@article{330, abstract = {A procedure for the continuous production of Cu 2ZnSnS 4 (CZTS) nanoparticles with controlled composition is presented. CZTS nanoparticles were prepared through the reaction of the metals' amino complexes with elemental sulfur in a continuous-flow reactor at moderate temperatures (300-330 °C). High-resolution transmission electron microscopy and X-ray diffraction analysis showed the nanocrystals to have a crystallographic structure compatible with that of the kesterite. Chemical characterization of the materials showed the presence of the four elements in each individual nanocrystal. Composition control was achieved by adjusting the solution flow rate through the reactor and the proper choice of the nominal precursor concentration within the flowing solution. Single-particle analysis revealed a composition distribution within each sample, which was optimized at the highest synthesis temperatures used. }, author = {Shavel, Alexey and Cadavid, Doris and Ibáñez, Maria and Carrete, Alex and Cabot, Andreu}, journal = {Journal of the American Chemical Society}, number = {3}, pages = {1438 -- 1441}, publisher = {ACS}, title = {{Continuous production of Cu inf 2 inf ZnSnS inf 4 inf nanocrystals in a flow reactor}}, doi = {10.1021/ja209688a}, volume = {134}, year = {2012}, } @article{3310, abstract = {The theory of persistent homology opens up the possibility to reason about topological features of a space or a function quantitatively and in combinatorial terms. We refer to this new angle at a classical subject within algebraic topology as a point calculus, which we present for the family of interlevel sets of a real-valued function. Our account of the subject is expository, devoid of proofs, and written for non-experts in algebraic topology.}, author = {Bendich, Paul and Cabello, Sergio and Edelsbrunner, Herbert}, journal = {Pattern Recognition Letters}, number = {11}, pages = {1436 -- 1444}, publisher = {Elsevier}, title = {{A point calculus for interlevel set homology}}, doi = {10.1016/j.patrec.2011.10.007}, volume = {33}, year = {2012}, } @article{3314, abstract = {We introduce two-level discounted and mean-payoff games played by two players on a perfect-information stochastic game graph. The upper level game is a discounted or mean-payoff game and the lower level game is a (undiscounted) reachability game. Two-level games model hierarchical and sequential decision making under uncertainty across different time scales. For both discounted and mean-payoff two-level games, we show the existence of pure memoryless optimal strategies for both players and an ordered field property. We show that if there is only one player (Markov decision processes), then the values can be computed in polynomial time. It follows that whether the value of a player is equal to a given rational constant in two-level discounted or mean-payoff games can be decided in NP ∩ coNP. We also give an alternate strategy improvement algorithm to compute the value. © 2012 World Scientific Publishing Company.}, author = {Chatterjee, Krishnendu and Majumdar, Ritankar}, journal = {International Journal of Foundations of Computer Science}, number = {3}, pages = {609 -- 625}, publisher = {World Scientific Publishing}, title = {{Discounting and averaging in games across time scales}}, doi = {10.1142/S0129054112400308}, volume = {23}, year = {2012}, } @article{3317, abstract = {The physical distance between presynaptic Ca2+ channels and the Ca2+ sensors that trigger exocytosis of neurotransmitter-containing vesicles is a key determinant of the signalling properties of synapses in the nervous system. Recent functional analysis indicates that in some fast central synapses, transmitter release is triggered by a small number of Ca2+ channels that are coupled to Ca2+ sensors at the nanometre scale. Molecular analysis suggests that this tight coupling is generated by protein–protein interactions involving Ca2+ channels, Ca2+ sensors and various other synaptic proteins. Nanodomain coupling has several functional advantages, as it increases the efficacy, speed and energy efficiency of synaptic transmission.}, author = {Eggermann, Emmanuel and Bucurenciu, Iancu and Goswami, Sarit and Jonas, Peter M}, journal = {Nature Reviews Neuroscience}, number = {1}, pages = {7 -- 21}, publisher = {Nature Publishing Group}, title = {{Nanodomain coupling between Ca(2+) channels and sensors of exocytosis at fast mammalian synapses}}, doi = {10.1038/nrn3125}, volume = {13}, year = {2012}, } @article{3331, abstract = {Computing the topology of an algebraic plane curve C means computing a combinatorial graph that is isotopic to C and thus represents its topology in R2. We prove that, for a polynomial of degree n with integer coefficients bounded by 2ρ, the topology of the induced curve can be computed with bit operations ( indicates that we omit logarithmic factors). Our analysis improves the previous best known complexity bounds by a factor of n2. The improvement is based on new techniques to compute and refine isolating intervals for the real roots of polynomials, and on the consequent amortized analysis of the critical fibers of the algebraic curve.}, author = {Kerber, Michael and Sagraloff, Michael}, journal = { Journal of Symbolic Computation}, number = {3}, pages = {239 -- 258}, publisher = {Elsevier}, title = {{A worst case bound for topology computation of algebraic curves}}, doi = {10.1016/j.jsc.2011.11.001}, volume = {47}, year = {2012}, } @inproceedings{3341, abstract = {We consider two-player stochastic games played on a finite state space for an infinite number of rounds. The games are concurrent: in each round, the two players (player 1 and player 2) choose their moves independently and simultaneously; the current state and the two moves determine a probability distribution over the successor states. We also consider the important special case of turn-based stochastic games where players make moves in turns, rather than concurrently. We study concurrent games with \omega-regular winning conditions specified as parity objectives. The value for player 1 for a parity objective is the maximal probability with which the player can guarantee the satisfaction of the objective against all strategies of the opponent. We study the problem of continuity and robustness of the value function in concurrent and turn-based stochastic parity gameswith respect to imprecision in the transition probabilities. We present quantitative bounds on the difference of the value function (in terms of the imprecision of the transition probabilities) and show the value continuity for structurally equivalent concurrent games (two games are structurally equivalent if the support of the transition function is same and the probabilities differ). We also show robustness of optimal strategies for structurally equivalent turn-based stochastic parity games. Finally we show that the value continuity property breaks without the structurally equivalent assumption (even for Markov chains) and show that our quantitative bound is asymptotically optimal. Hence our results are tight (the assumption is both necessary and sufficient) and optimal (our quantitative bound is asymptotically optimal).}, author = {Chatterjee, Krishnendu}, location = {Tallinn, Estonia}, pages = {270 -- 285}, publisher = {Springer}, title = {{Robustness of structurally equivalent concurrent parity games}}, doi = {10.1007/978-3-642-28729-9_18}, volume = {7213}, year = {2012}, } @article{338, abstract = {The ample chemical and structural freedom of quaternary compounds permits engineering materials that fulfill the requirements of a wide variety of applications. In this work, the mechanisms to achieve unprecedented size, shape, and composition control in quaternary nanocrystals are detailed. The described procedure allows obtaining tetrahedral and penta-tetrahedral quaternary nanocrystals with tuned size distributions and controlled compositions from a plethora of I 2-II-IV-VI 4 semiconductors.}, author = {Ibáñez, Maria and Zamani, Reza and Li, Wenhua and Shavel, Alexey and Arbiol, Jordi and Morante, Joan and Cabot, Andreu}, journal = {Crystal Growth and Design }, number = {3}, pages = {1085 -- 1090}, publisher = {American Chemical Society (ACS)}, title = {{Extending the nanocrystal synthesis control to quaternary compositions}}, doi = {10.1021/cg201709c}, volume = {12}, year = {2012}, } @article{339, abstract = {A high-yield and upscalable colloidal synthesis route for the production of quaternary I 2-II-IV-VI 4 nanocrystals, particularly stannite Cu 2+xCd 1-xSnSe 4, with narrow size distribution and precisely controlled composition is presented. It is also shown here how the diversity of valences in the constituent elements allows an effective control of their electrical conductivity through the adjustment of the cation ratios. At the same time, while the crystallographic complexity of quaternary chalcogenides is associated with intrinsically low thermal conductivities, the reduction of the lattice dimensions to the nanoscale further reduces the materials thermal conductivity. In the specific case of the stannite crystal structure, a convenient slab distribution of the valence band maximum states permits a partial decoupling of the p-type electrical conductivity from both the Seebeck coefficient and the thermal conductivity. Combining these features, we demonstrate how an initial optimization of the nanocrystals Cd/Cu ratio allowed us to obtain low-temperature solution-processed materials with ZT values up to 0.71 at 685 K.}, author = {Ibáñez, Maria and Cadavid, Doris and Zamani, Reza and García Castelló, Nuria and Izquierdo Roca, Victora and Li, Wenhua and Fairbrother, Andrew and Prades, Joan and Shavel, Alexey and Arbiol, Jordi and Pérez Rodríguez, Alejandro and Morante, Joan and Cabot, Andreu}, journal = {Chemistry of Materials}, number = {3}, pages = {562 -- 570}, publisher = {American Chemical Society}, title = {{Composition control and thermoelectric properties of quaternary chalcogenide nanocrystals: The case of stannite Cu2CdSnSe4}}, doi = {10.1021/cm2031812}, volume = {24}, year = {2012}, } @article{340, abstract = {A procedure for the continuous production of Cu 2ZnSnS 4 (CZTS) nanoparticles with controlled composition is presented. CZTS nanoparticles were prepared through the reaction of the metals' amino complexes with elemental sulfur in a continuous-flow reactor at moderate temperatures (300-330 °C). High-resolution transmission electron microscopy and X-ray diffraction analysis showed the nanocrystals to have a crystallographic structure compatible with that of the kesterite. Chemical characterization of the materials showed the presence of the four elements in each individual nanocrystal. Composition control was achieved by adjusting the solution flow rate through the reactor and the proper choice of the nominal precursor concentration within the flowing solution. Single-particle analysis revealed a composition distribution within each sample, which was optimized at the highest synthesis temperatures used. }, author = {Shavel, Alexey and Cadavid, Doris and Ibáñez, Maria and Carrete, Alex and Cabot, Andreu}, journal = {Journal of the American Chemical Society}, number = {3}, pages = {1438 -- 1441}, publisher = {ACS}, title = {{Continuous production of Cu inf 2 inf ZnSnS inf 4 inf nanocrystals in a flow reactor}}, doi = {10.1021/ja209688a}, volume = {134}, year = {2012}, } @article{345, abstract = {Nanocomposites are highly promising materials to enhance the efficiency of current thermoelectric devices. A straightforward and at the same time highly versatile and controllable approach to produce nanocomposites is the assembly of solution-processed nanocrystal building blocks. The convenience of this bottom-up approach to produce nanocomposites with homogeneous phase distributions and adjustable composition is demonstrated here by blending Ag2Te and PbTe colloidal nanocrystals to form Ag2Te–PbTe bulk nanocomposites. The thermoelectric properties of these nanocomposites are analyzed in the temperature range from 300 to 700 K. The evolution of their electrical conductivity and Seebeck coefficient is discussed in terms of the blend composition and the characteristics of the constituent materials. }, author = {Cadavid, Doris and Ibáñez, Maria and Gorsse, Stéphane and López, Antonio and Cirera, Albert and Morante, Joan and Cabot, Andreu}, journal = {Journal of Nanoparticle Research}, number = {12}, publisher = {Kluwer}, title = {{Bottom-up processing of thermoelectric nanocomposites from colloidal nanocrystal building blocks: The case of Ag2Te–PbTe}}, doi = {10.1007/s11051-012-1328-0}, volume = {14}, year = {2012}, } @article{346, abstract = {Arrays of vertically aligned ZnO : Cl/TiO2 and ZnO : Cl/ZnxTiOy/TiO2 core–shell nanowires (NWs) were prepared by means of the combination of two solution-growth processes. First, single-crystal ZnO NWs with controlled n-type doping were grown on conducting substrates by a low-cost, high-yield and seed-free electrochemical route. These NWs were covered by a titanium oxide shell of tunable thickness mediating successive adsorption-hydrolysis-condensation steps. Using this atomic-layer growth procedure, titania shells with controlled thickness and the anatase TiO2 phase were obtained after sintering at 450 °C. Higher sintering temperatures resulted in the formation of ZnO : Cl/ZnxTiOy/TiO2 core–shell NWs by the interdiffusion of Zn and Ti ions at the ZnO–TiO2 interface. The performance of ZnO : Cl/TiO2 and ZnO : Cl/ZnxTiOy/TiO2 core–shell NWs towards photoelectrochemical (PEC) water splitting was investigated as a function of the titania shell thickness. Furthermore, the performance of such core–shell NWs as photoelectrodes in dye-sensitized solar cells was also characterized. The TiO2 presence at the ZnO : Cl surface promoted a two-fold increase on the produced photocurrent densities, probing their potential for PEC and optoelectronic applications. Electrochemical impedance spectroscopy was used to corroborate the lower resistance for charge transfer between the NWs and the electrolyte in the presence of the TiO2 shell.}, author = {Fan, Jiandong and Zamani, Reza and Fábrega, Cristina and Shavel, Alexey and Flox, Cristina and Ibáñez, Maria and Andreu, Teresa and López, Amtonio and Arbiol, Jordi and Morante, Joan and Cabot, Andreu}, journal = {Journal of Physics D: Applied Physics}, number = {41}, publisher = {IOP Publishing Ltd.}, title = {{Solution-growth and optoelectronic performance of ZnO : Cl/TiO2 and ZnO : Cl/ZnxTiOy/TiO2 core–shell nanowires with tunable shell thickness}}, doi = {10.1088/0022-3727/45/41/415301}, volume = {45}, year = {2012}, } @article{347, abstract = {A synthetic route for producing Cu 2ZnGeSe 4 nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu 2ZnGeSe 4 is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450°C. }, author = {Ibáñez, Maria and Zamani, Reza and Lalonde, Aaron and Cadavid, Doris and Li, Wenhua and Shavel, Alexey and Arbiol, Jordi and Morante, Joan and Gorsse, Stéphane and Snyder, G Jeffrey and Cabot, Andreu}, journal = {Journal of the American Chemical Society}, number = {9}, pages = {4060 -- 4063}, publisher = {ACS}, title = {{Cu 2ZnGeSe 4 nanocrystals: Synthesis and thermoelectric properties}}, doi = {10.1021/ja211952z}, volume = {134}, year = {2012}, } @article{377, abstract = {The potential to control the composition and crystal phase at the nanometer scale enable the production of nanocrystalline materials with enhanced functionalities and new applications. In the present work, we detail a novel colloidal synthesis route to prepare nanoparticles of the ternary semiconductor Cu2GeSe3 (CGSe) with nanometer-scale control over their crystal phases. We also demonstrate the structural effect on the thermoelectric properties of bottom-up-prepared CGSe nanomaterials. By careful adjustment of the nucleation and growth temperatures, pure orthorhombic CGSe nanoparticles with cationic order or polytypic CGSe nanoparticles with disordered cation positions can be produced. In this second type of nanoparticle, a high density of twins can be created to periodically change the atomic plane stacking, forming a hexagonal wurtzite CGSe phase. The high yield of the synthetic routes reported here allows the production of single-phase and multiphase CGSe nanoparticles in the gram scale, which permits characterization of the thermoelectric properties of these materials. Reduced thermal conductivities and a related 2.5-fold increase of the thermoelectric figure of merit for multiphase nanomaterials compared to pure-phase CGSe are systematically obtained. These results are discussed in terms of the density and efficiency of phonon scattering centers in both types of materials.}, author = {Ibáñez, Maria and Zamani, Reza and Li, Wenhua and Cadavid, Doris and Gorse, Stéphane and Katchoi, Nebll and Shavel, Alexey and López, Antonioo and Morante, Joan and Arbiol, Jordi and Cabot, Andreu}, journal = {Chemistry of Materials}, number = {23}, pages = {4615 -- 4622}, publisher = {American Chemical Society}, title = {{Crystallographic control at the nanoscale to enhance functionality: Polytypic Cu2GeSe3 nanoparticles as thermoelectric materials}}, doi = {10.1021/cm303252q}, volume = {24}, year = {2012}, } @article{3836, abstract = {Hierarchical Timing Language (HTL) is a coordination language for distributed, hard real-time applications. HTL is a hierarchical extension of Giotto and, like its predecessor, based on the logical execution time (LET) paradigm of real-time programming. Giotto is compiled into code for a virtual machine, called the EmbeddedMachine (or E machine). If HTL is targeted to the E machine, then the hierarchicalprogram structure needs to be flattened; the flattening makes separatecompilation difficult, and may result in E machinecode of exponential size. In this paper, we propose a generalization of the E machine, which supports a hierarchicalprogram structure at runtime through real-time trigger mechanisms that are arranged in a tree. We present the generalized E machine, and a modular compiler for HTL that generates code of linear size. The compiler may generate code for any part of a given HTL program separately in any order.}, author = {Ghosal, Arkadeb and Iercan, Daniel and Kirsch, Christoph and Henzinger, Thomas A and Sangiovanni Vincentelli, Alberto}, journal = {Science of Computer Programming}, number = {2}, pages = {96 -- 112}, publisher = {Elsevier}, title = {{Separate compilation of hierarchical real-time programs into linear-bounded embedded machine code}}, doi = {10.1016/j.scico.2010.06.004}, volume = {77}, year = {2012}, } @article{3846, abstract = {We summarize classical and recent results about two-player games played on graphs with ω-regular objectives. These games have applications in the verification and synthesis of reactive systems. Important distinctions are whether a graph game is turn-based or concurrent; deterministic or stochastic; zero-sum or not. We cluster known results and open problems according to these classifications.}, author = {Chatterjee, Krishnendu and Henzinger, Thomas A}, journal = {Journal of Computer and System Sciences}, number = {2}, pages = {394 -- 413}, publisher = {Elsevier}, title = {{A survey of stochastic ω regular games}}, doi = {10.1016/j.jcss.2011.05.002}, volume = {78}, year = {2012}, } @article{387, abstract = {In this Letter we present detailed study of the density of states near defects in Bi 2Se 3. In particular, we present data on the commonly found triangular defects in this system. While we do not find any measurable quasiparticle scattering interference effects, we do find localized resonances, which can be well fitted by theory once the potential is taken to be extended to properly account for the observed defects. The data together with the fits confirm that while the local density of states around the Dirac point of the electronic spectrum at the surface is significantly disrupted near the impurity by the creation of low-energy resonance state, the Dirac point is not locally destroyed. We discuss our results in terms of the expected protected surface state of topological insulators. © 2012 American Physical Society.}, author = {Alpichshev, Zhanybek and Biswas, Rudro and Balatsky, Alexander and Analytis, James and Chu, Jiunhaw and Fisher, Ian and Kapitulnik, Aharon}, journal = {Physical Review Letters}, number = {20}, publisher = {American Physical Society}, title = {{STM imaging of impurity resonances on Bi 2Se 3}}, doi = {10.1103/PhysRevLett.108.206402}, volume = {108}, year = {2012}, } @article{492, abstract = {Background: Characterizing root system architecture (RSA) is essential to understanding the development and function of vascular plants. Identifying RSA-associated genes also represents an underexplored opportunity for crop improvement. Software tools are needed to accelerate the pace at which quantitative traits of RSA are estimated from images of root networks.Results: We have developed GiA Roots (General Image Analysis of Roots), a semi-automated software tool designed specifically for the high-throughput analysis of root system images. GiA Roots includes user-assisted algorithms to distinguish root from background and a fully automated pipeline that extracts dozens of root system phenotypes. Quantitative information on each phenotype, along with intermediate steps for full reproducibility, is returned to the end-user for downstream analysis. GiA Roots has a GUI front end and a command-line interface for interweaving the software into large-scale workflows. GiA Roots can also be extended to estimate novel phenotypes specified by the end-user.Conclusions: We demonstrate the use of GiA Roots on a set of 2393 images of rice roots representing 12 genotypes from the species Oryza sativa. We validate trait measurements against prior analyses of this image set that demonstrated that RSA traits are likely heritable and associated with genotypic differences. Moreover, we demonstrate that GiA Roots is extensible and an end-user can add functionality so that GiA Roots can estimate novel RSA traits. In summary, we show that the software can function as an efficient tool as part of a workflow to move from large numbers of root images to downstream analysis.}, author = {Galkovskyi, Taras and Mileyko, Yuriy and Bucksch, Alexander and Moore, Brad and Symonova, Olga and Price, Charles and Topp, Chrostopher and Iyer Pascuzzi, Anjali and Zurek, Paul and Fang, Suqin and Harer, John and Benfey, Philip and Weitz, Joshua}, journal = {BMC Plant Biology}, publisher = {BioMed Central}, title = {{GiA Roots: Software for the high throughput analysis of plant root system architecture}}, doi = {10.1186/1471-2229-12-116}, volume = {12}, year = {2012}, } @article{493, abstract = {The BCI competition IV stands in the tradition of prior BCI competitions that aim to provide high quality neuroscientific data for open access to the scientific community. As experienced already in prior competitions not only scientists from the narrow field of BCI compete, but scholars with a broad variety of backgrounds and nationalities. They include high specialists as well as students.The goals of all BCI competitions have always been to challenge with respect to novel paradigms and complex data. We report on the following challenges: (1) asynchronous data, (2) synthetic, (3) multi-class continuous data, (4) sessionto-session transfer, (5) directionally modulated MEG, (6) finger movements recorded by ECoG. As after past competitions, our hope is that winning entries may enhance the analysis methods of future BCIs.}, author = {Tangermann, Michael and Müller, Klaus and Aertsen, Ad and Birbaumer, Niels and Braun, Christoph and Brunner, Clemens and Leeb, Robert and Mehring, Carsten and Miller, Kai and Müller Putz, Gernot and Nolte, Guido and Pfurtscheller, Gert and Preissl, Hubert and Schalk, Gerwin and Schlögl, Alois and Vidaurre, Carmen and Waldert, Stephan and Blankertz, Benjamin}, journal = {Frontiers in Neuroscience}, publisher = {Frontiers Research Foundation}, title = {{Review of the BCI competition IV}}, doi = {10.3389/fnins.2012.00055}, volume = {6}, year = {2012}, } @article{494, abstract = {We solve the longstanding open problems of the blow-up involved in the translations, when possible, of a nondeterministic Büchi word automaton (NBW) to a nondeterministic co-Büchi word automaton (NCW) and to a deterministic co-Büchi word automaton (DCW). For the NBW to NCW translation, the currently known upper bound is 2o(nlog n) and the lower bound is 1.5n. We improve the upper bound to n2n and describe a matching lower bound of 2ω(n). For the NBW to DCW translation, the currently known upper bound is 2o(nlog n). We improve it to 2 o(n), which is asymptotically tight. Both of our upper-bound constructions are based on a simple subset construction, do not involve intermediate automata with richer acceptance conditions, and can be implemented symbolically. We continue and solve the open problems of translating nondeterministic Streett, Rabin, Muller, and parity word automata to NCW and to DCW. Going via an intermediate NBW is not optimal and we describe direct, simple, and asymptotically tight constructions, involving a 2o(n) blow-up. The constructions are variants of the subset construction, providing a unified approach for translating all common classes of automata to NCW and DCW. Beyond the theoretical importance of the results, we point to numerous applications of the new constructions. In particular, they imply a simple subset-construction based translation, when possible, of LTL to deterministic Büchi word automata.}, author = {Boker, Udi and Kupferman, Orna}, journal = {ACM Transactions on Computational Logic (TOCL)}, number = {4}, publisher = {ACM}, title = {{Translating to Co-Büchi made tight, unified, and useful}}, doi = {10.1145/2362355.2362357}, volume = {13}, year = {2012}, } @inproceedings{495, abstract = {An automaton with advice is a finite state automaton which has access to an additional fixed infinite string called an advice tape. We refine the Myhill-Nerode theorem to characterize the languages of finite strings that are accepted by automata with advice. We do the same for tree automata with advice.}, author = {Kruckman, Alex and Rubin, Sasha and Sheridan, John and Zax, Ben}, booktitle = {Proceedings GandALF 2012}, location = {Napoli, Italy}, pages = {238 -- 246}, publisher = {Open Publishing Association}, title = {{A Myhill Nerode theorem for automata with advice}}, doi = {10.4204/EPTCS.96.18}, volume = {96}, year = {2012}, }