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1.
The volume transport of the Florida Current is determined from the motionally induced voltage difference between Florida and Grand Bahama Island. Simultaneous measurements of potential differences and of volume transport by velocity profiling have a correlation of 0.97. The calibration factor is 25+/- 0.7 sverdrups per volt, and the root-mean-square discrepancy is 0.7 sverdrup. The induced voltage is about one-half the open-circuit value, implying that the conductance of the sediments and lithosphere is about equal to that of the water column.  相似文献   

2.
A 1-year time series of volume transport through the Florida Straits near 27 degrees N was derived from an array of five subsurface current meter moorings. The transport estimates, determined on the basis of constant shear extrapolation of the subsurface velocities to the surface, are in good agreement with transports derived from submarine cable and Pegasus measurements. The annual transport cycle in 1982-1983 is complicated by large-amplitude fluctuations on time scales of 1 to 3 weeks, but it does exhibit a transport maximum in summer and a minimum in fall-winter, consistent with historical results and of similar magnitude. The energy density spectrum of transports is continuous with a slope of about -1.5 and does not show a gap between the periods of weeks and seasonal. Evidence was found for atmospheric forcing of transport fluctuations, with highest coherence between transport and the local meridional wind stress at periods of 10 and 15 days during the summer and 5 and 40 days during the winter.  相似文献   

3.
Hydrogen gas crosses the pulmonary membrane and dissolves in blood, and it therefore appears immediately and in high concentration in the left heart and later and in lower concentration in the right heart. The hydrogen-sensing, platinum black-tipped catheter is uniquely sensitive in detecting the left-to-right shunts.  相似文献   

4.
Negative pions are useful for radiation therapy of localized carcinoma because of their large end-of-range energy deposition upon capture in nuclei and the potentially accurate spatial localization of the radiation dose. Accurate determination of the depth of penetration of the pion beam in vivo can be accomplished by counting the back-to-back annihilation gamma rays resulting from positron activity induced by the stopped pions.  相似文献   

5.
Climate changes in the Central Chernozem Region has increased the frequency of high evaporativity in the winter and spring, which both separately and in combination with other unfavorable factors intensifies transpiration losses, leading to a decrease in the yield of apple, strawberry, and winter crops. It is necessary to optimize the water regime of plants by selecting varieties with a high water-retaining capacity of one-year shoots and leaves as well as by reducing water losses during their growth.  相似文献   

6.
Mecrowear of mammalian teeth as an indicator of diet   总被引:1,自引:0,他引:1  
Microwear details on teeth of two sympatric species of hyrax are correlated with major dietary differences observed in the wild. Grazing (Procavia john-stoni) and browsing (Heterohyrax brucei) species can be distinguished. The results show that diets of extinct species may be deduced from tooth microwear.  相似文献   

7.
The removal of atmospheric effects from Nimbus-7 Coastal Zone Color Scanner (CZCS) images reveals eddy-like ocean turbidity patterns not apparent in the original calibrated images. Comparisons of the phytoplankton pigment concentrations derived from the corrected CZCS radiances with surface measurements agree to within less than 0.5 log C, where C is the sum of the concentrations of chlorophyll a plus phaeopigments a (in milligrams per cubic meter).  相似文献   

8.
Boersma PD 《Science (New York, N.Y.)》1978,200(4349):1481-1483
Surface water changes associated with El Ni?o have been known to affect deleteriously top carnivores along coastal South America. Data on the breeding strategies of Galápagos penguins and other seabirds indicate that the biological effects of El Ni?o extend much farther west. The breeding biology of these seabirds is adapted to frequent changes in productivity which are associated with El Ni?o.  相似文献   

9.
土壤微生物量碳作为林地土壤肥力指标   总被引:29,自引:0,他引:29  
分析了杉木林、常绿阔叶林和灌木林的土壤微生物量碳和养分含量。结果表明:3种林地土壤生物量碳和养分含量均呈现出灌木材>常绿阔叶林>杉木林的排序。灌木林和杉木林土壤微生物量碳与土壤养分含量都有很好的相关性,灌木林土壤微生物量碳与土壤有机质、全氮、全磷、水解氮含量和阳离子交换量的相关系数分别为0.6802^**,0.6734^**,0.5891^**,0.7485^**和0.5418^**;杉木林土壤微生物量碳与土壤有机质、全氮、全磷、全`钾水解氮、有效磷含量和阳防子交换量的相关系数分别为0.5456^*,0.6063^**,0.7047^**,0.4714^*,0.4455^*,0.4988^*和0.5125^*。土壤微生物量碳可以作为林地土壤肥力指标。图1表1参10  相似文献   

10.
Absolute velocity and temperature profiles are used to estimate the volume transport through the Straits of Florida and, in combination with historical midbasin data, to estimate the total meridional heat flux through a section at 27 degrees N. The mean annual volume transport of the Florida Current from April 1982 through August 1983 is 30.5 (+/- 1)x 10(6) cubic meters per second. The net northward heat flux through the 27 degrees N section is 1.2 (+/- 0.1)x 10(15) watts. The volume transport is characterized by high values in the late spring and early summer and low values in the late fall and early winter. There is a similar cycle in total heat flux.  相似文献   

11.
The change in the content of labile organic matter during anthropogenic evolution of gray forest soils of the right bank region of Nizhni Novgorod oblast has been studied. It has been established that its chemical and elemental compositions reflect the character of the biological cycle and direction of the pedogenic process in agrocenoses.  相似文献   

12.
Precision irrigation requires the mapping of within-field variations of water requirement. Conventional remote sensing techniques provide estimates of water status at only shallow soil depths. The ability of a water sensitive crop, sugar beet, to act as an intermediate sensor providing an integrated measure of water status throughout its rooting depth is tested here. Archive aerial photographs and satellite imagery of Eastern England show crop patterns resulting from past periglacial processes. The patterns were found to be spatially and temporally consistent. Field sampling of soil cores to 1 m depth established that the within-field wilting zones were significantly associated with coarser or shallow soils. The stress classes, determined by classification of the digitised images, were weakly correlated with total available water (Pearson correlation r = 0.588, P < 0.05). These results suggest that wilting in sugar beet can be used as an intermediate sensor for quantifying potential soil water availability within the root zone. Within-field stress maps generated in 1 year could be applied as a strategic tool allowing precision irrigation to be applied to high-value crops in following years, helping to make more sustainable use of water resources.  相似文献   

13.
It has recently been suggested that the solar irradiance has varied in phase with the 80- to 90-year period represented by the envelope of the 11-year sunspot cycle and that this variation is causing a significant part of the changes in the global temperature. This interpretation has been criticized for statistical reasons and because there are no observations that indicate significant changes in the solar irradiance. A set of data that supports the suggestion of a direct influence of solar activity on global climate is the variation of the solar cycle length. This record closely matches the long-term variations of the Northern Hemisphere land air temperature during the past 130 years.  相似文献   

14.
自20世纪60年代以来,现代性问题几乎成为很多研究领域中的核心概念和热点问题。现代性是一个内涵极其复杂的概念,在它的内部,同时并存着启蒙现代性与审美现代性这两个既相互联系又呈背反关系的层面。在电影《海上钢琴师》中,呈现出了现代性的这两种内在张力的紧张关系,即审美现代性对启蒙现代性的反思与批判。  相似文献   

15.
科研能力的培养是现代本科生教育的重要环节。该文以美国佛罗里达大学为例,概括了美国本科生物学专业课程设置情况,着重分析了课程设置中注重学生科研气质的培养特点;并通过比较国内综合性大学生物学专业课程设置,分析了由UF本科生物学专业注重科研能力培养课程设置给予国内综合性大学生物学课程设置的启示,从而为综合性大学本科生物学专业的教学改革提供一些合理化的建议,并有助于综合性大学本科生物学专业的发展。  相似文献   

16.
Rising mean sea level, it is proposed, is a significant indicator of global climate change. The principal factors that can have contributed to the observed increases of global mean sea level in recent decades are thermal expansion of the oceans and the discharge of polar ice sheets. Calculations indicate that thermal expansion cannot be the sole factor responsible for the observed rise in sea level over the last 40 years; significant discharges of polar ice must also be occurring. Global warming, due in some degree presumably to increasing atmospheric carbon dioxide, has been opposed by the extraction of heat necessary to melt the discharged ice. During the past 40 years more than 50,000 cubic kilometers of ice has been discharged and has melted, reducing the surface warming that might otherwise have occurred by as much as a factor of 2. The transfer of mass from the polar regions to a thin spherical shell covering all the oceans should have increased the earth's moment of inertia and correspondingly reduced the speed of rotation by about 1.5 parts in 10(8). This accounts for about three quarters of the observed fractional reduction in the earth's angular velocity since 1940. Monitoring of global mean sea level, ocean surface temperatures, and the earth's speed of rotation should be complemented by monitoring of the polar ice sheets, as is now possible by satellite altimetry. All parts of the puzzle need to be examined in order that a consistent picture emerge.  相似文献   

17.
Using a test site in the Saratov Near-Volga Region, the paper shows that the crop canopy heterogeneity detected based on MODIS satellite data can serve as an indicator of contrast in soil patterns. The results from the satellite analysis of the crop canopy heterogeneity are proposed to be used as additional data for digital soil mapping.  相似文献   

18.
台风、暴雨、雷电、大风、高温、强寒潮、龙卷等灾害性天气出现时,容易直接或者间接造成人员伤亡、较大财产损失或者发生生产安全事故。气象科普工作作为气象事业发展的重要组成部分,是促进全民科学素质提高的重要途径和普及防灾减灾知识的重要手段。气象科普工作的发展及普及状况在很大程度上决定了气象灾害所造成的安全事故的多寡以及公众对气象工作的认知和理解程度。县级气象部门是最基层的气象机构,县级气象科普工作机制和体系是否健全直接影响基层公众的气象灾害防御及安全技能提升。如何走出县级气象科普困境,突破气象科普工作发展瓶颈,寻求合理的气象科普工作发展途径是当前县级气象科普工作所面临的迫切问题。本文以天长市为例,从安全视角分析县级气象科普的现状、面临的困境,并对县级气象科普发展途径进行了探讨,有助于有效提升公众自我防灾避险能力,做好新时代气象科普宣传工作,为人民生命财产安全保驾护航。  相似文献   

19.
柔鱼是北太平洋海域的重要经济头足类,黑潮的变化直接影响着柔鱼渔场形成及其空间分布。利用1998-2007年黑潮分布类型,结合同期8-10月我国鱿钓渔船生产数据,分析北太平洋柔鱼渔场变化与黑潮分布的关系。在25°~40°N、125°~150°E海域内,以空间分布率经纬度5°×5°为一个空间单元,共分A(140°~145°E、35°~40°N)、B(145°~150°E、35°~40°N)、C(135°~140°E、30°~35°N)、D(140°~145°E、30°~35°N)和E(145°~150°E、30°~35°N)5个区,将黑潮分布类型分为大弯曲型、小弯曲型和平直型3种。利用渔场重心的纬度向变化作为柔鱼渔场变动的指标。研究认为,A区黑潮分布特征对柔鱼渔场重心纬度影响最大,其次为B区和C区,而其它区影响则不明显。A区出现黑潮大弯曲型时,柔鱼渔场重心明显偏北且概率高;小弯曲型或平直型时,柔鱼渔场重心明显偏南。研究认为,黑潮流轴的走向影响着柔鱼渔场的空间分布。  相似文献   

20.
西北太平洋柔鱼渔场变化与黑潮的关系   总被引:4,自引:3,他引:4  
柔鱼是北太平洋海域的重要经济头足类,黑潮的变化直接影响着柔鱼渔场形成及其空间分布。利用1998-2007年黑潮分布类型,结合同期8-10月我国鱿钓渔船生产数据,分析北太平洋柔鱼渔场变化与黑潮分布的关系。在25°~40°N、125°~150°E海域内,以空间分布率经纬度5°×5°为一个空间单元,共分A(140°~145°E、35°~40°N)、B(145°~150°E、35°~40°N)、C(135°~140°E、30°~35°N)、D(140°~145°E、30°~35°N)和E(145°~150°E、30°~35°N)5个区,将黑潮分布类型分为大弯曲型、小弯曲型和平直型3种。利用渔场重心的纬度向变化作为柔鱼渔场变动的指标。研究认为,A区黑潮分布特征对柔鱼渔场重心纬度影响最大,其次为B区和C区,而其它区影响则不明显。A区出现黑潮大弯曲型时,柔鱼渔场重心明显偏北且概率高;小弯曲型或平直型时,柔鱼渔场重心明显偏南。研究认为,黑潮流轴的走向影响着柔鱼渔场的空间分布。  相似文献   

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