A method for calculating the radiation power coefficients of black and gray bodies with dimensions commensurable with the radiated wavelengths

A technique is proposed and the calculations of the dependences of the emissivity of an abso-lute black body (BBB) on the size of the diaphragms of the emitting aperture are performed for hypothetical cases when the sizes of the diaphragms are commensurate with the emitted wavelengths, and the diaphragms are made of a dielectric opaque for radiation. The value of the cutoff wavelength  = 1.772A for the square aperture of the diaphragm was determined, where A is the side of the square and  = 1. 571D for the round hole. where D is the hole di-ameter, i.e. it is shown that the body cannot emit wavelengths λ greater than 1.772A in the case of a square hole and 1.571D in the case of a round hole. It is shown that if the “cut off” wavelengths made any significant contribution to the integral radiation of a blackbody with temperature T at standard diaphragm diameters (i.e., at diameters of much larger radiated wavelengths), then the emissivity of this body becomes less than unity and rapidly decreases when the size of the diaphragms is commensurate with . In these cases, such a body ceases to be an absolutely black body and the laws of Planck and Stefan–Boltzmann cannot be used to calculate the power of its radiation, but the technique proposed in this work can be used.

Satellite Microwave Radiometry for Earth Remote Sensing

The issues of development of the direction of satellite microwave radiometry in Russia in the interests of operational meteorology and oceanography are considered. The analysis of the current state of Russian and foreign radiometric ERS equipment in the microwave range is carried out. The technical characteristics of onboard multichannel microwave radiometers, combining the functions of a scanner and a sounder, are analyzed. The issues of metrological support of microwave measurements of equipment installed on Russian satellites of the Meteor-M series are considered. The original method of internal calibration of the MTVZA-GYA microwave scanner/sounding device is analyzed in detail in order to form the antenna temperature scale. The MTVZA-GYA calibration unit measures the radiation intensity of two matched loads with known brightness temperatures (“hot” and “cold”). An on-board calibrator is used as a “hot” load, it serves as an imitator of an absolutely black body, its brightness temperature of which is in the range of 240–300 K. Absolute (external) calibration is a transition from antenna to brightness temperatures and is performed using high-precision radiation calculations for specially selected natural testing sites. The issues of preliminary processing of MTVZA-GYA data are considered and examples of microwave images of the Earth in the scale of brightness temperatures are given.

Тепловое излучение абсолютно черного тела, движущегося в равновесном газе фотонов

The dynamics, kinetics of heat transfer and the intensity of thermal radiation of an absolutely black body with its own temperature T1 moving at an arbitrary speed in an equilibrium gas of photons with its own temperature T2 independent of time are considered. Formulas are obtained for the spectral-angular and total radiation intensity, as well as for other quantities in the rest frame of the body and in the frame of reference of the photon gas. It is shown that at the initial moment the radiation intensity of spherical and disk-shaped particles of the same radius depends differently on the speed of motion and the ratio of temperatures T1 and T2. Then a quasi-stationary thermal state of bodies is established with an effective temperature depending on the velocity and temperature T2, the intensity of thermal radiation does not depend on the shape, and the kinetic energy is transformed into radiation. The characteristic time for the establishment of a quasi-stationary state is many orders of magnitude shorter than the characteristic deceleration time.

Study of vertically aligned multi-walled carbon nanotubes array for an absolutely black body

An array of vertically oriented multi-walled carbon nanotubes (VOMWCNT), obtained by chemical vapor deposition (CVD) on a silicon substrate without preliminary catalyst deposition, has been comprehensively investigated. The synthesis was carried out for 30 minutes in the reactor of a carbon nanotube synthesis unit under conditions of decomposition of the reaction mixture (ferrocene in heptane) at a temperature of 800 °C at a carrier gas flow rate of 200 ml/min. The structure and geometric characteristics of the array’s carbon nanotubes were determined using scanning and transmission electron microscopy and Raman spectroscopy. The spectral coefficient of diffuse reflection (SDR) into the hemisphere in the wavelength range from 5,0 to 15,0 μm was determined. From the obtained experimental data, it was found that the emissivity (absorption coefficient) of an array of carbon nanotubes with a height of (230 – 250) μm is 0,98 – 0,99 in the spectral range from 5,0 to 13,7 μm and 0,975 – 0,995 in the range from 13,7 to 15,0 μm. Such a VOMWCNT array can be used to develop an absolutely black body with a high absorption coefficient and small mass and size characteristics, which is used for calibrating spacecraft’s infrared spectrometers.

On the role of evaporative wind in precataclysmic binaries (PCB)

Recently we have started a systematic reevaluation of the existing observational methods of analysis hitherto applied to PCB-s. Here we report the first results of our investigations. The improved Napier's algorithm (Napier, 1968) to model the light curves of PCB (with the aid of the set of our computer programs in Turbo Pascal) is used. The source function is taken either from Sobieski (1965) or Strittmatter (1974). The entire luminosity received from the cool companion is calculated by integration of the emerging radiation over its disk; contributions from the illuminated and unilluminated portions of the disk are accounted for. We assume: a) the validity of the LTE in the photosphere of cool component, b) constancy of the monochromatic to mean absorption coefficient ratio within the photosphere, c) the hot star radiates as the absolutely black body, d) there are no other effects influencing the light curve except for the reflection effect. We have modelled the light curves of EC11575-1845 (Chen et al (1995). The analysis of the temperature distributions in the heated photosphere indicates the occurence of the temperature inversion. To make a rough estimate of physical conditions which can induce generation of evaporative wind we have used two criteria: i) the temperature inversion, ii) relation between radiative pressure and the effective gravitational acceleration. We assumed the density varies with the height in the atmosphere of the illuminated star as ρ ≃ exp(−Φ/RgT), Φ - being the Roche potential. The integral equation following from the definition of the mean optical depth was solved numerically to establish the relation between the mean optical depth and the distance in the atmosphere. We find the characteristic height scale for X-ray and EUV radiation is ∼ 106 − 107cm (for concentration of particles ∼ 1013cm−3). To check the validity of the ii) criterium we used a simplified model of radially expanding evaporative stellar wind and mass flux J conservation condition along the stream tube of the form J ∼ ρsvsrs2 exp −(Φ/RgT) (Pustylnik (1995)) and found M ∼ 10−12–10−11M/y. Although mass loss of such a rate cannot compete with the effects of the angular momentum loss which is responsible for a secular orbital shrinkage, the evaporative wind should significantly alter the structure of the the cool irradiated components.