Comment on modeling ecological response to climatic change   总被引：6，自引：0，他引：6  

George P. Malanson 《Climatic change》1993,23(2):95-109

Researchers have developed many computer simulation models to project ecological responses to climatic change. Three general types of models are examined: transfer functions, stand models, and physiological models. Criteria for evaluation are, first, ability to represent observed and theoretical responses to climatic change i.e., geographical migration, individualistic responses, and disequilibrium or inertia, and second, ability to provide useful information on biological diversity and impacts on society. Because of their roots in ecological interactions at the species level, stand models best meet these criteria at present, but physiological models have greater potential, given unlimited computing power.  相似文献   

Study of the structure of the slab-mantle interface using reflected and converted seismic waves     

George Helffrich  Seth Stein 《Geophysical Journal International》1993,115(1):14-40

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Characterization of Transmissive Fractures by Simple Tracing of In-Well Flow   总被引：1，自引：0，他引：1  

Andrew Michalski  George M. Klepp 《Ground water》1990,28(2):191-198

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A National Evaluation of the Leaching Potential of Aldicarb Part 2. An Evaluation of Ground Water Monitoring Data     

Matthew N. Lorber  Stuart Z. Cohen  George D. DeBuchananne 《Ground Water Monitoring & Remediation》1990,10(1):127-141

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Maya utilization of karst groundwater resources     

George Veni 《Environmental Geology》1990,16(1):63-66

Much of the Maya civilization in pre-Columbian Meso-America was established on karst terrain that included parts of what are now Belize, Guatemala, northern Honduras and southern Mexico. By definition, little surface water exists in karst, so for the Maya to flourish on that terrain they had to effectively and efficiently utilize all their water resources. Access to groundwater was by means of springs and caves. Maya life, urban and rural, lay and elite, religious and secular was often a function of groundwater exploitation and surface water development. The Maya's use of groundwater was predominantly to supplement enhanced surface water supplies and was used more often in semiarid zones than in humid zones. The pattern of Maya settlements, especially in the semiarid zones, occurred in areas with greater access to the groundwater. Maya groundwater retrieval methods were primitive, inefficient, labor intensive, and uninnovative, as compared to their other technologic achievements. Groundwater contamination, from human effluent, could have resulted in widespread disease and contributed to the Maya's downfall.  相似文献   

Reliability of inexpensive charcoal and alpha-track radon monitors     

Douglas G. Mose  George W. Mushrush  Charles E. Chrosniak 《Natural Hazards》1990,3(4):341-355

A comparison between single short-term radon measurements and annual radon measurements in basements shows that significant uncertainties should be associated with the short-term measurements. Activated charcoal radon monitors which measure radon over a 3 to 7 day interval yield measurements that should carry a ± 90% uncertainty in terms of estimating annual radon concentration. Alpha-track radon monitors which measure radon over a 3 month interval should carry a ± 30% uncertainty. Decisions about home purchases, home remediation and the development of risk characterizations may often be incorrect if currently popular but unrealistically low estimates of uncertainty are applied to short-term radon measurements. Optimal results are obtained from year-long alpha-track measurements.  相似文献   

Pahoehoe and aa in Hawaii: volumetric flow rate controls the lava structure     

Scott K Rowland  George PL Walker 《Bulletin of Volcanology》1990,52(8):615-628

The historical records of Kilauea and Mauna Loa volcanoes reveal that the rough-surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate (>5–10 m³/s), and the smooth-surfaced variety called pahoehoe forms at a low volumetric rate (<5–10 m³/s). This relationship is well illustrated by the 1983–1990 and 1969–1974 eruptions of Kilauea and the recent eruptions of Mauna Loa. It is also illustrated by the eruptions that produced the remarkable paired flows of Mauna Loa, in which aa formed during an initial short period of high discharge rate (associated with high fountaining) and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate (with little or no fountaining). The finest examples of paired lava flows are those of 1859 and 1880–1881. We attribute aa formation to rapid and concentrated flow in open channels. There, rapid heat loss causes an increase in viscosity to a threshold value (that varies depending on the actual flow velocity) at which, when surface crust is torn by differential flow, the underlying lava is unable to move sufficiently fast to heal the tear. We attribute pahoehoe formation to the flowage of lava at a low volumetric rate, commonly in tubes that minimize heat loss. Flow units of pahoehoe are small (usually <1 m thick), move slowly, develop a chilled skin, and become virtually static before the viscosity has risen, to the threshold value. We infer that the high-discharge-rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers. Rapid near-surface vesiculation of gas-rich magma leads to eruptions with high discharge rates, high lava fountains, and fast-moving channelized flows. We also infer that long periods of sustained flow at a low discharge rate, which favor pahoehoe, result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption. Achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway.  相似文献   

Raman scattering study of the high-temperature vibrational properties and stability of CaGeO3 perovskite     

Dan J. Durben  George H. Wolf  Paul F. McMillan 《Physics and Chemistry of Minerals》1991,18(4):215-223

The vibrational properties of metastable Ca-GeO₃ perovskite are investigated as a function of temperature using Raman scattering. Mode-assignments are derived from polarized spectra of optically oriented single crystals. Neither symmetry-breaking structural transformations nor soft-mode behavior is revealed in the Raman spectra between room temperature and 650° C. Only a small decrease in the local static octahedral tilt angles can be inferred from the Raman data over this temperature range. A Landau extrapolation of the lowest frequency A_g modes suggests that these modes become critical near 2000° C, a temperature that is above the extrapolated zero pressure melting point.  相似文献   

Forests in a warming world: A time for new policies     

George M. Woodwell 《Climatic change》1991,19(1-2):245-251

Forests contain more than twice as much carbon as the atmosphere and process through their metabolism about 1/7 of the atmospheric carbon annually. Deforestation currently is adding carbon to the atmosphere as carbon dioxide at an increasing rate and causing the impoverishment of soils over large areas in the tropics. But deforestation is also occurring in the temperate and boreal forests. In most cases deforestation is the result of national policies. It proceeds in the United States in response to economic pressures and political weakness, even corruption.The re-establishment of forests has the potential for contributing to the stabilization of the composition of the atmosphere by removing carbon as carbon dioxide from the atmosphere and storing it on land for an indefinite period. Such a transition in land use is difficult to imagine in a world in which the human population is expanding continuously and impoverished land is accumulating.Global interests in management of forests introduce a new element into international relations. Progress in effecting the shifts in controls on land use required to control deforestation in the interests of stabilizing climate and preserving biotic resources will depend on clear definition of the details of the problem by the scientific community and a further definition of how to proceed.  相似文献   

The politics of urban entrepreneurialism in Glasgow     

Mark Boyle  George Hughes 《Geoforum》1994,25(4)

North American literature on the changing role of the local state these past two decades has been dominated by the view of a transition from urban managerialism to urban entrepreneurialism. Associated with the transition has been the emergence of a New Urban Politics (NUP). Within a political economy framework. the NUP has been rooted in the material redistributive effects of the transition. This paper explores the character of this NUP, as experienced by one British city, and highlights some fundamental differences with the established political economy reading. Our argument, based upon the city of Glasgow, draws attention to two distinctive features. First, the institutional structure of urban governance in Glasgow differs from that of cities in the United States. In Glasgow, it has been the Left controlled local Council which has orchestrated the transition to entrepreneurialism, rather than the North American model of a coalition between local capital and the local state. Secondly, the transition in Glasgow has been marked not by a significant transfer of local state revenue from service provision to local economic development, but by a symbolic reorientation of the local state as marked by the central importance of large place marketing hallmark events. These events represent the city in ways which differ from traditional ‘self’ identities. Consequently, the transition has evoked a political response which has focused upon the symbolic posturing of the local state rather than the material consequences of the shift. In focusing upon local identity, the politics of urban entrepreneurialism in Glasgow points to a dimension of conflict which has received inadequate treatment in accounts of the NUP to date.  相似文献