@article{1832, abstract = {Linearizability of concurrent data structures is usually proved by monolithic simulation arguments relying on the identification of the so-called linearization points. Regrettably, such proofs, whether manual or automatic, are often complicated and scale poorly to advanced non-blocking concurrency patterns, such as helping and optimistic updates. In response, we propose a more modular way of checking linearizability of concurrent queue algorithms that does not involve identifying linearization points. We reduce the task of proving linearizability with respect to the queue specification to establishing four basic properties, each of which can be proved independently by simpler arguments. As a demonstration of our approach, we verify the Herlihy and Wing queue, an algorithm that is challenging to verify by a simulation proof. }, author = {Chakraborty, Soham and Henzinger, Thomas A and Sezgin, Ali and Vafeiadis, Viktor}, journal = {Logical Methods in Computer Science}, number = {1}, publisher = {International Federation of Computational Logic}, title = {{Aspect-oriented linearizability proofs}}, doi = {10.2168/LMCS-11(1:20)2015}, volume = {11}, year = {2015}, } @article{2271, abstract = {A class of valued constraint satisfaction problems (VCSPs) is characterised by a valued constraint language, a fixed set of cost functions on a finite domain. Finite-valued constraint languages contain functions that take on rational costs and general-valued constraint languages contain functions that take on rational or infinite costs. An instance of the problem is specified by a sum of functions from the language with the goal to minimise the sum. This framework includes and generalises well-studied constraint satisfaction problems (CSPs) and maximum constraint satisfaction problems (Max-CSPs). Our main result is a precise algebraic characterisation of valued constraint languages whose instances can be solved exactly by the basic linear programming relaxation (BLP). For a general-valued constraint language Γ, BLP is a decision procedure for Γ if and only if Γ admits a symmetric fractional polymorphism of every arity. For a finite-valued constraint language Γ, BLP is a decision procedure if and only if Γ admits a symmetric fractional polymorphism of some arity, or equivalently, if Γ admits a symmetric fractional polymorphism of arity 2. Using these results, we obtain tractability of several novel and previously widely-open classes of VCSPs, including problems over valued constraint languages that are: (1) submodular on arbitrary lattices; (2) bisubmodular (also known as k-submodular) on arbitrary finite domains; (3) weakly (and hence strongly) tree-submodular on arbitrary trees. }, author = {Kolmogorov, Vladimir and Thapper, Johan and Živný, Stanislav}, journal = {SIAM Journal on Computing}, number = {1}, pages = {1 -- 36}, publisher = {SIAM}, title = {{The power of linear programming for general-valued CSPs}}, doi = {10.1137/130945648}, volume = {44}, year = {2015}, } @article{257, abstract = {For suitable pairs of diagonal quadratic forms in eight variables we use the circle method to investigate the density of simultaneous integer solutions and relate this to the problem of estimating linear correlations among sums of two squares.}, author = {Timothy Browning and Munshi, Ritabrata}, journal = {Forum Mathematicum}, number = {4}, pages = {2025 -- 2050}, publisher = {Walter de Gruyter GmbH}, title = {{Pairs of diagonal quadratic forms and linear correlations among sums of two squares}}, doi = {10.1515/forum-2013-6024}, volume = {27}, year = {2015}, } @inbook{258, abstract = {Given a number field k and a projective algebraic variety X defined over k, the question of whether X contains a k-rational point is both very natural and very difficult. In the event that the set X(k) of k-rational points is not empty, one can also ask how the points of X(k) are distributed. Are they dense in X under the Zariski topology? Are they dense in the set.}, author = {Browning, Timothy D}, booktitle = {Arithmetic and Geometry}, pages = {89 -- 113}, publisher = {Cambridge University Press}, title = {{A survey of applications of the circle method to rational points}}, doi = {10.1017/CBO9781316106877.009}, year = {2015}, } @article{259, abstract = {The Hasse principle and weak approximation is established for non-singular cubic hypersurfaces X over the function field }, author = {Timothy Browning and Vishe, Pankaj}, journal = {Geometric and Functional Analysis}, number = {3}, pages = {671 -- 732}, publisher = {Birkhäuser}, title = {{Rational points on cubic hypersurfaces over F_q(t) }}, doi = {10.1007/s00039-015-0328-5}, volume = {25}, year = {2015}, } @article{1598, abstract = {We consider Markov decision processes (MDPs) with specifications given as Büchi (liveness) objectives, and examine the problem of computing the set of almost-sure winning vertices such that the objective can be ensured with probability 1 from these vertices. We study for the first time the average-case complexity of the classical algorithm for computing the set of almost-sure winning vertices for MDPs with Büchi objectives. Our contributions are as follows: First, we show that for MDPs with constant out-degree the expected number of iterations is at most logarithmic and the average-case running time is linear (as compared to the worst-case linear number of iterations and quadratic time complexity). Second, for the average-case analysis over all MDPs we show that the expected number of iterations is constant and the average-case running time is linear (again as compared to the worst-case linear number of iterations and quadratic time complexity). Finally we also show that when all MDPs are equally likely, the probability that the classical algorithm requires more than a constant number of iterations is exponentially small.}, author = {Chatterjee, Krishnendu and Joglekar, Manas and Shah, Nisarg}, journal = {Theoretical Computer Science}, number = {3}, pages = {71 -- 89}, publisher = {Elsevier}, title = {{Average case analysis of the classical algorithm for Markov decision processes with Büchi objectives}}, doi = {10.1016/j.tcs.2015.01.050}, volume = {573}, year = {2015}, } @article{1805, abstract = {We consider the problem of deciding whether the persistent homology group of a simplicial pair (K,L) can be realized as the homology H∗(X) of some complex X with L ⊂ X ⊂ K. We show that this problem is NP-complete even if K is embedded in double-struck R3. As a consequence, we show that it is NP-hard to simplify level and sublevel sets of scalar functions on double-struck S3 within a given tolerance constraint. This problem has relevance to the visualization of medical images by isosurfaces. We also show an implication to the theory of well groups of scalar functions: not every well group can be realized by some level set, and deciding whether a well group can be realized is NP-hard.}, author = {Attali, Dominique and Bauer, Ulrich and Devillers, Olivier and Glisse, Marc and Lieutier, André}, journal = {Computational Geometry: Theory and Applications}, number = {8}, pages = {606 -- 621}, publisher = {Elsevier}, title = {{Homological reconstruction and simplification in R3}}, doi = {10.1016/j.comgeo.2014.08.010}, volume = {48}, year = {2015}, } @article{333, abstract = {We present a hybrid intercalation battery based on a sodium/magnesium (Na/Mg) dual salt electrolyte, metallic magnesium anode, and a cathode based on FeS2 nanocrystals (NCs). Compared to lithium or sodium, metallic magnesium anode is safer due to dendrite-free electroplating and offers extremely high volumetric (3833 mAh cm-3) and gravimetric capacities (2205 mAh g-1). Na-ion cathodes, FeS2 NCs in the present study, may serve as attractive alternatives to Mg-ion cathodes due to the higher voltage of operation and fast, highly reversible insertion of Na-ions. In this proof-of-concept study, electrochemical cycling of the Na/Mg hybrid battery was characterized by high rate capability, high Coulombic efficiency of 99.8%, and high energy density. In particular, with an average discharge voltage of ∼1.1 V and a cathodic capacity of 189 mAh g-1 at a current of 200 mA g-1, the presented Mg/FeS2 hybrid battery delivers energy densities of up to 210 Wh kg-1, comparable to commercial Li-ion batteries and approximately twice as high as state-of-the-art Mg-ion batteries based on Mo6S8 cathodes. Further significant gains in the energy density are expected from the development of Na/Mg electrolytes with a broader electrochemical stability window. Fully based on Earth-abundant elements, hybrid Na-Mg batteries are highly promising for large-scale stationary energy storage. }, author = {Walter, Marc and Kravchyk, Kostiantyn and Ibáñez, Maria and Kovalenko, Maksym}, journal = {Chemistry of Materials}, number = {21}, pages = {7452 -- 7458}, publisher = {ACS}, title = {{Efficient and inexpensive sodium magnesium hybrid battery}}, doi = {10.1021/acs.chemmater.5b03531}, volume = {27}, year = {2015}, } @article{354, abstract = {A simple and effective method to introduce precise amounts of doping in nanomaterials produced from the bottom-up assembly of colloidal nanoparticles (NPs) is described. The procedure takes advantage of a ligand displacement step to incorporate controlled concentrations of halide ions while removing carboxylic acids from the NP surface. Upon consolidation of the NPs into dense pellets, halide ions diffuse within the crystal structure, doping the anion sublattice and achieving n-type electrical doping. Through the characterization of the thermoelectric properties of nanocrystalline PbS, we demonstrate this strategy to be effective to control charge transport properties on thermoelectric nanomaterials assembled from NP building blocks. This approach is subsequently extended to PbTexSe1-x@PbS core-shell NPs, where a significant enhancement of the thermoelectric figure of merit is achieved. }, author = {Ibáñez, Maria and Korkosz, Rachel and Luo, Zhishan and Riba, Pau and Cadavid, Doris and Ortega, Silvia and Cabot, Andreu and Kanatzidis, Mercouri}, journal = {Journal of the American Chemical Society}, number = {12}, pages = {4046 -- 4049}, publisher = {American Chemical Society}, title = {{Electron doping in bottom up engineered thermoelectric nanomaterials through HCl mediated ligand displacement}}, doi = {10.1021/jacs.5b00091}, volume = {137}, year = {2015}, } @article{360, abstract = {A cation exchange-based route was used to produce Cu2ZnSnS4 (CZTS)-Ag2S nanoparticles with controlled composition. We report a detailed study of the formation of such CZTS-Ag2S nanoheterostructures and of their photocatalytic properties. When compared to pure CZTS, the use of nanoscale p-n heterostructures as light absorbers for photocatalytic water splitting provides superior photocurrents. We associate this experimental fact to a higher separation efficiency of the photogenerated electron-hole pairs. We believe this and other type-II nanoheterostructures will open the door to the use of CZTS, with excellent light absorption properties and made of abundant and environmental friendly elements, to the field of photocatalysis. }, author = {Yu, Xuelian and Liu, Jingjing and Genç, Aziz and Ibáñez, Maria and Luo, Zhishan and Shavel, Alexey and Arbiol, Jordi and Zhang, Guangjin and Zhang, Yihe and Cabot, Andreu}, journal = {Langmuir}, number = {38}, pages = {10555 -- 10561}, publisher = {American Chemical Society}, title = {{Cu2ZnSnS4-Ag2S nanoscale p-n heterostructures as sensitizers for photoelectrochemical water splitting}}, doi = {10.1021/acs.langmuir.5b02490}, volume = {31}, year = {2015}, } @article{362, abstract = {Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration. }, author = {Lu, Zhishan and Ibáñez, Maria and Antolín, Ana and Genç, Aziz and Shavel, Alexey and Contreras, Sandra and Medina, Francesc and Arbiol, Jordi and Cabot, Andreu}, journal = {Langmuir}, number = {13}, pages = {3952 -- 3957}, publisher = {American Chemical Society}, title = {{Size and aspect ratio control of Pd inf 2 inf Sn nanorods and their water denitration properties}}, doi = {10.1021/la504906q}, volume = {31}, year = {2015}, } @article{1731, abstract = {We consider two-player zero-sum games on graphs. These games can be classified on the basis of the information of the players and on the mode of interaction between them. On the basis of information the classification is as follows: (a) partial-observation (both players have partial view of the game); (b) one-sided complete-observation (one player has complete observation); and (c) complete-observation (both players have complete view of the game). On the basis of mode of interaction we have the following classification: (a) concurrent (both players interact simultaneously); and (b) turn-based (both players interact in turn). The two sources of randomness in these games are randomness in transition function and randomness in strategies. In general, randomized strategies are more powerful than deterministic strategies, and randomness in transitions gives more general classes of games. In this work we present a complete characterization for the classes of games where randomness is not helpful in: (a) the transition function probabilistic transition can be simulated by deterministic transition); and (b) strategies (pure strategies are as powerful as randomized strategies). As consequence of our characterization we obtain new undecidability results for these games. }, author = {Chatterjee, Krishnendu and Doyen, Laurent and Gimbert, Hugo and Henzinger, Thomas A}, journal = {Information and Computation}, number = {12}, pages = {3 -- 16}, publisher = {Elsevier}, title = {{Randomness for free}}, doi = {10.1016/j.ic.2015.06.003}, volume = {245}, year = {2015}, } @article{334, abstract = {A cation exchange-based route was used to produce Cu2ZnSnS4 (CZTS)-Ag2S nanoparticles with controlled composition. We report a detailed study of the formation of such CZTS-Ag2S nanoheterostructures and of their photocatalytic properties. When compared to pure CZTS, the use of nanoscale p-n heterostructures as light absorbers for photocatalytic water splitting provides superior photocurrents. We associate this experimental fact to a higher separation efficiency of the photogenerated electron-hole pairs. We believe this and other type-II nanoheterostructures will open the door to the use of CZTS, with excellent light absorption properties and made of abundant and environmental friendly elements, to the field of photocatalysis.}, author = {Yu, Xuelian and Liu, Jingjing and Genç, Aziz and Ibáñez, Maria and Luo, Zhishan and Shavel, Alexey and Arbiol, Jordi and Zhang, Guangjin and Zhang, Yihe and Cabot, Andreu}, journal = {Langmuir}, number = {38}, pages = {10555 -- 10561}, publisher = {American Chemical Society}, title = {{Cu2ZnSnS4–Ag2S Nanoscale p–n heterostructures as sensitizers for photoelectrochemical water splitting}}, doi = {10.1021/acs.langmuir.5b02490}, volume = {31}, year = {2015}, } @article{361, abstract = {We report the synthesis and photocatalytic and magnetic characterization of colloidal nanoheterostructures formed by combining a Pt-based magnetic metal alloy (PtCo, PtNi) with Cu2ZnSnS4 (CZTS). While CZTS is one of the main candidate materials for solar energy conversion, the introduction of a Pt-based alloy on its surface strongly influences its chemical and electronic properties, ultimately determining its functionality. In this regard, up to a 15-fold increase of the photocatalytic hydrogen evolution activity was obtained with CZTS–PtCo when compared with CZTS. Furthermore, two times higher hydrogen evolution rates were obtained for CZTS–PtCo when compared with CZTS–Pt, in spite of the lower precious metal loading of the former. Besides, the magnetic properties of the PtCo nanoparticles attached to the CZTS nanocrystals were retained in the heterostructures, which could facilitate catalyst purification and recovery for its posterior recycling and/or reutilization.}, author = {Yu, Xuelian and An, Xiaoqiang and Genç, Aziz and Ibáñez, Maria and Arbiol, Jordi and Zhang, Yihe and Cabot, Andreu}, journal = {Journal of Physical Chemistry C}, number = {38}, pages = {21882 -- 21888}, publisher = {American Chemical Society}, title = {{Cu2ZnSnS4–PtM (M = Co, Ni) nanoheterostructures for photocatalytic hydrogen evolution}}, doi = {10.1021/acs.jpcc.5b06199}, volume = {119}, year = {2015}, } @article{1856, abstract = {The traditional synthesis question given a specification asks for the automatic construction of a system that satisfies the specification, whereas often there exists a preference order among the different systems that satisfy the given specification. Under a probabilistic assumption about the possible inputs, such a preference order is naturally expressed by a weighted automaton, which assigns to each word a value, such that a system is preferred if it generates a higher expected value. We solve the following optimal synthesis problem: given an omega-regular specification, a Markov chain that describes the distribution of inputs, and a weighted automaton that measures how well a system satisfies the given specification under the input assumption, synthesize a system that optimizes the measured value. For safety specifications and quantitative measures that are defined by mean-payoff automata, the optimal synthesis problem reduces to finding a strategy in a Markov decision process (MDP) that is optimal for a long-run average reward objective, which can be achieved in polynomial time. For general omega-regular specifications along with mean-payoff automata, the solution rests on a new, polynomial-time algorithm for computing optimal strategies in MDPs with mean-payoff parity objectives. Our algorithm constructs optimal strategies that consist of two memoryless strategies and a counter. The counter is in general not bounded. To obtain a finite-state system, we show how to construct an ε-optimal strategy with a bounded counter, for all ε > 0. Furthermore, we show how to decide in polynomial time if it is possible to construct an optimal finite-state system (i.e., a system without a counter) for a given specification. We have implemented our approach and the underlying algorithms in a tool that takes qualitative and quantitative specifications and automatically constructs a system that satisfies the qualitative specification and optimizes the quantitative specification, if such a system exists. We present some experimental results showing optimal systems that were automatically generated in this way.}, author = {Chatterjee, Krishnendu and Henzinger, Thomas A and Jobstmann, Barbara and Singh, Rohit}, journal = {Journal of the ACM}, number = {1}, publisher = {ACM}, title = {{Measuring and synthesizing systems in probabilistic environments}}, doi = {10.1145/2699430}, volume = {62}, year = {2015}, } @article{388, abstract = {We use ultrafast optical spectroscopy to observe binding of charged single-particle excitations (SE) in the magnetically frustrated Mott insulator Na2IrO3. Above the antiferromagnetic ordering temperature (TN) the system response is due to both Hubbard excitons (HE) and their constituent unpaired SE. The SE response becomes strongly suppressed immediately below TN. We argue that this increase in binding energy is due to a unique interplay between the frustrated Kitaev and the weak Heisenberg-type ordering term in the Hamiltonian, mediating an effective interaction between the spin-singlet SE. This interaction grows with distance causing the SE to become trapped in the HE, similar to quark confinement inside hadrons. This binding of charged particles, induced by magnetic ordering, is a result of a confinement-deconfinement transition of spin excitations. This observation provides evidence for spin liquid type behavior which is expected in Na2IrO3.}, author = {Alpichshev, Zhanybek and Mahmood, Fahad and Cao, Gang and Gedik, Nuh}, journal = {Physical Review Letters}, number = {1}, publisher = {American Physical Society}, title = {{Confinement deconfinement transition as an indication of spin liquid type behavior in Na2IrO3}}, doi = {10.1103/PhysRevLett.114.017203}, volume = {114}, year = {2015}, } @inproceedings{1661, abstract = {The computation of the winning set for one-pair Streett objectives and for k-pair Streett objectives in (standard) graphs as well as in game graphs are central problems in computer-aided verification, with application to the verification of closed systems with strong fairness conditions, the verification of open systems, checking interface compatibility, well-formed ness of specifications, and the synthesis of reactive systems. We give faster algorithms for the computation of the winning set for (1) one-pair Streett objectives (aka parity-3 problem) in game graphs and (2) for k-pair Streett objectives in graphs. For both problems this represents the first improvement in asymptotic running time in 15 years.}, author = {Chatterjee, Krishnendu and Henzinger, Monika H and Loitzenbauer, Veronika}, booktitle = {Proceedings - Symposium on Logic in Computer Science}, location = {Kyoto, Japan}, publisher = {IEEE}, title = {{Improved algorithms for one-pair and k-pair Streett objectives}}, doi = {10.1109/LICS.2015.34}, volume = {2015-July}, year = {2015}, } @article{473, abstract = {We prove that nonlinear Gibbs measures can be obtained from the corresponding many-body, grand-canonical, quantum Gibbs states, in a mean-field limit where the temperature T diverges and the interaction strength behaves as 1/T. We proceed by characterizing the interacting Gibbs state as minimizing a functional counting the free-energy relatively to the non-interacting case. We then perform an infinite-dimensional analogue of phase-space semiclassical analysis, using fine properties of the quantum relative entropy, the link between quantum de Finetti measures and upper/lower symbols in a coherent state basis, as well as Berezin-Lieb type inequalities. Our results cover the measure built on the defocusing nonlinear Schrödinger functional on a finite interval, as well as smoother interactions in dimensions d 2.}, author = {Lewin, Mathieu and Phan Thanh, Nam and Rougerie, Nicolas}, journal = {Journal de l'Ecole Polytechnique - Mathematiques}, pages = {65 -- 115}, publisher = {Ecole Polytechnique}, title = {{Derivation of nonlinear gibbs measures from many-body quantum mechanics}}, doi = {10.5802/jep.18}, volume = {2}, year = {2015}, } @article{477, abstract = {Dendritic cells are potent antigen-presenting cells endowed with the unique ability to initiate adaptive immune responses upon inflammation. Inflammatory processes are often associated with an increased production of serotonin, which operates by activating specific receptors. However, the functional role of serotonin receptors in regulation of dendritic cell functions is poorly understood. Here, we demonstrate that expression of serotonin receptor 5-HT7 (5-HT7TR) as well as its downstream effector Cdc42 is upregulated in dendritic cells upon maturation. Although dendritic cell maturation was independent of 5-HT7TR, receptor stimulation affected dendritic cell morphology through Cdc42-mediated signaling. In addition, basal activity of 5-HT7TR was required for the proper expression of the chemokine receptor CCR7, which is a key factor that controls dendritic cell migration. Consistent with this, we observed that 5-HT7TR enhances chemotactic motility of dendritic cells in vitro by modulating their directionality and migration velocity. Accordingly, migration of dendritic cells in murine colon explants was abolished after pharmacological receptor inhibition. Our results indicate that there is a crucial role for 5-HT7TR-Cdc42-mediated signaling in the regulation of dendritic cell morphology and motility, suggesting that 5-HT7TR could be a new target for treatment of a variety of inflammatory and immune disorders.}, author = {Holst, Katrin and Guseva, Daria and Schindler, Susann and Sixt, Michael K and Braun, Armin and Chopra, Himpriya and Pabst, Oliver and Ponimaskin, Evgeni}, journal = {Journal of Cell Science}, number = {15}, pages = {2866 -- 2880}, publisher = {Company of Biologists}, title = {{The serotonin receptor 5-HT7R regulates the morphology and migratory properties of dendritic cells}}, doi = {10.1242/jcs.167999}, volume = {128}, year = {2015}, } @article{523, abstract = {We consider two-player games played on weighted directed graphs with mean-payoff and total-payoff objectives, two classical quantitative objectives. While for single-dimensional games the complexity and memory bounds for both objectives coincide, we show that in contrast to multi-dimensional mean-payoff games that are known to be coNP-complete, multi-dimensional total-payoff games are undecidable. We introduce conservative approximations of these objectives, where the payoff is considered over a local finite window sliding along a play, instead of the whole play. For single dimension, we show that (i) if the window size is polynomial, deciding the winner takes polynomial time, and (ii) the existence of a bounded window can be decided in NP ∩ coNP, and is at least as hard as solving mean-payoff games. For multiple dimensions, we show that (i) the problem with fixed window size is EXPTIME-complete, and (ii) there is no primitive-recursive algorithm to decide the existence of a bounded window.}, author = {Chatterjee, Krishnendu and Doyen, Laurent and Randour, Mickael and Raskin, Jean}, journal = {Information and Computation}, number = {6}, pages = {25 -- 52}, publisher = {Elsevier}, title = {{Looking at mean-payoff and total-payoff through windows}}, doi = {10.1016/j.ic.2015.03.010}, volume = {242}, year = {2015}, }