorphism caused by presence or absence of long, gene-containing DNA segments imply that some duplications are not under strong selection. The polymorphism to fixation ratios appear to be approximately the same for gene duplications and for presumably selectively neutral nucleotide substitutions, which, according to the McDonald-Kreitman test, is consistent with selective neutrality of duplications. However, this pattern can also be due to negative selection against most of segregating duplications and positive selection for at least some duplications which become fixed. Patterns in post-fixation evolution of duplicated genes do not easily reveal the causes of fixations. Many gene duplications which became fixed recently in a variety of organisms were positively selected because the increased expression of the corresponding genes was beneficial. The effects of gene dosage provide a unified framework for studying all phases of the life history of a gene duplication. Application of well-known methods of evolutionary genetics to accumulating data on new, polymorphic, and fixed duplication will enhance our understanding of the role of natural selection in the evolution by gene duplication.
AU - Fyodor Kondrashov
AU - Kondrashov, Alexey S
ID - 873
IS - 2
JF - Journal of Theoretical Biology
TI - Role of selection in fixation of gene duplications
VL - 239
ER -
TY - JOUR
AB - Background: Carcinogenesis typically involves multiple somatic mutations in caretaker (DNA repair) and gatekeeper (tumor suppressors and oncogenes) genes. Analysis of mutation spectra of the tumor suppressor that is most commonly mutated in human cancers, p53, unexpectedly suggested that somatic evolution of the p53 gene during tumorigenesis is dominated by positive selection for gain of function. This conclusion is supported by accumulating experimental evidence of evolution of new functions of p53 in tumors. These findings prompted a genome-wide analysis of possible positive selection during tumor evolution. Methods: A comprehensive analysis of probable somatic mutations in the sequences of Expressed Sequence Tags (ESTs) from malignant tumors and normal tissues was performed in order to access the prevalence of positive selection in cancer evolution. For each EST, the numbers of synonymous and non-synonymous substitutions were calculated. In order to identify genes with a signature of positive selection in cancers, these numbers were compared to: i) expected numbers and ii) the numbers for the respective genes in the ESTs from normal tissues. Results: We identified 112 genes with a signature of positive selection in cancers, i.e., a significantly elevated ratio of non-synonymous to synonymous substitutions, in tumors as compared to 37 such genes in an approximately equal-sized EST collection from normal tissues. A substantial fraction of the tumor-specific positive-selection candidates have experimentally demonstrated or strongly predicted links to cancer. Conclusion: The results of EST analysis should be interpreted with extreme caution given the noise introduced by sequencing errors and undetected polymorphisms. Furthermore, an inherent limitation of EST analysis is that multiple mutations amenable to statistical analysis can be detected only in relatively highly expressed genes. Nevertheless, the present results suggest that positive selection might affect a substantial number of genes during tumorigenic somatic evolution.
AU - Babenko, Vladimir N
AU - Basu, Malay K
AU - Fyodor Kondrashov
AU - Rogozin, Igor B
AU - Koonin, Eugene V
ID - 903
JF - BMC Cancer
TI - Signs of positive selection of somatic mutations in human cancers detected by EST sequence analysis
VL - 6
ER -
TY - JOUR
AB - This note proves combinatorially that the intersection pairing on the middle-dimensional compactly supported cohomology of a toric hyperkähler variety is always definite, providing a large number of non-trivial L 2 harmonic forms for toric hyperkähler metrics on these varieties. This is motivated by a result of Hitchin about the definiteness of the pairing of L 2 harmonic forms on complete hyperkähler manifolds of linear growth.
AU - Tamas Hausel
AU - Swartz, Edward
ID - 1461
IS - 8
JF - Proceedings of the American Mathematical Society
TI - Intersection forms of toric hyperkähler varieties
VL - 134
ER -
TY - JOUR
AB - A Fourier transform technique is introduced for counting the number of solutions of holomorphic moment map equations over a finite field. This technique in turn gives information on Betti numbers of holomorphic symplectic quotients. As a consequence, simple unified proofs are obtained for formulas of Poincaré polynomials of toric hyperkähler varieties (recovering results of Bielawski-Dancer and Hausel-Sturmfels), Poincaré polynomials of Hubert schemes of points and twisted Atiyah-Drinfeld-Hitchin-Manin (ADHM) spaces of instantons on ℂ2 (recovering results of Nakajima-Yoshioka), and Poincaré polynomials of all Nakajima quiver varieties. As an application, a proof of a conjecture of Kac on the number of absolutely indecomposable representations of a quiver is announced.
AU - Tamas Hausel
ID - 1462
IS - 16
JF - PNAS
TI - Betti numbers of holomorphic symplectic quotients via arithmetic Fourier transform
VL - 103
ER -
TY - JOUR
AB - Systems of three interacting particles are notorious for their complex physical behaviour. A landmark theoretical result in few-body quantum physics is Efimov\'s prediction1,2 of a universal set of bound trimer states appearing for three identical bosons with a resonant two-body interaction. Counterintuitively, these states even exist in the absence of a corresponding two-body bound state. Since the formulation of Efimov\'s problem in the context of nuclear physics 35 years ago, it has attracted great interest in many areas of physics3-8. However, the observation of Efimov quantum states has remained an elusive goal3,5. Here we report the observation of an Efimov resonance in an ultracold gas of caesium atoms. The resonance occurs in the range of large negative two-body scattering lengths, arising from the coupling of three free atoms to an Efimov trimer. Experimentally, we observe its signature as a giant three-body recombination loss9,10 when the strength of the two-body interaction is varied. We also detect a minimum 9,11,12 in the recombination loss for positive scattering lengths, indicating destructive interference of decay pathways. Our results confirm central theoretical predictions of Efimov physics and represent a starting point with which to explore the universal properties of resonantly interacting few-body systems7. While Feshbach resonances13,14 have provided the key to control quantum-mechanical interactions on the two-body level, Efimov resonances connect ultracold matter15 to the world of few-body quantum phenomena.
AU - Kraemer, Tobias
AU - Mark, Michael
AU - Waldburger, Philipp
AU - Danzl, Johann G
AU - Chin, Cheng
AU - Engeser, Bastian
AU - Lange, Adam
AU - Pilch, Karl
AU - Jaakkola, Antti
AU - Nägerl, Hanns
AU - Grimm, Rudolf
ID - 1033
IS - 7082
JF - Nature
TI - Evidence for Efimov quantum states in an ultracold gas of caesium atoms
VL - 440
ER -
TY - CONF
AB - Three interacting particles form a system which is well known for its complex physical behavior. A landmark theoretical result in few-body quantum physics is Efimov\'s prediction of a universal set of weakly bound trimer states appearing for three identical bosons with a resonant two-body interaction [1, 2]. Surprisingly, these states even exist in the absence of a corresponding two-body bound state and their precise nature is largely independent of the particular type of the two-body interaction potential. Efimov\'s scenario has attracted great interest in many areas of physics; an experimental test however has not been achieved. We report the observation of an Efimov resonance in an ultracold thermal gas of cesium atoms [3]. The resonance occurs in the range of large negative two-body scattering lengths and arises from the coupling of three free atoms to an Efimov trimer. We observe its signature as a giant three-body recombination loss when the strength of the two-body interaction is varied near a Feshbach resonance. This resonance develops into a continuum resonance at non-zero collision energies, and we observe a shift of the resonance position as a function of temperature. We also report on a minimum in the recombination loss for positive scattering lengths, indicating destructive interference of decay pathways. Our results confirm central theoretical predictions of Efimov physics and represent a starting point from which to explore the universal properties of resonantly interacting few-body systems.
AU - Nägerl, Hanns
AU - Kraemer, Tobias
AU - Mark, Michael
AU - Waldburger, Philipp
AU - Danzl, Johann G
AU - Engeser, Bastian
AU - Lange, Adam
AU - Pilch, Karl
AU - Jaakkola, Antti
AU - Chin, Cheng
AU - Grimm, Rudolf
ID - 1034
TI - Experimental evidence for Efimov quantum states
VL - 869
ER -
TY - JOUR
AB - Although the X chromosome is usually similar to the autosomes in size and cytogenetic appearance, theoretical models predict that its hemizygosity in males may cause unusual patterns of evolution. The sequencing of several genomes has indeed revealed differences between the X chromosome and the autosomes in the rates of gene divergence, patterns of gene expression and rates of gene movement between chromosomes. A better understanding of these patterns should provide valuable information on the evolution of genes located on the X chromosome. It could also suggest solutions to more general problems in molecular evolution, such as detecting selection and estimating mutational effects on fitness
AU - Beatriz Vicoso
AU - Charlesworth, Brian
ID - 2066
IS - 8
JF - Nature Reviews Genetics
TI - Evolution on the X chromosome: Unusual patterns and processes
VL - 7
ER -
TY - CONF
AB - We present an adaptive animation method for electrical discharges. Electrical discharges can be simulated using the dielectric breakdown model. Regular discretization of the governing Laplace equation leads to huge equation systems, and the computational cost of solving the equations quickly becomes prohibitive at high resolutions, especially for simulations in 3D. In contrast, our method discretizes the Laplace equation on an adaptive octree, reducing the size of the problem significantly, and making simulations of high resolution 3D datasets and even 3D animations feasible. In order to enhance realism for lightning animations, we propose a particle simulation that animates the residual positive charge. Thus, interaction of electrical discharges with their surroundings
can be simulated.
AU - Bernd Bickel
AU - Wicke, Martin
AU - Gross, Markus
ID - 2077
TI - Adaptive simulation of electrical discharges
ER -
TY - CONF
AB - We have measured 3D face geometry, skin reflectance, and subsurface scattering using custom-built devices for 149 subjects of varying age, gender, and race. We developed a novel skin reflectance model whose parameters can be estimated from measurements. The model decomposes the large amount of measured skin data into a spatially-varying analytic BRDF, a diffuse albedo map, and diffuse subsurface scattering. Our model is intuitive, physically plausible, and - since we do not use the original measured data - easy to edit as well. High-quality renderings come close to reproducing real photographs. The analysis of the model parameters for our sample population reveals variations according to subject age, gender, skin type, and external factors (e.g., sweat, cold, or makeup). Using our statistics, a user can edit the overall appearance of a face (e.g., changing skin type and age) or change small-scale features using texture synthesis (e.g., adding moles and freckles). We are making the collected statistics publicly available to the research community for applications in face synthesis and analysis.
AU - Weyrich, Tim
AU - Matusik, Wojciech
AU - Pfister, Hanspeter
AU - Bernd Bickel
AU - Donner, Craig
AU - Tu, Chien
AU - McAndless, Janet M
AU - Lee, Jinho
AU - Ngan, Addy
AU - Jensen, Henrik W
AU - Groß, Markus S
ID - 2088
TI - Analysis of human faces using a measurement-based skin reflectance model
ER -
TY - JOUR
AB - We have measured 3D face geometry, skin reflectance, and subsurface scattering using custom-built devices for 149 subjects of varying age, gender, and race. We developed a novel skin reflectance model whose parameters can be estimated from measurements. The model decomposes the large amount of measured skin data into a spatially-varying analytic BRDF, a diffuse albedo map, and diffuse subsurface scattering. Our model is intuitive, physically plausible, and - since we do not use the original measured data - easy to edit as well. High-quality renderings come close to reproducing real photographs. The analysis of the model parameters for our sample population reveals variations according to subject age, gender, skin type, and external factors (e.g., sweat, cold, or makeup). Using our statistics, a user can edit the overall appearance of a face (e.g., changing skin type and age) or change small-scale features using texture synthesis (e.g., adding moles and freckles). We are making the collected statistics publicly available to the research community for applications in face synthesis and analysis.
AU - Weyrich, Tim
AU - Matusik, Wojciech
AU - Pfister, Hanspeter
AU - Bernd Bickel
AU - Donner, Craig
AU - Tu, Chien
AU - McAndless, Janet M
AU - Lee, Jinho
AU - Ngan, Addy
AU - Jensen, Henrik W
AU - Groß, Markus S
ID - 2089
IS - 3
JF - ACM Transactions on Graphics
TI - Analysis of human faces using a measurement-based skin reflectance model
VL - 25
ER -
TY - CONF
AU - Bernd Bickel
AU - Weyrich, Tim
AU - Matusik, Wojciech
AU - Pfister, Hanspeter
AU - Donner, Craig
AU - Tu, Chien
AU - McAndless, Janet M
AU - Lee, Jinho
AU - Ngan, Addy
AU - Jensen, Henrik W
AU - Groß, Markus S
ID - 2090
TI - Processing and editing of faces using a measurement-based skin reflectance model
ER -
TY - JOUR
AB - For any integers d,n ≥2, let X ⊂ Pn be a non‐singular hypersurface of degree d that is defined over the rational numbers. The main result in this paper is a proof that the number of rational points on X which have height at most B is O(Bn − 1 + ɛ), for any ɛ > 0. The implied constant in this estimate depends at most upon d, ɛ and n. 2000 Mathematics Subject Classification 11D45 (primary), 11G35, 14G05 (secondary).
AU - Timothy Browning
AU - Heath-Brown, Roger
AU - Starr, Jason M
ID - 213
IS - 2
JF - Proceedings of the London Mathematical Society
TI - The density of rational points on non-singular hypersurfaces, II
VL - 93
ER -
TY - JOUR
AB - Predissociation of the N+2 C 2Σ+u(v') vibrational levels with v' ≥ 3 was observed via dispersed C 2Σ+u → X 2Σ+g fluorescence in the spectral range of 165–208 nm after resonant 1s−1π*(vr) excitation of N2 and its subsequent autoionization into the N+2 C state. This range is dominated by lines in atomic nitrogen, by overlapped C 2Σ+u(v') → X 2Σ+g(v'') vibrational band sequences with Δv = const and broad unresolved band systems (D, (2))2Πg(v') → A2Πu(v'') in the N+2 molecular ion. With very high fluorescence resolution of about 0.1 nm FWHM individual C 2Σ+u(v') → X 2Σ+g(v'') vibrational bands have been resolved. Calculation of the observed fluorescence spectra by taking into account predissociation and molecular rotation describes well the shape of both individual vibrational bands C 2Σ+u(v') → X 2Σ+g(v'') and the whole band system.
AU - Ehresmann, Arno
AU - Werner, Lutz
AU - Klumpp, Stefan
AU - Demekhin, Ph V
AU - Mikhail Lemeshko
AU - Sukhorukov, V. L
AU - Schartner, Karl H
AU - Schmoranzer, Hans P
ID - 2134
IS - 6
JF - Journal of Physics B: Atomic, Molecular and Optical Physics
TI - Predissociation of the N+2(C 2Σ+u) state observed via C 2Σ+u → X 2Σ+g fluorescence after resonant 1s−1π* excitation of N2 molecule
VL - 39
ER -
TY - JOUR
AB - Fluorescence from fragments formed after the de-excitation of the N*2(1s−1π*) resonance has been measured in the spectral range of 135–190 nm. This range is dominated by lines in atomic nitrogen and lines formed by overlapping C2Σ+u(v') → X2Σ+g(v'') bands with Δv = const in the N+2 molecular ion which result from the spectator Auger decays of the N*2(1s−1π*(vr)) resonances. Ab initio calculations of the corresponding potential curves and transition probabilities showed that the observed irregular intensity dependence of the C2Σ+u(v') → X2Σ+g(v'')(Δv = const) fluorescence lines on the vibrational quantum number vr is due to transitions between vibrational levels during the reaction N2(v0 = 0)→ N*2(1s−1π*(vr)) Longrightarrow C2Σ+u(v') → X2Σ+g(v'').
AU - Ehresmann, Arno
AU - Werner, Lutz
AU - Klumpp, Stefan
AU - Lucht, S
AU - Schmoranzer, Hans P
AU - Mickat, Sascha
AU - Schill, Rüdiger H
AU - Schartner, Karl H
AU - Demekhin, Philipp
AU - Mikhail Lemeshko
AU - Sukhorukov, Victor L
ID - 2142
IS - 2
JF - Journal of Physics B: Atomic, Molecular and Optical Physics
TI - Studying the N+2(C2Σ+u → X2Σ+g) fluorescence excited via the 1s−1π* resonance
VL - 39
ER -
TY - JOUR
AB - Temperature dependent preedge and extended x-ray absorption fine structure measurements at the Zr K edge for the perovskite-type zirconates Pb Zr0.515 Ti0.485 O3 (PZT), PbZr O3 (PZ), and BaZr O3 are performed. To carry out a more accurate study of the weak reconstruction of the local atomic structure we employed a combination of two techniques: (i) analysis of the preedge fine structure, and (ii) analysis of the Fourier transform of the difference between χ (k) functions obtained at different temperatures. A detailed investigation of local atomic structure in the cubic phase for all the crystals is also performed. It is shown that neither the displacive nor the order-disorder model can describe correctly the changes of local atomic structure during phase transitions in PZ and PZT. A spherical model describing the local atomic structure of perovskite-type crystals suffering structural phase transitions is proposed.
AU - Vedrinskiǐ, Rostislav V
AU - Nazarenko, Elena S
AU - Mikhail Lemeshko
AU - Nassif, Vivian M
AU - Proux, Olivier
AU - Novakovich, Alexander A
AU - Joly, Yves
ID - 2144
IS - 13
JF - Physical Review B - Condensed Matter and Materials Physics
TI - Temperature dependent XAFS studies of local atomic structure of the perovskite-type zirconates
VL - 73
ER -
TY - JOUR
AB - For any n≥3, let F ∈ Z[X0,...,Xn ] be a form of degree d *≥5 that defines a non-singular hypersurface X ⊂ Pn . The main result in this paper is a proof of the fact that the number N (F ; B) of Q-rational points on X which have height at most B satisfiesN (F ; B) = Od,ε,n (Bn −1+ε ), for any ε > 0. The implied constant in this estimate depends at most upon d, ε and n. New estimates are also obtained for the number of representations of a positive integer as the sum of three dth powers, and for the paucity of integer solutions to equal sums of like polynomials.*
AU - Timothy Browning
AU - Heath-Brown, Roger
ID - 215
IS - 3
JF - Bulletin of the London Mathematical Society
TI - The density of rational points on non-singular hypersurfaces, I
VL - 38
ER -
TY - JOUR
AB - For any N ≥ 2, let Z ⊂ ℙN be a geometrically integral algebraic variety of degree d. This article is concerned with the number Nz(B) of ℚ-rational points on Z which have height at most B. For any ε > 0, we establish the estimate NZ(B) = O d,ε,N(Bdim Z+ε), provided that d ≥ 6. As indicated, the implied constant depends at most on d, ε, and N.
AU - Timothy Browning
AU - Heath-Brown, Roger
AU - Salberger, Per
ID - 216
IS - 3
JF - Duke Mathematical Journal
TI - Counting rational points on algebraic varieties
VL - 132
ER -
TY - JOUR
AB - This paper is concerned with the average order of certain arithmetic functions, as they range over the values taken by binary forms.
AU - de la Bretèche, Régis
AU - Timothy Browning
ID - 218
IS - 3
JF - Acta Arithmetica
TI - Sums of arithmetic functions over values of binary forms
VL - 125
ER -
TY - CONF
AU - Lieb, Élliott H
AU - Robert Seiringer
AU - Solovej, Jan P
ID - 2333
TI - Ground-state energy of a dilute Fermi gas
VL - 412
ER -
TY - CONF
AU - Robert Seiringer
AU - Lieb, Élliott H
AU - Yngvason, Jakob
ED - Zambrini, Jean-Claude
ID - 2334
TI - One-dimensional behavior of dilute, trapped Bose gases in traps
ER -
TY - GEN
AB - We prove that the Gross-Pitaevskii equation correctly describes the ground state energy and corresponding one-particle density matrix of rotating, dilute, trapped Bose gases with repulsive two-body interactions. We also show that there is 100% Bose-Einstein condensation. While a proof that the GP equation correctly describes non-rotating or slowly rotating gases was known for some time, the rapidly rotating case was unclear because the Bose (i.e., symmetric) ground state is not the lowest eigenstate of the Hamiltonian in this case. We have been able to overcome this difficulty with the aid of coherent states. Our proof also conceptually simplifies the previous proof for the slowly rotating case. In the case of axially symmetric traps, our results show that the appearance of quantized vortices causes spontaneous symmetry breaking in the ground state.
AU - Lieb, Élliott H
AU - Robert Seiringer
ID - 2363
IS - 2
T2 - Communications in Mathematical Physics
TI - Derivation of the Gross-Pitaevskii equation for rotating Bose gases
VL - 264
ER -
TY - JOUR
AB - We present an inequality that gives a lower bound on the expectation value of certain two-body interaction potentials in a general state on Fock space in terms of the corresponding expectation value for thermal equilibrium states of non-interacting systems and the difference in the free energy. This bound can be viewed as a rigorous version of first-order perturbation theory for many-body systems at positive temperature. As an application, we give a proof of the first two terms in a high density (and high temperature) expansion of the free energy of jellium with Coulomb interactions, both in the fermionic and bosonic case. For bosons, our method works above the transition temperature (for the non-interacting gas) for Bose-Einstein condensation.
AU - Robert Seiringer
ID - 2364
IS - 3
JF - Reviews in Mathematical Physics
TI - A correlation estimate for quantum many-body systems at positive temperature
VL - 18
ER -
TY - JOUR
AB - We consider a gas of fermions with non-zero spin at temperature T and chemical potential μ. We show that if the range of the interparticle interaction is small compared to the mean particle distance, the thermodynamic pressure differs to leading order from the corresponding expression for non-interacting particles by a term proportional to the scattering length of the interparticle interaction. This is true for any repulsive interaction, including hard cores. The result is uniform in the temperature as long as T is of the same order as the Fermi temperature, or smaller.
AU - Robert Seiringer
ID - 2365
IS - 3
JF - Communications in Mathematical Physics
TI - The thermodynamic pressure of a dilute fermi gas
VL - 261
ER -
TY - JOUR
AB - Inequalities are derived for power sums of the real part and the modulus of the eigenvalues of a Schrödinger operator with a complex-valued potential.
AU - Frank, Rupert L
AU - Laptev, Ari
AU - Lieb, Élliott H
AU - Robert Seiringer
ID - 2366
IS - 3
JF - Letters in Mathematical Physics
TI - Lieb-Thirring inequalities for Schrödinger operators with complex-valued potentials
VL - 77
ER -
TY - CHAP
AB - The recent experimental success in creating Bose-Einstein condensates of alkali atoms, honored by the Nobel prize awards in 2001 [1,5], led to renewed interest in the mathematical description of interacting Bose gases.
AU - Robert Seiringer
ED - Dereziński, Jan
ED - Siedentop, Heinz
ID - 2368
T2 - Large Coulomb Systems
TI - Dilute, trapped Bose gases and Bose-Einstein condensation
VL - 695
ER -
TY - CHAP
AB - One of the most remarkable recent developments in the study of ultracold Bose gases is the observation of a reversible transition from a Bose Einstein condensate to a state composed of localized atoms as the strength of a periodic, optical trapping potential is varied. In [1] a model of this phenomenon has been analyzed rigorously. The gas is a hard core lattice gas and the optical lattice is modeled by a periodic potential of strength λ. For small λ and temperature Bose- Einstein condensation (BEC) is proved to occur, while at large λ BEC disappears, even in the ground state, which is a Mott-insulator state with a characteristic gap. The inter-particle interaction is essential for this effect. This contribution gives a pedagogical survey of these results.
AU - Aizenman, Michael
AU - Lieb, Élliott H
AU - Robert Seiringer
AU - Solovej, Jan P
AU - Yngvason, Jakob
ED - Asch, Joachim
ED - Joye, Alain
ID - 2369
T2 - Mathematical Physics of Quantum Mechanics
TI - Bose-Einstein condensation as a quantum phase transition in an optical lattice
VL - 690
ER -
TY - CHAP
AU - Bang-Jensen, Jørgen
AU - Reed, Bruce
AU - Schacht, Bruce
AU - Šámal, Robert
AU - Toft, Bjarne
AU - Uli Wagner
ID - 2416
T2 - Topics in Discrete Mathematics
TI - On six problems posed by Jarik Nešetřil
VL - 26
ER -
TY - JOUR
AB - We show, with an elementary proof, that the number of halving simplices in a set of n points in 4 in general position is O(n4-2/45). This improves the previous bound of O(n4-1/134). Our main new ingredient is a bound on the maximum number of halving simplices intersecting a fixed 2-plane.
AU - Matoušek, Jiří
AU - Sharir, Micha
AU - Smorodinsky, Shakhar
AU - Uli Wagner
ID - 2429
IS - 2
JF - Discrete & Computational Geometry
TI - K-sets in four dimensions
VL - 35
ER -
TY - JOUR
AB - We consider an online version of the conflict-free coloring of a set of points on the line, where each newly inserted point must be assigned a color upon insertion, and at all times the coloring has to be conflict-free, in the sense that in every interval I there is a color that appears exactly once in I. We present deterministic and randomized algorithms for achieving this goal, and analyze their performance, that is, the maximum number of colors that they need to use, as a function of the number n of inserted points. We first show that a natural and simple (deterministic) approach may perform rather poorly, requiring Ω(√̃) colors in the worst case. We then derive two efficient variants of this simple algorithm. The first is deterministic and uses O(log 2 n) colors, and the second is randomized and uses O(log n) colors with high probability. We also show that the O(log 2 n) bound on the number of colors used by our deterministic algorithm is tight on the worst case. We also analyze the performance of the simplest proposed algorithm when the points are inserted in a random order and present an incomplete analysis that indicates that, with high probability, it uses only O(log n) colors. Finally, we show that in the extension of this problem to two dimensions, where the relevant ranges are disks, n colors may be required in the worst case.
AU - Chent, Ke
AU - Fiat, Amos
AU - Kaplan, Haim
AU - Levy, Meital B
AU - Matoušek, Jiří
AU - Mossel, Elchanan
AU - Pach, János
AU - Sharir, Micha
AU - Smorodinsky, Shakhar
AU - Uli Wagner
AU - Welzl, Emo
ID - 2430
IS - 5
JF - SIAM Journal on Computing
TI - Online conflict-free coloring for intervals
VL - 36
ER -
TY - CONF
AB - We prove an upper bound, tight up to a factor of 2, for the number of vertices of level at most t in an arrangement of n halfspaces in R , for arbitrary n and d (in particular, the dimension d is not considered constant). This partially settles a conjecture of Eckhoff, Linhart, and Welzl. Up to the factor of 2, the result generalizes McMullen's Upper Bound Theorem for convex polytopes (the case ℓ = O) and extends a theorem of Linhart for the case d ≤ 4. Moreover, the bound sharpens asymptotic estimates obtained by Clarkson and Shor. The proof is based on the h-matrix of the arrangement (a generalization, introduced by Mulmuley, of the h-vector of a convex polytope). We show that bounding appropriate sums of entries of this matrix reduces to a lemma about quadrupels of sets with certain intersection properties, and we prove this lemma, up to a factor of 2, using tools from multilinear algebra. This extends an approach of Alon and Kalai, who used linear algebra methods for an alternative proof of the classical Upper Bound Theorem. The bounds for the entries of the h-matrix also imply bounds for the number of i-dimensional faces, i > 0, at level at most ℓ. Furthermore, we discuss a connection with crossing numbers of graphs that was one of the main motivations for investigating exact bounds that are valid for arbitrary dimensions.
AU - Uli Wagner
ID - 2431
TI - On a geometric generalization of the Upper Bound Theorem
ER -
TY - JOUR
AB - The highest densities of the two metabotropic GABA subunits, GABA B1 and GABAB2, have been reported as occurring around the glutamatergic synapses between Purkinje cell spines and parallel fibre varicosities. In order to determine how this distribution is achieved during development, we investigated the expression pattern and the cellular and subcellular localization of the GABAB1 and GABAB2 subunits in the rat cerebellum during postnatal development. At the light microscopic level, immunoreactivity for the GABAB1 and GABAB2 subunits was very prominent in the developing molecular layer, especially in Purkinje cells. Using double immunofluorescence, we demonstrated that GABAB1 was transiently expressed in glial cells. At the electron microscopic level, immunoreactivity for GABAB receptors was always detected both pre- and postsynaptically. Presynaptically, GABAB1 and GABAB2 were localized in the extrasynaptic membrane of parallel fibres at all ages, and only rarely in GABAergic axons. Postsynaptically, GABAB receptors were localized to the extrasynaptic and perisynaptic plasma membrane of Purkinje cell dendrites and spines throughout development. Quantitative analysis and three-dimensional reconstructions further revealed a progressive developmental movement of the GABAB1 subunit on the surface of Purkinje cells from dendritic shafts to its final destination, the dendritic spines. Together, these results indicate that GABAB receptors undergo dynamic regulation during cerebellar development in association with the establishment and maturation of glutamatergic synapses to Purkinje cells.
AU - Luján, Rafael
AU - Ryuichi Shigemoto
ID - 2657
IS - 6
JF - European Journal of Neuroscience
TI - Localization of metabotropic GABA receptor subunits GABAB1 and GABAB2 relative to synaptic sites in the rat developing cerebellum
VL - 23
ER -
TY - JOUR
AB - Transmembrane AMPA receptor regulatory proteins (TARPs), including stargazin/γ-2, are associated with AMPA receptors and participate in their surface delivery and anchoring at the postsynaptic membrane. TARPs may also act as a positive modulator of the AMPA receptor ion channel function; however, little is known about other TARP members except for stargazin/γ-2. We examined the synaptic localization of stargazin/γ-2 and γ-8 by immunoelectron microscopy and biochemical analysis. The analysis of sodium dodecyl sulfate-digested freeze-fracture replica labeling revealed that stargazin/γ-2 was concentrated in the postsynaptic area, whereas γ-8 was distributed both in synaptic and extra-synaptic plasma membranes of the hippocampal neuron. When a synaptic plasma membrane-enriched brain fraction was treated with Triton X-100 and separated by sucrose density gradient ultracentrifugation, a large proportion of NMDA receptor and stargazin/γ-2 was accumulated in raft-enriched fractions, whereas AMPA receptor and γ-8 were distributed in both the raft-enriched fractions and other Triton-insoluble fractions. Phosphorylation of stargazin/γ-2 and γ-8 was regulated by different sets of kinases and phosphatases in cultured cortical neurons. These results suggested that stargazin/γ-2 and γ-8 have distinct roles in postsynaptic membranes under the regulation of different intracellular signaling pathways.
AU - Inamura, Mihoko
AU - Itakura, Makoto
AU - Okamoto, Hirotsugu
AU - Hoka, Sumio
AU - Mizoguchi, Akira
AU - Fukazawa, Yugo
AU - Ryuichi Shigemoto
AU - Yamamori, Saori
AU - Takahashi, Masami
ID - 2659
IS - 1
JF - Neuroscience Research
TI - Differential localization and regulation of stargazin-like protein, γ-8 and stargazin in the plasma membrane of hippocampal and cortical neurons
VL - 55
ER -
TY - JOUR
AB - Pavlovian fear conditioning, a simple form of associative learning, is thought to involve the induction of associative, NMDA receptor-dependent long-term potentiation (LTP) in the lateral amygdala. Using a combined genetic and electrophysiological approach, we show here that lack of a specific GABAB receptor subtype, GABAB(1a,2), unmasks a nonassociative, NMDA receptor-independent form of presynaptic LTP at cortico-amygdala afferents. Moreover, the level of presynaptic GABA B(1a,2) receptor activation, and hence the balance between associative and nonassociative forms of LTP, can be dynamically modulated by local inhibitory activity. At the behavioral level, genetic loss of GABA B(1a) results in a generalization of conditioned fear to nonconditioned stimuli. Our findings indicate that presynaptic inhibition through GABAB(1a,2) receptors serves as an activity-dependent constraint on the induction of homosynaptic plasticity, which may be important to prevent the generalization of conditioned fear.
AU - Shaban, Hamdy
AU - Humeau, Yann
AU - Herry, Cyril
AU - Cassasus, Guillaume
AU - Ryuichi Shigemoto
AU - Ciocchi, Stéphane
AU - Barbieri, Samuel
AU - Van Der Putten, Herman V
AU - Kaupmann, Klemens
AU - Bettler, Bernhard
AU - Lüthi, Andreas
ID - 2660
IS - 8
JF - Nature Neuroscience
TI - Generalization of amygdala LTP and conditioned fear in the absence of presynaptic inhibition
VL - 9
ER -
TY - JOUR
AB - GABAB receptors are the G protein-coupled receptors for the main inhibitory neurotransmitter in the brain, γ-aminobutyric acid (GABA). Molecular diversity in the GABAB system arises from the GABAB1a and GABAB1b subunit isoforms that solely differ in their ectodomains by a pair of sushi repeats that is unique to GABAB1a. Using a combined genetic, physiological, and morphological approach, we now demonstrate that GABAB1 isoforms localize to distinct synaptic sites and convey separate functions in vivo. At hippocampal CA3-to-CA1 synapses, GABAB1a assembles heteroreceptors inhibiting glutamate release, while predominantly GABAB1b mediates postsynaptic inhibition. Electron microscopy reveals a synaptic distribution of GABAB1 isoforms that agrees with the observed functional differences. Transfected CA3 neurons selectively express GABAB1a in distal axons, suggesting that the sushi repeats, a conserved protein interaction motif, specify heteroreceptor localization. The constitutive absence of GABAB1a but not GABAB1b results in impaired synaptic plasticity and hippocampus-dependent memory, emphasizing molecular differences in synaptic GABAB functions.
AU - Vigot, Réjan
AU - Barbieri, Samuel
AU - Bräuner-Osborne, Hans
AU - Tureček, Rostislav
AU - Ryuichi Shigemoto
AU - Zhang, Yan Ping
AU - Luján, Rafael
AU - Jacobson, Laura H
AU - Biermann, Barbara
AU - Fritschy, Jean-Marc
AU - Vacher, Claire-Marie
AU - Müller, Matthias P
AU - Sansig, Gilles
AU - Guetg, Nicole
AU - Cryan, John F
AU - Kaupmann, Klemens
AU - Gassmann, Martin
AU - Oertner, Thomas G
AU - Bettler, Bernhard
ID - 2661
IS - 4
JF - Neuron
TI - Differential Compartmentalization and Distinct Functions of GABAB Receptor Variants
VL - 50
ER -
TY - JOUR
AB - G-protein-coupled inwardly rectifying K+ channels (Kir3 channels) coupled to metabotropic GABAB receptors are essential for the control of neuronal excitation. To determine the distribution of Kir3 channels and their spatial relationship to GABAB receptors on hippocampal pyramidal cells, we used a high-resolution immunocytochemical approach. Immunoreactivity for the Kir3.2 subunit was most abundant postsynaptically and localized to the extrasynaptic plasma membrane of dendritic shafts and spines of principal cells. Quantitative analysis of immunogold particles for Kir3.2 revealed an enrichment of the protein around putative glutamatergic synapses on dendritic spines, similar to that of GABA B1. Consistent with this observation, a high degree of coclustering of Kir3.2 and GABAB1 was revealed around excitatory synapses by the highly sensitive SDS-digested freeze-fracture replica immunolabeling. In contrast, in dendritic shafts receptors and channels were found to be mainly segregated. These results suggest that Kir3.2-containing K+ channels on dendritic spines preferentially mediate the effect of GABA, whereas channels on dendritic shafts are likely to be activated by other neurotransmitters as well. Thus, Kir3 channels, localized to different subcellular compartments of hippocampal principal cells, appear to be differentially involved in synaptic integration in pyramidal cell dendrites.
AU - Kulik, Ákos
AU - Vida, Imre
AU - Fukazawa, Yugo
AU - Guetg, Nicole
AU - Kasugai, Yu
AU - Marker, Cheryl L
AU - Rigato, Franck
AU - Bettler, Bernhard
AU - Wickman, Kevin D
AU - Frotscher, Michael
AU - Ryuichi Shigemoto
ID - 2662
IS - 16
JF - Journal of Neuroscience
TI - Compartment-dependent colocalization of Kir3.2-containing K+ channels and GABAB receptors in hippocampal pyramidal cells
VL - 26
ER -
TY - JOUR
AB - The rocker mice are hereditary ataxic mutants that carry a point mutation in the gene encoding the CaV2.1 (P/Q-type) Ca2+ channel α1 subunit, and show the mildest symptoms among the reported CaV2.1 mutant mice. We studied the basic characteristics of the rocker mutant Ca2+ channel and their impacts on excitatory synaptic transmission in cerebellar Purkinje cells (PCs). In acutely dissociated PC somas, the rocker mutant channel showed a moderate reduction in Ca2+ channel current density, whereas its kinetics and voltage dependency of gating remained nearly normal. Despite the small changes in channel function, synaptic transmission in the parallel fiber (PF)-PC synapses was severely impaired. The climbing fiber inputs onto PCs showed a moderate impairment but could elicit normal complex spikes. Presynaptic function of the PF-PC synapses, however, was unexpectedly almost normal in terms of paired-pulse facilitation, sensitivity to extracellular Ca2+ concentration and glutamate concentration in synaptic clefts. Electron microscopic analyses including freeze-fracture replica labeling revealed that both the number and density of postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors substantially decreased without gross structural changes of the PF-PC synapses. We also observed an abnormal arborization of PC dendrites in young adult rocker mice (∼ 1 month old). These lines of evidence suggest that even a moderate dysfunction of CaV2.1 Ca2+ channel can cause substantial changes in postsynaptic molecular composition of the PF-PC synapses and dendritic structure of PCs.
AU - Kodama, Takashi
AU - Itsukaichi-Nishida, Yuko
AU - Fukazawa, Yugo
AU - Wakamori, Minoru
AU - Miyata, Mariko
AU - Molnár, Elek
AU - Mori, Yasuo
AU - Ryuichi Shigemoto
AU - Imoto, Keiji
ID - 2663
IS - 11
JF - European Journal of Neuroscience
TI - A CaV2.1 calcium channel mutation rocker reduces the number of postsynaptic AMPA receptors in parallel fiber-Purkinje cell synapses
VL - 24
ER -
TY - GEN
AB - Metabotropic glutamate receptors (mGlus) are a family of G-protein-coupled receptors activated by the neurotransmitter glutamate. Molecular cloning has revealed eight different subtypes (mGlu1-8) with distinct molecular and pharmacological properties. Multiplicity in this receptor family is further generated through alternative splicing. mGlus activate a multitude of signalling pathways important for modulating neuronal excitability, synaptic plasticity and feedback regulation of neurotransmitter release. In this review, we summarize anatomical findings (from our work and that of other laboratories) describing their distribution in the central nervous system. Recent evidence regarding the localization of these receptors in peripheral tissues will also be examined. The distinct regional, cellular and subcellular distribution of mGlus in the brain will be discussed in view of their relationship to neurotransmitter release sites and of possible functional implications.
AU - Ferraguti, Francesco
AU - Ryuichi Shigemoto
ID - 2664
IS - 2
T2 - Cell and Tissue Research
TI - Metabotropic glutamate receptors
VL - 326
ER -
TY - JOUR
AB - We consider the dynamics of N boson systems interacting through a pair potential N -1 V a (x i -x j ) where V a (x)=a -3 V(x/a). We denote the solution to the N-particle Schrödinger equation by Ψ N, t . Recall that the Gross-Pitaevskii (GP) equation is a nonlinear Schrödinger equation and the GP hierarchy is an infinite BBGKY hierarchy of equations so that if u t solves the GP equation, then the family of k-particle density matrices [InlineMediaObject not available: see fulltext.] solves the GP hierarchy. Under the assumption that a = Nε for 0 < ε < 3/5, we prove that as N→∞ the limit points of the k-particle density matrices of Ψ N, t are solutions of the GP hierarchy with the coupling constant in the nonlinear term of the GP equation given by ∫ V (x)dx. The uniqueness of the solutions of this hierarchy remains an open question.
AU - Elgart, Alexander
AU - László Erdös
AU - Schlein, Benjamin
AU - Yau, Horng-Tzer
ID - 2745
IS - 2
JF - Archive for Rational Mechanics and Analysis
TI - Gross-Pitaevskii equation as the mean field limit of weakly coupled bosons
VL - 179
ER -
TY - CONF
AB - We consider random Schrödinger equations on Rd or Zd for d ≥ 3 with uncorrelated, identically distributed random potential. Denote by λ the coupling constant and ψt the solution with initial data ψ0.
AU - László Erdös
AU - Salmhofer, Manfred
AU - Yau, Horng-Tzer
ID - 2746
TI - Towards the quantum Brownian motion
VL - 690
ER -