Showing papers on "Absorption (electromagnetic radiation) published in 1980"

T‐Cell Growth Factor

Abstract: The mRNA of the Gibbon ape T-Cell Growth Factor concentrated from a Cell line identified as UCD-MLA-144 lead to. the production and cloning of its cDNA and the elucidation of its gene structure and that of the mature protein. Transfer vectors for production of the Gibbon ape T-Cell Growth Factor are disclosed along with useful intermediate expression products.

Many-particle effects in the optical spectrum of a semiconductor

Abstract: A local-orbital treatment of the two-particle Green's function for the electron-hole interaction is presented which takes into account both screened electron-hole attraction and its exchange counterpart. They give rise to the excitonic effects including Frenkel and intermediate coupling regimes and to the random-phase approximation local-field effects, respectively. An alternative formulation based on the Kohn-Sham density-functional scheme is also given and numerically tested. Quantitative calculations of the absorption and modulation spectra in Si show that electron-hole interaction effects significantly modify the absorption line shape and give rise to shifts of critical-point structure up to 0.2 eV. A model analysis indicates that deviations of the one-particle spectra of column IV, III-V, and II-VI semiconductors from experiment should similarly be accounted for.

Use of one‐electron theory for the interpretation of near edge structure in K‐shell x‐ray absorption spectra of transition metal complexes

Abstract: We report the results of multiple scattered wave SCF X‐alpha calculations of the one‐electron cross section for K‐shell photoabsorption in the molecular complexes MoO4−−, CrO4−−, and MoS4−−. We show that the method can successfully account for energy separations and relative cross sections of spectral features both below and above the K‐shell ionization threshold. Furthermore, we show: (a) that the first fairly intense peak on the low energy side of the rising edge for molybdate and chromate is due to a dipole allowed transition to a bound antibonding state of mainly nd character on the metal ion; this transition is possible because of the mixing with the ligand p orbitals having the proper T2 symmetry induced by the tetrahedral molecular potential; (b) the shoulder on the rising absorption edge can be explained by the beginning of the steplike continuum absorption when convolved with a Lorentzian function of frequency to imitate lifetime and monochromator broadening: (c) the main absorption peak is due t...

Sensitive measurement of photon lifetime and true reflectances in an optical cavity by a phase-shift method

Abstract: A simplified method for measuring the effective photon lifetime in an optical resonator was developed. The technique requires the passage of a modulated cw laser beam through the resonator and the measurement of the resultant shift in the phase of the transmitted intensity. The method not only permits a quick and precise measurement of the mirror reflectances, but also permits these measurements to be in situ. Such an on-the-spot evaluation capability should be extremely useful in applications ranging from the investigation of new laser systems to the development of improved optical coatings. The method is also sensitive to the effects of absorption, scattering, and transmission from elements in the cavity. Cavity losses <100 ppm were detected.

Sensitive measurement of photon lifetime and true reflectances in an optical cavity by a phase shift method. Technical report

Abstract: A simplified method for measuring the effective photon lifetime in an optical resonator was developed. The technique requires the passage of a modulated continuous-wave laser beam through the resonator and the measurement of the resultant shift in the phase of the transmitted intensity. The method not only permits a quick and precise measurement of the mirror reflectances, but also permits these measurements to be in situ. Such an 'on the spot' evaluation capability should be extremely useful in applications ranging from the investigation of new laser systems to the development of improved optical coatings. The method is also sensitive to the effects of absorption, scattering, and transmission from elements in the cavity. Cavity losses smaller than 100 ppm were detected.

Nickel pigmented anodic aluminum oxide for selective absorption of solar energy

Abstract: Spectrally selective surfaces on Al metal sheets were prepared by dc anodization in dilute phosphoric acid followed by black coloration via ac electrolysis in a bath containing NiSO4. These coatings had good durability, as found from several accelerated tests. The optical performance was studied by the recording of hemispherical reflectance or specular reflectance in conjunction with diffuse light scattering. From these results we extracted a solar absorptance of 0.93–0.96 and a corresponding thermal emittance of 0.10–0.20. The structure of the coatings was investigated by scanning electron microscopy on fractured specimens, Auger electron spectroscopy combined with depth profiling by sputtering, and atomic absorption analysis. Based on this information, a multilayer model was formulated, its most conspicuous feature being a sheath near to the Al interface comprised of metallic Ni particles in an Al2O3 matrix. The optical properties of this layer were described either by the Maxwell Garnett theory or the ...

Refractive-index and absorption fluctuations in the infrared caused by temperature, humidity, and pressure fluctuations

Abstract: The dependence of fluctuations in atmospheric absorption and refraction upon fluctuations in temperature, humidity, and pressure is found for infrared frequencies. This dependence has contributions from line and continuum absorption and from anomalous refraction by water vapor. The functions that relate these fluctuations are necessary for evaluating degradation of electromagnetic radiation by turbulence. They are computed for a given choice of mean atmospheric conditions and graphed as functions of frequency in the wavelength range 5.7 μm to radio waves. It is found that turbulent fluctuations in total pressure give a negligible contribution to absorption and refraction fluctuations. Humidity fluctuations dominate absorption fluctuations, but contributions by temperature and humidity affect refraction fluctuations. Sufficiently strong humidity fluctuations can dominate the refraction fluctuations for some infrared frequencies but not for visible frequencies. We examine the variance of log amplitude for scintillation of infrared light to determine whether absorption or refraction fluctuations dominate under several conditions.

Method and apparatus for molecular spectroscopy, particularly for the determination of products of metabolism

Abstract: Method and apparatus for molecular spectroscopy, particularly for the determination of products of metabolism. The absorption of infrared radiation by a specimen (2) which contains the substance to be determined is measured. The absorption is measured simultaneously at two different wavelengths (λ 1 , λ 2 ), the first wavelength (λ 1 ) being so selected that upon changes in concentration of the substance to be determined in the specimen (2) only a negligibly small change, if any, of the radiation absorption takes place, while the second wavelength (λ 2 ) lies in the region of a substance-specific absorption band of the substance to be determined. After measurement of the radiation intensities (I 1 and I 2 ) at the two wavelengths (λ 1 , λ 2 ) the signal is standardized by formation of the quotient (I 2 /I 1 ). The method makes it possible to effect a quantitative reproducible measurement in the natural biological medium or in dialysates without pretreatment of the specimen and with only small amounts of substance. By suitable selection of the second wavelength (λ 2 ) a plurality of substances can be determined.

Sensitivity enhancement of laser absorption spectroscopy by magnetic rotation effect

Abstract: The use of magnetic rotation spectroscopy (Faraday effect) to reduce the effects of source noise and improve sensitivity of spectroscopy with color center lasers has been analyzed theoretically and tested experimentally on the vibrational overtone band of NO. Sensitivity improvement of a factor of 30 compared with simple Zeeman modulation has been demonstrated. As an example of this technique, the first observation of the fundamental vibrational band of the OH radical in absorption is reported.

Infrared Microsampling by Diffuse Reflectance Fourier Transform Spectrometry

Abstract: It is shown that diffuse reflectance techniques enable increased sensitivity to be obtained for infrared microsampling compared with the use of KBr micropellets. When nonabsorbing matrices, such as KCl, are used, detection limits of less than 10 ng of samples are observed. Samples absorbed on graphitized substrates, which have a fairly strong general absorption but few intense absorption bands, may also be studied but at somewhat reduced sensitivity. Diffuse reflectance infrared Fourier transform spectrometry does not appear to be particularly useful for studying adsorbates on silica gel, which is not only a strong infrared absorber but also has a surface which is so active that small changes in the surface structure can change the spectrum significantly. Extraction of sample spots from thin layer chromatography plates followed by deposition onto KCl yields much better results than in situ measurements.

Photoinduced Defects in Chalcogenide Glasses

Abstract: Prolonged exposure to strongly absorbed light induces a large density of metastable defects in chalcogenide glasses. Observed properties of the new defects include light-in-duced ESR, extrinsic absorption below the band-gap energy and nonradiative recombination. The defect creation apparently underlies the well-known reversible photostructural change, and our data support a recent model of optically induced defect pairs.

Electrical and optical properties of hydrogenated amorphous carbon films

Abstract: We have measured the electrical conductivity (25 to 350C) and optical absorption (1.65 to 4 eV) of a series of hydrogenated amorphous carbon (a-C:H) films prepared via dc glow discharge decomposition of acetylene (C2H2) at deposition temperatures Td between 25 and 375C. The electrical conductivity is not simply activated, and varies by over 11 orders of magnitude for the samples studied. Optical energy gaps inferred from optical absorption data lie between 0.9 and 2.1eV, decreasing with increasing Td. It can be inferred from these measurements that the films will be “graphitic” in their electrical and optical properties for Td greater than about 425C.

Electronic and structural properties of plasma-deposited a-Si:O:H - The story of O2

Abstract: Measurements of luminescence, optical absorption and infrared vibrational spectra are reported for thin films plasma-deposited from SiH4/O2/Ar mixtures. The addition of oxygen causes the optical absorption edge and luminescence peak position to shift monotonically to higher photon energy. Increases in the luminescence peak width and in the temperature of thermal quenching result in room temperature luminescence in the visible at high oxygen contents.

CO and Temperature Measurements in a Flat Flame by Laser Ab orption Spectroscopy and Probe Techniques

Abstract: Carbon monoxide and temperature have been measured in the post-flame region of laminar, pre-mixed methane/air flat flames at atmospheric pressure using both laser absorption spectroscopy and conventional probe techniques. The laser absorption measurements employed a tunable diode laser to record fully resolved absorption lines in the fundamental band of CO near 4.7 microns. Probe measurements were made with thermocouples and sampling microprobes (uncooled quartz and water-cooled stainless steel). The extracted gases were analyzed for CO and CO2 using NDIR instruments. The laser absorption measurements of CO in rich flames were in good agreement with chemical equilibrium calculations based on metered fuel and air flow-rates and measured local temperature. In lean flames, measured levels of CO exceeded equilibrium values, as expected, due to incomplete reaction of CO to CO2 near the flame front. Temperatures inferred from the relative absorption in lines from different vibrational levels were in go...

Spectral adsorption properties of natural watres: contribtion of the soluble and particulate fractions to light absorption in some inland watres of south-eastern Australia

Abstract: A method has been developed for measuring the absorption spectra, and calculating the in situ absorption coefficients, of the particulate fraction (tripton/phytoplankton) of natural waters. The procedure involves concentrating the particulate fraction by filtration followed by resuspension in a smaller volume, and measuring the absorption spectrum with the help of an integrating sphere to minimize the effects of light scattering. The method has been applied to seven inland water bodies in the southern tablelands of New South Wales and the Australian Capital Territory. For comparative purposes the absorption spectra. and in situ absorption coefficients, of the soluble colouring matter (gilvin, gelbstoff) have also been measured. The absorption coefficients have been used to calculate what part of the total absorbed photosynthetically active radiation (PAR) is captured by each of the three major absorbing components. In clear but rather coloured waters, gilvin absorbs most of the quanta, followed by water itself. In two waters with fairly high phytoplankton levels, the particulate fraction absorbs as much PAR as the water, but gilvin still absorbs rather more than either. In highly turbid waters, the particulate fraction (consisting mainly of tripton) absorbs most of the quanta. The data show that tripton has an absorption spectrum in the visible region. which rises steadily with decreasing wavelength: this is attributed to humic materials. It is clear that in turbid waters the inanimate particulate fraction (tripton) is a major light absorber, in addition to being the most important light scatterer.

Absolute Absorption Intensity and Dispersion Measurements on Some Organic Liquids in the Infrared

Abstract: The infrared absorption spectra and corresponding dispersion spectra of the following liquids have been measured over the range 4200 to 250 cm−1: cyclo-C5H10, CH3•NO2, CH3•CN, CH2Br2, CH2Cl2, CBrCl3, CCl4, C6H6, C6H5•CH3, C6H5Cl, C6H5Br, C6H5I, and C6F6. The spectra were measured in the absence of solvent and the results are reported as the real and imaginary components of the complex refractive index (n, k). The experimental technique combines transmission measurements through thin films and attenuated total reflection measurements by a method which has been described previously. The complete spectral and dispersion curves are displayed graphically; the absorption maxima are tabulated as absorption indices (kmax) and as molar absorption coefficients (emax). The dispersion extrema (nmin, nmax) are also listed and the experimental uncertainties in these quantities are evaluated. Provision is made to supply the complete optical constant data on magnetic tape at encoded intervals of 0.5 cm−1.

Derivation of the low-energy optical-absorption spectra of a-Si: H from photoconductivity

Abstract: We outline a procedure to extract the optical-absorption coefficient as a function of energy from measurements of photoconductivity and assess the assumptions involved in applying it to $a$-Si: H. Using this procedure, we obtain accurate absorption spectra in the range from 1.8 to below 1.2 eV. These spectra show an absorption shoulder around 1.3 eV which we analyze in terms of possible optical transitions involving specific distributions of states in the gap.

Multiangular Absorption Diagnostics of a Turbulent Argon-Methane Jet

Abstract: Absorption techniques are being applied to three-dimensional combustion diagnostics. Convolution, Fourier transforms, and iterative algorithms have already been proven in x-ray absorption tomography and interferometric applications. They are currently being tested and compared on their ability to determine typical pollutant and radical concentrations as they appear in flames or exhausts. The effect of the number of scans is analyzed for parallel beams. A tradeoff exists between accuracy and the number of viewing angles. A five-angle procedure gives 10% accuracy with a moderately filtered convolution algorithm. An experiment feasibility study shows that the near time-continuous three-dimensional maps of concentration as low as 1 ppm can be obtained at repetition rates up to 20 KHz. The potential of this method was demonstrated in the laboratory. A diluted methane jet was observed at several sections along its axis. Time-averaged two-dimensional profiles were reconstructed from the absorption scans effected from six and twelve angles. The theoretically predicted dependence of the accuracy on the number of observation angles was verified. Real-time experiments are now being prepared.

Calcium-ion efflux from brain tissue: power-density versus internal field-intensity dependencies at 50-MHz RF radiation

Abstract: In previous experiments changes were found in calcium-ion efflux from chick-brain tissue that had been exposed in vitro to 147-MHz radiation across a specific range of power densities when the field was amplitude modulated at 16 Hz. In the present study, 50-MHz radiation, similarly modulated as a sinusoid, was found to produce changes in calcium-ion efflux from chick brains exposed in vitro in a Crawford cell. Exposure conditions were optimized to broaden any power-density window and to enhance the opportunity to detect changes in the calcium-ion efflux. The results of a power-density series demonstrated two effective ranges: One spanning a range from 1.44 to 1.67 mW/cm2, and the other including 3.64 mW/cm2, which were bracketed by no-effect results at 0.72, 2.17, and 4.32 mW/cm2. peaks of positive findings are associated with near-identical rates of energy absorption: 1.4 microW/g at 147 MHz, and 1.3 microW/g at 50 MHz, which indicates that the enhanced-efflux phenomenon is more dependent on the intensity of fields in the brain than on the power density of incident radiation. In addition, the phenomenon appears to occur at multiples of some, as yet unknown, rate of radiofrequency (RF) energy absorption. Because of the extremely small increments of temperaturemore » associated with positive findings (less than 4 X 10(-4) degrees C), and the existence of more than one productive absorption rate, a solely thermal explanation appears extremely unlikely.« less

Optical analyzer for measuring a construction ratio between components in the living tissue

Abstract: An optical analyzer such as oximeter is provided including a source of light having a plurality of different wavelengths. At least two or more of the different wavelengths have a fixed relationship of light absorption after coaction with hemoglobin oxide. The light is directed at the subject tissue and received after coaction by an optical probe. A first signal representative of the degree of light absorption at a predetermined standard wavelength is determined and then an attempt is made to match a second wavelength having a fixed relationship of light absorption to the predetermined standard wavelength, e.g., equal absorption, to generate a second signal representative of the second wavelength, whereby the amount of hemoglobin oxide can be determined in the bloodstream.