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61.
从南北极环境样品中分离到7株产脂肪酶的细菌,经16SrDNA序列分析表明,这些细菌分别属于假交替单胞菌属(Pseudoalteromonas)和嗜冷杆菌属(Psychrobacter).采用p-NPP法对这7株细菌所产的脂肪酶进行酶学性质研究,结果显示这些酶的最适作用温度在30~40cC、最适作用pH值在7—8之间,在低温下能保持较高的剩余活力,对热敏感,属于适冷脂肪酶.其中假交替单胞菌(Psychrobacter sp.7342)所产脂肪酶具有低温下酶的剩余活力高、有效作用温度和pH范围广、热稳定性较好及对多种金属离子抗性强等特点.该菌株能利用多种单一氮源和碳源产酶,最适产酶温度为25℃.在此基础上进行正交实验分析得到了该菌株的最佳发酵条件为:蛋白胨和淀粉含量各为1.33%,酵母膏含量为0.3%,温度为25℃. 相似文献
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63.
We developed generalised additive models (GAMs) to estimate standardised time-series of population abundance indices for assessment purposes and to infer ecological and behavioural information on northern Benguela hakes, Merluccius capensis and M. paradoxus, using haul-by-haul commercial trawl catch-rate data as proxies for hake densities. The modelling indicated that individual ship identifiers should be used rather than general vessel characteristics, such as vessel size. The final models explained 79% and 68% of the variability in the commercial catch rates of M. capensis and M. paradoxus, respectively. The spatial density patterns were consistent and confirmed existing knowledge about these species in the northern Benguela system. Furthermore, seasonal migration patterns were described for the first time and were found to correspond to the known spawning areas and seasons for M. capensis and M. paradoxus. Spatial density patterns were validated using the geostatistical modelling results of fisheries-independent trawl survey data. Improved understanding of the relationships between fleet dynamics and fish movement can be achieved by taking into consideration the present catch-rate model and spatial and seasonal distribution maps. We conclude that the yearly standardised CPUE time-series are problematic as proxies for total stock abundance because of spatial coverage issues. Consequently, such CPUE data should not be used for stock-size assessments and fisheries advice concerning northern Benguela hakes until this is solved. We generally recommend the exclusion of standardised CPUE time-series from stock assessments when important and changing parts of the stock distribution cannot be targeted by the fishery, such as due to closed areas or seasons. 相似文献
64.
The Atlantic inflow in the Fram Strait(78°50′N) has synoptic scale variability based on an array of moorings over the period of 1998–2010. The synoptic scale variability of Atlantic inflow, whose significant cycle is 3–16 d, occurs mainly in winter and spring(from January to April) and is related with polar lows in the Barents Sea. On the synoptic scale, the enhancement(weakening) of Atlantic inflow in the Fram Strait is accompanied by less(more)polar lows in the Barents Sea. Wind stress curl induced by polar lows in the Barents Sea causes Ekman-transport,leads to decrease of sea surface height in the Barents Sea, due to geostrophic adjustment, further induces a cyclonic circulation anomaly around the Barents Sea, and causes the weakening of the Atlantic inflow in the Fram Strait. Our results highlight the importance of polar lows in forcing the Atlantic inflow in the Fram Strait and can help us to further understand the effect of Atlantic warm water on the change of the Arctic Ocean. 相似文献
65.
为提高Kriging近似模型在船舶结构性能多维度响应预测方面的适用性,对常规Kriging近似模型进行分区间泛化改进:一是对设计样本点的各个维度(分量)进行划区,并在每一个分区间内采用最优拉丁超立方(OLhd)取样;二是引入比例系数w1组合高斯与指数型相关函数提高模型对数据的泛化能力,从而在每个划分的区间内建立泛化的Kriging近似模型。通过SCH测试函数,验证了构造的分区间泛化Kriging模型有效性。结合参数化建模和改进Kriging近似模型对某过渡肘板和舱口角隅边界进行形状优化,优化第一阶段由改进的近似模型通过多岛遗传算法得到全局初步的最优解,第二阶段在初步解的基础上缩小优化变量范围,由少量的FEM计算即可在小范围内搜寻到精确的最优设计变量。结果表明:分区间泛化Kriging近似模型在预测多维度响应时较常规Kriging模型预测精度更高;分阶段的形状优化流程在保证极小误差和缩小计算成本的情况下能够得到理想的应力分布和重量优化结果,有助于船舶结构的轻量化研究。 相似文献
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67.
2003年9月3日到14日,"雪龙"号考察船进入北冰洋楚科奇海观测期间,正值一次典型的北极极涡环流过程形成和发展。以往研究大多集中于极涡的平均水平环流特征和季节变化,该例为我们研究它的瞬时环流形势和特征提供了条件。利用NCEP全球分析资料及第二次北极科考资料对这次个例进行天气学分析,通过描述极涡个例的发展情况,平流层、对流层的环流特征以及二者之间的关系,并分析卫星遥感图像及"雪龙"号考察船的气象资料,分析结果发现:2003年中国第二次北极科考期间经历的极涡形成和发展,典型地表现出极地冬夏环流型的转换过程。首先在平流层发生,然后向对流层传播,该个例是一次在平流层西退加强,在对流层东移南下的过程。 相似文献
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69.
Wen-Yao Xu 《Pure and Applied Geophysics》1989,131(3):371-393
Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence. 相似文献
70.
H. R. Phillpot 《Pure and Applied Geophysics》1989,130(2-3):171-180
The behaviour of the Southern Hemisphere stratosphere has attracted considerable interest, and been compared with the Northern Hemisphere, since the International Geophysical Year (1957–58) when the sudden (explosive or accelerated) springtime warming phenomenon in the Antarctic was first observed. Over the years studies of upper air temperature and wind observations have been made, principally through the spring months when the polar vortex breakdown occurs, utilising both ground-based (rawinsonde, rocket) and more recently, satellite-derived data. Although the radiosonde-derived temperature data are limited both by the number of reporting stations, and the practical difficulty of securing observations much above the 100 hPa level, useful records exist from 1956 or 1957. These have shown that in the 1959 southern spring, the lower stratosphere was relatively colder, and the warming rate through the season was essentially more regular, with little evidence of the marked but short-lived temperature fluctuations usually found. Similar, but not quite such wide-spread conditions occurred again in the 1961 spring. In another study, 30 hPa temperature fields over the Antarctic continent, which could be drawn for the 1967 spring, showed the complexity of the polar vortex breakdown. These features are recalled because extension of the 100 hPa springtime temperature series for the Australian Antarctic station at Casey (66.3°S, 110.5°E) shows that in 1985 and part of 1986, the temperature behaviour there was similar to, but not quite so extreme as that which occurred at Mirny (66.5°S, 93.0°E) in 1959. 相似文献