一种基于物理机制的后继屈服面演化模型

考虑滑移为晶体塑性的主要变形机制,推广晶体塑性理论至多晶体,建立滑移构元模型,研究了后继屈服面的移动和畸变等演化规律.基于滑移构元的潜在硬化和包氏效应的影响,后继屈服面的前端凸出,尾部缩进,呈现"前凸后扁"的特征,计算了单轴拉伸、纯扭转和拉一扭组合比例/非比例加载下的后继屈服面演化过程,与已有实验结果相符合

基于pm2．5浓度的室内通风调控

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科尔沁沙地沙丘演替过程的土壤种子库特征

该文研究了科尔沁沙地沙丘演替阶段(流动沙丘-半流动沙丘-半固定沙丘-固定沙丘)的土壤种子库特征.土壤种子库物种组成和种子密度均以一年生植物为主.流动和半流动沙丘土壤种子库密度约为90和364粒/m2,半固定和固定沙丘种子密度显著增加到723和8 880粒/m2.沙丘演替阶段种子密度的时间动态和土壤种子垂直分布特征分析结果表明:流动半流动沙丘无显著差异(P>0.05),固定半固定沙丘则有显著差异(P≤0.002);固定半固定沙丘的植物种子表现为持久土壤种子库类型Ⅲa,并且随土壤深度增加,土壤种子密度显著下降.沙丘演替阶段土壤种子库的种子密度与植物在地上植被中出现的频度具有显著相关性,二者相关系数为0.568.

抢救“土壤水库”治理黄土高原生态环境

笔者最近从陆地生态的发生发展及其整个地质历史演变过程的研究中发现 ,“土壤水库”的发生发展及其演变是陆地生态发展的关键和“动力” ,只要维护“土壤水库”正常发展 ,就能更好地保护生态环境。黄土高原地区由于得天独厚的降尘堆积环境条件和持续的成壤过程 ,可使降水具有直接渗入“地下水库”的特殊功能。只要维护住高入渗“土壤水库”的存在 ,就能确保全部降水就地入渗拦蓄的顺利实现。为全面实现“黄土高原国土整治 2 8字方略” ,确保“土壤水库” ,首先必须转变观念。必须充分认识生态环境是经济发展的基础 ,也是农业和人类生存发展的生命线。同时 ,更应确认“土壤水库”在生态环境发生演变中无可替代的活力 ,对整个陆地生态环境是这样 ,对黄土高原的生态环境更是这样 ,因为它更能顺从黄土高原形成及其演变的自然规律 ,是当前快速、经济、有效合理利用降水资源和重建生态环境的有效途径。( 1 )维护“土壤水库” ,保证全部降水就地入渗拦蓄。很明显 ,在自然生态环境条件下 ,最初黄土高原的“土壤水库”就能拦蓄全部降水而为当地生物生长和人们生产所用 ,只有超过土壤田间持水量的水才会继续下渗而成地下水 ,并非常有序地顺着各级水路网汇入黄河干流...

单分散磁性纳米粒子靶向药物载体

本文综述了单分散磁性氧化铁纳米粒子的主要制备方法、表面修饰以及在生物医学靶向药物方面的应用研究进展。金属有机前驱体高温热分解法、溶剂热合成法和LSS(liquid-solid-solution)法是目前制备高质量单分散磁性纳米粒子比较有效的手段。通过表面修饰制备出的具有良好水溶性、生物相容性和活性功能基团的磁靶向药物载体将可能实现定位蓄积、高效载药、控制释药和可生物降解等靶向治疗癌症的目的。开发出具有荧光检测、主动靶向识别、高效载药、智能控药释放、无毒副作用和生物相容性于一体的多功能靶向药物载体将是其发展趋势。

晶体结构对化合物电学性质的影响

化合物的导电性包括电子（空穴）导电及离 子导电两大部分。新材料的发展已将化合物的电学性 质提到了急需研究的位置。随着对化合物电学性质研 究的不断深入，发现了许多新现象，新性质和新材料， 如氧化物高温超导体，稀土半导体，稀土巨磁阻材料 等。这些都是电子（空穴）导电的实际应用。而由于 新能源探索需适应保护环境的需要，传统的氧离子和 质子导体成了人们的首选研究对象，以开发它们在燃 料电池、氧分离膜，催化等方面的实际应用。由于不 等价置换，价态变化及氧离子具有大的双电荷与阳离 子基体的强相互作用及高迁移率，使得大多数的研究 工作集中于化合物的结构畸变分析及精化，试图发现 新的结构相或者新的电学材料。

Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization

Macroporous functionalized. polymer beads of poly(4-vinylpyridine-co-1,4-divinylbenzene) [P(VPy-co-DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier-free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy-co-DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10-50 mum, and the pore size was 0.1-1.5 mum. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated.

Solvent effects of a fluorescent polyquinoline chemosensor for metal ions

Red shift and quenching effects of the fluorecence spectra of polyquinoline (PQH) solutions in different solvents are observed upon the addition of metal ions, which demonstrates the extraordinary solvent effects on metal-ion recognition and sensing ability (including sensitivity and selectivity) of PQH.

Observation of autoionization levels in uranium I

A number of Rydberg and autoionization levels of U I have been studied using three-step resonant ionization methods with three pulsed tunable dye lasers. Energy levels of uranium atom have been measured,which were located in the 49 898-50 880 cm(-1) energy interval.

A new high efficiency green luminescent material - the system Al2O3-B2O3 containing Ce3+ and Tb3+ ions

To obtain high efficiency luminescent materials, the system Al2O3-B2O3 containing Ce3+ and Tb3+ ions with variation of B2O3-content, has been prepared by Al2O3, H3BO3, CeO2 and Tb4O7 under reducing atmosphere at 1250(j)ae. It is notable that the brightness of the sample with appropriate composition is similar to that of commercial phosphorous containing Ce3+ and Tb3+, indicating that a new high efficency green luminescent material was obtained with appropriate B2O3-content.

Code for chemical environment and computation of molecular similarity

A new code for chemical environment and an empirical mathematical pattern Sa(m) on computation of molecular similarity were suggested. Seven molecules which referred to as the probe compounds and the nearest neighbors of each probe structure were determined by the methods of Sa(m) and Tanimoto, The results show an intuitive notion of chemical similarity.