@article{235, abstract = {For given positive integers m and n, we consider the frequency of representations of m/n as a sum of unit fractions.}, author = {Browning, Timothy D and Elsholtz, Christian}, journal = {Illinois Journal of Mathematics}, number = {2}, pages = {685 -- 696}, publisher = {University of Illinois Press}, title = {{The number of representations of rationals as a sum of unit fractions}}, volume = {55}, year = {2011}, } @article{236, abstract = {An asymptotic formula is established for the number of Q-rational points of bounded height on a nonsingular quartic Del Pezzo surface with a conic bundle structure.}, author = {de la Bretèche, Régis and Timothy Browning}, journal = {Duke Mathematical Journal}, number = {1}, pages = {1 -- 69}, publisher = {Duke University Press}, title = {{Manin's conjecture for quartic Del Pezzo surfaces with a conic fibration}}, doi = {10.1215/00127094-1443466}, volume = {160}, year = {2011}, } @article{239, abstract = {An effective search bound is established for the least non-trivial integer zero of an arbitrary cubic form C ε ℤ[X 1,...,X n], provided that n ≥ 17.}, author = {Timothy Browning and Dietmann, Rainer and Elliott, Peter}, journal = {Mathematische Annalen}, number = {3}, pages = {745 -- 778}, publisher = {Springer}, title = {{Least zero of a cubic form}}, doi = {10.1007/s00208-011-0651-6}, volume = {352}, year = {2011}, } @article{2390, abstract = {We resolve several longstanding problems concerning the stability and the absence of multi-particle binding for N≥2 polarons. Fröhlich's 1937 polaron model describes non-relativistic particles interacting with a scalar quantized field with coupling √α, and with each other by Coulomb repulsion of strength U. We prove the following: (i) While there is a known thermodynamic instability for U<2α, stability of matter does hold for U>2α, that is, the ground state energy per particle has a finite limit as N→∞. (ii) There is no binding of any kind if U exceeds a critical value that depends on α but not on N. The same results are shown to hold for the Pekar-Tomasevich model.}, author = {Frank, Rupert L and Lieb, Élliott H and Robert Seiringer and Thomas, Lawrence E}, journal = {Publications Mathematiques de l Institut des Hautes Etudes Scientifiques}, number = {1}, pages = {39 -- 67}, publisher = {Springer}, title = {{Stability and absence of binding for multi-polaron systems}}, doi = {10.1007/s10240-011-0031-5}, volume = {113}, year = {2011}, } @article{2391, abstract = {The change in energy of an ideal Fermi gas when a local one-body potential is inserted into the system, or when the density is changed locally, are important quantities in condensed matter physics. We show that they can be rigorously bounded from below by a universal constant times the value given by the semiclassical approximation.}, author = {Frank, Rupert L and Lewin, Mathieu and Lieb, Élliott H and Robert Seiringer}, journal = {Physical Review Letters}, number = {15}, publisher = {American Physical Society}, title = {{Energy cost to make a hole in the fermi sea}}, doi = {10.1103/PhysRevLett.106.150402}, volume = {106}, year = {2011}, } @article{2393, abstract = {We investigate the low energy excitation spectrum of a Bose gas with weak, long range repulsive interactions. In particular, we prove that the Bogoliubov spectrum of elementary excitations with linear dispersion relation for small momentum becomes exact in the mean-field limit.}, author = {Robert Seiringer}, journal = {Communications in Mathematical Physics}, number = {2}, pages = {565 -- 578}, publisher = {Springer}, title = {{The excitation spectrum for weakly interacting Bosons}}, doi = {10.1007/s00220-011-1261-6}, volume = {306}, year = {2011}, } @article{6749, abstract = {This article refers to algorithms based on finite difference schemes for computing mean and affine curvature evolutions of digital images, introduced by Alvarez and Morel [L. Alvarez, J.M. Morel, “Formalization and computational aspects of image analysis”, Acta Numerica, pp. 159, 1994]. We discuss consistency, stability and convergence. Our analysis focuses on some possible choices of the parameters, choices that generate multiple variants in the implementations. Meaningful visual examples on how the algorithms actually work are provided.}, author = {Mondelli, Marco and Ciomaga, Adina}, issn = {2105-1232}, journal = {Image Processing On Line}, pages = {127--177}, publisher = {IPOL Image Processing On Line}, title = {{Finite difference schemes for MCM and AMSS}}, doi = {10.5201/ipol.2011.cm_fds}, volume = {1}, year = {2011}, } @inproceedings{6767, abstract = {In the present paper we give a thorough analysis of two finite difference schemes for the Mean Curvature Motion and its affine variant, the Affine Morphological Scale Space, schemes introduced in the Image Processing framework. This analysis brings in a series of parameters that allow us to compute an accurate discrete evolution of curvature motions. The choice of these parameters is based on intrinsic geometric properties of the evolution equations for linear, radial and elliptical functions. In the last part we present several examples, underlining the main advantages of the algorithms (the removal of pixelization effects and JPEG artifacts) as well as their major drawbacks (absence of contrast invariance and grid dependence). A detailed explanatory report, the ANSI C implementations and an on-line demo can be found at http://www.ipol.im/.}, author = {Mondelli, Marco and Ciomaga, Adina}, booktitle = {Proceedings of the International Student Conference on Pure and Applied Mathematics}, isbn = {978-973-703-602-5}, location = {Iasi, Romania}, pages = {137--156}, publisher = {Editura Universitãtii „Alexandru Ioan Cuza” Iasi}, title = {{On finite difference schemes for curvature motions}}, doi = {10.13140/2.1.1862.4646}, year = {2011}, } @article{7076, abstract = {Iron is a ubiquitous impurity in metamict (radiation-damaged and partially amorphized) materials such as titanite (CaSiTiO5). Using 57Fe Mössbauer spectroscopy we find that iron in metamict titanite is partitioned between amorphous and crystalline regions based on valence. Trivalent iron exists in the crystalline titanite matrix whereas divalent iron exists almost exclusively in radiation-amorphized regions. We find that the relative abundances of the oxidation states correlate with the volume fraction of amorphous and crystalline regions. Our data also show that oxidation of iron proceeds along with the recrystallization of the amorphized regions. Recrystallization is confirmed to occur over the range 700 °C < T < 925 °C, and no further structural changes are observed at higher temperatures. It is surprising that our Mössbauer measurements show divalent iron to be surrounded by titanite with a high degree of short-range structural order in the amorphized regions. This observation is fundamentally different from other metamict materials such as zircon (ZrSiO4), where amorphized regions show no short-range order.}, author = {Salje, E K H and Safarik, D J and Taylor, R D and Pasternak, M P and Modic, Kimberly A and Groat, L A and Lashley, J C}, issn = {0953-8984}, journal = {Journal of Physics: Condensed Matter}, number = {10}, publisher = {IOP Publishing}, title = {{Determination of iron sites and the amount of amorphization in radiation-damaged titanite (CaSiTiO5)}}, doi = {10.1088/0953-8984/23/10/105402}, volume = {23}, year = {2011}, } @article{7077, abstract = {Pb, Te, Ag and Se, when reacted in a 1:1:x:1 (x = 1.9, 2.0, 2.01) molar ratio, form a two phase composite which consists of a phase which crystallizes in the fcc cubic PbSe structure and a phase that crystallizes in the Ag2Te structure. In this article, we demonstrate that by varying the Ag concentration, we can manipulate which variant of the Ag2Te structure stabilizes at room temperature (monoclinic α-Ag2Te or cubic β-Ag1.9Te) and can consequently manipulate the electrical and thermal transport behavior of the composite and hence the thermoelectric performance. Additionally, we show that Cu-doping results in an overall improvement in thermoelectric performance. Our results suggest that formation of composites is a viable path for achieving a phonon-glass-electron-crystal (PGEC) alloy.}, author = {Capps, J. and Ma, B. and Drye, T. and Nucklos, C. and Lindsey, S. and Rhodes, D. and Zhang, Q. and Modic, Kimberly A and Cawthorne, S. and Drymiotis, F.}, issn = {0925-8388}, journal = {Journal of Alloys and Compounds}, number = {5}, pages = {1544--1549}, publisher = {Elsevier}, title = {{The effect of Ag concentration on the structural, electrical and thermal transport behavior of Pb:Te:Ag:Se mixtures and improvement of thermoelectric performance via Cu doping}}, doi = {10.1016/j.jallcom.2010.10.187}, volume = {509}, year = {2011}, } @article{7313, abstract = {Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li–air (O2) and Li–S. The energy that can be stored in Li–air (based on aqueous or non-aqueous electrolytes) and Li–S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li–air and Li–S justify the continued research effort that will be needed.}, author = {Bruce, Peter G. and Freunberger, Stefan Alexander and Hardwick, Laurence J. and Tarascon, Jean-Marie}, issn = {1476-1122}, journal = {Nature Materials}, number = {1}, pages = {19--29}, publisher = {Springer Nature}, title = {{Li–O2 and Li–S batteries with high energy storage}}, doi = {10.1038/nmat3191}, volume = {11}, year = {2011}, } @article{7314, abstract = {The electrolyte is one of the greatest challenges facing the development of the non‐aqueous Li–O2 battery. Although ether‐based electrolytes do from Li2O2 on the first discharge, it is shown by various techniques that they also decompose and that decomposition increases while Li2O2 decreases on cycling (see picture). Thus, these electrolytes are not suitable. }, author = {Freunberger, Stefan Alexander and Chen, Yuhui and Drewett, Nicholas E. and Hardwick, Laurence J. and Bardé, Fanny and Bruce, Peter G.}, issn = {1433-7851}, journal = {Angewandte Chemie International Edition}, number = {37}, pages = {8609--8613}, publisher = {Wiley}, title = {{The Lithium-Oxygen battery with ether-based electrolytes}}, doi = {10.1002/anie.201102357}, volume = {50}, year = {2011}, } @article{7315, abstract = {Spectroscopic data (see picture) provide direct evidence that in non‐aqueous Li+ electrolyte, O2 is reduced to O2−, which then forms LiO2 on the electrode surface which disproportionates to Li2O2. On charging, Li2O2 decomposes directly, in a one‐step reaction to evolve O2 and does not pass through LiO2 as an intermediate. }, author = {Peng, Zhangquan and Freunberger, Stefan Alexander and Hardwick, Laurence J. and Chen, Yuhui and Giordani, Vincent and Bardé, Fanny and Novák, Petr and Graham, Duncan and Tarascon, Jean-Marie and Bruce, Peter G.}, issn = {1433-7851}, journal = {Angewandte Chemie International Edition}, number = {28}, pages = {6351--6355}, publisher = {Wiley}, title = {{Oxygen reactions in a non-aqueous Li+ electrolyte}}, doi = {10.1002/anie.201100879}, volume = {50}, year = {2011}, } @article{7316, abstract = {The nonaqueous rechargeable lithium–O2 battery containing an alkyl carbonate electrolyte discharges by formation of C3H6(OCO2Li)2, Li2CO3, HCO2Li, CH3CO2Li, CO2, and H2O at the cathode, due to electrolyte decomposition. Charging involves oxidation of C3H6(OCO2Li)2, Li2CO3, HCO2Li, CH3CO2Li accompanied by CO2 and H2O evolution. Mechanisms are proposed for the reactions on discharge and charge. The different pathways for discharge and charge are consistent with the widely observed voltage gap in Li–O2 cells. Oxidation of C3H6(OCO2Li)2 involves terminal carbonate groups leaving behind the OC3H6O moiety that reacts to form a thick gel on the Li anode. Li2CO3, HCO2Li, CH3CO2Li, and C3H6(OCO2Li)2 accumulate in the cathode on cycling correlating with capacity fading and cell failure. The latter is compounded by continuous consumption of the electrolyte on each discharge.}, author = {Freunberger, Stefan Alexander and Chen, Yuhui and Peng, Zhangquan and Griffin, John M. and Hardwick, Laurence J. and Bardé, Fanny and Novák, Petr and Bruce, Peter G.}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, number = {20}, pages = {8040--8047}, publisher = {ACS}, title = {{Reactions in the rechargeable Lithium–O2 battery with alkyl carbonate electrolytes}}, doi = {10.1021/ja2021747}, volume = {133}, year = {2011}, } @article{7317, abstract = {Lithium-metal oxides with a high formal Li2O content, such as Li5FeO4 (5Li2O•Fe2O3) and a Li2MnO3•LiFeO2 composite ({Li2O•MnO2}•{Li2O•Fe2O3}) have been explored as electrocatalysts for primary and rechargeable Li-O2 cells. Activation occurs predominantly by Li2O removal, either electrochemically or chemically by acid-treatment. Superior electrochemical behavior is obtained if activation occurs by acid-treatment; Li2MnO3•LiFeO2 catalysts provide 2516 mAh/g (carbon) corresponding to 931 mAh/g (electrocatalyst + carbon) during the initial discharge. The reaction is reasonably reversible during the early cycles. The approach has implications for designing electrocatalysts that participate through electrochemical Li2O extraction/reformation reactions, offering exceptionally high capacities.}, author = {Trahey, L. and Johnson, C. S. and Vaughey, J. T. and Kang, S.-H. and Hardwick, L. J. and Freunberger, Stefan Alexander and Bruce, P. G. and Thackeray, M. M.}, issn = {1099-0062}, journal = {Electrochemical and Solid-State Letters}, number = {5}, publisher = {The Electrochemical Society}, title = {{Activated Lithium-Metal-Oxides as catalytic electrodes for Li–O2 cells}}, doi = {10.1149/1.3555366}, volume = {14}, year = {2011}, } @inproceedings{757, abstract = {Synchronous distributed algorithms are easier to design and prove correct than algorithms that tolerate asynchrony. Yet, in the real world, networks experience asynchrony and other timing anomalies. In this paper, we address the question of how to efficiently transform an algorithm that relies on synchronization into an algorithm that tolerates asynchronous executions. We introduce a transformation technique from synchronous algorithms to indulgent algorithms [1], which induces only a constant overhead in terms of time complexity in well-behaved executions. Our technique is based on a new abstraction we call an asynchrony detector, which the participating processes implement collectively. The resulting transformation works for a large class of colorless tasks, including consensus and set agreement. Interestingly, we also show that our technique is relevant for colored tasks, by applying it to the renaming problem, to obtain the first indulgent renaming algorithm.}, author = {Alistarh, Dan-Adrian and Gilbert, Seth and Guerraoui, Rachid and Travers, Corentin}, pages = {41 -- 52}, publisher = {Springer}, title = {{Generating fast indulgent algorithms}}, doi = {10.1007/978-3-642-17679-1_4}, volume = {6522 LNCS}, year = {2011}, } @inproceedings{759, abstract = {We study the complexity of renaming, a fundamental problem in distributed computing in which a set of processes need to pick distinct names from a given namespace. We prove an individual lower bound of Ω(k) process steps for deterministic renaming into any namespace of size sub-exponential in k, where k is the number of participants. This bound is tight: it draws an exponential separation between deterministic and randomized solutions, and implies new tight bounds for deterministic fetch-and-increment registers, queues and stacks. The proof of the bound is interesting in its own right, for it relies on the first reduction from renaming to another fundamental problem in distributed computing: mutual exclusion. We complement our individual bound with a global lower bound of Ω(k log (k/c)) on the total step complexity of renaming into a namespace of size ck, for any c ≥ 1. This applies to randomized algorithms against a strong adversary, and helps derive new global lower bounds for randomized approximate counter and fetch-and-increment implementations, all tight within logarithmic factors.}, author = {Alistarh, Dan-Adrian and Aspnes, James and Gilbert, Seth and Guerraoui, Rachid}, pages = {718 -- 727}, publisher = {IEEE}, title = {{The complexity of renaming}}, doi = {10.1109/FOCS.2011.66}, year = {2011}, } @inproceedings{760, abstract = {A randomized implementation is given of a test-and-set register with O(log log n) individual step complexity and O(n) total step complexity against an oblivious adversary. The implementation is linearizable and multi-shot, and shows an exponential complexity improvement over previous solutions designed to work against a strong adversary.}, author = {Alistarh, Dan-Adrian and Aspnes, James}, pages = {97 -- 109}, publisher = {Springer}, title = {{Sub-logarithmic test-and-set against a weak adversary}}, doi = {10.1007/978-3-642-24100-0_7}, volume = {6950 LNCS}, year = {2011}, } @inproceedings{761, abstract = {We give two new randomized algorithms for strong renaming, both of which work against an adaptive adversary in asynchronous shared memory. The first uses repeated sampling over a sequence of arrays of decreasing size to assign unique names to each of n processes with step complexity O(log3 n). The second transforms any sorting network into a strong adaptive renaming protocol, with an expected cost equal to the depth of the sorting network. Using an AKS sorting network, this gives a strong adaptive renaming algorithm with step complexity O(log k), where k is the contention in the current execution. We show this to be optimal based on a classic lower bound of Jayanti. We also show that any such strong renaming protocol can be used to build a monotone-consistent counter with logarithmic step complexity (at the cost of adding a max register) or a linearizable fetch-and-increment register (at the cost of increasing the step complexity by a logarithmic factor).}, author = {Alistarh, Dan-Adrian and Aspnes, James and Censor Hillel, Keren and Gilbert, Seth and Zadimoghaddam, Morteza}, pages = {239 -- 248}, publisher = {ACM}, title = {{Optimal-time adaptive strong renaming, with applications to counting}}, doi = {10.1145/1993806.1993850}, year = {2011}, } @article{7701, abstract = {During assembly of the Drosophila olfactory circuit, projection neuron (PN) dendrites prepattern the developing antennal lobe before the arrival of axons from their presynaptic partners, the adult olfactory receptor neurons (ORNs). We previously found that levels of transmembrane Semaphorin-1a, which acts as a receptor, instruct PN dendrite targeting along the dorsolateral-ventromedial axis. Here we show that two secreted semaphorins, Sema-2a and Sema-2b, provide spatial cues for PN dendrite targeting. Sema-2a and Sema-2b proteins are distributed in gradients opposing the Sema-1a protein gradient, and Sema-1a binds to Sema-2a-expressing cells. In Sema-2a and Sema-2b double mutants, PN dendrites that normally target dorsolaterally in the antennal lobe mistarget ventromedially, phenocopying cell-autonomous Sema-1a removal from these PNs. Cell ablation, cell-specific knockdown, and rescue experiments indicate that secreted semaphorins from degenerating larval ORN axons direct dendrite targeting. Thus, a degenerating brain structure instructs the wiring of a developing circuit through the repulsive action of secreted semaphorins.}, author = {Sweeney, Lora Beatrice Jaeger and Chou, Ya-Hui and Wu, Zhuhao and Joo, William and Komiyama, Takaki and Potter, Christopher J. and Kolodkin, Alex L. and Garcia, K. Christopher and Luo, Liqun}, issn = {0896-6273}, journal = {Neuron}, number = {5}, pages = {734--747}, publisher = {Elsevier}, title = {{Secreted semaphorins from degenerating larval ORN axons direct adult projection neuron dendrite targeting}}, doi = {10.1016/j.neuron.2011.09.026}, volume = {72}, year = {2011}, }