@article{12647, abstract = {Accurate quantification of the spatial distribution of precipitation in mountain regions is crucial for assessments of water resources and for the understanding of high-altitude hydrology, yet it is one of the largest unknowns due to the lack of high-altitude observations. The Hunza basin in Pakistan contains very large glacier systems, which, given the melt, cannot persist unless precipitation (snow input) is much higher than what is observed at the meteorological stations, mostly located in mountain valleys. Several studies, therefore, suggest strong positive vertical precipitation lapse rates; in the present study, we quantify this lapse rate by using glaciers as a proxy. We assume a neutral mass balance for the glaciers for the period from 2001 to 2003, and we inversely model the precipitation lapse by balancing the total accumulation in the catchment area and the ablation over the glacier area for the 50 largest glacier systems in the Hunza basin in the Karakoram. Our results reveal a vertical precipitation lapse rate that equals 0.21 ± 0.12% m−1, with a maximum precipitation at an elevation of 5500 masl. We showed that the total annual basin precipitation (828 mm) is 260% higher than what is estimated based on interpolated observations (319 mm); this has major consequences for hydrological modeling and water resource assessments in general. Our results were validated by using previously published studies on individual glaciers as well as the water balance of the Hunza basin. The approach is more widely applicable in mountain ranges where precipitation measurements at high altitude are lacking.}, author = {Immerzeel, Walter Willem and Pellicciotti, Francesca and Shrestha, Arun B.}, issn = {1994-7151}, journal = {Mountain Research and Development}, keywords = {General Environmental Science, Development, Environmental Chemistry}, number = {1}, pages = {30--38}, publisher = {International Mountain Society}, title = {{Glaciers as a proxy to quantify the spatial distribution of precipitation in the Hunza basin}}, doi = {10.1659/mrd-journal-d-11-00097.1}, volume = {32}, year = {2012}, } @article{12648, abstract = {Distributed glacier melt models generally assume that the glacier surface consists of bare exposed ice and snow. In reality, many glaciers are wholly or partially covered in layers of debris that tend to suppress ablation rates. In this paper, an existing physically based point model for the ablation of debris-covered ice is incorporated in a distributed melt model and applied to Haut Glacier d'Arolla, Switzerland, which has three large patches of debris cover on its surface. The model is based on a 10 m resolution digital elevation model (DEM) of the area; each glacier pixel in the DEM is defined as either bare or debris-covered ice, and may be covered in snow that must be melted off before ice ablation is assumed to occur. Each debris-covered pixel is assigned a debris thickness value using probability distributions based on over 1000 manual thickness measurements. Locally observed meteorological data are used to run energy balance calculations in every pixel, using an approach suitable for snow, bare ice or debris-covered ice as appropriate. The use of the debris model significantly reduces the total ablation in the debris-covered areas, however the precise reduction is sensitive to the temperature extrapolation used in the model distribution because air near the debris surface tends to be slightly warmer than over bare ice. Overall results suggest that the debris patches, which cover 10% of the glacierized area, reduce total runoff from the glacierized part of the basin by up to 7%.}, author = {Reid, T. D. and Carenzo, M. and Pellicciotti, Francesca and Brock, B. W.}, issn = {0148-0227}, journal = {Journal of Geophysical Research: Atmospheres}, keywords = {Paleontology, Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), Atmospheric Science, Earth-Surface Processes, Geochemistry and Petrology, Soil Science, Water Science and Technology, Ecology, Aquatic Science, Forestry, Oceanography, Geophysics}, number = {D18}, publisher = {American Geophysical Union}, title = {{Including debris cover effects in a distributed model of glacier ablation}}, doi = {10.1029/2012jd017795}, volume = {117}, year = {2012}, } @misc{13075, abstract = {Little is known about the stability of trophic relationships in complex natural communities over evolutionary timescales. Here, we use sequence data from 18 nuclear loci to reconstruct and compare the intraspecific histories of major Pleistocene refugial populations in the Middle East, the Balkans and Iberia in a guild of four Chalcid parasitoids (Cecidostiba fungosa, C. semifascia, Hobbya stenonota and Mesopolobus amaenus) all attacking Cynipid oak galls. We develop a likelihood method to numerically estimate models of divergence between three populations from multilocus data. We investigate the power of this framework on simulated data, and - using triplet alignments of intronic loci - quantify the support for all possible divergence relationships between refugial populations in the four parasitoids. Although an East to West order of population divergence has highest support in all but one species, we cannot rule out alternative population tree topologies. Comparing the estimated times of population splits between species, we find that one species, M. amaenus, has a significantly older history than the rest of the guild and must have arrived in central Europe at least one glacial cycle prior to other guild members. This suggests that although all four species may share a common origin in the East, they expanded westwards into Europe at different times.}, author = {Lohse, Konrad and Barton, Nicholas H and Stone, Graham and Melika, George}, publisher = {Dryad}, title = {{Data from: A likelihood-based comparison of population histories in a parasitoid guild}}, doi = {10.5061/DRYAD.0G0FS}, year = {2012}, } @article{9014, abstract = {In this Letter, we explore experimentally the phase behavior of a dense active suspension of self-propelled colloids. In addition to a solidlike and gaslike phase observed for high and low densities, a novel cluster phase is reported at intermediate densities. This takes the form of a stationary assembly of dense aggregates—resulting from a permanent dynamical merging and separation of active colloids—whose average size grows with activity as a linear function of the self-propelling velocity. While different possible scenarios can be considered to account for these observations—such as a generic velocity weakening instability recently put forward—we show that the experimental results are reproduced mathematically by a chemotactic aggregation mechanism, originally introduced to account for bacterial aggregation and accounting here for diffusiophoretic chemical interaction between colloidal swimmers.}, author = {Theurkauff, I. and Cottin-Bizonne, C. and Palacci, Jérémie A and Ybert, C. and Bocquet, L.}, issn = {10797114}, journal = {Physical Review Letters}, number = {26}, publisher = {American Physical Society }, title = {{Dynamic clustering in active colloidal suspensions with chemical signaling}}, doi = {10.1103/physrevlett.108.268303}, volume = {108}, year = {2012}, } @article{9142, abstract = {In models of radiative–convective equilibrium it is known that convection can spontaneously aggregate into one single localized moist region if the domain is large enough. The large changes in the mean climate state and radiative fluxes accompanying this self-aggregation raise questions as to what simulations at lower resolutions with parameterized convection, in similar homogeneous geometries, should be expected to produce to be considered successful in mimicking a cloud-resolving model. The authors investigate this self-aggregation in a nonrotating, three-dimensional cloud-resolving model on a square domain without large-scale forcing. It is found that self-aggregation is sensitive not only to the domain size, but also to the horizontal resolution. With horizontally homogeneous initial conditions, convective aggregation only occurs on domains larger than about 200km and with resolutions coarser than about 2km in the model examined. The system exhibits hysteresis, so that with aggregated initial conditions, convection remains aggregated even at our finest resolution, 500m, as long as the domain is greater than 200–300km. The sensitivity of self-aggregation to resolution and domain size in this model is due to the sensitivity of the distribution of low clouds to these two parameters. Indeed, the mechanism responsible for the aggregation of convection is the dynamical response to the longwave radiative cooling from low clouds. Strong longwave cooling near cloud top in dry regions forces downward motion, which by continuity generates inflow near cloud top and near-surface outflow from dry regions. This circulation results in the net export of moist static energy from regions with low moist static energy, yielding a positive feedback.}, author = {Muller, Caroline J and Held, Isaac M.}, issn = {0022-4928}, journal = {Journal of the Atmospheric Sciences}, keywords = {Atmospheric Science}, number = {8}, pages = {2551--2565}, publisher = {American Meteorological Society}, title = {{Detailed investigation of the self-aggregation of convection in cloud-resolving simulations}}, doi = {10.1175/jas-d-11-0257.1}, volume = {69}, year = {2012}, } @article{922, abstract = {We study theoretically the morphologies of biological tubes affected by various pathologies. When epithelial cells grow, the negative tension produced by their division provokes a buckling instability. Several shapes are investigated: varicose, dilated, sinuous, or sausagelike. They are all found in pathologies of tracheal, renal tubes, or arteries. The final shape depends crucially on the mechanical parameters of the tissues: Young's modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey information as to what causes the pathology. We calculate a phase diagram of tubular instabilities which could be a helpful guide for investigating the underlying genetic regulation.}, author = {Hannezo, Edouard B and Prost, Jacques and Joanny, Jean}, journal = {Physical Review Letters}, number = {1}, publisher = {American Physical Society}, title = {{Mechanical instabilities of biological tubes}}, doi = {10.1103/PhysRevLett.109.018101}, volume = {109}, year = {2012}, } @article{808, abstract = {Using correlated live-cell imaging and electron tomography we found that actin branch junctions in protruding and treadmilling lamellipodia are not concentrated at the front as previously supposed, but link actin filament subsets in which there is a continuum of distances from a junction to the filament plus ends, for up to at least 1 mm. When branch sites were observed closely spaced on the same filament their separation was commonly a multiple of the actin helical repeat of 36 nm. Image averaging of branch junctions in the tomograms yielded a model for the in vivo branch at 2.9 nm resolution, which was comparable with that derived for the in vitro actin- Arp2/3 complex. Lamellipodium initiation was monitored in an intracellular wound-healing model and was found to involve branching from the sides of actin filaments oriented parallel to the plasmalemma. Many filament plus ends, presumably capped, terminated behind the lamellipodium tip and localized on the dorsal and ventral surfaces of the actin network. These findings reveal how branching events initiate and maintain a network of actin filaments of variable length, and provide the first structural model of the branch junction in vivo. A possible role of filament capping in generating the lamellipodium leaflet is discussed and a mathematical model of protrusion is also presented.}, author = {Vinzenz, Marlene and Nemethova, Maria and Schur, Florian and Mueller, Jan and Narita, Akihiro and Urban, Edit and Winkler, Christoph and Schmeiser, Christian and Koestler, Stefan and Rottner, Klemens and Resch, Guenter and Maéda, Yuichiro and Small, John}, journal = {Journal of Cell Science}, number = {11}, pages = {2775 -- 2785}, publisher = {Company of Biologists}, title = {{Actin branching in the initiation and maintenance of lamellipodia}}, doi = {10.1242/jcs.107623}, volume = {125}, year = {2012}, } @article{171, abstract = {For given non-zero integers a, b, q we investigate the density of solutions (x, y) ∈ ℤ2 to the binary cubic congruence ax2 + by3 ≡ 0 mod q, and use it to establish the Manin conjecture for a singular del Pezzo surface of degree 2 defined over ℚ.}, author = {Timothy Browning and Baier, Stephan}, journal = {Journal fur die Reine und Angewandte Mathematik}, number = {680}, pages = {1 -- 65}, publisher = {Walter de Gruyter}, title = {{Inhomogeneous cubic congruences and rational points on del Pezzo surfaces}}, doi = {https://doi.org/10.1515/crelle.2012.039}, volume = {2013}, year = {2012}, } @article{1756, abstract = {We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature-dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be effective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid helium temperature. By independently tuning the effective Schottky barrier heights, a variety of reconfigurable device functionalities could be obtained. In particular, the same nanowire device could be configured to work as a Schottky barrier transistor, a Schottky diode, or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one.}, author = {Mongillo, Massimo and Spathis, Panayotis N and Georgios Katsaros and Gentile, Pascal and De Franceschi, Silvano}, journal = {Nano Letters}, number = {6}, pages = {3074 -- 3079}, publisher = {American Chemical Society}, title = {{Multifunctional devices and logic gates with undoped silicon nanowires}}, doi = {10.1021/nl300930m}, volume = {12}, year = {2012}, } @article{1757, abstract = {Self-assembled Ge wires with a height of only 3 unit cells and a length of up to 2 micrometers were grown on Si(001) by means of a catalyst-free method based on molecular beam epitaxy. The wires grow horizontally along either the [100] or the [010] direction. On atomically flat surfaces, they exhibit a highly uniform, triangular cross section. A simple thermodynamic model accounts for the existence of a preferential base width for longitudinal expansion, in quantitative agreement with the experimental findings. Despite the absence of intentional doping, the first transistor-type devices made from single wires show low-resistive electrical contacts and single-hole transport at sub-Kelvin temperatures. In view of their exceptionally small and self-defined cross section, these Ge wires hold promise for the realization of hole systems with exotic properties and provide a new development route for silicon-based nanoelectronics.}, author = {Zhang, Jianjun and Georgios Katsaros and Montalenti, Francesco and Scopece, Daniele and Rezaev, Roman O and Mickel, Christine H and Rellinghaus, Bernd and Miglio, Leo P and De Franceschi, Silvano and Rastelli, Armando and Schmidt, Oliver G}, journal = {Physical Review Letters}, number = {8}, publisher = {American Physical Society}, title = {{Monolithic growth of ultrathin Ge nanowires on Si(001) }}, doi = {10.1103/PhysRevLett.109.085502}, volume = {109}, year = {2012}, } @article{1758, abstract = {We studied the low-energy states of spin-1/2 quantum dots defined in InAs/InP nanowires and coupled to aluminum superconducting leads. By varying the superconducting gap Δ with a magnetic field B we investigated the transition from strong coupling Δ≪T K to weak-coupling Δ≫T K, where T K is the Kondo temperature. Below the critical field, we observe a persisting zero-bias Kondo resonance that vanishes only for low B or higher temperatures, leaving the room to more robust subgap structures at bias voltages between Δ and 2Δ. For strong and approximately symmetric tunnel couplings, a Josephson supercurrent is observed in addition to the Kondo peak. We ascribe the coexistence of a Kondo resonance and a superconducting gap to a significant density of intragap quasiparticle states, and the finite-bias subgap structures to tunneling through Shiba states. Our results, supported by numerical calculations, own relevance also in relation to tunnel-spectroscopy experiments aiming at the observation of Majorana fermions in hybrid nanostructures.}, author = {Lee, Eduardo J and Jiang, Xiaocheng and Aguado, Ramón and Georgios Katsaros and Lieber, Charles M and De Franceschi, Silvano}, journal = {Physical Review Letters}, number = {18}, publisher = {American Physical Society}, title = {{Zero-bias anomaly in a nanowire quantum dot coupled to superconductors}}, doi = {10.1103/PhysRevLett.109.186802}, volume = {109}, year = {2012}, } @article{1782, abstract = {Steering a quantum harmonic oscillator state along cyclic trajectories leads to a path-dependent geometric phase. Here we describe its experimental observation in an electronic harmonic oscillator. We use a superconducting qubit as a nonlinear probe of the phase, which is otherwise unobservable due to the linearity of the oscillator. We show that the geometric phase is, for a variety of cyclic paths, proportional to the area enclosed in the quadrature plane. At the transition to the nonadiabatic regime, we study corrections to the phase and dephasing of the qubit caused by qubit-resonator entanglement. In particular, we identify parameters for which this dephasing mechanism is negligible even in the nonadiabatic regime. The demonstrated controllability makes our system a versatile tool to study geometric phases in open quantum systems and to investigate their potential for quantum information processing.}, author = {Pechal, M and Berger, Stefan T and Abdumalikov, Abdufarrukh A and Johannes Fink and Mlynek, Jonas A and Steffen, L. Kraig and Wallraff, Andreas and Filipp, Stefan}, journal = {Physical Review Letters}, number = {17}, publisher = {American Physical Society}, title = {{Geometric phase and nonadiabatic effects in an electronic harmonic oscillator}}, doi = {10.1103/PhysRevLett.108.170401}, volume = {108}, year = {2012}, } @article{1783, abstract = {Nonlinearity and entanglement are two important properties by which physical systems can be identified as nonclassical. We study the dynamics of the resonant interaction of up to N=3 two-level systems and a single mode of the electromagnetic field sharing a single excitation dynamically. We observe coherent vacuum Rabi oscillations and their nonlinear √N speedup by tracking the populations of all qubits and the resonator in time. We use quantum state tomography to show explicitly that the dynamics generates maximally entangled states of the W class in a time limited only by the collective interaction rate. We use an entanglement witness and the 3-tangle to characterize the state whose fidelity F=78% is limited in our experiments by crosstalk arising during the simultaneous qubit manipulations which is absent in a sequential approach with F=91%.}, author = {Mlynek, Jonas A and Abdumalikov, Abdufarrukh A and Johannes Fink and Steffen, L. Kraig and Baur, Matthias P and Lang, C and Van Loo, Arjan F and Wallraff, Andreas}, journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, number = {5}, publisher = {American Physical Society}, title = {{Demonstrating W-type entanglement of Dicke states in resonant cavity quantum electrodynamics}}, doi = {10.1103/PhysRevA.86.053838}, volume = {86}, year = {2012}, } @inproceedings{2048, abstract = {Leakage resilient cryptography attempts to incorporate side-channel leakage into the black-box security model and designs cryptographic schemes that are provably secure within it. Informally, a scheme is leakage-resilient if it remains secure even if an adversary learns a bounded amount of arbitrary information about the schemes internal state. Unfortunately, most leakage resilient schemes are unnecessarily complicated in order to achieve strong provable security guarantees. As advocated by Yu et al. [CCS’10], this mostly is an artefact of the security proof and in practice much simpler construction may already suffice to protect against realistic side-channel attacks. In this paper, we show that indeed for simpler constructions leakage-resilience can be obtained when we aim for relaxed security notions where the leakage-functions and/or the inputs to the primitive are chosen non-adaptively. For example, we show that a three round Feistel network instantiated with a leakage resilient PRF yields a leakage resilient PRP if the inputs are chosen non-adaptively (This complements the result of Dodis and Pietrzak [CRYPTO’10] who show that if a adaptive queries are allowed, a superlogarithmic number of rounds is necessary.) We also show that a minor variation of the classical GGM construction gives a leakage resilient PRF if both, the leakage-function and the inputs, are chosen non-adaptively.}, author = {Faust, Sebastian and Pietrzak, Krzysztof Z and Schipper, Joachim}, booktitle = { Conference proceedings CHES 2012}, location = {Leuven, Belgium}, pages = {213 -- 232}, publisher = {Springer}, title = {{Practical leakage-resilient symmetric cryptography}}, doi = {10.1007/978-3-642-33027-8_13}, volume = {7428}, year = {2012}, } @inproceedings{2049, abstract = {We propose a new authentication protocol that is provably secure based on a ring variant of the learning parity with noise (LPN) problem. The protocol follows the design principle of the LPN-based protocol from Eurocrypt’11 (Kiltz et al.), and like it, is a two round protocol secure against active attacks. Moreover, our protocol has small communication complexity and a very small footprint which makes it applicable in scenarios that involve low-cost, resource-constrained devices. Performance-wise, our protocol is more efficient than previous LPN-based schemes, such as the many variants of the Hopper-Blum (HB) protocol and the aforementioned protocol from Eurocrypt’11. Our implementation results show that it is even comparable to the standard challenge-and-response protocols based on the AES block-cipher. Our basic protocol is roughly 20 times slower than AES, but with the advantage of having 10 times smaller code size. Furthermore, if a few hundred bytes of non-volatile memory are available to allow the storage of some off-line pre-computations, then the online phase of our protocols is only twice as slow as AES. }, author = {Heyse, Stefan and Kiltz, Eike and Lyubashevsky, Vadim and Paar, Christof and Pietrzak, Krzysztof Z}, booktitle = { Conference proceedings FSE 2012}, location = {Washington, DC, USA}, pages = {346 -- 365}, publisher = {Springer}, title = {{Lapin: An efficient authentication protocol based on ring-LPN}}, doi = {10.1007/978-3-642-34047-5_20}, volume = {7549}, year = {2012}, } @inproceedings{1384, abstract = {Software model checking, as an undecidable problem, has three possible outcomes: (1) the program satisfies the specification, (2) the program does not satisfy the specification, and (3) the model checker fails. The third outcome usually manifests itself in a space-out, time-out, or one component of the verification tool giving up; in all of these failing cases, significant computation is performed by the verification tool before the failure, but no result is reported. We propose to reformulate the model-checking problem as follows, in order to have the verification tool report a summary of the performed work even in case of failure: given a program and a specification, the model checker returns a condition Ψ - usually a state predicate - such that the program satisfies the specification under the condition Ψ - that is, as long as the program does not leave the states in which Ψ is satisfied. In our experiments, we investigated as one major application of conditional model checking the sequential combination of model checkers with information passing. We give the condition that one model checker produces, as input to a second conditional model checker, such that the verification problem for the second is restricted to the part of the state space that is not covered by the condition, i.e., the second model checker works on the problems that the first model checker could not solve. Our experiments demonstrate that repeated application of conditional model checkers, passing information from one model checker to the next, can significantly improve the verification results and performance, i.e., we can now verify programs that we could not verify before.}, author = {Beyer, Dirk and Henzinger, Thomas A and Keremoglu, Mehmet and Wendler, Philipp}, booktitle = {Proceedings of the ACM SIGSOFT 20th International Symposium on the Foundations of Software Engineering}, location = {Cary, NC, USA}, publisher = {ACM}, title = {{Conditional model checking: A technique to pass information between verifiers}}, doi = {10.1145/2393596.2393664}, year = {2012}, } @article{1471, abstract = {Given a possibly reducible and non-reduced spectral cover π: X → C over a smooth projective complex curve C we determine the group of connected components of the Prym variety Prym(X/C). As an immediate application we show that the finite group of n-torsion points of the Jacobian of C acts trivially on the cohomology of the twisted SL n-Higgs moduli space up to the degree which is predicted by topological mirror symmetry. In particular this yields a new proof of a result of Harder-Narasimhan, showing that this finite group acts trivially on the cohomology of the twisted SL n stable bundle moduli space.}, author = {Tamas Hausel and Pauly, Christian}, journal = {Geometry and Topology}, number = {3}, pages = {1609 -- 1638}, publisher = {University of Warwick}, title = {{Prym varieties of spectral covers}}, doi = {10.2140/gt.2012.16.1609}, volume = {16}, year = {2012}, } @article{1472, abstract = {For G = GL 2, PGL 2, SL 2 we prove that the perverse filtration associated with the Hitchin map on the rational cohomology of the moduli space of twisted G-Higgs bundles on a compact Riemann surface C agrees with the weight filtration on the rational cohomology of the twisted G character variety of C when the cohomologies are identified via non-Abelian Hodge theory. The proof is accomplished by means of a study of the topology of the Hitchin map over the locus of integral spectral curves.}, author = {De Cataldo, Mark A and Tamas Hausel and Migliorini, Luca}, journal = {Annals of Mathematics}, number = {3}, pages = {1329 -- 1407}, publisher = {Princeton University Press}, title = {{Topology of hitchin systems and Hodge theory of character varieties: The case A 1}}, doi = {10.4007/annals.2012.175.3.7}, volume = {175}, year = {2012}, } @misc{5396, abstract = {We consider the problem of inference in agraphical model with binary variables. While in theory it is arguably preferable to compute marginal probabilities, in practice researchers often use MAP inference due to the availability of efficient discrete optimization algorithms. We bridge the gap between the two approaches by introducing the Discrete Marginals technique in which approximate marginals are obtained by minimizing an objective function with unary and pair-wise terms over a discretized domain. This allows the use of techniques originally devel-oped for MAP-MRF inference and learning. We explore two ways to set up the objective function - by discretizing the Bethe free energy and by learning it from training data. Experimental results show that for certain types of graphs a learned function can out-perform the Bethe approximation. We also establish a link between the Bethe free energy and submodular functions.}, author = {Korc, Filip and Kolmogorov, Vladimir and Lampert, Christoph}, issn = {2664-1690}, pages = {13}, publisher = {IST Austria}, title = {{Approximating marginals using discrete energy minimization}}, doi = {10.15479/AT:IST-2012-0003}, year = {2012}, } @techreport{5398, abstract = {This document is created as a part of the project “Repository for Research Data on IST Austria”. It summarises the actual state of research data at IST Austria, based on survey results. It supports the choice of appropriate software, which would best fit the requirements of their users, the researchers.}, author = {Porsche, Jana}, publisher = {IST Austria}, title = {{Actual state of research data @ ISTAustria}}, year = {2012}, }