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1.
It is assumed that pulsar radiation originates in a polar cap region and that the emission mechanism is curvature radiation. It is further assumed the radiation reaching an observer at any one time may represent contributions from several particle bunches moving relativistically along different magnetic field lines and radiating mutually incoherently. These assumptions are used to explanation of the minimum of linear polarization appearing near the profile centre of some pulsars.The National Radio Astronomy Observatory is operated by the Associated Universities Inc., under contract with the National Science Foundation. 相似文献
2.
Compaction localization in the Earth and the laboratory: state of the research and research directions 总被引：1，自引：1，他引：1
Localized compaction in porous rocks is a recently recognized phenomenon that has been shown to reduce permeability dramatically.
Consequently, the phenomenon is relevant to a variety of technologies involving fluid injection or withdrawal. This article
summarizes current understanding of localized compaction and impediments to further progress. The article is based on discussions
at a small workshop on localized compaction sponsored by the Office of Science, U. S. Department of Energy. 相似文献
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Bogdan Wszolek Konrad Rudnicki Silvia Masi Paolo De Bernardis Antonio Salvi 《Astrophysics and Space Science》1989,152(1):29-34
We used theIRAS All Sky Maps in order to search for infrared emission in the direction of the Okroy Cloud (R.A.=12h50m, =22°). An enhancement of 100 m diffuse emission is evident in such a region, with an anomalous value of the ratioI
v (100 m)/A
v
; hydrogen 21 cm emission is also present with low radial speed, thus suggesting that the cloud could be a satellite of our Galaxy. 相似文献
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John W. Rudnicki 《Pure and Applied Geophysics》1988,126(2-4):531-554
This paper selectively reviews physical models of earthquake instability. In these models, instability arises as a result of interaction of a fault constitutive relation with deformation of the surrounding material that occurs in response to remote tectonic loading. In contrast to kinematic models in which the fault slip is imposed, it is calculated in physical models and, consequently, these models are essential for understanding precursory processes. Some kind of weakening behavior for the fault constitutive relation is required to produce an instability analogous to an earthquake. Two commonly employed idealizations discussed here are rate-independent slip weakening and rate/state-dependent friction. When these constitutive models are employed on surfaces embedded in elastic half-spaces or layers, possibly coupled to a viscoelastic substrate, the results are capable of simulating realistically some aspects of earthquake occurrence. Common to all models is the prediction that earthquake instability is preceded by precursory slip which produces a departure of surface strain-rate from the background level. Near the epicenter of a moderate to large earthquake, the magnitude of this departure appears to be well within the range of current geodetic measurement accuracy, and its duration is of the order of months to years. However, details depend on a variety of factors, including the modelling of the constitutive relation near peak stress, coupling of elastic crust to the asthenosphere, and coupling of deformation with pore fluid diffusion. 相似文献
7.
Trace element and REE composition of a low-temperature ridge-flank hydrothermal spring 总被引：1，自引：0，他引：1
C.Geoffrey Wheat Michael J. MottlMark Rudnicki 《Geochimica et cosmochimica acta》2002,66(21):3693-3705
Warm (25°C) hydrothermal springs have been sampled on Baby Bare, a basaltic outcrop on 3.5-Ma-old crust ∼100-km east of the Endeavor Segment of the Juan de Fuca Ridge. The source for these springs is a 62 to 64°C formation water that has cooled conductively as it ascends to feed the springs. This water originated as bottom seawater that probably descended into basement ∼52 km to the southwest at another, much larger outcrop called Grizzly Bare. As this seawater flows towards Baby Bare, it is heated and altered by reactions within basaltic basement and by diffusive fluxes to and from the overlying sediment. Concentrations of Mn, Co, Ni, Zn, Cd, and Mo in the spring waters are greater than in bottom seawater, indicating that the oceanic crust is a source for these elements to the oceans. At least a portion of this increase probably results from the redox cycling of Mn in sedimentary sources near the basement interface that produces a diffusive flux to basement formation waters. Additional removal of Mo and inputs of the other five elements to two of the three springs are observed locally near sites of venting, where density gradients can form shallow circulation cells within the sediment and diffusive exchange occurs. Concentrations of Cu, U, V, Y, and the rare earth elements (REEs, excluding Ce) in these samples are less than in bottom seawater, indicating that the oceanic crust is a net sink for these elements in this environment. Copper is probably removed into newly formed carbonate and/or sulfide phases. Removal of the oxyanions U and V is consistent with a net removal of phosphate demonstrated previously for ridge-flank hydrothermal systems. Similarly, removal of Y and the REEs is associated with carbonate, phosphate-rich, and oxide phases. Calculated maximum global chemical fluxes from “warm” ridge-flank hydrothermal systems such as Baby Bare are insignificant relative to riverine fluxes for these elements, except possibly for Mn and Mo. The impact on global geochemical budgets for these elements from lower temperature (<25°C) alteration on ridge flanks is still unknown, but it may well be larger than for warm ridge flanks. 相似文献
8.
A multiscale DEM-LBM analysis on permeability evolutions inside a dilatant shear band 总被引：1，自引：1，他引：0
This paper presents a multiscale analysis of a dilatant shear band using a three-dimensional discrete element method and a lattice Boltzmann/finite element hybrid scheme. In particular, three-dimensional simple shear tests are conducted via the discrete element method. A spatial homogenization is performed to recover the macroscopic stress from the micro-mechanical force chains. The pore geometries of the shear band and host matrix are quantitatively evaluated through morphology analyses and lattice Boltzmann/finite element flow simulations. Results from the discrete element simulations imply that grain sliding and rotation occur predominately with the shear band. These granular motions lead to dilation of pore space inside the shear band and increases in local permeability. While considerable anisotropy in the contact fabric is observed with the shear band, anisotropy of the permeability is, at most, modest in the assemblies composed of spherical grains. 相似文献
9.
Noah Brosch Elchanan Almoznino Bogdan Wszolek † Konrad Rudnicki 《Monthly notices of the Royal Astronomical Society》1999,308(3):651-663
We detected a ring-like distribution of far-infrared (FIR) emission in the direction of the centre of the Virgo cluster (VC). We studied this feature in the FIR, radio and optical domains, and deduced that the dust within the feature reddens the galaxies in the direction of the VC but does not affect stars within the Milky Way. This is likely to be a dusty feature in the foreground of the VC, presumably in the Galactic halo. The H i distribution follows the morphology of the FIR emission and shows peculiar kinematic behaviour. We propose that a highly supersonic past collision between an H i cloud and the Galactic H i formed a shock that heated the interface gas to soft X-ray temperatures. H i remnants from the projectile and from the shocked Galactic H i rain down on to the disc as intermediate-velocity gas.
Our finding emphasizes that extragalactic astronomy must consider the possibility of extinction by dust at high galactic latitude and far from the Galactic plane, which may show structure on 1° and smaller scales. This is particularly important for studies of the VC, e.g. in the determination of the Hubble constant from Cepheids in cluster galaxies. 相似文献
Our finding emphasizes that extragalactic astronomy must consider the possibility of extinction by dust at high galactic latitude and far from the Galactic plane, which may show structure on 1° and smaller scales. This is particularly important for studies of the VC, e.g. in the determination of the Hubble constant from Cepheids in cluster galaxies. 相似文献
10.
K. Rudnicki 《Astronomische Nachrichten》1976,297(6):317-322
A morphological box for the space distribution of galaxies and dark matter as the consequence of various types of cosmogonical hypotheses is presented. A short review of concepts of clustering of galaxies is given. One has to distinguish between the phenomena of “clusters of galaxies” and of “clustering of galaxies”. The second notion is more general. The investigations of KIANG , FLIN , and PEEBLES speak in favour of general clustering rather than overal existence of individual clusters. Individuals such as our Supergalaxy, Coma cluster etc. seem rather to be exceptional features. 相似文献