Mean Absorption Cross Section Research Articles

Reconstruction of the absorption spectrum of Synechocystis sp. PCC 6803 optical mutants from the in vivo signature of individual pigments.

In this work, we reconstructed the absorption spectrum of different Synechocystis sp. PCC 6803 optical strains by summing the computed signature of all pigments present in this organism. To do so, modifications to in vitro pigment spectra were first required: namely wavelength shift, curve smoothing, and the package effect calculation derived from high pigment densities were applied. As a result, we outlined a plausible shape for the in vivo absorption spectrum of each chromophore. These are flatter and slightly broader in physiological conditions yet the mean weight-specific absorption coefficient remains identical to the in vitro conditions. Moreover, we give an estimate of all pigment concentrations without applying spectrophotometric correlations, which are often prone to error. The computed cell spectrum reproduces in an accurate manner the experimental spectrum for all the studied wavelengths in the wild-type, Olive, and PAL strain. The gathered pigment concentrations are in agreement with reported values in literature. Moreover, different illumination set-ups were evaluated to calculate the mean absorption cross-section of each chromophore. Finally, a qualitative estimate of light-limited cellular growth at each wavelength is given. This investigation describes a novel way to approach the cell absorption spectrum and shows all its inherent potential for photosynthesis research.

Automation of CO 2 laser output power measurement as a function of the absorber gas pressure in a cell located inside or outside the laser cavity

The automation of CO 2 laser output power measurement is discussed in this paper as a function of the absorber gas pressure in a cell located inside or outside the laser cavity. A manually tunable laser was used which can be operated in one of about 44 different laser lines aligned by the user and registered respectively by the acquisition program for further analysis. The voltages representing the absorber gas pressure and the output power were very small (a few hundred μV), therefore a proper voltage amplification circuit was designed to amplify the analog outputs of both the pressure meter and the laser output power meter. These amplified signals were then applied directly to a PCI-9112 ADLINK data acquisition card using a personal computer (PC). A suitable controlling program using LabVIEW graphical programming language was written to measure the pressure and laser power signals, draw the relationship between them and save the results for later processing and analysis; such as, gas absorbance coefficient α, mean absorption cross section σ calculations that can be applied in many areas such as molecular spectroscopy and environmental pollution studies.

Quantitative x-ray absorption imaging with a broadband source: application to high-intensity discharge lamps

The case of x-ray absorption imaging in which the x-ray source is broadband and the detector does not provide spectral resolution is analysed. The specific motivation is observation of the Hg vapour distribution in high-intensity discharge (HID) lamps. When absorption by the vapour is small, the problem can be couched accurately in terms of a mean absorption cross section averaged over the x-ray spectral distribution, weighted by the energy-dependent response of the detector. The method is tested against a Au foil standard and then applied to Hg. The mean absorption cross section for Hg is calculated for a Ag-anode x-ray tube at accelerating voltages of 25, 30 and 35 kV, and for HIDs in fused silica or polycrystalline alumina arc tubes.

Calculated and Measured Absorption Cross Sections of Lossy Objects in Reverberation Chamber

Reverberation chambers can be used to measure radiation efficiency of small antennas when these are located close to lossy objects. The lossy objects represent a heavy loading of the chamber. This loading is characterized by the mean absorption cross section of the lossy objects. This paper describes how this mean absorption cross section can be calculated from the scattered far field of an object by using the forward scattering theorem, or from a more laborious near-field evaluation. Results for lossy spheres and cylinders are calculated by using three different codes, based on spherical mode expansion, finite difference time domain techniques, and moment methods, respectively. The results for the cylinder are compared with measured levels in a reverberation chamber.

Numerical approximations of the mean absorption cross-section of a variety of randomly oriented microalgal shapes.

The size, shape, and absorption coefficient of a microalgal cell determines, to a first order approximation, the rate at which light is absorbed by the cell. The rate of absorption determines the maximum amount of energy available for photosynthesis, and can be used to calculate the attenuation of light through the water column, including the effect of packaging pigments within discrete particles. In this paper, numerical approximations are made of the mean absorption cross-section of randomly oriented cells, aA. The shapes investigated are spheroids, rectangular prisms with a square base, cylinders, cones and double cones with aspect ratios of 0.25, 0.5, 1, 2, and 4. The results of the numerical simulations are fitted to a modified sigmoid curve, and take advantage of three analytical solutions. The results are presented in a non-dimensionalised format and are independent of size. A simple approximation using a rectangular hyperbolic curve is also given, and an approach for obtaining the upper and lower bounds of aA for more complex shapes is outlined.

Planck mean efficiency factors for six material candidates as interstellar grains

Planck mean absorption cross-sections have been computed for spherical grains composed of graphite, iron, ice, olivine, amorphous quartz and a lunar silicate. Experimentally determined infrared optical constants have been used for all these materials. Ice mantle particles and planetesimal particles (iron core and olivine mantle) have also been considered with values of outer and inner radii covering a wide range of astrophysical conditions.

The Equivalent Mean Absorption Cross Sections for the O2Schumann-Runge Bands: Application to the H2O and NO Photodissociation Rates

Abstract Absorption of solar radiation by O2 in the Schumann-Runge band region is important not only for the production of O(3P) in the atmosphere, but also for H2O and NO photodissociations which depend upon the rotational structure of the O2 absorption lines. The equivalent mean absorption cross sections for the O2 Schumann-Runge bands and NO band intensities are computed and presented in a form to be applicable in calculations of the O2, H2O and NO photodissociation rates under varied atmospheric conditions.

The Atmosphere of Venus Near HER Cloud Tops.

view Abstract Citations (82) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Atmosphere of Venus Near HER Cloud Tops. Chamberlain, Joseph W. Abstract The conclusions that one reaches about Venus' atmospheric structure and composition near her cloud tops depend on the theory of line formation adopted to interpret the spectra. Here it is argued that the absorption bands of CO2 are produced through multiple scatterings in an optically thick atmosphere and that consequently our knowledge of that atmosphere is much less precise than is commonly believed. First, the visual data are reviewed to obtain an estimate of the properties of the cloud particles Next the thermal-infrared observations are used to derive some idea of the temperature, T, and its variation with optical depth, r, in the cloud; the degree of uncertainty in these parameters is considerable, but the cloud tops are almost certainly cooler than the region where CO2 absorption occurs. This observational conclusion is interpreted as a natural consequence of the multiple-scattering mechanism of line formation, which alleviates the need for more elaborate models of cloud and haze layers. From the T(r) dependence combined with the rotational temperature of CO2, we can deduce the mean depth, (r), of band formation. (Incidentally, it becomes necessary here to modify the conventional concept of "rotational temperature" to allow for the fact that different lines in a band are formed at different depths and, therefore, different local temperatures) Finally, the radiative-transfer theory of line formation is used to relate (r) to the albedo for single scattering, . Knowing the mean absorption cross-section for the gas, we may then derive the amount of CO1 above depth (r . This indirect method of deriving abundances does not make use of the absolute equivalent widths of absorption. Unfortunately, the chain of deductive reasoning is so long and involves so many poorly known parameters that the CO2 content is exceedingly uncertain. The CO1 equivalent widths and the line profiles are discussed as a means of deriving the amount of collisional broadening and thence the CO2/total-gas ratio. With the present theory the "spectroscopic pressures" are about half the values derived from a number of high-resolution spectra by Spinrad. But since the CO1 content must also be less than Spinrad's values, we can at least reaffirm his important conclusion that CO1 is a minor constituent of Venus' atmosphere. A number of intriguing correlations among observables are examined in the light of this theory. The variation of band strength and rotational with planetary phase have the forms expected. For the phase variation of band strength, an error in an earlier paper is corrected, and it is shown that for weak bands the temperature should change very little with phase Sample values are computed for the relative variation of the equivalent width across the disk at various phase angles; observed values are not yet available for comparison. The sporadic variations of equivalent width, rotational temperatures, and spectroscopic pressures are correlated, according to Spinrad. As interpreted here this correlation suggests that the temperature gradient near the cloud tops is not far from the dry, adiabatic lapse rate, but this conclusion, like so many others, remains imprecise Taking the data literally, we conclude that the near-infrared CO1 bands are formed mostly within the first scale height (about 8 km) below the cloud tops This part of the atmosphere is much more important in producing absorption, because of the multiple scatterings of light, than is the region above the clouds. The theory predicts the correct relative equivalent widths of the different weak bands, which heretofore have paradoxically indicated different CO2 abundances. Interpreting the equivalent widths with the present theory reaffirms Kuiper's conclusion that the carbon and oxygen isotopes are in about the same ratios as on Earth. The water-vapor band recently measured by Bottema, Plummer, and Strong is probably formed mainly above the clouds, unlike the weak CO2 bands With the pressures and temperatures thought to be characteristic of this region, the clouds cannot be composed of H2O. It seems unlikely (but not impossible) that the observations or their interpretation could be in error enough that ice clouds might actually form. Publication: The Astrophysical Journal Pub Date: April 1965 DOI: 10.1086/148207 Bibcode: 1965ApJ...141.1184C full text sources ADS |