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1.
对于改进的Encke方法,选择适当的参考轨道是一个关键.然而,对于人造地球卫星长弧轨道计算,目前所给出的几种参考轨道均需要逐段校正,这将给定轨问题带来附加的复杂性.本文将仔细探讨如何选择参考轨道和减少校正次数. 相似文献
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介绍了自动高精度测距系统。该系统能以5×10-7的测距精度测定多个观测点的形变,可作为跨断层动态连续观测的新仪器。 相似文献
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Ralph A. M. J. Wijers 《Astrophysics and Space Science》1995,231(1-2):399-402
Since the discovery that dim gamma-ray bursts last longer on average than bright ones (time dilation) the cosmological origin of this effect has been contested by various researchers. I discuss the current status of this issue and conclude that current models for a non-cosmological time dilation only explain part of the observed phenomenon, and even then betray themselves by distinct signatures in the data. As those signatures have not been seen, the cosmological origin remains the favoured explanation of the time dilation. 相似文献
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AbstractThe ground vibrations during pile driving operation have a drastic potential to undermine the surrounding structures both in land and reclaimed land. Particularly, reclaimed land necessitates ample application of pile driving due to the weak land condition. To prevent the structural damage, attenuation of the ground vibrations to an allowable level through active isolation of circular open trench is the scope of this study. In this research, finite element simulations of continuous impact pile driving process from the ground surface was executed with particular attention to the pile-soil interaction, and thereby, the efficiency of open trench application in attenuation of the unsafe distance of different structures was surveyed using the vibration sensitivity degree. Regarding the crucial parameters of an open trench (depth, width, and location), it was concluded that a sufficient high depth can attenuate the unsafe distance up to 68%, the trench width variations are less effective, and an average pile-trench distance is the most efficient option. The excavation volume was also concluded as another crucial parameter in open trench design which takes all three parameters into account. The trench depth equal to the pile’s maximum critical depth of vibration was inferred for an optimum design. 相似文献
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海水中234Th的超低水平液闪谱仪测定 总被引:2,自引:1,他引:2
本文提出了利用超低水平液闪谱仪测定海水中234Th的方法.海水经氢氧化铁吸附共沉淀富集后,接着用阴离子交换和TBP/煤油萃取进行Th同位素的分离与纯化.对一系列测定条件进行了详细的研究,提出了测定海水中234Th的适宜程序,即在含有234Th和产额示踪剂230Th的纯化后的5mol/dm3HNO3溶液中加入TBP/煤油进行萃取,然后用0.1mol/dm3HNO3反萃取,后者是先用契伦柯夫计数法测量234Th(通过234mPa),后加入闪烁液Hisafe 3用α/β模式测量α放射体230Th.对于α和β放射体液闪谱仪的计数效率分别为100%和55.7%±2.7%.234Th的化学回收率和总探测效率分别为70%~80%和30%~45%.该法测定海水中的234Th快速、简便和高效. 相似文献
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Joana F.M.F. Cardoso Johannes IJ. Witte Henk W. van der Veer 《Journal of Sea Research》2007,57(4):316-324
The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm3. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns. 相似文献
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对虾体内氯霉素含量测定方法的研究 总被引:1,自引:0,他引:1
应用HPLC技术建立常用药物氯霉素的虾体动力学研究方法。该方法的特点是:与微生物法、比色法、气相色谱法、荧光法及免疫法比较.测试准确、快速且灵敏度高。应用该方法可以从虾体内的血液、肌肉、肝胰脏、肠胃中分离出被虾吸收的氯霉素,并定量测定。在1—50μg/ml范围内线性关系相关系数为0.9995。 相似文献