On the Principle of Least Interaction Action and the Laplacean satellites of Jupiter and Uranus     

Michael W. Ovenden  Terry Feagin  Otis Graf 《Celestial Mechanics and Dynamical Astronomy》1974,8(4):455-471

The Principle of Least Interaction Action, which explains the observed preference in the Solar System for two-satellite resonant configurations, is shown to apply also to the Laplacean satellites of Jupiter and Uranus, in the sense that these triplet resonant structures lie close to configurations for which the time-mean of the action associated with the mutual interaction of the satellites is an overall minimum. Far from the minimum configuration, significant changes take place in the major semi-axes on time-scales ～10⁶-10⁷y. Both systems require times ～10⁸ y to come close to the minimum configuration; to approach resonance to the observed precision of the Laplace relationship (3×10^?4 for the Uranian case, 2×10^?7 for the Jovian case) requires, for both systems, a time closely comparable with the age of the solar system.  相似文献   

Particle saturation of the outer zone: A nonlinear model     

Michael Schulz 《Astrophysics and Space Science》1974,29(1):233-242

Properties of the steady state and transient behavior of geomagnetically trapped radiation are analyzed by means of phenomenological equations that concisely summarize the operative dynamical processes. The equations provide for a realistic coupling between electromagnetic wave energy, particle intensity, and pitch-angle anisotropy in the context of the outer zone. Applications include magnetospheric enforcement of a limit on stably trapped particle flux. the smooth transition between weak pitch-angle diffusion and strong diffusion, parasitic particle precipitation by natural and man-made radio signals, natural and artificial injections of trapped radiation, and the consequences of magnetospheric cold-plasma injection.  相似文献   

The acquisition of post-depositional detrital remanent magnetization in a variety of natural sediments     

Michael A. Payne  Kenneth L. Verosub 《Geophysical Journal International》1982,68(3):625-642

Summary. Post-depositional detrital remanent magnetization (pDRM) is the primary means whereby many sediments acquire their palaeomagnetic signal. We have studied the acquisition of this magnetization in a variety of natural sediments. Our technique involves determining the magnetic direction recorded by a sediment as a function of the water content present in the sediment when the sediment experiences a change in the direction of the applied magnetic field. Most of the sediments used in this study were collected wet from natural environments and were preserved in their original state until they were used in the experiments. Grain sizes were measured by the settling tube method which led to the determination of the clay, silt and sand fractions in each sediment. Isothermal remanent magnetization acquisition studies indicated that the predominant magnetic carriers were magnetite. In the pDRM acquisition studies two distinct modes of behaviour were found. For sediments with a sand content less than 60 per cent, the original direction of magnetization was preserved regardless of the water content. Such behaviour is not consistent with a theoretical model which assumes that at high water contents the magnetic carriers remain mobile within fluid-filled voids and hence are able to realign along a new magnetic field direction. For sediments with a sand content in excess of 60%, remagnetization along a new magnetic field direction occurred as expected, provided the sediments were sufficiently wet. Studies of natural sediments and corresponding samples of dried and reconstituted sediments have demonstrated that the magnetic characterization of a sediment can be reliably determined even for older, desiccated sediments.  相似文献   

    

Mark E. Johnson  Ellis A. Monash  Michael S. Waterman 《Mathematical Geology》1979,11(1):63-74

Accepted practice dictates that waterflooding of gas reservoirs should commence, if ever, only when the reservoir pressure has declined to the minimum production pressure. Analytical proof of this hypothesis has yet to appear in the literature however. This paper considers a model for a gas-water reservoir with a variable production rate and enhanced recovery with waterflooding and, using an initial dynamic programming approach, confirms the above hypothesis.  相似文献   

Constraints on the composition of the Venus atmosphere from microwave measurements near 1.35 cm wavelength     

Michael A. Janssen  Michael J. Klein 《Icarus》1981,46(1):58-69

The determination of the brightness temperature of Venus near 1.35 cm wavelength is reviewed. The observed brightness temperature is compared with models for the microwave emission based on the physical and chemical structure of the atmosphere as obtained from spacecraft. Upper limits are set on the concentrations of microwave-absorbing minor constituents. In particular, upper limits are determined for SO₂ (180 ppm) and H₂O (0.3%) for a mixing-ratio profile that is uniformly mixed up to the cloud bottom at 50 km and is rapidly depleted ($\text{scale height}\text{? 1}\text{km}\text{)}$ at higher altitudes. The total optical depth of the cloud region at or above 50 km is <0.17 at 1.35 cm wavelength. The SO₂ upper limit is only in marginal agreement with the spacecraft results, and it may be that the latter have been overestimated, or that the distribution of SO₂ is more complex than given by the uniform mixing model.  相似文献   

Regional seismic travel times for central Asian epicentres     

Harold Jeffreys  Michael Shimshoni 《Geophysical Journal International》1984,79(3):773-778

Summary. Travel times for central Asia studied by Gogna, Jeffreys and Shimshoni are modified. Corrected surface times of P and S are tabulated and a structure is computed. We tabulate also full travel-time tables for all usual depths of focus.  相似文献   

The Distribution and Significance of Evaporitic Weathering Products on Antarctic Meteorites     

Michael Anthony Velbel 《Meteoritics & planetary science》1988,23(2):151-159

Abstract— The distribution of white evaporitic deposits differs among different meteorite compositional groups and weathering categories of Antarctic meteorites. Evaporites occur with unusual frequency on carbonaceous chondrites, and are especially common in carbonaceous chondrites of weathering categories A and B. Among achondrites, weathering categories A and A/B show the most examples of evaporite weathering. Unlike carbonaceous chondrites and achondrites, most evaporite-bearing ordinary (H and L) chondrites are from rustier meteorites of weathering categories B and, to a lesser degree, B/C and C. LL chondrites are conspicuous by their complete lack of any evaporitic weathering product. Almost two-thirds of all evaporite-bearing meteorites belong to weathering categories A, A/B, and B. Where chemical data are available, surficial evaporite deposits are associated with elemental anomalies in meteorite interiors. Meteorites of weathering classes B, A/B, and even A may have experienced significant element redistribution and/or contamination as a result of terrestrial exposure. Evaporite formation during terrestrial weathering cannot be neglected in geochemical, cosmochemical, and mineralogical studies of Antarctic meteorites. A lower-case “e” should be added to the weathering classification of evaporite-bearing Antarctic meteorites, to inform meteorite scientists of the presence of evaporite deposits and their associated compositional effects.  相似文献   

Centrifuge modeling of PGD response of buried pipe   总被引：1，自引：1，他引：0  

MichaelO＇Rourke VikramGadicherla TarekAbdoun 《地震工程与工程振动(英文版)》2005,4(1):69-73

A new centrifuge based method for determining the response of continuous buried pipe to PGD is presented. The physical characteristics of the RPI‘s 100 g-ton geotechnical centrifuge and the current lifeline experiment split-box are described: The split-box contains the model pipeline and surrounding soil and is manufactured such that half can be offset, in flight, simulating PGD. In addition, governing similitude relations which allow one to determine the physical characteristics, (diameter, wall thickness and material modulus of elasticity) of the model pipeline are presented. Finally, recorded strains induced in two buried pipes with prototype diameters of 0.63 m and 0.95 m (24 and 36 inch) subject to 0.6 and 2.0 meters (2 and 6 feet) of full scale fault offsets and presented and compared to corresponding FE results.  相似文献   

The Summer Arctic Boundary Layer during the Arctic Ocean Experiment 2001 (AOE-2001)   总被引：1，自引：0，他引：1  

Michael?Tjernstr?mEmail author 《Boundary-Layer Meteorology》2005,117(1):5-36

Boundary-layer measurements made from the Swedish icebreaker Oden during the Arctic Ocean Experiment 2001 (AOE-2001) are analysed. They refer mainly to ice drift in the central Arctic during the period 2–21 August 2001. On board Oden a remote sensing array with a wind profiler, cloud radar and a scanning microwave radiometer, and a regular weather station operated continuously; soundings were also released during research stations. Turbulence and profile measurements on an 18-m mast were deployed on the ice, along with two sodar systems, a microbarograph array and a tethered sounding system. Surface flux and meteorological stations were also deployed on nearby ice floes. There is a clear diurnal cycle in radiation and also in wind speed, cloud base and visibility. It is absent in temperature and humidity, probably due to the very strong control by melting/ freezing ice and snow. In the advection of warm air, latent heat of melting maintains the surface temperature at 0 °C, while with a negative energy balance the latent heat of freezing of the salty ocean water acts to maintain the surface temperature > −2 °C. The constant presence of water at the surface maintains a relative humidity close to 100%, and this is also often facilitated by an increasing specific humidity through the capping inversion, making entrainment a moisture source. This ensures cloudy conditions, with low cloud and fog prevailing most of the time. Intrusions of warm and moist air from beyond the ice edge are frequent, but the local Arctic boundary layer remains at a relatively constant temperature, and is shallow and well mixed with strong capping inversions. Power spectra of surface-layer wind speed sometimes show large variance at low frequency. A scanning radiometer provides a monitoring of the vertical thermal structure with a spatial and temporal resolution not seen before in the Arctic. There are often two inversions, an elevated main inversion and a weak surface inversion, and occasionally additional inversions occur. Enhanced entrainment across the main inversion appears to occur during frontal passages. Variance of the scanning radiometer temperatures occurs in large pulses rather than varying smoothly, and the height to the maximum variance appears to be a reasonable proxy for the boundary-layer depth.  相似文献   

Climate Suitability for Stable Malaria Transmission in Zimbabwe Under Different Climate Change Scenarios     

Kristie?L.?EbiEmail author  Jessica?Hartman  Nathan?Chan  John?Mcconnell  Michael?Schlesinger  John?Weyant 《Climatic change》2005,73(3):375-393

Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100. The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used within or across other African countries.  相似文献