@article{12632, abstract = {We investigate the performance of five glacier melt models over a multi-decadal period in order to assess their ability to model future glacier response. The models range from a simple degree-day model, based solely on air temperature, to more-sophisticated models, including the full shortwave radiation balance. In addition to the empirical models, the performance of a physically based energy-balance (EB) model is examined. The melt models are coupled to an accumulation and a surface evolution model and applied in a distributed manner to Rhonegletscher, Switzerland, over the period 1929–2012 at hourly resolution. For calibration, seasonal mass-balance measurements (2006–12) are used. Decadal ice volume changes for six periods in the years 1929–2012 serve for model validation. Over the period 2006–12, there are almost no differences in performance between the models, except for EB, which is less consistent with observations, likely due to lack of meteorological in situ data. However, simulations over the long term (1929–2012) reveal that models which include a separate term for shortwave radiation agree best with the observed ice volume changes, indicating that their melt relationships are robust in time and thus suitable for long-term modelling, in contrast to more empirical approaches that are oversensitive to temperature fluctuations.}, author = {Gabbi, Jeannette and Carenzo, Marco and Pellicciotti, Francesca and Bauder, Andreas and Funk, Martin}, issn = {1727-5652}, journal = {Journal of Glaciology}, keywords = {Earth-Surface Processes}, number = {224}, pages = {1140--1154}, publisher = {International Glaciological Society}, title = {{A comparison of empirical and physically based glacier surface melt models for long-term simulations of glacier response}}, doi = {10.3189/2014jog14j011}, volume = {60}, year = {2014}, } @article{12637, abstract = {The performance of glaciohydrological models which simulate catchment response to climate variability depends to a large degree on the data used to force the models. The forcing data become increasingly important in high-elevation, glacierized catchments where the interplay between extreme topography, climate, and the cryosphere is complex. It is challenging to generate a reliable forcing data set that captures this spatial heterogeneity. In this paper, we analyze the results of a 1 year field campaign focusing on air temperature and precipitation observations in the Langtang valley in the Nepalese Himalayas. We use the observed time series to characterize both temperature lapse rates (LRs) and precipitation gradients (PGs). We study their spatial and temporal variability, and we attempt to identify possible controlling factors. We show that very clear LRs exist in the valley and that there are strong seasonal differences related to the water vapor content in the atmosphere. Results also show that the LRs are generally shallower than the commonly used environmental lapse rates. The analysis of the precipitation observations reveals that there is great variability in precipitation over short horizontal distances. A uniform valley wide PG cannot be established, and several scale-dependent mechanisms may explain our observations. We complete our analysis by showing the impact of the observed LRs and PGs on the outputs of the TOPKAPI-ETH glaciohydrological model. We conclude that LRs and PGs have a very large impact on the water balance composition and that short-term monitoring campaigns have the potential to improve model quality considerably.}, author = {Immerzeel, W. W. and Petersen, L. and Ragettli, S. and Pellicciotti, Francesca}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {3}, pages = {2212--2226}, publisher = {American Geophysical Union}, title = {{The importance of observed gradients of air temperature and precipitation for modeling runoff from a glacierized watershed in the Nepalese Himalayas}}, doi = {10.1002/2013wr014506}, volume = {50}, year = {2014}, } @article{9050, abstract = {Self-propelled particles can exhibit surprising non-equilibrium behaviors, and how they interact with obstacles or boundaries remains an important open problem. Here we show that chemically propelled micro-rods can be captured, with little change in their speed, into close orbits around solid spheres resting on or near a horizontal plane. We show that this interaction between sphere and particle is short-range, occurring even for spheres smaller than the particle length, and for a variety of sphere materials. We consider a simple model, based on lubrication theory, of a force- and torque-free swimmer driven by a surface slip (the phoretic propulsion mechanism) and moving near a solid surface. The model demonstrates capture, or movement towards the surface, and yields speeds independent of distance. This study reveals the crucial aspects of activity–driven interactions of self-propelled particles with passive objects, and brings into question the use of colloidal tracers as probes of active matter.}, author = {Takagi, Daisuke and Palacci, Jérémie A and Braunschweig, Adam B. and Shelley, Michael J. and Zhang, Jun}, issn = {1744-6848}, journal = {Soft Matter}, keywords = {General Chemistry, Condensed Matter Physics}, number = {11}, publisher = {Royal Society of Chemistry }, title = {{Hydrodynamic capture of microswimmers into sphere-bound orbits}}, doi = {10.1039/c3sm52815d}, volume = {10}, year = {2014}, } @article{9166, abstract = {Light-activated self-propelled colloids are synthesized and their active motion is studied using optical microscopy. We propose a versatile route using different photoactive materials, and demonstrate a multiwavelength activation and propulsion. Thanks to the photoelectrochemical properties of two semiconductor materials (α-Fe2O3 and TiO2), a light with an energy higher than the bandgap triggers the reaction of decomposition of hydrogen peroxide and produces a chemical cloud around the particle. It induces a phoretic attraction with neighbouring colloids as well as an osmotic self-propulsion of the particle on the substrate. We use these mechanisms to form colloidal cargos as well as self-propelled particles where the light-activated component is embedded into a dielectric sphere. The particles are self-propelled along a direction otherwise randomized by thermal fluctuations, and exhibit a persistent random walk. For sufficient surface density, the particles spontaneously form ‘living crystals’ which are mobile, break apart and reform. Steering the particle with an external magnetic field, we show that the formation of the dense phase results from the collisions heads-on of the particles. This effect is intrinsically non-equilibrium and a novel principle of organization for systems without detailed balance. Engineering families of particles self-propelled by different wavelength demonstrate a good understanding of both the physics and the chemistry behind the system and points to a general route for designing new families of self-propelled particles.}, author = {Palacci, Jérémie A and Sacanna, S. and Kim, S.-H. and Yi, G.-R. and Pine, D. J. and Chaikin, P. M.}, issn = {1471-2962}, journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, keywords = {General Engineering, General Physics and Astronomy, General Mathematics}, number = {2029}, publisher = {The Royal Society}, title = {{Light-activated self-propelled colloids}}, doi = {10.1098/rsta.2013.0372}, volume = {372}, year = {2014}, } @techreport{7038, author = {Huszár, Kristóf and Rolinek, Michal}, pages = {5}, publisher = {IST Austria}, title = {{Playful Math - An introduction to mathematical games}}, year = {2014}, } @article{7071, abstract = {Spin and orbital quantum numbers play a key role in the physics of Mott insulators, but in most systems they are connected only indirectly—via the Pauli exclusion principle and the Coulomb interaction. Iridium-based oxides (iridates) introduce strong spin–orbit coupling directly, such that these numbers become entwined together and the Mott physics attains a strong orbital character. In the layered honeycomb iridates this is thought to generate highly spin–anisotropic magnetic interactions, coupling the spin to a given spatial direction of exchange and leading to strongly frustrated magnetism. Here we report a new iridate structure that has the same local connectivity as the layered honeycomb and exhibits striking evidence for highly spin–anisotropic exchange. The basic structural units of this material suggest that a new family of three-dimensional structures could exist, the ‘harmonic honeycomb’ iridates, of which the present compound is the first example.}, author = {Modic, Kimberly A and Smidt, Tess E. and Kimchi, Itamar and Breznay, Nicholas P. and Biffin, Alun and Choi, Sungkyun and Johnson, Roger D. and Coldea, Radu and Watkins-Curry, Pilanda and McCandless, Gregory T. and Chan, Julia Y. and Gandara, Felipe and Islam, Z. and Vishwanath, Ashvin and Shekhter, Arkady and McDonald, Ross D. and Analytis, James G.}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Science and Business Media LLC}, title = {{Realization of a three-dimensional spin–anisotropic harmonic honeycomb iridate}}, doi = {10.1038/ncomms5203}, volume = {5}, year = {2014}, } @article{7598, author = {Tan, Shutang and Xue, Hong-Wei}, issn = {2211-1247}, journal = {Cell Reports}, number = {5}, pages = {1692--1702}, publisher = {Elsevier}, title = {{Casein kinase 1 regulates ethylene synthesis by phosphorylating and promoting the turnover of ACS5}}, doi = {10.1016/j.celrep.2014.10.047}, volume = {9}, year = {2014}, } @inproceedings{772, abstract = {Lock-free concurrent algorithms guarantee that some concurrent operation will always make progress in a finite number of steps. Yet programmers prefer to treat concurrent code as if it were wait-free, guaranteeing that all operations always make progress. Unfortunately, designing wait-free algorithms is generally a very complex task, and the resulting algorithms are not always efficient. While obtaining efficient wait-free algorithms has been a long-time goal for the theory community, most non-blocking commercial code is only lock-free. This paper suggests a simple solution to this problem. We show that, for a large class of lock-free algorithms, under scheduling conditions which approximate those found in commercial hardware architectures, lock-free algorithms behave as if they are wait-free. In other words, programmers can keep on designing simple lock-free algorithms instead of complex wait-free ones, and in practice, they will get wait-free progress. Our main contribution is a new way of analyzing a general class of lock-free algorithms under a stochastic scheduler. Our analysis relates the individual performance of processes with the global performance of the system using Markov chain lifting between a complex per-process chain and a simpler system progress chain. We show that lock-free algorithms are not only wait-free with probability 1, but that in fact a general subset of lock-free algorithms can be closely bounded in terms of the average number of steps required until an operation completes. To the best of our knowledge, this is the first attempt to analyze progress conditions, typically stated in relation to a worst case adversary, in a stochastic model capturing their expected asymptotic behavior.}, author = {Alistarh, Dan-Adrian and Censor Hillel, Keren and Shavit, Nir}, pages = {714 -- 723}, publisher = {ACM}, title = {{Are lock-free concurrent algorithms practically wait-free?}}, doi = {10.1145/2591796.2591836}, year = {2014}, } @inproceedings{775, abstract = {The long-lived renaming problem appears in shared-memory systems where a set of threads need to register and deregister frequently from the computation, while concurrent operations scan the set of currently registered threads. Instances of this problem show up in concurrent implementations of transactional memory, flat combining, thread barriers, and memory reclamation schemes for lock-free data structures. In this paper, we analyze a randomized solution for long-lived renaming. The algorithmic technique we consider, called the Level Array, has previously been used for hashing and one-shot (single-use) renaming. Our main contribution is to prove that, in long-lived executions, where processes may register and deregister polynomially many times, the technique guarantees constant steps on average and O (log log n) steps with high probability for registering, unit cost for deregistering, and O (n) steps for collect queries, where n is an upper bound on the number of processes that may be active at any point in time. We also show that the algorithm has the surprising property that it is self-healing: under reasonable assumptions on the schedule, operations running while the data structure is in a degraded state implicitly help the data structure re-balance itself. This subtle mechanism obviates the need for expensive periodic rebuilding procedures. Our benchmarks validate this approach, showing that, for typical use parameters, the average number of steps a process takes to register is less than two and the worst-case number of steps is bounded by six, even in executions with billions of operations. We contrast this with other randomized implementations, whose worst-case behavior we show to be unreliable, and with deterministic implementations, whose cost is linear in n.}, author = {Alistarh, Dan-Adrian and Kopinsky, Justin and Matveev, Alexander and Shavit, Nir}, pages = {348 -- 357}, publisher = {IEEE}, title = {{The levelarray: A fast, practical long-lived renaming algorithm}}, doi = {10.1109/ICDCS.2014.43}, year = {2014}, } @article{7771, abstract = {In their Letter, Schreck, Bertrand, O'Hern and Shattuck [Phys. Rev. Lett. 107, 078301 (2011)] study nonlinearities in jammed particulate systems that arise when contacts are altered. They conclude that there is "no harmonic regime in the large system limit for all compressions" and "at jamming onset for any system size." Their argument rests on the claim that for finite-range repulsive potentials, of the form used in studies of jamming, the breaking or forming of a single contact is sufficient to destroy the linear regime. We dispute these conclusions and argue that linear response is both justified and essential for understanding the nature of the jammed solid. }, author = {Goodrich, Carl Peter and Liu, Andrea J. and Nagel, Sidney R.}, issn = {0031-9007}, journal = {Physical Review Letters}, number = {4}, publisher = {American Physical Society}, title = {{Comment on “Repulsive contact interactions make jammed particulate systems inherently nonharmonic”}}, doi = {10.1103/physrevlett.112.049801}, volume = {112}, year = {2014}, } @article{8021, abstract = {Most excitatory inputs in the mammalian brain are made on dendritic spines, rather than on dendritic shafts. Spines compartmentalize calcium, and this biochemical isolation can underlie input-specific synaptic plasticity, providing a raison d'etre for spines. However, recent results indicate that the spine can experience a membrane potential different from that in the parent dendrite, as though the spine neck electrically isolated the spine. Here we use two-photon calcium imaging of mouse neocortical pyramidal neurons to analyze the correlation between the morphologies of spines activated under minimal synaptic stimulation and the excitatory postsynaptic potentials they generate. We find that excitatory postsynaptic potential amplitudes are inversely correlated with spine neck lengths. Furthermore, a spike timing-dependent plasticity protocol, in which two-photon glutamate uncaging over a spine is paired with postsynaptic spikes, produces rapid shrinkage of the spine neck and concomitant increases in the amplitude of the evoked spine potentials. Using numerical simulations, we explore the parameter regimes for the spine neck resistance and synaptic conductance changes necessary to explain our observations. Our data, directly correlating synaptic and morphological plasticity, imply that long-necked spines have small or negligible somatic voltage contributions, but that, upon synaptic stimulation paired with postsynaptic activity, they can shorten their necks and increase synaptic efficacy, thus changing the input/output gain of pyramidal neurons. }, author = {Araya, R. and Vogels, Tim P and Yuste, R.}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, number = {28}, pages = {E2895--E2904}, publisher = {Proceedings of the National Academy of Sciences}, title = {{Activity-dependent dendritic spine neck changes are correlated with synaptic strength}}, doi = {10.1073/pnas.1321869111}, volume = {111}, year = {2014}, } @article{8022, abstract = {Populations of neurons in motor cortex engage in complex transient dynamics of large amplitude during the execution of limb movements. Traditional network models with stochastically assigned synapses cannot reproduce this behavior. Here we introduce a class of cortical architectures with strong and random excitatory recurrence that is stabilized by intricate, fine-tuned inhibition, optimized from a control theory perspective. Such networks transiently amplify specific activity states and can be used to reliably execute multidimensional movement patterns. Similar to the experimental observations, these transients must be preceded by a steady-state initialization phase from which the network relaxes back into the background state by way of complex internal dynamics. In our networks, excitation and inhibition are as tightly balanced as recently reported in experiments across several brain areas, suggesting inhibitory control of complex excitatory recurrence as a generic organizational principle in cortex.}, author = {Hennequin, Guillaume and Vogels, Tim P and Gerstner, Wulfram}, issn = {0896-6273}, journal = {Neuron}, number = {6}, pages = {1394--1406}, publisher = {Elsevier}, title = {{Optimal control of transient dynamics in balanced networks supports generation of complex movements}}, doi = {10.1016/j.neuron.2014.04.045}, volume = {82}, year = {2014}, } @article{8023, abstract = {Uniform random sparse network architectures are ubiquitous in computational neuroscience, but the implicit hypothesis that they are a good representation of real neuronal networks has been met with skepticism. Here we used two experimental data sets, a study of triplet connectivity statistics and a data set measuring neuronal responses to channelrhodopsin stimuli, to evaluate the fidelity of thousands of model networks. Network architectures comprised three neuron types (excitatory, fast spiking, and nonfast spiking inhibitory) and were created from a set of rules that govern the statistics of the resulting connection types. In a high-dimensional parameter scan, we varied the degree distributions (i.e., how many cells each neuron connects with) and the synaptic weight correlations of synapses from or onto the same neuron. These variations converted initially uniform random and homogeneously connected networks, in which every neuron sent and received equal numbers of synapses with equal synaptic strength distributions, to highly heterogeneous networks in which the number of synapses per neuron, as well as average synaptic strength of synapses from or to a neuron were variable. By evaluating the impact of each variable on the network structure and dynamics, and their similarity to the experimental data, we could falsify the uniform random sparse connectivity hypothesis for 7 of 36 connectivity parameters, but we also confirmed the hypothesis in 8 cases. Twenty-one parameters had no substantial impact on the results of the test protocols we used.}, author = {Tomm, Christian and Avermann, Michael and Petersen, Carl and Gerstner, Wulfram and Vogels, Tim P}, issn = {1522-1598}, journal = {Journal of Neurophysiology}, number = {8}, pages = {1801--1814}, publisher = {American Physiological Society}, title = {{Connection-type-specific biases make uniform random network models consistent with cortical recordings}}, doi = {10.1152/jn.00629.2013}, volume = {112}, year = {2014}, } @inproceedings{8044, abstract = {Many questions concerning models in quantum mechanics require a detailed analysis of the spectrum of the corresponding Hamiltonian, a linear operator on a suitable Hilbert space. Of particular relevance for an understanding of the low-temperature properties of a system is the structure of the excitation spectrum, which is the part of the spectrum close to the spectral bottom. We present recent progress on this question for bosonic many-body quantum systems with weak two-body interactions. Such system are currently of great interest, due to their experimental realization in ultra-cold atomic gases. We investigate the accuracy of the Bogoliubov approximations, which predicts that the low-energy spectrum is made up of sums of elementary excitations, with linear dispersion law at low momentum. The latter property is crucial for the superfluid behavior the system.}, author = {Seiringer, Robert}, booktitle = {Proceeding of the International Congress of Mathematicans}, isbn = {9788961058063}, location = {Seoul, South Korea}, pages = {1175--1194}, publisher = {International Congress of Mathematicians}, title = {{Structure of the excitation spectrum for many-body quantum systems}}, volume = {3}, year = {2014}, } @inproceedings{1507, abstract = {The Wigner-Dyson-Gaudin-Mehta conjecture asserts that the local eigenvalue statistics of large real and complex Hermitian matrices with independent, identically distributed entries are universal in a sense that they depend only on the symmetry class of the matrix and otherwise are independent of the details of the distribution. We present the recent solution to this half-century old conjecture. We explain how stochastic tools, such as the Dyson Brownian motion, and PDE ideas, such as De Giorgi-Nash-Moser regularity theory, were combined in the solution. We also show related results for log-gases that represent a universal model for strongly correlated systems. Finally, in the spirit of Wigner’s original vision, we discuss the extensions of these universality results to more realistic physical systems such as random band matrices.}, author = {Erdös, László}, booktitle = {Proceedings of the International Congress of Mathematicians}, location = {Seoul, Korea}, pages = {214 -- 236}, publisher = {International Congress of Mathematicians}, title = {{Random matrices, log-gases and Hölder regularity}}, volume = {3}, year = {2014}, } @inproceedings{1516, abstract = {We present a rigorous derivation of the BCS gap equation for superfluid fermionic gases with point interactions. Our starting point is the BCS energy functional, whose minimizer we investigate in the limit when the range of the interaction potential goes to zero. }, author = {Bräunlich, Gerhard and Hainzl, Christian and Seiringer, Robert}, booktitle = {Proceedings of the QMath12 Conference}, location = {Berlin, Germany}, pages = {127 -- 137}, publisher = {World Scientific Publishing}, title = {{On the BCS gap equation for superfluid fermionic gases}}, doi = {10.1142/9789814618144_0007}, year = {2014}, } @article{1629, abstract = {We propose a method for propagating edit operations in 2D vector graphics, based on geometric relationship functions. These functions quantify the geometric relationship of a point to a polygon, such as the distance to the boundary or the direction to the closest corner vertex. The level sets of the relationship functions describe points with the same relationship to a polygon. For a given query point, we first determine a set of relationships to local features, construct all level sets for these relationships, and accumulate them. The maxima of the resulting distribution are points with similar geometric relationships. We show extensions to handle mirror symmetries, and discuss the use of relationship functions as local coordinate systems. Our method can be applied, for example, to interactive floorplan editing, and it is especially useful for large layouts, where individual edits would be cumbersome. We demonstrate populating 2D layouts with tens to hundreds of objects by propagating relatively few edit operations.}, author = {Guerrero, Paul and Jeschke, Stefan and Wimmer, Michael and Wonka, Peter}, journal = {ACM Transactions on Graphics}, number = {2}, publisher = {ACM}, title = {{Edit propagation using geometric relationship functions}}, doi = {10.1145/2591010}, volume = {33}, year = {2014}, } @inproceedings{1643, abstract = {We extend the notion of verifiable random functions (VRF) to constrained VRFs, which generalize the concept of constrained pseudorandom functions, put forward by Boneh and Waters (Asiacrypt’13), and independently by Kiayias et al. (CCS’13) and Boyle et al. (PKC’14), who call them delegatable PRFs and functional PRFs, respectively. In a standard VRF the secret key sk allows one to evaluate a pseudorandom function at any point of its domain; in addition, it enables computation of a non-interactive proof that the function value was computed correctly. In a constrained VRF from the key sk one can derive constrained keys skS for subsets S of the domain, which allow computation of function values and proofs only at points in S. After formally defining constrained VRFs, we derive instantiations from the multilinear-maps-based constrained PRFs by Boneh and Waters, yielding a VRF with constrained keys for any set that can be decided by a polynomial-size circuit. Our VRFs have the same function values as the Boneh-Waters PRFs and are proved secure under the same hardness assumption, showing that verifiability comes at no cost. Constrained (functional) VRFs were stated as an open problem by Boyle et al.}, author = {Fuchsbauer, Georg}, booktitle = {SCN 2014}, editor = {Abdalla, Michel and De Prisco, Roberto}, location = {Amalfi, Italy}, pages = {95 -- 114}, publisher = {Springer}, title = {{Constrained Verifiable Random Functions }}, doi = {10.1007/978-3-319-10879-7_7}, volume = {8642}, year = {2014}, } @inproceedings{1702, abstract = {In this paper we present INTERHORN, a solver for recursion-free Horn clauses. The main application domain of INTERHORN lies in solving interpolation problems arising in software verification. We show how a range of interpolation problems, including path, transition, nested, state/transition and well-founded interpolation can be handled directly by INTERHORN. By detailing these interpolation problems and their Horn clause representations, we hope to encourage the emergence of a common back-end interpolation interface useful for diverse verification tools.}, author = {Gupta, Ashutosh and Popeea, Corneliu and Rybalchenko, Andrey}, booktitle = {Electronic Proceedings in Theoretical Computer Science, EPTCS}, location = {Vienna, Austria}, pages = {31 -- 38}, publisher = {Open Publishing}, title = {{Generalised interpolation by solving recursion free-horn clauses}}, doi = {10.4204/EPTCS.169.5}, volume = {169}, year = {2014}, } @article{1733, abstract = {The classical (boolean) notion of refinement for behavioral interfaces of system components is the alternating refinement preorder. In this paper, we define a distance for interfaces, called interface simulation distance. It makes the alternating refinement preorder quantitative by, intuitively, tolerating errors (while counting them) in the alternating simulation game. We show that the interface simulation distance satisfies the triangle inequality, that the distance between two interfaces does not increase under parallel composition with a third interface, that the distance between two interfaces can be bounded from above and below by distances between abstractions of the two interfaces, and how to synthesize an interface from incompatible requirements. We illustrate the framework, and the properties of the distances under composition of interfaces, with two case studies.}, author = {Cerny, Pavol and Chmelik, Martin and Henzinger, Thomas A and Radhakrishna, Arjun}, journal = {Theoretical Computer Science}, number = {3}, pages = {348 -- 363}, publisher = {Elsevier}, title = {{Interface simulation distances}}, doi = {10.1016/j.tcs.2014.08.019}, volume = {560}, year = {2014}, }