Changes In Absorption Coefficient Research Articles

Interaction between dyes and polyelectrolytes, 9. Effect of polyanions on alkaline fading reaction of methylene blue

AbstractThe effect of polyanions poly(potassium vinyl sulfate) (PVS), poly(sodium acrylate) (PANa), and poly(potassium p‐styrenesulfonate) (PSS), on the alkaline fading reaction of methylene blue (1) was investigated. The fading rate of 1 was extremely retarded on addition of polyanions. The binding type of 1 to polyanions was investigated spectrophotometrically by following the changes in the molar absorption coefficient (ε) at 664nm band. The relationship between the binding type and the fading rate of 1 in aqueous alkaline solution of polyanions is discussed.

X-ray diffraction topographic study of polarization reversal. I. Sodium nitrite

By applying the X-ray diffraction topography to the partly electroded ferroelectric NaNO2 crystals, Suzuki and Takagi1,2 have suggested that the NO2 radicals in the regions near the periphery of the electrodes are rotated by about 50° or 130° around the c-axis from the original orientation. By measuring the positional change in absorption coefficient of v2 infrared absorption associated with the internal vibration of NO2 radicals, the rotated orientation in the intermediate state regions was confirmed.

Interaction between dyes and polyelectrolytes, 7. Metachromatic behavior of methylene blue induced by poly(sodium acrylate) and its homologues

AbstractThe structural effect of polyanions on the metachromatic behavior of methylene blue (1) was investigated spectrophotometrically. The following polyanions were used: poly(sodium acrylate) (PAA), conventional poly(sodium methacrylate) (a‐PMA), isotactic poly(sodium methacrylate) (i‐PMA), syndiotactic poly(sodium methacrylate) (s‐PMA), and the copolymer poly(sodium maleate‐covinyl alcohol) (1:1) (PMVA). The metachromatic behavior was followed by the changes in the molar absorption coefficient (ε) at 664 nm of methylene blue (1) and in the wave length (λm) of the metachromatic band. Important factors for metachromasy were found to be the flexibility and charge density of the polymer. Differences between OSO and COO⊖ as binding sites are discussed.

Exciton Absorption in GaSe under Intense Excitation

High excitation absorption was investigated in GaSe at 2 K and 77 K, using a N 2 laser. Change in absorption coefficient was measured directly by a pulse-modulation technique. A structure was found at an excitonic transition around 2.1 eV. The structure shows peak shift and broadening of an exciton absorption line. Shift and broadening are due to an elastic collision between two excitons. Two kinds of induced absorption were also observed. One is possibly ascribed to exciton excitation associated with collision with the second exciton and the other to excitation of a trapped electron to a conduction band.

Collision induced shift of rotational transition of ammonia

Collision induced shift and change in absorption coefficient have been investigated theoretically for the (3,3) rotational transition of ammonia by pumping (4,3) transition. These results are in a good agreement with the experimental data.

Synthetic peptides for chymosin and pepsin assays: pH effect and pepsin independent-determination in mixtures.

Peptide I [H-Phe-Gly-His-Phe(NO2)-Phe-Ala-Phe-OMe] hydrolyzed by chymosin with kcat=.3+/-.3 s-1 and KM=7+/-3 mM (pH 4.7) inhibited competitively peptide II [H-Leu-Ser-Phe(NO2)-Nle-Ala-Leu-OMe] hydrolysis by chymosin with KI=.23 +/- .12 mM at pH 4.7. In reference conditions (.4 mM peptide, .01 M acetate buffer pH 4.7), the specific activities of porcine pepsin and chymosin on peptide I were 470 +/- 70 nM S-1 and .8 nM S-1 per mg of enzyme. This difference in specific activity for peptide I allowed development of a chymosin-independent pepsin assay for mixtures of these enzymes. In addition, peptide II with a specific activity of 2400 +/- 300 nM S-1 and 154 +/- 20 nM S-1 per mg of porcine pepsin and chymosin provides an alternative to measurement of milk clotting for measurement of chymosin- and pepsin-like activities in commercial rennets. Hydrolysis products of peptide II by chymosin exhibited one ionized group of apparent pK of 3.5 +/- .2 and a molar absorption coefficient change of 1000 +/- 100 at pH 4.7 and at 310 nm. From measurements of the kinetic constants, kcat and KM, from pH 2.5 to 7 with peptide II, chymosin activity depends on the protonation of one group of apparent pK 5.3 +/- .2 in the free enzyme. Rennet powder proved to be fairly stable after a 17-month storage at 4 C. Within the same period, a crystalline chymosin solution kept at --18 C lost 30 to 50% of its activity.

Temperature variation of the submillimetre wavelength optical constants of soda-lime-silica glass

The optical constants of soda-lime-silica glass are described from 10 to 45 cm −1 for temperatures of 1.8, 4.2 and 293°K. The power absorption coefficient changes from a wavenumber-squared dependence at 293°K to an almost cubic dependence at 1.8°K, while the refractive index falls from a mean value of 2.586 at 293°K to 2.51 at 1.8°K.

COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF POSTERIOR FOSSA LESIONS

A series of 3,500 cases examined by computed tomography (CT) of the head were reviewed to identify patients who had symptoms and signs suggestive of neurologic disease in the posterior fossa. Three hundred forty eight such cases (about 10%) were found, and the scans were reviewed to determine the character of lesions that could be detected and the accuracy of the neuroradiologic diagnosis. Overall, 16 errors were made (4.6%), of which 13 were false negatives and 3 were false positives. False negatives included nine tumors, two infarcts, and two arteriovenous malformations. Four of the tumors and the two arteriovenous malformations were small and caused no visible alterations in density even when analyzed retrospectively. In the remaining seven cases, specific findings either were overlooked or were obscured by artifacts, and, therefore, the diagnosis was not made. The three false positive diagnoses were made through a misinterpretation of density changes that were artifactual. No changes in the intracranial absorption coefficients were detected in 109 cases. Abnormal changes were evident in 226 cases in which structural lesions were subsequently found. Many of the lesions had a characteristic appearance, but in certain clinical situations, which include searches for metastatic disease, acoustic neuromas, meningiomas aneurysms of the basilar artery, and arteriovenous malformations, the injection of intravenous contrast medium was helpful, or even essential, for diagnostic success. The prominence of clinical signs and symptoms is not always an accurate index to the presence of structural alteration of the posterior fossa. We believe, therefore, that this portion of the cranium should be included in every CT study.

Proposed Measurement of the Acoustoelectric Effect by Electron-Photon-Phonon Interaction for Hypersonic Phonons in Semiconductors

It is proposed that amplification of phonons of frequencies in the order of hundreds of gigahertz can be investigated by measuring expected changes in the free carrier absorption coefficient which will occur from changes in the density of thermal phonons. It is shown that for photon energies greater than the thermal energy, there is a one-to-one correspondence between the energy of the incident photons and the momentum of the phonons that are required for free carrier absorption by means of intraband electron transitions. An important result derived is that the phonon energy per unit bandwidth, at a particular phonon frequency proportional to the incident radiation energy, is directly related to the ratio of the free carrier absorption coefficients during and before acoustoelectric amplification. As a specific example, the case of CO2 laser radiation absorption in n-type Ge is considered, leading to the result that at 10 K the free carrier absorption coefficient will increase by several orders of magnitude over its thermal equilibrium value during acoustoelectric amplification. In addition, the dependence of the free carrier absorption coefficient on the phonon density suggests applications in some laser devices such as photon drag detectors and amplitude modulators.

Effect of plasma and hole current on the optical absorption of InSb

The changes in absorption coefficient due to currents in p-type indium antimonide were measured at 87°K, using polarized radiation with energies from 0.052 to 0.22 eV. Data from injecting samples showed plasmon effects. Data from a noninjecting sample agreed qualitatively with the theory of Baumgardner and Woodruff.

Irreversible Photoinduced Changes in Optical Absorption of YIG(Si4+) and YIG(Ca2+)

Irradiation by white light at low temperatures produces drastic changes in the near-infrared absorption coefficient of YIG doped with divalent Ca or quadrivalent Si. For Ca2+ doping, α increases; for Si4+ doping, α decreases on irradiation. In both cases the magnitude of the effect varies sharply with concentration. For YIG(Si) the results are interpreted in terms of the different properties of Fe2+ in sites that are near or far from the Si4+ ions. A similar model holds for YIG(Ca) with Fe4+ rather than Fe2+ being the important impurity. In both cases irradiation enhances occupation of the far sites.

Radiation-induced Changes in Refractive Index and Absorption Coefficient for Several Optical Materials

An experiment was performed to determine the change in refractive index and absorptivity upon x radiation of several optical materials. Exposure to a radiation dose of 10(5) rad produced measurable changes at lambda = 0.5330 microm in the index of refraction and at lambda = 0.5000, microm in the absorption coefficient of ~5.8 x 10(-6) and ~0.1 cm(-1) for calcium fluoride. Optical glasses exhibited changes of ~5.8 x 10(-6) and ~1.1 cm(-1) for LaK 8, ~4.3 x 10(-6) and ~1.7 cm(-1) for PSK 53, ~5.1 x 10(-6) and ~1.4 cm(-1) for FK 50, and ~6.0 x 10(-6) and ~1.0 cm(-1) for SF 8. A change in the absorption coefficient of the optical glass KzFS 5 of ~0.52 cm(-1) was measured. Changes induced in an SiO(2) (Suprasil 2B) control sample were below measurement capability.

Transmission of bremsstrahlung through alkali-halide crystals for various beam collimations

In irradiating specimens with bremsstrahlung in radiation-physics investigations, two groups of problems are encountered requiring a knowledge of the energy parameters of the beam at various depths of the absorber. These are, first, the determination of the energy absorbed at various depths of the object irradiated and, second, the selection of conditions under which the use of a radiation source is most effective, i. e. . when energy absorption at the point of interest is the largest. It is known that when bremsstrahlung is transmitted through absorbers, its spectral content is modified [1-3], so that the absorption coefficient changes in value as the path traversed by radiat~on in the absorber increases. The authors [3-5] showed that this variation of the absorption coefficient of bremsstrahlung in a lkal i halide crystals is described for the range of maximum energies 0.2-80 MeV by a curve with saturation. The absolute value of the absorptioncoefficient variation and of the thickness of alkal i-hal ide crystals at which the transition to saturation occurs are determined by the radiation energy and by the crystal's effective atomic number [3-5]. The investigation of bremsstrahiung-spectrum transformation with absorber thickness by plotting calculated or measured spectra for various absorber thicknesses gives an accurate representation of the variations which occur, but it is not always convenient. The comparison Of different absorbers or different radiation intensities from the spectrum variation is difficult. Therefore, the authors [3] suggested using the mean spectrum energy for investigating bremsstrahlungspectrum variations. This quantity is convenient for comparing spectral-content variations in various materials, and it provides a convenient picture of the direction and rate of spectrum transformation as a function of the parameter of interest. Continuing the investigation of bremsstrahhing transmission through a lkal i -hal ide crystals, we studied the variation of spectral content with thickness in crystals of lithium fluoride, sodium chloride, and potassium chloride, bromide, and iodide for various collimations of the radiation beams. Investigations were carried out theoretically by calculating the bremsstrahlung spectra for various crystal thicknesses, using the Monte Carlo method on an M-20 computer. From the spectra calculated we determined the mean energy and plotted the mean energy as a function of absorber thickness for various collimations of tile radiation beams incident on the crystals. Bremsstrahlung beams 5 to 500 mm in diameter were investigated. Investigations of the accumulation factor as a function of beam diameter showed that an increase of the irradiation-field diameter above 200 mm gave no appreciable increase inthe scattered-radiation contribution to the total flux for crystal thicknesses of up to 100 g /cm 2. Therefore, to all practical accuracy, beams with more than 200 mm transverse cross section can be considered as beams of infinite cross section for 10 MeV maximum bremsstrahhing energy. Theoretical results of the mean energy of the bremsstrahlung beam for various thicknesses of alkal ihalide crystals of potassium chloride, bromide, and iodide are shown in the table. Data are given for irradiation fields 1 cm in diameter and for an infinite-diameter irradiation field. As can be seen from values of the mean energy calculated for various crystal thicknesses, it markediy increases with increasing absorber thickness. Thus. in the case of potassium iodide, it varies by more than twice in passing through a crystal layer 80 g /cm 2 in thickness for an irradiation field 1 cm in diameter. The rate of increase of the mean energy with absorber thickness depends to a greater extent upon the irradiation field than upon the crystal's effective atomic number. Thus, the maximum mean-energy difference in passing from potassium chloride to potassium iodide for constant irradiation fields is 0.2-0.3 MeV, whereas a beam-diameter increase from 10 to 100 mm causes a mean-energy variation of more than 0.5 MeV for 100 g /cm z crystal-layer thickness. In passing from a bremsstrahlung beam 10 mm in diameter to an infinite-diameter beam, the mean-energy variation is more than 1 MeV. An increase of the irradiation beam transverse cross section gives rise to a relative increase of its secondary-radiation content, and therefore the mean energy decreases in passing to wide irradiation beams.

Electric-Field Effects on Optical Absorption near Thresholds in Solids

The weak-field effective-mass-approximation calculations of the absorption coefficient in the presence of an electric field for direct and indirect transitions at a normal (${M}_{0}$) threshold are extended to an arbitrary orientation of the electric field in an anisotropic solid. To do this, a systematic method of evaluating density-of-states integrals arising in the electroabsorption or Franz-Keldysh effect is presented. Certain integrals obtained in prior calculations at the ${M}_{0}$ threshold which have not been previously evaluated are given in closed form. This method is also used to derive the change in absorption coefficient, $\ensuremath{\Delta}\ensuremath{\alpha}(\mathcal{E})$, occuring at the saddle-point edges ${M}_{1}$ and ${M}_{2}$, as well as the edge ${M}_{3}$, for an arbitrary field direction in an anisotropic solid. It is shown that there is a direct correlation between $\ensuremath{\Delta}\ensuremath{\alpha}(\mathcal{E})$ for the ${M}_{0}$ and ${M}_{3}$ edges, and also for the ${M}_{1}$ and ${M}_{2}$ thresholds. Reduced masses of opposite signs, as in the ${M}_{1}$ and ${M}_{2}$ edges, give rise to two branches in $\ensuremath{\Delta}\ensuremath{\alpha}(\mathcal{E})$.

Interband Optical Absorption in Crossed Electric and Magnetic Fields in Germanium

The theory for interband optical absorption in semiconductors in crossed electric and magnetic fields is developed for the case of low electric field strengths by considering the electric potential as a perturbation on the magnetic level structure. For simple parabolic valence and conduction bands the results agree with those of Aronov, obtained from an exact solution of the effective-mass Schr\"odinger equation in crossed fields, but the present method has the advantage that it can be applied to complicated bands, such as the degenerate valence bands in germanium, whenever the energy levels and eigenfunctions in the absence of an electric field are known. Actual calculations are presented for the case of germanium. Experimentally, the optical absorption in crossed fields was studied using a modulation technique in which both the transmission in the absence of an electric field and the modulation of this transmission by an ac electric field are measured to obtain the electric-field-induced change in absorption coefficient $\ensuremath{\Delta}\ensuremath{\alpha}$. Strain-free as well as strained thin germanium samples were used in magnetic fields up to 96 kOe and electric fields up to 1000 V/cm. Both allowed transitions ($\ensuremath{\Delta}n=0, \ensuremath{-}2$ for germanium) and electric-field-induced forbidden transitions ($\ensuremath{\Delta}n=\ensuremath{-}3, \ensuremath{-}1, +1$) can be observed in these differential spectra. A good agreement between theory and experiment is obtained. It is shown that under favorable conditions the electron and hole masses can be determined separately from the differential spectra. It is also found that the electric-field-modulation technique can sometimes be used to study the allowed transitions with greater sensitivity than in the normal magnetoabsorption experiments.In zero magnetic field the Stark broadening of the low-energy direct exciton line in a strained germanium sample was studied up to 1000 V/cm. The linewidth was found to vary linearly with electric field, increasing at a rate of about 160 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ eV/V ${\mathrm{cm}}^{\ensuremath{-}1}$. This phenomenon is tentatively explained in terms of an electric dipole moment of the short-lived exciton state.

Optical spectra of CaF2(Tb) crystals

The luminescence and absorption spectra of fluorite crystals, alloyed with terbium fluorides, oxyfluorides, and oxides at concentrations of 0.01 to 5 mol.% were studied. The change in the optical spectra was studied as a function of the chemical composition of the alloy addition and also as a function of the concentration. It is proposed that the change with the concentration in the spectra of the crystals takes place as a consequence of mutual interactions between the ions with formation of cation pairs. It was observed that the ratio of the relative luminescence intensities of the crystals to the absorption coefficient changes nonlinearly with the concentration of the alloying addition. The problem of an interaction between an isomorphic admixture and crystal defects is discussed.

Ultrasonic Absorption Measurements in Single Crystals of Naphthalene and p-Dichlorobenzene

The attenuation of ultrasonic waves has been measured in single crystals of naphthalene and p-dichlorobenzene at frequencies from 5 to 95 MHz for the former crystal, and 5 to 65 MHz for the latter. The absorption coefficients of the crystals were proportional to the square of the acoustic frequency. The change in absorption coefficient for the temperature range from 30°C down to —70°C was very small to about —40°C; a slight decrease was observed below this point. There was no appreciable change in the absorption coefficient within the limit of experimental error, up to a (uniaxial) pressure of 4.25×106 dyn/cm2 applied in a direction perpendicular to the direction of propagation of the acoustic wave. From these results, it is concluded that any contributions of dislocation damping and thermal conduction in the crystals to the total acoustic absorption were negligibly small. The sound velocity was determined for these same crystals at room temperature. This velocity was to be found to be a linear function of the temperature, with negative slope, and shows approximately the same temperature coefficient in both cases.

A differential absorption spectrometer for the infra-red

A method is described of measuring the small change in absorption coefficient due to the introduction of an impurity into a semiconductor. A chopped monochromatic beam of infra-red radiation is passed alternately through the doped and undoped halves of a compound specimen, and the resulting modulation measured. A change of less than 10-3 cm-1 can be observed in the presence of substantial background absorption. The method is illustrated by a measurement on oxygen-doped germanium.

Fading of Coloration of Irradiated Glass

Previous investigators have shown that the fading of coloration of gamma- irradiated phosphate glass can be represented by the formula mu (t) = Kt/sup - 0.067/, where mu (t) is the change in absorption coefficient of glass measured at t hours after short exposures and K is a constant of proportionality. A similar relation was found to hold for fading of coloration of ordinary window glass irradiated by Co/sup 60/ gamma rays. The formula mu (t) = Kt/sup - lambda /, lambda = exp(-A + BT), where A and B are constants dependent only on glass and wavelength and T denotes absolute temperature, gives very good agreement with observed data over wide temperature ranges. Comparisons of experimental data and calculated results are shown. (A.C.)

夜間輻射について

The equation for the radiative transfer was solved on earth's atmosphere to calculate the incoming radiation at the ground level. Different formulae were obtained for the incoming radiations due to absorption of water vapour both in the intermediate region where the change of absorption coefficient with wave-length is smooth and in the absorption bands where the absorption coefficient fluctuates rapidly with wave-length. The formula which is available for mixed gas of H2O and CO2 (or O3) was derived too.Using the values of the absorption coefficient of water vapour calculated by Yamamoto-Onishi and by Elsasser, and those of Co2 and O3 properly assumed, the incoming radiations were calculated for several weather conditions appropriate to clear skies. The comparison of calculations with observations shows that the calculated values based on Yamamoto-Onishi's absorption coefficient agree fairly well with observations, and that those based on Elsasser's absorption coefficient are generally smaller than the observed values.By formulating the calculated values the following formula was obtained: where G (O) is the incoming radiation and W is the amount of water vapour in the air column in cm unit of precipitable water. When the vapour pressure at the ground level, ε0 in mb, is taken as abscissa, the empirical formula of Brunt's type agree with many observations as a whole.The possibility of deriving these formulae was discussed also.