865 research outputs found
Using Simple Neural Networks to Correct Errors in Optical Data Transmission.
We have demonstrated the applicability of
neural-network-based systems to the problem
of reducing the effects of signal distortion,
and shown that such a system has the potential
to reduce the bit-error-rate in the digitized
version of the analogue electrical signal
derived from an optical data stream by a
substantial margin over existing techniques
Comparison of the simulation and experimental fatigue crack behaviors in the aluminum alloy HS6061-T6
AbstractThis work deals with rotating bending fatigue tests on aluminum alloy HS6061-T6. Results have been obtained for two sizes of narrow section diameter for specimens with one hole. Results show that fatigue endurance is reduced in the case of the hole. In order to explain this behavior, numerical analysis by FEM were carried out to determine the stress concentrations for the two types of specimens. It is found that the important factor affects fatigue life is the narrow section diameter of the specimens, and the maximum damage occurs in the outer part of the specimen at the first stages of loading, however, it moves toward the center of the bar under uniaxial loading. The number of cycles to failure predicted numerically is higher than the experimental one. This difference is attributed mainly to an upper stage of fatigue crack growth, particularly, the interaction between fatigue crack growth and growth that can not be accounted for in the numerical model
Stability of negative ionization fronts: regularization by electric screening?
We recently have proposed that a reduced interfacial model for streamer
propagation is able to explain spontaneous branching. Such models require
regularization. In the present paper we investigate how transversal Fourier
modes of a planar ionization front are regularized by the electric screening
length. For a fixed value of the electric field ahead of the front we calculate
the dispersion relation numerically. These results guide the derivation of
analytical asymptotes for arbitrary fields: for small wave-vector k, the growth
rate s(k) grows linearly with k, for large k, it saturates at some positive
plateau value. We give a physical interpretation of these results.Comment: 11 pages, 2 figure
Microstrip Dual-Band Bandpass Filter Using U-Shaped Resonators
Coupled resonators are widely used in the design of filters with dual-passband responses.
In this paper, we present a dual-band bandpass filter using only couplings between adjacent resonators
without cross-couplings. The dual-band bandpass filter with centre frequencies of 1747 MHz and
1879 MHz respectively is designed and fabricated using microstrip U-shaped resonators. Using the
coupled resonator pair as a dual-band cluster, a miniaturised structure is achieved as compared to the
conventional topology. The measured responses agree closely with the simulations
Dipolar Bose-Einstein condensate soliton on a two-dimensional optical lattice
Using a three-dimensional mean-field model we study one-dimensional dipolar
Bose-Einstein condensate (BEC) solitons on a weak two-dimensional (2D) square
and triangular optical lattice (OL) potentials placed perpendicular to the
polarization direction. The stabilization against collapse and expansion of
these solitons for a fixed dipolar interaction and a fixed number of atoms is
possible for short-range atomic interaction lying between two critical limits.
The solitons collapse below the lower limit and escapes to infinity above the
upper limit. One can also stabilize identical tiny BEC solitons arranged on the
2D square OL sites forming a stable 2D array of interacting droplets when the
OL sites are filled with a filling factor of 1/2 or less. Such an array is
unstable when the filling factor is made more than 1/2 by occupying two
adjacent sites of OL. These stable 2D arrays of dipolar superfluid BEC solitons
are quite similar to the recently studied dipolar Mott insulator states on 2D
lattice in the Bose-Hubbard model by Capogrosso-Sansone et al. [B.
Capogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Phys.
Rev. Lett. 104 (2010) 125301].Comment: 8 pages, 5 figures and 2 table
Open Issues on the Synthesis of Evolved Stellar Populations at Ultraviolet Wavelengths
In this paper we briefly review three topics that have motivated our (and
others') investigations in recent years within the context of evolutionary
population synthesis techniques. These are: The origin of the FUV up-turn in
elliptical galaxies, the age-metallicity degeneracy, and the study of the
mid-UV rest-frame spectra of distant red galaxies. We summarize some of our
results and present a very preliminary application of a UV grid of theoretical
spectra in the analysis of integrated properties of aged stellar populations.
At the end, we concisely suggest how these topics can be tackled once the World
Space Observatory enters into operation in the midst of this decade.Comment: 8 pages, 4 figures, accepted for publication in Astrophysics & Space
Science, UV Universe special issu
A batch-service queueing model with a discrete batch Markovian arrival process
Queueing systems with batch service have been investigated extensively during the past decades. However, nearly all the studied models share the common feature that an uncorrelated arrival process is considered, which is unrealistic in several real-life situations. In this paper, we study a discrete-time queueing model, with a server that only initiates service when the amount of customers in system (system content) reaches or exceeds a threshold. Correlation is taken into account by assuming a discrete batch Markovian arrival process (D-BMAP), i.e. the distribution of the number of customer arrivals per slot depends on a background state which is determined by a first-order Markov chain. We deduce the probability generating function of the system content at random slot marks and we examine the influence of correlation in the arrival process on the behavior of the system. We show that correlation merely has a small impact on the threshold that minimizes the mean system content. In addition, we demonstrate that correlation might have a significant influence on the system content and therefore has to be included in the model
SELF-DUAL ANYONS IN UNIFORM BACKGROUND FIELDS
We study relativistic self-dual Chern-Simons-Higgs systems in the presence of
uniform background fields that explicitly break CTP. A rich, but discrete
vacuum structure is found when the gauge symmetry is spontaneously broken,
while the symmetric phase can have an infinite vacuum degeneracy at tree level.
The latter is due to the proliferation of neutral solitonic states that cost
zero energy. Various novel self-dual solitons, such as these, are found in both
the symmetric and the asymmetric phases. Also by considering a similar system
on a two-sphere and the subsequent large sphere limit, we isolate sensible and
finite expressions for the conserved angular and linear momenta, which satisfy
anomalous commutation relations. We conclude with a few remarks on unresolved
issues.Comment: LaTeX, 20 pages, 4 uuencoded figures included
Defects induced ferromagnetism in Mn doped ZnO
Single phase Mn doped (2 at %) ZnO samples have been synthesized by
solid-state reaction technique. Before the final sintering at 500 C, the mixed
powders have been milled for different milling periods (6, 24, 48 and 96
hours). The grain sizes of the samples are very close to each other (~ 32 \pm 4
nm). However, the defective state of the samples is different from each other
as manifested from the variation of magnetic properties and electrical
resistivity with milling time. All the samples have been found to be
ferromagnetic with clear hysteresis loops at room temperature. The maximum
value for saturation magnetization (0.11 {\mu}_B / Mn atom) was achieved for 96
hours milled sample. Electrical resistivity has been found to increase with
increasing milling time. The most resistive sample bears the largest saturation
magnetization. Variation of average positron lifetime with milling time bears a
close similarity with that of the saturation magnetization. This indicates the
key role played by open volume vacancy defects, presumably zinc vacancies near
grain surfaces, in inducing ferromagnetic order in Mn doped ZnO. To attain
optimum defect configuration favorable for ferromagnetism in this kind of
samples proper choice of milling period and annealing conditions is required.Comment: Accepted in Journal of Magnetism and Magnetic Material
Dynamics of Baryons from String Theory and Vector Dominance
We consider a holographic model of QCD from string theory, a la Sakai and
Sugimoto, and study baryons. In this model, mesons are collectively realized as
a five-dimensional \ Yang-Mills field and baryons
are classically identified as solitons with a unit Pontryagin number
and electric charges. The soliton is shown to be very small in the large
't Hooft coupling limit, allowing us to introduce an effective field . Its coupling to the mesons are dictated by the soliton structure, and
consists of a direct magnetic coupling to the field strength as well
as a minimal coupling to the gauge field. Upon the dimensional
reduction, this effective action reproduces all interaction terms between
nucleons and an infinite tower of mesons in a manner consistent with the large
expansion. We further find that all electromagnetic interactions, as
inferred from the same effective action via a holographic prescription, are
mediated by an infinite tower of vector mesons, rendering the baryon
electromagnetic form factors completely vector-dominated as well. We estimate
nucleon-meson couplings and also the anomalous magnetic moments, which compare
well with nature.Comment: 65pages, 3 figures, vector mesons and axial-vector mesons are now
canonically normalized (comparisons with data and conclusions unaffected
- …