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101.
Chemical sympathectomy is widely used to study the impact of the noradrenergic system on neuronal and neuroendocrine circuits. We tested the effects of intraperitoneal injections of guanethidine, an adrenergic neuron blocking agent, on selected functional parameters of the rat pineal gland which are known to be under sympathetic influence. The reliability of the method was demonstrated by the clear enophthalmus developed by experimental animals. However, neither the numbers of synaptic ribbons nor melatonin synthesis differed between treated and control rats, both parameters exhibiting the nocturnal increase seen in intact animals. These results are in striking contrast to those obtained upon chemical sympathectomy with 6-hydroxydopamine or surgical superior cervical ganglionectomy. We conclude that guanethidine is not capable of sufficiently removing noradrenergic influence from the rat pineal gland, and that this substance is thus inferior to other experimental methods of sympathectomy. 相似文献
102.
103.
Bryozoans are common, often abundant, sessile, colonial invertebrates of freshwaters. By reviewing what is known of their general ecology and considering in further detail the population biology of specific groups, we provide evidence that 1) populations are locally ephemeral and regional persistence is attained via a dynamic equilibrium between dispersal and colonization, and 2) sex may often be infrequent and a high degree of clonality obtains at both local and regional scales. On the basis of these characteristics we discuss how the group offers exceptional opportunities for investigating a number of fundamentally important ecological and evolutionary questions.The highly curious modification of the Molluscan type which the Polyzoa [=Bryozoa] present... the great beauty of their forms, and the facility with which they can in general be observed in a living state, cannot but render them special favorites for every lover of Nature; and for the more profound student must confer on them a peculiar significance, and invest their study with a scientific interest which is scarcely surpassed by that of any other group of animals.... (Allman 1856) 相似文献
104.
G. Bergström A. -B. Wassgren O. Anderbrant J. Fägerhag H. Edlund E. Hedenström H. -E. Högberg C. Geri M. A. Auger M. Varama B. S. Hansson J. Löfqvist 《Cellular and molecular life sciences : CMLS》1995,51(4):370-380
The main component of the sex pheromone secretion of femaleDiprion pini L. (Hymenoptera: Diprionidae) from insects collected both in Finland and in France has been identified as athreo-3,7-dimethyl-2-tridecanol (8 ng per female) stereoisomer by GC-MS and synthesis. The secretion also contains lower and higher homologues in small amounts (1–4% of the main component). Combined gas chromatographic-electroantennographic detection showed activity in both natural and esterified extracts (acetates and propionates); the esters of the main component gave the largest responses. The acetates and propionates of the eight stereoisomers of 3,7-dimethyl-2-tridecanol were synthesized from enantiomerically highly enriched (>99% ee) building blocks. The stereochemistry of the main component was established to be (2S,3R,7R)-3,7-dimethyl-2-tridecanol by GC analysis of the natural material. It was purified by liquid chromatography prior to the GC analysis of both its pentafluorobenzoates and its isopropylcarbamates on a non-chiral polar column (ECD) and a chiral column (NPD), respectively. Field tests demonstrated that both the acetate and propionate of the main component (100 g of each applied on cotton roll dispensers) were active in attracting males, with or without the presence of several of the minor compounds. Experiments with smaller amounts of the acetate and the propionate (1 g in France and 50 g in Finland) demonstrated that the propionate was more active than the acetate, and that it also caught more males than a blend of the two compounds. 相似文献
105.
赵惠昌 《南京理工大学学报(自然科学版)》1998,22(6):489-491
该文以国外某舰炮弹药无线电近炸引信为例,分析研究了该无线电近炸引信炮口安全保险距离有关的参量,通过对火药燃烧时间和电路延迟时间的计算推出了几种不同情况下该无线电近炸引信炮口保险距离,分析计算方法具有普遍性。 相似文献
106.
该文简述了常用枪口火焰测量的几种方法,对各方法存在的问题下作了系统分析,类比于枪口噪声的测量科学地提出了评价枪口火焰大小及强弱的评价指标,在此基础上提出了一种行之有效的光电测试方法,文中阐明了该方法的原理及系统组成,通过枪口火焰的实弹实验,证明了该方法的可行性。 相似文献
107.
Under 2 100 bar of hydrostatic pressure, KNA N-glycosidase can still cleave the N-C bond of adenosine at position 4324 in
R/S domain of 28S RNA in rat ribosome, demonstrating that high pressure has no effect on the tertiary structure of S/R domain. 相似文献
108.
The smectite to illite transformation in active geothermal systems of New Zealand can be simulated by a first-order reaction
kinetic model, which provides direct estimates about the minumum ages of active geothermal systems themselves. The derived
kinetic values show that the smectite to illite transformation is sensitive to both temperature and time. 相似文献
109.
用^1H—NMR测定纤维素的摩尔取代度 总被引:1,自引:0,他引:1
用^1H-NMR测定羟丙基纤维素的摩尔取代度,根据纤维素在DCl中水解后的^1H-NMR谱峰面积来计算MS值。同时还应用铬酸氧化蒸馏法测定了羟丙基纤维素的MS值,以及利用MS与羟丙基含量的关系得到MS值,可以发现NMR的方法是可行的。 相似文献
110.
链条锅炉模糊控制研究 总被引:6,自引:0,他引:6
针对链条锅炉的运行特点,提出一套基于模糊控制理论的链条锅炉控制方案。链条锅炉滞后时间长、惯性大,采用传统控制方法控制效果不理想,但采用模糊控制方法可以取得良好的控制效果。本控制系统由负荷控制和燃烧控制子系统构成。控制系统通过调节供入的燃料量和合理组织炉内燃烧,提高了锅炉的运行效率。针对不同的调节对象,分别设计了不同的模糊控制器,改善了控制系统的整体控制效果。该系统已经成功地应用于北京市德宝锅炉房。 相似文献