Interpolation of Horizontal Transmissivity Anisotropy from Head and Flowpath Observations     

Perry H. Rahn  Roger L. Opp 《Mathematical Geology》2003,35(5):613-626

Rocks are rarely equally permeable in all directions. Ground water does not flow directly downgradient through anisotropic aquifers, but deviates at an angle determined by the direction and magnitude of the major and minor transmissivities. We show a mathematical model whereby the orientation and ratio of major to minor transmissivities can be estimated by an analysis of the deviation of ground-water flow from the hydraulic gradient. The solution is derived from the construction of transmissivity ellipse where the hydraulic gradient and flow direction are known. An example is given using an ethylene dibromide contaminant plume at Nemo, South Dakota, where the plume has been deflected because of bedrock foliation.  相似文献   

Fatty acids of bacterial origin in contemporary marine sediments     

G.J. Perry  J.K. Volkman  R.B. Johns  H.J. Bavor 《Geochimica et cosmochimica acta》1979,43(11):1715-1725

Contributions by bacteria to recent sediments have been recognized as one important source of input for the extractable lipids. It has, however, proved difficult so far to conclusively relate the components identified to the contributing bacteria. This fact is primarily related to the lack of information on both the lipid chemistry of marine bacteria, and of detailed structures of the sedimentary lipids. In this paper a study of the fatty acids from a tropical marine sediment selected because of its high biomass content is reported, and relationships between the sedimentary extracts of the surface layer to fatty acid components of bacteria cultured from the sediment sample are detailed. By selecting specific structural features, a group of fatty acids have been identified as valid markers for bacteria in this environment: these include iso- and anteiso-branched chain acids; 10-methylpalmitic acid; cyclopropyl 17:0 and 19:0 acids of which ▽19:0 (11,12) is unique to bacteria; cis-vaccenic acid; and the 15:1, 17:1 ω6 and ω8 isomers especially when these occur in pairs; iso Δ7–15: 1 and iso Δ9–17:1 are branched unsaturated acids apparently unique to bacteria. Trans-monoene fatty acids are likely to be a direct bacterial input, and the hydroxy acids identified are probably of bacterial cell wall origin. This study, whilst emphasizing the necessity for detailed structural information on fatty acids in order to use them validly as biological markers, considerably extends the range of fatty acids as markers of bacterial input to contemporary sediments.  相似文献   

GROUND–WATER EMPLOYMENT OPPORTUNITIES     

Perry H. Rahn 《Ground water》1976,14(2):108-108

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Hydrogeology of a Portion of the Sand Hills and Ogallala Aquifer, South Dakota and Nebraska     

Perry H. Rahn  Howard A. Paul 《Ground water》1975,13(5):428-437

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Microbial lipids of an intertidal sediment—I. Fatty acids and hydrocarbons     

J.K. Volkman  R.B. Johns  F.T. Gillan  G.J. Perry  H.J. Bavor 《Geochimica et cosmochimica acta》1980,44(8):1133-1143

A detailed study has been made of the solvent extractable monocarboxylic, dicarboxylic and hydroxylated fatty acids and n-alkanes in a surface intertidal sediment, and the distributions compared to microorganisms cultured from the sediment. Diatoms are shown to contribute most of the monocarboxylic acids, particularly the significant amounts of polyunsaturated acids present, and a small proportion of the n-alkanes. Bacteria contribute between 11 and 14% of the monocarboxylic acids and markers for this, including trans-monounsaturated acids, are proposed. Detritus from the sea-grass Zostera muelleri is a major source of the α-hydroxy-, ω-hydroxy and α,ω-dicarboxylic acids in the sediment and a minor contributor of n-alkanes and long-chain fatty acids.  相似文献   

Comparison Between Model Simulations and Field Results for In-Situ Biorestoration of Chlorinated Aliphatics: Part 1. Biostimulation of Methanotrophic Bacteria   总被引：2，自引：0，他引：2  

Lewis Semprini  Perry L. McCarty 《Ground water》1991,29(3):365-374

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NEW CORPORATE STRUCTURES, REGIONAL OFFICES AND SINGAPORE'S NEW ECONOMIC DIRECTIONS     

Martin Perry 《Singapore journal of tropical geography》1996,16(2):181-196

The adoption of new organisational structures and methods for controlling subsidiaries is affecting the role and characteristics of regional offices. Since 1986 Singapore's economic strategy has given priority to the attraction of regional offices as part of a wider search for new economic directions. This shift coincided with the emergence of a new Southeast Asian division of labour associated with the adoption of a regional focus in multinational investment and the integration of subsidiary investment. A survey of regional offices awarded “operational headquarters” (OHQ) status by the government shows how changes in corporate structures and the formation of the regional division of labour are influencing regional office activity and organisation. This analysis identifies four types of regional office, of which the largest function as centres of logistics and service support, Barriers to the adoption of corporate control functions amongst Singapore OHQs are explained.  相似文献   

Experiments to Study Radiation Transport in Clumpy Media     

P. A. Rosen  J. M. Foster  M. J. Taylor  P. A. Keiter  C. C. Smith  J. R. Finke  M. Gunderson  T. S. Perry 《Astrophysics and Space Science》2007,307(1-3):213-217

Clumpiness of the interstellar medium may play an important role in the transfer of infrared continuum radiation in star forming regions (Boisse, 1990). For example, in homogeneous models, C II emission should be confined to the cloud edge (Viala, 1986). However, in star formation regions (such as M17SW, M17 and W51), it is observed to extend deep into the molecular cloud (Stutzki et al., 1988; Keene et al., 1985). One plausible interpretation of these observations is that, due to their clumpiness, the clouds are penetrated by UV radiation far deeper than expected from simple homogeneous models. The interaction of H II regions around young massive stars with a clumpy medium is another area of interest. Molecular clouds are well established to be clumpy on length scales down to the limits of observational resolution. Clumps can act as localized reservoirs of gas which can be injected into the surroundings by photoionization and/or hydrodynamic ablation (Dyson et al., 1995; Mathis et al., 1998). The calculation of radiation transport in hot, clumpy materials is a challenging problem. Approximate, statistical treatments of this problem have been developed by several workers, but their application has not been tested in detail. We describe laboratory experiments, using the Omega laser to test modelling of radiation transport through clumpy media in the form of inhomogeneous plasmas.  相似文献   

Where They Lived: Studies in Local, Regional and Social History     

Peter Perry 《New Zealand geographer》2000,56(1):59-59

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Restoration prospects for Heitutan degraded grassland in the Sanjiangyuan   总被引：4，自引：1，他引：3  

LI Xi-lai  PERRY LW George  BRIERLEY Gary  GAO Jay  ZHANG Jing  YANG Yuan-wu 《山地科学学报》2013,10(4):687-698

In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as ’Heitutan’. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.  相似文献