Acoustic anisotropy related to anisotropic stress conditions during formation and unloading     

E. Fjaer  R. M. Holt  J. S. Rathore  B. Åhlén 《Geophysical Journal International》1991,107(3):687-691

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Microwave and hard X-ray bursts from solar flares     

Stephen S. Holt  Reuven Ramaty 《Solar physics》1969,8(1):119-141

We have applied detailed theories of gyro-synchrotron emission and absorption in a magnetoactive plasma, X-ray production by the bremsstrahlung of non-thermal electrons on ambient hydrogen, and electron relaxation in a partially ionized and magnetized gas to the solar flare burst phenomenon. The hard X-ray and microwave bursts are shown to be consistent with a single source of non-thermal electrons, where both emissions arise from electrons with energies < mc ². Further-more, the experimental X-ray and microwave data allow us to deduce the properties of the electron distribution, and the values of the ambient magnetic field, the hydrogen density, and the size of the emitting region. The proposed model, although derived mostly from observations of the 7 July 1966 flare, is shown to be representative of this type of event.NAS-NRC Resident Research Associate.  相似文献   

Elastic Dispersion Derived from a Combination of Static and Dynamic Measurements     

Erling Fjær  Anna M. Stroisz  Rune M. Holt 《Rock Mechanics and Rock Engineering》2013,46(3):611-618

Utilization of laboratory tests for calibration and interpretation of data from seismic surveys requires knowledge about elastic dispersion in the range from seismic to ultrasonic frequencies. Data on such dispersion are hard to obtain because it requires specially designed equipment and also relies on simplifying assumptions about rock symmetry. A new method for estimation of dispersion in this frequency range is presented here. This method requires only standard rock mechanical equipment with ultrasonic velocity measurements, and is based on comparison of static and dynamic data. A key element in this method is a procedure for elimination of strain amplitude as a source for differences between static and dynamic moduli. High-quality data is necessary, but the required accuracy is not extreme. Application of the method on one partly saturated shale and two dry sandstone samples indicates that dispersion increases with clay content, and decreases with stress.  相似文献   

Shifts of the Caii K line in Hei 10830 dark points     

Rush D. Holt  D. J. Mullan 《Solar physics》1986,107(1):63-72

We investigate the velocity field of the solar chromosphere at the location of 65 He i 10830 dark points (DP's). We have obtained spectra of such points in the vicinity of the Ca II K line. As a measure of differential chromospheric velocity, we use the shift of the K line center relative to a nearby photospheric Fe i line. We find that in He i DP's, the distribution of K line shifts is skewed towards the blue: the blueward skewing is more pronounced in He i DP's located in coronal holes. To the extent that He i DP's are proxies of coronal bright points, our study is relevant to previous reports of outflows from such bright points.  相似文献   

A new non-linear least squares algorithm for the seismic inversion problem     

S. J. Wright  J. N. Holt 《Geophysical Journal International》1986,87(3):1041-1056

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Is the IWC finished as an instrument for the conservation of whales and the regulation of whaling?     

Holt S 《Marine pollution bulletin》2003,46(7):924-926

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Discrete Element Modeling of Stress and Strain Evolution Within and Outside a Depleting Reservoir   总被引：1，自引：0，他引：1  

Haitham T. I. Alassi  Liming Li  Rune M. Holt 《Pure and Applied Geophysics》2006,163(5-6):1131-1151

Stress changes within and around a depleting petroleum reservoir can lead to reservoir compaction and surface subsidence, affect drilling and productivity of oil wells, and influence seismic waves used for monitoring of reservoir performance. Currently modeling efforts are split into more or less coupled geomechanical (normally linearly elastic), fluid flow, and geophysical simulations. There is evidence (from e.g. induced seismicity) that faults may be triggered or generated as a result of reservoir depletion. The numerical technique that most adequately incorporates fracture formation is the DEM (Discrete Element Method). This paper demonstrates the feasibility of the DEM (here PFC; Particle Flow Code) to handle this problem. Using an element size of 20 m, 2-D and 3-D simulations have been performed of stress and strain evolution within and around a depleting reservoir. Within limits of elasticity, the simulations largely reproduce analytical predictions; the accuracy is however limited by the element size. When the elastic limit is exceeded, faulting is predicted, particularly near the edge of the reservoir. Simulations have also been performed to study the activation of a pre-existing fault near a depleting reservoir.  相似文献   

Modelling the impact of climate extremes: an overview of the MICE project     

C. E. Hanson  J. P. Palutikof  M. T. J. Livermore  L. Barring  M. Bindi  J. Corte-Real  R. Durao  C. Giannakopoulos  P. Good  T. Holt  Z. Kundzewicz  G. C. Leckebusch  M. Moriondo  M. Radziejewski  J. Santos  P. Schlyter  M. Schwarb  I. Stjernquist  U. Ulbrich 《Climatic change》2007,81(1):163-177

This paper provides an overview of the aims, objectives, research activities undertaken, and a selection of results generated in the European Commission-funded project entitled “Modelling the Impact of Climate Extremes” (MICE) – a pan-European end-to-end assessment, from climate model to impact model, of the potential impacts of climate change on a range of economic sectors important to the region. MICE focussed on changes in temperature, precipitation and wind extremes. The research programme had three main themes – the evaluation of climate model performance, an assessment of the potential future changes in the occurrence of extremes, and an examination of the impacts of changes in extremes on six activity sectors using a blend of quantitative modelling and expert judgement techniques. MICE culminated in a large stakeholder-orientated workshop, the aim of which was not only to disseminate project results but also to develop new stakeholder networks, whose expertise can be drawn on in future projects such as ENSEMBLES. MICE is part of a cluster of three projects, all related to European climate change and its impacts. The other projects in the cluster are PRUDENCE (Prediction of Regional Scenarios and Uncertainties for Defining European Climate Change Risks and Effects) and STARDEX (Statistical and Regional Dynamical Downscaling of Extremes for European Regions).  相似文献   

Dems and Ortho-Images from Aerial Photographs     

M. J. Smith  D. G. Smith  G. Tragheim  & M. Holt 《The Photogrammetric Record》1997,15(90):945-950

Digital photogrammetry has produced new products and brought automation to a number of traditional photogrammetric procedures. Some of the new products have been produced by the integration of data and information. With new products comes the need to assess their quality as this can have a direct effect on their potential use. Some of the new products and a number of parameters that affect their quality are discussed in this paper.  相似文献   

Historical storminess and climate ‘see-saws’ in the North Atlantic region     

A. Dawson  L. Elliott  S. Noone  K. Hickey  T. Holt  P. Wadhams  I. Foster 《Marine Geology》2004,210(1-4):247-259

The existence of a well-defined climate ‘see-saw’ across the North Atlantic region and surrounding areas has been known for over 200 years. The occurrence of severe winters in western Greenland frequently coincides with mild winters in northern Europe. Conversely, mild winters in western Greenland are frequently associated with cold winters across northern Europe. Whereas this ‘see-saw’ is normally discussed in terms of air temperature and pressure differences, here we explore how the climate ‘see-saw’ is reflected in records of historic storminess from Scotland, NW Ireland and Iceland. It is concluded that the stormiest winters in these regions during the last ca. 150 years have occurred when western Greenland temperatures have been significantly below average. In contrast, winters of reduced storminess have coincided with winters when air temperatures have been significantly above average in western Greenland. This reconstruction of winter storminess implies a relationship between chronologies of coastal erosion and the history of North Atlantic climate ‘see-saw’ dynamics with sustained winter storminess, and hence increased coastal erosion, taking place when the Icelandic low pressure cell is strongly anchored within the circulation of the northern hemisphere. Considered over the last ca. 2000 years, it would appear that winter storminess and climate-driven coastal erosion was at a minimum during the Medieval Warm Period. By contrast, the time interval from ca. AD 1420 until present has been associated with sustained winter storminess across the North Atlantic that has resulted in accelerated coastal erosion and sand drift.  相似文献