排序方式： 共有14条查询结果，搜索用时 15 毫秒
1.
V. D. Bychkov L. V. Bychkova J. Madej 《Monthly notices of the Royal Astronomical Society》2009,394(3):1338-1350
This paper presents a catalogue and the method of determining averaged quadratic effective magnetic fields 〈 B e 〉 for 1212 main-sequence and giant stars, and 11 white dwarf stars. The catalogue includes stars that are members of several open clusters. We have compiled measurements of the longitudinal magnetic field for those stars, which were scattered in the existing literature. A new parameter, magnetization (MA), has been defined, and we present values of MA for stars of various spectral classes. Our sample includes a subset of 610 chemically peculiar early-type stars. We confirm the conclusion of our previous study that the number distribution of all chemically peculiar stars versus the averaged magnetic field strength is described by a decreasing exponential function. Relations of this type also hold for stars of all the analysed subclasses of chemical peculiarity. Magnetization tends to correlate with the effective temperature only at high MA, for He-weak and He-rich stars. 相似文献
2.
Teresa Oberc-Dziedzic Ryszard Kryza Christian Pin Stanisław Madej 《International Journal of Earth Sciences》2013,102(5):1289-1304
The Strzelin Massif in SW Poland (Central European Variscides) records a protracted igneous evolution, with three main magmatic stages: (1) tonalitic I, (2) granodioritic and (3) tonalitic II/granitic. In the northern part of this Massif, the Strzelin intrusion proper comprises three successively emplaced rock types: a medium-grained biotite granite (303 ± 2 Ma), a fine-grained biotite granite (283 ± 8 Ma) and a fine-grained biotite-muscovite granite; based on field evidence, the third variety postdates both types of the biotite granites. The structural data from the three granites, including their parallel, approximately E–W striking and steeply dipping lithological contacts and ENE–WSW trending subhorizontal magmatic lineations, suggest that the emplacement of all three successive granite varieties was controlled by an active, long-lived strike-slip fault, striking ESE–WNW, with a dextral sense of movement. After the emplacement of the youngest biotite-muscovite granite, the intrusion underwent brittle extension which produced “Q joints” striking NNW–SSE to N–S and dipping at 55–70° WSW to W, and showing evidence of broadly N–S directed sinistral displacements. The structural observations, supported by new geochronological data, indicate that the internal structure of the composite granitoid intrusion, including the faint magmatic foliation and lineation, formed in a long-lived strike-slip setting, different from the subsequent, post-emplacement extensional tectonics that controlled the development of brittle structures. 相似文献
3.
Mary Ann Madej Elizabeth A. Eschenbach Carlos Diaz Rebecca Teasley Kristine Baker 《地球表面变化过程与地形》2006,31(13):1643-1656
Many forested steeplands in the western United States display a legacy of disturbances due to timber harvest, mining or wildfires, for example. Such disturbances have caused accelerated hillslope erosion, leading to increased sedimentation in fish‐bearing streams. Several restoration techniques have been implemented to address these problems in mountain catchments, many of which involve the removal of abandoned roads and re‐establishing drainage networks across road prisms. With limited restoration funds to be applied across large catchments, land managers are faced with deciding which areas and problems should be treated first, and by which technique, in order to design the most effective and cost‐effective sediment reduction strategy. Currently most restoration is conducted on a site‐specific scale according to uniform treatment policies. To create catchment‐scale policies for restoration, we developed two optimization models – dynamic programming and genetic algorithms – to determine the most cost‐effective treatment level for roads and stream crossings in a pilot study basin with approximately 700 road segments and crossings. These models considered the trade‐offs between the cost and effectiveness of different restoration strategies to minimize the predicted erosion from all forest roads within a catchment, while meeting a specified budget constraint. The optimal sediment reduction strategies developed by these models performed much better than two strategies of uniform erosion control which are commonly applied to road erosion problems by land managers, with sediment savings increased by an additional 48 to 80 per cent. These optimization models can be used to formulate the most cost‐effective restoration policy for sediment reduction on a catchment scale. Thus, cost savings can be applied to further restoration work within the catchment. Nevertheless, the models are based on erosion rates measured on past restoration sites, and need to be updated as additional monitoring studies evaluate long‐term basin response to erosion control treatments. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
We investigate the variability of the magnetic field of a well-known Ap star 52 Her. The 15-year longmagnetic monitoring and analysis of the literature data demonstrates the lack of a long-period variability of the stellar magnetic field, and an absence of precession of the rotation axis of the binary’s main component. We refined the period of variability of the K Ca II line intensity, presumably being the rotation period of the main component. These measurements allowed to specify the parameters of the mean magnetic phase curve, obtained from the lines of metals, and to detect a significant difference from the phase curve, built from the hydrogen lines. Possible causes of the unusual variability of the stellar magnetic field are discussed. 相似文献
5.
We present the results of photometric and magnetic monitoring of a well-known long-period Ap star GY And. This research was inspired by the unusual “secular” variability of the B ? V color index. Photometric monitoring was carried out with the 60-cm reflector of the Crimean Laboratory of the Moscow State University, where 420 brightness estimates were obtained during 2011–2014 with the Johnson system broadband U, B, and V filters. Magnetic monitoring was carried out at the 1-m telescope of the Special Astrophysical Observatory. The duration of photometric observations is about 54 years, and the duration of magnetic monitoring is 64 years. As a result, we have refined the period and the parameters of variability of the magnetic field, and the photometric behavior. We demonstrate that the peculiar “secular” color variability is explained by the off-duty factor of the observations. 相似文献
6.
7.
Global magnetic fields of flare stars evolve very fast—at times of tens–hundreds of days. In our opinion, this is due to mutual addition of local magnetic fields generated by the differential rotation of these objects.With the example of two flare stars,OT Ser and YZCMi, we consider possiblemechanisms of generation and disspation of local and global magnetic fields and the mechanism of “magnetic deceleration” of these stars according to the scheme “differential rotation–generation of local magnetic fields–fluorescence of energy accumulated by local magnetic fields during flares.” We also estimated the rotation energy and global magnetic field for OT Ser and YZCMi. It is shown that even strong dissipation of the accumulated local magnetic energy in the flare on February 9, 2008 (UT 20:22:00) in YZCMi has not had any impact on the global magnetic field. 相似文献
8.
Channel responses to varying sediment input: A flume experiment modeled after Redwood Creek, California 总被引：1，自引：0，他引：1
At the reach scale, a channel adjusts to sediment supply and flow through mutual interactions among channel form, bed particle size, and flow dynamics that govern river bed mobility. Sediment can impair the beneficial uses of a river, but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing. We use a flume experiment, coupled with field measurements in a gravel-bed river, to explore sediment transport, storage, and mobility relations under various sediment supply conditions. Our flume experiment modeled adjustments of channel morphology, slope, and armoring in a gravel-bed channel. Under moderate sediment increases, channel bed elevation increased and sediment output increased, but channel planform remained similar to pre-feed conditions. During the following degradational cycle, most of the excess sediment was evacuated from the flume and the bed became armored. Under high sediment feed, channel bed elevation increased, the bed became smoother, mid-channel bars and bedload sheets formed, and water surface slope increased. Concurrently, output increased and became more poorly sorted. During the last degradational cycle, the channel became armored and channel incision ceased before all excess sediment was removed. Selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored. Our flume results of changes in bed elevation, sediment storage, channel morphology, and bed texture parallel those from field surveys of Redwood Creek, northern California, which has exhibited channel bed degradation for 30 years following a large aggradation event in the 1970s. The flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur, but the channel may return to a state of balancing sediment supply and transport capacity. 相似文献
9.
Models of the iron Kα fluorescent line and the Compton Shoulder in irradiated accretion disc spectra
We present a full set of model atmosphere equations for the accretion disc around a supermassive black hole irradiated by a hard X-ray lamp of power-law spectral distribution. Model equations allow for multiple Compton scattering of radiation on free electrons, and for large relative photon–electron energy exchange at the time of scattering. We present spectra in specific intensities integrated over the disc surface. Theoretical outgoing intensity spectra show soft X-ray excess below 1 keV, and distinct Kα and Kβ fluorescent lines of iron. We demonstrate the existence of the Compton Shoulder and claim that it can contribute to the asymmetry and equivalent widths of some observed Fe Kα lines in active galactic nuclei. Our models exhibit the effect of limb-brightening in reflected X-rays. 相似文献
10.
Pilar Burgos Engracia MadejónAlfredo Pérez-de-Mora Francisco Cabrera 《International Journal of Applied Earth Observation and Geoinformation》2008
The spatial distribution of some soil chemical properties and trace element contents of a plot affected by the Aznalcóllar mine spill were investigated using statistical and geostatistical methods to assess the extent of soil contamination. Total and EDTA-extractable soil trace element concentrations and total S content showed great variability and high coefficients of variation in the three examined depths. Soil in the plot was found to be significantly contaminated by As, Cd, Cu, Pb and Zn within a wide range of pH. Total trace element concentrations at all depths (0–60 cm) were much higher than background values of non-affected soil, indicating that despite the clean-up operations, the concentration of trace elements in the experimental plot was still high. The spatial distribution of the different variables was estimated by kriging to design contour maps. These maps allowed the identification of specific zones with high metal concentrations and low pH values corresponding to spots of residual sludge. Moreover, kriged maps showed distinct spatial distribution and hence different behaviour for the elements considered. This information may be applied to optimise remediation strategies in highly and moderately contaminated areas. 相似文献