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921.
A large number of papers and technical reports are available on the technically important problem of structural elements executing transverse vibrations and carrying concentrated masses. In general it is assumed that the attachment is perfectly rigid. On the other hand, a rather limited amount of published work is available when the mass is elastically connected to the structure. The system then exhibits a more complex behavior than in the case of rigid attachment. The present study deals with the solution of the title problem using the well-known normal mode, sinusoidal eigenfunction expansions. 相似文献
922.
不同年度收存的褶皱臂尾轮虫休眠卵的孵化及滞育胚胎“激活”效果的研究 总被引:3,自引:0,他引:3
比较了 1 985— 1 998年间由同一褶皱臂尾轮虫 (Brachionusplicatilis)种群在实验室内历年产生并收存的休眠卵的孵化效果 ,并初步探讨了胚胎“激活”处理对孵化的影响。结果表明 ,休眠卵的收存年度或时间对其在一定孵育期内的总孵化率 (THR)和日孵化率 (DHR)有极显著影响 (x2 检验 ,p<0 .0 0 1 ) ,但THR和DHR与储存时间间均无显著的相关性 ,而是呈极大波动。同时发现“激活”作用具有促使孵化高峰提前到来、增强孵化同步性的双重功效 ,从而可明显缩短孵育时间 ,提高孵化速率。但“激活”前后多数卵样的总孵化率无显著变化 (p >0 .0 5 )。详细讨论了可能导致孵化率波动的多种因素 ,例如遗传变异、培养历史、储存及孵化的环境条件等。 相似文献
923.
Underwater sounds near a fuel receiving facility in western Hong Kong: relevance to dolphins 总被引:1,自引:0,他引:1
Western Hong Kong is home to two species of marine mammals: Indo-Pacific humpbacked dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides). Both are threatened in many parts of their range in southeast Asia [for example, International Biological Research Institute Reports 9 (1997), 41; Asian Marine Biology 14 (1997) 111]. In 1998, when the new Hong Kong International Airport opened in western Hong Kong, small tankers (about 100 m long, cargo capacity about 6300 metric tons) began delivering fuel to the Aviation Fuel Receiving Facility (AFRF) just off Sha Chau Island, north of the airport. Calibrated sound recordings were taken over a 4-day period from a quiet, anchored boat at distances 80-2000 m from aviation fuel delivery activities at the AFRF. From the recordings, 143 sections were selected for analysis. Narrowband spectral densities on the sound pressures were computed, and one-third octave band levels were derived for center frequencies from 10 to 16,000 Hz. Broadband levels, viz. 10-20,000 Hz. were also computed. The results showed that the Sha Chau area is normally noisy underwater, with the lowest broadband levels measured corresponding to those expected during a storm at sea (sea state 6). This background noise is believed to come largely from heavy vessel traffic in the Urmston Road to the north and east of Sha Chau and from vessels in the Pearl River Estuary to the West. The sound levels from the AFRF tankers are comparable to the levels measured from similar- and smaller-sized supply vessels supporting offshore oil exploration. The strongest sounds recorded were from a tanker leaving the AFRF at distance 100 m from the hydrophone, for which the one-third octave band level at 100 Hz was 141 dB re 1 microPa (spectrum level 127 dB re 1 microPa2/Hz) and the 10-20,000 Hz broadband level was 146 dB. At distances of 100 m or more and frequencies above 300 Hz, the one-third octave band levels were less than 130 dB (spectrum level 111 dB re 1 microPa2/Hz) and decreased with increasing frequency and distance. At distances greater than about 500 m, AFRF-associated sounds were negligible, masked by the generally high noise level of the area and attenuated by poor transmission in the very shallow water (<10 m). Because it is believed that humpbacked dolphins and finless porpoises are not very sensitive to sounds below 300 Hz, the Airport Authority Hong Kong (AA) stipulated that dedicated terminal vessels not radiate underwater sounds at spectrum levels greater than 110 dB re 1 microPa2/Hz at frequencies above 300 Hz and distances greater than 300 m. The spectrum levels at 300 Hz and higher frequencies of sounds from the tankers arriving, departing, or off-loading at AFRF were less than 110 dB re 1 microPa2/Hz even at distances of 200 m or less. The AA stipulation was met. However, it is presently unknown whether the generally strong noise levels of western Hong Kong inhibit acoustically based feeding and communication, or result in increased stress or permanent shifts in hearing thresholds. 相似文献
924.
Taxonomy and ultrastructure of five species of Tetraselmis (Prasinophyceae) isolated from China seas
INTRODUCTIONThegenusTetraselmisStein ( 1 878)isagreenflagellates (Prasinophyceae)thatconsistsofmanymarineaswellasafewfreshwaterspecies .Marinespeciesoftenoccurindensepopula tionscausingbloomsintidepoolsorbays ,therebybeingimportanttoanunderstandingofthedynam… 相似文献
925.
926.
INTRODUCTIONTheOkinawaTrough (OT) ,locatednorthwestoftheRyukyuTrenchandtheRyukyugunto ,eastoftheEastChinaSeashelf,isaback arcbasinbulgedtotheRyukyuTrench .TheOTextendsfromKyushuinthesouthwestofJapantotheIlanPlaininthenortheasternTaiwan ,Chinainthesouthwest… 相似文献
927.
Glass inclusions in volcanic rocks in the Okinawa Trough back-arc basin:constraints on magma genesis and evolution 总被引:1,自引:0,他引:1
INTROOUcr1ONThe Okinawa Trough is a typical marginal back-arc basin, where its oPening began in rela-tively recent years* There is a great controversy about the origin of its initial magYna. haltand acid volcanic pumice make up the bimedal volcanism in the Okinawa Trough. MOSt of geol-ogists believed that the acid pumice was the preduct of extremely crystal fractionation of baseltInagTna, but the others argued that it should com from the melting of lower-crust. Som de-tailed petrolOgic… 相似文献
928.
一种新的波浪变形三维数值模式──0-1混合型边界元 总被引:4,自引:0,他引:4
为提高边界元法模拟三维波场波浪变形的数值计算精度,借鉴常数元和线性元剖分方式、波势函数及波势函数法向导数对单元节点设定的各自适应性,提出了一种新的单元剖分模式──0-1混合型边界元,以控制和减缓由于计算误差累计而造成的波浪数值计算上的“横向振动”,借此结合边界元法的分区模式可实现较大范围的波场线性波浪变形计算,并为时域内的波浪非线性变形计算提供时间步长的数值保证. 相似文献
929.
盐泽螺旋藻变种的生长和生化特性 总被引:1,自引:0,他引:1
采用1984年在美国加利福尼亚大学培育成功的盐泽螺旋藻变种,经扫描电镜,生物量测定和生化分析,进一步研究其基本特性。结果表明,其藻丝呈紧密的逆时针向等宽螺旋结构。 相似文献
930.