6,494 research outputs found
Comment on "On the ionization equilibrium of hot hydrogen plasma and thermodynamic consistency of formulating finite partition functions"
Zaghloul [Phys. Plasmas 17, 062701 (2010); arXiv:1010.1161v1] reconsiders the
occupation probability formalism in plasma thermodynamics and claims
inconsistencies in previous models. I show that the origin of this incorrect
claim is an omission of the configurational factor from the partition function.
This arXiv version is supplemented with two appendices, where I add remarks and
comments on two more recent publications of the same author on the same
subject: on his response to this Comment [Phys. Plasmas 17, 124705 (2010)] and
on his criticism towards the Hummer and Mihalas's (1988) formalism [Phys.
Plasmas 17, 122903 (2010); arXiv:1010.1102v1].Comment: 4 pages: 2 pages of the journal publication + 2 pages of the
electronic supplemen
Analysis of pion elliptic flows and HBT interferometry in a granular quark-gluon plasma droplet model
In many simulations of high-energy heavy-ion collisions on an event-by-event
analysis, it is known that the initial energy density distribution in the
transverse plane is highly fluctuating. Subsequent longitudinal expansion will
lead to many longitudinal tubes of quark-gluon plasma which have tendencies to
break up into many spherical droplets because of sausage instabilities. We are
therefore motivated to use a model of quark-gluon plasma granular droplets that
evolve hydrodynamically to investigate pion elliptic flows and
Hanbury-Brown-Twiss interferometry. We find that the data of pion transverse
momentum spectra, elliptic flows, and HBT radii in \sqrt{s_{NN}}=200 GeV Au +
Au collisions at RHIC can be described well by an expanding source of granular
droplets with an anisotropic velocity distribution.Comment: 9 pages, 6 figures, in Late
Superfluid pairing in a mixture of a spin-polarized Fermi gas and a dipolar condensate
We consider a mixture of a spin-polarized Fermi gas and a dipolar
Bose-Einstein condensate in which s-wave scattering between fermions and the
quasiparticles of the dipolar condensate can result in an effective attractive
Fermi-Fermi interaction anisotropic in nature and tunable by the dipolar
interaction. We show that such an interaction can significantly increase the
prospect of realizing a superfluid with a gap parameter characterized with a
coherent superposition of all odd partial waves. We formulate, in the spirit of
the Hartree-Fock-Bogoliubov mean-field approach, a theory which allows us to
estimate the critical temperature when the anisotropic Fock potential is taken
into consideration and to determine the system parameters that optimize the
critical temperature at which such a superfluid emerges before the system
begins to phase separate.Comment: 10 pages, 3 figure
Singlet and Triplet Superfluid Competition in a Mixture of Two-Component Fermi and One-Component Dipolar Bose Gases
We consider a mixture of two-component Fermi and (one-component) dipolar Bose
gases in which both dipolar interaction and s-wave scattering between fermions
of opposite spins are tunable. We show that in the long wavelength limit, the
anisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar
condensate can strongly enhance the scattering in the triplet channel. We
investigate in detail the conditions for achieving optimal critical temperature
at which the triplet superfluid begins to compete with the singlet superfluid.Comment: 5 pages, 2 figure
Quarkonia and Quark Drip Lines in Quark-Gluon Plasma
We extract the - potential by using the thermodynamic quantities
obtained in lattice gauge calculations. The potential is tested and found to
give dissociation temperatures that agree well with those from lattice gauge
spectral function analysis. Using such a - potential, we examine the
quarkonium states in a quark-gluon plasma and determine the `quark drip lines'
which separate the region of bound color-singlet states from the
unbound region. The characteristics of the quark drip lines severely limit the
region of possible bound states with light quarks to temperatures
close to the phase transition temperature. Bound quarkonia with light quarks
may exist very near the phase transition temperature if their effective quark
mass is of the order of 300-400 MeV and higher.Comment: 24 pages, 13 figures, in LaTe
Many-body effects on adiabatic passage through Feshbach resonances
We theoretically study the dynamics of an adiabatic sweep through a Feshbach
resonance, thereby converting a degenerate quantum gas of fermionic atoms into
a degenerate quantum gas of bosonic dimers. Our analysis relies on a zero
temperature mean-field theory which accurately accounts for initial molecular
quantum fluctuations, triggering the association process. The structure of the
resulting semiclassical phase space is investigated, highlighting the dynamical
instability of the system towards association, for sufficiently small detuning
from resonance. It is shown that this instability significantly modifies the
finite-rate efficiency of the sweep, transforming the single-pair exponential
Landau-Zener behavior of the remnant fraction of atoms Gamma on sweep rate
alpha, into a power-law dependence as the number of atoms increases. The
obtained nonadiabaticity is determined from the interplay of characteristic
time scales for the motion of adiabatic eigenstates and for fast periodic
motion around them. Critical slowing-down of these precessions near the
instability leads to the power-law dependence. A linear power law is obtained when the initial molecular fraction is smaller than the 1/N
quantum fluctuations, and a cubic-root power law is
attained when it is larger. Our mean-field analysis is confirmed by exact
calculations, using Fock-space expansions. Finally, we fit experimental low
temperature Feshbach sweep data with a power-law dependence. While the
agreement with the experimental data is well within experimental error bars,
similar accuracy can be obtained with an exponential fit, making additional
data highly desirable.Comment: 9 pages, 9 figure
Casimir-like force arising from quantum fluctuations in a slow-moving dilute Bose-Einstein condensate
We calculate a force due to zero-temperature quantum fluctuations on a
stationary object in a moving superfluid flow. We model the object by a
localized potential varying only in the flow direction and model the flow by a
three-dimensional weakly interacting Bose-Einstein condensate at zero
temperature. We show that this force exists for any arbitrarily small flow
velocity and discuss the implications for the stability of superfluid flow.Comment: v3: revised discussion of toroidal geometry; replotted figure; minor
editorial changes; quantitative and qualitative conclusions remain unchange
Electrically driven magnetism on a Pd thin film
Using first-principles density functional calculations we demonstrate that
ferromagnetism can be induced and modulated on an otherwise paramagnetic Pd
metal thin-film surface through application of an external electric field. As
free charges are either accumulated or depleted at the Pd surface to screen the
applied electric field there is a corresponding change in the surface density
of states. This change can be made sufficient for the Fermi-level density of
states to satisfy the Stoner criterion, driving a transition locally at the
surface from a paramagnetic state to an itinerant ferromagnetic state above a
critical applied electric field, Ec. Furthermore, due to the second-order
nature of this transition, the surface magnetization of the ferromagnetic state
just above the transition exhibits a substantial dependence on electric field,
as the result of an enhanced magnetoelectric susceptibility. Using a linearized
Stoner model we explain the occurrence of the itinerant ferromagnetism and
demonstrate that the magnetic moment on the Pd surface follows a square-root
variation with electric field consistent with our first-principles
calculations.Comment: 8 pages, 7 figure
Fluctuations in the presence of fields -Phenomenological Gaussian approximation and a new class of thermodynamic inequalities-
The work approaches the study of the fluctuations for the thermodynamic
systems in the presence of the fields. The approach is of phenomenological
nature and developed in a Gaussian approximation. The study is exemplified on
the cases of a magnetizable continuum in a magnetoquasistatic field, as well as
for the so called discrete systems. In the last case one finds that the
fluctuations estimators depends both on the intrinsic properties of the system
and on the characteristics of the environment. Following some earlier ideas of
one of the authors we present a new class of thermodynamic inequalities for the
systems investigated in this paper. In the case of two variables the mentioned
inequalities are nothing but non-quantum analogues of the well known quantum
Heisenberg (''uncertainty'') relations. Also the obtained fluctuations
estimators support the idea that the Boltzmann's constant k has the
signification of a generic indicator of stochasticity for thermodynamic
systems.
Pacs number(s): 05.20.-y, 05.40.-a, 05.70.-a, 41.20.GzComment: preprint, 24 page
Mapping between Hamiltonians with attractive and repulsive potentials on a lattice
Through a simple and exact analytical derivation, we show that for a particle
on a lattice, there is a one-to-one correspondence between the spectra in the
presence of an attractive potential and its repulsive counterpart
. For a Hermitian potential, this result implies that the number of
localized states is the same in both, attractive and repulsive, cases although
these states occur above (below) the band-continnum for the repulsive
(attractive) case. For a \mP\mT-symmetric potential that is odd under parity,
our result implies that in the \mP\mT-unbroken phase, the energy eigenvalues
are symmetric around zero, and that the corresponding eigenfunctions are
closely related to each other.Comment: 6 pages, 1 figur
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