576 research outputs found
Density of a gas of spin polarized fermions in a magnetic field
For a fermion gas with equally spaced energy levels that is subjected to a
magnetic field, the particle density is calculated. The derivation is based on
the path integral approach for identical particles, in combination with the
inversion techniques for the generating function of the static response
functions. Explicit results are presented for the ground state density as a
function of the magnetic field with a number of particles ranging from 1 to 45.Comment: 9 pages, 8 figures; To appear in Phys. Rev. E on December 1, 2000;
e-mail addresses: [email protected], [email protected],
[email protected], [email protected]
RPAE versus RPA for the Tomonaga model with quadratic energy dispersion
Recently the damping of the collective charge (and spin) modes of interacting
fermions in one spatial dimension was studied. It results from the nonlinear
correction to the energy dispersion in the vicinity of the Fermi points. To
investigate the damping one has to replace the random phase approximation (RPA)
bare bubble by a sum of more complicated diagrams. It is shown here that a
better starting point than the bare RPA is to use the (conserving) linearized
time dependent Hartree-Fock equations, i.e. to perform a random phase
approximation (with) exchange
(RPAE) calculation. It is shown that the RPAE equation can be solved
analytically for the special form of the two-body interaction often used in the
Luttinger liquid framework. While (bare) RPA and RPAE agree for the case of a
strictly linear disperson there are qualitative differences for the case of the
usual nonrelativistic quadratic dispersion.Comment: 6 pages, 3 figures, misprints corrected; to appear in PRB7
Inhibition of spontaneous emission in Fermi gases
Fermi inhibition is a quantum statistical analogue for the inhibition of
spontaneous emission by an excited atom in a cavity. This is achieved when the
relevant motional states are already occupied by a cloud of cold atoms in the
internal ground state. We exhibit non-trivial effects at finite temperature and
in anisotropic traps, and briefly consider a possible experimental realization.Comment: 4 pages with 3 figure
Transvaginal endoscopy and small ovarian endometriomas: unravelling the missing link?
The incidence of endometriosis in the infertile female is estimated to be between 20 and 50Â %. Although the causal relationship between endometriosis and infertility has not been proven, it is generally accepted that the disease impairs reproductive outcome. Indirect imaging techniques and transvaginal laparoscopy now offer the possibility of an early stage diagnosis. Although it remains debated whether the disease is progressive, treatment in an early stage is recommendable as it carries less risk for ovarian damage, hence premature ovarian failure. Under water, inspection with the technique of transvaginal hydrolaparoscopy (THL) accurately shows the invagination of the ovarian cortex as minimal superficial lesions but with the presence of well-differentiated endometrial like tissue at the base, the lateral walls and especially the inner edges of the small endometrioma. An inflammatory environment is responsible for the formation of connecting adhesions with the broad ligament and lateral wall with invasion of endometrial-like tissue and formation of adenomyotic lesions. In around 50Â % of the small endometriomas, adhesiolysis is necessary at the site of invagination with opening of the cyst, to free the chocolate content and hereby recognize the underlying endometrioma. The detailed inspection of these early-stage endometriotic lesions at THL reunites the hypothesis of Sampson with the observation of Hughesdon
Bipolaron Binding in Quantum Wires
A theory of bipolaron states in quantum wires with a parabolic potential well
is developed applying the Feynman variational principle. The basic parameters
of the bipolaron ground state (the binding energy, the number of phonons in the
bipolaron cloud, the effective mass, and the bipolaron radius) are studied as a
function of sizes of the potential well. Two cases are considered in detail: a
cylindrical quantum wire and a planar quantum wire. Analytical expressions for
the bipolaron parameters are obtained at large and small sizes of the quantum
well. It is shown that at [where means the radius (halfwidth) of a
cylindrical (planar) quantum wire, expressed in Feynman units], the influence
of confinement on the bipolaron binding energy is described by the function
for both cases, while at small sizes this influence is different
in each case. In quantum wires, the bipolaron binding energy increases
logarithmically with decreasing radius. The shapes and the sizes of a
nanostructure, which are favorable for observation of stable bipolaron states,
are determined.Comment: 17 pages, 6 figures, E-mail addresses: [email protected];
[email protected]
Condensation and interaction range in harmonic boson traps: a variational approach
For a gas of N bosons interacting through a two-body Morse potential a
variational bound of the free energy of a confined system is obtained. The
calculation method is based on the Feynman-Kac functional projected on the
symmetric representation. Within the harmonic approximation a variational
estimate of the effect of the interaction range on the existence of
many-particle bound states, and on the N-T phase diagram is obtained.Comment: 14 pages+4 figures, submitted to phys.rev.
Is adenomyosis the neglected phenotype of an endomyometrial dysfunction syndrome?
Since the dissociation between adenomyoma and endometriosis in the 1920s and the laparoscopic progress in the diagnosis and surgery of endometriosis, the literature has been greatly focused on the disease endometriosis. The study of adenomyosis, on the other hand, has been neglected as the diagnosis remained based on hysterectomy specimens. However, since the introduction of magnetic resonance and sonographic imaging techniques in the 1980s, the myometrial junctional zone has been identified as a third uterine zone and interest in adenomyosis was renewed. This has also been the start for the interest in the role of the myometrial junctional zone dysfunction and adenomyosis in reproductive and obstetrical disorders
Ground state and optical conductivity of interacting polarons in a quantum dot
The ground-state energy, the addition energies and the optical absorption
spectra are derived for interacting polarons in parabolic quantum dots in three
and two dimensions. A path integral formalism for identical particles is used
in order to take into account the fermion statistics. The approach is applied
to both closed-shell and open-shell systems of interacting polarons. Using a
generalization of the Jensen-Feynman variational principle, the ground-state
energy of a confined N-polaron system is analyzed as a function of N and of the
electron-phonon coupling constant. As distinct from the few-electron systems
without the electron-phonon interaction, three types of spin polarization are
possible for the ground state of the few-polaron systems: (i) a spin-polarized
state, (ii) a state where the spin is determined by Hund's rule, (iii) a state
with the minimal possible spin. A transition from a state fulfilling Hund's
rule, to a spin-polarized state occurs when decreasing the electron density. In
the strong-coupling limit, the system of interacting polarons turns into a
state with the minimal possible spin. These transitions should be
experimentally observable in the optical absorption spectra of quantum dots.Comment: 33 pages, 9 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected],
accepted for Phys. Rev.
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