1,065 research outputs found
Spectral density method in quantum nonextensive thermostatistics and magnetic systems with long-range interactions
Motived by the necessity of explicit and reliable calculations, as a valid
contribution to clarify the effectiveness and, possibly, the limits of the
Tsallis thermostatistics, we formulate the Two-Time Green Functions Method in
nonextensive quantum statistical mechanics within the optimal Lagrange
multiplier framework, focusing on the basic ingredients of the related Spectral
Density Method. Besides, to show how the SDM works we have performed, to the
lowest order of approximation, explicit calculations of the low-temperature
properties for a quantum -dimensional spin-1/2 Heisenberg ferromagnet with
long-range interactions decaying as ( is the distance between
spins in the lattice)Comment: Contribution to Next-SigmaPhi conference in Kolymbari, Crete, Greece,
August 13-18, 2005, 9 page
Two-time Green's functions and spectral density method in nonextensive quantum statistical mechanics
We extend the formalism of the thermodynamic two-time Green's functions to
nonextensive quantum statistical mechanics. Working in the optimal Lagrangian
multipliers representation, the -spectral properties and the methods for a
direct calculation of the two-time % -Green's functions and the related
-spectral density ( measures the nonextensivity degree) for two generic
operators are presented in strict analogy with the extensive ()
counterpart. Some emphasis is devoted to the nonextensive version of the less
known spectral density method whose effectiveness in exploring equilibrium and
transport properties of a wide variety of systems has been well established in
conventional classical and quantum many-body physics. To check how both the
equations of motion and the spectral density methods work to study the
-induced nonextensivity effects in nontrivial many-body problems, we focus
on the equilibrium properties of a second-quantized model for a high-density
Bose gas with strong attraction between particles for which exact results exist
in extensive conditions. Remarkably, the contributions to several thermodynamic
quantities of the -induced nonextensivity close to the extensive regime are
explicitly calculated in the low-temperature regime by overcoming the
calculation of the grand-partition function.Comment: 48 pages, no figure
The Classical Spectral Density Method at Work: The Heisenberg Ferromagnet
In this article we review a less known unperturbative and powerful many-body
method in the framework of classical statistical mechanics and then we show how
it works by means of explicit calculations for a nontrivial classical model.
The formalism of two-time Green functions in classical statistical mechanics is
presented in a form parallel to the well known quantum counterpart, focusing on
the spectral properties which involve the important concept of spectral
density. Furthermore, the general ingredients of the classical spectral density
method (CSDM) are presented with insights for systematic nonperturbative
approximations to study conveniently the macroscopic properties of a wide
variety of classical many-body systems also involving phase transitions. The
method is implemented by means of key ideas for exploring the spectrum of
elementary excitations and the damping effects within a unified formalism.
Then, the effectiveness of the CSDM is tested with explicit calculations for
the classical -dimensional spin- Heisenberg ferromagnetic model with
long-range exchange interactions decaying as () with distance
between spins and in the presence of an external magnetic field. The analysis
of the thermodynamic and critical properties, performed by means of the CSDM to
the lowest order of approximation, shows clearly that nontrivial results can be
obtained in a relatively simple manner already to this lower stage. The basic
spectral density equations for the next higher order level are also presented
and the damping of elementary spin excitations in the low temperature regime is
studied. The results appear in reasonable agreement with available exact ones
and Monte Carlo simulations and this supports the CSDM as a promising method of
investigation in classical many-body theory.Comment: Latex, 58 pages, 12 figure
A SspI PCR-RFLP detecting a silent allele at the goat CSN2 locus
The comparison between the cDNA sequence obtained
and the published sequences of the goat CSN2 alleles
showed a new single nucleotide polymorphism (SNP)
(transition C-T) at the 180th nucleotide of the ninth exon.
This mutation, which took place at 124 nt from the
polyadenylation site, identifies a silent allele at the CSN2
locus named CSN2 A1.
Since the 9th exon C-T transition creates a SspI
endonuclease restriction site, the SspI digestion
of a PCR product of 360 bp spanning the 9th exon and
flanking regions, would allow carriers for the presence of
thymine to be identified.
The allelic frequency of the CSN2 A1 allele, determined
in 170 goats belonging to an undefined genetic type reared
in the province of Naples (Italy), was 0.23
It has been observed that the sequences
in the 3’ untranslated regions (UTR), proximal to the
polyadenylation site, can affect the mechanism of mRNA
deadenylation and degradation. Therefore, it is reasonable
to hypothesize that the C-T transition might, directly or
indirectly, influence the stability of the mRNA and,
consequently, the amount of protein produced
Emergence and persistence of communities in coevolutionary networks
We investigate the emergence and persistence of communities through a
recently proposed mechanism of adaptive rewiring in coevolutionary networks. We
characterize the topological structures arising in a coevolutionary network
subject to an adaptive rewiring process and a node dynamics given by a simple
voterlike rule. We find that, for some values of the parameters describing the
adaptive rewiring process, a community structure emerges on a connected
network. We show that the emergence of communities is associated to a decrease
in the number of active links in the system, i.e. links that connect two nodes
in different states. The lifetime of the community structure state scales
exponentially with the size of the system. Additionally, we find that a small
noise in the node dynamics can sustain a diversity of states and a community
structure in time in a finite size system. Thus, large system size and/or local
noise can explain the persistence of communities and diversity in many real
systems.Comment: 6 pages, 5 figures, Accepted in EPL (2014
Genetic polymorphism of goat CSN1S1 and CSN1S2 genes and their impact on milk composition
by means of selection based on parent genotyping at the DNA level it will be possible to obtain goat populations producing milk characterised by the absence of either as1-casein, or s2-casein or -casein. Such milk could be useful for specific technological processes of transformation or for specific nutritional or dietary purposes in order to attenuate the negative consequence of some metabolic deficiencies and allergies and to contribute to the prevention of some diseases
Considering the remarkable quantitative polymorphism characterizing the main protein fractions encoding gene, some goat milk types are more similar to the woman milk and, therefore, could be used, with better results, in the human feeding. In fact, the woman milk possess particular characteristics. It is lacking in the -lactoglobulin fraction and it is characterized by a general low content in casein, in particular, as2 casein absence and as1 casein traces, similar to the milk produced by goats with genotype CSN1S2 0/0
Increasing rate of hospitalizations for food-induced anaphylaxis in Italian children: an analysis of the Italian Ministry of Health database.
emerged regarding other day-to-day issues. Physicians were
overall misinformed about the availability of epinephrine in
both restaurants and ambulances. When questioned regarding
quality of life, only 10% of family practitioners and 31% of
pediatricians believed that ‘‘severe allergies’’ have a major impact
on quality of life. This differs markedly from results of previous
studies about patients’ perceptions regarding the effects of food
allergy on quality of life.10 More pediatric A/I specialists (78%)
than others (P 5 .03) believed that life-threatening
allergic reactions today are more common than 10 years
ago, consistent with published data,11 and most physicians in
all groups recognized that asthma is a risk factor for severe
reactions.
Similar to our surveys of patients and the general public, this
study clearly demonstrates the need for ongoing education
regarding anaphylaxis. As with previous studies, knowledge
gaps are especially apparent for primary care and emergency
physicians, who are most often the physicians on the front line in
the treatment of this common and life-threatening condition
- …