338 research outputs found
Packing Hyperspheres in High-Dimensional Euclidean Spaces
We present the first study of disordered jammed hard-sphere packings in
four-, five- and six-dimensional Euclidean spaces. Using a collision-driven
packing generation algorithm, we obtain the first estimates for the packing
fractions of the maximally random jammed (MRJ) states for space dimensions
, 5 and 6 to be , 0.31 and 0.20, respectively. To
a good approximation, the MRJ density obeys the scaling form , where and , which appears to be
consistent with high-dimensional asymptotic limit, albeit with different
coefficients. Calculations of the pair correlation function and
structure factor for these states show that short-range ordering
appreciably decreases with increasing dimension, consistent with a recently
proposed ``decorrelation principle,'' which, among othe things, states that
unconstrained correlations diminish as the dimension increases and vanish
entirely in the limit . As in three dimensions (where ), the packings show no signs of crystallization, are isostatic,
and have a power-law divergence in at contact with power-law
exponent . Across dimensions, the cumulative number of neighbors
equals the kissing number of the conjectured densest packing close to where
has its first minimum. We obtain estimates for the freezing and
melting desnities for the equilibrium hard-sphere fluid-solid transition,
and , respectively, for , and
and , respectively, for .Comment: 28 pages, 9 figures. To appear in Physical Review
Protective Role of S-Adenosylmethionine Against Fructose-Induced Oxidative Damage in Obesity
Introduction. It has been shown that S-adenosylmethionine (S-AMe) stimulates glutathione synthesis and increases cell resistance to the cytotoxic action of free radicals and pro-inflammatory cytokines. The aim of this study was to determine the effect of S-adenosylmethionine on the oxidative stress in adipose tissue in a model of fructose-induced obesity. Methods. The study was performed on male Wistar rats divided into 3 groups: control, fructose fed (HFD) (35%, 16 weeks), and HFD + S-AMe (20 mg/kg). We examined the changes in the ratio of retroperitoneal adipose tissue weight / body weight; levels of reduced glutathione (GSH) and malondialdehyde (MDA) in the retroperitoneal adipose tissue, and serum levels of GSH and TNF-Ξ±. Results. Significant increases in the retroperitoneal adipose tissue, MDA, and serum TNF-Ξ± were identified, as well as decreased tissue and serum levels of GSH in rats fed with a high-fructose diet as compared with the control group. In the group fed with HFD and S-AMe, we found significant reduction in the retroperitoneal adipose tissue and decreased levels of MDA and serum TNF-Ξ±, as well as increased tissue and serum levels of GSH as compared with the group only on HFD. In conclusion, our results show that fructose-induced obesity causes oxidative stress in hypertrophic visceral adipose tissue. The administration of S-AMe improves the antioxidative protection of adipocytes, and reduces oxidative damage and excessive accumulation of lipids and inflammation
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