Elastic properties of double-porosity rocks using the differential effective medium model     

M. Markov  V. Levine  A. Mousatov  E. Kazatchenko 《Geophysical Prospecting》2005,53(5):733-754

An approach to determining the effective elastic moduli of rocks with double porosity is presented. The double‐porosity medium is considered to be a heterogeneous material composed of a homogeneous matrix with primary pores and inclusions that represent secondary pores. Fluid flows in the primary‐pore system and between primary and secondary pores are neglected because of the low permeability of the primary porosity. The prediction of the effective elastic moduli consists of two steps. Firstly, we calculate the effective elastic properties of the matrix with the primary small‐scale pores (matrix homogenization). The porous matrix is then treated as a homogeneous isotropic host in which the large‐scale secondary pores are embedded. To calculate the effective elastic moduli at each step, we use the differential effective medium (DEM) approach. The constituents of this composite medium – primary pores and secondary pores – are approximated by ellipsoidal or spheroidal inclusions with corresponding aspect ratios. We have applied this technique in order to compute the effective elastic properties for a model with randomly orientated inclusions (an isotropic medium) and aligned inclusions (a transversely isotropic medium). Using the special tensor basis, the solution of the one‐particle problem with transversely isotropic host was obtained in explicit form. The direct application of the DEM method for fluid‐saturated pores does not account for fluid displacement in pore systems, and corresponds to a model with isolated pores or the high‐frequency range of acoustic waves. For the interconnected secondary pores, we have calculated the elastic moduli for the dry inclusions and then applied Gassmann's tensor relationships. The simulation of the effective elastic characteristic demonstrated that the fluid flow between the connected secondary pores has a significant influence only in porous rocks containing cracks (flattened ellipsoids). For pore shapes that are close to spherical, the relative difference between the elastic velocities determined by the DEM method and by the DEM method with Gassmann's corrections does not exceed 2%. Examples of the calculation of elastic moduli for water‐saturated dolomite with both isolated and interconnected secondary pores are presented. The simulations were verified by comparison with published experimental data.  相似文献   

Soil development in till of various ages in northeastern Pennsylvania   总被引：1，自引：0，他引：1  

Elissa R. Levine  Edward J. Ciolkosz 《Quaternary Research》1983,19(1):85-99

Eleven well-drained soils formed in till parent materials of varying ages in northeastern Pennsylvania were studied to determine changes in the soils with time. Four profiles (three Lackawanna and one Bath) were formed in Woodfordian till (15,000 yr B.P.), and two (Leck Kill) were formed in Altonian till (>28,000, <75,000 yr B.P.). The remaining five (Allenwood) were formed in pre-Wisconsinan till (>75,000 yr B.P.). In these soils, the extractable iron oxide, extractable aluminum oxide, and kaolinite contents increase with age, as do the total clay and fine/total clay ratio. With increasing age, the maximum accumulation of these constituents is found deeper in the profile. The extractable silicon oxide distribution is constant with depth, but it decreases in overall amount with time. Gibbsite is found only in small amounts in the A horizon of Altonian soils, but occurs throughout the profile of pre-Wisconsinan soils, although only in small amounts. In general, differences were found in these soils which separated them into three groups representing varying degrees of soil development. A regression equation was derived to predict the age of soils formed from the Altonian till based on a “clay accumulation index” value for soils of known Woodfordian and Holocene ages. The equation log Y = 1.80 + 0.992(logX) best fit the data, with an r² value of 0.913. Using this equation, a mean age of 41,000 yr was calculated for the Altonian soils. This date was used to derive a second equation to predict ages for pre-Wisconsinan soils. The equation with the highest r² value (0.934) was log Y = 1.81 + 0.998(logX). Dates for soils developed in the White Deer till and the Laurelton till of the pre-Wisconsinan stage were calculated to be 86,000 and 91,000 yr B.P., respectively. These dates fall within ages estimated for the Sangamon Interglaciation and thus would appear to be too young for pre-Sangamonian materials. The probable reason for the “too-young age” is that the C-horizon material of the pre-Wisconsinan soils was weathered and did not provide an accurate estimate of clay accumulation for the prediction equation.  相似文献   

Design of an extended-range, three-wavelength distance-measuring instrument     

S.E. Moody  Judah Levine   《Tectonophysics》1979,52(1-4)

We describe an extension of current multiwavelength Electromagnetic Distance Measurement (EDM) techniques which should allow the range of multiwavelength measurements to be extended to approximately 50 km. The basic modification needed is the replacement of the retro-reflector commonly used by an active station containing lasers and a microwave source. Because the system will always be operated as a full three-wave-length instrument, accuracies of about 5 · 10⁻⁸ at 50 km should be obtainable on a routine basis under reasonably clear weather conditions.  相似文献   

Microwave scatter and sea state estimation: Two-scale ocean wave models     

Robert O. Harger  David M. Levine 《Boundary-Layer Meteorology》1978,13(1-4):107-118

The efficient estimation of ocean wave-structure parameters with a remote, narrow-beam, pulsed, microwave radar at intermediate incidence angles is discussed. The sea surface is described as the sum of random small- and large-scale structures (waves), the latter the sum of a sinusoid and a random field. It is shown that the small-scale structure is responsible for scattering and that the scatter depends parametrically on the large-scale structure. For the estimation problem it is assumed, reasonably, that the received signal is normally distributed: a relatively simple processor which will efficiently estimate parameters of the sinusoidal structure is illustrated and its performance discussed. A brief comparison is made with a normal incidence system with which the variance of the large-scale random roughness can be estimated.Research supported by NASA Grant NSG-5048.  相似文献   

Dependence of Indian monsoon rainfall on moisture fluxes across the Arabian Sea and the impact of coupled model sea surface temperature biases   总被引：2，自引：2，他引：0  

Richard C. Levine  Andrew G. Turner 《Climate Dynamics》2012,38(11-12):2167-2190

The Arabian Sea is an important moisture source for Indian monsoon rainfall. The skill of climate models in simulating the monsoon and its variability varies widely, while Arabian Sea cold sea surface temperature (SST) biases are common in coupled models and may therefore influence the monsoon and its sensitivity to climate change. We examine the relationship between monsoon rainfall, moisture fluxes and Arabian Sea SST in observations and climate model simulations. Observational analysis shows strong monsoons depend on moisture fluxes across the Arabian Sea, however detecting consistent signals with contemporaneous summer SST anomalies is complicated in the observed system by air/sea coupling and large-scale induced variability such as the El Ni?o-Southern Oscillation feeding back onto the monsoon through development of the Somali Jet. Comparison of HadGEM3 coupled and atmosphere-only configurations suggests coupled model cold SST biases significantly reduce monsoon rainfall. Idealised atmosphere-only experiments show that the weakened monsoon can be mainly attributed to systematic Arabian Sea cold SST biases during summer and their impact on the monsoon-moisture relationship. The impact of large cold SST biases on atmospheric moisture content over the Arabian Sea, and also the subsequent reduced latent heat release over India, dominates over any enhancement in the land-sea temperature gradient and results in changes to the mean state. We hypothesize that a cold base state will result in underestimation of the impact of larger projected Arabian Sea SST changes in future climate, suggesting that Arabian Sea biases should be a clear target for model development.  相似文献   

The role of northern Arabian Sea surface temperature biases in CMIP5 model simulations and future projections of Indian summer monsoon rainfall     

Richard C. Levine  Andrew G. Turner  Deepthi Marathayil  Gill M. Martin 《Climate Dynamics》2013,41(1):155-172

Many climate models have problems simulating Indian summer monsoon rainfall and its variability, resulting in considerable uncertainty in future projections. Problems may relate to many factors, such as local effects of the formulation of physical parametrisation schemes, while common model biases that develop elsewhere within the climate system may also be important. Here we examine the extent and impact of cold sea surface temperature (SST) biases developing in the northern Arabian Sea in the CMIP5 multi-model ensemble, where such SST biases are shown to be common. Such biases have previously been shown to reduce monsoon rainfall in the Met Office Unified Model (MetUM) by weakening moisture fluxes incident upon India. The Arabian Sea SST biases in CMIP5 models consistently develop in winter, via strengthening of the winter monsoon circulation, and persist into spring and summer. A clear relationship exists between Arabian Sea cold SST bias and weak monsoon rainfall in CMIP5 models, similar to effects in the MetUM. Part of this effect may also relate to other factors, such as forcing of the early monsoon by spring-time excessive equatorial precipitation. Atmosphere-only future time-slice experiments show that Arabian Sea cold SST biases have potential to weaken future monsoon rainfall increases by limiting moisture flux acceleration through non-linearity of the Clausius–Clapeyron relationship. Analysis of CMIP5 model future scenario simulations suggests that such effects are small compared to other sources of uncertainty, although models with large Arabian Sea cold SST biases may suppress the range of potential outcomes for changes to future early monsoon rainfall.  相似文献   

The kinematics of lopsided galaxies     

Edo Noordermeer †  Linda S. Sparke  Stephen E. Levine 《Monthly notices of the Royal Astronomical Society》2001,328(4):1064-1080

Lopsidedness is a common feature in galaxies, both in the distribution of light and in the kinematics. We investigate the kinematics of a model for lopsided galaxies that consists of a disc lying off-centre in a dark halo, and circling around the halo centre. We search for families of stable, closed, non-crossing orbits, and assume that gas in our galaxies moves on these orbits. Several of our models show strong lopsided gas kinematics, especially those in which the disc spins around its axis in a retrograde sense compared with its motion around the halo centre. We are able to reproduce the H  i velocity map of the kinematically lopsided galaxy NGC 4395.
The lopsidedness in our models is most pronounced in the models where the halo provides a relatively large fraction of the total mass at small radii. This may explain why the gas shows lopsidedness more frequently in late-type galaxies, which are dominated by dark matter. Surfaces of section show large regions of irregular orbits in the models where the halo density is low. This may indicate that these models are unstable.  相似文献   

Last glacial ice‐rafted debris off southwestern Europe: the role of the British–Irish Ice Sheet     

Grant R. Bigg  Richard C. Levine  Chris D. Clark  Sarah L. Greenwood  Haflidi Haflidason  Anna L. C. Hughes  Atlé Nygård  Hans Petter Sejrup 《第四纪科学杂志》2010,25(5):689-699

Ice‐rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short‐lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British–Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short‐lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Evidence for opposed currents in active region loops     

Randolph H. Levine 《Solar physics》1976,46(1):159-170

EUV and X-ray images of the Sun are used as tracers of the magnetic field structure in the Solar atmosphere in order to study the existence of currents in active regions. Criteria are suggested for comparing the data with theoretical extrapolations of magnetic field lines above the level of magnetograph observations. Analysis of the data presented in conjunction with force-free field calculations suggests the existence of currents flowing in opposite directions in nearby sets of loops in the active regions shown. Some simple qualitative implications of opposed current structures are suggested.  相似文献   

Extraterrestrial accretion from the GISP2 ice core     

Daniel B. Karner  Jonathan Levine  Frank Asaro  Michael R. Stolz 《Geochimica et cosmochimica acta》2003,67(4):751-763

The rate of extraterrestrial accretion for particles in the size range 0.45 μm to ∼20 μm was determined from dust concentrates extracted from Greenland Ice Sheet Project 2 (GISP2) ice core samples. Using instrumental neutron activation analysis (INAA), we determined the iridium (Ir) content of the dust. Following a core-specific correction for terrestrial Ir and assuming a chondritic Ir abundance of 500 ppb, we measure an average accretion rate for 0.45 μm to ∼20 μm particles over the entire Earth of 0.22 (± 0.11) × 10⁹ g/yr (kton/yr) for 317 years of ice through the interval 6 to 20 ka. This is consistent with the interplanetary dust accretion rate of 0.17 (± 0.08) x 10⁹ g/yr that we derive from published ³He data for the GISP2 core. Accounting for particles that are larger and smaller than those detected by or experiment, our best estimate of the total accretion rate (including particle sizes up to about 4 cm in diameter) is 2.5 × 10⁹ g/yr. The uncertainty in this estimate is dominated by statistical fluctuations in the number of particles expected to end up in the ice core and not by measurement error. Based on Monte Carlo simulations, we estimate the upper limit for total extraterrestrial accretion to Earth of 6.25 × 10⁹ g/yr (95% confidence level). This accretion rate is consistent with some estimates from micrometeorite concentrations in polar ice, estimates from ground-based radar studies, and with accretion estimates of ³He-bearing interplanetary dust particles, assuming that ³He is correlated with particle surface area. It is, however, lower than estimates based on platinum group element studies of marine sediments. The conflict may indicate systematic errors with either the marine or the non-marine samples, departures from the assumed particle spectrum of Grün and coauthors, or time-variable accretion rates, with the early Holocene period being characterized by low levels of accretion.  相似文献