692 research outputs found
Incipient quantum melting of the one-dimensional Wigner lattice
A one--dimensional tight--binding model of electrons with long--range Coulomb
interactions is studied in the limit where double site occupancy is forbidden
and the Coulomb coupling strength is large with respect to the hopping
amplitude . The quantum problem of a kink--antikink pair generated in the
Wigner lattice (the classical ground state for ) is solved for fillings
, where is an integer larger than 1. The pair energy becomes
negative for a relatively high value of , . This signals
the initial stage of the quantum melting of the Wigner lattice
Variational Wave Function for Generalized Wigner Lattices in One Dimension
We study a system of electrons on a one-dimensional lattice, interacting
through the long range Coulomb forces, by means of a variational technique
which is the strong coupling analog of the Gutzwiller approach. The problem is
thus the quantum version of Hubbard's classical model of the generalized Wigner
crystal [J. Hubbard, Phys. Rev. B 17, 494 (1978)]. The magnetic exchange energy
arising from quantum fluctuations is calculated, and turns out to be smaller
than the energy scale governing charge degrees of freedom. This approach could
be relevant in insulating quasi-one-dimensional compounds where the long range
Coulomb interactions are not screened. In these compounds charge order often
appears at high temperatures and coexists with magnetic order at low
temperatures.Comment: 4 pages, proceedings of ECRYS-200
Polaron Crystallization and Melting: Effects of the Long-Range Coulomb Forces
On examining the stability of a Wigner crystal in an ionic dielectric, two
competitive effects due to the polaron formation are found to be important: (i)
the screening of the Coulomb force, which destabilizes the crystal, compensated
by (ii) the increase of the carrier mass (polaron mass). The competition
between the two effects is carefully studied, and the quantum melting of the
polaronic Wigner crystal is examined by varying the density at zero
temperature. By calculating the quantum fluctuations of both the electron and
the polarization, we show that there is a competition between the dissociation
of the polarons at the insulator-to-metal transition (IMT), and a melting
towards a polaron liquid. We find that at strong coupling, a liquid state of
dielectric polarons cannot exist, and the IMT is driven by the polaron
dissociation. Next, taking into account the dipolar interactions between
localized carriers, we show that these are responsible for an instability of
the transverse vibrational modes of the polaronic Wigner crystal as the density
increases. This provides a new mechanism for the IMT in doped dielectrics,
which yields interesting dielectric properties below and beyond the transition.
An optical signature of such a mechanism for the IMT is provided.Comment: 10 pages, 3 figures, to be published in Int.J.Mod.Phys.
Analytical evaluation of atomic form factors: application to Rayleigh scattering
Atomic form factors are widely used for the characterization of targets and
specimens, from crystallography to biology. By using recent mathematical
results, here we derive an analytical expression for the atomic form factor
within the independent particle model constructed from nonrelativistic screened
hydrogenic wavefunctions. The range of validity of this analytical expression
is checked by comparing the analytically obtained form factors with the ones
obtained within the Hartee-Fock method. As an example, we apply our analytical
expression for the atomic form factor to evaluate the differential cross
section for Rayleigh scattering off neutral atoms.Comment: 7 pages, 1 figur
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 =90 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
TUTELA CAUTELARE ATIPICA E CRISI DELLA FAMIGLIA
ATYPICAL INJUNCTION AND FAMILY CRISES
This thesis deals with the application of atypical injunction in cases of family crises, including both married couples and families not founded on marriage. After giving a synthetic framework of Italian atypical injunction, a focus is made on the large variety of typical provisions ruled by our civil system, as a result of the stratification of laws existing, regarding the family.
Atypical injunction is then compared with the other measures regulating the rights of married couples, in order to establish whether the obtaining of an atypical injunction in such a field is permitted.
To follow, a brief mention is made of the recent law (D.l. 132/2014, converted into Law 162/2014) regulating a new proceeding (\u201cassisted negotiation\u201d), which is now an alternative to separation and divorce proceedings and takes place solely with the assistance of lawyers, without court participation.
The second part of this document is dedicated to unmarried couples; it examines some of the numerous questions of interpretation created by the latest rules (Law 219/2012 and Law 154/2013) regarding children born out of wedlock.
The main body of the thesis analyzes the compatibility between an atypical injunction and the \u201ctemporary and urgent provisions\u201d given during separation and divorce proceedings, leading to a discussion on the possibility of obtaining an urgent injunction after the settlement of a separation or divorce sentence.
The thesis concludes with a brief examination of the very recent (and it is to be hoped much less fragmentary and incomplete than laws effective until now) project of reform, regarding the efficiency of our system of law
Local structure of REFeAsO (RE=La, Pr, Nd, Sm) oxypnictides studied by Fe K-edge EXAFS
Local structure of REOFeAs (RE=La, Pr, Nd, Sm) system has been studied as a
function of chemical pressure varied due to different rare-earth size. Fe
K-edge extended X-ray absorption fine structure (EXAFS) measurements in the
fluorescence mode has permitted to compare systematically the inter-atomic
distances and their mean square relative displacements (MSRD). We find that the
Fe-As bond length and the corresponding MSRD hardly show any change, suggesting
the strongly covalent nature of this bond, while the Fe-Fe and Fe-RE bond
lengths decrease with decreasing rare earth size. The results provide important
information on the atomic correlations that could have direct implication on
the superconductivity and magnetism of REOFeAs system, with the chemical
pressure being a key ingredient
Effect of Ru susbstitution on atomic displacements in the layered SmFe_{1-x}Ru_xAsO_{0.85}F_{0.15} superconductor
The effect of Ru substitution on the local structure of layered
SmFeRuAsOF superconductor has been studied by As
- and Sm - edges x-ray-absorption spectroscopy. The extended
x-ray-absorption fine-structure measurements reveal distinct Fe-As and Ru-As
bondlengths in the Ru substituted samples with the latter being 0.03 \AA\
longer. Local disorder induced by the Ru substitution is mainly confined to the
FeAs layer while the SmO spacer layer sustains a relative order, consistent
with the x-ray-absorption near-edge structure spectra. The results suggest
that, in addition to the order/disorder in the active active iron-arsenide
layer, its coupling to the rare-earth\textminus oxygen spacer layer needs to be
considered for describing the electronic properties of these layered
superconductors
Listeria monocytogenes contamination of Tenebrio molitor larvae rearing substrate: Preliminary evaluations
Today, edible insects represent a hot topic as an emerging and eco-friendly source of protein. The mealworm (Tenebrio molitor L.) is among the most employed insects for human consumption and feed purposes. So far Listeria monocytogenes, have never been detected either in products sold on the market or during the rearing process. In this study, the substrate employed for mealworm rearing was deliberately contaminated with L. monocytogenes and the bacterium was enumerated during the rearing period and after technological treatments of the larvae. L. monocytogenes persisted during the rearing period. Washing the larvae did not produce any significant effect, while fasting the larvae for 24 or 48 h reduced the L. monocytogenes load (P < 0.001). Oven cooking eliminated L. monocytogenes cells from the product, reducing the risk associated to this foodborne pathogen to zero
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