Standing and travelling waves in cylindrical Rayleigh-Benard convection

The Boussinesq equations for Rayleigh-Benard convection are simulated for a cylindrical container with an aspect ratio near 1.5. The transition from an axisymmetric stationary flow to time-dependent flows is studied using nonlinear simulations, linear stability analysis and bifurcation theory. At a Rayleigh number near 25,000, the axisymmetric flow becomes unstable to standing or travelling azimuthal waves. The standing waves are slightly unstable to travelling waves. This scenario is identified as a Hopf bifurcation in a system with O(2) symmetry

Towards dense object tracking in a 2D honeybee hive

From human crowds to cells in tissue, the detection and efficient tracking of multiple objects in dense configurations is an important and unsolved problem. In the past, limitations of image analysis have restricted studies of dense groups to tracking a single or subset of marked individuals, or to coarse-grained group-level dynamics, all of which yield incomplete information. Here, we combine convolutional neural networks (CNNs) with the model environment of a honeybee hive to automatically recognize all individuals in a dense group from raw image data. We create new, adapted individual labeling and use the segmentation architecture U-Net with a loss function dependent on both object identity and orientation. We additionally exploit temporal regularities of the video recording in a recurrent manner and achieve near human-level performance while reducing the network size by 94% compared to the original U-Net architecture. Given our novel application of CNNs, we generate extensive problem-specific image data in which labeled examples are produced through a custom interface with Amazon Mechanical Turk. This dataset contains over 375,000 labeled bee instances across 720 video frames at 2 FPS, representing an extensive resource for the development and testing of tracking methods. We correctly detect 96% of individuals with a location error of ~7% of a typical body dimension, and orientation error of 12 degrees, approximating the variability of human raters. Our results provide an important step towards efficient image-based dense object tracking by allowing for the accurate determination of object location and orientation across time-series image data efficiently within one network architecture.Comment: 15 pages, including supplementary figures. 1 supplemental movie available as an ancillary fil

Self-localization of a small number of Bose particles in a superfluid Fermi system

We consider self-localization of a small number of Bose particles immersed in a large homogeneous superfluid mixture of fermions in three and one dimensional spaces. Bosons distort the density of surrounding fermions and create a potential well where they can form a bound state analogous to a small polaron state. In the three dimensional volume we observe the self-localization for repulsive interactions between bosons and fermions. In the one dimensional case bosons self-localize as well as for attractive interactions forming, together with a pair of fermions at the bottom of the Fermi sea, a vector soliton. We analyze also thermal effects and show that small non-zero temperature affects the pairing function of the Fermi-subsystem and has little influence on the self-localization phenomena.Comment: 7 pages, 7 fiqures, improved versio

Relaxation under outflow dynamics with random sequential updating

In this paper we compare the relaxation in several versions of the Sznajd model (SM) with random sequential updating on the chain and square lattice. We start by reviewing briefly all proposed one dimensional versions of SM. Next, we compare the results obtained from Monte Carlo simulations with the mean field results obtained by Slanina and Lavicka . Finally, we investigate the relaxation on the square lattice and compare two generalizations of SM, one suggested by Stauffer and another by Galam. We show that there are no qualitative differences between these two approaches, although the relaxation within the Galam rule is faster than within the well known Stauffer rule.Comment: 9 figure

Lukewarm black holes in quadratic gravity

Perturbative solutions to the fourth-order gravity describing spherically-symmetric, static and electrically charged black hole in an asymptotically de Sitter universe is constructed and discussed. Special emphasis is put on the lukewarm configurations, in which the temperature of the event horizon equals the temperature of the cosmological horizon

Fluctuations of the azimuthal particle distribution in NA49 at the CERN SPS

Event-by-event fluctuations and correlations in azimuthal angle are currently widely investigated in various experiments. In this paper the $\Phi$ measure (earlier used in experiments to evaluate fluctuations in transverse momentum) is now applied to azimuthal angle $\phi$. Properties of this $\Phi_{\phi}$ function are investigated through fast generators and with complex models such as Pythia, Hijing, and UrQMD. Preliminary results of NA49 on $\Phi_{\phi}$ are also presented. The system size dependence (p+p, C+C, Si+Si and 6 centralities of Pb+Pb) at the highest SPS energy (158$A$ GeV) is shown, as well as the energy dependence (20$A$ - 158$A$ GeV) for the 7.2\% most central Pb+Pb interactions.Comment: Proceedings from Hot Quarks 2010,June 21-2

Complete disentanglement by partial pure dephasing

We study the effect of pure dephasing on the entanglement of a pair of two-level subsystems (qubits). We show that partial dephasing induced by a super-Ohmic reservoir, corresponding to well-established properties of confined charge states and phonons in semiconductors, may lead to complete disentanglement. We show also that the disentanglement effect increases with growing distance between the two subsystems.Comment: Final, considerably extended version, 6 pages, 4 figure

HDAC6 is a bruchpilot deacetylase that facilitates neurotransmitter release

Presynaptic densities are specialized structures involved in synaptic vesicle tethering and neurotransmission; however, the mechanisms regulating their function remain understudied. In Drosophila, Bruchpilot is a major constituent of the presynaptic density that tethers vesicles. Here, we show that HDAC6 is necessary and sufficient for deacetylation of Bruchpilot. HDAC6 expression is also controlled by TDP-43, an RNA-binding protein deregulated in amyotrophic lateral sclerosis (ALS). Animals expressing TDP-43 harboring pathogenic mutations show increased HDAC6 expression, decreased Bruchpilot acetylation, larger vesicle-tethering sites, and increased neurotransmission, defects similar to those seen upon expression of HDAC6 and opposite to hdac6 null mutants. Consequently, reduced levels of HDAC6 or increased levels of ELP3, a Bruchpilot acetyltransferase, rescue the presynaptic density defects in TDP-43-expressing flies as well as the decreased adult locomotion. Our work identifies HDAC6 as a Bruchpilot deacetylase and indicates that regulating acetylation of a presynaptic release-site protein is critical for maintaining normal neurotransmission

Pricing Options with Portfolio-based Option Trading Agents in Direct Double Auction

Options constitute integral part of modern financial trades, and are priced according to the risk associated with buying or selling certain asset in future. Financial literature mostly concentrates on risk-neutral methods of pricing options such as Black- Scholes model. However, using trading agents with utility function to determine the option’s potential payoff is an emerging field in option pricing theory. In this paper, we use one of such methodologies developed by Othman and Sandholm to design portfolioholding agents that are endowed with popular option portfolios such as bullish spread, bearish spread, butterfly spread, straddle, etc to price options. Agents use their portfolios to evaluate how buying or selling certain option would change their current payoff structure. We also develop a multi-unit direct double auction which preserves the atomicity of orders at the expense of budget balance. Agents are simulated in this mechanism and the emerging prices are compared to risk-neutral prices under different market conditions. Through an appropriate allocation of option portfolios to trading agents, we can simulate market conditions where the population of agents are bearish, bullish, neutral or non-neutral in their beliefs