145 research outputs found
Statistical Model of Superconductivity in a 2D Binary Boson-Fermion Mixture
A two-dimensional (2D) assembly of noninteracting, temperature-dependent,
composite-boson Cooper pairs (CPs) in chemical and thermal equilibrium with
unpaired fermions is examined in a binary boson-fermion statistical model as
the superconducting singularity temperature is approached from above. The model
is derived from {\it first principles} for the BCS model interfermion
interaction from three extrema of the system Helmholtz free energy (subject to
constant pairable-fermion number) with respect to: a) the pairable-fermion
distribution function; b) the number of excited (bosonic) CPs, i.e., with
nonzero total momenta--usually ignored in BCS theory--and with the appropriate
(linear, as opposed to quadratic) dispersion relation that arises from the
Fermi sea; and c) the number of CPs with zero total momenta. Compared with the
BCS theory condensate, higher singularity temperatures for the Bose-Einstein
condensate are obtained in the binary boson-fermion mixture model which are in
rough agreement with empirical critical temperatures for quasi-2D
superconductorsComment: 16 pages and 4 figures. This is a improved versio
Cooper pair dispersion relation for weak to strong coupling
Cooper pairing in two dimensions is analyzed with a set of renormalized
equations to determine its binding energy for any fermion number density and
all coupling assuming a generic pairwise residual interfermion interaction. \
Also considered are Cooper pairs (CPs) with nonzero center-of-mass momentum
(CMM)--usually neglected in BCS theory--and their binding energy is expanded
analytically in powers of the CMM up to quadratic terms. A Fermi-sea-dependent
{\it linear} term in the CMM dominates the pair excitation energy in weak
coupling (also called the BCS regime) while the more familiar quadratic term
prevails in strong coupling (the Bose regime). The crossover, though strictly
unrelated to BCS theory {\it per se,} is studied numerically as it is expected
to play a central role in a model of superconductivity as a Bose-Einstein
condensation of CPs where the transition temperature vanishes for all
dimensionality for quadratic dispersion, but is {\it nonzero} for all
for linear dispersion.Comment: 11 pages plus 3 figures, revised version accepted in Physical Review
Aportaciones al conocimiento de la flora briológica española. Notula X: musgos y hepåticas de la vertiente noroccidental de Sierra Morena (Badajoz)
Se presenta un catålogo de 157 briófitos (33 Hepaticae y 124 Musci) de la vertiente noroccidental de Sierra Morena (Badajoz). Destacamos la presencia de Orthotrichum acuminatum, Phascum cuspidatum, Triquetrella arapilensis, Tortula baetica, T. Virescens, Didymodon nicholsonii y Cephaloziella stellulifera, raras o encontradas por primera vez en Extremadura (España). Summary: A list of 157 bryophytes (33 Liverworts and 124 Mosses) of the northwestern slope of Sierra Morena (Badajoz) is given. We remark the presence of Orthotrichum acuminatum, Phascum cuspidatum, Triquetrella arapilensis, Tortula baetica, T. Virescens, Didymodon nicholsonii and Cephaloziella stellulifera, rares or found for the first time in Extremadura (Spain)
Evidence of short time dynamical correlations in simple liquids
We report a molecular dynamics (MD) study of the collective dynamics of a
simple monatomic liquid -interacting through a two body potential that mimics
that of lithium- across the liquid-glass transition. In the glassy phase we
find evidences of a fast relaxation process similar to that recently found in
Lennard-Jones glasses. The origin of this process is ascribed to the
topological disorder, i.e. to the dephasing of the different momentum
Fourier components of the actual normal modes of vibration of the disordered
structure. More important, we find that the fast relaxation persists in the
liquid phase with almost no temperature dependence of its characteristic
parameters (strength and relaxation time). We conclude, therefore, that in the
liquid phase well above the melting point, at variance with the usual
assumption of {\it un-correlated} binary collisions, the short time particles
motion is strongly {\it correlated} and can be described via a normal mode
expansion of the atomic dynamics.Comment: 7 pages, 7 .eps figs. To appear in Phys. Rev.
Inelastic X-ray scattering study of the collective dynamics in liquid sodium
Inelastic X-ray scattering data have been collected for liquid sodium at
T=390 K, i.e. slightly above the melting point. Owing to the very high
instrumental resolution, pushed up to 1.5 meV, it has been possible to
determine accurately the dynamic structure factor, , in a wide
wavevector range, nm, and to investigate on the dynamical
processes underlying the collective dynamics. A detailed analysis of the
lineshape of , similarly to other liquid metals, reveals the
co-existence of two different relaxation processes with slow and fast
characteristic timescales respectively. The present data lead to the conclusion
that: i) the picture of the relaxation mechanism based on a simple viscoelastic
model fails; ii) although the comparison with other liquid metals reveals
similar behavior, the data do not exhibit an exact scaling law as the principle
of corresponding state would predict.Comment: RevTex, 7 pages, 6 eps figures. Accepted by Phys. Rev.
A Community Program of Integrated Care for Frail Older Adults : +AGIL Barcelona
Objectives: To assess the 3-month impact on physical function of a program for community-dwelling frail older adults, based on the integration of primary care, geriatric medicine, and community resources, implemented in \u201creal life\u201d. Design: Interventional cohort study. Setting: Primary care in Barcelona, Spain. Participants: Individuals aged 6580 years (n=134), presenting at least one sign of frailty (i.e., slow gait speed, weakness, memory complaints, involuntary weight loss, poor social support). Intervention: After frailty screening by the primary care team, candidates were referred to a geriatric team (geriatrician + physical therapist), who performed a comprehensive geriatric assessment and designed a tailored multidisciplinary intervention in the community, including a) multi-modal physical activity (PA) sessions, b) promotion of adherence to a Mediterranean diet c) health education and d) medication review. Measurements: Participants were assessed based on a comprehensive geriatric assessment including physical performance (Short Physical Performance Battery -SPPB- and gait speed), at baseline and at a three month follow-up. Results: A total of 112 (83.6%) participants (mean age=80.8 years, 67.9% women) were included in this research. Despite being independent in daily life, participants\u2019 physical performance was impaired (SPPB=7.5, SD=2.1, gait speed=0.71, SD=0.20 m/sec). After three months, 90.2% of participants completed 657.5 physical activity sessions. The mean improvements were +1.47 (SD 1.64) points (p<0.001) for SPPB, +0.08 (SD 0.13) m/sec (p<0.001) for gait speed, 125.5 (SD 12.10) sec (p<0.001) for chair stand test, and 53% (p<0.001) improved their balance. Results remained substantially unchanged after stratifying the analyses according to the severity of frailty. Conclusions: Our results suggested that a \u201creal-world\u201d multidisciplinary intervention, integrating primary care, geriatric care, and community services may improve physical function, a marker of frailty, within 3 months. Further studies are needed to address the long-term impact and scalability of this implementation program
An initial examination of the epidemiology of malaria in the State of Roraima, in the Brazilian Amazon Basin
Physics Implications of Flat Directions in Free Fermionic Superstring Models I: Mass Spectrum and Couplings
From the "top-down" approach we investigate physics implications of the class
of D- and F- flat directions formed from non-Abelian singlets which are proven
flat to all orders in the nonrenormalizable superpotential, for a prototype
quasi-realistic free fermionic string model with the standard model gauge group
and three families (CHL5). These flat directions have at least an additional
U(1)' unbroken at the string scale. For each flat direction, the complete set
of effective mass terms and effective trilinear superpotential terms in the
observable sector are computed to all orders in the VEV's of the fields in the
flat direction. The "string selection-rules" disallow a large number of
couplings allowed by gauge invariance, resulting in a massless spectrum with a
large number of exotics, in most cases excluded by experiment, thus signifying
a generic flaw of these models. Nevertheless, the resulting trilinear couplings
of the massless spectrum possess a number of interesting features which we
analyse for two representative flat directions: for the fermion texture;
baryon- and lepton-number violating couplings; R-parity breaking; non-canonical
mu terms; and the possibility of electroweak and intermediate scale symmetry
breaking scenarios for U(1)'. The gauge coupling predictions are obtained in
the electroweak scale case. Fermion masses possess t-b and tau-mu universality,
with the string scale Yukawa couplings g and , respectively.
Fermion textures are present for certain flat directions, but only in the
down-quark sector. Baryon- and lepton- number violating couplings can trigger
proton-decay, oscillations, leptoquark interactions and R-parity
violation, leading to the absence of a stable LSP.Comment: 36 pages, 5 tables, 4 figures, RevTeX, minor change
The effects of the mediterranean diet on biomarkers of vascular wall inflammation and plaque vulnerability in subjects with high risk for cardiovascular disease. A randomized trial
Background: Adherence to the Mediterranean diet (MD) is associated with reduced morbidity and mortality due to
cardiovascular disease. However, how the MD exerts its effects is not fully known.
Aim: To assess the 12-month effects of two enhanced MDs compared to a low-fat diet on inflammatory biomarkers related
to atherosclerosis and plaque vulnerability in a subcohort of the PREDIMED (PrevencioÂŽn con Dieta MediterraÂŽnea) study.
Methods: A total of 164 participants at high risk for cardiovascular disease were randomized into three diet groups: MD
supplemented with 50 mL/d of extra virgin olive oil (MD+EVOO) or 30 g/d of nuts (MD+Nuts) and a low-fat diet. Changes in
classical cardiovascular risk factors, inflammatory biomarkers of atherosclerosis and plaque vulnerability were measured
after 12 months of intervention.
Results: Compared to participants in the low-fat diet group, those receiving MD+EVOO and MD+Nuts showed a higher
decrease in systolic (6 mmHg) and diastolic (3 mmHg) blood pressure (P = 0.02; both), as well as a reduction of 10% and 8%
in LDL-cholesterol (P = 0.04), respectively. Patients in the MD+Nuts group showed a significant reduction of 34% in CD40
expression on monocyte surface compared to low-fat diet patients (P = 0.03). In addition, inflammatory biomarkers related
to plaque instability such as C-reactive protein and interleukin-6 were reduced by 45% and 35% and 95% and 90% in the
MD+EVOO and MD+Nuts groups, respectively (P,0.05; all) compared to the low-fat diet group. Likewise, sICAM and Pselectin
were also reduced by 50% and 27%, respectively in the MD+EVOO group (P = 0.04) and P-selectin by 19% in MD+
Nuts group (P = 0.04) compared to the low-fat diet group.
Conclusions: Adherence to the MD is associated with an increase in serum markers of atheroma plaque stability which may
explain, at least in part, the protective role of MD against ischemic heart disease
Early life risk factors and their cumulative effects as predictors of overweight in Spanish children
Objectives: To explore early life risk factors of overweight/obesity at age 6 years and their cumulative effects on overweight/obesity at ages 2, 4 and 6 years.
Methods: Altogether 1031 Spanish children were evaluated at birth and during a 6-year follow-up. Early life risk factors included: parental overweight/obesity, parental origin/ethnicity, maternal smoking during pregnancy, gestational weight gain, gestational age, birth weight, caesarean section, breastfeeding practices and rapid infant weight gain collected via hospital records. Cumulative effects were assessed by adding up those early risk factors that significantly increased the risk of overweight/obesity. We conducted binary logistic regression models.
Results: Rapid infant weight gain (OR 2.29, 99% CI 1.54â3.42), maternal overweight/obesity (OR 1.93, 99% CI 1.27â2.92), paternal overweight/obesity (OR 2.17, 99% CI 1.44â3.28), Latin American/Roma origin (OR 3.20, 99% CI 1.60â6.39) and smoking during pregnancy (OR 1.61, 99% CI 1.01â2.59) remained significant after adjusting for confounders. A higher number of early life risk factors accumulated was associated with overweight/obesity at age 6 years but not at age 2 and 4 years.
Conclusions: Rapid infant weight gain, parental overweight/obesity, maternal smoking and origin/ethnicity predict childhood overweight/obesity and present cumulative effects. Monitoring children with rapid weight gain and supporting a healthy parental weight are important for childhood obesity prevention
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