@article{9147, abstract = {As part of an ongoing effort to develop a parameterization of wave-induced abyssal mixing, the authors derive an heuristic model for nonlinear wave breaking and energy dissipation associated with internal tides. Then the saturation and dissipation of internal tides for idealized and observed topography samples are investigated. One of the main results is that the wave-induced mixing could be more intense and more confined to the bottom than previously assumed in numerical models. Furthermore, in this model wave breaking and mixing clearly depend on the small scales of the topography below 10 km or so, which is below the current resolution of global bathymetry. This motivates the use of a statistical approach to represent the unresolved topography when addressing the role of internal tides in mixing the deep ocean.}, author = {Muller, Caroline J and Bühler, Oliver}, issn = {1520-0485}, journal = {Journal of Physical Oceanography}, keywords = {Oceanography}, number = {9}, pages = {2077--2096}, publisher = {American Meteorological Society}, title = {{Saturation of the internal tides and induced mixing in the abyssal ocean}}, doi = {10.1175/2009jpo4141.1}, volume = {39}, year = {2009}, } @article{9148, abstract = {Several observational studies have shown a tight relationship between tropical precipitation and column‐integrated water vapor. We show that the observed relationship in the tropics between column‐integrated water vapor, precipitation, and its variance can be qualitatively reproduced by a simple and physically motivated two‐layer model. It has previously been argued that features of this relationship could be explained by analogy with the theory of continuous phase transitions. Instead, our model explicitly assumes that the onset of precipitation is governed by a stability threshold involving boundary‐layer water vapor. This allows us to explain the precipitation‐humidity relationship over a broader range of water vapor values, and may explain the observed temperature dependence of the relationship.}, author = {Muller, Caroline J and Back, Larissa E. and O'Gorman, Paul A. and Emanuel, Kerry A.}, issn = {0094-8276}, journal = {Geophysical Research Letters}, keywords = {General Earth and Planetary Sciences, Geophysics}, number = {16}, publisher = {American Geophysical Union}, title = {{A model for the relationship between tropical precipitation and column water vapor}}, doi = {10.1029/2009gl039667}, volume = {36}, year = {2009}, } @article{9453, abstract = {Parent-of-origin-specific (imprinted) gene expression is regulated in Arabidopsis thaliana endosperm by cytosine demethylation of the maternal genome mediated by the DNA glycosylase DEMETER, but the extent of the methylation changes is not known. Here, we show that virtually the entire endosperm genome is demethylated, coupled with extensive local non-CG hypermethylation of small interfering RNA–targeted sequences. Mutation of DEMETER partially restores endosperm CG methylation to levels found in other tissues, indicating that CG demethylation is specific to maternal sequences. Endosperm demethylation is accompanied by CHH hypermethylation of embryo transposable elements. Our findings demonstrate extensive reconfiguration of the endosperm methylation landscape that likely reinforces transposon silencing in the embryo.}, author = {Hsieh, Tzung-Fu and Ibarra, Christian A. and Silva, Pedro and Zemach, Assaf and Eshed-Williams, Leor and Fischer, Robert L. and Zilberman, Daniel}, issn = {1095-9203}, journal = {Science}, keywords = {Multidisciplinary}, number = {5933}, pages = {1451--1454}, publisher = {American Association for the Advancement of Science}, title = {{Genome-wide demethylation of Arabidopsis endosperm}}, doi = {10.1126/science.1172417}, volume = {324}, year = {2009}, } @inproceedings{964, abstract = {A theory of the fluctuation-induced Nernst efl'ect is developed for a two-dimensional superconductor in a perpendicular magnetic field. First, we derive a simple phenomenological formula for the Nernst coefficient, which naturally explains the giant Nernst signal due to fluctuating Cooper pairs. The latter signal is shown to be large even far from the transition and may exceed by orders of magnitude the Fermi liquid terms. We also present a complete microscopic calculation of the Nernst coefficient for arbitrary magnetic fields and temperatures, which is based on the standard definition of heat current vertices. It is shown that the magnitude and the behavior of the Nernst signal observed experimentally in disordered superconducting films can be well understood on the basis of superconducting fluctuation theory.}, author = {Maksym Serbyn and Skvortsov, Mikhail A and Varlamov, Andrei A and Galitski, Victor M}, pages = {140 -- 145}, publisher = {American Institute of Physics}, title = {{Giant nernst effect due to fluctuating cooper Pairs in superconductors}}, doi = {10.1063/1.3149485}, volume = {1134}, year = {2009}, } @article{7080, abstract = {We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high magnetic fields. The effect of the magnetic field is considered unusual as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical framework, which can be used to describe the effect of the magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant.}, author = {Yang, X.-D. and Riseborough, P.S. and Modic, Kimberly A and Fisher, R.A. and Opeil, C.P. and Finlayson, T.R. and Cooley, J.C. and Smith, J.L. and Goddard, P.A. and Silhanek, A.V. and Lashley, J.C.}, issn = {1478-6443}, journal = {Philosophical Magazine}, number = {22-24}, pages = {2083--2091}, publisher = {Taylor & Francis}, title = {{Influence of magnetic fields on structural martensitic transitions}}, doi = {10.1080/14786430902865518}, volume = {89}, year = {2009}, } @article{7319, abstract = {In the first paper of this series, an experimental technique for measuring the current-density distribution with a resolution better than the sub-millimeter scale of the channel and rib structures in the flow-field plates of polymer electrolyte fuel cells (PEFCs) was introduced. This method is extended to the determination of local membrane resistance with the same spatial resolution in the present paper. The combined measurement of current and resistance allows for investigating the interaction of mass- and charge-transport processes, which determine the local rate distribution across the domain of channels and ribs. Therewith, the influence of relevant operating parameters such as reactant composition, dew points, and cell compression on local current generation is investigated. The results show that the distribution of water and oxidant across the channel and rib are the main reasons for significant current gradients on a scale smaller than a millimeter. Humidity variation mainly affects the membrane resistance under the channel, while reactant concentration predominantly influences current generation under the rib-covered cell area.}, author = {Reum, Mathias and Freunberger, Stefan Alexander and Wokaun, Alexander and Büchi, Felix N.}, issn = {0013-4651}, journal = {Journal of The Electrochemical Society}, number = {3}, publisher = {The Electrochemical Society}, title = {{Measuring the current distribution with sub-millimeter resolution in PEFCs: II. Impact of operating parameters}}, doi = {10.1149/1.3043422}, volume = {156}, year = {2009}, } @inproceedings{752, abstract = {Set agreement is a fundamental problem in distributed computing in which processes collectively choose a small subset of values from a larger set of proposals. The impossibility of fault-tolerant set agreement in asynchronous networks is one of the seminal results in distributed computing. The complexity of set agreement in synchronous networks has also been a significant research challenge. Real systems, however, are neither purely synchronous nor purely asynchronous. Rather, they tend to alternate between periods of synchrony and periods of asynchrony. In this paper, we analyze the complexity of set agreement in a "partially synchronous" setting, presenting the first (asymptotically) tight bound on the complexity of set agreement in such systems. We introduce a novel technique for simulating, in fault-prone asynchronous shared memory, executions of an asynchronous and failure-prone messagepassing system in which some fragments appear synchronous to some processes. We use this technique to derive a lower bound on the round complexity of set agreement in a partially synchronous system by a reduction from asynchronous wait-free set agreement. We also present an asymptotically matching algorithm that relies on a distributed asynchrony detection mechanism to decide as soon as possible during periods of synchrony. By relating environments with differing degrees of synchrony, our simulation technique is of independent interest. In particular, it allows us to obtain a new lower bound on the complexity of early deciding k-set agreement complementary to that of [12], and to re-derive the combinatorial topology lower bound of [13] in an algorithmic way.}, author = {Alistarh, Dan-Adrian and Gilbert, Seth and Guerraoui, Rachid and Travers, Corentin}, pages = {943 -- 953}, publisher = {Springer}, title = {{Of choices, failures and asynchrony: the many faces of set agreement}}, doi = {10.1007/978-3-642-10631-6_95}, volume = {5878 LNCS}, year = {2009}, } @article{3197, abstract = {The problem of obtaining the maximum a posteriori estimate of a general discrete Markov random field (i.e., a Markov random field defined using a discrete set of labels) is known to be NP-hard. However, due to its central importance in many applications, several approximation algorithms have been proposed in the literature. In this paper, we present an analysis of three such algorithms based on convex relaxations: (i) LP-S: the linear programming (LP) relaxation proposed by Schlesinger (1976) for a special case and independently in Chekuri et al. (2001), Koster et al. (1998), and Wainwright et al. (2005) for the general case; (ii) QP-RL: the quadratic programming (QP) relaxation of Ravikumar and Lafferty (2006); and (iii) SOCP-MS: the second order cone programming (SOCP) relaxation first proposed by Muramatsu and Suzuki (2003) for two label problems and later extended by Kumar et al. (2006) for a general label set. We show that the SOCP-MS and the QP-RL relaxations are equivalent. Furthermore, we prove that despite the flexibility in the form of the constraints/objective function offered by QP and SOCP, the LP-S relaxation strictly dominates (i.e., provides a better approximation than) QP-RL and SOCP-MS. We generalize these results by defining a large class of SOCP (and equivalent QP) relaxations which is dominated by the LP-S relaxation. Based on these results we propose some novel SOCP relaxations which define constraints using random variables that form cycles or cliques in the graphical model representation of the random field. Using some examples we show that the new SOCP relaxations strictly dominate the previous approaches.}, author = {Kumar, M Pawan and Vladimir Kolmogorov and Torr, Philip H}, journal = {Journal of Machine Learning Research}, pages = {71 -- 106}, publisher = {Microtome Publishing}, title = {{An analysis of convex relaxations for MAP estimation of discrete MRFs}}, volume = {10}, year = {2009}, } @inproceedings{3199, abstract = {Many interactive image segmentation approaches use an objective function which includes appearance models as an unknown variable. Since the resulting optimization problem is NP-hard the segmentation and appearance are typically optimized separately, in an EM-style fashion. One contribution of this paper is to express the objective function purely in terms of the unknown segmentation, using higher-order cliques. This formulation reveals an interesting bias of the model towards balanced segmentations. Furthermore, it enables us to develop a new dual decomposition optimization procedure, which provides additionally a lower bound. Hence, we are able to improve on existing optimizers, and verify that for a considerable number of real world examples we even achieve global optimality. This is important since we are able, for the first time, to analyze the deficiencies of the model. Another contribution is to establish a property of a particular dual decomposition approach which involves convex functions depending on foreground area. As a consequence, we show that the optimal decomposition for our problem can be computed efficiently via a parametric maxflow algorithm.}, author = {Vicente, Sara and Vladimir Kolmogorov and Rother, Carsten}, pages = {755 -- 762}, publisher = {IEEE}, title = {{Joint optimization of segmentation and appearance models}}, doi = {10.1109/ICCV.2009.5459287}, year = {2009}, } @article{3200, abstract = {Motivated by various applications to computer vision, we consider the convex cost tension problem, which is the dual of the convex cost flow problem. In this paper, we first propose a primal algorithm for computing an optimal solution of the problem. Our primal algorithm iteratively updates primal variables by solving associated minimum cut problems. We show that the time complexity of the primal algorithm is O (K {dot operator} T (n, m)), where K is the range of primal variables and T (n, m) is the time needed to compute a minimum cut in a graph with n nodes and m edges. We then develop an improved version of the primal algorithm, called the primal-dual algorithm, by making good use of dual variables in addition to primal variables. Although its time complexity is the same as that of the primal algorithm, we can expect a better performance in practice. We finally consider an application to a computer vision problem called the panoramic image stitching.}, author = {Vladimir Kolmogorov and Shioura, Akiyoshi}, journal = {Discrete Optimization}, number = {4}, pages = {378 -- 393}, publisher = {Elsevier}, title = {{New algorithms for convex cost tension problem with application to computer vision}}, doi = {10.1016/j.disopt.2009.04.006}, volume = {6}, year = {2009}, } @inproceedings{3203, abstract = {In recent years the Markov Random Field (MRF) has become the de facto probabilistic model for low-level vision applications. However, in a maximum a posteriori (MAP) framework, MRFs inherently encourage delta function marginal statistics. By contrast, many low-level vision problems have heavy tailed marginal statistics, making the MRF model unsuitable. In this paper we introduce a more general Marginal Probability Field (MPF), of which the MRF is a special, linear case, and show that convex energy MPFs can be used to encourage arbitrary marginal statistics. We introduce a flexible, extensible framework for effectively optimizing the resulting NP-hard MAP problem, based around dual-decomposition and a modified mincost flow algorithm, and which achieves global optimality in some instances. We use a range of applications, including image denoising and texture synthesis, to demonstrate the benefits of this class of MPF over MRFs.}, author = {Woodford, Oliver J and Rother, Carsten and Vladimir Kolmogorov}, pages = {2319 -- 2326}, publisher = {IEEE}, title = {{A global perspective on MAP inference for low level vision}}, doi = {10.1109/ICCV.2009.5459434}, year = {2009}, } @inproceedings{3230, abstract = {We present a new approach to the design of IND-CCA2 secure hybrid encryption schemes in the standard model. Our approach provides an efficient generic transformation from 1-universal to 2-universal hash proof systems. The transformation involves a randomness extractor based on a 4-wise independent hash function as the key derivation function. Our methodology can be instantiated with efficient schemes based on standard intractability assumptions such as Decisional Diffie-Hellman, Quadratic Residuosity, and Paillier's Decisional Composite Residuosity. Interestingly, our framework also allows to prove IND-CCA2 security of a hybrid version of 1991's Damgård's ElGamal public-key encryption scheme under the DDH assumption. }, author = {Kiltz, Eike and Krzysztof Pietrzak and Stam, Martijn and Yung, Moti}, pages = {590 -- 609}, publisher = {Springer}, title = {{A new randomness extraction paradigm for hybrid encryption}}, doi = {10.1007/978-3-642-01001-9_34}, volume = {5479}, year = {2009}, } @inproceedings{3231, abstract = {We investigate the security of "padding-based" encryption schemes in the standard model. This class contains all public-key encryption schemes where the encryption algorithm first applies some invertible public transformation to the message (the "padding"), followed by a trapdoor permutation. In particular, this class contains OAEP and its variants. Our main result is a black-box impossibility result showing that one cannot prove any such padding-based scheme chosen-ciphertext secure even assuming the existence of ideal trapdoor permutations. The latter is a strong ideal abstraction of trapdoor permutations which inherits all security properties of uniform random permutations. }, author = {Kiltz, Eike and Krzysztof Pietrzak}, pages = {389 -- 406}, publisher = {Springer}, title = {{On the security of padding based encryption schemes Why We cannot prove OAEP secure in the standard model}}, doi = {10.1007/978-3-642-01001-9_23}, volume = {5479}, year = {2009}, } @inproceedings{3232, abstract = {A weak pseudorandom function (wPRF) is a cryptographic primitive similar to - but weaker than - a pseudorandom function: for wPRFs one only requires that the output is pseudorandom when queried on random inputs.We show that unlike "normal" PRFs, wPRFs are seedincompressible, in the sense that the output of a wPRF is pseudorandom even if a bounded amount of information about the key is leaked. As an application of this result we construct a simple mode of operation which - when instantiated with any wPRF - gives a leakage-resilient stream-cipher. The implementation of such a cipher is secure against every side-channel attack, as long as the amount of information leaked per round is bounded, but overall can be arbitrary large. The construction is simpler than the previous one (Dziembowski-Pietrzak FOCS'08) as it only uses a single primitive (a wPRF) in a straight forward manner. }, author = {Krzysztof Pietrzak}, pages = {462 -- 482}, publisher = {Springer}, title = {{A leakage resilient mode of operation}}, doi = {10.1007/978-3-642-01001-9_27}, volume = {5479}, year = {2009}, } @article{3292, abstract = {Galactofuranose (Galf) containing molecules have been described at the cell surface of several eukaryotes and shown to contribute to the virulence of the parasite Leishmania major and the fungus Aspergillus fumigatus. It is anticipated that a number of the surface glycoconjugates such as N-glycans or glycolipids are galactofuranosylated in the Golgi apparatus. This raises the question of how the substrate for galactofuranosylation reactions, UDP-Galf, which is synthesized in the cytosol, translocates into the organelles of the secretory pathway. Here we report the first identification of a Golgi-localized nucleotide sugar transporter, named GlfB, with specificity for a UDP-Galf. In vitro transport assays established binding of UDP-Galf to GlfB and excluded transport of several other nucleotide sugars. Furthermore, the implication of glfB in the galactofuranosylation of A. fumigatus glycoconjugates and galactomannan was demonstrated by a targeted gene deletion approach. Our data reveal a direct connection between galactomannan and the organelles of the secretory pathway that strongly suggests that the cell wall-bound polysaccharide originates from its glycosylphosphatidylinositol-anchored form.}, author = {Engel, Jakob and Schmalhorst, Philipp S and Dörk Bousset, Thilo and Ferrières, Vincent and Routier, Françoise}, journal = {Journal of Biological Chemistry}, number = {49}, pages = {33859 -- 33868}, publisher = {American Society for Biochemistry and Molecular Biology}, title = {{A single UDP galactofuranose transporter is required for galactofuranosylation in Aspergillus fumigatus}}, doi = {10.1074/jbc.M109.070219 }, volume = {284}, year = {2009}, } @article{3293, abstract = {Chemotactic responses of Drosophila to certain esters and alcohols are experience dependent. When the flies are exposed after eclosion to these chemicals, the odorants become strongly attractive. We show that behavioral conditioning is accompanied by an increase in the electrophysiological responses of single neurons in sensilla basiconica. Sensitization involves odorants that act on a common olfactory receptor. The possible mechanism of imaginal conditioning and its ecological and evolutionary significance are discussed.}, author = {Chakraborty Tuhin, Subhra and Sarit Goswami and Siddiqi, Obaid}, journal = {Journal of Neurogenetics}, number = {1-2}, pages = {210 -- 9}, publisher = {Informa Healthcare}, title = {{Sensory correlates of imaginal conditioning in Drosophila melanogaster}}, doi = {10.1080/01677060802491559 }, volume = {23}, year = {2009}, } @article{3304, abstract = {Complex traits often involve interactions between different genetic loci. This can lead to sign epistasis, whereby mutations that are individually deleterious or neutral combine to confer a fitness benefit. In order to acquire the beneficial genotype, an asexual population must cross a fitness valley or plateau by first acquiring the deleterious or neutral intermediates. Here, we present a complete, intuitive theoretical description of the valley-crossing process across the full spectrum of possible parameter regimes. We calculate the rate at which a population crosses a fitness valley or plateau of arbitrary width, as a function of the mutation rates, the population size, and the fitnesses of the intermediates. We find that when intermediates are close to neutral, a large population can cross even wide fitness valleys remarkably quickly, so that valley-crossing dynamics may be common even when mutations that directly increase fitness are also possible. Thus the evolutionary dynamics of large populations can be sensitive to the structure of an extended region of the fitness landscape — the population may not take directly uphill paths in favor of paths across valleys and plateaus that lead eventually to fitter genotypes. In smaller populations, we find that below a threshold size, which depends on the width of the fitness valley and the strength of selection against intermediate genotypes, valley-crossing is much less likely and hence the evolutionary dynamics are less influenced by distant regions of the fitness landscape.}, author = {Daniel Weissman and Desai, Michael M and Fisher, Daniel S and Feldman, Marcus W}, journal = {Theoretical Population Biology}, number = {4}, pages = {286 -- 300}, publisher = {Academic Press}, title = {{The rate at which asexual populations cross fitness valleys}}, doi = {10.1016/j.tpb.2009.02.006}, volume = {75}, year = {2009}, } @article{3309, abstract = { Mastitis, a worldwide endemic disease of dairy cows, is an important cause of decreased efficiency in milk production. Early medical treatment can reduce the nonreversible losses in milk production caused by this infection. Various diagnostic tests for mastitis are available, including a test measuring the electrical conductivity of milk (MEC test), the industry standard of somatic cell counting (SCC test), a bacteriological test, and a recently developed test measuring mammary associated amyloid A (MAA test). None of these tests is considered a gold standard, however. The aim of the present study was to determine which of these tests provides the best results, and at what cost, to improve the efficiency of milk production. For this study, 25 cows were tested at all four quarters of the udder with each of the aforementioned mastitis diagnostic tests. Based on the data, the disease prevalence as well as the sensitivity and the specificity of the four tests were estimated with a Bayesian approach by extending the Hui and Walter model with two independent tests and two populations to a model with four partially dependent tests and one population. This model was further combined with a receiver operating characteristics analysis to estimate the overall test accuracy.}, author = {Caroline Uhler}, journal = {Journal of Agricultural Biological and Environmental Statistics}, number = {1}, pages = {79 -- 98}, publisher = {Springer}, title = {{Mastitis in dairy production: Estimation of sensitivity, specificity and disease prevalence in the absence of a gold standard}}, doi = {10.1198/jabes.2009.0005}, volume = {14}, year = {2009}, } @article{337, abstract = {The formation of hollow vs solid particles by means of the oxidation reaction of solid metal particles depends on the differential self-diffusivities of the reactants through the composite shell, the reaction probabilities at each interface, and the concentration and diffusivity of the element in solution. By means of a kinetic model of the oxidation process, we determine the phase diagrams for the geometry of the oxidized particles and propose four shell growth regimes. We experimentally illustrate the different growth scenarios by changing the conditions of oxidation of cadmium spherical crystals using different chalcogen precursors. }, author = {Cabot, Andreu and Ibáñez, Maria and Guardia, Pablo and Alivisatos, Paul}, journal = {Journal of the American Chemical Society}, number = {32}, pages = {11326 -- 11328}, publisher = {ACS}, title = {{Reaction regimes on the synthesis of hollow particles by the Kirkendall effect}}, doi = {10.1021/ja903751p}, volume = {131}, year = {2009}, } @article{3398, abstract = {Why is a particular architecture for a pathway chosen over seemingly equivalent alternatives? Çağatay et al. (2009) use a synthetic biology approach to show that fluctuations—or noise—in protein levels may play a key role in determining which network design is selected during evolution.}, author = {Bollenbach, Tobias and Kishony, Roy}, journal = {Cell}, number = {3}, pages = {460 -- 461}, publisher = {Cell Press}, title = {{Quiet gene circuit more fragile than its noisy peer}}, doi = {10.1016/j.cell.2009.10.005}, volume = {139}, year = {2009}, }