@article{3797, author = {Bauer, Wolfgang and Kleine Berkenbusch, Marco and Bollenbach, Mark Tobias}, journal = {Revista Mexicana De Fisica}, number = {4}, pages = {1 -- 6}, publisher = {Sociedad Mexicana de Física}, title = {{Breaking atomic nuclei into little pieces: evidence for a phase transition}}, volume = {49}, year = {2003}, } @inproceedings{3897, abstract = {Many verification, planning, and control problems can be modeled as games played on state-transition graphs by one or two players whose conflicting goals are to form a path in the graph. The focus here is on simple stochastic parity games, that is, two-player games with turn-based probabilistic transitions and omega-regular objectives formalized as parity (Rabin chain) winning conditions. An efficient translation from simple stochastic parity games to nonstochastic parity games is given. As many algorithms are known for solving the latter, the translation yields efficient algorithms for computing the states of a simple stochastic parity game from which a player can win with probability 1. An important special case of simple stochastic parity games are the Markov decision processes with Buchi objectives. For this special case a first provably subquadratic algorithm is given for computing the states from which the single player has a strategy to achieve a Buchi objective with probability 1. For game graphs with m edges the algorithm works in time O(mrootm). Interestingly, a similar technique sheds light on the question of the computational complexity of solving simple Buchi games and yields the first provably subquadratic algorithm, with a running time of O(n(2)/log n) for game graphs with n vertices and O(n) edges.}, author = {Krishnendu Chatterjee and Jurdziński, Marcin and Thomas Henzinger}, pages = {100 -- 113}, publisher = {Springer}, title = {{Simple stochastic parity games}}, doi = {10.1007/978-3-540-45220-1_11}, volume = {2803}, year = {2003}, } @inproceedings{3898, abstract = {We study the problem of determining stack boundedness and the exact maximum stack size for three classes of interrupt-driven programs. Interrupt-driven programs axe used in many real-time applications that require responsive interrupt handling. In order to ensure responsiveness, programmers often enable interrupt processing in the body of lower-priority interrupt handlers. In such programs a programming error can allow interrupt handlers to be interrupted in cyclic fashion to lead to an unbounded stack, causing the system to crash. For a restricted class of interrupt-driven programs, we show that there is a polynomial-time procedure to check stack boundedness, while determining the exact maximum stack size is PSPACE-complete. For a larger class of programs, the two problems are both PSPACE-complete, and for the largest class of programs we consider, the two problems are PSPACE-hard and can be solved in exponential time.}, author = {Krishnendu Chatterjee and Ma, Di and Majumdar, Ritankar S and Zhao, Tian and Thomas Henzinger and Palsberg, Jens}, pages = {109 -- 126}, publisher = {Springer}, title = {{Stack size analysis for interrupt-driven programs}}, doi = {10.1007/3-540-44898-5_7}, volume = {2694}, year = {2003}, } @article{3993, abstract = {We present algorithms for constructing a hierarchy of increasingly coarse Morse-Smale complexes that decompose a piecewise linear 2-manifold. While these complexes are defined only in the smooth category, we extend the construction to the piecewise linearcategory by ensuring structural integrity and simulating differentiability. We then simplify Morse-Smale complexes by canceling pairs of critical points in order of increasing persistence.}, author = {Herbert Edelsbrunner and Harer, John and Zomorodian, Afra}, journal = {Discrete & Computational Geometry}, number = {1}, pages = {87 -- 107}, publisher = {Springer}, title = {{Hierarchical Morse-Smale complexes for piecewise linear 2-manifolds}}, doi = {10.1007/s00454-003-2926-5}, volume = {30}, year = {2003}, } @article{3994, abstract = {The body defined by a finite collection of disks is a subset of the plane bounded by a tangent continuous curve, which we call the skin. We give analytic formulas for the area, the perimeter, the area derivative, and the perimeter derivative of the body. Given the filtrations of the Delaunay triangulation and the Voronoi diagram of the disks, all formulas can be evaluated in time proportional to the number of disks.}, author = {Cheng, Ho-Lun and Herbert Edelsbrunner}, journal = {Computational Geometry: Theory and Applications}, number = {2}, pages = {173 -- 192}, publisher = {Elsevier}, title = {{Area, perimeter and derivatives of a skin curve}}, doi = {10.1016/S0925-7721(02)00124-4}, volume = {26}, year = {2003}, } @misc{3139, abstract = {Significant advances have been made during the past few years in our understanding of how the spinal monosynaptic reflex develops. Transcription factors in the Neurogenin, Runt, ETS, and LIM families control sequential steps of the specification of various subtypes of dorsal root ganglia sensory neurons. The initiation of muscle spindle differentiation requires neuregulin 1, derived from Ia afferent sensory neurons, and signaling through ErbB receptors in intrafusal muscle fibers. Several retrograde signals from the periphery are important for the establishment of late connectivity in the reflex circuit. Finally, neurotrophin 3 released from muscle spindles regulates the strength of sensory-motor connections within the spinal cord postnatally.}, author = {Chen, Hsiao Huei and Simon Hippenmeyer and Arber, Silvia and Frank, Eric}, booktitle = {Current Opinion in Neurobiology}, number = {1}, pages = {96 -- 102}, publisher = {Elsevier}, title = {{Development of the monosynaptic stretch reflex circuit}}, doi = {10.1016/S0959-4388(03)00006-0}, volume = {13}, year = {2003}, } @inproceedings{3171, abstract = {Reconstructing a 3-D scene from more than one camera is a classical problem in computer vision. One of the major sources of difficulty is the fact that not all scene elements are visible from all cameras. In the last few years, two promising approaches have been developed 11,12 that formulate the scene reconstruction problem in terms of energy minimization, and minimize the energy using graph cuts. These energy minimization approaches treat the input images symmetrically, handle visibility constraints correctly, and allow spatial smoothness to be enforced. However, these algorithm propose different problem formulations, and handle a limited class of smoothness terms. One algorithm 11 uses a problem formulation that is restricted to two-camera stereo, and imposes smoothness between a pair of cameras. The other algorithm 12 can handle an arbitrary number of cameras, but imposes smoothness only with respect to a single camera. In this paper we give a more general energy minimization formulation for the problem, which allows a larger class of spatial smoothness constraints. We show that our formulation includes both of the previous approaches as special cases, as well as permitting new energy functions. Experimental results on real data with ground truth are also included. }, author = {Vladimir Kolmogorov and Zabih, Ramin and Gortler, Steven}, pages = {501 -- 516}, publisher = {Springer}, title = {{Generalized multi camera scene reconstruction using graph cuts}}, doi = {10.1007/978-3-540-45063-4_32}, volume = {2683}, year = {2003}, } @inproceedings{3174, abstract = {We address visual correspondence problems without assuming that scene points have similar intensities in different views. This situation is common, usually due to non-lambertian scenes or to differences between cameras. We use maximization of mutual information, a powerful technique for registering images that requires no a priori model of the relationship between scene intensities in different views. However, it has proven difficult to use mutual information to compute dense visual correspondence. Comparing fixed-size windows via mutual information suffers from the well-known problems of fixed windows, namely poor performance at discontinuities and in low-texture regions. In this paper, we show how to compute visual correspondence using mutual information without suffering from these problems. Using 'a simple approximation, mutual information can be incorporated into the standard energy minimization framework used in early vision. The energy can then be efficiently minimized using graph cuts, which preserve discontinuities and handle low-texture regions. The resulting algorithm combines the accurate disparity maps that come from graph cuts with the tolerance for intensity changes that comes from mutual information.}, author = {Kim, Junhwan and Vladimir Kolmogorov and Zabih, Ramin}, pages = {1033 -- 1040}, publisher = {IEEE}, title = {{Visual correspondence using energy minimization and mutual information}}, doi = {10.1109/ICCV.2003.1238463}, volume = {2}, year = {2003}, } @inproceedings{3170, abstract = {Geodesic active contours and graph cuts are two standard image segmentation techniques. We introduce a new segmentation method combining some of their benefits. Our main intuition is that any cut on a graph embedded in some continuous space can be interpreted as a contour (in 2D) or a surface (in 3D). We show how to build a grid graph and set its edge weights so that the cost of cuts is arbitrarily close to the length (area) of the corresponding contours (surfaces) for any anisotropic Riemannian metric. There are two interesting consequences of this technical result. First, graph cut algorithms can be used to find globally minimum geodesic contours (minimal surfaces in 3D) under arbitrary Riemannian metric for a given set of boundary conditions. Second, we show how to minimize metrication artifacts in existing graph-cut based methods in vision. Theoretically speaking, our work provides an interesting link between several branches of mathematics -differential geometry, integral geometry, and combinatorial optimization. The main technical problem is solved using Cauchy-Crofton formula from integral geometry.}, author = {Boykov, Yuri and Vladimir Kolmogorov}, pages = {26 -- 33}, publisher = {IEEE}, title = {{Computing geodesics and minimal surfaces via graph cuts}}, doi = {10.1109/ICCV.2003.1238310}, volume = {1}, year = {2003}, } @article{3526, abstract = {Neurons can produce action potentials with high temporal precision(1). A fundamental issue is whether, and how, this capability is used in information processing. According to the `cell assembly' hypothesis, transient synchrony of anatomically distributed groups of neurons underlies processing of both external sensory input and internal cognitive mechanisms(2-4). Accordingly, neuron populations should be arranged into groups whose synchrony exceeds that predicted by common modulation by sensory input. Here we find that the spike times of hippocampal pyramidal cells can be predicted more accurately by using the spike times of simultaneously recorded neurons in addition to the animals location in space. This improvement remained when the spatial prediction was refined with a spatially dependent theta phase modulation(5-8). The time window in which spike times are best predicted from simultaneous peer activity is 10-30 ms, suggesting that cell assemblies are synchronized at this timescale. Because this temporal window matches the membrane time constant of pyramidal neurons(9), the period of the hippocampal gamma oscillation(10) and the time window for synaptic plasticity(11), we propose that cooperative activity at this timescale is optimal for information transmission and storage in cortical circuits.}, author = {Harris, Kenneth D and Jozsef Csicsvari and Hirase, Hajima and Dragoi, George and Buzsáki, György}, journal = {Nature}, number = {6948}, pages = {552 -- 556}, publisher = {Nature Publishing Group}, title = {{Organization of cell assemblies in the hippocampus}}, doi = {0.1038/nature01834}, volume = {424}, year = {2003}, } @article{3529, abstract = {Parallel recording of neuronal activity in the behaving animal is a prerequisite for our understanding of neuronal representation and storage of information. Here we describe the development of micro-machined silicon microelectrode arrays for unit and local field recordings. The two-dimensional probes with 96 or 64 recording sites provided high-density recording of unit and field activity with minimal tissue displacement or damage. The on-chip active circuit eliminated movement and other artifacts and greatly reduced the weight of the headgear. The precise geometry of the recording tips allowed for the estimation of the spatial location of the recorded neurons and for high-resolution estimation of extracellular current source density. Action potentials could be simultaneously recorded from the soma and dendrites of the same neurons. Silicon technology is a promising approach for high-density, high-resolution sampling of neuronal activity in both basic research and prosthetic devices.}, author = {Jozsef Csicsvari and Henze, Darrell A and Jamieson, Brian G and Harris, Kenneth D and Sirota, Anton M and Bartho, Peter and Wise, Kensall D and Buzsáki, György}, journal = {Journal of Neurophysiology}, number = {2}, pages = {1314 -- 1323}, publisher = {American Physiological Society}, title = {{Massively parallel recording of unit and local field potentials with silicon-based electrodes}}, doi = {10.1152/jn.00116.2003}, volume = {90}, year = {2003}, } @article{3528, abstract = {Gamma frequency oscillations (30-100 Hz) have been suggested to underlie various cognitive and motor functions. Here, we examine the generation of gamma oscillation currents in the hippocampus, using two-dimensional, 96-site silicon probes. Two gamma generators were identified, one in the dentate gyrus and another in the CA3-CA1 regions. The coupling strength between the two oscillators varied during both theta and nontheta states. Both pyramidal cells and interneurons were phase-locked to gamma waves. Anatomical connectivity, rather than physical distance, determined the coupling strength of the oscillating neurons. CA3 pyramidal neurons discharged CA3 and CA1 interneurons at latencies indicative of monosynaptic connections. Intrahippocampal gamma oscillation emerges in the CA3 recurrent system, which entrains the CA1 region via its interneurons.}, author = {Jozsef Csicsvari and Jamieson, Brian G and Wise, Kensall D and Buzsáki, György}, journal = {Neuron}, number = {2}, pages = {311 -- 322}, publisher = {Elsevier}, title = {{Mechanisms of gamma oscillations in the hippocampus of the behaving rat}}, doi = {10.1016/S0896-6273(02)01169-8}, volume = {37}, year = {2003}, } @article{3543, abstract = {Both neocortical and hippocampal networks organize the firing patterns of their neurons by prominent oscillations during sleep, but the functional role of these rhythms is not well understood. Here, we show a robust correlation of neuronal discharges between the somatosensory cortex and hippocampus on both slow and fine time scales in the mouse and rat. Neuronal bursts in deep cortical layers, associated with sleep spindles and delta waves/slow rhythm, effectively triggered hippocampal discharges related to fast (ripple) oscillations. We hypothesize that oscillation-mediated temporal links coordinate specific information transfer between neocortical and hippocampal cell assemblies. Such a neocortical-hippocampal interplay may be important for memory consolidation.}, author = {Sirota, Anton M and Jozsef Csicsvari and Buhl, Derek L and Buzsáki, György}, journal = {PNAS}, number = {4}, pages = {2065 -- 2069}, publisher = {National Academy of Sciences}, title = {{Communication between neocortex and hippocampus during sleep in rodents}}, doi = {10.1073/pnas.0437938100}, volume = {100}, year = {2003}, } @article{3593, abstract = {Temporal logics such as Computation Tree Logic (CTL) and Linear Temporal Logic (LTL) have become popular for specifying temporal properties over a wide variety of planning and verification problems. In this paper we work towards building a generalized framework for automated reasoning based on temporal logics. We present a powerful extension of CTL with first-order quantification over the set of reachable states for reasoning about extremal properties of weighted labeled transition systems in general. The proposed logic, which we call Weighted Quantified Computation Tree Logic (WQCTL), captures the essential elements common to the domain of planning and verification problems and can thereby be used as an effective specification language in both domains. We show that in spite of the rich, expressive power of the logic, we are able to evaluate WQCTL formulas in time polynomial in the size of the state space times the length of the formula. Wepresent experimental results on the WQCTL verifier.}, author = {Krishnendu Chatterjee and Dasgupta, Pallab and Chakrabarti, Partha P}, journal = {Journal of Automated Reasoning}, number = {2}, pages = {205 -- 232}, publisher = {Springer}, title = {{A branching time temporal framework for quantitative reasoning}}, doi = {10.1023/A:1023217515688}, volume = {30}, year = {2003}, } @phdthesis{3678, author = {Christoph Lampert}, booktitle = {Bonner Mathematische Schriften}, pages = {1 -- 165}, publisher = {Universität Bonn, Fachbibliothek Mathematik}, title = {{The Neumann operator in strictly pseudoconvex domains with weighted Bergman metric }}, volume = {356}, year = {2003}, } @article{3725, abstract = {The combination of high-resolution atomic force microscopy (AFM) imaging and single-molecule force-spectroscopy was employed to unfold single bacteriorhodopsins (BR) from native purple membrane patches at various physiologically relevant temperatures. The unfolding spectra reveal detailed insight into the stability of individual structural elements of BR against mechanical unfolding. Intermittent states in the unfolding process are associated with the stepwise unfolding of alpha-helices, whereas other states are associated with the unfolding of polypeptide loops connecting the alpha-helices. It was found that the unfolding forces of the secondary structures considerably decreased upon increasing the temperature from 8 to 52°C. Associated with this effect, the probability of individual unfolding pathways of BR was significantly influenced by the temperature. At lower temperatures, transmembrane alpha-helices and extracellular polypeptide loops exhibited sufficient stability to individually establish potential barriers against unfolding, whereas they predominantly unfolded collectively at elevated temperatures. This suggests that increasing the temperature decreases the mechanical stability of secondary structural elements and changes molecular interactions between secondary structures, thereby forcing them to act as grouped structures.}, author = {Harald Janovjak and Kessler, Max and Oesterhelt, Dieter and Gaub, Hermann and Mueller, Daniel J}, journal = {EMBO Journal}, number = {19}, pages = {5220 -- 5229}, publisher = {Wiley-Blackwell}, title = {{Unfolding pathways of native bacteriorhodopsin depend on temperature}}, doi = {10.1093/emboj/cdg509}, volume = {22}, year = {2003}, } @article{3804, abstract = {Kv3 channels are thought to be essential for the fast-spiking (FS) phenotype in GABAergic interneurons, but how these channels confer the ability to generate action potentials (APs) at high frequency is unknown. To address this question, we developed a fast dynamic-clamp system (approximately 50 kHz) that allowed us to add a Kv3 model conductance to CA1 oriens alveus (OA) interneurons in hippocampal slices. Selective pharmacological block of Kv3 channels by 0.3 mm 4-aminopyridine or 1 mm tetraethylammonium ions led to a marked broadening of APs during trains of short stimuli and a reduction in AP frequency during 1 sec stimuli. The addition of artificial Kv3 conductance restored the original AP pattern. Subtraction of Kv3 conductance by dynamic clamp mimicked the effects of the blockers. Application of artificial Kv3 conductance also led to FS in OA interneurons after complete K+ channel block and even induced FS in hippocampal pyramidal neurons in the absence of blockers. Adding artificial Kv3 conductance with altered deactivation kinetics revealed a nonmonotonic relationship between mean AP frequency and deactivation rate, with a maximum slightly above the original value. Insertion of artificial Kv3 conductance with either lowered activation threshold or inactivation also led to a reduction in the mean AP frequency. However, the mechanisms were distinct. Shifting the activation threshold induced adaptation, whereas adding inactivation caused frequency-dependent AP broadening. In conclusion, Kv3 channels are necessary for the FS phenotype of OA interneurons, and several of their gating properties appear to be optimized for high-frequency repetitive activity.}, author = {Lien, Cheng-Chang and Peter Jonas}, journal = {Journal of Neuroscience}, number = {6}, pages = {2058 -- 68}, publisher = {Society for Neuroscience}, title = {{Kv3 potassium conductance is necessary and kinetically optimized for high-frequency action potential generation in hippocampal interneurons}}, volume = {23}, year = {2003}, } @article{3806, abstract = {To probe exocytosis at a cortical glutamatergic synapse, we made capacitance measurements in whole-cell recorded hippocampal mossy fiber terminals. Evaluation of different methods by using a morphology-based equivalent electrical model revealed that quantitative capacitance measurements are possible in this presynaptic structure. Voltage pulses leading to presynaptic Ca2+ inflow evoked large capacitance signals that showed saturation with increasing pulse duration. The mean peak capacitance increase was 100 fF, corresponding to a pool of approximately 1,400 releasable vesicles. Thus hippocampal mossy fiber synapses have a vesicular "maxipool." Large pool size and rapid vesicle recycling may underlie the uniquely large extent of activity-dependent plasticity in this synapse.}, author = {Hallermann, Stefan and Pawlu, Christian and Peter Jonas and Heckmann, Manfred}, journal = {PNAS}, number = {15}, pages = {8975 -- 80}, publisher = {National Academy of Sciences}, title = {{A large pool of releasable vesicles in a cortical glutamatergic synapse}}, doi = {10.1073/pnas.1432836100}, volume = {100}, year = {2003}, } @article{3921, abstract = {Unlike most social insects, many Cardiocondyla ant species have two male morphs: wingless (ergatoid) males, who remain in the natal nest, and winged males who disperse but, strangely, before leaving may also mate within the nest. Whereas ergatoid males are highly intolerant of each other and fight among themselves, they tend to tolerate their winged counterparts. This is despite the fact that these winged males, like ergatoid males, represent mating competition. Why should ergatoid males tolerate their winged rivals? We developed a mathematical model to address this question. Our model focuses on a number of factors likely toinfluence whether ergatoid males are tolerant of winged males: ergatoid male–winged male relatedness, number of virgin queens, number of winged males, and the number of ejaculates a winged male has (winged males are sperm limited, whereas ergatoid males have lifelong spermatogenesis). Surprisingly, we found that increasing the number of virgin queens favors a kill strategy, whereas an increase in the other factors favors a let-live strategy; these predictions appear true for C. obscurior and for a number of other Cardiocondyla species. Two further aspects, unequal insemination success and multiple mating in queens, were also incorporated into the model and predictions made about their effects on toleration of winged males. The model is applicable more generally in species that have dimorphic males, such as some other ants, bees, and fig wasps.}, author = {Anderson, Carl and Cremer, Sylvia and Heinze, Jürgen}, journal = {Behavioral Ecology}, number = {1}, pages = {54 -- 62}, publisher = {Oxford University Press}, title = {{Live and let die: Why fighter males of the ant Cardiocondyla kill each other but tolerate their winged rivals}}, doi = {10.1093/beheco/14.1.54}, volume = {14}, year = {2003}, } @article{3922, abstract = {Dispersal is advantageous, but, at the same time, it implies high costs and risks. Due to these counteracting selection pressures, many species evolved dispersal polymorphisms, which, in ants, are typically restricted to the female sex (queens). Male polymorphism is presently only known from a few genera, such as Cardiocondyla, in which winged dispersing males coexist with wingless fighter males that mate exclusively inside their maternal nests. We studied the developmental mechanisms underlying these alternative male morphs and found that, first, male dimorphism is not genetically determined, but is induced by environmental conditions (decreasing temperature and density). Second, male morph is not yet fixed at the egg stage, but it differentiates during larval development. This flexible developmental pattern of male morphs allows Cardiocondyla ant colonies to react quickly to changes in their environment. Under good conditions, they invest exclusively in philopatric wingless males. But, when environmental conditions turn bad, colonies start to produce winged dispersal males, even though these males require a many times higher investment by the colony than their much smaller wingless counterparts. Cardiocondyla ants share this potential of optimal resource allocation with other colonial animals and some seed dimorphic plants.}, author = {Cremer, Sylvia and Heinze, Jürgen}, journal = {Current Biology}, number = {3}, pages = {219 -- 223}, publisher = {Cell Press}, title = {{Stress grows wings: Environmental induction of winged dispersal males in Cardiocondyla ants}}, doi = {10.1016/S0960-9822(03)00012-5}, volume = {13}, year = {2003}, }