Sausage MHD Waves in Incompressible Flux Tubes with Twisted Magnetic Fields     

Robert Erdélyi  Viktor Fedun 《Solar physics》2006,238(1):41-59

Twisted magnetic flux tubes are of considerable interest because of their natural occurrence from the Sun’s interior, throughout the solar atmosphere and interplanetary space up to a wide range of applicabilities to astrophysical plasmas. The aim of the present work is to obtain analytically a dispersion equation of linear wave propagation in twisted incompressible cylindrical magnetic waveguides and find appropriate solutions for surface, body and pseudobody sausage modes (i.e. m = 0) of a twisted magnetic flux tube embedded in an incompressible but also magnetically twisted plasma. Asymptotic solutions are derived in long- and short-wavelength approximations. General solutions of the dispersion equation for intermediate wavelengths are obtained numerically. We found, that in case of a constant, but non-zero azimuthal component of the equilibrium magnetic field outside the flux tube the index ν of Bessel functions in the dispersion relation is not integer any more in general. This gives rise to a rich mode-structure of degenerated magneto-acoustic waves in solar flux tubes. In a particular case of a uniform magnetic twist the total pressure is found to be constant across the boundary of the flux tube. Finally, the effect of magnetic twist on oscillation periods is estimated under solar atmospheric conditions. It was found that a magnetic twist will increase, in general, the periods of waves approximately by a few percent when compared to their untwisted counterparts.  相似文献   

UK pollution control—Whitehall v parliament     

Viktor Sebek 《Marine Policy》1979,3(3):240-242

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A new global ocean hydrographic climatology          下载免费PDF全文

GOURETSKI Viktor 《大气和海洋科学快报》2019,(3):226-229

This report describes the main features of the recently published World Ocean Experiment–Argo Global Hydrographic Climatology. This climatology is based on profile data from ships, Argo floats, and sensors attached to marine mammals. As an important deviation from the widely used climatologies produced previously by the National Oceanographic Data Center, the spatial interpolation was performed on local potential density surfaces, so that no ‘artificial water masses’ were created. In addition to monthly fields of temperature and salinity, gridded maps of the upper mixed layer depth are now provided.  相似文献   

Experimental and numerical investigations on CO2 injection and enhanced gas recovery effects in Altmark gas field (Central Germany)     

Leonhard Ganzer  Viktor Reitenbach  Dieter Pudlo  Daniel Albrecht  Arron Tchouka Singhe  Kilian Nhungong Awemo  Joachim Wienand  Reinhard Gaupp 《Acta Geotechnica》2014,9(1):39-47

The feasibility of CO₂ storage and enhanced gas recovery (EGR) effects in the mature Altmark natural gas field in Central Germany has been studied in this paper. The investigations were comprehensive and comprise the characterization of the litho- and diagenetic facies, mineral content, geochemical composition, the petrophysical properties of the reservoir rocks with respect to their potential reactivity to CO₂ as well as reservoir simulation studies to evaluate the CO₂ wellbore injectivity and displacement efficiency of the residual gas by the injected CO₂. The Rotliegend sediments of the Altmark pilot injection area exhibit distinct mineralogical, geochemical, and petrophysical features related to litho- and diagenetic facies types. The reservoir rock reactivity to CO₂ has been studied in autoclave experiments and associated effects on two-phase transport properties have been examined by means of routine and special core analysis before and after the laboratory runs. Dissolution of calcite and anhydrite during the short-term treatments leading to the enhancements of permeability and porosity as well as stabilization of the water saturation relevant for CO₂ injection have been observed. Numerical simulation of the injection process and EGR effects in a sector of the Altmark field coupled with a wellbore model revealed the possibility of injecting the CO₂ gas at temperatures as low as 10 °C and pressures around 40 bar achieving effective inflow in the reservoir without phase transition in the wellbore. The small ratio of injected CO₂ volume versus reservoir volume indicated no significant EGR effects. However, the retention and storage capacity of CO₂ will be maximized. The migration/extension of CO₂ varies as a function of heterogeneity both in the layers and in the reservoir. The investigation of CO₂ extension and pressure propagation suggested no breakthrough of CO₂ at the prospective production well during the 3-year injection period studied.  相似文献   

Precambrian Collision Orogen Formation and Supercontinents: Tectonic, Petrologic and Isotope Geochronological Evidence     

Viktor A. Glebovitsky   《Gondwana Research》2001,4(4):621

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The Dnepr Canyon: evidence for a continuous submarine channel link between the outer shelf and the deep-sea basin of the northwestern Black Sea     

Sergei B. Gulin  Yuriy G. Artemov  Viktor N. Egorov  Dmitriy B. Evtushenko 《Geo-Marine Letters》2013,33(4):319-324

Multibeam bathymetric surveys and single-beam profiles were collected in 2003–2010 from aboard the Ukrainian RV Professor Vodyanitskiy (cruises PV-58 and PV-60, 2003 and 2004), and the German RV Meteor (cruise M-72, legs 1 and 4, 2007) and RV Maria S. Merian (cruise MSM-15, leg 2, 2010) along the continental margin of the NW Black Sea. Integrating published, reprocessed and novel data has revealed the existence of a major continuous channel extending from the Dnepr paleo-delta into greater water depths. It is more than 90 km long, 1.1 km wide and up to 125 m deep. On the upper slope (120–960 m water depth), a number of smaller channels merge into the large, Y-shaped Dnepr Canyon, which then continues obliquely downslope via this submarine channel to at least 1,815 m water depth off the Crimean continental margin, NW Black Sea. The channel could be an important, hitherto unknown link between the shallow oxic and deep anoxic environments of the Black Sea, along which sediment and organic matter could be funneled into the deep-sea basin. This would have far-reaching implications for investigations dealing with marine geology and biology, climate change, as well as oil and natural gas exploitation. The unusual alignment of the channel along the margin of the basin, as well as the location and mode of channel termination in deeper waters deserve future research.  相似文献   

Magnetic signature of different vegetation species in polluted environment   总被引：2，自引：0，他引：2  

Diana Jordanova  Petar Petrov  Viktor Hoffmann  Tilman Gocht  Cristian Panaiotu  Tsenka Tsacheva  Neli Jordanova 《Studia Geophysica et Geodaetica》2010,54(3):417-442

Detailed magnetic study on vegetation samples from several strongly polluted and clean sites in Bulgaria is carried out in order to evaluate suitability of different species as passive dust collectors in magnetometry. From each location, available species among lichens, mosses, poplar leaves, dandelion, needles have been sampled. Magnetic susceptibility calculated on mass-specific basis shows wide variability between diamagnetic signal up to 846 × 10⁻⁸ m³/kg. Lichens and mosses are found to be the species, showing magnetic signals with the strongest contrast between clean and polluted environment. The main magnetic phase is magnetite-like according to the results from thermomagnetic analysis of susceptibility on magnetic extracts. Scanning electron microscopy (SEM) microphotographs reveal the presence of abundant particulate matter on vegetation surface both with anthropogenic (spherules) and lithogenic origin. Magnetic grain size deduced by the ratio of saturation remanent magnetization (SIRM) and mass-specific magnetic susceptibility (χ) and coercivities (B_c and B_cr) suggest that different species accumulate preferentially small SD-like grains from pollution emissions. Contrasting relationship of the ratio of anhysteretic remanent magnetization (ARM) and χ for polluted vs clean sites deduced by needles and lichens may be related to transformation of the accumulated dust particles within lichens’ tissue. This finding indicates that the exact species used as biological dust collector is of importance when studying spatial grain size distribution of magnetic dust particles. Pilot study on polycyclic aromatic hydrocarbons (PAH) content and its relation to magnetic parameters shows good correspondence between high levels of PAHs and high SIRM values for locations affected by non-ferrous industrial production.  相似文献   

The restricted three-body problem in cylindrical clouds     

Barnabás Deme  Bálint Érdi  L. Viktor Tóth 《Celestial Mechanics and Dynamical Astronomy》2018,130(11):73

The fragmentation of interstellar molecular clouds has been investigated with great effort by many authors. In this paper, a simple model is given to describe the dynamics of two fragments moving in a special cylindrical potential. Using a modified version of the restricted three-body problem and the corresponding Jacobian integral, some constraints are given for the motion of the fragments.  相似文献   

Velocities of shallow overland flow on semiarid hillslopes          下载免费PDF全文

Viktor Polyakov  Mark A. Nearing  Jeffry Stone 《地球表面变化过程与地形》2018,43(12):2578-2583

A series of 188 rainfall plot simulations was conducted on grass, shrub, oak savanna, and juniper sites in Arizona and Nevada. A total of 897 flow velocity measurements were obtained on 3.6% to 39.6% slopes with values ranging from 0.007 m s^‐1 to 0.115 m s^‐1. The experimental data showed that shallow flow velocity on rangelands was related to discharge and ground litter cover and was largely independent of slope gradient or soil characteristics. A power model was proposed to express this relationship. These findings support the slope–velocity equilibrium hypothesis. Namely, eroding soil surfaces evolve such that steeper areas develop greater hydraulic roughness. As a result overland flow velocity becomes independent of the slope gradient over time. Our findings have implications for soil erosion modeling suggesting that hydraulic friction is a dynamic, slope and discharge dependent property. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Directional interpolation of multicomponent data          下载免费PDF全文

Fredrik Andersson  Adriana Citlali Ramírez  Torgeir Wiik  Viktor V. Nikitin 《Geophysical Prospecting》2017,65(5):1246-1263

A method for interpolation of multicomponent streamer data based on using the local directionality structure is presented. The derivative components are used to estimate a vector field that locally describes the direction with the least variability. Given this vector field, the interpolation can be phrased in terms of the solution of a partial differential equation that describes how energy is transported between regions of missing data. The approach can be efficiently implemented using readily available routines for computer graphics. The method is robust to noise in the measurements and particularly towards high levels of low‐frequent noise that is present in the derivative components of the multicomponent streamer data.  相似文献