25,979 research outputs found
Surface spectral function in the superconducting state of a topological insulator
We discuss the surface spectral function of superconductors realized from a
topological insulator, such as the copper-intercalated BiSe. These
functions are calculated by projecting bulk states to the surface for two
different models proposed previously for the topological insulator. Dependence
of the surface spectra on the symmetry of the bulk pairing order parameter is
discussed with particular emphasis on the odd-parity pairing. Exotic spectra
like an Andreev bound state connected to the topological surface states are
presented.Comment: 12 pages, 9 figures, 1 tabl
Fusing Censored Dependent Data for Distributed Detection
In this paper, we consider a distributed detection problem for a censoring
sensor network where each sensor's communication rate is significantly reduced
by transmitting only "informative" observations to the Fusion Center (FC), and
censoring those deemed "uninformative". While the independence of data from
censoring sensors is often assumed in previous research, we explore spatial
dependence among observations. Our focus is on designing the fusion rule under
the Neyman-Pearson (NP) framework that takes into account the spatial
dependence among observations. Two transmission scenarios are considered, one
where uncensored observations are transmitted directly to the FC and second
where they are first quantized and then transmitted to further improve
transmission efficiency. Copula-based Generalized Likelihood Ratio Test (GLRT)
for censored data is proposed with both continuous and discrete messages
received at the FC corresponding to different transmission strategies. We
address the computational issues of the copula-based GLRTs involving
multidimensional integrals by presenting more efficient fusion rules, based on
the key idea of injecting controlled noise at the FC before fusion. Although,
the signal-to-noise ratio (SNR) is reduced by introducing controlled noise at
the receiver, simulation results demonstrate that the resulting noise-aided
fusion approach based on adding artificial noise performs very closely to the
exact copula-based GLRTs. Copula-based GLRTs and their noise-aided counterparts
by exploiting the spatial dependence greatly improve detection performance
compared with the fusion rule under independence assumption
Relativistic DNLS and Kaup-Newell Hierarchy
By the recursion operator of the Kaup-Newell hierarchy we construct the
relativistic derivative NLS (RDNLS) equation and the corresponding Lax pair. In
the nonrelativistic limit it reduces to DNLS equation
and preserves integrability at any order of relativistic corrections. The
compact explicit representation of the linear problem for this equation becomes
possible due to notions of the -calculus with two bases, one of which is the
recursion operator, and another one is the spectral parameter
Spatial Whitening Framework for Distributed Estimation
Designing resource allocation strategies for power constrained sensor network
in the presence of correlated data often gives rise to intractable problem
formulations. In such situations, applying well-known strategies derived from
conditional-independence assumption may turn out to be fairly suboptimal. In
this paper, we address this issue by proposing an adjacency-based spatial
whitening scheme, where each sensor exchanges its observation with their
neighbors prior to encoding their own private information and transmitting it
to the fusion center. We comment on the computational limitations for obtaining
the optimal whitening transformation, and propose an iterative optimization
scheme to achieve the same for large networks. We demonstrate the efficacy of
the whitening framework by considering the example of bit-allocation for
distributed estimation.Comment: 4 pages, 2 figures, this paper has been presented at CAMSAP 2011;
Proc. 4th Intl. Workshop on Computational Advances in Multi-Sensor Adaptive
Processing (CAMSAP 2011), San Juan, Puerto Rico, Dec 13-16, 201
Optimal Identical Binary Quantizer Design for Distributed Estimation
We consider the design of identical one-bit probabilistic quantizers for
distributed estimation in sensor networks. We assume the parameter-range to be
finite and known and use the maximum Cram\'er-Rao Lower Bound (CRB) over the
parameter-range as our performance metric. We restrict our theoretical analysis
to the class of antisymmetric quantizers and determine a set of conditions for
which the probabilistic quantizer function is greatly simplified. We identify a
broad class of noise distributions, which includes Gaussian noise in the
low-SNR regime, for which the often used threshold-quantizer is found to be
minimax-optimal. Aided with theoretical results, we formulate an optimization
problem to obtain the optimum minimax-CRB quantizer. For a wide range of noise
distributions, we demonstrate the superior performance of the new quantizer -
particularly in the moderate to high-SNR regime.Comment: 6 pages, 3 figures, This paper has been accepted for publication in
IEEE Transactions in Signal Processin
Gcn4p and novel upstream activating sequences regulate targets of the unfolded protein response.
Eukaryotic cells respond to accumulation of unfolded proteins in the endoplasmic reticulum (ER) by activating the unfolded protein response (UPR), a signal transduction pathway that communicates between the ER and the nucleus. In yeast, a large set of UPR target genes has been experimentally determined, but the previously characterized unfolded protein response element (UPRE), an upstream activating sequence (UAS) found in the promoter of the UPR target gene KAR2, cannot account for the transcriptional regulation of most genes in this set. To address this puzzle, we analyzed the promoters of UPR target genes computationally, identifying as candidate UASs short sequences that are statistically overrepresented. We tested the most promising of these candidate UASs for biological activity, and identified two novel UPREs, which are necessary and sufficient for UPR activation of promoters. A genetic screen for activators of the novel motifs revealed that the transcription factor Gcn4p plays an essential and previously unrecognized role in the UPR: Gcn4p and its activator Gcn2p are required for induction of a majority of UPR target genes during ER stress. Both Hac1p and Gcn4p bind target gene promoters to stimulate transcriptional induction. Regulation of Gcn4p levels in response to changing physiological conditions may function as an additional means to modulate the UPR. The discovery of a role for Gcn4p in the yeast UPR reveals an additional level of complexity and demonstrates a surprising conservation of the signaling circuit between yeast and metazoan cells
Self-Dual Vortices in Chern-Simons Hydrodynamics
The classical theory of non-relativistic charged particle interacting with
U(1) gauge field is reformulated as the Schr\"odinger wave equation modified by
the de-Broglie-Bohm quantum potential nonlinearity. For, (1 - )
deformed strength of quantum potential the model is gauge equivalent to the
standard Schr\"odinger equation with Planck constant , while for the
strength (1 + ), to the pair of diffusion-anti-diffusion equations.
Specifying the gauge field as Abelian Chern-Simons (CS) one in 2+1 dimensions
interacting with the Nonlinear Schr\"odinger field (the Jackiw-Pi model), we
represent the theory as a planar Madelung fluid, where the Chern-Simons Gauss
law has simple physical meaning of creation the local vorticity for the fluid
flow. For the static flow, when velocity of the center-of-mass motion (the
classical velocity) is equal to the quantum one (generated by quantum potential
velocity of the internal motion), the fluid admits N-vortex solution. Applying
the Auberson-Sabatier type gauge transform to phase of the vortex wave function
we show that deformation parameter , the CS coupling constant and the
quantum potential strength are quantized. Reductions of the model to 1+1
dimensions, leading to modified NLS and DNLS equations with resonance soliton
interactions are discussed.Comment: 12 pages, Tex, to be published in Proc. "NEEDS'2000", Gokova, Turkey,
2000; Theor. and Math.Physic
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