11,015 research outputs found
Design of Amplify and Forward MIMO Relay Networks with QoS Constraint
In this paper, we design the optimal precoding matrices for amplify-and-forward (AF) multiple-input multipleoutput(MIMO) relay networks. Specifically, we consider a dualhop relay network and minimize the total power consumed bysource and relay under predetermined quality of service (QoS) constraints, i.e., mean square error (MSE) constraints. By using majorization theory, we simplify the matrix-valued problem into a scalar-valued one. Since the problem is non-convex, we then propose two convex suboptimal problems that provide the upper and lower bound of the original objectives. Numerical results demonstrate that the lower bound and the upper bound are tight in high signal-to-noise ratio (SNR)
Adaptive design of nano-scale dielectric structures for photonics
Using adaptive algorithms, the design of nano-scale dielectric structures for
photonic applications is explored. Widths of dielectric layers in a linear
array are adjusted to match target responses of optical transmission as a
function of energy. Two complementary approaches are discussed. The first
approach uses adaptive local random updates and progressively adjusts
individual dielectric layer widths. The second approach is based on global
updating functions in which large subgroups of layers are adjusted
simultaneously. Both schemes are applied to obtain specific target responses of
the transmission function within selected energy windows, such as discontinuous
cut-off or power-law decay filters close to a photonic band edge. These
adaptive algorithms are found to be effective tools in the custom design of
nano-scale photonic dielectric structures.Comment: 4 pages Revtex, 4 embedded EPS figure
New interpretation of matter-antimatter asymmetry based on branes and possible observational consequences
Motivated by the AMS project, we assume that after the Big Bang or inflation
epoch, antimatter was repelled onto one brane which is separated from our brane
where all the observational matter resides. It is suggested that CP may be
spontaneously broken, the two branes would correspond to ground states for
matter and antimatter respectively. Generally a complex scalar field which is
responsible for the spontaneous CP violation, exists in the space between the
branes and causes a repulsive force against the gravitation. A possible
potential barrier prevents the mater(antimatter) particles to enter the space
between two branes. However, by the quantum tunnelling, a sizable anti-matter
flux may come to our brane. In this work by considering two possible models,
i.e. the naive flat space-time and Randall-Sundrum models and using the
observational data on the visible matter in our universe as inputs, we derive
the antimatter flux which would be observed by the AMS detector.Comment: 10 pages, 4 figures and 2 tables. Replaced by new versio
Evolving small-world networks with geographical attachment preference
We introduce a minimal extended evolving model for small-world networks which
is controlled by a parameter. In this model the network growth is determined by
the attachment of new nodes to already existing nodes that are geographically
close. We analyze several topological properties for our model both
analytically and by numerical simulations. The resulting network shows some
important characteristics of real-life networks such as the small-world effect
and a high clustering.Comment: 11 pages, 4 figure
Fatou flowers and parabolic curves
In this survey we collect the main results known up to now (July 2015) regarding possible generalizations to several complex variables of the classical Leau-Fatou flower theorem about holomorphic parabolic dynamics
Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles
The temporal purity of single photons is crucial to the indistinguishability of independent photon sources for the fundamental study of the quantum nature of light and the development of photonic technologies. Currently, the technique for single photons heralded from time-frequency entangled biphotons created in nonlinear crystals does not guarantee the temporal-quantum purity, except using spectral filtering. Nevertheless, an entirely different situation is anticipated for narrow-band biphotons with a coherence time far longer than the time resolution of a single-photon detector. Here we demonstrate temporally pure single photons with a coherence time of 100 ns, directly heralded from the time-frequency entangled biphotons generated by spontaneous four-wave mixing in cold atomic ensembles, without any supplemented filters or cavities. A near-perfect purity and indistinguishability are both verified through Hong-Ou-Mandel quantum interference using single photons from two independent cold atomic ensembles. The time-frequency entanglement provides a route to manipulate the pure temporal state of the single-photon source
Influence of Fermion Velocity Renormalization on Dynamical Mass Generation in QED
We study dynamical fermion mass generation in (2+1)-dimensional quantum
electrodynamics with a gauge field coupling to massless Dirac fermions and
non-relativistic scalar bosons. We calculate the fermion velocity
renormalization and then examine its influence on dynamical mass generation by
using the Dyson-Schwinger equation. It is found that dynamical mass generation
takes place even after including the scalar bosons as long as the bosonic
compressibility parameter is sufficiently small. In addition, the fermion
velocity renormalization enhances the dynamically generated mass.Comment: 6 pages, 3 figures, Chinese Physics Letter, Vol 29, page 057401(2012
Bose-Einstein condensation and chiral phase transition in linear sigma model
With the linear sigma model, we have studied Bose-Einstein condensation and
the chiral phase transition in the chiral limit for an interacting pion system.
A phase diagram including these two phenomena is presented. It is found
that the phase plane has been divided into three areas: the Bose-Einstein
condensation area, the chiral symmetry broken phase area and the chiral
symmetry restored phase area. Bose-Einstein condensation can happen either from
the chiral symmetry broken phase or from the restored phase. We show that the
onset of the chiral phase transition is restricted in the area where there is
no Bose-Einstein condensation.Comment: 13 pages, 7 figure
Dynamical study of the light scalar mesons below 1 GeV in a flux-tube model
The light scalar mesons below 1 GeV as tetraquark states are studied in the
framework of the flux-tube model, the multi-body confinement instead of the
additive two-body confinement is used. From the calculated results, we find
that the light scalar mesons, , could be well accommodated in
the diquark-antidiquark tetraquark picture in the flux-tube model and they
could be color confinement resonances. The mass of the first radial excited
state of is 1019 MeV, which is close to the mass of
. Whereas can not be fitted in this interpretation.Comment: 11 pages, 1 figur
High Dimensional Apollonian Networks
We propose a simple algorithm which produces high dimensional Apollonian
networks with both small-world and scale-free characteristics. We derive
analytical expressions for the degree distribution, the clustering coefficient
and the diameter of the networks, which are determined by their dimension
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