897 research outputs found

### Bose-Fermi mixtures in the molecular limit

We consider a Bose-Fermi mixture in the molecular limit of the attractive
interaction between fermions and bosons. For a boson density smaller or equal
to the fermion density, we show analytically how a T-matrix approach for the
constituent bosons and fermions recovers the expected physical limit of a
Fermi-Fermi mixture of molecules and atoms. In this limit, we derive simple
expressions for the self-energies, the momentum distribution function, and the
chemical potentials. By extending these equations to a trapped system, we
determine how to tailor the experimental parameters of a Bose-Fermi mixture in
order to enhance the 'indirect Pauli exclusion effect' on the boson momentum
distribution function. For the homogeneous system, we present finally a
Diffusion Monte Carlo simulation which confirms the occurrence of such a
peculiar effect.Comment: 13 pages, 7 figures; final versio

### Quantum Monte Carlo Study of a Resonant Bose-Fermi Mixture

We study a resonant Bose-Fermi mixture at zero temperature by using the
fixed-node diffusion Monte Carlo method. We explore the system from weak to
strong boson-fermion interaction, for different concentrations of the bosons
relative to the fermion component. We focus on the case where the boson density
$n_B$ is smaller than the fermion density $n_F$, for which a first-order
quantum phase transition is found from a state with condensed bosons immersed
in a Fermi sea, to a Fermi-Fermi mixture of composite fermions and unpaired
fermions. We obtain the equation of state and the phase diagram, and we find
that the region of phase separation shrinks to zero for vanishing $n_B$.Comment: 5 pages, 3 figures, published versio

### Polaronic features in the optical properties of the Holstein-t-J model

We derive the exact solution for the optical conductivity $\sigma(\omega)$ of
one hole in the Holstein-t-J model in the framework of dynamical mean-field
theory (DMFT). We investigate the magnetic and phonon features associated with
polaron formation as a function of the exchange coupling $J$, of the
electron-phonon interaction $\lambda$ and of the temperature. Our solution
directly relates the features of the optical conductivity to the excitations in
the single-particle spectral function, revealing two distinct mechanisms of
closing and filling of the optical pseudogap that take place upon varying the
microscopic parameters. We show that the optical absorption at the polaron
crossover is characterized by a coexistence of a magnon peak at low frequency
and a broad polaronic band at higher frequency. An analytical expression for
$\sigma(\omega)$ valid in the polaronic regime is presented.Comment: improved version, as submitted to Phys. Rev.

### Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen

We study the total cross section and angular distribution in Rayleigh
scattering by hydrogen atom in the ground state, within the framework of Dirac
relativistic equation and second-order perturbation theory. The relativistic
states used for the calculations are obtained by making use of the finite basis
set method and expressed in terms of B-splines and B-polynomials. We pay
particular attention to the effects that arise from higher (non-dipole) terms
in the expansion of the electron-photon interaction. It is shown that the
angular distribution of scattered photons, while it is symmetric with respect
to the scattering angle $\theta$=90$^\circ$ within the electric dipole
approximation, becomes asymmetric when higher multipoles are taken into
account. The analytical expression of the angular distribution is parametrized
in terms of Legendre polynomials. Detailed calculations are performed for
photons in the energy range 0.5 to 10 keV. When possible, results are compared
with previous calculations.Comment: 8 pages, 5 figure

### Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen

A relativistic analysis of the polarization properties of light elastically
scattered by atomic hydrogen is performed, based on the Dirac equation and
second order perturbation theory. The relativistic atomic states used for the
calculations are obtained by making use of the finite basis set method and
expressed in terms of $B$ splines and $B$ polynomials. We introduce two
experimental scenarios in which the light is circularly and linearly polarized,
respectively. For each of these scenarios, the polarization-dependent angular
distribution and the degrees of circular and linear polarization of the
scattered light are investigated as a function of scattering angle and photon
energy. Analytical expressions are derived for the polarization-dependent
angular distribution which can be used for scattering by both hydrogenic as
well as many-electron systems. Detailed computations are performed for Rayleigh
scattering by atomic hydrogen within the incident photon energy range 0.5 to 10
keV. Particular attention is paid to the effects that arise from higher
(nondipole) terms in the expansion of the electron-photon interaction.Comment: 8 pages, 5 figure

### A Fabry-Perot interferometer with quantum mirrors: nonlinear light transport and rectification

Optical transport represents a natural route towards fast communications, and
it is currently used in large scale data transfer. The progressive
miniaturization of devices for information processing calls for the microscopic
tailoring of light transport and confinement at length scales appropriate for
the upcoming technologies. With this goal in mind, we present a theoretical
analysis of a one-dimensional Fabry-Perot interferometer built with two highly
saturable nonlinear mirrors: a pair of two-level systems. Our approach captures
non-linear and non-reciprocal effects of light transport that were not reported
previously. Remarkably, we show that such an elementary device can operate as a
microscopic integrated optical rectifier

### Isotope effect on the E2g phonon and mesoscopic phase separation near the electronic topological transition in Mg1-xAlxB2

We report the boron isotope effect on the E2g phonon mode by micro-Raman
spectroscopy on the ternary Mg1-xAlxB2 system, synthesized with pure isotopes
10B and 11B. The isotope coefficient on the phonon frequency is near 0.5 in the
full range decreasing near x = 0. The intraband electron-phonon (e-ph)
coupling, for the electrons in the sigma band, has been extracted from the E2g
line-width and frequency softening. Tuning the Fermi energy near the electronic
topological transition (ETT), where the sigma Fermi surface changes from 2D to
3D topology the E2g mode, shows the known Kohn anomaly on the 2D side of the
ETT and a splitting of the E2g phonon frequency into a hard and soft component
from x = 0 to x = 0.28. The results suggest a minor role of the intraband
phonon mediated pairing in the control of the high critical temperature in
Mg1-xAlxB2. The common physical features of diborides with the novel multigap
FeAs-based superconductors and cuprates is discussed.Comment: 19 pages, 6 figure

### A numerical approach for the modelling of forming limits in hot incremental forming of AZ31 magnesium alloy

Magnesium alloys, because of their good specific material strength, can be considered attractive by different industry fields, as the aerospace and the automotive one. However, their use is limited by the poor formability at room temperature. In this research, a numerical approach is proposed in order to determine an analytical expression of material formability in hot incremental forming processes. The numerical model was developed using the commercial software ABAQUS/Explicit. The Johnson-Cook material model was used, and the model was validated through experimental measurements carried out using the ARAMIS system. Different geometries were considered with temperature varying in a range of 25â€“400 Â°C and wall angle in a range of 35â€“60Â°. An analytical expression of the fracture forming limit, as a function of temperature, was established and finally tested with a different geometry in order to assess the validity

### Preliminary evaluation of in vitro bacteriostatic and bactericidal effect of salt on leptospira spp

Environmental resistance is an important factor for understanding the epidemiology of leptospirosis. Recently, new Leptospira hosts were identified, including also marine mammals. Moreover, halotolerant Leptospira strain, isolated from the environment and animals, highlighted the capability of this microorganism to persist in the seawater. The aim of this research was to investigate the bacteriostatic and bactericidal effect of salt on Leptospira strains belonging to 16 different serovars. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were verified through the microdilutions method starting from a 20% sodium chloride concentration. MIC values obtained were between 0.3125% and 10% of salt, while MBC values between 0.625% and >20%. Icterohaemorrhagiae (MIC: 0.3125%; MBC: 0.625%) resulted the most inhibited serovar, while the most resistant was Tarassovi (MIC: 10%; MBC: >20%). Interestingly, trends were reported for Pomona (MIC: 1.25%; MBC: >20%) and Bratislava (MIC: 0.625%; MBC: 20%), highlighting low MIC values but high MBC values. This is the first investigation aimed at the in vitro effect of salt on the growth of Leptospira spp. reference strains

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