15,860 research outputs found
Analysis of a Cone-Based Distributed Topology Control Algorithm for Wireless Multi-hop Networks
The topology of a wireless multi-hop network can be controlled by varying the
transmission power at each node. In this paper, we give a detailed analysis of
a cone-based distributed topology control algorithm. This algorithm, introduced
in [16], does not assume that nodes have GPS information available; rather it
depends only on directional information. Roughly speaking, the basic idea of
the algorithm is that a node transmits with the minimum power
required to ensure that in every cone of degree around
, there is some node that can reach with power . We show
that taking is a necessary and sufficient condition to
guarantee that network connectivity is preserved. More precisely, if there is a
path from to when every node communicates at maximum power, then, if
, there is still a path in the smallest symmetric graph
containing all edges such that can communicate with
using power . On the other hand, if ,
connectivity is not necessarily preserved. We also propose a set of
optimizations that further reduce power consumption and prove that they retain
network connectivity. Dynamic reconfiguration in the presence of failures and
mobility is also discussed. Simulation results are presented to demonstrate the
effectiveness of the algorithm and the optimizations.Comment: 10 page
Relative entropy of entanglement of a kind of two qubit entangled states
We in this paper strictly prove that some block diagonalizable two qubit
entangled state with six none zero elements reaches its quantum relative
entropy entanglement by the a separable state having the same matrix structure.
The entangled state comprises local filtering result state as a special case.Comment: 5 page
Multimodal estimation of distribution algorithms
Taking the advantage of estimation of distribution algorithms (EDAs) in preserving high diversity, this paper proposes a multimodal EDA. Integrated with clustering strategies for crowding and speciation, two versions of this algorithm are developed, which operate at the niche level. Then these two algorithms are equipped with three distinctive techniques: 1) a dynamic cluster sizing strategy; 2) an alternative utilization of Gaussian and Cauchy distributions to generate offspring; and 3) an adaptive local search. The dynamic cluster sizing affords a potential balance between exploration and exploitation and reduces the sensitivity to the cluster size in the niching methods. Taking advantages of Gaussian and Cauchy distributions, we generate the offspring at the niche level through alternatively using these two distributions. Such utilization can also potentially offer a balance between exploration and exploitation. Further, solution accuracy is enhanced through a new local search scheme probabilistically conducted around seeds of niches with probabilities determined self-adaptively according to fitness values of these seeds. Extensive experiments conducted on 20 benchmark multimodal problems confirm that both algorithms can achieve competitive performance compared with several state-of-the-art multimodal algorithms, which is supported by nonparametric tests. Especially, the proposed algorithms are very promising for complex problems with many local optima
Time History Extrapolation for FDTD Modeling of Shielding Enclosure Designs and EMI Antenna Geometries
The GPOF (generalized pencil-of-function) method was used to extrapolate the time response from FDTD simulations of EMI problems by approximating the time history as a sum of complex exponentials. This method can significantly shorten the FDTD program execution time. However, various difficulties can arise from parameterization during data-processing. The GPOF is applied to, and studied for, two relevant EMI problems, enclosure design and EMI antenna modeling. The merits of GPOF in modeling shielding enclosures and EMI antennas is evaluated through several example
FDTD Modeling of Lumped Ferrites
Implementing ferrites in finite-difference time-domain (FDTD) modeling requires special care because of the complex nature of the ferrite impedance. Considerable computational resources and time are required to directly implement a ferrite in the FDTD method. Fitting the ferrite impedance to an exponential series with the generalized-pencil-of-function (GPOF) method and using recursive convolution is an approach that minimizes the additional computational burden. An FDTD algorithm for a lumped ferrite using GPOF and recursive convolution is presented herein. Two different ferrite impedances in a test enclosure were studied experimentally to demonstrate the FDTD modeling approach. The agreement is generally good
The thermal evolution of nuclear matter at zero temperature and definite baryon number density in chiral perturbation theory
The thermal properties of cold dense nuclear matter are investigated with
chiral perturbation theory.
The evolution curves for the baryon number density, baryon number
susceptibility, pressure and the equation of state are obtained.
The chiral condensate is calculated and our result shows that when the baryon
chemical potential goes beyond , the absolute value of the
quark condensate decreases rapidly, which indicates a tendency of chiral
restoration.Comment: 17 pages, 9 figures, revtex
Entangling two distant nanocavities via a waveguide
In this paper, we investigate the generation of continuous variable
entanglement between two spatially-separate nanocavities mediated by a coupled
resonator optical waveguide in photonic crystals. By solving the exact dynamics
of the cavity system coupled to the waveguide, the entanglement and purity of
the two-mode cavity state are discussed in detail for the initially separated
squeezing inputs. It is found that the stable and pure entangled state of the
two distant nanocavities can be achieved with the requirement of only a weak
cavity-waveguide coupling when the cavities are resonant with the band center
of the waveguide. The strong couplings between the cavities and the waveguide
lead to the entanglement sudden death and sudden birth. When the frequencies of
the cavities lie outside the band of the waveguide, the waveguide-induced cross
frequency shift between the cavities can optimize the achievable entanglement.
It is also shown that the entanglement can be easily manipulated through the
changes of the cavity frequencies within the waveguide band.Comment: 8 pages, 8 figure
New application of decomposition of U(1) gauge potential:Aharonov-Bohm effect and Anderson-Higgs mechanism
In this paper we study the Aharonov-Bohm (A-B) effect and Anderson-Higgs
mechanism in Ginzburg-Landau model of superconductors from the perspective of
the decomposition of U(1) gauge potential. By the Helmholtz theorem, we derive
exactly the expression of the transverse gauge potential in A-B
experiment, which is gauge-invariant and physical. For the case of a bulk
superconductor, we find that the gradient of the total phase field
provides the longitudinal component , which reflects the
Anderson-Higgs mechanism. For the case of a superconductor ring, the gradient
of the longitudinal phase field provides the longitudinal component
, while the transverse phase field produces
new physical effects such as the flux quantization inside a superconducting
ring.Comment: 6 pages, no figures, final version to appear in Modern Physics
Letters
Fire responses and resistance of concrete-filled steel tubular frame structures
This paper presents the results of dynamic responses and fire resistance of concretefilled
steel tubular (CFST) frame structures in fire conditions by using non-linear finite element
method. Both strength and stability criteria are considered in the collapse analysis. The frame
structures are constructed with circular CFST columns and steel beams of I-sections. In order to
validate the finite element solutions, the numerical results are compared with those from a fire
resistance test on CFST columns. The finite element model is then adopted to simulate the
behaviour of frame structures in fire. The structural responses of the frames, including critical
temperature and fire-resisting limit time, are obtained for the ISO-834 standard fire. Parametric
studies are carried out to show their influence on the load capacity of the frame structures in fire.
Suggestions and recommendations are presented for possible adoption in future construction and
design of these structures
Coupling of Caged Molecule Dynamics to JG β-Relaxation II: Polymers
At temperatures below the nominal glass transition temperature Tgα, the structural α-relaxation and the Johari-Goldstein (JG) β-relaxation are too slow to contribute to susceptibility measured at frequencies higher than 1 GHz. This is particularly clear in the neighborhood of the secondary glass transition temperature Tgβ, which can be obtained directly by positronium annihilation lifetime spectroscopy (PALS) and adiabatic calorimetry, or deduced from the temperature at which the JG β-relaxation time τβ reaches 1000 s. The fast process at such high frequencies comes from the vibrations and caged molecules dynamics manifested as the nearly constant loss (NCL) in susceptibility measurements, elastic scattering intensity, I(Q, T), or the mean-square-displacement, «u2(T)», in quasielastic neutron scattering experiment. Remarkably, we find for many different glass-formers that the NCL, I, or «u2» measured in the glassy state changes its temperature dependence at temperature THF near Tgβ. In paper I (Capaccioli, S.; et al. J. Phys. Chem. B 2015, 119 (28), 8800-8808) we have made known this property in the case of the polyalcohols and a pharmaceutical glass former, flufenamic acid studied by THz dielectric spectroscopy, and explained it by the coupling of the NCL to the JG β-relaxation, and the density dependence of these processes. In this paper II, we extend the consideration of the high frequency response to broader range from 100 MHz to THz in the glassy state of many polymers observed by quasielastic light scattering, Brillouin scattering, quasielastic neutron scattering, and GHz-THz dielectric relaxation. In all cases, the NCL changes its T-dependence at some temperature, THF, below Tgα, which is approximately the same as Tgβ. The latter is independently determined by PALS, or adiabatic calorimetry, or low frequency dielectric and mechanical spectroscopy. The property, THF Tgβ, had not been pointed out before by others or in any of the quasielastic neutron and light scattering studies of various amorphous polymers and van der Waals small molecular glass-formers over the past three decades. The generality and fundamental importance of this novel property revitalize the data from these previous publications, making it necessary to be reckoned with in any attempt to solve the glass transition problem. In our rationalization, the property arises first from the fact that the JG β-relaxation and the caged dynamics both depends on density and entropy. Second, the JG β-relaxation is the terminator of the caged dynamics, and hence the two processes are inseparable or effectively coupled. Consequently, the occurrence of the secondary glass transition at Tgβ necessarily is accompanied by corresponding change in the temperature dependence of the NCL, I, or «u2» of the fast caged dynamics at THF =Tg
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