Apparent Absorption Coefficient Research Articles

Intrinsic microcrystalline silicon (μc-Si:H) deposited by VHF-GD (very high frequency-glow discharge): a new material for photovoltaics and optoelectronics

The development of μc-Si:H technology and the introduction of intrinsic 〈i〉 μc-Si:H as photovotaically active material is retraced. Special emphasis is laid on the use of very high frequency glow discharge as a particularly propitious deposition method for μc-Si:H. Thereby, the use of a gas purifier to reduce oxygen content and obtain intrinsic layers with ‘midgap’ character is described. Recent results obtained with single-junction μc-Si:H solar cells and a-Si:H/μc-Si:H tandem solar cells are given. The analysis of carrier collection in single-junction μc-Si:H solar cells is undertaken with the variable intensity measurements method. It yields effective mobility×lifetime ( μτ) eff products for the i-layer in p–i–n and n–i–p solar cells in the range 10 −7–10 −6 cm 2 V −1. Similar values have been found for μτ-products in individual layers based on photoconductivity and ambipolar diffusion length measurements. Transmission electron microscopy images for μc-Si:H layers are given. They display a complex microstructure not suspected before. On the other hand, atomic force microscopy data reveal a pronounced surface roughness that correlates well with the optical light scattering and with the pronounced enhancement of the apparent optical absorption coefficient, in the 1–2 eV region, as already observed before.

Hydroperoxide Assay with the Ferric–Xylenol Orange Complex

A range of hydroperoxides were reduced by ferrous ions in acid solutions and the amount of ferric product was measured as a xylenol orange complex at 560 nm. Dilute sulfuric acid, 50% acetic acid, and acidified 90% methanol proved to be suitable solvents. The color developed within 15 min and was stable for several hours in most solvents. The apparent molar absorption coefficients (εapp) of H2O2 and of the t-butyl, cumene, bovine serum albumin, and linoleate hydroperoxides were measured, using known hydroperoxide concentrations determined independently by an iodometric assay. The εapp values differed significantly and depended on the hydroperoxide, the solvent, and the source of the xylenol orange. The numbers of Fe3+ ions formed by a range of hydroperoxides in different solvents showed that H2O2 gave 2.5, t-butyl and cumene hydroperoxides 5, and the other hydroperoxides 2 Fe3+ ions per –OOH group. This general finding allows the determination of approximate hydroperoxide concentrations even in chemically complex systems. Accurate measurements require knowledge of the nature of the hydroperoxide and its εapp and careful control of the assay conditions. However, the convenience of the assay makes it potentially useful in a variety of applications.

All-rac-α-Tocopherol Acetate Is a Better Vitamin E Source than all-rac-α-Tocopherol Succinate for Broilers

The difference in bioavailabilities of the acetate and succinate esters of all-rac-α-tocopherol was investigated in a feeding experiment with broilers. The experiment was initiated with 96 12-d-old male Cobb broilers and lasted for 4 wk. The two sources of vitamin E were fed to eight groups of broilers at four different dietary levels (50, 100, 150 and 200 mg/kg feed, including the naturally occurring α-tocopherol). A total collection of droppings for determination of apparent tocopherol absorption were performed at two separate time periods (d 28–34 and d 35–41). There were no differences among the eight experimental groups with respect to animal performance or feed intake. At all dietary levels, the apparent absorption coefficient for all-rac-α-tocopherol succinate was significantly lower than that of the acetate ester. The mean (± SD) apparent absorption coefficient for all-rac-α-tocopherol succinate was 58.0 ± 5.4 compared with 70.8 ± 5.6 for all-rac-α-tocopherol acetate. Furthermore, the apparent absorption coefficients for both esters was significantly lower in the first collection period (d 28–34) than in the second collection period (d 35–41). This difference in the apparent absorption coefficient between the succinate and the acetate ester was accompanied by significant differences in α-tocopherol concentrations in plasma, breast muscle, liver and adipose tissue of the broilers, which were lower in those fed the succinate ester. Based on a comparison of plasma and tissue responses, the succinate ester was utilized only 69–76% as efficiently as the acetate ester. In vitro studies showed a significantly higher capacity of pancreatic carboxyl ester hydrolase to hydrolyze α-tocopherol acetate compared to α-tocopherol succinate. This difference in intestinal hydrolysis of the two vitamin E sources may explain the observed differences in biopotency.

Determination of fosfomycin by indirect spectrophotometric method

2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a sensitive photometric reagent for determination of zirconium, when fosfomycin is added, it can quantitatively replace 5-Br-PADAP by complexing with zirconium, thus, an indirect spectrophotometric method based on ligand exchange has been established. The detection wavelength is at 605 nm, and the apparent molar absorption coefficient was found to be 4.59×10 4 l mol −1 cm −1. Beer’s law is obeyed in the range of 0–28×10 −6 M. The composition and stability constant of zirconium with 5-Br-PADAP and with fosfomycin has also been estimated. The proposed method is simple and reproducible, it was applicable to the analysis of fosfomycin from pharmaceutical manufacture.

Consumo e absorção aparente total de macroelementos inorgânicos (Ca, P, Mg, K e Na), em bezerros da raça holandesa alimentados com dietas contendo diferentes níveis de volumoso

Este estudo visou avaliar os efeitos dos diferentes níveis de volumoso nas dietas sobre os consumos e as absorções aparentes de cálcio (Ca), fósforo (P), magnésio (Mg), potássio (K) e sódio (Na). Trinta e cinco bezerros da raça Holandesa puros por cruzamento, não-castrados, com idade média de 60 dias e peso vivo inicial de 78 kg, foram distribuídos em delineamento inteiramente casualizado, com nove repetições por dieta, exceto para a dieta com 10% de volumoso, com oito repetições. Os animais foram alimentados à vontade com dietas contendo níveis de 10, 25, 40 e 55% de volumoso, na base da MS, usando-se feno de capim coast-cross (Cynodon dactylon), fubá de milho e farelo de soja, os quais constituíram dietas com aproximadamente 16% de PB. Os coeficientes de absorção aparente foram obtidos por intermédio de ensaios de digestibilidade, realizados aos 120 e 180 dias de idade dos animais, sendo usado como indicador o óxido crômico para estimar a excreção fecal. O consumo máximo diário de 10,96 g de P foi estimado com 42,40% de volumoso na dieta. Os consumos de Mg e K aumentaram, o de Na decresceu linearmente e o de Ca não foi influenciado com o aumento de volumoso na dieta. Os coeficientes de absorção aparente de Ca, P, Mg e Na não foram influenciados, enquanto o de K decresceu linearmente com aumento dos níveis de volumoso nas dietas. Os consumos de P, Mg, K e Na e a absorção aparente de K foram influenciados pelos níveis de volumoso nas dietas.

Sampling Considerations for FT-Raman Spectroscopy of Polymers and Solutions

The apparent absorption coefficient and optimal sample thickness for Fourier transform (FT)-Raman analysis of polyethylene, polyethylene terephthalate, cellulose, and cyclohexane were experimentally determined. With the use of these results, a relationship was developed that permits the optimal sample thickness for FT-Raman measurements to be determined by simply measuring the absorbance spectrum of a sample whose thickness is known. For samples with an apparent absorption coefficient of less than 0.08 cm-1, the sampling depth is limited by the depth of view of the instrument. For samples with an apparent absorption coefficient greater than 0.08 cm-1, the samples' optical and physical properties limit the sampling depth. The results are discussed in the context of scattering theory, sampling considerations, and spectral artifacts. Sampling considerations include the application of FT-Raman spectroscopy to the study of coated materials and layered structures.

Synthesis of meso-tetra-(2-chloro-4-sulfophenyl) prophyrin and spectrophotometric determination of trace amounts of cadmium

Synthesis of a new high sensitive water soluble chromogenic reagent meso-tetra-(2-chloro-4-sulfophenyl) prophyrin and the conditions for the reaction of this reagent with cadmium (I) were studied. The apparent molar absorption coefficient at 434 nm is 5.20×105 L·mol−1·cm−1. The method has been applied to the determination of 5.0×10−9 (content by weight) Cadmium (I) in honey.

Penetration of Infrared Radiation within a Vegetable Model.

A vegetable model was constructed in order to evaluate its apparent absorption coefficient and penetration of infrared radiation within it. Carrot, daikon (Japanese radish), eggplant, potato, pumpkin and sweet potato were prepared as the test vegetables. This vegetable model was composed of the dry vegetable material, liquid and gas, and its apparent absorption coefficient was calculated with their absorption coefficients and volumetric fractions. The volumetric fraction of the voids (void fraction) was obtained experimentally by a method provided in this study. Thus the damping of infrared rays within the vegetable model irradiated by near-infrared (NIR) or far-infrared (FIR) radiation was estimated in consideration of the spectral distribution of the radiation. The infrared radiation absorbed by the vegetable model was indicated to be damped to 1/100 of the initial value at a depth of 0.21 to 2.54 mm, and the penetration depth in the case of NIR irradiation was deeper than that of FIR irradiation. Moreover, the calculation results suggested that the penetration depth of infrared radiation became deeper with a decrease in the water content.

Use of the true absorption coefficient as a measure of bioavailability of radiocaesium in ruminants.

Limitations of existing methods to describe the bioavailability of dietary radionuclides to ruminants (the transfer coefficient and apparent absorption coefficient) have led to the alternative suggestion of using the true absorption coefficient (A(t)). Various approaches to estimating A(t) for radiocaesium, involving the intravenous administration of a second isotope, are presented and discussed with reference to results from studies in which a range of radiocaesium sources were examined in sheep. Although estimates of A(t) differed between the sources, they were reasonably consistent between measurement techniques. Those methods which involved the estimation of endogenous faecal excretion of radiocaesium could be used with previously contaminated animals and did not require continuous administrations of radiocaesium isotopes, but gave unreliable results for sources of low bioavailability. Methods based on estimating the turnover rate of dietary radiocaesium through blood plasma were sufficiently sensitive to measure A(t) for the range of sources studied. However, they require previously uncontaminated animals and continuous administration of both isotopes for approximately 7 days. Bioavailability is more effectively measured as A(t) than as the transfer or apparent absorption coefficients since A(t) does not incorporate factors relating to the metabolism of radiocaesium in the tissues of the animal. The results of these studies show that differences in transfer coefficients between sheep and cattle and between sheep of differing ages are not due to variation in absorption across the gut. The potential for applying these approaches to other radioactive elements is discussed.

Measurement of Translucency of Porcelain Bodies

Two methods for evaluating absorption coefficients of porcelain bodies in the visible wavelength range were proposed and applied to Japanese porcelain. The comparative merits of the methods were discussed. Apparent absorption coefficients could be obtained more precisely than conventional ones by measuring the transmittances for different sample thicknesses. Variations in translucency due to compositional change of the porcelain bodies could be explained quantitatively using these coefficients. The scattering and absorption coefficients of bodies were calculated from their reflectances and transmittances using the Kubelka-Munk equations. The accuracy of these coefficients was lower than that of the apparent absorption coefficient because of difficulties in the transmittance measurements. Nevertheless these coefficients were very useful for understanding the optical properties of porcelain bodies. The relationship between the reflectance and scattering coefficient of bodies was also discussed.

Influence of blood vessels on the measurement of hemoglobin oxygenation as determined by time-resolved reflectance spectroscopy

We report the development of a heterogeneous resin-tube model to study the influence of blood vessels on the apparent absorption of the system, mu a(sys), using a time-resolved technique. The experimental results show that mu a(sys) depends on the absorption inside the tubes, mu a(tube), tube diameters, and tube-to-sample volume ratios. A mathematical expression relating mu a(sys) and mu a(tube) is derived based on the experimental results and is verified by time-resolved Monte Carlo simulations for heterogeneous models. This analytical formula predicts that the apparent absorption coefficient measured on a biological organ is a volume-weighted sum of the absorption coefficients of different absorbing components. We present some apparent absorption coefficients measured in vivo in animals and humans and discuss improved algorithms that calculate the hemoglobin saturation by including background-tissue absorption and blood vessel distribution.

Near-IR molar absorption coefficient for the OH-stretching mode of cis-9-octadecenoic acid and dissociation of the acid dimers in the pure liquid state

The molar absorption coefficient, IµOH, at 1445 nm for the stretching mode of the unbonded OH in the carboxy group of cis-9-octadecenoic acid has been successfully determined by examination and correlation of both the absorbance at 1445 nm for a dilute CCl4 solution of the acid and the degree of dissociation, αo, of the dimeric acid into free molecules in solution. αo was obtained from the ratio of the original concentration of the acid to its apparent concentration measured on a molecular weight apparatus. Even in dilute solutions ranging in concentration from 5 × 10–3 to 2.6 × 10–2 mol dm–3, αo fell within the range 0.35–0.22 at 50 °C, implying that the dissociation of the acid dimers into the monomeric species is not complete. Combination of the IµOH and the apparent molar absorption coefficient of the OH-vibration mode for the monomeric cis-9-octadecenoic acid in the pure liquid state gave the degree of dissociation, α, of the acid dimer into its monomers in the pure liquid phase as a function of temperature, T. Dissociation of the acid dimer occurs even at room temperature and increases with temperature. The α–T relationship has two break points at 30 and 55 °C. The break-point temperatures correspond to the transition temperatures in the liquid structures of cis-9-octadecenoic acid. At 30 °C the quasi-smectic liquid crystal changes to a more disordered liquid crystal, while at 55 °C the disordered liquid crystal is converted into an isotropic liquid. In addition, thermodynamic properties such as the standard enthalpy and entropy for the dissociation of the cis-9-octadecenoic acid dimer into its monomeric species also suggest that the clusters with the quasi-smectic liquid-crystal structure exist in the pure liquid state below 30 °C and the isotropic liquid structure exists above 55 °C.

Novel approaches to the estimation of intake and bioavailability of radiocaesium in ruminants grazing forested areas.

It is difficult to measure transfer of radiocaesium to the tissues of forest ruminants because they can potentially ingest a wide range of plant types. Measurements on undomesticated forest ruminants incur further difficulties. Existing techniques of estimating radiocaesium intake are imprecise when applied to forest systems. New approaches to measure this parameter are discussed. Two methods of intake estimation are described and evaluated. In the first method, radiocaesium intake is estimated from the radiocaesium activity concentrations of plants, combined with estimates of dry-matter (DM) intake and plant species composition of the diet, using plant and orally-dosed hydrocarbons (n-alkanes) as markers. The second approach estimates the total radiocaesium intake of an animal from the rate of excretion of radiocaesium in the faeces and an assumed value for the apparent absorption coefficient. Estimates of radiocaesium intake, using these approaches, in lactating goats and adult sheep were used to calculate transfer coefficients for milk and muscle; these compared favourably with transfer coefficients previously obtained under controlled experimental conditions. Potential variations in bioavailability of dietary radiocaesium sources to forest ruminants have rarely been considered. Approaches that can be used to describe bioavailability, including the true absorption coefficient and in vitro extractability, are outlined.

Novel approaches to the estimation of intake and bioavailability of radiocaesium in ruminants grazing forested areas

It is difficult to measure transfer of radiocaesium to the tissues of forest ruminants because they can potentially ingest a wide range of plant types. Measurements on undomesticated forest ruminants incur further difficulties. Existing techniques of estimating radiocaesium intake are imprecise when applied to forest systems. New approaches to measure this parameter are discussed. Two methods of intake estimation are described and evaluated. In the first method, radiocaesium intake is estimated from the radiocaesium activity concentrations of plants, combined with estimates of dry-matter (DM) intake and plant species composition of the diet, using plant and orally-dosed hydrocarbons (n-alkanes) as markers. The second approach estimates the total radiocaesium intake of an animal from the rate of excretion of radiocaesium in the faeces and an assumed value for the apparent absorption coefficient. Estimates of radiocaesium intake, using these approaches, in lactating goats and adult sheep were used to calculate transfer coefficients for milk and muscle; these compared favourably with transfer coefficients previously obtained under controlled experimental conditions. Potential variations in bioavailability of dietary radiocaesium sources to forest ruminants have rarely been considered. Approaches that can be used to describe bioavailability, including the true absorption coefficient and in vitro extractability, are outlined.

Stimulation of growth by intravenous injection of copper in weanling pigs

This study was conducted to examine whether Cu could exert its growth-promoting effect when injected, rather than being fed, and thus bypass the gastrointestinal tract. In two 18-d experiments, pigs were injected every 2 d with a Cu histidinate or histidine solution. Amounts of Cu injected were calculated to simulate varying absorption rates in pigs fed 250 ppm of dietary Cu. In Exp. 1, 44 pigs were randomly assigned to four groups of 11 pigs each. Pigs were injected with four levels of Cu histidinate (0, 5, 10, and 15% estimated apparent absorption coefficients based on calculated feed intake). Average daily gain responded quadratically (P < .05) to levels of Cu histidinate; maximum growth was seen in the 5% group. At d 6, serum mitogenic activity also exhibited a similar quadratic response (P < .05). In Exp. 2, estimated Cu absorptions of 0, 2, 4, 6, and 8% were tested. Forty-five pigs were randomly assigned to five groups of nine pigs each and injected as in Exp. 1. Both ADG and serum mitogenic activity displayed a quadratic response (P < .05); the maximum response was seen in the 4% group. Liver Cu content, superoxide dismutase activity, and serum Cu concentrations were linearly increased (P < .05) with increasing dosage of Cu in both Exp. 1 and 2. Also, brain Cu content linearly increased (P < .05) with increasing dosage of Cu in both Exp. 1 and 2. Also, brain Cu hormone mRNA concentrations in Exp. 2 were not significantly influenced by treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal protein absorption in malnourished mice with acute schistosomiasis mansoni.

Intestinal protein absorption was studied in undernourished albino Swiss mice with acute schistosomiasis mansoni. Undernutrition was induced by feeding mice with the Regional Basic Diet (RBD) ingested by human populations in Northeast Brazil, an experimental model previously developed in our laboratory. Weaning mice were infected with 40 cercariae and compared to undernourished non-infected mice and/or to infected mice fed a balanced control diet. Apparent and True Protein Absorption Coefficients were determined by nitrogen balance during five consecutive days ending at the 63rd day of the trial (acute phase of murine schistosomiasis). Fecal metabolic nitrogen (FMN) was determined after administration of a non-protein diet and was also calculated through linear regression. Our results showed a reduced protein absorption in non-infected RBD-fed mice as compared to mice fed a casein control diet. Infection with Schistosoma mansoni had apparently no effect on intestinal protein absorption in well-nourished mice. However, infection seemed to interfere with protein absorption in under-nourished animals, since the lowest absorption ratios have been detected among RBD-fed infected mice. A brief discussion is made on the advantages of using the method of linear regression for the determination of FMN.

Effect of grain boundary states on CPM spectra of hydrogenated nanocrystalline silicon

The aim of the work is to study the mechanism of optical transitions and transport in nc-Si:H by the Constant Photocurrent Method (CPM). As the crystalline fraction Xc increases an apparent absorption coefficient at 1.2 eV (αref) as high as 5×102 cm−1 and an Urbach energy of 200 meV can be obtained from CPM spectra. The values have no direct relation to the defect density as in amorphous silicon. These results are explained in terms of a different opto-electronic transport mechanism in nc-Si:H.

Characterization of interface properties in a-Si:H/a-Si x C1−x:H multilayers by the constant photocurrent method

Abstract In this work the constant photocurrent method (CPM) has been extended to characterize the interface properties of a-Si:H/a-Si x C1−x :H multilayers. The experimental results show that the interface defect density (N di) and the width of the interface region (l) strongly affect the apparent Urbach energy (Ecpm u) and the apparent defect absorption coefficient (α cpm d ) of CPM spectra in multilayers. Based on the assumption that the defect density decreases exponentially away from the interfaces, the CPM spectra of the multilayers have been analytically described. The calculated results show that the CPM spectra do not follow the absorption coefficient spectra in the multilayers, which is different from the case of a-Si: H bulk material. CPM spectra not only depend on N di , but also strongly on l, in contrast to the absorption coefficient spectra. The parameters l and N di can be obtained by fitting the measured CPM spectra to our theoretical expression. With this method it is found that, as the ...

Influence of halogenation and aggregation on photosensitizing properties of zinc phthalocyanine (ZnPC)

The effects of halogenation and aggregation on photosensitizing properties of zinc phthalocyanine (ZnPC) have been examined by photophysical methods. Halogenation decreases the fluorescence yield and lifetime, increases triplet formation and shortens the triplet lifetime. These effects, which increase in the order Cl < Br < l, can be explained in terms of spin–orbit coupling theory. The aggregation behaviour for halogenated ZnPC in dimethyl sulfoxide (DMSO) was observed by absorption spectroscopy. Assuming that no higher aggregates than dimers are formed, dimerization equilibrium constants were calculated using a modified non-linear least-squares fitting method. Quantitative analysis for the influence of dimerization on apparent molar absorption coefficient, fluorescence quantum yield and the quantum yield of singlet oxygen generation was given. Factors that govern the photosensitized production of singlet oxygen were also discussed quantitatively in order to explain the ability of singlet oxygen production by halogenated ZnPC. The enhanced intersystem crossing process between the triplet state of sensitizer and oxygen was not affected by the nature of the halogen atom.

Absorption Measurements with an Integrating Plate Photometer Calibration and Error Analysis

In this study, the integrating plate photometer (Lin et al., 1973), used at the University of Vienna, was calibrated with nonabsorbing and absorbing test aerosols to determine the systematical errors of the technique, which can be interpreted as apparent absorption coefficients σa a. A nonlinear calibration curve was obtained from measurements with polystyrene latex particles of various sizes, which includes the scattering properties (expressed in terms of the scattering coefficient σs of the particles) and the area coverage ƒ of the filter. Application of this curve σa a/σs = 0.0398 f −0.441 to polydisperse paraffin aerosols gave satisfactory results. For the soot aerosol, σa a is < 10% of the calculated “true” absorption coefficient