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51.
Two hypotheses are explored to explain the thinness of the fresh water lens on Andros Island, Bahamas. The lens is an order of magnitude thinner than predicted by the Ghyben-Herzberg theory. One hypothesis previously posed in the literature is that the base of the lens is governed by the contact between the Lucayan Formation and the pre-Lucayan limestones. An alternate hypothesis, posed here, is that thinning is caused by the hydraulic influence of low-permeability paleosols in the Lucayan Formation. These hypotheses were explored, along with the influence of recharge and other factors, using a numerical model for variable-density flow and salt transport. In the layered system of grainstones/packstones and paleosols within the Lucayan Formation itself, the velocity vectors are nearly horizontal in the grainstones/packstones, and they are nearly vertical in the paleosols. These strata above the pre-Lucayan, all lower than it in permeability, draw the base of the lens upward to a position well above the contact by significantly reducing pressure within and below the strata relative to hydrostatic pressure. It is the loss of pressure across the paleosols that dramatically thins the fresh water lens, and thus the predominant hydraulic control on lens thickness arises from the existence of paleosols. 相似文献
52.
本文基于南加里弗尼亚地价昂贵且土地逐渐减少,大部分建筑开始修建填土斜坡上这一事实,对压实粘土斜坡进行地下勘探和现场测试,并对压实粘土做了室内试验。从而探讨了压实粘土软化和蠕变的规律及其影响因素。 相似文献
53.
Howe R Christensen-Dalsgaard J Hill F Komm RW Larsen RM Schou J Thompson MJ Toomre J 《The Astrophysical journal》2000,534(2):L163-L166
We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power-law distribution of energies. The FC spectrum has so far been described by four power-law segments divided by three break frequencies nusa相似文献
54.
�ϲ���ά�������ʷ��ݵ��㷨�Ա� 总被引:1,自引:0,他引:1
?????????????λ????????????????????????????????????????????????????????????????????巨???????????????????ú???????2001~2004???GPS?????????????????????????????з????????????????б?????????????????????????Ч?????????????????????????????? 相似文献
55.
56.
大地震辐射的地震波穿过整个地球。因为这些波仅在地球内部传播,所以经历了多次反射,并且沿相反方向传播的波之间的相互干涉形成了一种驻波形态:地球的简正振型(图1)。这些“体”波也受到传播它的介质的影响。因此它也就带有关于地球弹性分布和间断位置的有价值信息。 相似文献
57.
Porosity and permeability in sediment mixtures 总被引:1,自引:1,他引:0
Porosity in sediments that contain a mix of coarser- and finer-grained components varies as a function of the porosity and volume fraction of each component. We considered sediment mixtures representing poorly sorted sands and gravely sands. We expanded an existing fractional-packing model for porosity to represent mixtures in which finer grains approach the size of the pores that would exist among the coarser grains alone. The model well represents the porosity measured in laboratory experiments in which grain sizes and volume fractions were systematically changed within sediment mixtures. Permeability values were determined for these sediment mixtures using a model based on grain-size statistics and the expanded fractional-packing porosity model. The permeability model well represents permeability measured in laboratory experiments using air- and water-based permeametry on the model sediment mixtures. 相似文献
58.
Gavand MR McClintock JB Amsler CD Peters RW Angus RA 《Marine pollution bulletin》2007,54(11):1777-1788
Uptake and release of ship-borne ballast water is a major factor contributing to introductions of aquatic phytoplankton and invasive macroinvertebrates. Some invasive unicellular algae can cause harmful algal blooms and produce toxins that build up in food chains. Moreover, to date, few studies have compared the efficacy of ballast water treatments against different life history phases of aquatic macroinvertebrates. In the present study, the unicellular green alga Dunaliella tertiolecta, and three discrete life history phases of the brine shrimp Artemia salina, were independently used as model organisms to study the efficacy of sonication as well as the advanced oxidants, hydrogen peroxide and ozone, as potential ballast water treatments. Algal cells and brine shrimp cysts, nauplii, and adults were subjected to individual and combined treatments of sonication and advanced oxidants. Combined rather than individual treatments consistently yielded the highest levels of mortality in algal cells (100% over a 2 min exposure) and in brine shrimp (100% and 95% for larvae and adults, respectively, over a 2 min exposure). In contrast, mortality levels in brine shrimp cysts (66% over 2 min; increased to 92% over a 20 min exposure) were moderately high but consistently lower than that detected for larval or adult shrimp. Our results indicate that a combination of sonication and advanced chemical oxidants may be a promising method to eradicate aquatic unicellular algae and macroinvertebrates in ballast water. 相似文献
59.
Forest carbon stocks and fluxes in physiographic zones of India 总被引:1,自引:0,他引:1
Background
Reducing carbon Emissions from Deforestation and Degradation (REDD+) is of central importance to combat climate change. Foremost among the challenges is quantifying nation's carbon emissions from deforestation and degradation, which requires information on forest carbon storage. Here we estimated carbon storage in India's forest biomass for the years 2003, 2005 and 2007 and the net flux caused by deforestation and degradation, between two assessment periods i.e., Assessment Period first (ASP I), 2003-2005 and Assessment Period second (ASP II), 2005-2007. 相似文献60.
针对目前利用GPS快速静态相对定位进行控制测量的不足,研究了采用CORS测量技术进行控制测量的可行性,并以某地区的控制测量为例,分别采用两种方法进行了控制测量,结果表明:二者测量结果的精密程度完全符合《全球定位系统(GPS)测量规范》D级要求,并且利用CORS技术能够大大提高工作效率和节约测量成本。 相似文献