20,733 research outputs found
Modal analysis of Bragg onion resonators
From analysis of the high Q modes in a Bragg onion resonator with an omnidirectional reflector cladding, we establish a close analogy between such a resonator and a spherical hollow cavity in perfect metal. We demonstrate that onion resonators are ideal for applications that require a large spontaneous-emission factor ß, such as thresholdless lasers and single-photon devices
Coherent transport on Apollonian networks and continuous-time quantum walks
We study the coherent exciton transport on Apollonian networks generated by
simple iterative rules. The coherent exciton dynamics is modeled by
continuous-time quantum walks and we calculate the transition probabilities
between two nodes of the networks. We find that the transport depends on the
initial nodes of the excitation. For networks less than the second generation
the coherent transport shows perfect revivals when the initial excitation
starts at the central node. For networks of higher generation, the transport
only shows partial revivals. Moreover, we find that the excitation is most
likely to be found at the initial nodes while the coherent transport to other
nodes has a very low probability. In the long time limit, the transition
probabilities show characteristic patterns with identical values of limiting
probabilities. Finally, the dynamics of quantum transport are compared with the
classical transport modeled by continuous-time random walks.Comment: 5 pages, 6 figues. Submitted to Phys. ReV.
A Novel FastICA Method for the Reference-based Contrast Functions
This paper deals with the efficient optimization problem of Cumulant-based contrast criteria in the Blind Source Separation (BSS) framework, in which sources are retrieved by maximizing the Kurtosis contrast function. Combined with the recently proposed reference-based contrast schemes, a new fast fixed-point (FastICA) algorithm is proposed for the case of linear and instantaneous mixture. Due to its quadratic dependence on the number of searched parameters, the main advantage of this new method consists in the significant decrement of computational speed, which is particularly striking with large number of samples. The method is essentially similar to the classical algorithm based on the Kurtosis contrast function, but differs in the fact that the reference-based idea is utilized. The validity of this new method was demonstrated by simulations
Host and bacterial proteases influence biofilm formation and virulence in a murine model of enterococcal catheter-associated urinary tract infection
Urinary tract infections: targeting enzymes might help Identifying bacterial and host enzymes that support biofilm formation may help prevent urinary tract infections caused by catheters. Enterococcus faecalis bacteria is a leading cause of catheter-associated urinary tract infections, the most common type of hospital-acquired infections. Michael Caparon and colleagues at Washington University School of Medicine in Missouri, USA, studied these infections in mice. They examined the effects of two protein-degrading enzymes, both from the bacterium and one can be activated by urine trypsin-like protease from the animals. Mutations that impaired either one of the enzymes had no effect on the infection, but when both the bacterial enzymes were impaired by mutation the formation of biofilms was significantly reduced. Treating the mice with chemicals that inhibited both bacterial and host enzymes dramatically reduced catheter-induced inflammation and related problems. This suggests drugs targeting these enzymes could be useful in clinical care
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
Plaquette order and deconfined quantum critical point in the spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice
We have precisely determined the ground state phase diagram of the quantum
spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice using the
tensor renormalization group method. We find that the ferromagnetic,
ferroquadrupolar, and a large part of the antiferromagnetic phases are stable
against quantum fluctuations. However, around the phase where the ground state
is antiferroquadrupolar ordered in the classical limit, quantum fluctuations
suppress completely all magnetic orders, leading to a plaquette order phase
which breaks the lattice symmetry but preserves the spin SU(2) symmetry. On the
evidence of our numerical results, the quantum phase transition between the
antiferromagnetic phase and the plaquette phase is found to be either a direct
second order or a very weak first order transition.Comment: 6 pages, 9 figures, published versio
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