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761.
Research on the coefficient of sound absorption in turbid water 总被引:2,自引:0,他引:2
China’s coastal waters are turbid and the properties of the seabed are complex. This negatively impacts the performance of underwater detection equipment. The properties of sound absorption in turbid water are not well understood. In this paper, the coefficient of sound absorption in turbid water was measured by the reverberation technique. All work was done in a reverberation barrel made of seamless aluminum. First, pure water was poured into the reverberation barrel and its reverberation time measured. Next, various concentrations of turbid water were poured into the barrel and their reverberation time measured. After all data had been gathered, the coefficient of sound absorption in turbid water of different concentrations was calculated. From this we determined a law of sound absorption in turbid water as summarized in the paper. 相似文献
762.
按电气集中设计规范关于控制台之要求:和行车安全直接有关系的按钮需要加计数器.6502电气集中车站区段事故按钮增设计数器,用以记录区段事故按钮的按压次数.为此许多设计单位将计数器接在CJ继电器的励磁电路上,如图1所示. 相似文献
763.
Bing Yan Jing Zhao 《西安交通大学学报(英文版)》2009,21(1):1-10
In the paper, we develop the fundamental solutions for a graded half-plane subjected to concentrated forces acting perpendicularly and parallel to the surface. In the solutions, Young's modulus is assumed to vary in the form of E(y) = E0e(ay) and Poisson's ratio is assumed to be constant. On the basis of the fundamental solutions, the singular integral equations are formulated for the unknown traction distributions with Green's function method. From the fundamental integral equations, a series of integral equations for special cases may be deduced corresponding to practical contact situations. The validity of the fundamental solutions and the integral equations is demonstrated with the degenerate solutions and two typical numerical examples. 相似文献
764.
765.
根据异型螺杆的加工原理,本文提出了一种适合于螺杆粗加工的插补算法。并以此算法为基础,提出了复合控制的策略,采用这种控制方法,可有效地提高螺杆粗加工的加工精度和生产效率。 相似文献
766.
In order to more accurately examine developing trends in gross cargo throughput, we have modeled the probability distribution of cargo throughput. Gross cargo throughput is determined by the time spent by cargo ships in the port and the operating efficiency of handling equipment. Gross cargo throughput is the sum of all compound variables determining each aspect of cargo throughput for every cargo ship arriving at the port. Probability distribution was determined using the Wald equation. The results show that the variability of gross cargo throughput primarily depends on the different times required by different cargo ships arriving at the port. This model overcomes the shortcoming of previous models: inability to accurately determine the probability of a specific value of future gross cargo throughput. Our proposed model of cargo throughput depends on the relationship between time required by a cargo ship arriving at the port and the operational capacity of handling equipment at the port. At the same time, key factors affecting gross cargo throughput are analyzed. In order to test the efficiency of the model, the cargo volume of a port in Shandong Province was used as an example. In the case study the actual results matched our theoretical analysis. 相似文献
767.
768.
以离体蟾蜍脊髓为标本,观察亚硒酸钠对腹根反射的作用。发现硒对腹根反射的作用是先兴奋、后抑制。用蔗糖间隙法记录表明硒对腹根有去极化作用。Mg~(2+)明显削弱这一作用,提示硒对中间神经元的作用占主要地位。亚硒酸钠可时抗腹根的强直后超极化电位(即强直VRP的正相波)进一步从反面印证了它对腹根的去极化作用。本文所得结果说明亚硒酸钠对蟾蜍脊髓具有先兴奋、后抑制的双相效应。 相似文献
769.
“Today, the idea of allowing aircraft pilots to operate as they see fit, without any control from the land, is unthinkable. Will the same things apply to ships in twenty to thirty years’ time?”Current maritime pilotage regimes are clearly seen in some quarters as too restrictive and old fashioned. Change is “in the air” and VTS, pilotage, and the relationship between them cannot be immune to it. Subject to the attainment of the appropriate standards by both ships and their crews there is no practical reason why more flexible Vessel Traffic Management cannot be introduced. The required technology is largely available and, with the introduction of AIS, the required dynamic data can be available. Technical problems foreseen are believed capable of solution. The more significant obstacles to implementation are, therefore, largely political, commercial, organisational, and cultural. These issues are discussed in this paper taking into account the viewpoints of major stakeholders. 相似文献
770.
选大鼠及小鼠用醋酸铅腹腔染毒法,初步探讨了铅对鼠红细胞免疫功能的影响。结果表明,连续染毒2周后,大鼠及小鼠的RBC-C_3b受体花环率未见明显改变,而RBC-IC受体花环率随染毒剂量的增加呈递增趋势,高剂量组与对照组比较均有显著性差异(P<0.05)。 相似文献