Heavy Ion Abundances in Impulsive Solar Flares: Influence of Pre-Acceleration in a Current Sheet     

Yuri E. Litvinenko 《Solar physics》2002,205(2):341-349

Competition between stochastic energy gains and collisional energy losses is known to lead to preferential acceleration of heavy ions in flare loops. Ion acceleration in a reconnecting current sheet is shown to mitigate the influence of collisional energy losses on stochastic particle acceleration in impulsive solar flares. This effect decreases the sensitivity of the resulting abundance ratios on initial ion charge states. The resulting abundances are determined by the fact that the energy loss rate falls off rapidly with increasing energy. As an example, the expected Fe/O enhancement ratios are computed and shown to be comparable with those observed with ACE SEPICA in several impulsive flares in 1998. One consequence of the model is that the preferential acceleration of heavy ions can occur only when the plasma gas pressure is large enough, m _e/m _p, which may explain the observed correlation between the heavy ion enrichment and selective ³He acceleration in impulsive flares.  相似文献   

The isolation of prophyra-334 from marine algae and its UV-absorption behavior     

张朝辉  高昕Department of Food Engineering  Ocean University of China  Qingdao  China  Yuri Tashiro  Shingo Matsukawa  Hiroo Ogawa 《中国海洋湖沼学报》2005,23(4):400-405

1 INTRODUCTIONSolar ultraviolet radiation on the earth's surfaceincreases with the depletion of stratospheric ozone(Crutzen, 1992; Kerr and McElroy, 1993; Mad-ronich et al., 1998). Ultraviolet radiation is a highlyactive component of solar spectrum. The excessiveUV radiation has deleterious effects on all plant,animal and microbial groups exposed to solar radia-tion, including the destruction of DNA, proteins andother molecules (Harm, 1980), inhibition of photo-synthesis and growth (W…  相似文献   

Semi-automatic approach toward mapping of flat-roofed buildings within a non-stereoscopic environment     

Yair  Avrahami  Yuri  Raizman  Yerach  Doytsher 《The Photogrammetric Record》2007,22(117):53-74

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Asian dustfall in the St. Elias Mountains, Yukon, Canada   总被引：1，自引：0，他引：1  

Christian Zdanowicz  Gwendy Hall  Yuri Amelin  Isabelle Girard  Aloys Bory 《Geochimica et cosmochimica acta》2006,70(14):3493-3507

In April 2001, a major atmospheric dustfall event occurred in the St. Elias Mountains, Yukon Territory, Canada. Field samples were collected and analyzed for particle size, mineralogy, chemical composition and Sr, Nd and Pb isotopes. Dusts found above ∼3000 m had their source in the Gobi desert region of northern China and Inner Mongolia, and were transported to the Yukon following a series of major dust storms that took place in early April. Dusts found below 3000 m had local (Yukon) or mixed source(s). The Asian dusts had a modal volume diameter of ∼4 μm typical of far-traveled mineral aerosols. However larger (>10 μm) particles were also found at ∼5000 m, suggesting a very rapid trans-Pacific transport in the mid-troposphere. We estimate that the April 2001 event deposited from 5500 to 6335 tons of dust over an area of 21,000 km² in the southwestern Yukon, most of which probably fell within a week. Our findings are consistent with instrumental observations and model simulations of the April 2001 event. While the dust cloud was reportedly mixed with volatile pollutants from Asia, we found no evidence of metal pollution associated with the dustfall in the Yukon. Our findings contribute to clarify the dynamics and the geochemical impact of Asian dust long-range transport events, and to better estimate eolian fluxes of dustborne elements (e.g., Fe) to the Ocean associated with such events. They may also assist in identifying past Asian dust events in ice cores drilled from the St. Elias Mountains icefields, to develop a long-term record of their frequency, magnitude and source(s).  相似文献   

植被冠层立体结构与叶片倾角的偏振光效应     

杨彬  晏磊  Yuri Knyazikhin  刘思远 《遥感学报》2018,22(6):935-946

植被偏振特性研究对于植被监测与组分定量反演具有极其重要的作用。植被冠层的反射辐射具有偏振特性,这种特性与入射辐射和植被冠层结构相关。本文分析了偏振对光子—叶片—冠层之间细微相互作用及其变化的有效探测能力,并利用研究型扫描式偏振辐射仪RSP(Research Scanning Polarimeter)数据系统对比分析了偏振对不同叶倾角分布的估测。通过上述研究得出以下结论:(1)偏振观测能够对光线在冠层立体结构中的透射反射再出射过程给出精细刻画,若不用偏振手段对这一过程进行甄别并去除,则直接测算的植被散射系数会产生高达140%的误差;(2)利用偏振手段可以为高精度大倾角、多时相遥感观测提供可能,以此可改变目前光学遥感小角度、垂直观测的较严格约束;(3)偏振辐射呈现出随波长的稳定特性(相关系数0.96),使得利用偏振手段可以更好地研究冠层结构;(4)不同叶倾角分布对入射辐射存在不同的偏振反射,为利用多角度偏振信息进行遥感植被精细分类提供了新的途径。本文详细描述冠层结构和植被偏振特性的相互作用,通过对冠层立体结构与叶倾角的研究,刻画了植被定量遥感的方向性信息与高精度实现,为高分辨率遥感定量化的有效信息挖掘提供了新手段。  相似文献   

On the normal mode instability of modons and Wu-Verkley waves     

Yuri N. Skiba  Anderi Y. Strelkov 《地球物理与天体物理流体动力学》2013,107(1-2):39-54

Abstract

The normal mode instability of steady Wu-Verkley (1993) wave and modons by Verkley (1984, 1987, 1990) and Neven (1992) is considered. All these flows are solutions to the vorticity equation governing the motion of an ideal incompressible fluid on a rotating sphere. A conservation law for infinitesimal perturbations to each solution is derived and used to obtain a necessary condition for its exponential instability. By these conditions, Fjörtoft's (1953) average spectral number of the amplitude of an unstable mode must be equal to a specific number that depends on the degree of the solution in its inner and outer regions as well as on spectral distribution of the mode energy in these regions. Some properties of the conditions for different types of modons are discussed. The maximum growth (and decay) rate of the modes is estimated, and the orthogonality of the amplitude of each unstable, decaying, or non-stationary mode to the basic solution is shown in the energy inner product.

The new instability conditions confine the unstable disturbances of the WV wave and modon to a hypersurface in the perturbation space and allow interpretation of their energy structure. They are also useful both in estimating the maximum growth rate of unstable modes and in testing the numerical algorithms designed for the linear stability study.  相似文献   

Monazite stability,composition and geochronology as tracers of Paleoproterozoic events at the eastern margin of the East European Craton (Taratash complex,Middle Urals)     

Sven Sindern  Axel Gerdes  Yuri L. Ronkin  Annika Dziggel  Ralf Hetzel  Bernd Aloys Schulte 《Lithos》2012

The Precambrian Taratash complex (Middle Urals) is one of the rare windows into the Palaeoproterozoic and earlier history of the eastern margin of the East European Craton. Monazite from intensively deformed rocks within a major amphibolite-facies shear zone in the Taratash complex has been investigated by means of electron-probe microanalysis and laser-ablation SF-ICP-MS.Metamorphic and magmatic cores of monazite from metasedimentary and metagranitoid rocks yield U–Pb ages of 2244 ± 19 and 2230 ± 22 Ma (± 2 σ) and record a previously unknown pre-deformational HT-metamorphic event in the Taratash complex. Subsequent dissolution–reprecipitation of monazite, during shear zone formation under amphibolite-facies conditions, caused patchy zonation and chemical alteration of the recrystallised monazite domains, leading to higher cheralite and huttonite components. This process, which was mediated by a probable (alkali + OH)-bearing metamorphic fluid also caused a total resetting of the U–Pb-system. The patchy domains yield concordant U–Pb-ages between 2052 ± 16 and 2066 ± 22 Ma, interpreted as the age of the shear zone. In line with previously published ages of high grade metamorphism and migmatisation, the data may point to a Palaeoproterozoic orogenic event at the eastern margin of the East European Craton.Post-deformational fluid-induced greenschist-facies retrogression caused partial to complete breakdown of monazite to fluorapatite, REE + Y-rich epidote, allanite and Th-orthosilicate.The retrograde assemblages either form coronas around monazite, or occur as dispersed reaction zones, indicating that the REE, Y, and Th were mobile at least on the thin section scale. The greenschist-facies metamorphic fluid was aqueous and rich in Ca. Monazite affected by advanced breakdown responded to the retrogression by incorporating the cheralite or huttonite components during a fluid-induced dissolution–reprecipitation process. This event did not reset the U–Pb-system but caused partial Pb loss reflected by discordant U–Pb-dates.  相似文献   

Design of two crushing devices for release of the fluid inclusion volatiles   总被引：1，自引：0，他引：1  

Yuri V. Dublyansky 《Central European Journal of Geosciences》2012,4(2):219-224

Two crushing cells have been described for the release of volatiles from fluid inclusions in minerals in vacuum, static gas, and gas-flow applications. To minimize the adsorption of released volatiles on the freshly created mineral surfaces, both devices employed heated crushing. In the MTSN (Museo Tridentine di Scienze Naturali) crusher, samples were disintegrated by a piston driven by an induction coil. For efficient crushing, the electromagnet operated in dynamic impulse mode. In the LFU (Leopold-Franzens-Universit?t) crusher, the sample was disintegrated through the combined action of compression (manually operated hydraulic ram) and attrition. Crushers are able to be used in off-line and on-line modes, in gas chromatographic and mass spectrometric analyses.  相似文献   

A monotone nonlinear finite volume method for diffusion equations and multiphase flows     

Kirill Nikitin  Kirill Terekhov  Yuri Vassilevski 《Computational Geosciences》2014,18(3-4):311-324

We present a new nonlinear monotone finite volume method for diffusion equation and its application to two-phase flow model. We consider full anisotropic discontinuous diffusion or permeability tensors on conformal polyhedral meshes. The approximation of the diffusive flux uses the nonlinear two-point stencil which provides the conventional seven-point stencil for the discrete diffusion operator on cubic meshes. We show that the quality of the discrete flux in a reservoir simulator has great effect on the front behavior and the water breakthrough time. We compare two two-point flux approximations (TPFA), the proposed nonlinear TPFA and the conventional linear TPFA, and multipoint flux approximation (MPFA). The new nonlinear scheme has a number of important advantages over the traditional linear discretizations. Compared to the linear TPFA, the nonlinear TPFA demonstrates low sensitivity to grid distortions and provides appropriate approximation in case of full anisotropic permeability tensor. For nonorthogonal grids or full anisotropic permeability tensors, the conventional linear TPFA provides no approximation, while the nonlinear flux is still first-order accurate. The computational work for the new method is higher than the one for the conventional TPFA, yet it is rather competitive. Compared to MPFA, the new scheme provides sparser algebraic systems and thus is less computational expensive. Moreover, it is monotone which means that the discrete solution preserves the nonnegativity of the differential solution.  相似文献