Influence of tidal inundation on internal oxygen supply of Spartina alterniflora and Spartina patens     

Mark L. Gleason  Joseph C. Zieman 《Estuarine, Coastal and Shelf Science》1981,13(1):47-57

  相似文献   

More Editorial Response     

Mark K. Levorsen 《Ground water》1990,28(5):805-805

  相似文献   

Magnetic mineralogy of the Yaxcopoil‐1 core,Chicxulub     

Mark Pilkington  Doreen E. Ames  Alan R. Hildebrand 《Meteoritics & planetary science》2004,39(6):831-841

Abstract— Core from the Yaxcopoil‐1 (Yax‐1) hole, drilled as a result of the Chicxulub Scientific Drilling Project (CSDP), has been analyzed to investigate the relationship between opaque mineralogy and rock magnetic properties. Twenty one samples of suevite recovered from the depth range 818–894 m are generally paramagnetic, with an average susceptibility of 2000 times 10^?6 SI and have weak remanent magnetization intensities (average 0.1 A/m). The predominant magnetic phase is secondary magnetite formed as a result of low temperature (<150 °C) alteration. It occurs in a variety of forms, including vesicle infillings associated with quartz and clay minerals and fine aggregates between plagioclase/diopside laths in the melt. Exceptional magnetic properties are found in a basement clast (metamorphosed quartz gabbro), which has a susceptibility of >45000 times 10^?6 SI and a remanent magnetization of 77.5 A/m. Magnetic mafic basement clasts are a common component in the Yax‐1 impactite sequence. The high susceptibility and remanence in the mafic basement clasts are caused by the replacement of amphiboles and pyroxenes by an assemblage with fine <1 μm magnetite, ilmenite, K‐feldspar, and stilpnomelane. Replacement of the mafic minerals by the magnetic alteration assemblage occurred before impact. Similar alteration mechanisms, if operative within the melt sheet, could explain the presence of the high amplitude magnetic anomalies observed at Chicxulub.  相似文献   

RHESSI as a Hard X-Ray Polarimeter     

McConnell  Mark L.  Ryan  James M.  Smith  David M.  Lin  Robert P.  Emslie  A. Gordon 《Solar physics》2002,210(1-2):125-142

Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (20–100 keV) from solar flares. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine germanium detectors. The Ge detectors are segmented, with both a front and rear active volume. Low-energy photons (below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low-energy photons from the Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Sensitivity estimates, based on Monte Carlo simulations and in-flight background measurements, indicate that a 20–100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares.  相似文献   

Magnetic investigations of the West Hawk,Deep Bay and Clearwater impact structures,Canada     

Ronald G. SCOTT  Mark PILKINGTON  Elizabeth I. TANCZYK 《Meteoritics & planetary science》1997,32(2):293-308

Abstract— Due to the effects of erosion, tectonism and burial, impact structures are often obscured or destroyed. Geophysical methods are increasingly being used in detecting the signatures of impact structures. While gravity lows associated with impact structures are well understood, associated magnetic anomaly lows are not. In this study, drill cores from three Canadian impact structures were analyzed for rock magnetic properties and mineralogy, in order to explain the magnetic anomaly lows associated with these structures. Samples from the drill cores were cut and measured for anisotropy of magnetic susceptibility (AMS) and natural remanent magnetization (NRM) parameters. Drill cores from the twin impact craters of the Clearwater structure exhibited different NRM characteristics, and samples from their respective drill cores were subject to demagnetization by alternating field and thermal techniques. The difference noted in their NRM characteristics was attributed to the acquisition of a viscous remanent magnetization (VRM) at depth in Clearwater East. At all three structures, both magnetic susceptibilities and remanent magnetizations are well below regional values in impact generated breccias, melt rocks, shocked crystalline rocks, and in postimpact sedimentary infill. The processes of brecciation, alteration, shock, and infill by nonmagnetic sediments contribute to the development of the magnetic lows. However, a significant contribution to the observed magnetic anomalies was found, by first-order forward modelling, to arise from basement rocks beneath the impact structures. This zone of reduced magnetization may be caused by the partial demagnetization of magnetite by the impact-induced transient stress wave traveling away from the point of impact.  相似文献   

Supplemental Colorado River water for a developed groundwater agriculture: A problem of quantities,qualities and conjunctive use     

Mark A. Boster  William E. Martin 《Advances in water resources》1977,1(2):103-109

Upon completion of the Central Arizona Project (CAP), Colorado River water will be delivered some 200 miles inland for agricultural, domestic, and industrial use. Any new importation of water to an area implies adjustments in the organization of the economy of the area. For irrigated agriculture, adjustments will occur in input mix, output mix, acreage farmed, and in gross and net incomes. A complicating factor associated with importation of Colorado River water is that the imported water will contain different dissolved salt concentrations than the groundwater and surface water currently being used.Mathematical programming models of representative irrigated farms in Pinal County, Arizona, are used to project adjustments implied under several assumptions as to the availability, cost and salinity of the various sources of irrigation water. Conclusions are drawn as to the potential winners and losers from project development. Conclusions include the following: Increased salinity should not be of concern to the farmers in the county and Indian farms will reap the greatest share of benefits from the Project.  相似文献   

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