TY - JOUR
AB - SiGe islands move laterally on a Si(001) substrate during in situ postgrowth annealing. This surprising behavior is revealed by an analysis of the substrate surface morphology after island removal using wet chemical etching. We explain the island motion by asymmetric surface-mediated alloying. Material leaves one side of the island by surface diffusion, and mixes with additional Si from the surrounding surface as it redeposits on the other side. Thus the island moves laterally while becoming larger and more dilute.
AU - Denker, Ulrich
AU - Rastelli, Armando
AU - Stoffel, Mathieu
AU - Tersoff, Jerry
AU - Georgios Katsaros
AU - Costantini, Giovanni
AU - Kern, Klaus
AU - Jin-Phillipp, Neng Y
AU - Jesson, David E
AU - Schmidt, Oliver G
ID - 1741
IS - 21
JF - Physical Review Letters
TI - Lateral motion of SiGe islands driven by surface-mediated alloying
VL - 94
ER -
TY - JOUR
AB - The effects of substrate temperature, growth rate, and postgrowth annealing on the composition of Ge islands grown on Si(001) were investigated with a combination of selective wet chemical etching and atomic force microscopy. A simple kinetic model comprising only surface diffusion processes can explain all the experimentally observed compositional profiles for pyramid and dome islands grown in the 560-620°C range. From this model three-dimensional compositional maps were extracted. By performing annealing experiments a change in the composition of the domes was observed. This could be explained as the result of the islands' movement induced by alloying-driven energy minimization. Also in this case kinetically hindered bulk diffusion processes are not needed to explain the experimental observations.
AU - Georgios Katsaros
AU - Costantini, Giovanni
AU - Stoffel, Mathieu
AU - Esteban, Rubén
AU - Bittner, Alexander M
AU - Rastelli, Armando
AU - Denker, Ulrich
AU - Schmidt, Oliver G
AU - Kern, Klaus
ID - 1742
IS - 19
JF - Physical Review B - Condensed Matter and Materials Physics
TI - Kinetic origin of island intermixing during the growth of Ge on Si (001)
VL - 72
ER -
TY - JOUR
AB - Laterally aligned multilayer GeSiSi islands grown on a patterned Si (001) substrate are disclosed by selective etching of Si in a KOH solution. This procedure allows us to visualize the vertical alignment of the islands in a three-dimensional perspective. Our technique reveals that partly coalesced double islands in the initial layer do not merge together, but instead gradually reproduce into well-separated double islands in upper layers. We attribute this effect to very thin spacer layers, which efficiently transfer the strain modulation of each island through the spacer layer to the surface. The etching rate of Si is reduced in tensile strained regions, which helps to preserve sufficient Si between the stacked islands to form a periodic array of freestanding and vertically modulated heterostructure pillars.
AU - Zhong, Zheyang
AU - Georgios Katsaros
AU - Stoffel, Mathieu
AU - Costantini, Giovanni
AU - Kern, Klaus
AU - Schmidt, Oliver G
AU - Jin-Phillipp, Neng Y
AU - Bauer, Günther
ID - 1743
IS - 26
JF - Applied Physics Letters
TI - Periodic pillar structures by Si etching of multilayer GeSi/Si islands
VL - 87
ER -
TY - JOUR
AB - This paper presents optical duobinary and dicode signalling, as alternatives to the binary format, in order to improve the transmission performance in the presense of non-linear effects in a dense wavelength division multiplex (WDM) optical system. Duobinary signalling is applied to an optical system to explore the reduction of stimulated Brillouin scattering (SBS) effects. Duobinary signalling suppresses the SBS effects, and an eye-opening improvement of 0.25 to 1.2 dB is achieved relative to binary transmission over a range of input power levels. An experimental study demonstrates that duobinary modulation suppresses the four wave mixing (FWM) products of a dense WDM system by a maximum of 3 dB. The suppression is maintained over a range of channel spacings. An investigation of the impact of fibre dispersion on FWM products under binary, duobinary and dicode modulation in a dense WDM system is then performed, with interchannel spacing and optical power variation. This leads to the development of a set of guidelines for the application areas, in which it is appropriate to use duobinary or dicode modulation in WDM systems as a means of mitigating the impact of FWM.
AU - Georgios Katsaros
AU - Darwazeh, Izzat Z
AU - Lane, Phil M
ID - 1744
IS - 6
JF - IEE Proceedings - Optoelectronics
TI - Non linear transmission effects in duobinary and dicode optical systems
VL - 152
ER -
TY - JOUR
AB - Background: Murine leukemia virus (MLV) vector particles can be pseudotyped with a truncated variant of the human immunodeficiency virus type 1 (HIV-1) envelope protein (Env) and selectively target gene transfer to human cells expressing both CD4 and an appropriate co-receptor. Vector transduction mimics the HIV-1 entry process and is therefore a safe tool to study HIV-1 entry. Results: Using FLY cells, which express the MLV gag and pol genes, we generated stable producer cell lines that express the HIV-1 envelope gene and a retroviral vector genome encoding the green fluorescent protein (GFP). The BH10 or 89.6 P HIV-1 Env was expressed from a bicistronic vector which allowed the rapid selection of stable cell lines. A codon-usage-optimized synthetic env gene permitted high, Rev-independent Env expression. Vectors generated by these producer cells displayed different sensitivity to entry inhibitors. Conclusion: These data illustrate that MLV/HIV-1 vectors are a valuable screening system for entry inhibitors or neutralizing antisera generated by vaccines.
AU - Sandra Siegert
AU - Thaler, Sonja
AU - Wagner, Ralf
AU - Schnierle, Barbara S
ID - 1795
IS - 1
JF - AIDS Research and Therapy
TI - Assessment of HIV-1 entry inhibitors by MLV/HIV-1 pseudotyped vectors
VL - 2
ER -
TY - JOUR
AB -
Complex I of respiratory chains plays a central role in bioenergetics and is implicated in many human neurodegenerative diseases. An understanding of its mechanism requires a knowledge of the organization of redox centers. The arrangement of iron-sulfur clusters in the hydrophilic domain of complex I from Thermus thermophilus has been determined with the use of x-ray crystallography. One binuclear and six tetranuclear clusters are arranged, maximally 14 angstroms apart, in an 84-angstrom-long electron transfer chain. The binuclear cluster N1a and the tetranuclear cluster N7 are not in this pathway. Cluster N1a may play a role in the prevention of oxidative damage. The structure provides a framework for the interpretation of the large amounts of data accumulated on complex I.
AU - Hinchliffe, Philip
AU - Leonid Sazanov
ID - 1962
IS - 5735
JF - Science
TI - Biochemistry: Organization of iron-sulfur clusters in respiratory complex I
VL - 309
ER -
TY - BOOK
AB - Harold Davenport was one of the truly great mathematicians of the twentieth century. Based on lectures he gave at the University of Michigan in the early 1960s, this book is concerned with the use of analytic methods in the study of integer solutions to Diophantine equations and Diophantine inequalities. It provides an excellent introduction to a timeless area of number theory that is still as widely researched today as it was when the book originally appeared. The three main themes of the book are Waring's problem and the representation of integers by diagonal forms, the solubility in integers of systems of forms in many variables, and the solubility in integers of diagonal inequalities. For the second edition of the book a comprehensive foreword has been added in which three prominent authorities describe the modern context and recent developments. A thorough bibliography has also been added.
AU - Davenport, Harold
AU - Timothy Browning
ID - 210
T2 - Analytic methods for diophantine equations and diophantine inequalities
TI - Analytic methods for diophantine equations and diophantine inequalities
ER -
TY - JOUR
AB - Let f ∈ ℤ[x] be a polynomial of degree d. The paucity of non-trivial positive integer solutions to the equation f(x1)+f(x 2)=f(x3)+f(x4) is established, provided that d ≤ 7$. Also the corresponding situation is investigated for equal sums of three like polynomials.
AU - Timothy Browning
ID - 211
IS - 6
JF - Bulletin of the London Mathematical Society
TI - Equal sums of like polynomials
VL - 37
ER -
TY - JOUR
AB - For any n ≧ 2, let F ∈ ℤ [ x 1, … , xn ] be a form of degree d≧ 2, which produces a geometrically irreducible hypersurface in ℙn–1. This paper is concerned with the number N(F;B) of rational points on F = 0 which have height at most B. For any ε > 0 we establish the estimate N(F; B) = O(B n− 2+ ε ), whenever either n ≦ 5 or the hypersurface is not a union of lines. Here the implied constant depends at most upon d, n and ε.
AU - Timothy Browning
AU - Heath-Brown, Roger
ID - 212
IS - 584
JF - Journal fur die Reine und Angewandte Mathematik
TI - Counting rational points on hypersurfaces
ER -
TY - JOUR
AB - Given an absolutely irreducible ternary form F, the purpose of this paper is to produce better upper bounds for the number of integer solutions to the equation F=0, that are restricted to lie in very lopsided boxes. As an application of the main result, a new paucity estimate is obtained for equal sums of two like powers.
AU - Timothy Browning
AU - Heath-Brown, Roger
ID - 214
IS - 2
JF - Mathematische Zeitschrift
TI - Plane curves in boxes and equal sums of two powers
VL - 251
ER -
TY - JOUR
AB - We show that the number of nontrivial rational points of height at most B, which lie on the cubic surface x1 x2 x3 = x4 (x1 + x2 + x3)2, has order of magnitude B (log B)6. This agrees with Manin's conjecture.
AU - Timothy Browning
ID - 217
IS - 2
JF - Journal of Number Theory
TI - The density of rational points on a certain singular cubic surface
VL - 119
ER -
TY - CONF
AB - Surveying results from [5] and [6], we motivate and introduce the theory behind formalizing rich interfaces for software and hardware components. Rich interfaces specify the protocol aspects of component interaction. Their formalization, called interface automata, permits a compiler to check the compatibility of component interaction protocols. Interface automata support incremental design and independent implementability. Incremental design means that the compatibility checking of interfaces can proceed for partial system descriptions, without knowing the interfaces of all components. Independent implementability means that compatible interfaces can be refined separately, while still maintaining compatibility.
AU - de Alfaro, Luca
AU - Thomas Henzinger
ID - 4624
TI - Interface-based design
VL - 195
ER -
TY - JOUR
AB - Temporal logic is two-valued: formulas are interpreted as either true or false. When applied to the analysis of stochastic systems, or systems with imprecise formal models, temporal logic is therefore fragile: even small changes in the model can lead to opposite truth values for a specification. We present a generalization of the branching-time logic CTL which achieves robustness with respect to model perturbations by giving a quantitative interpretation to predicates and logical operators, and by discounting the importance of events according to how late they occur. In every state, the value of a formula is a real number in the interval [0,1], where 1 corresponds to truth and 0 to falsehood. The boolean operators and and or are replaced by min and max, the path quantifiers ∃ and ∀ determine sup and inf over all paths from a given state, and the temporal operators ⋄ and □ specify sup and inf over a given path; a new operator averages all values along a path. Furthermore, all path operators are discounted by a parameter that can be chosen to give more weight to states that are closer to the beginning of the path.
We interpret the resulting logic DCTL over transition systems, Markov chains, and Markov decision processes. We present two semantics for DCTL: a path semantics, inspired by the standard interpretation of state and path formulas in CTL, and a fixpoint semantics, inspired by the μ-calculus evaluation of CTL formulas. We show that, while these semantics coincide for CTL, they differ for DCTL, and we provide model-checking algorithms for both semantics.
AU - de Alfaro, Luca
AU - Faella, Marco
AU - Thomas Henzinger
AU - Majumdar, Ritankar S
AU - Stoelinga, Mariëlle
ID - 4625
IS - 1
JF - Theoretical Computer Science
TI - Model checking discounted temporal properties
VL - 345
ER -
TY - CONF
AB - We present the first demonstration of Jozsa's "counterfactual computation", using an optical Grover's search algorithm. We put the algorithm in a superposition of 'running' and 'not-running', obtaining information even though the algorithm does not run.
AU - Onur Hosten
AU - Rakher, Matthew T
AU - Barreiro, Julio T
AU - Peters, Nicholas A
AU - Kwiat, Paul G
ID - 575
TI - Counterfactual quantum computation
VL - 1
ER -
TY - JOUR
AB - A current challenge in neuroscience is to bridge the gaps between genes, proteins, neurons, neural circuits, and behavior in a single animal model. The nematode Caenorhabditis elegans has unique features that facilitate this synthesis. Its nervous system includes exactly 302 neurons, and their pattern of synaptic connectivity is known. With only five olfactory neurons, C. elegans can dynamically respond to dozens of attractive and repellant odors. Thermosensory neurons enable the nematode to remember its cultivation temperature and to track narrow isotherms. Polymodal sensory neurons detect a wide range of nociceptive cues and signal robust escape responses. Pairing of sensory stimuli leads to long-lived changes in behavior consistent with associative learning. Worms exhibit social behaviors and complex ultradian rhythms driven by Ca2+ oscillators with clock-like properties. Genetic analysis has identified gene products required for nervous system function and elucidated the molecular and neural bases of behaviors.
AU - de Bono, Mario
AU - Villu Maricq, Andres
ID - 6153
JF - Annual Review of Neuroscience
SN - 0147-006X
TI - Neuronal substrates of complex behaviors in C. elegans
VL - 28
ER -
TY - JOUR
AU - Cheung, Benny H.H.
AU - Cohen, Merav
AU - Rogers, Candida
AU - Albayram, Onder
AU - de Bono, Mario
ID - 6154
IS - 10
JF - Current Biology
SN - 0960-9822
TI - Experience-dependent modulation of C. elegans behavior by ambient oxygen
VL - 15
ER -
TY - JOUR
AB - Genetically encoded fluorescent probes of neural activity represent new promising tools for systems neuroscience. Here, we present a comparative in vivo analysis of 10 different genetically encoded calcium indicators, as well as the pH-sensitive synapto-pHluorin. We analyzed their fluorescence changes in presynaptic boutons of the Drosophila larval neuromuscular junction. Robust neural activity did not result in any or noteworthy fluorescence changes when Flash-Pericam, Camgaroo-1, and Camgaroo-2 were expressed. However, calculated on the raw data, fractional fluorescence changes up to 18% were reported by synapto-pHluorin, Yellow Cameleon 2.0, 2.3, and 3.3, Inverse-Pericam, GCaMP1.3, GCaMP1.6, and the troponin C-based calcium sensor TN-L15. The response characteristics of all of these indicators differed considerably from each other, with GCaMP1.6 reporting high rates of neural activity with the largest and fastest fluorescence changes. However, GCaMP1.6 suffered from photobleaching, whereas the fluorescence signals of the double-chromophore indicators were in general smaller but more photostable and reproducible, with TN-L15 showing the fastest rise of the signals at lower activity rates. We show for GCaMP1.3 and YC3.3 that an expanded range of neural activity evoked fairly linear fluorescence changes and a corresponding linear increase in the signal-to-noise ratio (SNR). The expression level of the indicator biased the signal kinetics and SNR, whereas the signal amplitude was independent. The presented data will be useful for in vivo experiments with respect to the selection of an appropriate indicator, as well as for the correct interpretation of the optical signals.
AU - Reiff, Dierk F
AU - Ihring, Alexandra
AU - Guerrero, Giovanna
AU - Isacoff, Ehud Y
AU - Maximilian Jösch
AU - Nakai, Junichi
AU - Borst, Alexander
ID - 1298
IS - 19
JF - Journal of Neuroscience
TI - In vivo performance of genetically encoded indicators of neural activity in flies
VL - 25
ER -
TY - CHAP
AB - The paper surveys the mirror symmetry conjectures of Hausel-Thaddeus and Hausel-Rodriguez-Villegas concerning the equality of certain Hodge numbers of SL(n, ℂ) vs. PGL(n, ℂ) flat connections and character varieties for curves, respectively. Several new results and conjectures and their relations to works of Hitchin, Gothen, Garsia-Haiman and Earl-Kirwan are explained. These use the representation theory of finite groups of Lie-type via the arithmetic of character varieties and lead to an unexpected conjecture for a Hard Lefschetz theorem for their cohomology.
AU - Tamas Hausel
ID - 1444
T2 - Geometric Methods in Algebra and Number Theory
TI - Mirror symmetry and Langlands duality in the non-Abelian Hodge theory of a curve
VL - 235
ER -
TY - JOUR
AB - Building on a recent paper [8], here we argue that the combinatorics of matroids are intimately related to the geometry and topology of toric hyperkähler varieties. We show that just like toric varieties occupy a central role in Stanley’s proof for the necessity of McMullen’s conjecture (or g-inequalities) about the classification of face vectors of simplicial polytopes, the topology of toric hyperkähler varieties leads to new restrictions on face vectors of matroid complexes. Namely in this paper we will give two proofs that the injectivity part of the Hard Lefschetz theorem survives for toric hyperkähler varieties. We explain how this implies the g-inequalities for rationally representable matroids. We show how the geometrical intuition in the first proof, coupled with results of Chari [3], leads to a proof of the g-inequalities for general matroid complexes, which is a recent result of Swartz [20]. The geometrical idea in the second proof will show that a pure O-sequence should satisfy the g-inequalities, thus showing that our result is in fact a consequence of a long-standing conjecture of Stanley.
AU - Tamas Hausel
ID - 1447
IS - 1
JF - Open Mathematics
TI - Quaternionic geometry of matroids
VL - 3
ER -
TY - JOUR
AB - We study an integration theory in circle equivariant cohomology in order to prove a theorem relating the cohomology ring of a hyperkähler quotient to the cohomology ring of the quotient by a maximal abelian subgroup, analogous to a theorem of Martin for symplectic quotients. We discuss applications of this theorem to quiver varieties, and compute as an example the ordinary and equivariant cohomology rings of a hyperpolygon space.
AU - Tamas Hausel
AU - Proudfoot, Nicholas J
ID - 1463
IS - 1
JF - Topology
TI - Abelianization for hyperkähler quotients
VL - 44
ER -