Plastic deformation of the stack of alternating crystal and amorphous layers typical of semicrystalline polyethylene is studied by molecular dynamics simulation. A previous investigation of the semicrystalline layered stack undergoing isochoric extension is extended here to include several new modes of deformation: isostress extension, isostress compression, and isochoric shear, at 350 K and deformation rates of 5 × 107 and 5 × 106 s–1. The observed stress–strain responses are interpreted in terms of the underlying structural evolution of the material for each mode of deformation. Under tensile deformation, crystallographic slip was observed at low strains (0 < e 3 < 0.08) regardless of deformation rate. Different yield mechanisms were observed for the different deformation rates. To explain the response at intermediate strains (0.08 < e 3 < 0.26), we introduce the concept of “bridging entanglements”, which are temporary, physical bridges between crystal lamellae comprising entanglements involving chain segments belonging to different crystal lamellae. At high strains (e 3 > 0.26), melting and recrystallization were observed at the slower deformation rate, while surface melting and cavitation were observed at the faster deformation rate. Under compressive deformation at the slower deformation rate, crystallographic slip was again observed at low strains. For the faster compressive deformation, an initial period of rapid stress growth at low strain was observed. This initial stress growth then transitions to a process of fine crystallographic slip at a strain of e 3 = −0.005. At intermediate strains under compressive deformation, the release of bridging entanglements is observed for both strain rates. However, no melting or recrystallization phenomena were observed under compression, even at the highest strains simulated (e 3 = −0.33). Under shear deformation, interlamellar slip was observed for both zx and zy shear (strain gradient parallel to stacking direction). Chain segments tend to stretch and align in the shear direction. Interestingly, under shear deformation this semicrystalline polyethylene exhibits transient behavior typical of non-Newtonian fluids.

It has been well established that women generally have lower incidence rates of hypertension than men at similar ages and these differences may vary with age. It also has been observed in many studies that after menopause, blood pressure (BP) increases in women to levels even higher than in men. The lack of estrogens may not be suggested as the only component involved in the development of postmenopausal hypertension. Thus, in this mini-review, the possible mechanisms by which sex hormones may influence the BP are discussed. This review also examines the renal regulatory mechanisms for gender differences in BP and explores the effects of salt intake on BP (salt-sensitivity) in pre and post-menopausal women.Estrogen has been shown to stimulate nitric oxide (NO) production, thus female sex hormones have a beneficial effect on BP control. Evidences that angiotensin type 2 receptor (AT2R) is up-regulated by estrogen support the favorable effects on BPs in women than men. The kidney plays an integral role in the regulation of arterial pressure through the mechanism of pressure-natriuresis, which has been shown to be modulated by the RAS. The prevalence of salt-sensitivity increases with age and low-salt diets has shown to help reduce systolic BP (SBP) and diastolic BP. While oral hormone replacement therapy has yielded only a neutral or minimal effect on the elevation of SBP, both the transdermal route replacement and a novel progestin with anti-aldosterone activity (drospirenone) has also shown to reduce SBP.

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Use of nasal septal bone to straighten deviated septal cartilage appears to be feasible in corrective rhinoplasty, and may be particularly beneficial in cartilage-depleted patients.

In this work, we analyzed the individual chain dynamics for linear polymer melts under shear flow for bulk and confined systems using atomistic nonequilibrium molecular dynamics simulations of unentangled (C50H102) and slightly entangled (C178H358) polyethylene melts. While a certain similarity appears for the bulk and confined systems for the dynamic mechanisms of polymer chains in response to the imposed flow field, the interfacial chain dynamics near the boundary solid walls in the confined system are significantly different from the corresponding bulk chain dynamics. Detailed molecular-level analysis of the individual chain motions in a wide range of flow strengths are carried out to characterize the intrinsic molecular mechanisms of the bulk and interfacial chains in three flow regimes (weak, intermediate, and strong). These mechanisms essentially underlie various macroscopic structural and rheological properties of polymer systems, such as the mean-square chain end-to-end distance, probability distribution of the chain end-to-end distance, viscosity, and the first normal stress coefficient. Further analysis based on the mesoscopic Brightness method provides additional structural information about the polymer chains in association with their molecular mechanisms.