共查询到20条相似文献，搜索用时 31 毫秒
1.
Shadia Rifai Habbal 《Astrophysics and Space Science》1996,243(1):49-56
The temperature in the acceleration region of the solar wind remains one of the most elusive parameters to measure. Knowledge of the temperature as well as its gradient in the inner corona is fundamental for placing constraints on physical mechanisms thought to be responsible for the coronal heating process, as well as for understanding the flow properties of the solar wind. Estimates of the helium abundance is essential for understanding the puzzling behavior of heavier ions in the solar wind. As an illustration of the difficulties and uncertainties involved in the inferences of plasma parameters in the wolar wind acceleration region, The inference of electron temperature and helium abundance will be described. Prospects for future observations will be briefly discussed. 相似文献
2.
F. Mignard 《Earth, Moon, and Planets》1980,23(2):185-201
We present here a model for the tidal evolution of an isolated two-body system. Equations are derived, including the dissipation in the planet as in the satellite, in a frequency dependent lag model. The set of differential equations obtained is still valid for large eccentricity, as well as for all inclinations. The reference plane chosen enables us to study the evolution for both the orbital plane and the equatorial plane.The results obtained show the Moon, after having approached the Earth with small variations for the inclination and the eccentricity, exhibits strong increase for the two parameters in the vicinity of the closest approach. In every case the eccentricity tends towards the value 1, whereas the variations of the in clinations are dependent on the magnitude of the dissipation in the satellite.Some qualitative results are also investigated for the final behaviour of satellites such as Triton and the Galilean satellites. 相似文献
3.
A. G. Nikoghossian 《Astrophysics》2004,47(3):412-421
The approach proposed in the previous parts of this series of papers is used to solve the radiative transfer problem in scattering and absorbing multicomponent atmospheres. Linear recurrence relations are obtained for both the reflectance and transmittance of these kinds of atmospheres, as well as for the emerging intensities when the atmosphere contains energy sources. Spectral line formation in a one-dimensional inhomogeneous atmosphere is examined as an illustration of the possibility of generalizing our approach to the matrix case. It is shown that, in this case as well, the question reduces to solving an initial value problem for linear differential equations. Some numerical calculations are presented. 相似文献
4.
Abstract— Twenty ～100-mg random fragments of the Bruderheim chondrite were analyzed by INAA to determine extents of heterogeneity and to check earlier results that gave anomalous LREE concentrations. Considerable compositional heterogeneity was observed in both concentrations (maximum/minimum of 1.7 for Ir, 1.8 for Na, 6.8 for La, 7.4 for Co) and concentration ratios (>3 × for Ni/Co and La/Eu). Compositions could be modelled quantitatively in terms of end-member components of constant composition representing the minerals olivine + orthopyroxene, clinopyroxene, plagioclase, kamacite, taenite, troilite, chromite, and phosphate. The model yields the proportions of minerals in each sample as well as the meteorite as a whole; accurate determination of the end members depends on high intrasample precision for many elements. No evidence of compositional heterogeneity of end members for trace elements was found. It is shown that these analyses, which used only ～2 grams of the meteorite, are equivalent in accuracy to a single sample of several tens of grams, and that knowledge of the extent of heterogeneity is essential to knowing the quality of sampling as well as for comparing results from one analysis with another and of one meteorite with another. 相似文献
5.
P. R. Wilson 《Solar physics》1987,110(1):59-71
Departures from the mean solar differential rotation rate as a function of latitude, longitude, and epoch of the solar cycle, together with variations in the rotation rate as determined by spectroscopic and tracer measurements are reviewed. It is shown that, if giant convection cells do exist as predicted, real variations in the subsurface rotation rate should occur and that this may be responsible for the observed surface anomalies.In terms of this hypothesis, a simple account is given for the anomalous rotation rates of sunspots. Furthermore, the torsional oscillations are identified as a modulation of the differential rotation produced by a system of toroidal convective rolls generated near the poles and propagating towards the equator. It is suggested that, as these rolls progress through lower latitudes, they break up into a system of cells which are the long sought for giant cells of the convection zone. Thus the torsional oscillations are identified as direct surface evidence for the existence of these cells.Solar Cycle Workshop Paper. 相似文献
6.
Observations of bi-polar type I storm centers with the Culgoora radioheliograph operating at 80 MHz show that in many cases they are not oriented as we should expect for emission in the ordinary mode and for the simplest magnetic field geometry. We interpret this as evidence for a twist in the magnetic field. 相似文献
7.
We have simulated asteroid lightcurves for simple shape models using a realistic surface scattering law. The scattering law includes a shadowing function computed with numerical ray‐tracing. We computed lightcurves in a variety of illumination geometries for both the traditional Lommel–Seeliger law and our seminumerical law. We observe a shift in the rotational phase of the lightcurves, which depends on the parameters of the scattering law as well as the illumination geometry and the direction of the spin axis of the asteroid. This phase shift is always zero at opposition, and can be as large as 10° for illumination geometries typical for Main Belt asteroids. The phase shift has implications on the accuracy of other results which are based on asteroid lightcurve analysis, such as spin‐state or shape determination. 相似文献
8.
The intensity of a sunspot was measured in eight wavelength regions during the Mercury transit of 9 May 1970. The observations have been corrected for scattered light in the Earth's atmosphere as well as in the instrument using two different methods plus a combination of these. One method consists of using Mercury as a calibration spot. In the second method the corrections for scattered light are determined from solar limb observations. 相似文献
9.
A. V. Dolgopolov E. V. Dolgopolova N. V. Steshenko Ya. N. Chernykh 《Bulletin of the Crimean Astrophysical Observatory》2014,110(1):138-145
A method for finishing the surface shape of large mirrors for space telescopes that are accurate up to λ/20 is described, as well as training of the method for manufacturing a systall mirror 2.6 m in diameter for the ZTSH telescope. 相似文献
10.
Demands for a broad range of integrated geospatial data-analysis tools and methods for planetary data organization have been growing considerably since the late 1990s when a plethora of missions equipped with new instruments entered planetary orbits or landed on the surface. They sent back terabytes of new data which soon became accessible for the scientific community and public and which needed to be organized. On the terrestrial side, issues of data access, organization and utilization for scientific and economic analyses are handled by using a range of well-established geographic information systems (GIS) that also found their way into the field of planetary sciences in the late 1990s. We here address key issues concerning the field of planetary mapping by making use of established GIS environments and discuss methods of addressing data organization and mapping requirements by using an easily integrable datamodel that is—for the time being—designed as file-geodatabase (FileGDB) environment in ESRI's ArcGIS. A major design-driving requirement for this datamodel is its extensibility and scalability for growing scientific as well as technical needs, e.g., the utilization of such a datamodel for surface mapping of different planetary objects as defined by their respective reference system and by using different instrument data. Furthermore, it is a major goal to construct a generic model which allows to perform combined geologic as well as geomorphologic mapping tasks making use of international standards without loss of information and by maintaining topologic integrity. An integration of such a datamodel within a geospatial DBMS context can practically be performed by individuals as well as groups without having to deal with the details of administrative tasks and data ingestion issues. Besides the actual mapping, key components of such a mapping datamodel deal with the organization and search for image-sensor data and previous mapping efforts, as well as the proper organization of cartographic representations and assignments of geologic/geomorphologic units within their stratigraphic context. 相似文献
11.
B. E. Burke J. A. Gregory R.W. Mountain B. B. Kosicki E. D. Savoye P. J. Daniels V. S. Dolat T. L. Lind A. H. Loomis D. J. Young G. A. Luppino J. L. Tonry 《Experimental Astronomy》1998,8(1):31-40
We describe recent work in the area of large, back-illuminated CCD imagers at M.I.T. Lincoln Laboratory as well as new technology applicable to astronomy. We completed in 1995 the development of a 2560 x 1960-pixel frame-transfer imager that filled a 100-mm wafer and several back-illuminated versions of this device were completed. More recently we have begun the development, in collaboration with the U. of Hawaii, of a three-side abuttable 2k x 4k CCD for a multi-chip focal plane. In the unused chord area of the wafer layout, we added test imagers as development vehicles for blooming control and for the demonstration of a CCD that is capable of charge transfer in all four directions. We expect the latter to find application as an electronic means of performing tip-tilt correction to compensate for atmospheric turbulence. 相似文献
12.
Similarity solutions for propagation of plane relativistic shock waves through a medium of decreasing nucleon density and approaching the edge of the gas as well as for the subsequent motion of the gas after the shock front arrives at the vacuous boundary are studied in this paper. The medium in the pre-disturbed stage is assumed cold and in the disturbed stage its equation of state is taken as that of a photonic gas. 相似文献
13.
S. A. Naroenkov B. M. Shustov Yu. D. Medvedev V. A. Shor A. V. Devyatkin 《Solar System Research》2014,48(6):439-445
The concept is presented of the Russian information and analytical center for asteroid and comet hazards (IAC ACH) as a part of the national IAC for space threats. An overview is given of the center’s goals and objectives, as well as the requirements for the center, its structure, and the possible cooperation between the institutes of the Russian Academy of Sciences and other organizations in the creation of the center. 相似文献
14.
A. F. Kholtygin 《Astrophysics》2008,51(3):294-312
Diagnostics for the rarefied plasmas in gaseous nebulae are reviewed, beginning with the pioneering papers of V. A. Ambartsumian.
These papers, as well as the diagnostic techniques which have been developed on the basis of ideas contained in them, are
discussed. Diagnostic techniques for homogeneous, as well as inhomogeneous, plasmas are described.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 363–383 (August 2008). 相似文献
15.
Wacław Waniak 《Experimental Astronomy》2006,21(3):151-168
A feed-forward artificial neural network has been implemented to the problem of removing cosmic-ray hits (CRH) from CCD images.
The results of a number of tests demonstrate the effectiveness of this method especially for undersampled stellar profiles.
The problem of optimal and low price preparing of training data, which could enable real-time or at least fast post-processing
filtering out of CRH is discussed. The training and test ensembles were composed of a number of synthetic stellar profiles
involving different S/N ratios and CRH images taken from real data. Certain aspects of the network’s architecture and its
training efficiency for different modes of the back-propagation procedure as well as for the pre-process normalization of
data have been examined. It is shown that for training set composed of stellar images and CRH at a ratio of 1:2 recognition
can reach 99% in the case of stars and 96% for CRH. To determine the extent to which the cognition power of a network trained
using an ensemble of circular symmetric stellar profiles of a given radius can be generalised the test data included stellar
profiles of different radii, as well as elongated profiles. The goal was to mimic temporal changes in seeing as well as such
problems as image defocusing, the lack of isoplanatism and improper sideral tracking of a telescope. The experiments provided
us with the conclusion that for S/N > 10 excellent classification property is maintained in cases where the change in the
radius of a circular profile is up to 30%, as well as for elongated profiles where the longest dimension is almost double
that of the shortest one. Moreover, the generalization capability has been investigated for test images of synthetic pairs
of overlapping stars with different distances between components. Almost 99% recognition efficiency was achieved even if the
separation was nearly three times the radius of the stellar profile, a case when two stars could be analyzed by appropriate
software as separate objects. The example of removal of CRH from real CCD images is presented to give an idea of how an algorithm
based on a neural network can work in practice. The result of such an experiment appears fully consistent with the conclusions
drawn from the tests made on synthetic data. 相似文献
16.
A catalog of 232 apparently interacting galaxy pairs of the M51 class is presented. Catalog members were identified from visual inspection of multi-band images in the IRSA archive. The major findings in the compilation of this catalog are (1) A surprisingly low number of the main galaxies in M51 systems are early type spirals and barred spirals. (2) Over 70% of the main galaxies in M51 systems are 2-armed spirals. (3) Some systems that were classified as M51 types in previous studies are not M51 types as defined in this catalog. There were a number of systems previously classified as M51 systems for which the “companion” is identified as an HII region within the main galaxy or foreground star within the Milky Way. (4) It was found that only 18% of the M51 type companions have redshift measurements in the literature. There is a significant need for spectroscopic study of the companions in order to improve the value of the catalog as a sample for studying the effects of M51 type interaction on galaxy dynamics, morphology, and star formation. Further spectroscopy will also help constrain the statistics of possible chance projections between foreground and background galaxies in the catalog. The catalog also contains over 430 additional systems which are classified as “possible M51” systems. The reasons for classifying certain systems as possible M51 systems are discussed. 相似文献
17.
G. A. Shah 《Astrophysics and Space Science》1991,178(2):251-260
The asymmetry parameter of the scattering diagram and the efficiency for radiation pressure for scattering by a very large dielectric sphere conforming to geometrical optics and diffraction, have been investigated beyond the limit of existing literature. A new feature of shallow broad extremum (resonance) has been found in the asymmetry parameter as well as in the radiation pressure both as function of the index of refraction. 相似文献
18.
The solutions for the mass of single-line close binaries with Main-Sequence primaries are given in a tabular form as a result of the application of the mass-luminosity relation. Linear interpolation in a compact bi-variate table suffices to give the values of mass of the two components for a wide range of masses and to a very good approximation. The indeterminacy of the solutions depending on the formulation of the mass-luminosity relation for the primaries is discussed, as well as the condition of filling up their Roche lobes by the secondaries. 相似文献
19.
G. W. Pneuman 《Solar physics》1984,94(2):299-313
Recent coronagraph observations of rising priminences such as in the 14 April and 5 May, 1980 coronal transient events, as well as other older observations, have shown evidence for helical structure in the prominences. If this is true, then a study of the dynamical evolution of rising helical structures in a nonuniform atmosphere is worthwhile. For this study, three important considerations become apparent: (1) Since the ends of the prominence remain rooted in the photosphere, significant stretching of the configuration will result as it rises, (2) due to the fall-off with height of the external quantities, such as gas and magnetic pressure, the prominence will experience time-varying boundary conditions as it rises, and (3) significant lateral expansion of the prominence is expected as the external conditions weaken with height. The interplay of all these effects togehter result in a quite complex dynamical behavior of the prominence.We have tried to obtain some insight into this general problem through a simple model - that of a helical pinch rising in a low beta atmosphere under the influence of an ambient external magnetic field which declines in strength with radial distance from the solar center. Under the general assumptions of an internal uniform, but time-varying, temperature and neglecting gravitational stratification within the prominence, expressions are derived for associated variations in the prominence structure as it rises. We discuss in some detail, particular quantities which are potentially most accessible to observation such as prominence radius, density, and pitch angle as they vary with height during the eruptive process.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
Expressions for the mass quadrupole moment tensor in the model for a wide variety of astrophysical objects are shown to be identical in form. This makes it possible to obtain analytical expressions for the gravitational radiation emitted by the sources, as well as the angular distribution, polarization dependence, and the wave forms of the radiation. 相似文献