Assessment of vulnerability for rockfalls in Cozia Gorge (Southern Carpathians,Romania)     

Ovreiu  Adriana Bianca  Bărsoianu  Iulian Andrei  Nistor  Constantin  Nedelea  Alexandru  Comănescu  Laura 《Natural Hazards》2019,99(1):117-140

Natural Hazards - Rockfalls represents a sudden, extremely important geomorphological hazard and may become a threat for people’s life, as well as goods and transport. The present study aims...  相似文献   

Instrumental and digital coronagraphy for the observation of the Uranus satellites’ upcoming mutual events     

M. Assafin  R.P. Campos  D.N. da Silva Neto  A.H. Andrei 《Planetary and Space Science》2008,56(14):1882-1887

Ground-based observations of faint satellites nearby their planets with 1-2 m class telescopes usually do not allow for high quality astrometry and photometry, due to saturation by the primary or to poor S/N ratio on the satellite images, generally embedded on the scattered light of the planet. Earth-based observations of the Uranus satellites’ upcoming mutual events in 2007-2008 are no exception. In most cases, the event will take place at 4 arcs or less from the planet, with “planet minus satellite” brightness differences of 10 magnitudes. So as to make feasible the observations of these important phenomena, we have developed a prototype of a coronagraph of simple design making use of good quality commercial optical systems. Pilot tests made with this coronagraph with a telescope of show that it is possible to obtain S/N ratios of 50 or higher for 10 s exposures, for satellites as close as 2 Uranus radii from the planet center. We have also developed numerical algorithms which perform digital coronagraphy in the images, with the elimination of the influence of the planets’ scattered light. This procedure considerably improves the S/N ratio of the satellite images (with or without a coronagraph instrument) and shall be applied in the reduction of the observations of the Uranus events so as to achieve the highest possible photometric and astrometric quality.  相似文献   

Russian cities at a crossroads   总被引：1，自引：0，他引：1  

Andrei Treivish  Izolde Brade  Tatyana Nefedova 《GeoJournal》1999,49(1):117-129

The research project `Changes in the Russian urban system after the dissolution of the Soviet Union' supported by the German Science and Research Society aims to reveal the impact of change in (1) the national and regional urban network, (2) the type and condition of Russian cities, and (3) the factors and actors affecting urban development. In this contribution the focus is made on the first task. The authors argue that visible stabilisation of the Russian urbanisation under crisis and/or under a new stage involves a good deal of restructuring and qualitative change. The hierarchy of the nation-wide functional centres is in flux. Within regions `alternative' foci attract industries, capital and people, and compete with regional capitals. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Effects of sonochemical treatment on meteoritic nanodiamonds          下载免费PDF全文

Anatolii V. Fisenko  Sasha B. Verchovsky  Andrei A. Shiryaev  Luba F. Semjonova 《Meteoritics & planetary science》2017,52(1):60-71

A nanodiamond‐rich fraction (NDF) separated from the Orgueil meteorite was subjected to a high‐intensity ultrasonic treatment in a weakly acidic aqueous solution. After sedimentation by centrifugation, two fractions of grains (suspension, designated as OD7C and sediment, designated as OD7D) with different properties have been obtained. The following effects of the sonication were revealed from comparison of the contents and isotope compositions of C, N, and Xe released during stepped pyrolysis and combustion of the fractions OD7C and OD7D, the initial NDF and two grain‐size fractions (OD10 and OD15) produced without sonication (a) surface layer of the sonicated diamond grains is modified to different extent in comparison with nontreated ones, (b) in some grains concentrations of the bulk N and Xe a reduced significantly, and (c) nondiamond nitrogen containing phases (e.g., Si₃N₄) have been destroyed. It is suggested that combined effects of the sonication and centrifugation observed for the fractions OD7C and OD7D are due to differences in surface chemistry of the nanodiamond grains, which statistically influences behavior of nanoparticles during the sonication resulting in their preferential modification in the different reaction zones of the cavitating fluid.  相似文献   

Automatic detection and correction algorithms for magnetic saturation in the SMFT/HSOS longitudinal magnetograms     

徐海清  刘锁  苏江涛  邓元勇  Andrei Plotnikov  白先勇  陈洁  杨潇  郭晶晶  王晓帆  宋永亮 《天文和天体物理学研究(英文版)》2021,(3):158-166

A longitudinal magnetic field often suffers the saturation effect in a strong magnetic field region when the measurement is performed at a single-wavelength point and linear calibration is adopted.In this study,we develop a method that can judge the threshold of saturation in Stokes V/I observed by the Solar Magnetic Field Telescope(SMFT)and correct it automatically.The procedure is to first perform the second-order polynomial fit to the Stokes V/I vs.I/I_m(I_m is the maximum value of Stokes I)curve to estimate the threshold of saturation,then reconstruct Stokes V/I in a strong field region to correct for saturation.The algorithm is demonstrated to be effective by comparing with the magnetograms obtained by the Helioseismic and Magnetic Imager(HMI).The accuracy rate of detection and correction for saturation is~99.4%and~88%respectively among 175 active regions.The advantages and disadvantages of the algorithm are discussed.  相似文献   

The interaction of ash flows with ridges   总被引：1，自引：0，他引：1  

Andrew W. Woods  Marcus I. Bursik  Andrei V. Kurbatov 《Bulletin of Volcanology》1998,60(1):38-51

 Using both laboratory experiments and theoretical models, we examine the different flow regimes that may develop when an ash flow encounters a ridge. For very small ridges, all the flow may pass over the ridge. For intermediate-size ridges, the flow may be partially blocked, with a fraction of the flow reflected upstream as a travelling bore. In this case, the remainder of the flow, which does pass over the ridge, is hydraulically controlled at the ridge crest. Finally, if the ridge is sufficiently high, then the flow will be totally blocked. New laboratory experiments show that the sedimentation patterns associated with these flow regimes may be very different. Most importantly, flows that involve partial blocking and the formation of upstream propagating bores display enhanced sedimentation upstream of the ridge, analogous to valley-ponded and caldera-fill deposits. In contrast, under some circumstances, if the flow is able to scale a ridge, the deposit may be relatively unaffected by the presence of the ridge. The minimum ridge height that leads to total blocking of the flow increases with mass eruption rate and has a complex variation with distance from the source. In a one-dimensional channel, the minimum ridge height that causes blocking increases with distance downstream. This is because the flow becomes less dense through sedimentation of particles and entrainment of air and so requires less energy to scale a ridge of a particular height. In axisymmetric flow, the minimum ridge height initially decreases with distance downstream as the flow spreads radially, but subsequently increases as the flow becomes less dense through sedimentation and entrainment. A new quantitative model of dilute ash flows propagating over ridges indicates that flows with mass fluxes in excess of 10⁸–10⁹ kg/s can partially scale barriers as high as 1000 m at distances of tens of kilometres from the source, whereas smaller flows are likely to be totally blocked by such an obstacle. Our results shed new insight on the possible long-range transport mechanism of several large flows including the Ata, Fisher and Aniakchak pyroclastic flows. Received: 20 December 1996 / Accepted: 15 March 1998  相似文献   

Modeling Dynamic Vegetation Response to Rapid Climate Change Using Bioclimatic Classification   总被引：2，自引：0，他引：2  

Andrei P. Kirilenko  Allen M. Solomon 《Climatic change》1998,38(1):15-49

Modeling potential global redistribution of terrestrial vegetation frequently is based on bioclimatic classifications which relate static regional vegetation zones (biomes) to a set of static climate parameters. The equilibrium character of the relationships limits our confidence in their application to scenarios of rapidly changing climate. Such assessments could be improved if vegetation migration and succession would be incorporated as response variables in model simulations. We developed the model MOVE (Migration Of VEgetation), to simulate the geographical implications of different rates of plant extirpation and in-migration. We used the model to study the potential impact on terrestrial carbon stocks of climate shifts hypothesized from a doubling of atmospheric greenhouse gas concentration. The model indicates that the terrestrial vegetation and soil could release carbon; the amount of this carbon pulse depends on the rate of migration relative to the rate of climate change. New temperate and boreal biomes, not found on the landscape today, increase rapidly in area during the first 100 years of simulated response to climate change. Their presence for several centuries and their gradual disappearance after the climate ceases to change adds uncertainty in calculating future terrestrial carbon fluxes.  相似文献   

Measuring the Spatial Focus of Migration Patterns     

Andrei Rogers  Stuart Sweeney 《The Professional geographer》1998,50(2):232-242

The changing territorial concentration of migration flows is of interest to many geographers, yet we still do not have a widely accepted index of spatial focus. The much used index of migration efficiency has been shown to be an inadequate index of such spatial concentration, and two candidates have been suggested to replace it: the Gini index and the coefficient of variation. Both are examined in this paper, and a comparative assessment is offered. Data from the 1970, 1980, and 1990 censuses are used to illustrate the two measures. An examination of the findings reveals that the coefficient of variation measure indicates higher levels of spatial focus than does the Gini index for states with highly concentrated flows.  相似文献   

Statistical theory of thermal instability     

Andrei F. Illarionov  & Igor V. Igumenshchev 《Monthly notices of the Royal Astronomical Society》1998,298(3):909-919

A new statistical approach is presented to study the thermal instability of an optically thin unmagnetized plasma. In the framework of this approach the time evolution of the mass distribution function over temperature φ( T ) is calculated. Function φ( T ) characterizes the statistical properties of the multiphase medium of arbitrarily spaced three-dimensional structure of arbitrary (small or large) temperature perturbations. We construct our theory under the isobarical condition ( P  = constant over space), which is satisfied in the short-wavelength limit of the perturbations. The developed theory is illustrated for the case of the thermal instability of a slowly expanding interstellar cloud (smooth scenario). Numerical solutions of equations of the statistical theory are constructed and compared with hydrodynamical solutions. The results of both approaches are identical in the short-wavelength range when the isobarity condition is satisfied. Also the limits of applicability of the statistical theory are estimated. The possible evolution of the initial spectrum of perturbations is discussed. The proposed theory and numerical models can be relevant to the formation of the two-phase medium in the ∼ 1 pc region around quasars. Then small warm ( T  ≃ 10⁴  K ) clouds are formed as the result of thermal instability in an expanded gas fragment, which is a product of either star–star or star–accretion disc collision.  相似文献   

Maser Action in Methanol Transitions     

Maxim Voronkov  Andrej Sobolev  Simon Ellingsen  Andrei Ostrovskii  Alexei Alakoz 《Astrophysics and Space Science》2005,295(1-2):217-223

We report the detection with the ATCA of 6.7 GHz methanol emission towards OMC-1. The source has a size between 40 and 90, is located to the south-east of Ori-KL and may coincide in position with the 25 GHz masers. The source may be an example of an interesting case recently predicted in theory where the transitions of traditionally different methanol maser classes show maser activity simultaneously. In addition, results of recent search for methanol masers from the 25 and 104.3 GHz transitions are reported.  相似文献