Decrease In Absorption Coefficient Research Articles

A unified model of carrier diffusion and sampling aperture effects on MTF in solid-state image sensors

A unified model is used for calculating the modulation-transfer function (MTF) of a front-side-illuminated, solid-state image sensor including the effects of lateral diffusion of charge carriers within the substrate and less than full pixel sampling apertures. Moreover, it is found that, in general, these two effects cannot be treated independently and then combined, using the convolution theorem to arrive at the total sensor MTF as has often been done in the past. It is found that the actual MTF is higher than predicted by simply multiplying the diffusion and aperture MTFs together. This discrepancy is seen to increase as pixel-to-pixel crosstalk increases for a given aperture size due to an increase in diffusion length, a decrease in depletion depth, or a decrease in the substrate's absorption (coefficient) and/or as the pixel's aperture decreases with respect to the pixel size. >

The effect of internal rotation on absorption and fluorescence of dye molecules

Internal rotation around an essential single bond within a chromophoric system very often leads to a hypsochromic shift of the longest-wavelength absorption band, associated with a decrease in absorption coefficient and an increase of Stokes shift. In the case that a non-fluorescent nπ* state lies near to a fluorescent CT state, this hypsochromic shift can cause a dramatic drop of the fluorescence quantum yield and/or a strong dependence of it on solvent polarity.

Permittivity and refraction index of ferroelectric in intensive external field

Abstract The behaviour of a ferroelectric in an intensive external electro-magnetic field is discussed. It is shown that, in fields with the amplitude E 0 > 105 V/cm, the phase transition temperature becomes higher, the static permittivity and Curie-Weiss constant increase. The optical absorption coefficient decrease changes to its increase. There is a threshold field, passing by which the system divides into layers of periodical structure of para-and ferroelectric phases. A difference for damping and refraction index was studied, while the field propagation was directed along and against the spontaneous polarization vector.

Faraday Rotation of Co-Ferrite Thin Films Prepared by Single Source Evaporation

Fe-Co alloy film was oxidized to produce a transparent cobalt ferrite film. The amount of Faraday rotation was measured as a function of the quantity of Fe2+, which was increased and decreased by reduction and oxidation. In the film reduced to increase the amount of Fe2+, the Faraday rotation curve becomes positive. The absorption coefficient increases with increase in Fe2+. When the film is oxidized at 600°C, the Faraday rotation curve becomes negative again and the absorption coefficient decreases.

Effect of absorber geometry on apparent absorption coefficients as measured in a reverberation chamber

Measurements were made in the NBS reverberation chamber to determine the apparent random incidence absorption coefficient as a function of the area, perimeter, and shape of the test specimens for three different materials arrayed as combinations of rectangular pieces. Measurements made with the specimen edges exposed and with the edges covered with reflecting material were compared. The experimental results were compared with a theoretical model [T.D. Northwood, J. Acoust. Soc. Am. 35, 1173–1177 (1963)] using values of the acoustical admittance obtained from impedance tube measurements performed on the same materials. Both the experimental and theoretical results indicate that the random incidence absorption coefficient increases approximately linearly with E, the ratio of the perimeter to the area of the specimen for values of E ranging from 1.3 to 3.3 m−1. The theoretical analysis indicates, however, that a linear extrapolation to the value E = 0 is not necessarily valid. It was also found that if the specimen area and perimeter are kept constant, the values of the random incidence absorption coefficient decrease by a few percent as the specimen shape is changed to increase the number of vertices (inside plus outside right-angle corners) in the configuration.

Cerebral edema, mass effects, and regional blood volume in man.

The authors conducted quantitative analysis of computerized tomography (CT) scans to measure tumor size, cerebral edema, and regional blood volume in man. Mass lesions without edema caused a local reduction in blood volume. Cerebral edema also reduced blood volume in proportion to its severity. Consideration of the electrolyte changes and water shifts in white-matter edema suggested that the decrease in absorption coefficient seen in CT scans was due to the increase in water content. Thus, in cerebral edema separation of blood vessels as well as increased interstitial pressure decrease blood volume, and the regional differences in turn reflect pressure gradients within the brain.

Contribution of molecular water in the infrared spectra of kerogens and coals

The intensity of the OH stretching band and of the band at 1630 cm −1 recorded for kerogens and coals decreases when the potassium bromide pellet is stored in a dry atmosphere, as a result of removal of moisture. Storage under these conditions can be considered as an efficient and reproducible drying procedure. The decrease of absorption coefficient has been measured for a series of kerogens from the same parent material and the data show that moisture is related to the oxygen content and not to the surface area; as observed for coals, the water seems to be retained by association with hydroxyl groups. Spectroscopic measurements aimed at the interpretation or analytical use of the 1630 cm 1̄ band should be performed on pellets stored for a sufficient time in a desiccator.

Thermoluminescence and Color Centers in rf-Sputtered SiO2 Films

Thermoluminescent (TL) glow curves of rf-sputtered SiO2 films deposited on silicon have been measured and correlated with optical absorption of the films. As-sputtered SiO2 films are thermoluminescent without further exposure to exciting radiation. Films with a strong optical-absorption band at 7.6 eV (E band) give first-order glow curves. They have a TL center with energy ∼ 0.66 eV and a low-frequency factor s ∼ 104 sec−1, which suggests that trapping centers and recombination centers are physically separated. Irradiation of sputtered SiO2 films with x rays produces complex TL glow curves which have been analyzed by thermal cleaning techniques. Trapping centers with energies of 0.66, 0.84, and 1.04 eV are found. The complexity of TL glow curves in sputtered SiO2 films after x-ray irradiation arises primarily from variations in s, rather than from a broad spectrum of trapping energies. The effect on TL glow curves of annealing SiO2 films in oxygen and forming gas has been studied. When samples with a strong E band are annealed in O2, a decrease in absorption coefficient at 7.6 eV is paralleled by an increase in TL intensity. A trapping center with E ∼ 1.40 eV is produced by annealing of the E band followed by x-ray irradiation. A hyperbolic heating rate 1/T=1/T0 - at, used for all TL measurements, simplified analysis of TL glow curves.

Semi-empirical self-consistent field molecular orbital calculation of transition energy and oscillatory strength for the stacked complexes of pyrene and 3,4-benzopyrene with DNA bases.

Abstract The transition energy and oscillator strength of stacked complexes of pyrene and 3, 4-benzopyrene with DNA bases are calculated using semi-empirical ASMO SGF CI method, and they are compared with those of free pyrene or 3, 4-benzopyrene. Among the assumed stacking models, the intercalation-like one with guanine reproduced well the experimentally observed red shift and decrease of absorption coefficient in DNA aqueous solution, and this result seems to support the intercalation-like stacking of these hydrocarbons with the DNA bases.

Electron Microscope Study on the Extinction and Absorption of 100 kV Electrons in Magnesium Oxide Single Crystals

The intensity profile of equal thickness fringes due to 200 reflection was studied by the photographic method. The orientation of the specimen crystal was systematically changed by use of a tilting stage in the electron microscope. The real part of 200-Fourier coefficient and the imaginary part of the mean inner potential were determined to be V200r=7.43±0.11 volt and V0i=0.58±0.04 volt, respectively, provided no simultaneous reflection took place. When the deviation from the exact Bragg position, viz. the Bethe's parameter W, was varied, the behavior of intensity profile was found to be entirely different from that predicted by the two-beam approximation of the dynamical theory assuming the phenomenological complex potential. It was shown that the so-called anomalous transmission in the case of electrons can not be ascribed to the decrease of effective absorption coefficient at the Bragg position.

Sound Absorption at the Surface of the Body of Man and Animals

The results of measurements of sound absorption by the body surface of man and fur-bearing animals are reported for the frequency range 100 to 12,000 c.p.s. The acoustical impedances and the absorption coefficients of the surfaces were determined from the resonance characteristics of an air-filled tube. The end of the tube was closed first by a rigid wall and then by the unknown surface. From the change in the resonance characteristic induced by the unknown surface the desired quantities were calculated. In order to speed up the measurements, which is important with living test material, a second method was used. In this method the air column was excited by sound pulses, and the decay time of the sound pressure was measured from the photographs of the cathode-ray trace. At the higher frequencies an aluminum rod, pressed against the body surface, replaced the air column. The desired quantities were calculated from the change in longitudinal resonance characteristics in a manner similar to that employed for the air column. The absorption coefficient of the human body surface varies frown 10 percent to 0.1 percent and decreases at higher frequency. The resistances per cm2 varies between 103 and 105 ohms and are dependent upon the area of application and the pressure upon the skin and muscles. The measurements on rats show that up to 1000 c.p.s. the absorption coefficient decreases and then increases up to 6000 c.p.s. The behavior below 1000 c.p.s. is determined largely by the tissues beneath the skin while the increased absorption above 1000 c.p.s. is the result of the presence of the fur. This is demonstrated by measurements on shaved animals where the absorption decreases steadily as the frequency increases, whereas in the case of furred skin supported on a rigid wall the absorption increases as the frequency increases. These absorption coefficients permit the estimation of the sound energy absorbed by a whole animal. The sound intensity required to cause heat death can then be calculated approximately.

A Note on Saturation in Microwave Spectroscopy

The investigation of Van Vleck and Weisskopf, on the shape of collision-broadened absorption lines, is extended to high power levels of the exciting radiation. Transitions among the molecular states are then induced at a rate that is not negligible compared with the collision rate, thus invalidating the assumption of thermal equilibrium. The theory is based on a quantum transcription of the previous semiclassical treatment, the essential tool being the density matrix. When the resonant frequencies of the molecule are widely spaced, an absorption line is ultimately broadened as the power level increases. Correspondingly, the peak absorption coefficient decreases, the power absorbed per unit volume approaching saturation with increasing incident power. It is shown that the broadening of an absorption line is not to be attributed to any intrinsic modification of the line shape, but rather to a frequency dependent alteration of the energy level populations. A molecule for which all resonant frequencies coincide, a one-dimensional harmonic oscillator, is treated in Appendix II. No saturation effect occurs here, since the absorption is independent of the molecular distribution among the oscillator energy levels.

Measurements on the absorption of sound in CO 2 gas, in CO 2 containing small quantities of H 2, D 2, H 2O, D 2O and also in mixtures of CO 2 and O 2. Collision efficiencies

Measurements were made on the absorption of sound in highly purified CO 2 -gas up to 50°C. From these measurements the relaxation time and the number of efficient collisions for the excitation of the vibrational energy of the CO 2 molecule were calculated. Measurements were also made on CO 2 to which had been added small amounts of H 2 , D 2 , H 2 O and D 2 O. From these measurements, the difference between the excitation of the vibrational energy by these various molecules could be determined. If O 2 is added to CO 2 , the absorption coefficient decreases. The absorption was studied in mixtures of CO 2 and O 2 . The experimental curve can be interpreted as pointing to the fact that the CO 2 molecules are not excited at all by the oxygen.