284 research outputs found
A composite score combining waist circumference and body mass index more accurately predicts body fat percentage in 6- to 13-year-old children
Purpose: Body mass index (BMI) and waist circumference (WC) are widely used to predict % body fat (BF) and classify degrees of pediatric adiposity. However, both measures have limitations. The aim of this study was to evaluate whether a combination of WC and BMI would more accurately predict %BF than either alone. Methods: In a nationally representative sample of 2,303 6- to 13-year-old Swiss children, weight, height, and WC were measured, and %BF was determined from multiple skinfold thicknesses. Regression and receiver operating characteristic (ROC) curves were used to evaluate the combination of WC and BMI in predicting %BF against WC or BMI alone. An optimized composite score (CS) was generated. Results: A quadratic polynomial combination of WC and BMI led to a better prediction of %BF (r 2=0.68) compared with the two measures alone (r 2=0.58-0.62). The areas under the ROC curve for the CS [0.6*WC-SDS+0.4*BMI-SDS] ranged from 0.962±0.0053 (overweight girls) to 0.982±0.0046 (obese boys) and were somewhat greater than the AUCs for either BMI or WC alone. At a given specificity, the sensitivity of the prediction of overweight and obesity based on the CS was higher than that based on either WC or BMI alone, although the improvement was small. Conclusion: Both BMI and WC are good predictors of %BF in primary school children. However, a composite score incorporating both measures increased sensitivity at a constant specificity as compared to the individual measures. It may therefore be a useful tool for clinical and epidemiological studies of pediatric adiposit
Mechanical properties and deformation mechanisms of manganese sulphide inclusions
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Surface structure in simple liquid metals. An orbital free first principles study
Molecular dynamics simulations of the liquid-vapour interfaces in simple
sp-bonded liquid metals have been performed using first principles methods.
Results are presented for liquid Li, Na, K, Rb, Cs, Mg, Ba, Al, Tl, and Si at
thermodynamic conditions near their respective triple points, for samples of
2000 particles in a slab geometry. The longitudinal ionic density profiles
exhibit a pronounced stratification extending several atomic diameters into the
bulk, which is a feature already experimentally observed in liquid K, Ga, In,
Sn and Hg. The wavelength of the ionic oscillations shows a good scaling with
the radii of the associated Wigner-Seitz spheres. The structural rearrangements
at the interface are analyzed in terms of the transverse pair correlation
function, the coordination number and the bond-angle distribution between
nearest neighbors. The valence electronic density profile also shows (weaker)
oscillations whose phase, with respect to those of the ionic profile, changes
from opposite phase in the alkalis to almost in-phase for Si.Comment: 16 pages, 18 figures, 5 tables. Submitted to Phys. Rev.
Experimental Observation of Energy Modulation in Electron Beams Passing Through Terahertz Dielectric Wakefield Structures
We report observation of a strong wakefield induced energy modulation in an
energy-chirped electron bunch passing through a dielectric-lined waveguide.
This modulation can be effectively converted into a spatial modulation forming
micro-bunches with a periodicity of 0.5 - 1 picosecond, hence capable of
driving coherent THz radiation. The experimental results agree well with
theoretical predictions.Comment: v3. Reviewers' suggestions incorporated. Accepted by PR
Thermal activation of plasticity in BCC materials investigated by cryo-micropillar compression
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On the effects of microstructural orientation on fracture toughness in (V,Al)-nitride and -oxynitride thin films
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Impurity effects on the melting of Ni clusters
We demonstrate that the addition of a single carbon impurity leads to
significant changes in the thermodynamic properties of Ni clusters consisting
of more than a hundred atoms. The magnitude of the change induced is dependent
upon the parameters of the Ni-C interaction. Hence, thermodynamic properties of
Ni clusters can be effectively tuned by the addition of an impurity of a
particular type. We also show that the presence of a carbon impurity
considerably changes the mobility and diffusion of atoms in the Ni cluster at
temperatures close to its melting point. The calculated diffusion coefficients
of the carbon impurity in the Ni cluster can be used for a reliable estimate of
the growth rate of carbon nanotubes.Comment: 27 pages, 13 figure
An orbital-free molecular dynamics study of melting in K_20, K_55, K_92, K_142, Rb_55 and Cs_55 clusters
The melting-like transition in potasium clusters K_N, with N=20, 55, 92 and
142, is studied by using an orbital-free density-functional constant-energy
molecular dynamics simulation method, and compared to previous theoretical
results on the melting-like transition in sodium clusters of the same sizes.
Melting in potasium and sodium clusters proceeds in a similar way: a surface
melting stage develops upon heating before the homogeneous melting temperature
is reached. Premelting effects are nevertheless more important and more easily
established in potasium clusters, and the transition regions spread over
temperature intervals which are wider than in the case of sodium. For all the
sizes considered, the percentage melting temperature reduction when passing
from Na to K clusters is substantially larger than in the bulk. Once those two
materials have been compared for a number of different cluster sizes, we study
the melting-like transition in Rb_55 and Cs_55 clusters and make a comparison
with the melting behavior of Na_55 and K_55. As the atomic number increases,
the height of the specific heat peaks decreases, their width increases, and the
melting temperature decreases as in bulk melting, but in a more pronounced way.Comment: LaTeX file. 6 pages with 17 pictures. Final version with minor
change
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