@article{11760, abstract = {We study a novel load balancing problem that arises in web search engines. The problem is a combination of an offline assignment problem, where files need to be (copied and) assigned to machines, and an online load balancing problem, where requests ask for specific files and need to be assigned to a corresponding machine, whose load is increased by this. We present simple deterministic algorithms for this problem and exhibit an interesting trade-off between the available space to make file copies and the obtainable makespan. We also give non-trivial lower bounds for a large class of deterministic algorithms and present a randomized algorithm that beats these bounds with high probability.}, author = {Dütting, Paul and Henzinger, Monika H and Weber, Ingmar}, issn = {0020-0190}, journal = {Information Processing Letters}, number = {4}, pages = {178--183}, publisher = {Elsevier}, title = {{Offline file assignments for online load balancing}}, doi = {10.1016/j.ipl.2010.11.022}, volume = {111}, year = {2011}, } @inproceedings{11796, abstract = {The design of truthful auctions that approximate the optimal expected revenue is a central problem in algorithmic mechanism design. 30 years after Myerson’s characterization of Bayesian optimal auctions in single-parameter domains [8], characterizing but also providing efficient mechanisms for multi-parameter domains still remains a very important unsolved problem. Our work improves upon recent results in this area, introducing new techniques for tackling the problem, while also combining and extending recently introduced tools. In particular we give the first approximation algorithms for Bayesian auctions with multiple heterogeneous items when bidders have additive valuations, budget constraints and general matroid feasibility constraints.}, author = {Henzinger, Monika H and Vidali, Angelina}, booktitle = {19th Annual European Symposium on Algorithms}, isbn = {9783642237188}, issn = {1611-3349}, location = {Saarbrücken, Germany}, pages = {192–202}, publisher = {Springer Nature}, title = {{Multi-parameter mechanism design under budget and matroid constraints}}, doi = {10.1007/978-3-642-23719-5_17}, volume = {6942}, year = {2011}, } @article{8025, abstract = {Chandelier (axoaxonic) cells (ChCs) are a distinct group of GABAergic interneurons that innervate the axon initial segments of pyramidal cells. However, their circuit role and the function of their clearly defined anatomical specificity remain unclear. Recent work has demonstrated that chandelier cells can produce depolarizing GABAergic PSPs, occasionally driving postsynaptic targets to spike. On the other hand, other work suggests that ChCs are hyperpolarizing and may have an inhibitory role. These disparate functional effects may reflect heterogeneity among ChCs. Here, using brain slices from transgenic mouse strains, we first demonstrate that, across different neocortical areas and genetic backgrounds, upper Layer 2/3 ChCs belong to a single electrophysiologically and morphologically defined population, extensively sampling Layer 1 inputs with asymmetric dendrites. Consistent with being a single cell type, we find electrical coupling between ChCs. We then investigate the effect of chandelier cell activation on pyramidal neuron spiking in several conditions, ranging from the resting membrane potential to stimuli designed to approximate in vivo membrane potential dynamics. We find that under quiescent conditions, chandelier cells are capable of both promoting and inhibiting spike generation, depending on the postsynaptic membrane potential. However, during in vivo-like membrane potential fluctuations, the dominant postsynaptic effect was a strong inhibition. Thus, neocortical chandelier cells, even from within a homogeneous population, appear to play a dual role in the circuit, helping to activate quiescent pyramidal neurons, while at the same time inhibiting active ones.}, author = {Woodruff, A. R. and McGarry, L. M. and Vogels, Tim P and Inan, M. and Anderson, S. A. and Yuste, R.}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {49}, pages = {17872--17886}, publisher = {Society for Neuroscience}, title = {{State-dependent function of neocortical chandelier cells}}, doi = {10.1523/jneurosci.3894-11.2011}, volume = {31}, year = {2011}, } @article{8074, abstract = {Cortical neurons receive balanced excitatory and inhibitory synaptic currents. Such a balance could be established and maintained in an experience-dependent manner by synaptic plasticity at inhibitory synapses. We show that this mechanism provides an explanation for the sparse firing patterns observed in response to natural stimuli and fits well with a recently observed interaction of excitatory and inhibitory receptive field plasticity. The introduction of inhibitory plasticity in suitable recurrent networks provides a homeostatic mechanism that leads to asynchronous irregular network states. Further, it can accommodate synaptic memories with activity patterns that become indiscernible from the background state but can be reactivated by external stimuli. Our results suggest an essential role of inhibitory plasticity in the formation and maintenance of functional cortical circuitry.}, author = {Vogels, Tim P and Sprekeler, H. and Zenke, F. and Clopath, C. and Gerstner, W.}, issn = {0036-8075}, journal = {Science}, number = {6062}, pages = {1569--1573}, publisher = {American Association for the Advancement of Science}, title = {{Inhibitory plasticity balances excitation and inhibition in sensory pathways and memory networks}}, doi = {10.1126/science.1211095}, volume = {334}, year = {2011}, } @article{8464, abstract = {Nonsymmetric motion: Solid‐state NMR measurements of dipolar coupling tensors provide insight into protein dynamics. The hitherto ignored asymmetry of the dipolar coupling tensor contains valuable information about motional asymmetry, which was used in the first direct site‐resolved measurement of such tensors. Important motions such as rotamer jumps can now be directly detected in the solid state.}, author = {Schanda, Paul and Huber, Matthias and Boisbouvier, Jérôme and Meier, Beat H. and Ernst, Matthias}, issn = {1433-7851}, journal = {Angewandte Chemie International Edition}, number = {46}, pages = {11005--11009}, publisher = {Wiley}, title = {{Solid-state NMR measurements of asymmetric dipolar couplings provide insight into protein side-chain motion}}, doi = {10.1002/anie.201103944}, volume = {50}, year = {2011}, } @article{8468, author = {Lalli, Daniela and Schanda, Paul and Chowdhury, Anup and Retel, Joren and Hiller, Matthias and Higman, Victoria A. and Handel, Lieselotte and Agarwal, Vipin and Reif, Bernd and van Rossum, Barth and Akbey, Ümit and Oschkinat, Hartmut}, issn = {0925-2738}, journal = {Journal of Biomolecular NMR}, number = {4}, pages = {477--485}, publisher = {Springer Nature}, title = {{Three-dimensional deuterium-carbon correlation experiments for high-resolution solid-state MAS NMR spectroscopy of large proteins}}, doi = {10.1007/s10858-011-9578-1}, volume = {51}, year = {2011}, } @article{8469, abstract = {The accurate experimental determination of dipolar-coupling constants for one-bond heteronuclear dipolar couplings in solids is a key for the quantification of the amplitudes of motional processes. Averaging of the dipolar coupling reports on motions on time scales up to the inverse of the coupling constant, in our case tens of microseconds. Combining dipolar-coupling derived order parameters that characterize the amplitudes of the motion with relaxation data leads to a more precise characterization of the dynamical parameters and helps to disentangle the amplitudes and the time scales of the motional processes, which impact relaxation rates in a highly correlated way. Here. we describe and characterize an improved experimental protocol – based on REDOR – to measure these couplings in perdeuterated proteins with a reduced sensitivity to experimental missettings. Because such effects are presently the dominant source of systematic errors in experimental dipolar-coupling measurements, these compensated experiments should help to significantly improve the precision of such data. A detailed comparison with other commonly used pulse sequences (T-MREV, phase-inverted CP,R18 5/2, and R18 7/1) is provided.}, author = {Schanda, Paul and Meier, Beat H. and Ernst, Matthias}, issn = {1090-7807}, journal = {Journal of Magnetic Resonance}, keywords = {Nuclear and High Energy Physics, Biophysics, Biochemistry, Condensed Matter Physics}, number = {2}, pages = {246--259}, publisher = {Elsevier}, title = {{Accurate measurement of one-bond H–X heteronuclear dipolar couplings in MAS solid-state NMR}}, doi = {10.1016/j.jmr.2011.03.015}, volume = {210}, year = {2011}, } @article{8470, abstract = {Adding a new dimension: 4D or 3D proton‐detected spectra of perdeuterated protein samples with 1H labelled amides and methyl groups permit collecting unambiguous distance restraints with high sensitivity and determining protein structure by solid‐state NMR (see picture).}, author = {Huber, Matthias and Hiller, Sebastian and Schanda, Paul and Ernst, Matthias and Böckmann, Anja and Verel, René and Meier, Beat H.}, issn = {1439-4235}, journal = {ChemPhysChem}, keywords = {Physical and Theoretical Chemistry, Atomic and Molecular Physics, and Optics}, number = {5}, pages = {915--918}, publisher = {Wiley}, title = {{A proton-detected 4D solid-state NMR experiment for protein structure determination}}, doi = {10.1002/cphc.201100062}, volume = {12}, year = {2011}, } @article{8471, abstract = {Despite the importance of protein fibrils in the context of conformational diseases, information on their structure is still sparse. Hydrogen/deuterium exchange measurements of backbone amide protons allow the identification hydrogen-bonding patterns and reveal pertinent information on the amyloid β-sheet architecture. However, they provide only little information on the identity of residues exposed to solvent or buried inside the fibril core. NMR spectroscopy is a potent method for identifying solvent-accessible residues in proteins via observation of polarization transfer between chemically exchanging side-chain protons and water protons. We show here that the combined use of highly deuterated samples and fast magic-angle spinning greatly attenuates unwanted spin diffusion and allows identification of polarization exchange with the solvent in a site-specific manner. We apply this measurement protocol to HET-s(218–289) prion fibrils under different conditions (including physiological pH, where protofibrils assemble together into thicker fibrils) and demonstrate that each protofibril of HET-s(218–289), is surrounded by water, thus excluding the existence of extended dry interfibril contacts. We also show that exchangeable side-chain protons inside the hydrophobic core of HET-s(218–289) do not exchange over time intervals of weeks to months. The experiments proposed in this study can provide insight into the detailed structural features of amyloid fibrils in general.}, author = {Van Melckebeke, Hélène and Schanda, Paul and Gath, Julia and Wasmer, Christian and Verel, René and Lange, Adam and Meier, Beat H. and Böckmann, Anja}, issn = {0022-2836}, journal = {Journal of Molecular Biology}, number = {3}, pages = {765--772}, publisher = {Elsevier}, title = {{Probing water accessibility in HET-s(218–289) amyloid fibrils by solid-state NMR}}, doi = {10.1016/j.jmb.2010.11.004}, volume = {405}, year = {2011}, } @article{8505, abstract = {The classical principle of least action says that orbits of mechanical systems extremize action; an important subclass are those orbits that minimize action. In this paper we utilize this principle along with Aubry-Mather theory to construct (Birkhoff) regions of instability for a certain three-body problem, given by a Hamiltonian system of 2 degrees of freedom. We believe that these methods can be applied to construct instability regions for a variety of Hamiltonian systems with 2 degrees of freedom. The Hamiltonian model we consider describes dynamics of a Sun-Jupiter-comet system, and under some simplifying assumptions, we show the existence of instabilities for the orbit of the comet. In particular, we show that a comet which starts close to an orbit in the shape of an ellipse of eccentricity e=0.66 can increase in eccentricity up to e=0.96. In the sequels to this paper, we extend the result to beyond e=1 and show the existence of ejection orbits. Such orbits are initially well within the range of our solar system. This might give an indication of why most objects rotating around the Sun in our solar system have relatively low eccentricity.}, author = {Galante, Joseph and Kaloshin, Vadim}, issn = {0012-7094}, journal = {Duke Mathematical Journal}, keywords = {General Mathematics}, number = {2}, pages = {275--327}, publisher = {Duke University Press}, title = {{Destruction of invariant curves in the restricted circular planar three-body problem by using comparison of action}}, doi = {10.1215/00127094-1415878}, volume = {159}, year = {2011}, } @inbook{881, author = {Fyodor Kondrashov}, booktitle = {Evolution after Gene Duplication}, pages = {57 -- 76}, publisher = {Wiley-Blackwell}, title = {{Gene Dosage and Duplication}}, doi = {10.1002/9780470619902.ch4}, year = {2011}, } @article{890, abstract = {Recent discovery of the Large-billed Reed Warbler (Acrocephalus orinus) in museums and in the wild significantly expanded our knowledge of its morphological traits and genetic variability, and revealed new data on geographical distribution of the breeding grounds, migration routes and wintering locations of this species. It is now certain that A. orinus is breeding in Central Asia; however, the precise area of distribution remains unclear. The difficulty in the further study of this species lies in the small number of known specimens, with only 13 currently available in museums, and in the relative uncertainty of the breeding area and habitat of this species. Following morphological and genetic analyses from Svensson, et al, we describe 14 new A. orinus specimens from collections of Zoological Museums of the former USSR from the territory of Central Asian states. All of these specimens were erroneously labeled as Blyth's Reed Warbler (A. dumetorum), which is thought to be a breeding species in these areas. The 14 new A. orinus specimens were collected during breeding season while most of the 85 A. dumetorum specimens from the same area were collected during the migration period. Our data indicate that the Central Asian territory previously attributed as breeding grounds of A. dumetorum is likely to constitute the breeding territory of A. orinus. This rare case of a re-description of the breeding territory of a lost species emphasizes the importance of maintenance of museum collections around the world. If the present data on the breeding grounds of A. orinus are confirmed with field observations and collections, the literature on the biology of A. dumetorum from the southern part of its range may have to be reconsidered.}, author = {Koblik, Evgeniy A and Red'Kin, Yaroslav A and Meer, Margarita S and Derelle, Romain and Golenkina, Sofia A and Fyodor Kondrashov and Arkhipov, Vladimir Y}, journal = {PLoS One}, number = {4}, publisher = {Public Library of Science}, title = {{Acrocephalus orinus: A case of Mistaken identity}}, doi = {10.1371/journal.pone.0017716}, volume = {6}, year = {2011}, } @article{90, abstract = {A popular method for generating micron-sized aerosols is to submerge ultrasonic (ω ∼ MHz) piezoelectric oscillators in a water bath. The submerged oscillator atomizes the fluid, creating droplets with radii proportional to the wavelength of the standing wave at the fluid surface. Classical theory for the Faraday instability predicts a parametric instability driving a capillary wave at the subharmonic (ω / 2) frequency. For many applications it is desirable to reduce the size of the droplets; however, using higher frequency oscillators becomes impractical beyond a few MHz. Observations are presented that demonstrate that smaller droplets may also be created by increasing the driving amplitude of the oscillator, and that this effect becomes more pronounced for large driving frequencies. It is shown that these observations are consistent with a transition from droplets associated with subharmonic (ω/2) capillary waves to harmonic (ω) capillary waves induced by larger driving frequencies and amplitudes, as predicted by a stability analysis of the capillary waves.}, author = {Higginbotham, Andrew P and Guillen, A and Jones, Nick and Donnelly, Tom and Bernoff, Andrew}, journal = {Journal of the Acoustical Society of America}, number = {5}, pages = {2694 -- 2699}, publisher = {Acoustical Society of America}, title = {{Evidence of the harmonic Faraday instability in ultrasonic atomization experiments with a deep, inviscid fluid}}, doi = {10.1121/1.3643816}, volume = {130}, year = {2011}, } @article{1723, abstract = {The emergence of differences in the arrangement of cells is the first step towards the establishment of many organs. Understanding this process is limited by the lack of systematic characterization of epithelial organisation. Here we apply network theory at the scale of individual cells to uncover patterns in cell-to-cell contacts that govern epithelial organisation. We provide an objective characterisation of epithelia using network representation, where cells are nodes and cell contacts are links. The features of individual cells, together with attributes of the cellular network, produce a defining signature that distinguishes epithelia from different organs, species, developmental stages and genetic conditions. The approach permits characterization, quantification and classification of normal and perturbed epithelia, and establishes a framework for understanding molecular mechanisms that underpin the architecture of complex tissues.}, author = {Escudero, Luis M and Costa, Luciano and Anna Kicheva and Briscoe, James and Freeman, Matthew and Babu, Madan M}, journal = {Nature Communications}, number = {1}, publisher = {Nature Publishing Group}, title = {{Epithelial organisation revealed by a network of cellular contacts}}, doi = {10.1038/ncomms1536}, volume = {2}, year = {2011}, } @article{1724, abstract = {Morphogens, such as Decapentaplegic (Dpp) in the fly imaginal discs, form graded concentration profiles that control patterning and growth of developing organs. In the imaginal discs, proliferative growth is homogeneous in space, posing the conundrum of how morphogen concentration gradients could control position-independent growth. To understand the mechanism of proliferation control by the Dpp gradient, we quantified Dpp concentration and signaling levels during wing disc growth. Both Dpp concentration and signaling gradients scale with tissue size during development. On average, cells divide when Dpp signaling levels have increased by 50%. Our observations are consistent with a growth control mechanism based on temporal changes of cellular morphogen signaling levels. For a scaling gradient, this mechanism generates position-independent growth rates.}, author = {Wartlick, Ortrud and Mumcu, Peer and Anna Kicheva and Bittig, Thomas and Seum, Carole and Jülicher, Frank and González-Gaitán, Marcos A}, journal = {Science}, number = {6021}, pages = {1154 -- 1159}, publisher = {American Association for the Advancement of Science}, title = {{Dynamics of Dpp signaling and proliferation control}}, doi = {10.1126/science.1200037}, volume = {331}, year = {2011}, } @article{1754, abstract = {We report on a technique enabling electrical control of the contact silicidation process in silicon nanowire devices. Undoped silicon nanowires were contacted by pairs of nickel electrodes and each contact was selectively silicided by means of the Joule effect. By a realtime monitoring of the nanowire electrical resistance during the contact silicidation process we were able to fabricate nickel-silicide/silicon/nickel- silicide devices with controlled silicon channel length down to 8 nm. }, author = {Mongillo, Massimo and Spathis, Panayotis and Katsaros, Georgios and Gentile, Pascal and Sanquer, Marc and De Franceschi, Silvano}, journal = {ACS Nano}, number = {9}, pages = {7117 -- 7123}, publisher = {American Chemical Society}, title = {{Joule-assisted silicidation for short-channel silicon nanowire devices}}, doi = {10.1021/nn202524j}, volume = {5}, year = {2011}, } @article{1755, abstract = {Spin-selective tunneling of holes in SiGe nanocrystals contacted by normal-metal leads is reported. The spin selectivity arises from an interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. We demonstrate both experimentally and theoretically that spin-selective tunneling in semiconductor nanostructures can be achieved without the use of ferromagnetic contacts. The reported effect, which relies on mixing the light and heavy holes, should be observable in a broad class of quantum-dot systems formed in semiconductors with a degenerate valence band.}, author = {Georgios Katsaros and Golovach, Vitaly N and Spathis, Panayotis N and Ares, Natalia and Stoffel, Mathieu and Fournel, Frank and Schmidt, Oliver G and Glazman, Leonid I and De Franceschi, Silvano}, journal = {Physical Review Letters}, number = {24}, publisher = {American Physical Society}, title = {{Observation of spin-selective tunneling in sige nanocrystals}}, doi = {10.1103/PhysRevLett.107.246601}, volume = {107}, year = {2011}, } @article{1775, abstract = {At optical frequencies the radiation produced by a source, such as a laser, a black body or a single-photon emitter, is frequently characterized by analysing the temporal correlations of emitted photons using single-photon counters. At microwave frequencies, however, there are no efficient single-photon counters yet. Instead, well-developed linear amplifiers allow for efficient measurement of the amplitude of an electromagnetic field. Here, we demonstrate first- and second-order correlation function measurements of a pulsed microwave-frequency single-photon source integrated on the same chip with a 50/50 beam splitter followed by linear amplifiers and quadrature amplitude detectors. We clearly observe single-photon coherence in first-order and photon antibunching in second-order correlation function measurements of the propagating fields.}, author = {Bozyigit, Deniz and Lang, C and Steffen, L. Kraig and Johannes Fink and Eichler, Christopher and Baur, Matthias P and Bianchetti, R and Leek, Peter J and Filipp, Stefan and Da Silva, Marcus P and Blais, Alexandre and Wallraff, Andreas}, journal = {Nature Physics}, number = {2}, pages = {154 -- 158}, publisher = {Nature Publishing Group}, title = {{Antibunching of microwave-frequency photons observed in correlation measurements using linear detectors}}, doi = {10.1038/nphys1845}, volume = {7}, year = {2011}, } @inproceedings{1776, abstract = {Superconducting circuits have been successfully established as systems to prepare and investigate microwave light fields at the quantum level. In contrast to optical experiments where light is detected using photon counters, microwaves are usually measured with well developed linear amplifiers. This makes measurements of correlation functions - one of the important tools in optics - harder to achieve because they traditionally rely on photon counters and beam splitters. Here, we demonstrate a system where we can prepare on demand single microwave photons in a cavity and detect them at the two outputs of the cavity using linear amplifiers. Together with efficient data processing, this allows us to measure different observables of the cavity photons, including the first-order correlation function. Using these techniques we demonstrate cooling of a thermal background field in the cavity.}, author = {Bozyigit, Deniz and Lang, C and Steffen, L. Kraig and Johannes Fink and Eichler, Christopher and Baur, Matthias P and Bianchetti, R and Leek, Peter J and Filipp, Stefan and Wallraff, Andreas and Da Silva, Marcus P and Blais, Alexandre}, number = {1}, publisher = {IOP Publishing Ltd.}, title = {{Correlation measurements of individual microwave photons emitted from a symmetric cavity}}, doi = {10.1088/1742-6596/264/1/012024}, volume = {264}, year = {2011}, } @article{1777, abstract = {A wide range of experiments studying microwave photons localized in superconducting cavities have made important contributions to our understanding of the quantum properties of radiation. Propagating microwave photons, however, have so far been studied much less intensely. Here we present measurements in which we reconstruct the quantum state of itinerant single photon Fock states and their superposition with the vacuum by analyzing moments of the measured amplitude distribution up to fourth order. Using linear amplifiers and quadrature amplitude detectors, we have developed efficient methods to separate the detected single photon signal from the noise added by the amplifier. From our measurement data we have also reconstructed the corresponding Wigner function.}, author = {Eichler, Christopher and Bozyigit, Deniz and Lang, C and Steffen, L. and Fink, Johannes M and Wallraff, Andreas}, journal = {Physical Review Letters}, number = {22}, publisher = {American Physical Society}, title = {{Experimental state tomography of itinerant single microwave photons}}, doi = {10.1103/PhysRevLett.106.220503}, volume = {106}, year = {2011}, }