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31.
心电场是由心肌的电活动产生的。心肌细胞的电特性及心肌细胞间的传导关系决定了体表电位的分布及心电图的变化。心肌电兴奋传导速度则是影响心肌间兴奋传导关系的重要参数之一。由于很难通过实验方法来人为改变电兴奋传导速度,因而临床上有关该参数对心律影响的定量知识相当缺乏。本文采用真实三雏躯干模型及心脏模型,对心肌电兴奋传导速度与心律变化的关系进行定量仿真研究。结果表明,兴奋传导速度决定了整个心电图的变化,而局部普通心肌的传导速度在相当范围内变化似乎对心电图影响不明显,但传导速度超过一定范围后可能产生突变。 相似文献
32.
林带中阻力分布的理论与实验研究 总被引:7,自引:1,他引:6
推导了风向垂直于林带走向时林带内的阻力分布的解析式,比较了3种所面形状林带的阻力分布特点,并用风洞实验资料进行了验证,简析了在实际生产中的应用. 相似文献
33.
异源八倍体小冰麦体细胞无性系的建立及其染色体变异 总被引:3,自引:0,他引:3
从5个异源八倍体小冰麦(Triticum -Agropyron)的叶片、幼穗及成熟胚诱导愈伤组织,建立体细胞无性系,获得大量再生植株。附加一个冰草染色体组的异源八倍体小冰麦杂种无性系中37.5% 表现变异,其中非整倍体植株变异较多,很多变异的再生植株形态与小麦近似,同时出现一定数量染色体重排、交换、易位、断裂、融合等变异。结果表明,通过杂种无性系变异进行染色体基因转化及遗传修饰是一条可行的途径。实验还观察了小冰麦愈伤组织分化过程中绿点的形成过程,首次提出两种类型绿点,即芽绿点和根绿点,并描述了两者的差异 相似文献
34.
帕里红景天的化学成分研究 总被引:10,自引:0,他引:10
从帕里红景天根茎的石油醚和乙醇提取部分共分得14种结晶性化合物,经光谱分析和化学反应,分别鉴定为二十二醇、二十六酸、十九醇、β-谷甾醇、二十九醇、红景天甙、麦芽糖、棉皮素-8-葡萄糖甙、胡萝卜甙、酪醇、咖啡酸、没食子酸、形花内酯和新化合物帕里甙。 相似文献
35.
锦橙汁囊的超微结构 总被引:1,自引:0,他引:1
用常规电镜方法观察了锦橙[Citrussinensis (L.) Osb.]汁囊从原始细胞到发育为一个具柄的成熟汁囊的过程中,汁囊构成细胞超微结构的变化。锦橙汁囊原始细胞及发育为球状体时的构成细胞以及柱状结构顶端的细胞都是一种典型的分生组织细胞。在细胞质中有包括线粒体、质体、内质网、核糖体等丰富的细胞器,但没有观察到高尔基体。这些分生细胞分裂一段时期后就停止活动,逐渐分化为适应贮藏功能的液泡化薄壁细胞。分生细胞开始分化时,在细胞中出现许多小液泡和高尔基体。这些小液泡逐渐地融合,同时细胞质变少,最后形成一个有中央大液泡的薄壁细胞,在紧贴细胞膜的薄薄的一层细胞质中有线粒体、质体、高尔基体以及含有许多脂滴的杂色体。但成熟果实中汁囊的薄壁细胞中几乎没有任何细胞器。 相似文献
36.
37.
本文报告了从烧伤病人感染创面分离、鉴定的35株变形杆菌的药敏试验及接合性R质粒的检测结果。35株变形杆菌双测试的6种抗菌药物都具有不同程度的耐药性。其中,对6种药物同时耐受的有26株(74.3%)。对其中的27株做了接合试验,接合性R质粒的检出率为70.4%。 相似文献
38.
Phagocytic cell molecules that bind the collagen-like region of C1q. Involvement in the C1q-mediated enhancement of phagocytosis 总被引:5,自引:0,他引:5
E N Guan W H Burgess S L Robinson E B Goodman K J McTigue A J Tenner 《The Journal of biological chemistry》1991,266(30):20345-20355
C1q binds to and elicits cellular responses by several cell types, including monocytes, macrophages, neutrophils, B cells, and fibroblasts. The cell-binding domain is located within the collagen-like pepsin-resistant region of the C1q molecule (C1q tails). An affinity matrix of C1q tails coupled to Sepharose was used to select C1q-binding proteins from detergent extracts of surface-iodinated human monocytes, polymorphonuclear leukocytes, and the U937 cells. The major radiolabeled polypeptide eluted specifically from the ligand affinity column had an apparent molecular mass (Mr) of 126,000. Minor iodinated components eluted from Sepharose-tails migrated with Mr of 216,000 and 55,000. When subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions no change in the migration of any of these polypeptide bands was detected. None of these polypeptides reacted with antibodies directed against the integrins alpha 5 beta 1 (fibronectin receptor) or alpha v beta 3 (vitronectin receptor), LFA-1, or to several other cell adhesion molecules. The Mr 126,000 band was found to contain more than one polypeptide. Lectin binding properties, susceptibility to glycosidases and proteases, and immunoreactivity with the monoclonal antibody L-10, indicated that CD43 (sialophorin/leukosialin) is a component of this band. However, further data show that a monoclonal antibody, generated by immunization with the isolated Clq-binding fractions, recognizes a cell surface sialoglycoprotein distinct from CD43 and inhibits the C1q-mediated enhancement of phagocytosis in monocytes. These latter observations provide the first definitive connection between a specific phagocytic cell surface protein and a known C1q-mediated function. While these proteins contain sialic acid, binding assays and functional assays using neuraminidase-treated cells demonstrate that the functional interaction between C1q and the cell surface is not via sialic acid. The data taken together indicate either that the functional C1q receptor on phagocytic cells is a multi-subunit complex or that multiple proteins can interact with the fragment of C1q containing the cell-binding domain, at least one of which is involved in the C1q-mediated enhancement of phagocytosis. 相似文献
39.
Location-dependent variations in the material properties of the anterior cruciate ligament. 总被引:4,自引:0,他引:4
D L Butler Y Guan M D Kay J F Cummings S M Feder M S Levy 《Journal of biomechanics》1992,25(5):511-518
Our recent anterior drawer studies in human cadaveric knees [Guan and Butler, Adv. Bioengng 17, 5 (1990); Guan et al., Trans. orthop. Res. Soc. 16, 589 (1991)] have suggested that anterior bundles of the anterior cruciate ligament (ACL) develop higher load-related material properties than posterior bundles. This was confirmed when we reevaluated the axial failure data for these bundle-bone specimens from an earlier study [Butler et al., J. Biomechanics 19, 425-432 (1986)]. The purpose of this study was to determine, in a larger data set, if anteromedial and anterolateral bundles of the anterior cruciate ligament exhibit significantly larger load-related material properties than the posterior ligament bundles. Seven ACL-bone units from seven donors (the three tissues from the original study plus four new ones) were subdivided into three subunits, preserving the bone insertions. The subunits were failed in tension at a constant strain rate (100% s-1) and four material properties were compared within and between donors. The anterior bundles developed significantly larger moduli, maximum stresses, and strain energy densities to maximum stress than the posterior subunits. Moduli for the anterior vs posterior subunits averaged 284 MPa vs 155 MPa, maximum stresses averaged 38 MPa vs 15 MPa, and strain energy densities averaged 2.7 N m cc-1 vs 1.1 N m cc-1, respectively. No significant differences were found, however, among strains to maximum stress or between any of the other properties for the two anterior subunits. These results are important to the design of ligament replacements and suggest new experiments designed to distinguish in vivo force levels in these ACL bands, a possible reason for the material differences. 相似文献
40.
A method of enzyme release and aqueous two-phase extraction is described for the separation of penicillin acylase from Escherichia coli cells. Butyl acetate, 12% (v/v), treatment combined with freeze-thawing gives up to 70% enzyme release. For polyethylene glycol (PEG) + phosphate two-phase extraction systems the enzyme purity and yield were rather low. Modified PEG, including PEG-ampicillin, PEG-aniline, PEG-phosphate, and PEG-trimethylamine, were synthesized and used in aqueous two-phase systems; PEG-trimethylamine is the most satisfactory. A system containing 12% (w/w) PEG4000, 8% (w/w) of which is PEG-trimethylamine, with 0.7M potasium phosphate at pH 7.2, resulted in the enzyme selective partition being greatly enhanced by charge directed effects. Possible mechanisms for the separation process are discussed. (c) 1992 John Wiley & Sons, Inc. 相似文献