9,423 research outputs found
Stacked High-Impedance Surface (HIS) for 5 GHz WLAN Applications
In this work we present a stacked high-impedance surface (HIS) for low-profile, high-gain, 5 GHz WLAN antennas. The structure consists of two layers: a lower mushroom layer and an upper planar layer. We demonstrate that the stacked geometry has much better properties than conventional single-layer structures for achieving simultaneously surface-wave suppression and zero reflection phase at a given frequency. We show by measurements that the designed stacked HIS exhibits both a large band gap and in-phase wave reflection over the entire range from 4.6 GHz to 6.4 GHz. The structure is realized on FR4 substrate using standard etching technology to make fabrication easy and cheap
Influence of the isospin and hypercharge chemical potentials on the location of the CEP in the mu_B-T phase diagram of the SU(3)_L x SU(3)_R chiral quark model
We investigate the influence of the asymmetric quark matter (rho_u\ne
rho_d\ne rho_s) on the mass of the quasiparticles and the phase diagram of the
chiral quark model parametrized at one-loop level of the renormalized theory,
using the optimized perturbation theory for the resummation of the perturbative
series. The effect of various chemical potentials introduced in the grand
canonical ensemble is investigated with the method of relativistic many-body
theory. The temperature dependence of the topological susceptibility is
estimated with the help of the Witten-Veneziano mass formula.Comment: RevTeX4, 13 pages, 6 figures, version accepted for publication in
Phys. Rev.
Chopped basalt fibres: A new perspective in reinforcing poly(lactic acid) to produce injection moulded engineering composites from renewable and natural resources
This paper focuses on the reinforcing of Poly(lactic acid) with chopped basalt fibres by using silane treated and
untreated basalt fibres. Composite materials with 5â10â15â20â30â40 wt% basalt fibre contents were prepared from silane
sized basalt fibres using extrusion, and injection moulding, while composites with 5â10â15 wt% basalt fibre contents were
also prepared by using untreated basalt fibres as control. The properties of the injection moulded composites were extensively
examined by using quasi-static (tensile, three-point bending) and dynamic mechanical tests (notched and unnotched
Charpy impact tests), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), heat deflection temperature
(HDT) analysis, dimensional stability test, as well as melt flow index (MFI) analysis and scanning electron microscopic
(SEM) observations. It was found that silane treated chopped basalt fibres are much more effective in reinforcing
Poly(lactic acid) than natural fibres; although basalt fibres are not biodegradable but they are still considered as natural (can
be found in nature in the form of volcanic rocks) and biologically inert. It is demonstrated in this paper that by using basalt
fibre reinforcement, a renewable and natural resource based composite can be produced by injection moulding with excellent
mechanical properties suitable even for engineering applications. Finally it was shown that by using adequate drying of
the materials, composites with higher mechanical properties can be achieved compared to literature data
Zero temperature properties of mesons in a vector meson extended linear sigma model
A three flavor linear sigma model with vector and axial-vector mesons is
discussed. Preliminary results concerning on the symmetry breaking pattern, the
question of parameterization, as well as the resulting meson masses are
presented.Comment: 4 pages, 0 figures, submitted to the Hot and Cold Baryonic Matter
(HCBM 2010) conference proceeding
Scalar mesons in a linear sigma model with (axial-)vector mesons
The structure of the scalar mesons has been a subject of debate for many
decades. In this work we look for states among the physical
resonances using an extended Linear Sigma Model that contains scalar,
pseudoscalar, vector, and axial-vector mesons both in the non-strange and
strange sectors. We perform global fits of meson masses, decay widths and
amplitudes in order to ascertain whether the scalar states are below
or above 1 GeV. We find the scalar states above 1 GeV to be preferred as
states.Comment: 6 pages, 1 figure, To appear in the proceedings of the XII. Hadron
Physics Conference, Bento Goncalves, Brasil, April, 22 - 27, 201
Global Evolutionary Algorithms in the Design of Electromagnetic Band Gap Structures with Suppressed Surface Waves Propagation
The paper is focused on the automated design and optimization of electromagnetic band gap structures suppressing the propagation of surface waves. For the optimization, we use different global evolutionary algorithms like the genetic algorithm with the single-point crossover (GAs) and the multi-point (GAm) one, the differential evolution (DE) and particle swarm optimization (PSO). The algorithms are mutually compared in terms of convergence velocity and accuracy. The developed technique is universal (applicable for any unit cell geometry). The method is based on the dispersion diagram calculation in CST Microwave Studio (CST MWS) and optimization in Matlab. A design example of a mushroom structure with simultaneous electromagnetic band gap properties (EBG) and the artificial magnetic conductor ones (AMC) in the required frequency band is presented
The Spontaneous Emergence of Social Influence in Online Systems
Social influence drives both offline and online human behaviour. It pervades
cultural markets, and manifests itself in the adoption of scientific and
technical innovations as well as the spread of social practices. Prior
empirical work on the diffusion of innovations in spatial regions or social
networks has largely focused on the spread of one particular technology among a
subset of all potential adopters. It has also been difficult to determine
whether the observed collective behaviour is driven by natural influence
processes, or whether it follows external signals such as media or marketing
campaigns. Here, we choose an online context that allows us to study social
influence processes by tracking the popularity of a complete set of
applications installed by the user population of a social networking site, thus
capturing the behaviour of all individuals who can influence each other in this
context. By extending standard fluctuation scaling methods, we analyse the
collective behaviour induced by 100 million application installations, and show
that two distinct regimes of behaviour emerge in the system. Once applications
cross a particular threshold of popularity, social influence processes induce
highly correlated adoption behaviour among the users, which propels some of the
applications to extraordinary levels of popularity. Below this threshold, the
collective effect of social influence appears to vanish almost entirely in a
manner that has not been observed in the offline world. Our results demonstrate
that even when external signals are absent, social influence can spontaneously
assume an on-off nature in a digital environment. It remains to be seen whether
a similar outcome could be observed in the offline world if equivalent
experimental conditions could be replicated
The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves is the Oosterhoff/Arp/Preston Period Ratio Effect in Disguise
The correlation of particular Fourier components of the light curves of RR
Lyrae variables with metallicity, discovered by Simon and later by Kovacs and
his coworkers, is shown to have the same explanation as the period ratios
(period shifts in log P) between RRab Lyrae variables that have the same
colors, amplitudes, and light-curve shapes but different metallicities. A
purpose of this paper is to demonstrate that the model which predicts the
period-metallicity relations is the mediating parameters of colors, amplitudes,
and light-curve shapes also explains the Simon/Kovacs et al. correlation
between period, Phi_31, and metallicity. The proof is made by demonstrating
that the combination of the first and third phase terms in a Fourier
decomposition of RRab light curves, called Phi_31 by Simon and Lee, varies
monotonically across the RR Lyrae instability strip in the same way that
amplitude, color, and rise time vary with period within the strip. The premise
of the model is that if horizontal branches at the RR Lyrae strip are stacked
in luminosity according to the metallicity, then there necessarily must be a
log period shift between RR Lyraes with different metallicities at the same
Phi_31 values. However, there are exceptions to the model. (...)Comment: 17 pages, 8 figures, 1 table. Accepted for publication in The A
Critical surface of the SU(3)(L) x SU(3)(R) chiral quark model at nonzero baryon density
The boundary of the first order chiral phase transition region is studied in the m(pi)-m(K)-mu(B) space using the one-loop optimized perturbation theory for the resummation of the perturbative series. Chiral perturbation theory for mesons and baryons is used for the T=0 parametrization of the model. The surface of second order transition points bends with increasing mu(B) towards the physical point of the m(pi)-m(K) mass plane allowing for the existence of the critical end point in the mu(B)-T plane at the physical point. The location and scaling region of the CEP is explored
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