排序方式: 共有13条查询结果,搜索用时 15 毫秒
1.
Alexandrov YN Crymov AA Kotelnikov VA Petrov GM Rzhiga ON Sidorenko AI Sinilo VP Zakharov AI Akim EL Basilevski AT Kadnichanski SA Tjuflin YS 《Science (New York, N.Y.)》1986,231(4743):1271-1273
From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled. 相似文献
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A nonsteady axi-symmetric ideal flow solution is obtained here. It is based on the rigid perfect-plastic constitutive law
with the Tresca yield condition and its associated flow rule. The process is to deform a circular solid disk into a spherical
shell of prescribed geometry. It is assumed that there are no rigid zones and friction stresses. The solution obtained provides
the distribution of kinematic variables and involves one undetermined function of the time. This function can be in general
found by superimposing an optimality criterion. 相似文献
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Preston RA Hildebrand CE Purcell GH Ellis J Stelzried CT Finley SG Sagdeev RZ Linkin VM Kerzhanovich VV Altunin VI Kogan LR Kostenko VI Matveenko LI Pogrebenko SV Strukov IA Akim EL Alexandrov YN Armand NA Bakitko RN Vyshlov AS Bogomolov AF Gorchankov YN Selivanov AS Ivanov NM Tichonov VF Blamont JE Boloh L Laurans G Boischot A Biraud F Ortega-Molina A Rosolen C Petit G 《Science (New York, N.Y.)》1986,231(4744):1414-1416
A global array of 20 radio observatories was used to measure the three-dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the Venus atmosphere near Venus midnight by the VEGA spacecraft on 11 and 15 June 1985. Initial analysis of only radial velocities indicates that each balloon was blown westward about 11,500 kilometers (8,000 kilometers on the night side) by zonal winds with a mean speed of about 70 meters per second. Excursions of the data from a model of constant zonal velocity were generally less than 3 meters per second; however, a much larger variation was evident near the end of the flight of the second balloon. Consistent systematic trends in the residuals for both balloons indicate the possibility of a solar-fixed atmospheric feature. Rapid variations in balloon velocity were often detected within a single transmission (330 seconds); however, they may represent not only atmospheric motions but also self-induced aerodynamic motions of the balloon. 相似文献
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Sagdeev RZ Linkin VM Kerzhanovich VV Lipatov AN Shurupov AA Blamont JE Crisp D Ingersoll AP Elson LS Preston RA Hildebrand CE Ragent B Seiff A Young RE Petit G Boloh L Alexandrov YN Armand NA Bakitko RV Selivanov AS 《Science (New York, N.Y.)》1986,231(4744):1411-1414
The VEGA balloons made in situ measurements of pressure, temperature, vertical wind velocity, ambient light, frequency of lightning, and cloud particle backscatter. Both balloons encountered highly variable atmospheric conditions, with periods of intense vertical winds occurring sporadically throughout their flights. Downward winds as large as 3.5 meters per second occasionally forced the balloons to descend as much as 2.5 kilometers below their equilibrium float altitudes. Large variations, in pressure, temperature, ambient light level, and cloud particle backscatter (VEGA-1 only) correlated well during these excursions, indicating that these properties were strong functions of altitude in those parts of the middle cloud layer sampled by the balloons. 相似文献
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近年来牛结节性皮肤病(LSD)已扩散至俄罗斯和哈萨克斯坦,有可能在数月或数年内传入中国,从而对中国牛群带来严重威胁。本文阐述了LSD在全球扩散情况、预警信息、流行特征、诊断方法,以及相应的风险管理措施。分析了保加利亚LSD防控经验,包括:政府和科学界高度重视,基于传播风险调整防控措施,抓好感染牛群的快速扑杀和无害化处理,大规模开展疫苗免疫,限制活牛运输等。 相似文献
8.
Krassimir D. Naydenov Michel K. Naydenov Francine Tremblay Alexander Alexandrov Louis Daniel Aubin-Fournier 《New Forests》2011,42(2):179-193
As one of the principal coniferous species of commercial importance in Bulgaria, Scots Pine has been subjected to strict management,
which has posed a challenge for the conservation and management of its gene pool. In this study, we measured genetic diversity
and population structure using 6 microsatellite loci in 12 populations from Bulgarian mountain ranges. Our analysis showed
good intrapopulation divergence (18.22%; AMOVA) and genetic evidence of bottlenecks. “NJ-IAM” and “non-admixing” clusters divided the populations into 3 large groups. Our microsatellite analysis was consistent with the documented “mountain effect” influence on genetic diversity. Two methods—the Coalescent Bayesian model and M-stat analysis—implicated recent bottlenecks for all populations, suggesting that the genetic structure of Bulgarian Scots Pine
was shaped over a long period (one thousand generations; i.e. 20,000 years) by the interaction of genetic and autoecological
processes. Our results suggest that conservation and management practices should strive to maintain this genetic differentiation,
specifically by emphasizing reforestation efforts with stocks from local provenances to avoid nonlocal introductions. 相似文献
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Krassimir D. Naydenov Michel K. Naydenov Alexander Alexandrov Kole Vasilevski Georgi Hinkov Vlado Matevski Biljana Nikolic Venceslas Goudiaby Dave Riegert Despina Paitaridou Andreas Christou Irina Goia Christopher Carcaillet Adrian Escudero Alcantara Cengiz Ture Suleyman Gulcu Veselka Gyuleva Srdjan Bojovic Lorenzo Peruzzi Salim Kamary Anatoly Tsarev Faruk Bogunic 《European Journal of Forest Research》2017,136(5-6):767-786
The historical changes in European Black Pine population size across the whole natural distribution in Europe and Asia Minor were analyzed facing the Plio-Pleistocene climatic fluctuations. Thirteen chloroplast SSRs and SNPs markers have been studied under the assumptions of “neutral evolution.” Populations and meta-populations had different histories of migration routes, and they were strongly affected by complex patterns of isolation, fragmentation, speciation, expansion (1.88–4.28 Ma), purification selection (2.09–21.41 Ma) and bottleneck (1.85–21.76 Ma). A significant number of populations (min. 29–41%) were in equilibrium for very long periods. Generally, the bottleneck revealed by chloroplast DNA is weaker than the bottleneck revealed by nuclear DNA. The N e immediately after the bottleneck reaches between 1820 and 3640 individuals. Generally, the historical effective population sizes shrink significantly for the Tertiary period from 10–15 up to 2.5 Ma in Western Europe (by 82%), followed by Asia Minor (69%) and the Balkan Peninsula (28%), likely resulting from important climatic changes. The rates and frequencies of stepwise westwards migration waves have been not sufficient to prevent isolation between the meta-populations and to suppress “sympatric speciation.” The migration was weak for the Pliocene, but was maximal for the Pleistocene, and finally silent for the present interglacial period, namely the Holocene. 相似文献
10.
Breithaupt A Depner K Haas B Alexandrov T Polihronova L Georgiev G Meyer-Gerbaulet H Beer M 《Veterinary microbiology》2012,159(1-2):33-39
Foot and mouth disease (FMD) was detected in a wild boar in Southeastern Bulgaria in December 2010. The occurrence and spread of the disease in wild cloven-hoofed animals may pose an unexpected and significant threat to FMD virus (FMDV)-free areas within and outside the European Union. So far, only one well documented experimental infection with FMD in wild boar has been published. In order to obtain more epidemiologically relevant data regarding the disease in wild boar we conducted an experiment with the 2010 Bulgarian FMDV type O isolate. Two young wild boar were challenged while two domestic pigs and two additional wild boar served as contact controls. While the domestic pigs developed severe clinical signs of FMD, the wild boar showed relatively mild course of the disease. Viremia started in contact wild boar 2 days post exposure (DPE) and lasted until 6 DPE. The virus shedding lasted until 9 DPE. On 27 DPE, when the animals were slaughtered, viral RNA was detected in lymphoid tissues and oropharyngeal fluid but no virus could be isolated. Commercial ELISAs and virus neutralisation tests detected antibodies against FMDV on 8 or 6 DPE, respectively. The data of the present study will help to understand FMD in wild boar populations and can be used in models to evaluate the potential role of wild boar in FMD epidemiology. 相似文献