20,929 research outputs found
The effects of environmental exposure on reusable surface insulation for space shuttle
Coated specimens of reusable surface insulation (RSI) were exposed to alternate radiant heating and atmospheric exposure cycles to study the effects of surface contamination on the RSI coating. Different methods of heating were employed on clean and artificially contaminated specimens to determine the contributions of heating conditions to coating devitrification
Changes in BMI and waist circumference in Scottish adults: use of repeated cross-sectional surveys to explore multiple age groups and birth-cohorts
Objective: To document changes in body mass index (BMI) and waist circumference (WC) over a 10-year period 1998-2008, in representative surveys of adults.<p></p>
Subjects: Adults aged 18-72 in the Scottish Health Surveys conducted in 1998, 2003 and 2008 were divided, separately for men and women, into eleven 5-year age bands. ‘Synthetic birth-cohorts’ were created by dividing participants into thirteen 5-years-of-birth bands (n=20,423). Weight, height and waist circumference were objectively measured by trained observers.<p></p>
Results: Subjects with data available on BMI/waist circumference were 7743/6894 in 1998, 5838/4437 in 2003 and 4688/925 in 2008 with approximately equal gender distributions. Mean BMI and waist were both greater in successive surveys in both men and women. At most specific ages, people were consistently heavier in 2008 than in 1998 by about 1-1.5 BMI units, and waist circumferences were greater, by about 2-6 cm in men and 5-7 cm in women. Greater increases were seen at younger ages between 1998 and 2003 than between 2003 and 2008, however increases continued at older ages, particularly in waist. All birth-cohorts observed over the 10 years 1998-2008 showed increases in both BMI and waist, most marked in the younger groups. The 10-year increases in waist within birth-cohorts (mean 7.4 cm (8.1%) in men and 8.6 cm (10.9%) in women) were more striking than BMI (mean 1.8 kg/m2 (6.6%) in men and 1.5 kg/m2 (6.4%) in women) were particularly steep in older women.<p></p>
Conclusion: People were heavier and fatter in 2003 than those of the same age in 1998, with less marked increases in WC between 2003 and 2008 than 1998 and 2003. There were proportionally greater increases in waist circumference than BMI, especially in older women. This suggests a disproportionate increase in body fat, compared to muscle, particularly among older women.<p></p>
Theoretical Perspectives on Protein Folding
Understanding how monomeric proteins fold under in vitro conditions is
crucial to describing their functions in the cellular context. Significant
advances both in theory and experiments have resulted in a conceptual framework
for describing the folding mechanisms of globular proteins. The experimental
data and theoretical methods have revealed the multifaceted character of
proteins. Proteins exhibit universal features that can be determined using only
the number of amino acid residues (N) and polymer concepts. The sizes of
proteins in the denatured and folded states, cooperativity of the folding
transition, dispersions in the melting temperatures at the residue level, and
time scales of folding are to a large extent determined by N. The consequences
of finite N especially on how individual residues order upon folding depends on
the topology of the folded states. Such intricate details can be predicted
using the Molecular Transfer Model that combines simulations with measured
transfer free energies of protein building blocks from water to the desired
concentration of the denaturant. By watching one molecule fold at a time, using
single molecule methods, the validity of the theoretically anticipated
heterogeneity in the folding routes, and the N-dependent time scales for the
three stages in the approach to the native state have been established. Despite
the successes of theory, of which only a few examples are documented here, we
conclude that much remains to be done to solve the "protein folding problem" in
the broadest sense.Comment: 48 pages, 9 figure
Generalized poisson brackets and nonlinear Liapunov stability application to reduces mhd
A method is presented for obtaining Liapunov
functionals (LF) and proving nonlinear stability. The method
uses the generalized Poisson bracket (GPB) formulation of
Hamiltonian dynamics. As an illustration, certain stationary
solutions of ideal reduced MHD (RMHD) are shown to be nonlinearly
stable. This includes Grad-Shafranov and Alfven
solutions
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