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排序方式: 共有157条查询结果,搜索用时 828 毫秒
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U.Deva Priyakumar 《Tetrahedron letters》2004,45(12):2495-2498
A novel preference for planar tetracoordination was observed over the conventional tetrahedral arrangement in a new series of C5H2, C5H4, C5H41+/2+ and related compounds. The stability of these molecules is assessed with the ring-opening barriers, HOMO-LUMO gap, singlet-triplet energy differences and nucleus independent chemical shift values. 相似文献
3.
Complete Surjections and Complete Epimorphisms over Completely Distributive Lattices 总被引:1,自引:0,他引:1
Generators and lattice properties of the poset of complete homomorphisic images of a completely distributive lattice are exploited via the localic methods. Some intrinsic and extrinsic conditions about this poset to be a completely distributive lattice are given. It is shown that the category of completely distributive lattices is co-well-powered,and complete epimorphisms on completely distributive lattice are not necessary to be surjections. Finally, some conditions about complete epimorphisms to be surjections are given. 相似文献
4.
M. A. Kumakhov 《辐射效应与固体损伤》2013,168(1-2):85-99
The redistribution of the channeled ion flux in the transverse plane has been examined. General formulae describing the flux peaking effect are obtained. Main factors on which the effect depends are investigated. An analysis is made of back-scattering experiments. The study has been made for the axial and planar channeling. 相似文献
5.
Anju Singh Ritushree Kukreti Luciano Saso Shrikant Kukreti 《Molecules (Basel, Switzerland)》2022,27(3)
Oxidative stress (OS) is a metabolic dysfunction mediated by the imbalance between the biochemical processes leading to elevated production of reactive oxygen species (ROS) and the antioxidant defense system of the body. It has a ubiquitous role in the development of numerous noncommunicable maladies including cardiovascular diseases, cancers, neurodegenerative diseases, aging and respiratory diseases. Diseases associated with metabolic dysfunction may be influenced by changes in the redox balance. Lately, there has been increasing awareness and evidence that diabetes mellitus (DM), particularly type 2 diabetes, is significantly modulated by oxidative stress. DM is a state of impaired metabolism characterized by hyperglycemia, resulting from defects in insulin secretion or action, or both. ROS such as hydrogen peroxide and the superoxide anion introduce chemical changes virtually in all cellular components, causing deleterious effects on the islets of β-cells, in turn affecting insulin production. Under hyperglycemic conditions, various signaling pathways such as nuclear factor-κβ (NF-κβ) and protein kinase C (PKC) are also activated by ROS. All of these can be linked to a hindrance in insulin signaling pathways, leading to insulin resistance. Hyperglycemia-induced oxidative stress plays a substantial role in complications including diabetic nephropathy. DM patients are more prone to microvascular as well as atherosclerotic macrovascular diseases. This systemic disease affects most countries around the world, owing to population explosion, aging, urbanization, obesity, lifestyle, etc. However, some modulators, with their free radical scavenging properties, can play a prospective role in overcoming the debilitating effects of OS. This review is a modest approach to summarizing the basics and interlinkages of oxidative stress, its modulators and diabetes mellitus. It may add to the understanding of and insight into the pathophysiology of diabetes and the crucial role of antioxidants to weaken the complications and morbidity resulting from this chronic disease. 相似文献
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The influence of nucleus density on optical properties in nucleated isotactic polypropylene 总被引:1,自引:0,他引:1
Alfrd Menyhrd Markus Gahleitner Jzsef Varga Klaus Bernreitner Pirjo Jskelinen Harry
ysd Bla Puknszky 《European Polymer Journal》2009,45(11):3138-3148
The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0–200 ppm, while the other two in 0–2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density. 相似文献
8.
Today, the mobile phone industry witnesses important changes, shifting from a value chain to a burgeoning business ecosystem. This paper deals with the relationships that are at the very core of mobile OS ecosystems for IMTs (smartphones and PDA): Microsoft-OS, Symbian-OS, Palm-OS and RIM-OS over the period 1998–2006. Our study confirms that an ecosystem’s borders are unclear. More than half of our sample’ relationships are shared by at least two different ecosystems. The ecosystems we studied do not differ in terms of exclusive relationship which suggests that coopetitive strategies are particularly relevant in mobile platforms war. 相似文献
9.
本文首先介绍了LPC1343的硬件架构和UCOS-Ⅱ实时操作系统的特点,最后介绍了UCOS-Ⅱ在LPC1343上移植的方法和注意事项。 相似文献
10.
智能手机操作系统群雄并起 总被引:1,自引:0,他引:1
近年来,随着全球移动数据业务使用量的迅猛增长,智能手机销量不断攀升。代表不同市场阵营的智能手机操作系统竞争日益激烈。笔者在回顾市场上主流操作系统形成现今市场地位的历史原因同时,对其未来的发展机遇逐一作了分析,在此基础上,对未来智能手机操作系统的市场格局做出了预测。 相似文献