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1.
The radiative transfer problem in a plane medium with a highly forward-scattering phase function has been solved by Siewertet al. (1980) with reflective boundaries, and by Mengüç and Viskanta (1983) without reflective boundaries. In the present paper a moment method is devised to solve the same problem. The results computed are found to be in good agreement with the exact results. 相似文献
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3.
A. G. Nikoghossian 《Astrophysics》2009,52(1):1-23
The purpose of this article is to provide some insight into Ambartsumian’s methods in the theory of radiative transfer, their
applications, and further development. Two of these methods are emphasized--the invariance principle and the method of addition
of layers, proposed by Ambartsumian in the 1940’s. The difference between these methods and the classical approach for solving
radiative transfer problems is discussed. We discuss only a small portion of the subsequent work by others that we believe
reveals, in a more intuitive way, the essence and significance of Ambartsumian’s methods and their efficiency for applications.
Thus, for example, a separate section is devoted to applications of the Lagrangian formalism to radiative transfer and it
is shown that the invariance principle is a special case of a more general variational principle that reflects an invariance
with respect to translational transformation of the optical depth. Our discussion of the method of addition of layers points
out its generality and the major role it has played in the later creation of such methods as Bellman’s invariant imbedding
method and the method for solving radiative transfer problems in inhomogeneous media. The latter method has yielded a number
of new analytic results. The concluding section is a brief summary of Ambartsumian’s results in the nonlinear theory of radiative
transfer, where he was a pioneer in the study of the class of multilevel problems. This article also sets out to demonstrate
the place and role of Ambartsumian’s methods in the theory of radiative transfer, which, to a great extent, set the path along
which this theory developed for many years to come.
Translated from Astrofizika, Vol. 52, No. 1, pp. 5–27 (February 2009). 相似文献
4.
Protons from the Earth's bow shock are observed by the Suprathermal Ion detector Experiment (SIDE) in two regions of the lunar orbit. The dawn region begins at the dawn side bow shock crossing and ends ç 5 days later and the dusk region begins at ç 2 days prior to entering the dusk side magnetosheath and ends at the inbound bow shock crossing. Dusk and dawn refer to a terrestrial coordinate system. The dominant contribution to the ion spectra observed by the SIDE in these regions is from particles with energies between ç 750 eV q–1 and 3500 eV q–1. 3500 eVq–1 is the upper limit of the energy range of the detector. Analysis of simultaneous data from the Explorer 35 magnetometer and the SIDE indicates that the observability of bow shock protons at the lunar distance is dependent on the configuration of the interplanetary magnetic field.Paper presented at the Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon, sponsored by the Lunar Science Institute, Houston, Texas and held at the Lake Geneva Campus of George Williams College, Wisconsin, between September 30 and October 4, 1974. 相似文献
5.
We have developed observational and data processingtechniques for detecting millisecond pulsars. Themethod of data processing consists in correlating timeseries of data by folding them in two steps accordingto a trial period. While very time consuming,especially for very short periods, this methods allowsus in principle to detect very fast and dispersedmillisecond pulsars. The experimental set-up has beenintegrated into a data acquisition system developed atCentre national d'études spatiales (CNES).Observations of known millisecond pulsars atNançay radio observatory are used to validate thesystem and assess the sensitivity of the survey, whichis 3.5 mJy for 240 sec of integration. Futureimprovements in the radio-telescope and the systemshould bring it down to below 1 mJy. The applicationof the method to a millisecond pulsar survey is underway at Nançay radio observatory in collaborationbetween the Bureau international des poids et mesure(BIPM), Observatoire Midi-Pyrénées (OMP), and CNES. 相似文献
6.
Sh. Sh. Dolginov Ye. G. Yeroshenko V. A. Sharova T. A. Vnuchkova L. L. Vanyan B. A. Okulessky A. T. Bazilevsky 《Earth, Moon, and Planets》1976,15(1-2):3-14
The data of three-times repeated magnetic survey of the section of Lunokhod-2 route 1.5 km long are analyzed. The linear size of the regions of magnetic field anomalies disclosed is 200–300 m. The results of magnetic survey near the tectonic break of Straight Rille and near the south rim of crater Le Monnier were used for estimation of rock magnetization in situ. It is shown that mare basalts in south-east region of crater Le Monnier have oblique magnetization (at the angle ç30° to horizon). The magnitude of magnetization is × 5 × 10–5 G cm g–1. The south-east slope of the crater Le Monnier is magnetized roughly vertically, the upper limit of magnetization of the rocks of the rim is ç 1 × 10–5 G cm3 g–1. The results of an analysis of 160 magnetic field variations recorded by Lunokhod-2 indicate that the horizontal components of variations have nearly linear polarization. The principal axes of hodographs stretch in the direction north-west-south-east. Such a polarization of variations may be due to an increase of the thickness of the upper isolated layer under Mare Serenitatis. 相似文献
7.
The energy balance for cool quiescent prominences is examined using a 6000 km, 6000 K isothermal slab model prominence with a density gradient dictated by a modified Kippenhahn-Schlüter model. The model is irradiated from both sides by the coronal, chromospheric, and photospheric radiation fields. The radiative transfer problem is solved in detail for the Lyman continuum and H to determine the net radiative energy loss for hydrogen. An estimate of the energy loss for Ca ii H and K indicates that this source of energy loss is unimportant when compared with the hydrogen radiation. The radiative energy loss is easily balanced by the conductive energy gain from the corona.The only difficulty with our model is that the total hydrogen density must be of the order of 3 × 1012/ cm3 to match the n = 2 population density of 5 × 104/cm3 obtained from observation. To support a prominence of this density and a thickness of 6000 km against gravity requires magnetic fields of the order of 20 G which is much higher than the average magnetic field in quiescent prominences deduced from limb observations. Two possible explanations for this discrepancy are given.Currently at the Max-Planck-Institut für Physik und Astrophysik, München, Germany.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
8.
Intermediate-term periodicities in solar activity 总被引：2，自引：0，他引：2
The presence of intermediate-term periodicities in solar activity, at approximately 323 and 540 days, has been claimed by different authors. In this paper, we have performed a search for them in the historical records of two main indices of solar activity, namely, the daily sunspot areas (cycles 12–21) and the daily Zürich sunspot number (cycles 6–21). Two different methods to compute power spectra have been used, one of them being especially appropriate to deal with gapped time series. The results obtained for the periodicity near 323 days indicate that it has only been present in cycle 21, while in previous cycles no significant evidence for it has been found. On the other hand, a significant periodicity at 350 days is found in sunspot areas and Zürich sunspot number during cycles 12–21 considered all together, also having been detected in some individual cycles. However, this last periodicity must be looked into with care due to the lack of confirmation for it coming from other features of solar activity. The periodicity around 540 days is found in cycles 12, 14, and 17 in sunspot areas, while during cycles 18 and 19 it is present, with a very high significance, in sunspot areas and Zürich sunspot number. It also appears at 528 days in sunspot areas during cycles 12–21. On the other hand, it is important to note the coincidence between the asymmetry, favouring the northern hemisphere, of sunspot areas and solar flares during cycle 19, and the fact that the periodicity at 540 days was only present, with high significance, in that hemisphere during that solar cycle. 相似文献
9.
We examine the `Group' sunspot numbers constructed by Hoyt and Schatten to determine their utility in characterizing the solar activity cycle. We compare smoothed monthly Group sunspot numbers to Zürich (International) sunspot numbers, 10.7-cm radio flux, and total sunspot area. We find that the Zürich numbers follow the 10.7-cm radio flux and total sunspot area measurements only slightly better than the Group numbers. We examine several significant characteristics of the sunspot cycle using both Group numbers and Zürich numbers. We find that the `Waldmeier Effect' – the anti-correlation between cycle amplitude and the elapsed time between minimum and maximum of a cycle – is much more apparent in the Zürich numbers. The `Amplitude–Period Effect' – the anti-correlation between cycle amplitude and the length of the previous cycle from minimum to minimum – is also much more apparent in the Zürich numbers. The `Amplitude–Minimum Effect' – the correlation between cycle amplitude and the activity level at the previous (onset) minimum is equally apparent in both the Zürich numbers and the Group numbers. The `Even–Odd Effect' – in which odd-numbered cycles are larger than their even-numbered precursors – is somewhat stronger in the Group numbers but with a tighter relationship in the Zürich numbers. The `Secular Trend' – the increase in cycle amplitudes since the Maunder Minimum – is much stronger in Group numbers. After removing this trend we find little evidence for multi-cycle periodicities like the 80-year Gleissberg cycle or the two- and three-cycle periodicities. We also find little evidence for a correlation between the amplitude of a cycle and its period or for a bimodal distribution of cycle periods. We conclude that the Group numbers are most useful for extending the sunspot cycle data further back in time and thereby adding more cycles and improving the statistics. However, the Zürich numbers are slightly more useful for characterizing the on-going levels of solar activity. 相似文献
10.
In order to prepare the analysis of the forthcoming near-IR surveys (DENIS, 2MASS) and to interpret them in terms of galactic structure and AGB evolution, we present model predictions of AGB distributions in K, in 12m and in (J-K, [12–25]) space, as they will be obtained from these surveys, cross-correlated with IRAS Catalog. The simulations have been made by adding the AGB to the Besançon model. 相似文献
11.
Simultaneous 6 and 11 cm maps of the quiet Sun have been obtained with the Nançay radiotelescope during the 1968–69 cycle maximum.On leave from the University of Tucuman, Tucuman, Argentina. 相似文献
12.
V. P. Grinin 《Astrophysics》1984,20(2):190-223
Conclusions It can be seen from the above review that the theory of radiative transfer in moving media in its classical field of applications is a well-developed branch of theoretical astrophysics. Studies i n recent years have clarified important questions such as the asymptotic behavior of the kernel functions and the characteristic lengths of the theory. It has been established that there are two types of radiative coupling, and the influence of nonlocal radiative coupling on the formation of spectral lines and radiation pressure has been investigated. The theory now has at its disposal a large selection of asymptotic, approximate, and numerical methods for solving different applied problems.Despite the competition from numerical methods, the overwhelming majority of calculations of emission spectra in the region of supersonic motions has been made on the basis of the escape-probability method and its generalization to the case of nonlocal radiative coupling. This is explained not only by the simplicity and economy of the method but even more by the fact that the greater accuracy of the calculations that can be achieved by using numerical methods is frequently spurious, since it certainly exceeds the accuracy of the basic assumptions. The real way to increase the reliability in the diagnosis of a radiating gas is, first, to solve simultaneously many-level problems for the group of elements whose lines are observed in the spectrum of the object. Second, where possible, one must solve simultaneously the stationary equations and the heat balance equations.Crimean Astrophysical Observatory. Translated from Astrofizika, Vol. 20, No. 2, pp. 365–417, March–April, 1984. 相似文献
13.
We present measurements of ratios of elements of the scattering matrix of martian analogue palagonite particles for scattering angles ranging from 3° to 174° and a wavelength of 632.8 nm. To facilitate the use of these measurements in radiative transfer calculations we have devised a method that enables us to obtain, from these measurements, a normalized synthetic scattering matrix covering the complete scattering angle range from 0° to 180°. Our method is based on employing the coefficients of the expansions of scattering matrix elements into generalized spherical functions. The synthetic scattering matrix elements and/or the expansion coefficients obtained in this way, can be used to include multiple scattering by these irregularly shaped particles in (polarized) radiative transfer calculations, such as calculations of sunlight that is scattered in the dusty martian atmosphere. 相似文献
14.
D. Eschbach 《Celestial Mechanics and Dynamical Astronomy》1980,21(3):321-331
Résumé Ce sont principalement les investigations de Cartan, Madame Losco et Mac Gehee qui ont inspiré le travail qui suit. Un changement de variables simple et spécialement adapté au problème de la collision triple conduit de façon naturelle à une étude directe et intuitive du phénomène.
This work paper has been mainly inspired by the investigations of Cartan, Madame Losco and McGehee. A simple change of variables that is especially adapted to the problem of triple collision leads in a natural way to a direct and intuitive study of the phenomenon.相似文献
15.
S. J. Wilson 《Astrophysics and Space Science》1987,138(1):191-196
A simple method for solving the radiation transfer due to a point source in an isotropically-scattering sphere with space-dependent albedo is presented. The results are compared with the only other available results obtained by Thynell and Özisik (1986) for inhomogeneous sphere. The present method is applicable for a wider class of albedo functions. 相似文献
16.
A standard problem of radiative transfer theory — calculating the diffuse reflection and transmission of radiation by a plane
scattering atmosphere — is considered. The recently proposed albedoshift method is used to calculate the X and Y functions
(and the H function) for the case of anisotropic scattering with a Henyey-Greenstein indicatrix. The method enables one to
“suppress” scattering and obtain iterative solutions of high accuracy in only a few iterations, even when the mean number
of photon scatterings in the atmosphere is very large.
Translated from Astrofizika, Vol. 41. No. 4, pp. 623–646, October–December, 1998. 相似文献
17.
Based on the method of dimensional analysis, the energy transfer rate from the solar wind into the magnetosphere can be characterized by a magnetic coupling parameter α on open field lines and by a viscous coupling parameter β on closed field lines. By assuming that the energy transfer rate can be monitored by the total energy dissipation rate of the magnetosphere, the histogram of α is constructed and is found to peak around ?0.1 < α < 0.1. This result implies that the energy transfer is governed primarily by the MHD dynamo process on open field lines and indicates that the ? function obtained by Perreault and Akasofu is verified as the first approximation of the solar wind-magnetosphere energy coupling function. 相似文献
18.
The use of invariant manifolds for transfers between unstable periodic orbits of different energies 总被引：1，自引：0，他引：1
Kathryn E. Davis Rodney L. Anderson Daniel J. Scheeres George H. Born 《Celestial Mechanics and Dynamical Astronomy》2010,107(4):471-485
Techniques from dynamical systems theory have been applied to the construction of transfers between unstable periodic orbits
that have different energies. Invariant manifolds, trajectories that asymptotically depart or approach unstable periodic orbits,
are used to connect the initial and final orbits. The transfer asymptotically departs the initial orbit on a trajectory contained
within the initial orbit’s unstable manifold and later asymptotically approaches the final orbit on a trajectory contained
within the stable manifold of the final orbit. The manifold trajectories are connected by the execution of impulsive maneuvers.
Two-body parameters dictate the selection of the individual manifold trajectories used to construct efficient transfers. A
bounding sphere centered on the secondary, with a radius less than the sphere of influence of the secondary, is used to study
the manifold trajectories. A two-body parameter, κ, is computed within the bounding sphere, where the gravitational effects of the secondary dominate. The parameter κ is defined as the sum of two quantities: the difference in the normalized angular momentum vectors and eccentricity vectors
between a point on the unstable manifold and a point on the stable manifold. It is numerically demonstrated that as the κ parameter decreases, the total cost to complete the transfer decreases. Preliminary results indicate that this method of
constructing transfers produces a significant cost savings over methods that do not employ the use of invariant manifolds. 相似文献
19.
Christian Spannagl 《Solar physics》1978,58(2):319-321
A 5303 Å-photometer was constructed for the 20 cm coronagraph of the Wendelstein solar observatory. Details of the photometer, the method of measurement and an example for measured isophotes are given. The Wendelstein photometer is compared with the 5303 Å-Sac Peak photometer.Mitteilungen der Sternwarte München Bd. 2 Nr. 5. 相似文献
20.
A close temporal and spatial association has been found between erupting filaments/coronal transients and radio noise storm continua. The three transients studied occurred away from active regions and are members of a class not usually accompanied by chromospheric emission. The data analyzed were from the S-054 soft X-ray telescope on Skylab and from one- and two-dimensional interferometers at meter and decameter wavelengths at Nançay and Clark Lake observatories. Calculations confirmed that observed microwave radiation from the transients is due to thermal bremsstrahlung. The results are consistent with an interpretation of heating of an increased amount of coronal plasma by nonthermal, 10–100 keV electrons. Three possibilities for the source of the material are described: (1) The filament material; (2) evaporation from the chromosphere or transition region; and (3) via a long-lived reconnection process. 相似文献