41,612 research outputs found
Sympathetic cooling of trapped fermions by bosons in the presence of particle losses
We study the sympathetic cooling of a trapped Fermi gas interacting with an
ideal Bose gas below the critical temperature of the Bose-Einstein
condensation. We derive the quantum master equation, which describes the
dynamics of the fermionic component, and postulating the thermal distribution
for both gases we calculate analytically the rate at which fermions are cooled
by the bosonic atoms. The particle losses constitute an important source of
heating of the degenerate Fermi gas. We evaluate the rate of loss-induced
heating and derive analytical results for the final temperature of fermions,
which is limited in the presence of particle losses.Comment: 7 pages, 2 figures, EPL style; final versio
Antiresonance and interaction-induced localization in spin and qubit chains with defects
We study a spin chain with an anisotropic XXZ coupling in an external field.
Such a chain models several proposed types of a quantum computer. The chain
contains a defect with a different on-site energy. The interaction between
excitations is shown to lead to two-excitation states localized next to the
defect. In a resonant situation scattering of excitations on each other might
cause decay of an excitation localized on the defect. We find that destructive
quantum interference suppresses this decay. Numerical results confirm the
analytical predictions.Comment: Updated versio
Quantum open systems and turbulence
We show that the problem of non conservation of energy found in the
spontaneous localization model developed by Ghirardi, Rimini and Weber is very
similar to the inconsistency between the stochastic models for turbulence and
the Navier-Stokes equation. This sort of analogy may be useful in the
development of both areas.Comment: to appear in Physical Review
Gender and politics: A descriptive and comparative analysis of the statutes of Brazilian and Portuguese political parties
This paper presents a descriptive and comparative analysis of the statutes of Brazilian and Portuguese political parties regarding women’s political participation. The main objective was to evaluate if and in what way women are included in the statutory guidelines. By means of the document analysis technique, we analyzed the statutes of political parties represented in the Chamber of Deputies in the case of Brazil and the Assembly of the Republic in the case of Portugal. Our research hypothesis is that although the explanatory potential of party ideology has declined as political parties from different positions on the spectrum have started to adopt discourses in favor of women’s political participation, left-wing parties remain more inclusive in their texts. We could observe that in both countries, leftist parties remain the main encouragers of women’s political participation, at least in their statutory rules.info:eu-repo/semantics/publishedVersio
Quasivariational solutions for first order quasilinear equations with gradient constraint
We prove the existence of solutions for an evolution quasi-variational
inequality with a first order quasilinear operator and a variable convex set,
which is characterized by a constraint on the absolute value of the gradient
that depends on the solution itself. The only required assumption on the
nonlinearity of this constraint is its continuity and positivity. The method
relies on an appropriate parabolic regularization and suitable {\em a priori}
estimates. We obtain also the existence of stationary solutions, by studying
the asymptotic behaviour in time. In the variational case, corresponding to a
constraint independent of the solution, we also give uniqueness results
Gauge Theories with Lorentz-Symmetry Violation by Symplectic Projector Method
The violation of Lorentz symmetry is studied from the point of view of a
canonical formulation. We make the usual analysis on the constraints structure
of the Carroll-Field-Jackiw model. In this context we derive the equations of
motion for the physical variables and check out the dispersion relations
obtained from them. Therefore, by the analysis using Symplectic Projector
Method (SPM), we can check the results about this type of Lorentz breaking with
those in the recent literature: in this sense we can confirm that the
configuration of space-like is stable, and the time-like
carry tachionic modes.Comment: 7 pages and no figure
Continuous optical loading of a Bose-Einstein Condensate
The continuous pumping of atoms into a Bose-Einstein condensate via
spontaneous emission from a thermal reservoir is analyzed. We consider the case
of atoms with a three-level scheme, in which one of the atomic
transitions has a very much shorter life-time than the other one. We found that
in such scenario the photon reabsorption in dense clouds can be considered
negligible. If in addition inelastic processes can be neglected, we find that
optical pumping can be used to continuously load and refill Bose-Einstein
condensates, i.e. provides a possible way to achieve a continuous atom laser.Comment: 12 pages, 8 figure
The Mass of the Convective Zone in FGK Main Sequence Stars and the Effect of Accreted Planetary Material on Apparent Metallicity Determinations
The mass of the outer convective zone in FGK main sequence stars decreases
dramatically with stellar mass. Therefore, any contamination of a star's
atmosphere by accreted planetary material should affect hotter stars much more
than cool stars. If recent suggestions that high metal abundances in stars with
planets are caused by planetesimal accretion are correct, then metallicity
enhancements in earlier-type stars with planets should be very pronounced. No
such trend is seen, however.Comment: Submitted ApJ Letters March 26th; accepted April 30th. 12 pages, 2
figure
The CORALIE survey for southern extra-solar planets. X. A Hot Jupiter orbiting HD73256
Recent radial-velocity measurements obtained with the CORALIE spectrograph on
the 1.2-m Euler Swiss telescope at La Silla unveil the presence of a new
Jovian-mass Hot Jupiter around HD 73256. The 1.85-M_Jup planet moves on an
extremely short-period (P=2.5486 d), quasi-circular orbit. The best Keplerian
orbital solution is presented together with an unsuccessful photometric
planetary-transit search performed with the SAT Danish telescope at La Silla.
Over the time span of the observations, the photometric follow-up of the
candidate has nevertheless revealed a P=14-d photometric periodicity
corresponding to the rotational period of the star. This variation as well as
the radial-velocity jitter around the Keplerian solution are shown to be
related to the fair activity level known for HD 73256.Comment: 7 pages, 7 figures. Accepted in A&
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