Intermediate Absorbing Research Articles

Effects of Epidermal Cell Shape and Pigmentation on Optical Properties of Antirrhinum Petals at Visible and Ultraviolet Wavelengths.

We used the Mixta+ and mixta- lines of Antirrhinum majus as a model system to investigate the effects of epidermal cell shape and pigmentation on tissue optical properties in the visible and ultraviolet (UV) spectral regions. Adaxial epidermal cells of Mixta+ flowers have a conical-papillate shape; in the mixta- line the cells are slightly domed. Mixta+ cells contained significantly more anthocyanin and other flavonoids than mixta- cells when plants were grown under either high- or low-UV conditions. Mixta+ cells focused light (3.5-4.7 times incident) within their pigmented interiors, whereas mixta- cells focused light (2.1-2.7 times incident) in the unpigmented mesophyll. UV light penetrated the epidermis (commonly 20-50% transmittance at 312 nm) mainly through the unpigmented peripheral regions of the cells that were similar for the two lines, so that overall penetration through Mixta+ and mixta- epidermises was equal. However, maximum UV absorption in the central region of epidermal cells was slightly greater in Mixta+ than mixta-, and intact Mixta+ flowers reflected less light in the spectral regions with intermediate flavonoid absorbance. In both cases, about 50 to 75% of the difference could be attributed to cell shape and resulting changes in the optical pathlength or focusing.

High spectral resolution solar radiative transfer in absorbing and scattering media: Application to the satellite simulation

In the shortwave and for a scattering medium, the “exact” radiance can be calculated by solving the radiative transfer equation for each frequency using a line-by-line absorption model. In practice, however, this technique requires exhaustive amounts of computer time. This article describes a fast, accurate method for approximating radiances at the same spectral resolution as satellite observations and for an absorbing and scattering atmosphere that is vertically heterogeneous. In the method, interactions between molecular absorption and scattering are treated using an extension of the Scaling Approximation (SA). The original SA can be applied when the absorption coefficient k v ( z) at the frequency v and the altitude z can be factored as k v ( z) = h( z) k v ( z 0). This approximation, however, is only accurate for the Lorentz line wings. For a given atmosphere, the exact radiance is calculated for the profile h( z), which represents the vertical variation of the absorption profile for the line wings and for some absorption coefficients k v ( z 0) distributed in the interval [0, + ∞[. Due to the slow spectral variation of atmospheric scattering parameters, these calculations can be considered valid for large spectral bands. In the line wings the monochromatic radiances can then be obtained through interpolation. In the more general case, the SA is modified in order to compensate for errors it introduces to the line centres and the intermediate absorbing regimes: k v(z) = h(z)k v ∗(z 0) , thus giving the Modified Scaling Approximation (MSA). The modified absorption coefficient k v ∗(z 0) is calculated by (1) defining an equivalent reflecting level for the scattering photons and (2) requiring that the absorption of the non-scattering atmosphere, defined by the equivalent reflecting level, be the same for the “exact” vertical absorption profile and the line wings profile h( z). The equivalent reflecting level is obtained from simulations performed for an intermediate absorption regime between the wings and the line centre. The approximate radiances are interpolated according to the modified absorption coefficient. The maximum error introduced to the monochromatic radiance computation, corresponding to the line centre, is less than 10% of the radiance without absorption and typically less than 1% in the wings and the intermediate regimes. Upon integrating the monochromatic radiances over the spectral interval, the maximum error is on the order of 1% for a resolution of 1 cm −1 and on the order of 0.1% above 5 cm −1.

Sensory rhodopsin I photocycle intermediate SRI 380 contains 13- cis retinal bound via an unprotonated Schiff base

Sensory rhodopsin I (SRI), the mutated derivative SRI-D76N and the complex of SRI with its transducer HtrI were overexpressed in Halobacterium salinarium and analyzed by resonance Raman spectroscopy. In the initial state SRI contains all- trans retinal bound via a protonated Schiff base as confirmed by retinal extraction which yields 95 ± 3% all- trans retinal. The photocycle intermediate absorbing maximally at 380 nm (SRI 380) contains a Schiff base linkage between the protein and 13- cis retinal. Extraction of illuminated SRI yields up to 93% 13- cis retinal. Neither the mutation D76N nor HtrI changed the vibrational pattern of the chromophore.

One-hour test for estimating intestinal absorption of calcium by using stable strontium as a marker

Intestinal absorption of calcium is a relevant marker in a broad spectrum of diseases; however, its determination in clinical practice is difficult. Our aim was to design a simple test for this based on stable strontium (88Sr). The correlation between the intestinal absorption of simultaneously administered 45Ca and 88Sr was investigated in patients with various disorders of the bone and calcium metabolism. The area under the curve for the period 0-60 min after dosing (AUC0-60 in mmol.L-1.min), being a representative measure of intestinal absorption, showed a close correlation between both elements (r = 0.90, P < 0.001). Moreover, the measure of agreement in classifying the patients as low, intermediate, or high absorbers was high (kappa = 0.80). We conclude that a test based on measuring AUC0-60 of strontium is a fast and inexpensive way to obtain reliable information about the level of intestinal calcium absorption.

Doppler shift effects on infrared band models

Band-model calculations typically are employed in the analysis of low-spectral-resolution radiometer, photometer, and spectrometer measurements of hot-gas emission and absorption. Although they are not used to compute the profiles of individual lines directly, nevertheless, band models are sensitive to line shape. This line-shape sensitivity causes the net band-model emission and absorption to be sensitive to Doppler shift effects. This paper reviews the treatment of Doppler shifts on a Voigt profile spectral line, and then generalizes this result to the curve of growth, i.e., equivalent width, for both single-line and infrared band models. Finally, a synthetic spectrum for the COi 4.3-ji band is computed with and without Doppler shifts to illustrate the magnitude of the effect. It is found that band-model computations are unaffected by Doppler shift in the limiting cases of small and large absorber amounts. In the case of intermediate absorber amounts, significant effects are predicted for hypersonic flows.

Effects of volatile anesthetics on bacteriorhodopsin in purple membrane, Halobacterium halobium cells and reconstituted vesicles

In this study, we have investigated effects of volatile anesthetics on absorption spectra, proton pumping activity and decay of photointermediate M of bacteriorhodopsin (bR) in differently aggregated states. Anesthetics used in this study are ether-type general anesthetics; enflurane and sevoflurane. The observed effects on bR depend not only on variety or concentration of anesthetics but also strongly on the aggregation state of (bR) molecules in the membrane. In purple membrane (PM), bR having maximum light absorption at 567 nm (bR 567 is formed in the presence of sevoflurane or a small amount of enflurane, while a species absorbing maximally at 480 nm (bR 480) is formed upon the addition of large amounts of enflurane. X-ray diffraction studies show that the former species maintains crystallinity of PM, but the latter does not. In reconstituted vesicles where bR molecules exist as monomer, even sevoflurane forms bR 480. Flash photolysis experiments show that bR 567 contains a shorter-lived M intermediate absorbing maximally at 412 nm in the photoreaction cycle than bR does and that bR 480 contains at least two long-lived M intermediates which seem to absorb maximally near and at lower than 380 nm. The measurements of light-induced pH changes of the whole cells and of the reconstituted vesicles in the presence of the anesthetics indicate that bR 567 has a enhanced proton pumping efficiency, while bR 480 has a quite low or no activity. No significant difference was observed in the anesthetic action between two inversely pumping vesicles. These observations suggest that on the formation of bR 480, anesthetics enter into the membrane and affect the protein-lipid interaction.

Rhodopsin in dimyristoylphosphatidylcholine-reconstituted bilayers forms metarhodopsin II and activates Gt

The photochemical intermediate metarhodopsin II (meta II; lambda max = 380 nm) is generally identified with rho*, the conformation of photolyzed rhodopsin which binds and activates the visual G-protein, Gt [Emeis, D., & Hoffman, K.P. (1981) FEBS Lett. 136, 201-207]. Purified bovine rhodopsin was incorporated into vesicles consisting of dimyristoylphosphatidylcholine (DMPC), and the rapid formation of a photochemical intermediate absorbing maximally at 380 nm was quantified via both flash photolysis and equilibrium spectral measurements. Kinetic and equilibrium spectral measurements performed above the Tm of DMPC showed that Gt, in the absence of GTP, enhances the production of the 380-nm-absorbing species while reducing the concentration of the 478-nm-absorbing species, metarhodopsin I (meta I), in a manner similar to that observed in the native rod outer segment disk membrane. This Gt-induced shift in the equilibrium concentration of photointermediates indicated that the species with an absorbance maximum at 380 nm was meta II. The presence of rho* in the DMPC bilayer was established via measurements of photolysis-induced exchange of tritiated GMPPNP, a nonhydrolyzable analogue of GTP, on Gt. Above Tm, the metarhodopsin equilibrium is strongly shifted toward meta I relative to the native rod outer segment disk membrane; however, at 37 degrees C, 40% of the photointermediates are in the form of meta II. The formation of meta II above Tm is slowed by a factor of ca. 2 relative to the disk membrane. Below Tm, the equilibrium is shifted still further toward meta I, and meta II forms ca. 7 times slower than in the disk membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

The N intermediate of bacteriorhodopsin at low temperatures: Stabilization and photoconversion

In aqueous suspensions of purple membranes (pH 10.2, 0.4 M KCl) an intermediate having an absorption maximum at 570–575 nm (at −196°C) was produced by first heating the M intermediate up to −30°C and then stabilizing it by subsequent cooling to −60°C. We suggest that this species is the intermediate N (or P or R) found and characterized earlier near room temperature. Upon illumination at −196°C N is transformed into a bathochromically absorbing species K n which has an absorption maximum near 605 nm and an extinction 1.35 times that of N. This light reaction is photoreversible. The quantum yield ratio for the forward and back reaction is 0.18 ± 0.02. The maximum photo steady state concentration of K n is about 0.24. The N intermediate was also trapped in water suspensions of purple membranes at neutral pH and low salt concentration by illumination at λ > 620 nm during cooling. In addition to N another intermediate absorbing in the red (maximum at 610–620 nm) was accumulated in smaller amounts. It is not photoactive at 196°C and apparently is the O intermediate or a photoproduct of N.

Microspectrophotometry of Phenolic Compounds in Bermudagrass Cell Walls in Relation to Rumen Microbial Digestion

The amount and location of phenolic compounds within plant cell walls are important factors in limiting forage digestibility. The present study was undertaken to evaluate phenolic compounds within plant cell wall types that differed in digestibility in leaf blades of ‘Coastal’ (CB) and ‘Coastcross‐1’ (CX) bermudagrasses [Cynodon dactylon (L.) Pers]. The ultraviolet (UV) spectra of the cell wall types in bermudagrass leaf blades were obtained by microspectrophotometry and the results related to their digestibilities (measured by microscopy after in vitro incubation in rumen fluid) and to their histochemical reactions for phenolic compounds. Cell walls of all tissues gave three absorption peaks in the ranges of 317 to 324, 285 to 293, and 244 to 254 nm. Indigestible cell walls (sclerenchyma and mestomc sheath) had high UV absorbance (ca. 1.8 at 320 nm) and had positive tests with histochemical reagents for phenolics. In contrast, totally digestible cell walls (mesophyll and phloem) had low UV absorbance (ca. 0.2 at 320 nm) and had negative or weak reactions for phenolics. Partially digestible cell walls (parenchyma bundle sheath and epidermis) had intermediate UV absorbance (ca. 0.45 at 320 nm) and were positive for phenolics with chlorine‐sulfite and diazotized sulfanilic acid reagents. Comparison of cell wall types in leaf blades of CB and the more highly digestible CX showed that corresponding tissues of the two cultivars had similar UV absorbance values, with the exception of parenchyma bundle sheath; the parenchyma bundle sheath cell walls of CX had approximately two‐thirds the UV absorbance values of those of CB and were more digestible. Hence, improved digestibility of CX leaf blades appears to result from a lower concentration of phenolic compounds within cell walls of parenchyma bundle sheaths.

An indium-free mount for GaAs substrate heating during molecular beam epitaxial growth

The substrate mounting system for a Varian GEN/II molecular beam epitaxy (MBE) system was modified to allow the growth of device quality GaAs and AlGaAs epitaxial layers on GaAs substrates without the use of indium bonding. The indium-free holders are compatible and interchangeable with the standard molybdenum blocks that use indium bonding. The wafer is heated by direct radiation from the unmodified spiral filaments with no intermediate absorbers or backside wafer coatings. A commercial pyrometer with a silicon detector was used to measure the absolute temperature. The silicon detector is sensitive to radiation from 0.8 to 1.1 μm, which is primarily above the band gap energy of GaAs at substrate temperatures above 550 °C. For photon energies above the band gap the spectral emittance of GaAs is nearly independent of the substrate doping, thickness, and temperature. With this pyrometer a maximum temperature difference of 3 °C was measured over the central two-thirds of a 2 in. diam semi-insulating GaAs wafer. In contrast, the maximum temperature difference on n+GaAs substrates was significantly larger (30 °C over the central two-thirds of the wafer) and showed the same pattern as the filament configuration. This large difference is explained by a simple model which takes into account the smaller thermal conductivity and larger total emittance of n+GaAs compared to undoped GaAs.

Interference filters for thermophotovoltaic solar energy conversion

In a thermophotovoltaic (TPV) energy converter the necessary selectivity of the radiation incident on the solar cells may be obtained with a filter. Filters consisting of a metal layer and a sequence of dielectric layers with given indices of refraction are optimized with respect to the layer thicknesses and the number of layers. No sensible improvement is obtained by increasing the number of layers to more than seven. The computed performance of a solar TPV converter equipped with a black intermediate absorber, an optimized filter and silicon solar cells is expected to be superior by a factor of 1.4 to that of direct conversion by silicon cells. A TPV converter equipped with germanium cells and an optimized filter yields even an improvement by a factor of 2.1 over direct conversion by germanium cells and an improvement by a factor of 1.8 over direct conversion by silicon cells. No further improvement is achieved by the combination of a filter and a selective emitter instead of a filter and a black emitter.

Summary Abstract: Intermediate temperature selective absorber coatings, their testings and characterization

Summary Abstract: Intermediate temperature selective absorber coatings, their testings and characterization

PHOTOTRANSFORMATION KINETICS OF UNDEGRADED OAT AND PEA PHYTOCHROME INITIATED BY LASER FLASH EXCITATION OF THE RED‐ABSORBING FORM

Abstract— Phototransformation at 2°C of the red‐absorbing form of phytochrome (Pr) to the far‐redabsorbing form (Pfr) was studied with both undegraded oat (Avena sativa L., cv. Garry) and undergraded pea Pisum sativum L., cv. Alaska) phytochrome. Phototransformation was initiated by a 15‐ns laser pulse with maximum emission near 600 nm and output power of 30 mJ. The first resolvable transformation intermediate exhibited relative to Pr a maximum absorbance increase near 700 nm and was fully present at the earliest time measured, which was 60 ns after the flash. This intermediate absorbance decayed by two reactions for oat phytochrome (half‐lives of 11 and 140 μs assuming parallel reactions) and by three for pea phytochrome (half‐lives of 14, 280 and 1600 μs assuming parallel reactions). The kinetics of the slowest reaction for pea phytochrome, however, might be somewhat distorted by an instrument artifact. The appearance of the far‐red‐absorbing phytochrome, as monitored by absorbance increase at 720 nm, occurred by at least two reactions for both oat (half‐lives of 47 and 250 ms assuming parallel reactions) and pea (half‐lives of 170 and 770 ms assuming parallel reactions) phytochrome. The possibility of slower reactions was not tested. Assays for possible proteolysis of the phytochrome samples studied here indicated that the presence of degraded phytochrome could not account for the observed multiphasic kinetics except possibly for one phase of the triphasic intermediate decay seen with pea phytochrome.

Fast stages of photoelectric processes in biological membranes. I. Bacteriorhodopsin.

Bacteriorhodopsin-containing fragments of Halobacterium halobium membrane (bacteriorhodopsin sheets) were incorporated into a lecithin-impregnated collodion film, and fast stages of flash-induced electrogenesis were measured by two electrodes separated by this film. It is found that a single turnover of bacteriorhodopsin results in an electrogenic response composed of three main stages of the following tau: the first less than 200 ns, the second 15 - 70 microseconds and the third 10 ms. The second and third phases are of the same direction as an electric response to continuous illumination, whereas the first one is oppositely directed. The microseconds and ms stages were shown to correlate, in the first approximation, with formation and decomposition of the bacteriorhodopsin intermediate absorbing with 412 nm, respectively. Both the second and third phases of the photoelectric response are sums of at least two exponents. The third stage is specifically inhibition by La3+ ions which are also shown to decrease the rate of regeneration of the original bacteriorhodopsin absorbing at 570 nm from the intermediate absorbing at 412 nm. Acidification of the medium induces parallel inhibition of the second and third phases and of formation of the intermediate absorbing at 412 nm as if protonation of a group with pK = 3.6 were responsible for this inhibition. The first (opposite) phase survives acidification. It even increases at pH lower than 1.5. At such a low pH, one can show a good correlation of decays of photopotential and of a bacteriorhodopsin bathointermediate. The decays are biphasic (tau 1 = 200 microseconds and tau 2 = 2 ms), formation of both the photopotential and the bathointermediate being faster than 200 ns. At higher pH, when a three-phase photoelectric response is revealed, decay of the formed electric potential difference gives the average tau value of about 1 s. It can be accelerated by compounds that increase ionic conductance of biomembranes. At pH below 4, fluoride is found to completely inhibit the second and third phases, so that only the first phase is observed. The results are discussed in terms of a scheme postulating that the first electrogenic phase is a result of translocation of the protonated Schiff base inside the membrane due to a light-induced conformation change in retinal or protein. The second and third phases are explained by H+ transfer from the Schiff base to the outer membrane surface and from inner (cytoplasmic) surface of membrane to the Schiff base, respectively.

Upper limit of thermophotovoltaic solar-energy conversion

The efficiency of the conversion of solar energy into electrical energy by solar cells is improved if the incident solar radiation is first absorbed by an intermediate absorber. The reemitted radiation is directed onto the solar cell. This mode of operation is known as thermophotovoltaic energy conversion. A black-body intermediate absorber is advantageous for small-bandgap solar cells. An even higher improvement is, however, achieved by a selective intermediate absorber with an absorption edge at the energy of the bandgap of the solar cell. Furthermore, if only a narrow spectral interval of radiation near the absorption edge is transmitted through a filter from the intermediate absorber to the solar cell, a maximum efficiency of 65 percent is obtained for a solar cell and absorber with a bandgap of 0.8 eV.

Reactions of DOPA (3,4-dihydroxyphenylalanine) decarboxylase with DOPA.

The study of DOPA (3,4-dihydroxyphenylalanine) decarboxylase by steady-state methods is difficult because multiple reactions occur. The reaction with DOPA was studied at enzyme concentrations between 20 and 50 micrometer by direct observation of the bound coenzyme by using stopped-flow and conventional spectrophotometry. Four processes were observed on different time scales and three of these were attributed to stages in the decarboxylation. The fourth was attributed to an accompanying transamination that renders the enzyme inactive. It was clear that much, if not all, of the 330 nm-absorbing coenzyme present in the free enzyme plays an active part in the decarboxylation, since it is converted into 420 nm-absorbing material in the first observable step. An intermediate absorbing maximally at 390 nm is formed in a slower step. Rate and equilibrium constants have been determined and the ratio of decarboxylation to transamination was estimated to be 1200:1.

Comparative study of the radiation-physical aspects of product-statical gamma-irradiation

Abstract The comparative study intends to explore different new technological possibilities, in order to increase the economical feasibility of this technique in thefield of food preservation. As an extreme, the product-statical geometry is considered. The radiation-physical calculations are carried out for a tissue-like product with a given bulk density. The effective and economiccal dose uniformity, besides the apparent and effective utilisation efficiency are defined as new concepts. It has been found that in order to obtain a technological acceptable value of distance between two semi-infinite plane sources in a two-side irradiation geometry, the 60 Co-isotope with low volume-restrictiion of the dose uniformity is to be chosen, without any intermediate absorbing element. From considerations on the efficiency follows that the optimal U ec is about (2.0) 80 or (2.5) 100 . A value of 0.32 for η eff can be reached. Starting from a limited number of dimensional parameters for a concentral hollow cylindrical geometry, it is shown that in order to have a good dose uniformity a maximal source-setting without any absorbing element is needed. The cylindrical geometry might be not so efficient as the plane geometry.