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排序方式： 共有131条查询结果，搜索用时 15 毫秒
91.
Jeremy S. Johnson Keith D. Gaddis David M. Cairns Charles W. Lafon Konstantin V. Krutovsky 《自然地理学》2016,37(2):93-119
Global change has become a major ecological concern that has the potential to dramatically alter plant distributions and assemblages worldwide. The specific response of plants to global change will depend on their ability to move, evolve, or adjust through phenotypic plasticity. Advances in biogeographic research are on the verge of a giant leap forward if we can take advantage of emerging tools in genetics and genomics. In this review, we appraise how new, post-Sanger, high-throughput sequencing and associated technologies can be used by next generation biogeographers to assess plant responses to global change. First, we briefly review the recent advances in genome sequencing and available approaches of genomic analysis. Secondly, we discuss the three main plant responses to global change: migration, adaptation, and phenotypic plasticity. This review is intended to spark the interest of biogeographers who do not traditionally use genetics but could benefit from including genetic and genomic tools into their research. Our goal is to illustrate that their use can contribute to new perspective and add an additional level of resolution into future biogeographic research. 相似文献
92.
The occurrence of rockfall incidents on the transportation network may cause injuries, and even casualties, as well as severe damage to infrastructure such as dwellings, railways, road corridors, etc. Passive protective measures (i.e., rockfall barriers, wire nets, etc.) are mainly deployed by operators of ground transport networks to minimize the impact of detrimental effects on these networks. In conjunction with these passive measures, active rockfall monitoring should ideally include the magnitude of each rockfall, its initial and final position, and the triggering mechanism that might have caused its detachment from the slope. In this work, the operational principle of a low-cost rockfall monitoring and alerting system is being presented. The system integrates measurements from a multi-channel seismograph and commercial cameras as the primary equipment for event detection. A series of algorithms analyze these measurements independently in order to reduce alarms originated by surrounding noise and sources other than rockfall events. The detection methodology employs two different sets of algorithms: Time–frequency analyses of the rockfall event’s seismic signature are performed using moving window pattern recognition algorithms, whereas image processing techniques are utilized to deliver object detection and localization. Training and validation of the proposed approach was performed through field tests that involved manually induced rockfall events and recording of sources (i.e., passing car, walking people) that may cause a false alarm. These validation tests revealed that the seismic monitoring algorithms produce a 4.17 % false alarm rate with an accuracy of 93 %. Finally, the results of a 34-day operational monitoring period are presented and the ability of the imaging system to identify and exclude false alarms is discussed. The entire processing cycle is 10–15 s. Thus, it can be considered as a near real-time system for early warning of rockfall events. 相似文献
93.
ＫｏｎｓｔａｎｔｉｎＦ．Ｔｙａｐｋｉｎ 《地学前缘》1998,(1)
文章叙述地质构造的新旋转概念,它可以解释地质构造激活的实质。每一次地质构造激活产生某些断裂系统,沿着这些断裂,地壳块体会发生一定的位移,并伴有一些地质现象产生。每一断裂系统的形成产生该系统特定的金属成矿条件,此规律性可用于金属矿预测。沉积盆地前景研究表明,沉积盖层中含碳氢化合物的局部构造仅与基底某些特定断裂系统的激活相关,用综合地球物理方法可揭示这种相关性的具体形式,并进行盆地前景评价。 相似文献
94.
Significant drag reduction of large displacement vessels can be achieved by applying multi-wave air cavities arranged on the hull bottom. Waves generated on the air–water interface of air cavities impose requirements on the dimensions of a hull recess that accommodates the air cavity. An approximate model for calculating wave patterns in the critical upstream part of long air cavities in a simplified, horizontal-plane geometry is presented in this paper. The influence of the recess planform boundaries and other factors on the wave patterns is studied parametrically. Some hydrodynamic aspects of multi-wave air cavities are discussed. 相似文献
95.
The first systematic model series of hulls with small waterplane area (both single hulls and twin-hulls) was designed and tested in Krylov Shipbuilding Research Institute in the middle of the 1980's. The series was intended to cover a broad range of Froude numbers, hull aspect ratios, design drafts, and spacing between hulls. In the present paper, these test results are re-analyzed by accounting for the scale effect in the form drag, obtained from the comparison with test data of larger out-of-series models. Illustrative results are also given for the influence of the cross-section hull shape, strut configuration, and shifted hulls on the residual resistance and for dynamic trim and draft. Some data are compared with those of the later series tests of twin-hull models with small waterplane area carried out in HSVA, Germany. Factors influencing the residual resistance of ships of this type are discussed. 相似文献
96.
Modelling of water levels in the Baltic Sea, aimed at evaluating the influence of the trajectories and propagation speeds of a deep idealized cyclone on sea-level extremes in the Gulf of Finland, is done using the hydrodynamic model BSM6. An analytical expression for determination of the atmospheric pressure in this cyclone takes into account the existence of the cold front and the time evolution of the cyclone intensity. The empirical parameters in this relation are based on those of the deep cyclone ‘Erwin’ which passed over the Baltic Sea region in 2005. 相似文献
97.
Academy Bay in the Sea of Okhotsk is an important summertime feeding ground for pelagic-feeding Bowhead whales (Balaena mysticetus) in the western subarctic North Pacific. The present work combines satellite observations with physical (CTD, currents, tides) and biological (zooplankton sampling) measurements. Data obtained aboard the RV Lugovoe in August–September 2003 and July–August 2004 show dense populations of zooplankton (such as copepods Calanus glacialis, Pseudocalanus sp., pteropods Limacina helicina, and chaetognaths Sagitta sp.) that are concentrated by physical mechanisms within this critically important ecosystem. We show that near-bottom, cold water intrusions from the northern Sea of Okhotsk associated with the estuarine circulation advect arctic herbivorous calanoids (Calanus glacialis) and mollusks Limacina helicina into the region. 相似文献
98.
Konstantin B. Klokov 《Polar research》2000,19(1):39-47
The article is dedicated to the problems of survival and development among the aboriginal peoples of northern Russia in the context of current conditions. Data collected in the western art of the Taimyr Autonomous District allowed us to divide the non-sedentary population of this territory into three groups differentiated by overall way of life, land use and economic "calendar." These groups are: the nomadic reindeer herders of the tundra (about 250–300 people), the semi-nomadic fishermenherders of Yenisei delta (about 500), and the nomadic herders of the forest-tundra (300–350). The economy and ways of life of the three non-sedentary groups are are described. Communities whose traditional subsistence base is reindeers have entered a crucial period. In response to the pressure of the dominant society, these peoples have three ossible strategies: isolation, passive adaptation and active adaptation. Only the last strategy can preserve their culture, and create a "neoculture". Now, however, passive adaptation predominates. The mutual, bi-directional process of cultural integration needs to reinforce positive aspects of acculturation and promote active, rather than passive, adaptation. A necessary condition for this is the appearance among the Nenets of an intermediate social stratum which maintains close links to nomadic reindeer-husbandry and is simultaneously integrated into the dominant society. 相似文献
99.
100.
Konstantin V. Kholshevnikov Vakhit Sh. Shaidulin 《Celestial Mechanics and Dynamical Astronomy》2017,128(1):75-94
The main form of the representation of a gravitational potential V for a celestial body T in outer space is the Laplace series in solid spherical harmonics \((R/r)^{n+1}Y_n(\theta ,\lambda )\) with R being the radius of the enveloping T sphere. The surface harmonic \(Y_n\) satisfies the inequality The angular brackets mark the maximum of a function’s modulus over a unit sphere. For bodies with an irregular structure \(\sigma = 5/2\), and this value cannot be increased generally. However, a class of irregular bodies (smooth bodies with peaked mountains) has been found recently in which \(\sigma = 3\). In this paper, we will prove the exactness of this estimate, showing that a body belonging to the above class does exist and for it.
相似文献
$$\begin{aligned} \langle Y_n\rangle < Cn^{-\sigma }. \end{aligned}$$
$$\begin{aligned} 0<\varlimsup n^3\langle Y_n\rangle <\infty \end{aligned}$$