399 research outputs found
Surface melting of the vortex lattice
We discuss the effect of an (ab)-surface on the melting transition of the
pancake-vortex lattice in a layered superconductor within a density functional
theory approach. Both discontinuous and continuous surface melting are
predicted for this system, although the latter scenario occupies the major part
of the low-field phase diagram. The formation of a quasi-liquid layer below the
bulk melting temperature inhibits the appearance of a superheated solid phase,
yielding an asymmetric hysteretic behavior which has been seen in experiments.Comment: 4 pages, 3 figure
Surface Melting of the Vortex Lattice in Layered Superconductors: Density Functional Theory
We study the effects of an -surface on the vortex-solid to vortex-liquid
transition in layered superconductors in the limit of vanishing inter-layer
Josephson coupling. We derive the interaction between pancake vortices in a
semi-infinite sample and adapt the density functional theory of freezing to
this system. We obtain an effective one-component order-parameter theory which
can be used to describe the effects of the surface on vortex-lattice melting.
Due to the absence of protecting layers in the neighbourhood of the surface,
the vortex lattice formed near the surface is more susceptible to thermal
fluctuations. Depending on the value of the magnetic field, we predict either a
continuous or a discontinuous surface melting transition. For intermediate
values of the magnetic field, the surface melts continuously, assisting the
formation of the liquid phase and suppressing hysteresis above the melting
transition, a prediction consistent with experimental results. For very low and
very high magnetic fields, the surface melts discontinuously. The two different
surface melting scenarios are separated by two surface multicritical points,
which we locate on the melting line.Comment: 16 pages, 12 figure
Dissociation of vortex stacks into fractional-flux vortices
We discuss the zero field superconducting phase transition in a finite system
of magnetically coupled superconducting layers. Transverse screening is
modified by the presence of other layers resulting in topological excitations
with fractional flux. Vortex stacks trapping a full flux and present at any
finite temperature undergo an evaporation transition which corresponds to the
depairing of fractional-flux vortices in individual layers. We propose an
experiment with a bi-layer system allowing us to identify the dissociation of
bound vortex molecules.Comment: 4 pages, 1 figure; revised version, to appear in Phys. Rev. Let
Relationship between fatty liver and glucose metabolism: A cross-sectional study in 571 obese children
BACKGROUND AND AIMS: Early onset type 2 diabetes mellitus (T2DM) is associated with obesity, insulin resistance and impaired beta-cell function. Non-alcoholic fatty liver disease (NAFLD) may be an independent risk factor for T2DM. We investigated the relationship between NAFLD and glucose metabolism in a large sample of obese children. METHODS AND RESULTS: A total of 571 obese children (57% males and 43% females) aged 8-18 years were consecutively studied at a tertiary care centre specialised in paediatric obesity. Liver ultrasonography was used to diagnose NAFLD after exclusion of hepatitis B and C and alcohol consumption. Oral-glucose tolerance testing (OGTT) was performed; insulin sensitivity was evaluated by using the insulin sensitivity index (ISI) and beta-cell function by using the ratio between the incremental areas under the curve (AUC) of insulin and glucose (incAUCins/incAUCglu). A total of 41% of the obese children had NAFLD. Impaired glucose tolerance or T2DM was present in 25% of the children with NAFLD versus 8% of those without it (p<0.001). Children with NAFLD had higher body mass index (BMI), fasting glucose, 120-min OGTT glucose, incAUCins/incAUCglu and lower ISI as compared with children without NAFLD (p</=0.002). At bootstrapped multivariable median regression analysis controlling for gender, age, pubertal status and BMI, NAFLD was an independent predictor of 120-min OGTT glucose and ISI, but not of incAUCins/incAUCglu. Similar findings were obtained using continuous liver steatosis as the predictor, instead of dichotomous NAFLD. CONCLUSION: NAFLD was present in 41% of our obese children and was associated with higher insulin resistance, but not with impaired beta-cell function
Density functional theory of vortex lattice melting in layered superconductors: a mean-field--substrate approach
We study the melting of the pancake vortex lattice in a layered
superconductor in the limit of vanishing Josephson coupling. Our approach
combines the methodology of a recently proposed mean-field substrate model for
such systems with the classical density functional theory of freezing. We
derive a free-energy functional in terms of a scalar order-parameter profile
and use it to derive a simple formula describing the temperature dependence of
the melting field. Our theoretical predictions are in good agreement with
simulation data. The theoretical framework proposed is thermodynamically
consistent and thus capable of describing the negative magnetization jump
obtained in experiments. Such consistency is demonstrated by showing the
equivalence of our expression for the density discontinuity at the transition
with the corresponding Clausius-Clapeyron relation.Comment: 11 pages, 4 figure
Effects of a 3-Week In-Hospital Body Weight Reduction Program on Cardiovascular Risk Factors, Muscle Performance, and Fatigue : A Retrospective Study in a Population of Obese Adults with or without Metabolic Syndrome
Background: In clinical practice, there is the diffuse conviction that obese subjects with metabolic syndrome may be more difficult to treat.
Objectives and methods: The aim of the present study was that to investigate the effectiveness of a 3-week in-hospital body weight reduction program (BWRP) in a large population of obese subjects with and without metabolic syndrome (n = 1922; 222 men and 1700 women, age range 18-83 yr). Outcomes such as body mass index (BMI), total (TOT) and HDL cholesterol, systolic and diastolic blood pressures (SBP and DBP, respectively), coronary heart disease (CHD) score, fatigue severity score (FSS), and stair climbing test (SCT) time were evaluated before and after the intervention (\u394). A sex-, BMI-, and age-related stratification of the obese population with or without metabolic syndrome was applied.
Results: When compared to obese subjects without metabolic syndrome, at the basal conditions, obese subjects had a poorer cardiometabolic profile, as demonstrated by higher triglycerides, TOT-cholesterol, DBP, SBP, and CHD score, and a more compromised muscle performance (evaluated by SCT), associated with more perception of fatigue (measured by FSS). Nevertheless, obese subjects with metabolic syndrome obtained more benefits from BWRP than those without metabolic syndrome for some outcomes (i.e., \u394TOT-cholesterol, \u394SBP, and \u394CHD score). Despite these differences, the BWRP-induced weight loss was similar between the two groups (i.e., \u394BMI) as well as the gain of muscle performance (i.e., \u394SCT) and the reduction of fatigue (i.e., \u394FSS). Interestingly, the potentially deleterious fall in HDL-cholesterol levels after BWRP was less evident in obese subjects with metabolic syndrome than those without metabolic syndrome. When pooling all data, the \u394CHD score was associated with age, sex, and metabolic syndrome. The remaining outcomes, such as \u394BMI, \u394FSS, and \u394SCT time, were associated with sex and age but not with metabolic syndrome. Finally, \u394BMI was positively correlated with \u394CHD score, \u394FSS, and \u394SCT time in both obese subjects without metabolic syndrome and obese subjects with metabolic syndrome.
Conclusions: When comparing obese subjects undergoing a BWRP, metabolic syndrome is not a negative predictive factor affecting the effectiveness of this intervention in terms of weight loss, muscle performance, and psychological well-being
External Validation of Equations to Estimate Resting Energy Expenditure in 2037 Children and Adolescents with and 389 without Obesity : a Cross-Sectional Study
We performed an external cross-validation study of 10 equations to estimate resting energy expenditure (REE) in 2037 children with and 389 without obesity. Inclusion criteria were Caucasian ethnicity, age 64 18 years, and availability of REE. REE was measured using indirect calorimetry. The correct classification fraction (CCF) of an equation was defined as the fraction of subjects whose estimated REE was within 10% of measured REE. The Moln\ue1r equation was the most accurate REE prediction equation with CCFs of 0.70 (95% CI 0.65 to 0.76) in girls without obesity, 0.64 (95% CI 0.61 to 0.66) in girls with obesity, 0.76 (95% CI 0.67 to 0.83) in boys without obesity, and 0.66 (95% CI 0.63 to 0.69) in boys with obesity. The Mifflin equation was the second most accurate equation with CCFs of 0.67 (95% CI 0.61 to 0.73) in girls without obesity, 0.61 (95% CI 0.58 to 0.64) in girls with obesity, 0.75 (95% CI 0.66 to 0.82) in boys without obesity, and 0.66 (95% CI 0.63 to 0.69) in boys with obesity
The Appetite-Suppressant and GLP-1-Stimulating Effects of Whey Proteins in Obese Subjects are Associated with Increased Circulating Levels of Specific Amino Acids
The satiating effect of whey proteins depends upon their unique amino acid composition because there is no difference when comparing whey proteins or a mix of amino acids mimicking the amino acid composition of whey proteins. The specific amino acids underlying the satiating effect of whey proteins have not been investigated to date. Aims and Methods. The aim of the present study was to evaluate the appetite-suppressant effect of an isocaloric drink containing whey proteins or maltodextrins on appetite (satiety/hunger measured by a visual analogue scale or VAS), anorexigenic gastrointestinal peptides (circulating levels of glucagon-like peptide 1 (GLP-1) and peptide tyrosine tyrosine (PYY)) and amino acids (circulating levels of single, total [TAA] and branched-chain amino acids [BCAA]) in a cohort of obese female subjects (n = 8; age: 18.4 \ub1 3.1 years; body mass index, BMI: 39.2 \ub1 4.6 kg/m2). Results. Each drink significantly increased satiety and decreased hunger, the effects being more evident with whey proteins than maltodextrins. Similarly, circulating levels of GLP-1, PYY and amino acids (TAA, BCAA and alanine, arginine, asparagine, citrulline, glutamine, hydroxyproline, isoleucine, histidine, leucine, lysine, methionine, ornithine, phenylalanine, proline, serine, threonine, tyrosine, and valine) were significantly higher with whey proteins than maltodextrins. In subjects administered whey proteins (but not maltodextrins), isoleucine, leucine, lysine, methionine, phenylalanine, proline, tyrosine, and valine were significantly correlated with hunger (negatively), satiety, and GLP-1 (positively). Conclusions. Eight specific amino acids (isoleucine, leucine, lysine, methionine, phenylalanine, proline, tyrosine, and valine) were implicated in the appetite-suppressant and GLP-1-stimulating effects of whey proteins, which may be mediated by their binding with nutrient-sensing receptors expressed by L cells within the gastrointestinal wall. The long-term satiating effect of whey proteins and the effectiveness of a supplementation with these amino acids (i.e., as a nutraceutical intervention) administered during body weight reduction programs need to be further investigated
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