5,111 research outputs found
Spectral weight suppression in response functions of ultracold fermion-boson mixtures
We study the dynamical response of ultracold fermion-boson mixture in the
Bogoliubov regime, where the interactions between fermionic impurities and
bosonic excitations (phonons) are described by an effective Frohlich model
under the Bogoliubov approximation. A characteristic suppression of the
single-particle spectral weight is found in the small momentum region where the
impurity band and phonon mode intersect. Using diagrammatic technique we
compute the Bragg spectra as well as the momentum dependent force-force
correlation function. We fnd that both of them are heavily affected by the
spectral weight suppression effect at low impurity densities in both 1D and 2D
systems. We show that the the spectral weight suppression feature in Bragg
spectra, which was previously found in the quantum Monte Carlo simulations and
which cannot be recovered by the random phase approximation, can be accurately
reproduced with the help of vertex corrections.Comment: 14 pages, 10 figures. Final version with a new title, some revisions
and a new figur
Gene specific co-regulation discovery: an improved approach
[Abstract]: Discovering gene co-regulatory relationships is a new but important research problem in DNA microarray data analysis. The problem of gene specific co-regulation discovery is to, for a particular gene of interest, called the target gene, identify its strongly co-regulated genes and the condition subsets where such strong gene co-regulations are observed. The study on this problem can contribute to a better understanding and characterization of the target gene. The existing method, using the genetic algorithm (GA), is slow due to its expensive fitness evaluation and long individual representation. In this paper, we propose an improved method for finding gene specific co-regulations. Compared with the current method, our method features a notably improved effciency. We employ kNN Search Table to substantially speed up fitness evaluation in the GA. We also propose a more compact representation scheme for encoding individuals in the GA, which contributes to faster crossover and mutation operations. Experimental results with a real-life gene mi-croarray data set demonstrate the improved effciency of our technique compared with the current method
Dynamical response of ultracold interacting fermion-boson mixtures
We analyze the dynamical response of a ultracold binary gas mixture in
presence of strong boson-fermion couplings. Mapping the problem onto that of
the optical response of a metal/semiconductor electronic degrees of freedom to
electromagnetic perturbation we calculate the corresponding dynamic linear
response susceptibility in the non-perturbative regimes of strong boson-fermion
coupling using diagrammatic resummation technique as well as quantum Monte
Carlo simulations. We evaluate the Bragg spectral function as well as the
optical conductivity and find a pseudogap, which forms in certain parameter
regimes.Comment: 32 pages, 13 figure
The spatial coherence of weakly interacting one-dimensional non-equilibrium Bosonic quantum fluids
We present a theoretical analysis of spatial correlations in a
one-dimensional driven-dissipative non-equilibrium condensate. Starting from a
stochastic generalized Gross-Pitaevskii equation, we derive a noisy
Kuramoto-Sivashinsky equation for the phase dynamics. For sufficiently strong
interactions, the coherence decays exponentially in close analogy to the
equilibrium Bose gas. When interactions are small on a scale set by the
nonequilibrium condition, we find through numerical simulations a crossover
between a Gaussian and exponential decay with peculiar scaling of the coherence
length on the fluid density and noise strength.Comment: 5 pages, 2 figures, supplemental materia
Caching in Combination Networks: Novel Multicast Message Generation and Delivery by Leveraging the Network Topology
Maddah-Ali and Niesen's original coded caching scheme for shared-link
broadcast networks is now known to be optimal to within a factor two, and has
been applied to other types of networks. For practical reasons, this paper
considers that a server communicates to cache-aided users through
intermediate relays. In particular, it focuses on combination networks where
each of the users is connected to a distinct -subsets of
relays. By leveraging the symmetric topology of the network, this paper
proposes a novel method to general multicast messages and to deliver them to
the users. By numerical evaluations, the proposed scheme is shown to reduce the
download time compared to the schemes available in the literature. The idea is
then extended to decentralized combination networks, more general relay
networks, and combination networks with cache-aided relays and users. Also in
these cases the proposed scheme outperforms known ones.Comment: 6 pages, 3 figures, accepted in ICC 2018, correct the typo in (6) of
the previous versio
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