Theory of Radiative Transfer

1989 ◽  
Author(s):  
R. M. Goody ◽  
Y. L. Yung
Keyword(s):  
Radiative Transfer ◽  
Wavelength Range ◽  
Unit Area ◽  
Solid Angle ◽  
Unit Vector ◽  
Small Element ◽  
Frequency Range ◽  
Specific Intensity ◽  
Intensity Field ◽  
The Given

In common with astrophysical usage the word intensity will denote specific intensity of radiation, i.e., the flux of energy in a given direction per second per unit frequency (or wavelength) range per unit solid angle per unit area perpendicular to the given direction. In Fig. 2.1 the point P is surrounded by a small element of area dπs, perpendicular to the direction of the unit vector s. From each point on dπs a cone of solid angle dωs is drawn about the s vector. The bundle of rays, originating on dπs, and contained within dωs, transports in time dt and in the frequency range v to v + dv, the energy . . . Ev = Iv(P,S) dπs dωs dv dt, (2.1). . . where Iv(P, s) is the specific intensity at the point P in the s-direction. If Iv is not a function of direction the intensity field is said to be isotropic ; if Iv is not a function of position the field is said to be homogeneous.

scholarly journals The Pulsation of M-type Miras: Multi-Epoch ISO-SWS Observations and Dynamical Models

2002 ◽  
Vol 185 ◽  
pp. 538-541 ◽  
Author(s):  
B. Aringer ◽  
U.G. Jørgensen ◽  
F. Kerschbaum ◽  
J. Hron ◽  
S. Höfner
Keyword(s):  
Time Series ◽  
Radiative Transfer ◽  
Wavelength Range ◽  
Infrared Range ◽  
Dynamical Models ◽  
Long Period ◽  
Mira Variables ◽  
Long Period Variables ◽  
Hydrostatic Model ◽  
Additional Assumptions

AbstractWe present time series of observed and synthetic ISO-SWS spectra of oxygen-rich Mira variables covering the wavelength range between 2.36 and 7.75 μm. The calculations are based on new dynamical models, which have been computed with a non-grey radiative transfer taking into account all relevant molecular opacities. It turns out that many features in the ISO spectra of cool long period variables which could not be reproduced within the framework of classical hydrostatic model atmospheres nor with grey dynamical calculations can now be understood without any additional assumptions. This is especially true for the water bands, which dominate the opacity in the infrared range of M-type Miras.

scholarly journals Spectroscopic Observations of Be Stars Especially in the Infrared

1982 ◽  
Vol 98 ◽  
pp. 211-228
Author(s):  
L. Houziaux ◽  
Y. Andrillat
Keyword(s):  
Wavelength Range ◽  
Be Stars ◽  
Frequency Range ◽  
Infrared Wavelength ◽  
Spectroscopic Observations ◽  
The Continuum

Since the time of I.A.U. Colloquium n° 70, new data have been obtained in the infrared, far less however than in the ultraviolet or in the visible. Few line spectra have been recorded but numerous results have been published in the field of spectrometry of the continuum. It is however neither easy nor very useful to report on the infrared wavelength range alone, and therefore we shall consider when appropriate other spectral regions in this review. After all, the astrophysicist nowadays has the advantage to seek for information in a spectrum which encompasses a fantastic frequency range of about 10 dex, from ν = 108s−1 up to ν = 1018s−1. This means that a contemporary astronomer will have to become familiar with a somewhat larger span of phenomena than with the rather narrow one he has been accustomed to for the last 40 or 50 years.

Microwave studies of the stratosphere and mesosphere

1965 ◽  
Vol 288 (1415) ◽  
pp. 556-557
Keyword(s):  
Magnetic Dipole ◽  
Wavelength Range ◽  
Dipole Moments ◽  
Molecular Rotation ◽  
Upper Atmosphere ◽  
Electromagnetic Spectrum ◽  
Frequency Range ◽  
Frequency Limit ◽  
Atmospheric Physics ◽  
Microwave Techniques

The purpose of this note is to draw attention to a region of the electromagnetic spectrum that has so far received very little attention as far as studies of the upper atmosphere are concerned. This is the region which lies in the frequency range of about 20 to 300 Gc/s (or corresponding wavelength range of 15 to 1 mm). It is a part of the spectrum where conventional microwave techniques can still be used (300 Gc/s represents the present approximate upper frequency limit for these techniques), but which contains frequencies corresponding to molecular rotation lines of a number of gases that possess permanent electric or magnetic dipole moments. Among these gases are several which are important to atmospheric physics. In particular the absorption due to the pressure-broadened molecular rotation lines of O 2 and H 2 O is sufficient to render several parts of this frequency range useless as far as earth-bound communications are concerned, and to seriously affect much of the remainder of it.

scholarly journals New Computational Geometry Methods Applied to Solve Complex Problems of Radiative Transfer

2020 ◽  
Author(s):  
Francisco Salguero-Andújar ◽  
Joseph Cabeza-Lainez
Keyword(s):  
Radiative Transfer ◽  
Computational Geometry ◽  
Solid Angle ◽  
Computer Time ◽  
Graphical Interface ◽  
New Approach ◽  
Thermal Exchange ◽  
Complex Problems ◽  
Geometrically Complex ◽  
Aided Design

Several problems of radiative transfer are yet unsolved because of the difficulties of the calculations involved in them, especially if the intervening shapes are geometrically complex. The main goal of our investigation in this domain is to convert the formulas that were previously derived, into a graphical interface based on the projected solid-angle principle. Such procedure is now feasible by virtue of several widely diffused programs for Algorithms Aided Design (AAD). Accuracy and reliability of the process is controlled by means of the analytical software DianaX developed at an earlier stage by the authors. With this new approach the often cumbersome procedure of lighting and thermal exchange calculations can be simplified and made available for the neophyte, with the undeniable advantage of reduced computer time.

scholarly journals Фотодиэлектрические процессы в поликристаллических слоях ZnS:Cu

2018 ◽  
Vol 60 (2) ◽  
pp. 265
Author(s):  
В.Т. Аванесян ◽  
А.В. Ракина ◽  
В.Г. Пак ◽  
М.М. Сычев
Keyword(s):  
Space Charge ◽  
Zinc Sulfide ◽  
Wavelength Range ◽  
Low Frequency ◽  
Frequency Range ◽  
Dielectric Parameters ◽  
Visible Wavelength Range ◽  
Light Excitation ◽  
Polycrystalline Structures ◽  
Frequency Dependences

AbstractThe frequency dependences of dielectric parameters of zinc sulfide electroluminescent polycrystalline structures doped with copper are studied in the dark and under light excitation in the visible wavelength range. A positive photodielectric effect most pronounced in the low-frequency range was revealed. The experimental results are explained within framework of formation of a space charge in the bulk of a semiconductor. The analysis of data indicates they can be correlated with luminance characteristics of an electroluminescent layer.

scholarly journals The TBOSS (Taurus Boundary of Stellar/Substellar) Survey of Disk Properties

2013 ◽  
Vol 8 (S299) ◽  
pp. 224-225
Author(s):  
J. Patience ◽  
J. Bulger ◽  
K. Ward-Duong ◽  
H. Bouy ◽  
C. Pinte ◽  
...  
Keyword(s):  
Grain Size ◽  
Radiative Transfer ◽  
Wavelength Range ◽  
Detection Rate ◽  
Outer Radius ◽  
Scale Height ◽  
Brown Dwarf ◽  
Star Forming ◽  
Dust Grain ◽  
Best Fit

AbstractWith the combination of Herschel PACS (far-IR), submillimeter (submm) and millimeter (mm) ground-based observations, we are leading an investigation of all members with spectral types M4 and onwards in the Taurus star-forming region. This complete census spans the stellar to substellar boundary (M6.25), and the wavelength range covers the transition from optically thick to optically thin emission. From our Hershel PACS observations of ~135 sources, we obtain a detection rate of ~40% at 70 μm and a detection rate of ~20% at 160 μm, and provide the first far-IR measurements for the majority of these members. With our complementary submm and mm observations, best fit SED models from the radiative transfer code MCFOST will be used to infer disk properties such as scale height, mass, outer radius and maximum dust grain size. These comprehensive population statistics of disks are critical for testing star/brown dwarf and planet formation models around these later type members of Taurus.

Solar and Earth Radiation

2001 ◽  
Author(s):  
Fred V. Brock ◽  
Scott J. Richardson
Keyword(s):  
Solar Radiation ◽  
Physical Quantity ◽  
Unit Area ◽  
Solid Angle ◽  
Global Solar Radiation ◽  
Radiant Flux ◽  
Direct Solar Radiation ◽  
Radiant Intensity ◽  
The Earth ◽  
Earth Radiation

This chapter is concerned with the measurement of solar radiation that reaches the earth’s surface and with the measurement of earth radiation, the long wave band of radiation emitted by the earth. The unit of radiation used in this chapter is the Wm-2. Table 10-1 lists some conversion factors. Radiant flux is the amount of radiation coming from a source per unit time in W. Radiant intensity is the radiant flux leaving a point on the source, per unit solid angle of space surrounding the point, in W sr-1 (sr is a steradian, a solid angle unit). Radiance is the radiant flux emitted by a unit area of a source or scattered by a unit area of a surface in Wm-2 sr-1. Irradiance is the radiant flux incident on a receiving surface from all directions, per unit area of surface, in Wm-2. Absorptance, reflectance, and transmittance are the fractions of the incident flux that are absorbed, reflected, or transmitted by a medium. Global solar radiation is the solar irradiance received on a horizontal surface, Wm-2. This is the sum of the direct solar beam plus the diffuse component of skylight, and is the physical quantity measured by a pyranometer. Direct solar radiation is the radiation emitted from the solid angle of the sun’s disc, received on a surface perpendicular to the axis of this cone, comprising mainly unscattered and unreflected solar radiation in Wm-2. At the top of the atmosphere this is usually taken to be 1367 W m-2 ± 3% due to changes in the earth orbit and due to sunspots. The direct beam is attenuated by absorption and scattering in the atmosphere. The direct solar radiation at the earth’s surface is the physical quantity measured by a pyrheliometer. Diffuse solar radiation (sky radiation) is the downward scattered and reflected radiation coming from the whole hemisphere, with the exception of the solid angle subtended by the sun’s disc in Wm-2. Diffuse radiation can be measured by a pyranometer mounted in a shadow band, or it can be calculated using global solar radiation and direct solar radiation.

Structurally Sensitive Changes in Absorption THz Spectra of Corticosteroids

2010 ◽  
Vol 5 (4) ◽  
pp. 162-167
Author(s):  
Irina N. Smirnova ◽  
Elena V. Fedulova ◽  
Maxim M. Nazarov ◽  
Оlga P. Cherkasova
Keyword(s):  
Steroid Hormones ◽  
Absorption Spectra ◽  
Time Domain ◽  
Spectral Response ◽  
Frequency Range ◽  
Terahertz Time Domain Spectroscopy ◽  
Characteristic Lines ◽  
Pure Substances ◽  
Thz Absorption ◽  
The Given

The series of steroid hormones, such as progesterone, 17α-hydroxyprogesterone, cortisol and other was measured by terahertz time-domain spectroscopy (THz TDS). It was obtained that THz absorption spectra of steroid hormones have characteristic lines of absorption in the frequency range 0.1-3.0 THz. We investigate the relation between the position of side functional groups and THz spectral response. Besides pellets of polycrystalline pure substances, steroids solution in methanol was analyzed. The given method can be applied for express diagnostics of different classes of steroid

scholarly journals Experimental observation of backscattered light based on different coherence between incident laser beams

2013 ◽  
Vol 1 (2) ◽  
pp. 94-97 ◽  
Author(s):  
Xiangfu Meng ◽  
Chen Wang ◽  
Honghai An ◽  
Guo Jia ◽  
Huazhen Zhou ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Experimental Observation ◽  
Solid Angle ◽  
Stimulated Raman Scattering ◽  
Brillouin Scattering ◽  
Laser Beams ◽  
Incident Laser ◽  
The Difference ◽  
Stimulated Brillouin ◽  
The Given

AbstractRecent experimental results on NIF revealed a much higher stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) backscatter than expected; one possible reason was due to the coherence between incident laser beams. In our research, two laser beams (${\sim }1~\mathrm{ns} $, ${\sim }250~\mathrm{J} , 527~\mathrm{nm} $ in each one) with different coherent degrees between them from the SG-II facility were employed to irradiate an Au plate target; the backscatter of SBS and SRS in the range of the given solid angle had been measured. The results showed that it could change dramatically corresponding to the difference of the coherent degree between the two laser beams, and there was usually more intense backscatter the higher the coherent degree between the incident beams.

scholarly journals Time-dependent molecular emission in IRC + 10216

2018 ◽  
Vol 615 ◽  
pp. L4 ◽  
Author(s):  
J. R. Pardo ◽  
J. Cernicharo ◽  
L. Velilla Prieto ◽  
J. P. Fonfría ◽  
M. Agúndez ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Asymptotic Giant Branch ◽  
Frequency Range ◽  
Systematic Observation ◽  
Molecular Emission ◽  
Chemical Effects ◽  
Observation Program ◽  
Molecular Lines ◽  
Phase Lags ◽  
Erroneous Interpretation

Context. The variability in IRC+10216, the envelope of the asymptotic giant branch (AGB) star CW Leo, has attracted increasing attention in recent years. Studying the details of this variability in the molecular emission required a systematic observation program. Aims. We aim to reveal and characterize the periodical variability of the rotational lines from several molecules and radicals in IRC+10216, and to compare it with previously reported IR variability. Methods. We carried out systematic monitoring within the ~80–116 GHz frequency range with the IRAM 30 m telescope. Results. We report on the periodical variability in IRC+10216 of several rotational lines from the following molecules and radicals: HC3N, HC5N, CCH, C4H, C5H, and CN. The analysis of the variable molecular lines provides periods that are consistent with previously reported IR variability, and interesting phase lags are revealed that point toward radiative transfer and pumping, rather than chemical effects. Conclusions. This study indicates that observations of several lines of a given molecule have to be performed simultaneously or at least at the same phase in order to avoid erroneous interpretation of the data. In particular, merging ALMA data from different epochs may prove to be difficult, as shown by the example of the variability we studied here. Moreover, radiative transfer codes have to incorporate the effect of population variability in the rotational levels in CW Leo.

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