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1.
Effect of moderate shock waves on magnetic susceptibility and microstructure of a magnetite‐bearing ore
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This study demonstrates a relationship between changes of magnetic susceptibility and microstructure developing in minerals of a magnetite‐bearing ore, experimentally shocked to pressures of 5, 10, 20, and 30 GPa. Shock‐induced effects on magnetic properties were quantified by bulk magnetic susceptibility measurements while shock‐induced microstructures were studied by high‐resolution scanning electron microscopy. Microstructural changes were compared between magnetite, quartz, amphibole, and biotite grains. In the 5 GPa sample, a sharp drop of magnetic susceptibility correlates with distinct fragmentation as well as with formation of shear bands and twins in magnetite. At 10 GPa, shear bands and twins in magnetite are accompanied by droplet‐shaped nanograins. In this shock pressure regime, quartz and amphibole still show intensive grain fragmentation. Twins in quartz and foam‐shaped, highly porous amphibole are formed at 20 and 30 GPa. The formation of porous minerals suggests that shock heating of these mineral grains resulted in localized temperature spikes. The identified shock‐induced features in magnetite strongly advise that variations in the bulk magnetic susceptibility result from cooperative grain fragmentation, plastic deformation and/or localized amorphization, and probably postshock annealing. In particular, the increasing shock heating at high pressures is assumed to be responsible for a partial defect annealing which we suggest to be responsible for the almost constant values of magnetic susceptibility above 10 GPa. 相似文献
2.
Weakly nonlinear triad interactions between spherical Rossby harmonics are studied. Each of the harmonics has the form APnm(sin θ)exp[i(mλ − σt)], where A is an amplitude and Pnm is the associated Legendre function. Equations for the amplitudes are derived and resonance conditions are analysed. The resonance conditions differ substantially from the usual resonance conditions on a β-plane and include a Diophantine equation and a few inequalities for the integer wavenumbers n and m of the interacting modes. Particular analytical series of solutions to the resonance conditions are constructed, which show that modes with arbitrary large wavenumbers can participate in the interactions. A numerical study of the resonance conditions reveals that no more than 21% of the Rossby harmonics can participate in the triad interactions and that chains of the interacting triads soon break. Thus precise interactions (for which the resonance conditions hold exactly) do not result in any significant redistribution of energy over the spectrum. On the other hand, approximate interactions (for which the resonance conditions hold approximately) generate an intensive energy redistribution among short Rossby modes with typical scales much smaller than the Earth's radius. Thus the energy cascade is concentrated mainly in the short-wave part of the spectrum and is very weak in the large-scale domain. The efficiency of the triad interaction of Rossby modes with scales much smaller than the Earth's radius depends strongly on the existence of the so-called interaction latitude at which the local wave-vectors and frequencies of the interacting modes satisfy resonance conditions for plane Rossby waves on the β-plane approximating the neighbourhood of the latitude. If the interaction latitude exists, the interaction is intensive; in the opposite case, it is weak. 相似文献
3.
Gregory M. Reznik 《Ocean Dynamics》2018,68(8):987-1000
Theory of wave boundary layers (WBLs) developed by Reznik (J Mar Res 71: 253–288, 2013, J Fluid Mech 747: 605–634, 2014, J Fluid Mech 833: 512–537, 2017) is extended to a rotating stratified fluid. In this case, the WBLs arise in the field of near-inertial oscillations (NIOs) driven by a tangential wind stress of finite duration. Near-surface Ekman layer is specified in the most general form; tangential stresses are zero at the lower boundary of Ekman layer and viscosity is neglected below the boundary. After the wind ceases, the Ekman pumping at the boundary becomes a linear superposition of inertial oscillations with coefficients dependent on the horizontal coordinates. The solution under the Ekman layer is obtained in the form of expansions in the vertical wave modes. We separate from the solution a part representing NIO and demonstrate development of a WBL near the Ekman layer boundary. With increasing time t, the WBL width decays inversely proportional to \( \sqrt{t} \) and gradients of fields in the WBL grow proportionally to \( \sqrt{t} \); the most part of NIO is concentrated in the WBL. Structure of the WBL depends strongly on its horizontal scale L determined by scale of the wind stress. The shorter the NIO is, the thinner and sharper the WBL is; the short-wave NIO with L smaller than the baroclinic Rossby scale LR does not penetrate deep into the ocean. On the contrary, for L?≥?LR, the WBL has a smoother vertical structure; a significant long-wave NIO signal is able to reach the oceanic bottom. An asymptotic theory of the WBL in rotating stratified fluid is suggested. 相似文献
4.
The international conference “Vortices and coherent structures: from ocean to microfluids” was held at the Pacific Oceanological Institute of the Russian Academy of Sciences in Vladivostok (Russia) from August 28 to August 31, 2017. The event gathered experimentalists and theoreticians, oceanographers and physicists, with a common interest in observing and modelling fluid flows in different media, from the ocean to laboratory flows. It was a fruitful idea to bring together researchers from a variety of backgrounds to benefit from a vigorous discussion of concepts across different disciplines in oceanography and hydrodynamics.
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Numerical studies of barotropic modons 总被引:1,自引:0,他引:1
James C. McWilliams Glenn R. Flierl Vitaly D. Larichev Gregory M. Reznik 《Dynamics of Atmospheres and Oceans》1981,5(4):219-238
Numerical solutions of barotropic modons are examined to assess the accuracy with which they can be calculated, their behavior under the influence of dissipation, and their resistance to perturbations. 相似文献
6.
Oceanology - The theory of wave boundary layers developed in [7] is generalized to the case of a stably neutrally stratified ocean consisting of a homogeneous upper layer and a stably stratified... 相似文献
7.
G. M. Reznik 《Izvestiya Atmospheric and Oceanic Physics》2010,46(6):784-797
This paper studies the joint influence that rotation and the earth’s sphericity have on the dynamics of localized synoptic
scale vortices within the quasi-geostrophic barotropic model in the beta-plane approximation. Rossby solitons (two-dimensional
vortices exponentially localized in space which propagate without changing their form along the latitude circles) are considered
in the first part of the article. The general properties of such solutions are discussed. The simplest examples are presented,
and a brief review of the main results is given. The second part is dedicated to the theory of nonstationary monopoles. The
physical mechanisms governing the evolution of such vortices are described; different stages of this evolution are determined
for intense vortices. Analytical and numerical results are used to confirm the qualitative explanations. 相似文献
8.
The present-day contribution of coastal-marine placers into the bulk gold production is insignificant. As usual, only gold
of coarse- and medium-grained classes is recovered while the fine-grained and dispersed gold are disposed into tailings. During
the sedimentation, such a floating gold is removed far from the wave-surf zone. Despite the common belief about poor prospects
of the Black Sea shelf for modern gold placers, we have proved the expediency to study the distribution of floating microscopic
gold in Holocene marine sediments and carried out the respective works. Using the special concentrating methods, we enabled
to detect the gold in most of the 830 samples collected. Geomorphological, lithological, hydrodynamic, and other factors controlling
the gold potential were determined. In some cases, the gold content exceeds the minimal economic grade in continental placers.
The prospective sites for further investigation were outlined. It was established that the polygenic microscopic gold can
be divided into at least clastic, authigenic, and clastic-authigenic types. According to our data, the alluvial, lagoonal-marine,
liman, and other sediments at the adjacent land also contain substantial amounts of microscopic gold. The pre10987nary study
of oceanic bottom sediments near the Antarctic Peninsula and within the Argentine Basin proved the possibility of microscopic
gold to accumulate under various facies conditions. The microscopic gold, mainly of clastic type, was detected here in 82%
of samples. The obtained results testify to the global-scale deposition of floating microscopic gold in sedimentation basins
of various age and may serve as a basis for the further comprehensive tackling of the problem in different regions. 相似文献
9.
Alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure,Sweden: A new shock wave‐induced deformation feature
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A. Agarwal B. Reznik L. M. Alva‐Valdivia D. C. Srivastava 《Meteoritics & planetary science》2017,52(3):458-470
This paper reports peculiar alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden. The combined microscopic and spectroscopic studies of the micro/nanoscale wedges reveal that these are deformation‐induced features. First, samples showing wedges, 12 out of 18 studied, are distributed in the impact structure within a radius of up to 10 km from the crater center. Second, the margins between the augite and labradorite wedges are sharp and the {110} prismatic cleavage of augite develops into fractures and thereafter into wedges. The fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain. Third, compared to the bulk labradorite, the dislocation density and the residual strain in the labradorite wedges are significantly higher. A possible mechanism of genesis of the wedges is proposed. The mechanism explains that passing of the shock waves in the basement dolerite induced (i) formation of microfractures in augite and labradorite; (ii) development of the augite prismatic cleavages into the wedges, which overprint the microfracture in the labradorite wedges; and (iii) thereafter, infilling of microfractures in the augite wedges by labradorite. 相似文献
10.
Yakov M. Reznik 《Engineering Geology》1998,50(3-4):319-327
Footing settlements depend not only on physical and mechanical properties of base soils, but also on applied load intensities and their distributions with depth, as well as on footing rigidity, shape and dimensions. An analytical expression relating rigid bearing plate and/or footing settlements to thicknesses of deformation (active) zones, which form below footing bottoms, has been previously offered by the author. The results of tests performed with 0.5, 1.0 and 4.0 m2-area square footings, constructed on undisturbed clayey soils and containing data describing active zone development, were collected from literature and analyzed. This paper presents graphical relationships between square footing settlements, active zone thicknesses and footing dimensions, which are verified by published test results performed with experimental square footings, having areas different than the ones selected for statistical analyses. 相似文献