Preface and Dedication     

A'Hearn  Michael F.  Boehnhardt  Hermann  Kidger  Mark  West  Richard M. 《Earth, Moon, and Planets》1997,78(1-3):3-3

Earth, Moon, and Planets -  相似文献   

Structures in a non-magnetic solar corona     

Mark A. Cross  James V. Blockwood 《Solar physics》1974,38(1):157-164

A fluid mechanical convective instability is examined under the conditions found in the solar corona. Linearized density perturbations are shown to grow as they are carried outward by the solar wind. The non-linear instability may be proposed as a cause of coronal structures in non-magnetic stars, or in regions of the solar corona with weak magnetic fields.  相似文献   

Spatio-temporal pattern of viral meningitis in Michigan, 1993-2001     

Sharon K. Greene  Mark A. Schmidt  Mary Grace Stobierski  Mark L. Wilson 《Journal of Geographical Systems》2005,7(1):85-99

To characterize Michigans high viral meningitis incidence rates, 8,803 cases from 1993–2001 were analyzed for standard epidemiological indices, geographic distribution, and spatio-temporal clusters. Blacks and infants were found to be high-risk groups. Annual seasonality and interannual variability in epidemic magnitude were apparent. Cases were concentrated in southern Michigan, and cumulative incidence was correlated with population density at the county level (r=0.45, p<0.001). Kulldorffs Scan test identified the occurrence of spatio-temporal clusters in Lower Michigan during July–October 1998 and 2001 (p=0.01). More extensive data on cases, laboratory isolates, sociodemographics, and environmental exposures should improve detection and enhance the effectiveness of a Space-Time Information System aimed at prevention.The authors gratefully acknowledge Dr. Duane Newton, former manager of the Virology Section, Michigan Department of Community Health Bureau of Laboratories, for his provision of data on viral isolates. We also appreciate the contributions of Drs. Leah Estberg and Dunrie Greiling for ClusterSeer support, Scott Swan for his assistance with ArcView GIS, and Dr. Edward L. Ionides for his advice on time series analysis. We are grateful to Dr. Pierre Goovaerts and two anonymous reviewers for their insightful comments on an earlier draft of this paper. This project was supported in part by a grant from the National Oceanic and Atmospheric Administrations Joint Program on Climate Variability and Human Health, a consortium including the EPA, NASA, NSF, and EPRI (NA16GP2361) to MLW.  相似文献   

Measuring similarity between geospatial lifelines in studies of environmental health   总被引：3，自引：0，他引：3  

Gaurav Sinha  David M. Mark 《Journal of Geographical Systems》2005,7(1):115-136

Many epidemiological studies involve analysis of clusters of diseases to infer locations of environmental hazards that could be responsible for the disease. This approach is however only suitable for sedentary populations or diseases with small latency periods. For migratory populations and diseases with long latency periods, people may change their residential location between time of exposure and onset of ill health. For such situations, clusters are diffused and diluted by in- and out-migration and may become very difficult to detect. One way to address the problem of diffused clusters is to include in analyses not only current residential locations, but all past locations at which cases might have been exposed to environmental hazardous. In this paper, we assume that a persons residential history provides such information and represent it through a discrete geospatial lifeline data model. Clusters of similar geospatial lifelines represent individuals who have similar residential histories—and therefore represent people who are more likely to have had similar environmental exposure histories. We therefore introduce a lifeline distance (dissimilarity) measure to detect clusters of cases, providing a basis for revealing possible regions in space-time where environmental hazards might have existed in the past. The ability of the measure to distinguish cases from controls is tested using two sets of synthetically generated cases and controls. Results indicate that the measure is able to consistently distinguish between populations of cases and controls with statistically significant results. The lifeline distance measure consistently outperforms another measure which uses only the distance between subjects residences at time of diagnosis. However, the advantages of using the entire residential history are only partly realized, since the ability to distinguish between cases and controls is only moderately better for the lifeline distance function. Future work is needed to investigate modifications to the inter-lifeline distance measure in order to enhance the potential of this approach to detect locations of environmental hazards over the lifespan.This project is supported by grant number 1 R01 ES09816-01 from the National Institute of Environmental Health Sciences, NIH. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS or NIH. We wish to thank Peter Rogerson for helpful discussions of the migration models, and the anonymous reviewers for pointing out areas where the paper could be improved.  相似文献   

Length Scales of Scalar Diffusion in the Convective Boundary Layer: Laboratory Observations   总被引：1，自引：1，他引：0  

Han?van?DopEmail author  Dirk?van?As  Alec?van?Herwijnen  Mark?F.?Hibberd  Harm?Jonker 《Boundary-Layer Meteorology》2005,116(1):1-35

A laboratory study of scalar diffusion in the convective boundary layer has found results that are consistent with a 1999 large-eddy simulation (LES) study by Jonker, Duynkerke and Cuijpers. For bottom-up and top-down scalars (introduced as ‘infinite’ area sources of passive tracer at the surface and inversion, respectively) the dominant length scale was found to be much larger than the length scale for density fluctuations, the latter being equal to the boundary-layer depth h. The variance of the normalized passive scalar grew continuously with time and its magnitude was about 3–5 times larger for the top-down case than for the bottom-up case. The vertical profiles of the normalized passive scalar variance were found to be approximately constant through the convective boundary layer (CBL) with a value of about 3–8c_*² for bottom-up and 10–50c_*² for top-down diffusion. Finally, there was some evidence of a minimum in the variance and dominant length scale for scalar flux ratios (top-down to bottom-up flux) close to −0.5. All these convection tank results confirm the LES results and support the hypothesis that there is a distinct difference in behaviour between the dynamic and passive variables in the CBL.  相似文献   

Global Analysis of Changes in Water Supply Yields and Costs under Climate Change: A Case Study in China   总被引：3，自引：1，他引：2  

Paul?KirshenEmail author  Mark?McCluskey  Richard?Vogel  Kenneth?Strzepek 《Climatic change》2005,68(3):303-330

Using China as a case study, a methodology is presented to estimate the changes in yields and costs of present and future water production systems under climate change scenarios. Yield is important to consider because it measures the actual supply available from a river basin. Costs are incurred in enhancing the natural yield of river basins by the construction and operation of reservoirs and ground water pumping systems. The interaction of ground and surface waters within a river basin and instream flow maintenance are also modeled. The water demands considered are domestic, irrigation, and instream flow needs. We found that under climate change the maximum yields of some basins in China may increase or decrease, depending upon location, and that in some basins it may cost significantly more or it may not be possible to meet the demands. While our results for China could be improved with more hydrologic and economic data, we believe that the cost curves developed have suitable accuracy for initial analysis of water supply costs in Integrated Assessment Models.  相似文献   

Temporal and spatial dynamics of urea uptake and regeneration rates and concentrations in Chesapeake Bay     

Michael?W.?LomasEmail author  T.?Mark Trice  Patricia?M.?Glibert  Deborah?A.?Bronk  James?J.?McCarthy 《Estuaries and Coasts》2002,25(3):469-482

We examined the temporal and spatial variability of urea concentrations and urea uptake and regeneration rates collected on cruises along the longitudinal axis of the Chesapeake Bay between 1972 and 1998. Interannually, mean Bay-wide surface urea concentrations ranged between 0.49 and 0.91 μg-at N l^?1 with a nearly 50% decrease in surface concentrations observed between 1988 and 1998. Concentrations of urea from samples collected within ～1 m of the bottom were generally higher and much more varable than surface samples. Seasonally, two different patterns were observed in mean Bay-wide surface urea concentrations. Urea concentrations from near surface waters exhibited a clear summer peak for 1988 through 1994, while for 1973 and 1996 to 1998 a distinct winter-spring peak in concentration was observed. Urea concentrations from deeper waters showed a similar seasonal trend each year with peak concentrations measured in spring. Spatially, urea concentrations in the surface waters decreased in a conservative-type pattern from 0.91 μg-at N I^?1 at the freshwater end member to 0.46 μg-at N I^?1 at the ocean end member. Mean Bay-wide surface urea uptake rates displayed a seasonal pattern throughout the data set with maximum uptake rates (up to 0.33 μg-at N I^?1 h^?1) consistently observed during summer. Mean Bay-wide surface regeneration rates were highest but most variable during fall (1.63±0.82 μg-at N I^?1 h^?1). Mean urea uptake and regeneration rates displayed opposing spatial trends along the axis of the Bay with uptake rates being lowest in the North Bay where regeneration rates were highest. The average temporal and spatial patterns of urea concentration in Chesapeake Bay appear to reflect a balance between external inputs and internal biological recycling.  相似文献   

The Impact of Precipitation Scavenging on the Transport of Trace Gases: A 3-Dimensional Model Sensitivity Study   总被引：1，自引：0，他引：1  

Paul J. Crutzen  Mark G. Lawrence 《Journal of Atmospheric Chemistry》2000,37(1):81-112

With the global Chemistry-Transport model MATCHsensitivity simulations were performed to determinethe degree to which especially upward transport ofgases from the earth's surface is limited byconvective and large-scale precipitation scavenging.When only dissolution of species in the liquid phaseis taken into account, mixing ratio reductions in themiddle and upper troposphere by 10% arecalculated for gases with a Henry's Law constant H of10³ mol/l/atm. The removal increases to 50% forH = 10⁴ mol/l/atm, and to 90% for H =10⁵ mol/l/atm. We also consider scavenging by theice phase, which is generally much less efficient thanby the aqueous phase. In fact, rejection of gases fromfreezing water droplets may be a source of trace gasat higher altitudes.H₂O₂ and the strong acids (H₂SO₄,HNO₃, HCl, HBr, HI) have such large solubilitiesthat they become largely removed by precipitation.When significant concentrations of these gases andsulfate aerosol exist above the liquid water domain ofthe atmosphere, they have likely been produced thereor at higher altitudes, although some could have comefrom trace gas rejection from ice particles or fromevaporating hydrometeors. Several other gases areaffected by precipitation, but not strongly enough toprevent fractional transfer to the middle and uppertroposphere: e.g., HNO₄, HNO₂ at pH 5,CH₂O, the organic acids at pH 6,CH₃SOCH₃, HOCl, HOBr, and HOI. NH₃ islargely removed by liquid phase scavenging at pH 7 and SO₂ atpH 7. At pH less thanabout 6, upward transport of SO₂ should largelydepend on the efficiency of oxidation processes in thewater droplets by O₃ and H₂O₂.Most gases have solubilities which are too low forsignificant precipitation scavenging and aqueous phaseoxidation to occur. This holds, e.g., for O₃, CO,the hydrocarbons, NO, NO₂, HCN, CH₃CN,CH₃SCH₃, CH₃O₂H, CH₃CHOandhigher aldehydes, CH₃OH and higher alcohols,peroxyacetylnitrate (PAN), CH₃COCH₃ andother ketones (note that some of these are not listedin Table I because their solubilities are below 10mol/l/atm). Especially for the short-lived gases,transfer from the boundary layer to the middle andupper troposphere is actually promoted by the enhancedupward transport that occurs in clouds.  相似文献   

Localized spectral analysis on the sphere   总被引：5，自引：0，他引：5  

Mark A. Wieczorek  Frederik J. Simons 《Geophysical Journal International》2005,162(3):655-675

  相似文献   

The case for inductive and visual techniques in the analysis of spatial data     

Mark Gahegan 《Journal of Geographical Systems》2000,2(1):77-83

  相似文献