271 resultados para 225
Resumo:
综述了DNA辐射损伤导致的细胞阻遏于G1期以及在该时期对DNA的修复活动,提出了较大剂量辐射诱导的三磷酸腺苷不足导致细胞凋亡的假说,并分析了细胞走向凋亡与修复的辨正关系。
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利用160Gd(35Cl,5nγ)190Tl反应研究了双奇核190Tl的高自旋态,建立了由πh9/2?νi13/2扁椭球转动带和一个具有单粒子激发特征的级联组成的190Tl能级纲图.确定地指定了190Tl扁椭球转动带的自旋值,首次发现了190Tlπh9/2?νi13/2扁椭球转动带的低自旋旋称反转.基于双奇核Tl能级结构的相似性,重新指定了双奇核192~200Tlπh9/2?νi13/2扁椭球转动带能级自旋值,在这些扁椭形变核中均出现了低自旋旋称反转.考虑了p-n剩余相互作用的2-准粒子-转子模型能够定性地解释πh9/2?νi13/2扁椭球转动带出现的低自旋旋称反转现象.
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文章介绍了电源控制系统在以太网中的设计与实现。为了完成在以太网中对电源实施控制和实时监控,采用了COM组件技术和服务技术。借助于组件,允许拥有一定权限的用户从Intranet上直接对多个电源进行远程控制,采用服务实时监控电源状态,将运行情况提交于远端数据库,进行数据交换并提取数据改变电源的运行。在实现控制的过程中,采用了ADO访问远端数据库,WMI访问外部设备。
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应用137Cs示踪技术研究了半干旱干草原地区土壤风蚀过程和强度.根据不同地貌和植被条件 下土壤剖面中的137Cs沉积特征与背景值样点的对比分析,认为缓起伏草地和半固定沙丘处于轻度风 蚀与堆积状态,蚀积速率小于0.108 cm/a;半流动沙丘表面风沙活动强烈,背风坡堆积速率大于1.35cm/a.
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在BUU框架下,讨论了中能重离子碰撞过程中的平衡过程,以及相关的物理量,如集体流、温度、化学势.研究发现,一定时间以后达到局域平衡,且中心区域最先达到平衡,同时周边碰撞时也发现存在局域平衡.平衡时温度为5一7MeV.
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Magnetic nanoparticles of nickel ferrite (NiFe2O4) have been synthesized by co-precipitation route using stable ferric and nickel salts with sodium hydroxide as the precipitating agent and oleic acid as the surfactant. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of single-phase nickel ferrite nanoparticles in the range 8-28 nm depending upon the annealing temperature of the samples during the synthesis. The size of the particles (d) was observed to be increasing linearly with annealing temperature of the sample while the coercivity with particle size goes through a maximum, peaking at similar to 11 nm and then decreases for larger particles. Typical blocking effects were observed below similar to 225 K for all the prepared samples. The superparamagnetic blocking temperature (T-B) was found to be increasing with increasing particle size that has been attributed to the increased effective anisotropy energy of the nanoparticles. The saturation moment of all the samples was found much below the bulk value of nickel ferrite that has been attributed to the disordered surface spins or dead/inert layer in these nanoparticles. (c) 2008 Elsevier B. V. All rights reserved.
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The beam matching status between the two isochronous cyclotrons in the Heavy Ion Research Facility at the Lanzhou-Cooling Storage Ring (HIRFL-CSR) is described. Several methods which can be used to accomplish 100% matching are proposed. By comparing of them, the best method is determined. The advantage due to this method is discussed.
Probing into the catalytic nature of Co/sulfated zirconia for selective reduction of NO with methane
Resumo:
In this work, the structural and surface properties of Co-loaded sulfated zirconia (SZ) catalysts were studied by X-ray diffraction (XRD), N-2 adsorption, NH3-TPD, FT-IR spectroscopy, H-2-TPR, UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and NO-TPD. NH3-TPD and FT-IR spectra results of the catalysts showed that the sulfation process of the support resulted in the generation of strong Bronsted and Lewis acid sites, which is essential for the SCR of NO with methane. On the other hand, the N-2 adsorption, H-2-TPR, UV/vis DRS, and XPS of the catalysts demonstrated that the presence of the SO42- species promoted the dispersion of the Co species and prevented the formation Of Co3O4. Such an increased dispersion of Co species suppressed the combustion reaction of CH4 by O-2 and increased the selectivity toward NO reduction. The NO-TPD proved that the loading of Co increased the adsorption of NO over SZ catalysts, which is another reason for the promoting effect of Co. (C) 2004 Elsevier Inc. All rights reserved.
Resumo:
根据马尔可夫决策过程理论和森林资源连续清查的固定样地调查资料,对南平地区的树种结构进行了预测与调整,结果表明,按现状发展,针阔比例将日趋严重,并且毛竹、经济林的占有率呈下降趋势,最终达到以杉木28.05%、马尾松16.63%、阔叶树19.01%、毛竹5.43%、经济林2.26%、其它类28.71%的树种结构.经调整后稳定状态的树种结构基本趋于合理,即各树种的占有率分别为杉木18.72%、马尾松13.24%、阔叶树26.98%、毛竹10.84%、经济林5.45%、其它类24.77%.