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51.
为了研究著名的Schneider投影问题,E.Lutwak,D.Yang和张高勇最近引进了一个关于对称多胞形的新的仿射不变量U(P),并提出了关于U(P)下界的猜想.本文就二维、三维在一特定条件下的情形给予了此猜想的肯定回答并给出了严格的数学证明. 相似文献
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The effect of ZnO on phase emergence and microstructure properties of glass and glass-ceramics with composition 25SiO2-50CaO-15P2O5-(10 − x)Fe2O3-xZnO (where x = 0, 2, 5, 7 mol%) has been studied. They have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Surface modifications of these glass-ceramics in simulated body fluid have been studied using Fourier transform infrared reflection spectroscopy (FTIR), XPS and SEM. Results have shown a decrease in the fraction of non-bridging oxygen with increase in zinc oxide content. Emergence of crystalline phases in glass-ceramics at different heat treatment temperatures was studied using XRD. When glass is heat treated at 800 °C calcium phosphate, hematite and magnetite are developed as major phases in the glass-ceramics samples with ZnO up to 5 mol%. In addition to these, calcium silicate (Ca3Si2O7) phase is also observed when glass is heat treated at 1000 °C. The microstructure of the glass-ceramics heat treated at 800 °C exhibits the formation of nano-size (40-50 nm) grains. On heat treatment at 1000 °C crystallites grow to above 50 nm size and more than one phase are observed in the microstructure. The formation of thin flake-like structure with coarse particles is observed at high zinc oxide concentration (x = 7 mol%). In vitro studies have shown the surface modifications and formation of Ca-P-rich layer on the glass-ceramics when immersed in simulated body fluids (SBF) for different durations. The bioactive response was found to depend on ZnO content. 相似文献
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在文献[1]关于电子 离子束缚态的基本概念的基础上, 对电子-离子束缚态三体系统给出严格的薛定谔方程, 给出能量的近似解:(1)对pep束缚态, 释放单能Ep≈12.5keV的X射线; (2)对D+eD+束缚态, 释放单能ED≈25keV的X射线, 同时引发少量的核聚变, 放出γ、质子、中子、氚、3He和4He。这是两个独立发生的过程。以Ni-H和氘气辉光放 电实验为例,用束缚态模型给出定量的解释。进而提出太阳耀斑发生过程中也包含电子-离子束缚态放射12.5keV和25keV两种X射线并引发少量核聚变的过程, 给出了观测结果验证。 相似文献
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吴力荣 《应用数学与计算数学学报》2012,26(2):185-192
Sobolev不等式是联系分析和几何的基础不等式之一,而优化Sobolev体是优化Sobolev范数的临界几何核.首先,证明优化Sobolev体的一些仿射性质.然后,运用Barthe的优化迁移方法研究了凸体的特征函数和多胞形仿射函数的优化Sobolev体. 相似文献
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The effect of pre or post-administration of vitamin A in ameliorating the radiation-induced alteration in intestinal and spleen Na+/K+-ATPase activity of rats was determined. Rats subjected to multifractionated γ-radiation (20 × 0.5 Gy) over the whole-body showed a significant reduction in Na+/K+-ATPase activity being more obvious in spleen than in intestine. Administration of vitamin A at a daily i. p. dose of 15,000 IU/kg bd. wt. for 7 days prior to fractionated γ-irradiation and thereafter twice weekly throughout the exposure period (as pretreatment regimen) or following the end of irradiation for 7 days (as posttreament regimen) afforded a significant protection from radiation-induced inhibition of spleen and intestinal Na+/K+-ATPase activity. Even though, pretreatment regimen is more efficient against radiation injury to this enzyme than posttreatment, so that its activity was nearly normalized in the first regimen. The regeneration of normal enzyme activity in the tissues of the vitamin A-pretreated group suggests that the intestinal and spleen epithelia in presence of vitamin A are rendered relatively radioresistant. 相似文献
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Hans Adriaensen Maja Musse Stéphane Quellec Alexandre Vignaud Mireille Cambert François Mariette 《Magnetic resonance imaging》2013
The transverse relaxation signal from vegetal cells can be described by multi-exponential behaviour, reflecting different water compartments. This multi-exponential relaxation is rarely measured by conventional MRI imaging protocols; mono-exponential relaxation times are measured instead, thus limiting information about of the microstructure and water status in vegetal cells. In this study, an optimised multiple spin echo (MSE) MRI sequence was evaluated for assessment of multi-exponential transverse relaxation in fruit tissues. The sequence was designed for the acquisition of a maximum of 512 echoes. Non-selective refocusing RF pulses were used in combination with balanced crusher gradients for elimination of spurious echoes. The study was performed on a bi-compartmental phantom with known T2 values and on apple and tomato fruit. T2 decays measured in the phantom and fruit were analysed using bi- and tri-exponential fits, respectively. The MRI results were compared with low field non-spatially resolved NMR measurements performed on the same samples. 相似文献
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An Approximated Solution of the Einstein Equations for a Rotating Body with Negligible Mass 总被引:1,自引:0,他引:1
A. Tartaglia 《General Relativity and Gravitation》2003,35(3):371-387
The paper considers the problem of finding the metric of space time around a rotating, weakly gravitating body. Both external and internal metric tensors are consistently found, together with an appropriate source tensor. All tensors are calculated at the lowest meaningful approximation in a power series. The two physical parameters entering the equations (the mass and the angular momentum per unit mass) are assumed to be such that the mass effects are negligible with respect to the rotation effects. A non zero Riemann tensor is obtained. The order of magnitude of the physical effects is discussed. 相似文献