11,649 research outputs found
Experimental Determination of Thermal Entanglement in Spin Clusters using Magnetic Susceptibility Measurements
The present work reports an experimental observation of thermal entanglement
in a clusterized spin chain formed in the compound NaCuSiO.
The presence of entanglement was investigated through two measured quantities,
an Entanglement Witness and the Entanglement of Formation, both derived from
the magnetic susceptibility. It was found that pairwise entanglement exists
below K. Tripartite entanglement was also observed below K. A theoretical study of entanglement evolution as a function of applied
field and temperature is also presented.Comment: Submited to Phys. Rev.
Reflectance of Polytetrafluoroethylene (PTFE) for Xenon Scintillation Light
Gaseous and liquid xenon particle detectors are being used in a number of
applications including dark matter search and neutrino-less double beta decay
experiments. Polytetrafluoroethylene (PTFE) is often used in these detectors
both as electrical insulator and as a light reflector to improve the efficiency
of detection of scintillation photons. However, xenon emits in the vacuum
ultraviolet wavelength region (175 nm) where the reflecting properties of PTFE
are not sufficiently known.
In this work we report on measurements of PTFE reflectance, including its
angular distribution, for the xenon scintillation light. Various samples of
PTFE, manufactured by different processes (extruded, expanded, skived and
pressed) have been studied. The data were interpreted with a physical model
comprising both specular and diffuse reflections. The reflectance obtained for
these samples ranges from about 47% to 66% for VUV light. Fluoropolymers,
namely ETFE, FEP and PFA were also measured
Schwinger's Method for the Massive Casimir Effect
We apply to the massive scalar field a method recently proposed by Schwinger
to calculate the Casimir effect. The method is applied with two different
regularization schemes: the Schwinger original one by means of Poisson formula
and another one by means of analytical continuation.Comment: plain TeX, 6 pages, DFTUZ-93-2
A new method for the solution of the Schrodinger equation
We present a new method for the solution of the Schrodinger equation
applicable to problems of non-perturbative nature. The method works by
identifying three different scales in the problem, which then are treated
independently: An asymptotic scale, which depends uniquely on the form of the
potential at large distances; an intermediate scale, still characterized by an
exponential decay of the wave function and, finally, a short distance scale, in
which the wave function is sizable. The key feature of our method is the
introduction of an arbitrary parameter in the last two scales, which is then
used to optimize a perturbative expansion in a suitable parameter. We apply the
method to the quantum anharmonic oscillator and find excellent results.Comment: 4 pages, 4 figures, RevTex
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History
We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ( Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap
Development of membranes with regions with different characteristics by phase inversion technique
Separation membrane cells comprising membrane sections with different characteristics can be thebase for new separation processes. Hybrid membrane cells require new membranes with regions withdifferent characteristics. In this paper we present numerical and experimental approaches to developsuch membranes by the phase inversion technique. The two main steps of the phase inversiontechnique, the evaporation step and the immersion precipitation step, are studied by numericalmethods. The numerical approach is based on the solution of the mass transport equation to predict thefilm composition after the evaporation step and in the solution of the CahnHilliard equations topredict the structure of the membrane after the immersion precipitation step. The equations are solvedby finite difference methods. The numerical simulations are used to predict the influence of severalexperimental parameters (temperature, composition of the initial polymeric solution, evaporation time,precipitation time, immersion bath composition) in the structure of the membrane. The experimentalapproach is based on the manipulation of the experimental conditions to produce regions of differentcharacteristics in the same membrane. An experimental method to create different regions from twodifferent initial polymeric solutions is presented
Critical and Tricritical Points for the Massless 2d Gross-Neveu Model Beyond Large N
Using optimized perturbation theory, we evaluate the effective potential for
the massless two dimensional Gross-Neveu model at finite temperature and
density containing corrections beyond the leading large-N contribution. For
large-N, our results exactly reproduce the well known 1/N leading order results
for the critical temperature, chemical potential and tricritical points. For
finite N, our critical values are smaller than the ones predicted by the
large-N approximation and seem to observe Landau's theorem for phase
transitions in one space dimension. New analytical results are presented for
the tricritical points that include 1/N corrections. The easiness with which
the calculations and renormalization are carried out allied to the seemingly
convergent optimized results displayed, in this particular application, show
the robustness of this method and allows us to obtain neat analytical
expressions for the critical as well as tricritical values beyond the results
currently known.Comment: 29 pages, 14 figure
How Many Templates for GW Chirp Detection? The Minimal-Match Issue Revisited
In a recent paper dealing with maximum likelihood detection of gravitational
wave chirps from coalescing binaries with unknown parameters we introduced an
accurate representation of the no-signal cumulative distribution of the
supremum of the whole correlator bank. This result can be used to derive a
refined estimate of the number of templates yielding the best tradeoff between
detector's performance (in terms of lost signals among those potentially
detectable) and computational burden.Comment: submitted to Class. Quantum Grav. Typing error in eq. (4.8) fixed;
figure replaced in version
Couple relationship moderates anxiety and depression trajectories over the transition to parenthood
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