Absorption Coefficient Of Air Research Articles

Micro-reinforced polymer composite materials studied by correlative X-ray imaging

Three-dimensional insights into the microstructure of composite materials are vital for enhancing their performance under operational conditions. Phase-sensitive methods can offer supplementary data, especially for materials with low absorption, compared to standard absorption-based techniques. This work presents the correlative X-ray imaging and computed tomography results of polymer composites reinforced with glass fibers using an inverted Hartmann mask. This method identified areas with enhanced refraction and scattering due to glass fibers and discriminated signals based on their orientation, offering an advantage in evaluating anisotropic materials. The simplicity of the setup, adding the inverted Hartmann mask, makes integration feasible in commercial CT scanners and existing radiography laboratories, enabling simultaneous phase, scattering, and absorption information extraction. Our approach, which combines refraction and scattering with absorption signals, exposes intricate structures beyond the usual spatial resolution threshold. Despite the distinct absorption coefficients of air, polymer-based, and glass fibers, the inverted Hartmann mask is crucial for examining similar absorption composites and low-absorbing materials. This research offers profound insights into the microstructures of fiber-reinforced polymer composites, laying the groundwork for studies of nanostructured functional composite materials.

Calculation of the absorption coefficient of air at different heights using the HITRAN and ACE-FTS databases

Subject of study. Increasing requirements for the accuracy of modeling the brightness characteristics of the atmosphere at different heights motivate the development of more detailed methods for the calculation of the absorption coefficient of air. Method. Modern databases of satellite sounding of the atmosphere that contain information on the volume fractions of air components at different heights in combination with a database of the parameters of the spectral lines of gases can be used in this task to calculate the spectral absorption coefficient. The possibility of specifying the geographic position of the height profiles of the air components (by specifying latitude and longitude) is an additional advantage of using the databases of satellite sounding. This method enables the differences in air compositions above different regions of the Earth to be considered. These databases usually provide information starting from a certain height; thus, databases of satellite sounding must be combined with the data obtained either from ground-based meteorological stations or using model distributions. The ACE-FTS database was used in this study, and it was combined with the standard atmosphere MODTRAN models at low heights. A filter for the ACE-FTS database was implemented using C++. The HITRAN database was used to calculate absorption coefficients. The ACE-FTS database provides data for 43 components of air, and the HITRAN database contains data for line-by-line calculation for 27 of these components and data on spectral absorption cross-sections for the remaining 16 components. Main results. A program for the calculation of the absorption coefficient of a multicomponent gas mixture was developed using C++. A Voigt profile was used in the line-by-line calculation, the effects of pressure and temperature on the line shift were considered, and line broadening owing to the following processes was considered: self-broadening, broadening resulting from interaction with water and carbon dioxide molecules, and broadening owing to interaction with other components of the air. The software explicitly considers the isotopic composition of molecules, thus enabling the calculation of not only the air mixture but also an arbitrary mixture with specified isotopic composition, information on which is in the HITRAN database. Moreover, the data of the high-temperature version HITEMP are considered. Practical significance. The combination of the ACE-FTS and HITRAN databases enables the calculation of a detailed profile of the spectral absorption coefficient of air for the specified month, temperature at the surface of the Earth, and geographic latitude and longitude, thus increasing the information content of the input data for the calculation of the brightness and transmission of the atmosphere at different heights. The data readout rate (parsing) and calculation speed of the developed program and the program HAPI implemented using Python are compared.

Thermal radiation from impact plumes

AbstractPlumes produced by the impacts of asteroids and comets consist of rock vapor and heated air. They emit visible light, ultraviolet, and infrared radiation, which can greatly affect the environment. We have carried out numerical simulations of the impacts of stony and cometary bodies with a diameter of 0.3, 1, and 3 km, which enter the atmosphere at various angles, using a hydrodynamic model supplemented by radiation transfer. We assumed that the cosmic object has no strength, and deforms, fragments, and vaporizes in the atmosphere. After the impact on the ground, the formation of craters and plumes was simulated, taking the internal friction of destroyed rocks and the trail formed in the atmosphere into account. The equation of radiative transfer, added to the equations of gas dynamics, was used in the approximation of radiative heat conduction or, if the Rosseland optical depth of a radiating volume of gas and vapor was less than unity, in the volume‐emission approximation. We used temperature and density distributions obtained in these simulations to calculate radiation fluxes on the Earth's surface by integrating the equation of radiative transfer along rays passing through a luminous region. We used tables of the equation of state of dunite and quartz (for stony impactors and a target) and air, as well as tables of absorption coefficients of air, vapor of ordinary chondrite, and vapor of cometary material. We have calculated the radiation impulse on the ground and the impact radiation efficiency (a ratio of thermal radiation energy incident on the ground to the kinetic energy of a body), which ranges from ~0.5% to ~9%, depending on the impactor size and the angle of entry into the atmosphere. Direct thermal radiation from fireballs and impact plumes, poses a great danger to people, animals, plants, and economic objects. After the impacts of asteroids at a speed of 20 km s−1 at an angle of 45°, a fire can occur at a distance of 250 km if the asteroid has a diameter of 0.3 km, and at a distance of 2000 km if the diameter is 3 km.

Accuracy validation of incident photon fluence on DQE for various measurement conditions and X-ray units

Detective quantum efficiency (DQE) is widely used as a comprehensive metric for X-ray image evaluation in digital X-ray units. The incident photon fluence per air kerma (SNR²(in)) is necessary for calculating the DQE. The International Electrotechnical Commission (IEC) reports the SNR²(in) under conditions of standard radiation quality, but this SNR²(in) might not be accurate as calculated from the X-ray spectra emitted by an actual X-ray tube. In this study, we evaluated the error range of the SNR²(in) presented by the IEC62220-1 report. We measured the X-ray spectra emitted by an X-ray tube under conditions of standard radiation quality of RQA5. The spectral photon fluence at each energy bin was multiplied by the photon energy and the mass energy absorption coefficient of air; then the air kerma spectrum was derived. The air kerma spectrum was integrated over the whole photon energy range to yield the total air kerma. The total photon number was then divided by the total air kerma. This value is the SNR²(in). These calculations were performed for various measurement parameters and X-ray units. The percent difference between the calculated value and the standard value of RQA5 was up to 2.9%. The error range was not negligibly small. Therefore, it is better to use the new SNR²(in) of 30694 (1/(mm(2) μGy)) than the current [Formula: see text] of 30174 (1/(mm(2) μGy)).

Onset conditions for positive direct current corona discharges in air under the action of photoionization

This paper presents a numerical model for the inception of positive dc corona discharges in air near cylindrical anodes, which plays a bridge role between the classic positive corona onset criterion and the photoionization model considering the effective radiation wavelength. The predicted onset voltages agree well with Peek’s experimental data in a wide range of conductor radii and relative air densities. The influence of the collisional quenching of emitting excited states on the surface onset field is significant with low air density or small conductor radius. Within the effective radiation wavelength, numerical expressions for the photon absorption coefficient in air and Townsend’s second coefficient due to photoionization are deduced on the basis of the new model. A different perspective on the classic coefficients is given.

SU‐C‐220‐06: Comparison of the Absorption Coefficient and Diffraction Enhanced Imagingˈˈs Apparent Absorption Coefficient of Lung Tissue

Purpose: Diffraction enhanced imaging (DEI) generates image contrast in a fundamentally different way than absorption x‐ray imaging—the refraction and extinction of x‐rays yield unique contrast. The purpose of this study was to measure the apparent absorption coefficient of the lung tissue in normal rats and to quantify the difference in contrast between DEIˈs peak image and radiography. Methods: Chest radiographs and DEI peak images (analyzer crystal aligned to the Bragg peak) were acquired of anesthetized and paralyzed Sprague Dawley rats (n=14) at Beamline X15A of the National Synchrotron Light Source at an x‐ray energy of 60 keV. The images were acquired in the anteroposterior (AP) direction. Intensity measurements were used to calculate an approximate apparent absorption coefficient of rat lung tissue. Measurements of the transmitted intensity of both the radiograph and DEI peak images were then used to calculate contrast within the lung. Results: The measured apparent absorption coefficient for the inflated lungs was 0.86 +/− 0.15 cm̂−1. To put this in context, the absorption coefficient of air, water and bone at 60 keV are 0.0002 cm̂−1, 0.21 cm̂−1 and 0.50 cm̂−1, respectively. Thus, the DEI contrast generated by the lung is about two times that generated by the same thickness of bone. DEI showed a significant gain in contrast over radiography (C_DEI/C_Rad) of 1.7 +/− 0.6. Conclusions: DEI generates 70% greater lung contrast than radiography at 60 keV. The large difference in the apparent absorption coefficient of DEI and the absorption coefficient of conventional radiography shows that DEI can be used to either enhance lung contrast for the same radiation dose, or could be used to substantially reduce the required radiation dose for a chest x‐ray while maintaining the same contrast‐to‐noise ratio.Drs. Connor, Parham, Pisano and Zhong are equity holders in NextRay, Inc. Dr. Pisano is on the Board of Directors at NextRay, Inc. Drs. Connor, Parham and Zhong are consultants to NextRay, Inc.

Mean absorption coefficients of air plasmas

Mean absorption coefficients of air (both Planck and Rosseland mean) have been computed for different splitting procedures of the whole frequency interval (1013 – 6×1015 s−1) and various temperatures (1 000 – 30 000 K). Results have been compared and discussed to find the optimal values of mean absorption coefficients for the multigroup method of solution of the equation of radiation transfer.

DÜŞÜK VE YÜKSEK ENERJİLİ GAMA IŞINLARININ MARUZ KALMA YIĞILMA FAKTÖRLERİNİN ETKİN ATOM NUMARASINA BAĞIMLILIĞI

The Zeff dependence of exposure buildup factors for plane incident source gamma rays of 200keV, 500keV, 1MeV, 5MeV, 10MeV and 50MeV have been investigated by using electron gamma shower Monte Carlo code, EGS4. To prepare materials with different Zeff, homogen mixtures composed of Li, Cu, Fe and Pb were used in different ratios. All the EGS4 calculations were performed in two dimensional plane geometry for each mixture. To check the accuracy of EGS4 calculations, an extra work has been performed for the exposure buildup factors of Pb, Fe and H2O. Results of these calculations are agreed well with the published data. In the EGS4 calculations, the exposure was obtained from the photon flux and the energy absorption coefficient of air. The effect of Rayleigh scattering was included but effects of bremstrahlung and fluorescent radiation were not taken into account. All calculations were performed with the exponential transform. The calculated data showed that buildup factors vary smoothly with increasing Z. At deep penetration depths, variation of buildup factors has more rapid variation. The value of the buildup factor for an arbitrary atomic number can be obtained by using data resulted from this calculations

Influence of Ablation on Radiative Heating for Earth Entry

Using the coupled ablation and radiation capability recently included in the LAURA flowfield solver, this paper investigates the influence of ablation on the shock-layer radiative heating for Earth entry. The extension of the HARA radiation model, which provides the radiation predictions in LAURA, to treat a gas consisting of the elements C, H, O, and N is discussed. It is shown that the absorption coefficient of air is increased with the introduction of the C and H elements. A simplified shock layer model is studied to show the impact of temperature, as well as the abundance of C and H, on the net absorption or emission from an ablation contaminated boundary layer. It is found that the ablation species reduce the radiative flux in the vacuum ultraviolet, through increased absorption, for all temperatures. However, in the infrared region of the spectrum, the ablation species increase the radiative flux, through strong emission, for temperatures above 3,000 K. Thus, depending on the temperature and abundance of ablation species, the contaminated boundary layer may either provide a net increase or decrease in the radiative flux reaching the wall. To assess the validity of the coupled ablation and radiation LAURA analysis, a previously analyzed Mars-return case (15.24 km/s), which contains significant ablation and radiation coupling, is studied. Exceptional agreement with previous viscous shock-layer results is obtained. A 40% decrease in the radiative flux is predicted for ablation rates equal to 20% of the free-stream mass flux. The Apollo 4 peak-heating case (10.24 km/s) is also studied. For ablation rates up to 3.4% of the free-stream mass flux, the radiative heating is reduced by up to 19%, while the convective heating is reduced by up to 87%. Good agreement with the Apollo 4 radiometer data is obtained by considering absorption in the radiometer cavity. For both the Mars return and the Apollo 4 cases, coupled radiation alone is found to reduce the radiative heating by 30 60% and the convective heating by less than 5%.

Theoretical calculation of the translation-rotation collision-induced absorption in N 2–N 2, O 2–O 2, and N 2–O 2 pairs

The translation-rotation collision-induced spectra of N 2–N 2, O 2–O 2 and N 2–O 2 mixtures are calculated theoretically. For N 2–N 2, using the matrix elements for the quadrupole and hexadecapole moments and the isotropic and anisotropic polarizabilities obtained previously from a global analysis of the fundamental band spectra, we obtain numerical values for the zeroth moment that are smaller than the measured values by 9–14%, depending on the temperature. By increasing the value for the matrix element of the isotropic polarizability slightly, good agreement with experiment is obtained. For O 2–O 2, the theoretical spectrum is significantly smaller than the experimental result. By increasing the matrix element of the hexadecapole moment by a factor of 1.7, we can obtain good agreement. This larger value for the hexadecapole moment will not appreciably affect the agreement found previously in the fundamental region because the hexadecapole contribution to the intensity is very small, unlike the translation-rotation band where it is larger than the contribution due to the quadrupole moment. Using these parameters, we then calculate the collision-induced absorption for N 2–O 2 mixtures for which no experimental data exist. Finally, we calculate the collision-induced absorption for air, and compare our results with previous work; we express the results for the ratio of the absorption coefficient of air to that of N 2–N 2 as a function of wavenumber and temperature, R( ω, T), which can easily be implemented in atmospheric models.

Traffic and seasonal dependence of the light absorption coefficient in Santiago de Chile

We have designed and built a compact, low-cost automated system to measure the optical absorption coefficient of air. Because most of the light absorption is due to black carbon, this method is a direct measure of the amount of black carbon in the atmosphere. The equipment was used to measure absorption over a period of one year in a central area of Santiago. Our results show a strong correlation with the daily traffic pattern. The highest value of the absorption coefficient during most of the year occurs during the morning rush hour (0700-0800), and the lowest value either early in the morning (0300-0500) or in the afternoon (1400-1700). The absorption coefficient also shows a strong dependence with the season of the year, with values 10-20 times higher in winter than in summer. The data show that, during most of the year, the amount of black carbon present in the atmosphere is due to traffic. At night, during winter, the high concentration of black carbon is due to the temperature inversion effect.

Water vapor absorption coefficients in the 8–13-μm spectral region: a critical review

Measurements of water vapor absorption coefficients in the thermal IR atmospheric window (8-13 microm) during the past 20 years obtained by a variety of techniques are reviewed for consistency and are compared with computed values based on the AFGL spectral data tapes. The methods of data collection considered were atmospheric long path absorption with a CO(2) laser or a broadband source and filters, a White cell and a CO(2) laser or a broadband source and a spectrometer, and a spectrophone with a CO(2) laser. Advantages and disadvantages of each measurement approach are given as a guide to further research. Continuum absorption has apparently been measured accurately to about the 5-10% level in five of the measurements reported. However, the effect of oxygen broadening has not been fully considered, since most laboratory measurements were made using nitrogen buffering. Oxygen could lead to a small reduction in the adopted value of the water vapor continuum absorption coefficient in air. Also, the temperature dependence does not seem to have been measured well for temperatures <20 degrees C. The rotational and v(2) line absorption coefficients do not appear to have been determined well in this spectral region except at CO(2) laser line frequencies, because the agreement between such measurements and the AFGL spectral data tapes is generally not good.

Laboratory investigation of the absorption coefficients of air at ? = 10.6 ?m

Laboratory investigation of the absorption coefficients of air at ? = 10.6 ?m

ATMOSPHERIC ABSORPTION OF 2.62 MEV GAMMA‐RAY PHOTONS EMITTED FROM THE GROUND

The actual measured decrease in gamma radiation with altitude, as measured by a gamma‐ray spectrometer, was found to be less than predicted on simple theoretical grounds. The various factors which reduced this apparent absorption were Compton scattering in the ground and in the air, the variation of detector efficiency with angle, the mass of material of the aircraft structure and detector housing below the detectors, the dead‐time of the electronic circuitry, and an increase in ground radioactive concentration with depth. When these effects were incorporated, experimental and theoretical values of the linear absorption coefficient in air for 2.62 Mev photons were found to agree.

Quantitative measurement of small absorption coefficients in intracavity absorption spectroscopy using a cw dye laser

The influence of the generation time on the sensitivity in intracavity absorption spectroscopy is investigated. The modulation technique for quantitative measurements of small absorption coefficients using a cw dye laser is suggested. The measured values of a number of absorption coefficients of air are in range 10 -6-10 -7 cm -1

Study of the non-viscous flows of a radiating gas by means of differential approximations

The problem of the hypersonic streamlining of a blunt body by a non-viscous gas flow allowing for radiative transfer in the shock layer was considered and solved in [1, 2]. The solution of the problem was based on the method of integral ratios. The P 1-th (differential) approximation of the spherical harmonics method was used to allow for the two-dimensional nature of the radiation field and the reabsorption of radiation in the shock layer. The selectivity of the radiation was taken into account by the partition of the continuous radiation spectrum into a number of frequency intervals within each of which the absorption coefficient k v ( p, T) was regarded as being independent of the frequency. In this paper higher P 3-th and P 5-th approximations of the spherical harmonic method are considered and are compared with the P 1-th approximation. In view of the unwieldiness of the P 3-th and P 5-th approximations, unlike [1, 2] a simpler gas-dynamical model is considered: the flow of a radiating gas is studied in the neighbourhood of the leading critical point of a blunt body. Moreover, in this paper a two-stage frequency approximation of the real absorption coefficients of air is investigated for the purpose of explaining the possibility of using such a model to allow for radiation selectivity approximately. The results of calculations of temperature profiles and radiative heat flows are presented for different models of the radiating gas. The presence of local thermodynamic equilibrium in the gas is assumed.

Blunt body flow of a viscous radiating gas

THE results of a number of papers D-41 show that in the calculation of the blunt body flow of a hypersonic air stream taking radiation into account, it is necessary to take into consideration the radiation cooling of the shock layer, the absorption of energy and the dependence of the absorption coefficient not only on the temperature and density, but also on the frequency. The radiation cooling may lead to the appearance of a significant temperature gradient in the main part of the shock wave, which throws some doubt on possibility of dividing the shock layer into a region of non-viscous flow and a boundary layer. When there is absorption the radiative transfer of energy leads to interaction between the main and boundary flow regions. It is extremely difficult to take account of consideration of these regions of the shock layer, especially if we take into account the complex nature of the dependence of the absorption coefficient of air on the frequency. Therefore, in studying the blunt flow of radiating air taking into account radiation cooling and absorption, it is necessary at the same time to consider the entire flow between the shock wave and the frontal surface of the body.

X-Ray Images of Hailstones

Abstract : Crystal structure analysis of hailstones may result, when used alone, in ambiguous conclusions about growth conditions of the hailstones. Therefore, size and distribution patterns of air bubbles, and radial concentration of soluble and insoluble contaminants have also been investigated. Kidder and Carte (1964), on the basis of analysis of artificial hailstones, indicate that more than one mechanism may be responsible for formation of air inclusions in accreted ice, either in ring-like patterns or in radial lines. This note presents a new technique for investigating those features with high resolution. It is based on the different x-ray absorption coefficients of air and high density materials relative to ice. (Author)

Radiating hypervelocity couette and boundary-layer flow in air

An analytical solution for high speed Couette flow of a gray gas is given for the situation in which the dominant physical mechanisms are the production of energy by viscous dissipation and its transfer by radiation. The analysis is extended to air for the non-gray, optically thin case including thermal conduction, and numerical results are presented to show the range of validity of the radiation controlled solution. The Couette flow results are then applied to the problem of the hypervelocity, laminar boundary layer on a flat plate in air. An approximate expression for the Planck mean absorption coefficient of air is used, and the results obtained confirm the hypotheses that these boundary layers will be optically thin and radiation controlled. The analysis results in simple expressions for estimating the boundary-layer temperature and heat-transfer coefficient.

Экcпe⇁cermmльrhe hп⇁eдeлerиe cпeкm⇁mльrьiч пhкmзmmeлe пhглhыerия phздДчm п⇁и mecпыe⇁mmД⇁mч 10 000–12 000° K

This work gives the results of an experimental determination for the absorption coefficient of air at wavelengths of 3000–5000 Åover the temperature range 10 000°–12 000° K, at pressures of 50–60 atm.