Microstructures in type III events in the solar wind     

D. B. Melrose  M. V. Goldman 《Solar physics》1987,107(2):329-350

A model is presented for the generation and evolution of bump-in-tail driven Langmuir waves in the solar wind during type III emission, which removes a number of apparent inconsistencies between theory and observations. It is argued that there must be localized enhancements of f _b /v by a factor of 10² over the measured average values. Growth rates and energy densities of Langmuir waves are, therefore, considerably enhanced, permitting growth to overcome linear scattering losses, and also allowing nonlinear decay into ion-acoustic waves, in line with observations. Estimates are made of the probability distribution p(E), of wave field strengths E, based on linear and nonlinear wave-packet evolution, yielding p(E) E ^–a, 3. This helps explain why very high values of E are rarely found in the measured spiky wave turbulence.  相似文献   

Wave velocities and attenuation of shaley sandstones as a function of pore pressure and partial saturation   总被引：3，自引：0，他引：3  

Nam H. Pham  †  José M. Carcione  Hans B. Helle  Bjørn Ursin 《Geophysical Prospecting》2002,50(6):615-627

We obtain the wave velocities and quality factors of clay‐bearing sandstones as a function of pore pressure, frequency and partial saturation. The model is based on a Biot‐type three‐phase theory that considers the coexistence of two solids (sand grains and clay particles) and a fluid mixture. Additional attenuation is described with the constant‐Q model and viscodynamic functions to model the high‐frequency behaviour. We apply a uniform gas/fluid mixing law that satisfies the Wood and Voigt averages at low and high frequencies, respectively. Pressure effects are accounted for by using an effective stress law. By fitting a permeability model of the Kozeny– Carman type to core data, the model is able to predict wave velocity and attenuation from seismic to ultrasonic frequencies, including the effects of partial saturation. Testing of the model with laboratory data shows good agreement between predictions and measurements.  相似文献   

Alpine medicinal plant trade and Himalayan mountain livelihood strategies   总被引：5，自引：0，他引：5  

Carsten Smith Olsen  Helle Overgaard Larsen 《The Geographical journal》2003,169(3):243-254

Commercial alpine medicinal plants are collected from the wild by local rural households throughout the Himalaya and sold in order to increase household incomes. Recent studies indicate that this annual trade amounts to thousands of tonnes of roots, rhizomes, tubers, leaves, etc., worth millions of US dollars. The main market is in India. Based on a national survey, including the most commonly traded species, and a village study this paper investigates the importance of the alpine medicinal plant trade at national and local levels in Nepal. The national survey included standardized open-ended interviews with 232 harvesters, 64 local traders, 66 central wholesalers, 47 regional wholesalers, and 16 production companies. The village survey is based on the daily records of household activities in 15 households in a one-year period. The annual Nepalese alpine and sub-alpine medicinal plant trade is conservatively estimated to vary from 480 to 2500 t with a total harvester value of US$0.8–3.3 million; the average harvester value is estimated at US$66.0 ± 99.0. The trade in 1997/98 amounted to 1600 t with a harvester value of US$2.3 million and an export value equivalent to 2.5% of total export from Nepal. Medicinal plant harvesting was found to constitute an integrated part of local livelihood strategies, contributing from 3 to 44% (average of 12%) of the annual household income. Importance at household level depended on land and animal holdings, and the availability of adult male labour. The validity and reliability of methods and analyses is evaluated, and issues of conservation and management of alpine medicinal plant species under the community forestry scheme are discussed.  相似文献   

Foreword     

Helle Valborg Goldman 《Polar research》2005,24(1-2):1-3

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Changes in surface solar radiation in Northeastern Spain over the past six centuries recorded by tree-ring δ13C     

I. Dorado-Liñán  A. Sanchez-Lorenzo  E. Gutiérrez Merino  O. Planells  I. Heinrich  G. Helle  E. Zorita 《Climate Dynamics》2016,47(3-4):937-950

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Algorithmic techniques of identifying discriminative ocean areas in oceanology problems     

R. S. Goldman  L. P. Smirnykh  G. I. Yurasov 《GeoJournal》1988,16(1):35-43

A problem of locating and comprehensively investigating ocean areas that exercise a significant influence over the migration dynamics of fishing ranks among important problems of fisheries oceanology. Among all the environment factors affecting various fishery situations, factors should be chosen that are constantly logged on large water areas for a long time comparable with fishery observation time. As described in a number of works, the most suitable information for these purposes is data on the distribution of surface temperature fields. The problem of locating discriminative areas can then be stated as follows. For a particular fishery situation (e.g., for the period of maximum catch in fishing season), temperature values or thermostructural features should be singled out that are suitable to define the situation, using hydrological charts of surface temperature fields. Correlating the feature with the areas where they were observed, we will obtain discriminative areas. The important problem is then to develop techniques and means for algorithmically identifying areas. This relates to a vast volume of information and complex structure. Logical-mathematical models of locating discriminative areas are being developed at the Pacific Oceanological Institute for some years. These models are to be for forecasting fishery situations in the NW Pacific. Techniques for representing isotherm fields in a computer have been developed. Formal operations of comparing the fields have been proposed which aid in distinguishing significant differences in their structure. A software for analyzing isotherm fields has been developed based on threshold logic models. This approach allows one not only to identify discriminative areas for relatively stable fishery situations but also to trace their dynamics. This has been achieved due to multiple-alternative computations and the presentations of data obtained in the form suitable for their interpretation. Some components of proposed models have been used in the system of short-term forecasting saira and sardine fishery in the South-Kuril area.  相似文献   

On reducing ambiguity in the interpretation of transient electromagnetic sounding data1     

M. Goldman  A. Du Plooy  M. Eckard 《Geophysical Prospecting》1994,42(1):3-25

An attempt to resolve non-uniqueness in the interpretation of transient electromagnetic (TEM) sounding data using measured data alone is made. It is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence. The early delay times thus play a dual role in transient soundings: they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets. This is illustrated by the results of a follow-up TEM survey at the Dead Sea coast of Israel where the use of supplementary early time measurements allowed non-uniqueness in the determination of the depth to fresh/saline groundwater interface to be resolved.  相似文献   

Intercomparison of stratospheric water vapor profiles obtained during the Balloon Intercomparison Campaign     

D. Murcray  A. Goldman  J. Kosters  R. Zander  W. Evans  N. Louisnard  C. Alamichel  M. Bangham  S. Pollitt  B. Carli  B. Dinelli  S. Piccioli  A. Volboni  W. Traub  K. Chance 《Journal of Atmospheric Chemistry》1990,10(2):159-179

The Balloon Intercomparison Campaign (BIC) was set up to intercompare remote sensing measurements of a number of compounds other than water vapor; however, water vapor has strong absorption features throughout the infrared and mm wave regions of the spectrum. Therefore many of the investigators involved in BIC have absorption or emission features due to water vapor in the data they obtained during the balloon flights made under the campaign. These features have been used by the investigators to determine the stratospheric water vapor profiles which are compared in this paper. The profiles allow comparison of a wide range of remote sensing techniques involving both emission and absorption in the mid-infrared and emission techniques in the far infrared.  相似文献   

Synthetic seismograms from generalized ray tracing1     

Andrzej Hanyga  Hans B. Helle 《Geophysical Prospecting》1995,43(1):51-75

A new method of numerical computation of elastic wavefields in regions containing caustics is tested. The method is an extension of the asymptotic ray theory (ART). The essential features of the method consist of the application of expressions which are well defined at caustics and expressed in terms of ray tracing combined with complex ray tracing in caustic shadows. The method and an outline of the underlying theory are briefly presented, followed by a comparison with finite differences on a test model involving a caustic cusp. The comparison reveals the unexpectedly high degree of accuracy of the new method.  相似文献   

Water clarity modeling in Lake Tahoe: Linking suspended matter characteristics to Secchi depth     

Theodore J. Swift  Joaquim Perez-Losada  S. Geoffrey Schladow  John E. Reuter  Alan D. Jassby  Charles R. Goldman 《Aquatic Sciences - Research Across Boundaries》2006,68(1):1-15

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