794 research outputs found
Ground state of a partially melted Wigner molecule
We consider three spinless fermions free to move on 2d square lattice with
periodic boundary conditions and interacting via a U/r Coulomb repulsion. When
the Coulomb energy to kinetic energy ratio r_s is large, a rigid Wigner
molecule is formed. As r_s decreases, we show that melting proceeds via an
intermediate regime where a floppy two particle molecule coexists with a
partially delocalized particle. A simple ansatz is given to describe the ground
state of this mesoscopic solid-liquid regime.Comment: to appear in Europhysics Letter
Effects of Particle Size in Forage Samples for Protein Breakdown Studies
Coupling ruminal processes of hydrolysis and synthesis continues to be a research issue where more progress is needed. This requires the development of good protein assessment methods, particularly when representing the breakdown processes that occur in fresh pastures eaten by herbivores. Laboratory analyses need to deal with small and homogeneous samples, but the mechanical reduction of particle size may not reflect the actual digestion kinetics occurring when the original fresh forage is consumed. Such physical traits may alter the release of non-structural compounds and the penetration of microbial enzymes (Boudon et al., 2002). The objective of this work was to assess in fresh samples the effect of reducing particle size upon the in vitro breakdown of proteins during the early rumen fermentation period
Ruminal Proteolysis in Forages with Distinct Endopeptidases Activities
Improving livestock efficiency in utilisation of nitrogen resources continues to be a major environmental and economic objective. Zhu et al. (1999) have shown that plant endopeptidases are activated as a response to cutting stress. Previous work in our laboratory explored over 300 entries of forage genotypes and found a broad diversity in enzymatic activity by means of hydrolysis in gelatine and direct autolysis assays in forage tissues. The objective of this work was to assess if the species previously identified as having high or low endopeptidase activity, would behave consistently when exposed to ruminal microbial proteolysis
Web-assisted tunneling in the kicked harmonic oscillator
We show that heating of harmonically trapped ions by periodic delta kicks is
dramatically enhanced at isolated values of the Lamb-Dicke parameter. At these
values, quasienergy eigenstates localized on island structures undergo avoided
crossings with extended web-states.Comment: 4 pages, 4 figures. Accepted for publication in Phys. Rev. Let
Role of a parallel magnetic field in two dimensional disordered clusters containing a few correlated electrons
An ensemble of 2d disordered clusters with a few electrons is studied as a
function of the Coulomb energy to kinetic energy ratio r_s. Between the Fermi
system (small r_s) and the Wigner molecule (large r_s), an interaction induced
delocalization of the ground state takes place which is suppressed when the
spins are aligned by a parallel magnetic field. Our results confirm the
existence of an intermediate regime where the Wigner antiferromagnetism
defavors the Stoner ferromagnetism and where the enhancement of the Lande g
factor observed in dilute electron systems is reproduced.Comment: 4 pages, 3 figure
Level Statistics and Localization for Two Interacting Particles in a Random Potential
We consider two particles with a local interaction in a random potential
at a scale (the one particle localization length). A simplified
description is provided by a Gaussian matrix ensemble with a preferential
basis. We define the symmetry breaking parameter
associated to the statistical invariance under change of basis. We show that
the Wigner-Dyson rigidity of the energy levels is maintained up to an energy
. We find that when (the
inverse lifetime of the states of the preferential basis) is smaller than
(the level spacing), and when . This implies that the two-particle localization length first
increases as before eventually behaving as .Comment: 4 pages REVTEX, 4 Figures EPS, UUENCODE
Overweight and obesity in a Swiss city: 10-year trends
Abstract Background Increased rates of overweight/obesity have been reported in recent years in developed countries. This population study of healthy subjects evaluated the changes in overweight/obesity prevalence in 2003, compared with 1993, and determined the association of age, sex and leisure-time activity with body mass index (BMI), fat-free mass index (FFMI) and fat mass index (FMI). Design Two transversal samples of convenience. Participants Healthy volunteers (1993, n=802; 2003, n=1631). Methods Fat-free mass was determined using the bioelectrical impedance multiple regression equation. Multivariable linear regression, including confounding variables (age, sex, leisure-time activity), was used to model the body composition evolution between the 1993 and the 2003 subjects. Results BMI and FMI were higher in 2003 than in 1993, P<0.001. FFMI was not higher in 2003 than in 1993, P=0.38. More subjects were overweight/obese in 2003 than in 1993 (27.5 versus 17.2%, chi-square P<0.001), and had a high FFMI (30.2 versus 21.8%, chi-square P<0.001) and high FMI (28.0 versus 20.3%, chi-square P<0.001). Multivariate linear regressions showed that leisure-time activity was negatively, and sex, age and inclusion year were positively associated with BMI, FFMI and FMI (the exception was a negative association with sex) (P<0.001). Conclusion Overweight prevalence increased between 1993 and 2003 in a Swiss city, and was associated with a higher fat mass. This observation remained statistically significant after adjustment for age, sex and leisure-time activit
Transport properties of one-dimensional Kronig-Penney models with correlated disorder
Transport properties of one-dimensional Kronig-Penney models with binary
correlated disorder are analyzed using an approach based on classical
Hamiltonian maps. In this method, extended states correspond to bound
trajectories in the phase space of a parametrically excited linear oscillator,
while the on site-potential of the original model is transformed to an external
force. We show that in this representation the two probe conductance takes a
simple geometrical form in terms of evolution areas in phase-space. We also
analyze the case of a general N-mer model.Comment: 16 pages in Latex, 12 Postscript figures include
Low fat-free mass as a marker of mortality in community-dwelling healthy elderly subjectsâ
Background: low fat-free mass has been related to high mortality in patients. This study evaluated the relationship between body composition of healthy elderly subjects and mortality. Methods: in 1999, 203 older subjects underwent measurements of body composition by bioelectrical impedance analysis, Charlson co-morbidity index and estimation of energy expenditure through physical activity by a validated questionnaire. These measurements were repeated in 2002, 2005 and 2008 in all consenting subjects. Mortality data between 1999 and 2010 were retrieved from the local death registers. The relationship between mortality and the last indexes of fat and fat-free masses was analysed by multiple Cox regression models. Results: women's and men's data at last follow-up were: age 81.1±5.9 and 80.9±5.8 years, body mass index 25.3±4.6 and 26.1±3.4kg/m2, fat-free mass index 16.4±1.8 and 19.3±1.9kg/m2 and fat mass index 9.0±3.2 and 6.8±2.0kg/m2. Fifty-eight subjects died between 1999 and 2010. The fat-free mass index (hazard ratio 0.77; 95% confidence interval 0.63-0.95) but not the fat mass index, predicted mortality in addition to sex and Charlson index. The multiple Cox regression model explained 31% of the variance of mortality. Conclusion: a low fat-free mass index is an independent risk factor of mortality in elderly subjects, healthy at the time of body composition measuremen
Cross-Over between universality classes in a magnetically disordered metallic wire
In this article we present numerical results of conduction in a disordered
quasi-1D wire in the possible presence of magnetic impurities. Our analysis
leads us to the study of universal properties in different conduction regimes
such as the localized and metallic ones. In particular, we analyse the
cross-over between universality classes occurring when the strength of magnetic
disorder is increased. For this purpose, we use a numerical Landauer approach,
and derive the scattering matrix of the wire from electron's Green's function.Comment: Final version, accepted for publication in New Journ. of Physics, 27
pages, 28 figures. Replaces the earlier shorter preprint arXiv:0910.427
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