Twisted accretion curtains in the intermediate polar FO Aquarii     

P. A. Evans  Coel Hellier  Gavin Ramsay  Mark Cropper 《Monthly notices of the Royal Astronomical Society》2004,349(2):715-721

  相似文献   

A transect across the Mesozoic accretionary margin of central California     

Carl M. Wentworth  Mark D. Zoback  rew Griscom  Robert C. Jachens  Walter D. Mooney 《Geophysical Journal International》1987,89(1):105-110

  相似文献   

Magnetorotational Instability in Weakly Ionised, Stratified Accretion Discs     

Raquel Salmeron  Mark Wardle 《Astrophysics and Space Science》2004,292(1-4):451-456

We present a linear analysis of the vertical structure and growth of the magnetorotational instability in weakly ionised, stratified accretion discs. The method includes the effects of the magnetic coupling, the conductivity regime of the fluid and the strength of the magnetic field, which is initially vertical. The conductivity is treated as a tensor and assumed constant with height. The Hall effect causes the perturbations to grow faster and act over a much more extended section of the disc, when the magnetic coupling is low. As a result, significant accretion can occur closer to the midplane, despite the weak magnetic coupling, because of the high column density of the fluid. This is an interesting alternative to the commonly held view that accretion is relevant mainly in the surface regions of discs, which have a better coupling, but a much lower fluid density.  相似文献   

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