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31.
Neurological tumours are common neoplasms of both adults and children. Recent studies have begun to delineate the genetic abnormalities that underlie such tumours, and have implicated two classes of genes, oncogenes and tumour suppressor genes. Most investigations have focused on those astrocytomas that affect the cerebral hemispheres of adults, since these are the most common and malignant brain tumours. The high-grade astrocytomas that affect adults, such as glioblastoma multiforme, often have amplification of the epidermal growth factor receptor (EGFR) oncogene and loss of a variety of chromosomal loci that probably harbour tumour suppressor genes. Of the various tumour suppressor gene loci, the p53 gene on chromosome 17p has been studied most closely and has been shown to be mutated in both low- and high-grade astrocytomas. These genetic alterations may provide a means for subdividing astrocytomas into diagnostic categories. For instance, p53 gene mutations occur more commonly in glioblastomas from young adults and women, while EGFR gene amplification is more common in glioblastomas from older adults and men. For the other primary CNS tumours, genetic studies remain in their infancy. The neurocutaneous syndromes, such as neurofibromatosis types 1 and 2, have provided unique insights into neurological oncogenesis. The NF1 gene on chromosomes 17q and its product, neurofibromin, may be important in the formation of neurofibrosarcomas, while the NF2 gene on chromosome 22q and its product, merlin, are probably involved in the formation of schwannomas and other nervous system tumours. The further characterization of these and other neurological tumour genes will undoubtedly illuminate many other areas in neurooncology. 相似文献
32.
For Tanzanian soils dominant in hydrous oxides of iron and amorphous ferri-alumino silicate, a 48-hour (hr) mixing period with the sulphate (SO4) solution was adequate for a near-equilibrium condition. Although differing in their SO4 sorption capacity, all the soils sorbed SO4 at or beyond 1µg ml–1 sulphur (S) concentration in the supernatant. Hydroxyl (OH) ions were displaced during SO4 sorption as indicated by a significant positive correlation between the amount of sorbed SO4 and the difference in pH values determined in 0.1N K2 SO4 and 0.1N KCl, i.e. the dpH values.In a greenhouse experiment, alfalfa was grown on eight soils at six adjusted S concentrations. Sulphur deficiency symptoms appeared in the control pots of those soils which were low in native sorbed SO4, SO4 sorption capacity and initial soil solution S concentration. Sulphur fertilization increased dry matter (DM) yield as well as response to applied S. The external S concentration, i.e. adjusted S concentration required for 95% of the maximum DM yield, ranged from 0.8 to 8.2µg S ml–1 with values less than 2.0 on most of the soils. The external S concentration decreased hyperbolically as the SO4 sorption capacity of the soils increased. The total amount of fertilizer S required to obtain the external S concentration in solution, and at the same time satisfy the SO4 sorption capacity of the soil at the external S concentration (determined from the sorption isotherm) was defined as the external S requirement for the specified yield level of alfalfa. The external S requirement for 95% of the maximum yield of alfalfa varied from soil to soil due to differences in their capacity and intensity for S nutrition.Part of a thesis by the senior author for the MSc (Agric) degree of the University of Dar es Salaam 相似文献
33.
纳米级无机粒子对聚乙烯的增强与增韧 总被引:50,自引:2,他引:50
对μm级CaCO3、TiO2和nm级SiC/Si3N4粒子填充LDPE的性能进行了研究。实验证明,μm级粒子对LDPE虽无明显的增强增韧作用,但也未使基体的机械性能大幅度下降。nm级SiC/Si3N4对LDPE有较大的增强增韧作用,在5%质量分数时冲击强度出现最大值,缺口冲击强度达55.7kJ/m2为纯LDPE的203%;伸长率到625%时仍未断裂,为纯LDPE的500%,但熔体流动速率急剧下降,仅为纯LDPE的26%,当含量在3%和15%质量分数时,熔体流动速率分别为纯LDPE的337%和151%。 相似文献
34.
针对散乱数据,提出一种拟合误差驱动的自适应隐式曲面重建算法。算法根据二次曲面的拟合误差进行自适应拟合,改变了传统方法从八叉树中顶层节点开始拟合,减少了拟合次数,加快了重建速度;并修正权函数,加入密度函数,削弱由于散乱数据密度的不一致对重建曲面影响。实验结果表明,该算法原理简单,重建速度快,重建效果良好。 相似文献
35.
Shujing Yang Guojun Song Yunguo Zhao Chao Yang Xilin She 《Polymer Engineering and Science》2007,47(7):1004-1008
A high-melt-strength polypropylene (HMSPP) with partially cross-linking, modified from a normal isotactic polypropylene (IPP), is prepared by a one-step silane grafting and cross-linking method in a twin-screw reactive extruder. The melt grafting and cross-linking of IPP is achieved by using vinyl unsaturated silane with long chain as a grafting monomer, benzoyl peroxide (BPO) as an initiator, styrene as a coagent, and a little water as a catalyst for cross-linking. By analyzing the difference of the Fourier transformed infrared spectra between raw and modified PP, comparing the variety of the melt flow rate (MFR) and gel percentage between cured and uncured PP samples, and investigating the effect of catalyst on the MFR and gel percentage of modified PP, the partially cross-linked polypropylene in the way of one-step reactive extrusion has been verified. We put forward the reactive mechanism of one-step method based on our experimental results. In this mechanism, the hydrolysis and condensation of silane occur first through the catalysis of water and a compound with two or more double-bond is formed, which then the compound reacts with PP macroradicals to form the partially cross-linked PP. POLYM. ENG. SCI., 47:1004–1008, 2007. © 2007 Society of Plastics Engineers 相似文献
36.
介绍一种基于罗宾康高压变频器的调速监控系统,详细阐述了系统构成、工作原理。在分析了ModBus通信协议的基础上,设计并完成了基于VB的调速系统远程监控软件的开发。工程应用效果良好,实现了某钢厂冲渣工艺的节能自动控制。该系统的软硬件设计方案对同类型系统设计有参考价值。 相似文献
37.
从某类装备测试保障能力现状分析入手,论证了测试保障及技术支援保障面向使用模式转型的智能化使用需求,分析了当前测试设备通用化和标准化的快速推进与栅格化、智能化的技术推动基础,然后以标准测试系统为背景介绍了基于栅格的智能化测试保障方案,并深入介绍了云服务测试保障、网络仪器资源虚拟化等栅格应用的关键技术,为形成智能化保障指挥、构建指挥保障一体化提供思路。 相似文献
38.
针对智能电能表非常容易发生开关跳闸、断电无法工作等故障问题,研究出了一种完善的解决方法;通过调研智能电能表生产企业的信息化系统和生产过程数据,发现生产企业的信息化系统在不同企业间都存在各个信息系统之间分割严重的问题,导致企业内部的数据分布在各个数据仓库内,数据分散,需要对每个生产企业采集装置的采集功能进行定制化对接,基于边缘计算技术的业务系统能够更加切合采集终端,并进行数据处理;本研究将SVG技术和Ajax技术结合使用,构成智能电能表质量监控系统方案框架;经过实验结果表明,通过SVG技术和Ajax技术对智能电力表各项数据信息处理,得到了很好的效果. 相似文献
39.
碳化钽的加入方式对合金结构和性能的影响研究 总被引:2,自引:0,他引:2
对TaC加入到合金中的方式进行了研究,结果表明,以固溶体形式加入的合金的WC相和TiC-TaC-WC相较之以单质(TaC)形式加入的合金的WC相和TiC-TaC-WC相有较粗的亚晶结构和较小的微观应变。与此相对应的是,合金亦具有较好的物理力学性能和较长的切削寿命。 相似文献
40.