Showing papers on "Absorption (electromagnetic radiation) published in 1991"
TL;DR: In this article, the ultraviolet-visible absorption spectra of colloidal particles of 52 of the metallic elements, calculated from the optical constants of the metals by means of Mie theory, are given.
Abstract: The ultraviolet–visible absorption spectra are given for 10 nm diameter colloidal particles of 52 of the metallic elements, calculated from the optical constants of the metals by means of Mie theory. For most of the elements the spectra cover the range 200–900 nm. Well resolved absorption bands are observed for colloidal Sc, Ti, V, Y, Cd, Eu, Yb, Hg and Th as well as for colloids of Cu, Ag, Au and the s-block metals. However, for the majority of the colloidal metallic elements in this size range there is only a continuous absorption in the visible range, rising to broad and poorly resolved absorption bands in the ultraviolet near 200 nm. The difference in the way that the spectra of colloidal particles of different metals change when the particle shape is varied from spherical to spheroidal is investigated systematically in the dipole approximation. This is achieved by means of contour plots of the absorbance cross-section for the particles vs. the real and imaginary parts of the dielectric function for the metals, and this method of investigation is extended also to hollow spherical particles. The results suggest that Ca, Sr, Ba, Eu, Yb, Th and possibly Sc, Ti, V and Y may merit experimental investigation as new metals for exhibiting surface-enhanced Raman scattering.
1,501 citations
TL;DR: A radiative transfer method for treating nongray gaseous absorption and thermal emission in vertically inhomogeneous multiple scattering atmospheres is described in this paper, where probability density distributions of absorption coefficient strength are derived from line-by-line calculations to construct line-By-line and band model based k distributions.
Abstract: A radiative transfer method for treating nongray gaseous absorption and thermal emission in vertically inhomogeneous multiple scattering atmospheres is described. Probability density distributions of absorption coefficient strength are derived from line-by-line calculations to construct line-by-line and band model based k distributions. The monotonic ordering of absorption coefficient strengths in these k distributions implicitly preserves the monochromatic structure of the atmosphere at different pressure levels, thus simulating monochromatic spectral integration at a fraction of the line-by-line computing cost. The k distribution approach also permits accurate modeling of overlapping absorption by different atmospheric gases and accurate treatment of nongray absorption in multiple scattering media. It is shown that the correlated k distribution method is capable of achieving numerical accuracy to within 1 percent of cooling rates obtained with line-by-line calculations throughout the troposphere and most of the stratosphere.
1,020 citations
TL;DR: The apparent optical depth (OOP) method as mentioned in this paper is a procedure for analyzing the absorption lines of an ionized gas toward HD 64760, where the absorption-line data are directly converted into a form that provides direct scientific interpretations of the physical conditions in the interstellar absorbing medium as a function of velocity.
Abstract: Attention is given to the apparent optical depth method, a procedure for analyzing interstellar absorption lines. Observed absorption-line profiles are converted into profiles of apparent optical depth, and apparent column density per unit velocity. By comparing the latter for a given interstellar species having two or more absorption lines which differ in the product, the presence or absence of unresolved saturated structure in the profiles can be directly inferred. The method is illustrated using absorption-line data from the IUE satellite for the highly ionized gas toward HD 64760. Additional illustrations and a study of the method's accuracy are provided through a series of numerical simulations of multicomponent interstellar absorption situations. The method is compared to the standard growth curve method for deriving interstellar column densities. The principal value of the apparent optical depth method is that the absorption-line data are directly converted into a form that provides for direct scientific interpretations of the physical conditions in the interstellar absorbing medium as a function of velocity.
775 citations
TL;DR: In this paper, the Eddington approximation is used to model the transfer of radiation within a multiphase scattering medium, and an estimate is derived for the fraction of H Ly-alpha photons that escape from a galaxy with a two-phase interstellar medium in which dusty gas clouds lie embedded within an intercloud medium of negligible absorption and scattering coefficients.
Abstract: The Eddington approximation is used to model the transfer of radiation within a multiphase scattering medium. An estimate is thereby derived for the fraction of H Ly-alpha photons that escape from a galaxy with a two-phase interstellar medium in which dusty gas clouds lie embedded within an intercloud medium of negligible absorption and scattering coefficients. Under suitable conditions, Ly-alpha photons may actually suffer less attenuation than radiation which is not resonantly scattered, due to the fact that such photons spend most of their time in the intercloud medium as they bounce their way from one interstellar cloud surface to the next. This effect may lead to an enhancement in the observed line-to-continuum ratio, and to a Ly-alpha line profile which may be considerably narrower than that which would emerge from uniform medium of the same total atomic column density. 21 refs.
360 citations
TL;DR: Measurements of the phase and modulation of amplitudemodulated light diffusely reflected by turbid media can be used to deduce absorption and scattering coefficients.
Abstract: Measurements of the phase and modulation of amplitude-modulated light diffusely reflected by turbid media can be used to deduce absorption and scattering coefficients.
280 citations
TL;DR: It is shown that dc-electric-field coupling of the 2 {ital s} and 2{ital p} states in atomic hydrogen leads to resonantly enhanced second-order susceptibility with reduced absorption at the second-harmonic wavelength, and exact phase matching at the center of the Stark-split components.
Abstract: We show that dc-electric-field coupling of the 2s and 2p states in atomic hydrogen leads to resonantly enhanced second-order susceptibility with reduced absorption at the second-harmonic wavelength, and exact phase matching at the center of the Stark-split components.
243 citations
TL;DR: In this article, an extensive biological and optical data set was collected during a 4 month cruise as part of the Research on Antarctic Coastal Ecosystem Rates (RACER) program conducted in coastal waters of the Antarctic Peninsula and adjacent open ocean waters of Drake Passage.
240 citations
TL;DR: In this article, the authors used a Gaussian shape to represent the absorption spectra of individual photosynthetic components and used the results to reconstruct the in vivo absorption spectrum of a multi-species sample.
Abstract: Absorption spectra of several phytoplankton species were decomposed, after correction for the particle effect, to estimate in vivo absorption properties of the major light-harvesting pigments in algae. A Gaussian shape is suitable, theoretically and empirically, to represent the absorption spectra of individual photosynthetic components. The Gaussian parameters agreed well with the expected pigment compositions of 3 groups of algae, and the peak heights were linearly correlated with the concentrations of any one of the 4 major pigments measured in the samples. The linear relationship did not vary with phytoplankton species. We present here the first estimates of the 'true' in vivo specific absorption coefficients of 4 major pigments, after correction for particle effect. The results are used to reconstruct the in vivo absorption spectrum of a multi-species sample.
229 citations
TL;DR: In this paper, an end-column conductivity detector is described, where a sensing electrode is placed in the outlet end of a capillary that has a hole in its side wall through which electrolyte moves past the sensing electrode into a reservoir that contains the ground electrode.
Abstract: An end-column conductivity detector is described. A sensing electrode is placed in the outlet end of a capillary that has a hole in its side wall through which electrolyte moves past the sensing electrode into a reservoir that contains the ground electrode. This structure is simple to construct, has almost no dead volume, and minimizes electrolyte contact with adhesives used to mount the sensing electrode. The end-column conductivity detector is operated in conjunction with a commercial capillary zone electrophoresis system that has a capillary cartridge and a UV absorption detector. This design thus permits sequential measurement of the absorption and conductivity characteristics of separated analyte zones. When a species can be detected by both conductivity and UV absorption, then the absorption coefficient can be determined from the relation between the conductivity signal and the concentration of the species.
219 citations
TL;DR: The performance of thermally distorted interferometers is treated quantitatively, and the two schemes for increasing the optical path, the delay-line and Fabry-P\'erot methods, are compared.
Abstract: The ultimate sensitivity of interferometric gravitational-wave detectors requires extremely high light powers sensing the separation of test masses. Absorption of light at the optical components causes wave-front distortions via the thermally deformed substrates or via thermal lensing. The performance of thermally distorted interferometers is treated quantitatively, and the two schemes for increasing the optical path, the delay-line and Fabry-P\'erot methods, are compared.
215 citations
TL;DR: The data do not support the water equivalence of solid water at 125I energies indicating that solid-water measurements underestimate 125I specific dose-rate constants in water by 4.3%.
Abstract: Recent theoretical and experimental work indicates that currently accepted 125I dosimetry data may overestimate dose in water at 1 cm by 10%-24%. Among the most comprehensive measurements are those of the NCI-sponsored brachytherapy contract participants. Absolute dose rates in water calculated by the Monte Carlo method have been compared with the NCI dose measurements about 125I and 192Ir seeds embedded in solid-water phantoms. The photon transport code allows realistic geometric simulation of the complex internal seed structure, the National Institute of Standards and Technology air-kerma strength standardization geometry, and the dose measurement setup. When the appropriate measurement medium and geometry are assumed, agreement between theory and measurement is excellent, within 3% at 1 cm and averaging 3% at larger distances. However, the data do not support the water equivalence of solid water at 125I energies indicating that solid-water measurements underestimate 125I specific dose-rate constants in water by 4.3%. Because of its higher ratio of absorption to scatter, 125I dose distributions measured in solid water are less penetrating (by 35% at 10 cm) than those measured in liquid water. For model 6711, model 6702, and steel-clad 192Ir seeds, Monte Carlo calculations yielded specific dose-rate constants (assuming liquid water medium) of 0.877, 0.932, and 1.122 cGy cm2 h-1 per unit air-kerma strength, respectively. For 125I, currently accepted values are 18% and 11% larger for the two seed models.
TL;DR: Metal-insulator-semiconductor structures with poly (3-hexyl thienylene) as the active semiconductor are fabricated and the strong confinement deduced for the polaron is contrasted with the weak confinement observed for bipolarons.
Abstract: We have fabricated metal-insulator-semiconductor structures with poly(3-hexyl thienylene) as the active semiconductor. Optical-absorption bands due to injected carriers seen near 0.4, 1.80, and 2.16 eV are assigned to the optical transitions of the singly charged polaron, which is expected to be the thermodynamically favored excitation under these experimental conditions. Additional absorption bands at 0.5 and 1.18 eV are assigned to optical transitions of doubly charged bipolarons. We contrast the strong confinement deduced for the polaron (gap states separated by 1.80 eV) with the weak confinement observed for bipolarons (gap states separated by 0.7 eV).
TL;DR: In this paper, the authors presented visible transient absorption spectra of C{sub 60} in solution for time delays of 15 ps to 30 ns following the excitation of the ground-state molecule.
Abstract: Visible transient absorption spectra of C{sub 60} in solution are presented for time delays of 15 ps to 30 ns following the excitation of the ground-state molecule. These spectra demonstrate the presence of a hitherto unreported strong absorption feature in the triplet spectrum peaking near 740 nm. Kinetics measurements near the peak of this absorption band yield a singlet state lifetime of 650 {plus minus} 100 ps.
TL;DR: In this article, the far infrared spectrum of liquid water at room temperature is calculated by molecular dynamics simulation over the spectral range 0.5-1000 cm−1, provided that the dipole induced dipole mechanism is conveniently implemented in the calculation and the classical profile corrected for quantum effects.
Abstract: The far infrared spectrum of liquid water at room temperature is calculated by molecular dynamics simulation over the spectral range 0.5–1000 cm−1. It is shown that the experimental absorption intensity can be reproduced satisfactorily provided that the dipole induced dipole mechanism is conveniently implemented in the calculation and the classical profile corrected for quantum effects. The contribution due to exchange overlap dipoles between O and H atoms is also investigated but its role in the genesis of the far infrared (FIR) spectrum is negligible. Although the dipole induced dipole (DID) mechanism is found to be responsible for the peculiar band shape near 200 cm−1 by revealing the intermolecular oscillations of the hydrogen bond network, no other translational band is detected in the region 10–60 cm−1, a result in contradistinction with data put forward recently. Moreover, it is shown that the absorption spectrum is the seat of various cancellation effects between permanent and induced dipoles, eff...
TL;DR: In this paper, a linear combination of high-resolution photoemission and soft X-ray absorption spectroscopies was used to fit the electronic structure near the Fermi energy in the superconducting copper oxide compounds to constrain the possible mechanisms of superconductivity.
Abstract: HIGH-resolution photoemission and soft X-ray absorption spectroscopies have provided valuable information on the electronic structure near the Fermi energy in the superconducting copper oxide compounds1–4, helping to constrain the possible mechanisms of superconductivity. Here we describe the application of these techniques to KxC60, found recently to be superconducting below 19.3 K for x ≈ 3 (refs 5–7). The photoemission and absorption spectra as a function of x can be fitted by a linear combination of data from just three phases, C60, K3C60 and K6C60 indicating that there is phase separation in our samples. The photoemission spectra clearly show a well defined Fermi edge in the K3C60 phase with a density of states of 5.2 x 10-3 electrons eV-1 A-3 and an occupied-band width of 1.2 eV, suggesting that this phase may be a weakly coupled BCS-like (conventional) superconductor. The Cls absorption spectra show large non-rigid-band shifts between the three phases with half and complete filling, in the K3C60 and K6C60 phases respectively, of the conduction band formed from the lowest unoccupied molecular orbital of C60. These observations clearly demonstrate that the conduction band has C 2p character. The non-rigid-band shift coupled with the anomalous occupied-band width implies that there is significant mixing of the electronic states of K and C60 in the superconducting phase.
TL;DR: In this article, a discussion of how the fundamental optical interaction coefficients of tissue may be measured is presented, both direct and indirect methods, in which the coefficients are inferred from measurements on bulk samples are described.
Abstract: This paper is the second of two reviewing the propagation of electromagnetic radiation of wavelength 0.25–10μm in tissue. This part begins with a discussion of how the fundamental optical interaction coefficients of tissue may be measured. Both direct methods, in which the coefficients are measured for optically thin samples, and indirect methods, in which the coefficients are inferred from measurements on bulk samples are described. The difficulties inherent in both types of measurement are outlined. Next the wavelength dependence of the scattering and absorption coefficient is discussed, both from a heuristic point of view and by illustration from current literature. We illustrate how the optical spectrum can be divided into regions where the propagation of light is dominated by absorption or scattering effects. Finally we show how the distribution of light fluence in these spectral regions is dramatically different and illustrate the important features of these distributions.
TL;DR: In this article, the diffusion and absorption coefficients of microwave radiation in random mixtures of metallic and dielectric spheres are determined from measurements of the intensity correlation function with frequency shift and of the scale dependence of transmission.
Abstract: The diffusion and absorption coefficients of microwave radiation in random mixtures of metallic and dielectric spheres are determined from measurements of the intensity correlation function with frequency shift and of the scale dependence of transmission. We find a narrow window of localization in frequency and metallic concentration. The transition is rounded by the presence of absorption.
TL;DR: In this article, six different sandstone units were studied to investigate and quantify the relationship between their mechanical properties (compressive strength, tensile strength, Young's modulus, Poisson's ratio), petrographic characteristics, and engineering index properties.
Abstract: Six different sandstone units were studied to investigate and quantify the relationship between their mechanical properties (compressive strength, tensile strength, Young's modulus, Poisson's ratio), petrographic characteristics, and engineering index properties. Sandstones investigated included the Sharon sandstone, the Juniata sandstone, the Morgantown-Grafton sandstone, and three Berea sandstone units. These sandstones were tested for percent absorption, density, slake durability, total pore volume, uniaxial compressive strength, tensile strength, Young's modulus, and Poisson's ratio. Petrographic characteristics studied included grain size, grain shape, grain sorting, packing density, packing proximity, degree of grain interlocking, and mineral composition. The data were analyzed statistically to determine the quantitative relationships between various properties.
Results indicate that compressive strength, tensile strength, and Young's modulus values for the sandstones studied are closely related (r>0.7) to their density, percent absorption, total pore volume, and type of grain-to-grain contacts. Generally, sandstones with higher densities, lower percent absorption, lower total pore volume, and higher percentage of sutured contacts exhibited higher values of compressive strength, tensile strength, and Young's modulus. For Poisson's ratio, however, inverse relationships were observed with compressive strength and Young's modulus. Based on these results, equations were developed for predicting mechanical properties from values of density, percent absorption, total pore volume, and percent sutured contacts.
TL;DR: In this paper, a model for the thermal structure of Titan's upper atmosphere, between 0.1 mbar and 0.01 nbar, is presented, which predicts a well-developed mesopause with a temperature of 135-140 K at an altitude of approximately 600 km and pressure of about 0. 1 microbar.
Abstract: Models for the thermal structure of Titan's upper atmosphere, between 0.1 mbar and 0.01 nbar are presented. The calculations include non-LTE heating/cooling in the rotation-vibration bands of CH4, C2H2, and C2H6, absorption of solar IR radiation in the near-IR bands of CH4 and subsequent cascading to the nu-4 band of CH4, absorption of solar EUV and UV radiation, thermal conduction and cooling by HCN rotational lines. Unlike earlier models, the calculated exospheric temperature agrees well with observations, because of the importance of HCN cooling. The calculations predict a well-developed mesopause with a temperature of 135-140 K at an altitude of approximately 600 km and pressure of about 0.1 microbar. The mesopause is at a higher pressure than predicted by earlier calculations because non-LTE radiative transfer in the rotation-vibration bands of CH4, C2H2, and C2H6 is treated in an accurate manner. The accuracy of the LTE approximation for source functions and heating rates is discussed.
TL;DR: In this article, measurements of the absorption of X-rays by 1 to 2 transitions in Al XII through Al VIII have been made in a laser-heated slab plasma at the measured temperature and density of 58 ^ 4e V and 0.020 g cm~3.
Abstract: Measurements of the opacity of aluminum in a well characterized, hot, dense, laser produced plasma are reported. Measurements of the absorption of X-rays by 1 to 2 transitions in Al XII through Al VIII have been made in a laser-heated slab plasma at the measured temperature and density of 58 ^ 4e V and 0.020 ^ 0.007 g cm~3. Separate measurements of the temperature and density were made. The con- ditions in the plasma were determined to be reproducible, spatially uniform, and in nearly complete local thermodynamic equilibrium. The absorption spectra and the temperature-density data obtained provide an improved means for comparison with detailed atomic physics and opacity calculations. Subject headings: atomic datamethods: laboratoryplasmasX-rays: general
TL;DR: Temporal analyses of the transmittance have illustrated that the differences in the optical density among the slabs having different absorption coefficients with the same scattering coefficient vary linearly with time, thus verifying the microscopic Beer-Lambert law in highly scattering media when temporally resolved measurement is used.
Abstract: To analyze the fundamental characteristics of light transmitted through living tissues, we used the Monte Carlo method to trace the paths of the rays incident upon slabs of particles. The slabs contained either (i) two types of scattering particles in a solution or (ii) one type of particle with pigment added to the solution. Temporal analyses of the transmittance have illustrated that the differences in the optical density among the slabs having different absorption coefficients with the same scattering coefficient vary linearly with time. Also, their gradients have been shown to be proportional to the differences in the absorption coefficients, thus verifying the microscopic Beer-Lambert law in highly scattering media when temporally resolved measurement is used.
TL;DR: In this paper, the absolute molar extinction coefficients of benzene in jets have been determined by scaling measured free jet values to the known value in the vapor phase for a broadband at 200.1 nm in the S2 state.
Abstract: The direct absorption spectrum of benzene in a free jet has been measured in the 130–260 nm region (S1, S2, and S3 states, Rydberg series, and the first ionization limit) using synchrotron radiation as a light source. The absolute molar extinction coefficients (e) of benzene in jets have been determined by scaling measured free‐jet values to the known value in the vapor phase for a broadband at 200.1 nm in the S2 state. The vibrational temperature for ν16 mode was estimated to be 185 K. The maximum value of e of the S1 absorption system was found to be 1400 l mol−1 cm−1 (spectral bandwidth=0.065 nm). A shoulder observed at 205.45 nm in the S2 absorption system is assigned to the S2 origin, induced by pseudo‐Jahn–Teller distortion.
TL;DR: In this article, the authors used the absorption density, measured using conventional absorption tomography, to remove absorption effects and compared the resulting corrected reconstructions with the reconstructions degraded by attenuation efforts.
Abstract: The distributions of individual trace elements within a sample can be found using fluorescent computed tomography (FCT). The absorption of incident and fluorescent X-rays results in degraded reconstructions of the distributions. The proposed method uses the absorption density, measured using conventional absorption tomography, to remove absorption effects. A model for FCT with absorption is developed and simulated. The resulting corrected reconstructions are compared to the reconstructions degraded by attenuation efforts. A comparison is made with other methods which utilize knowledge of the sample composition and a standard source to estimate the absorption coefficients used to correct for attenuation effects. >
TL;DR: In this article, a method to separate scattering attenuation and intrinsic absorption from total attenuation is proposed for a case where scattering is isotropic and the random distribution of scatterers and that of absorbers are uniform.
Abstract: Seismic wave attenuation is caused by two major factors, scattering attenuation and intrinsic absorption. A method to separate these two factors from total attenuation is proposed for a case where scattering is isotropic and the random distribution of scatterers and that of absorbers are uniform. The seismic waves recorded at a station from an earthquake can be divided into three portions: a direct wave plus an earlier part of coda waves, a middle part of coda waves and a later part of coda waves. The latter two portions are composed of scattered waves only. The time integral of energy density of each portion is numerically simulated based on the Monte-Carlo method, and is plotted against hypocentral distance. The curves of integrated energy are very sensitive to the seismic albedo which is the ratio of scattering loss to the total attenuation. We offer a set of curves of the integrated energy vs. hypocentral distance for different values of the seismic albedos and different strengths of total attenuation. These curves make it possible to evaluate separately the scattering strength and intrinsic absorption by comparison of the time integrals of actually observed band-pass filtered seismogram's power with the simulated curves.
TL;DR: In this article, the vibrational dynamics of excited CO layers on Pt(111) were studied using infrared (IR) pump-probe methods, with time resolution < 1 ps and monochromator resolution <1 cm−1.
Abstract: The vibrational dynamics of excited CO layers on Pt(111) were studied using infrared (IR) pump–probe methods. Resonant IR pulses of 0.7 ps duration strongly pumped the absorption line (ν≊2106 cm−1 ) of top‐site CO. Weak probe pulses delayed a time tD after the pump were reflected from the CO‐covered Pt(111) surface, and dispersed in a monochromator to determine the absorption spectrum of the vibrationally excited CO band, with time resolution <1 ps and monochromator resolution <1 cm−1. Transient spectra were obtained as a function of CO coverage, surface temperature, and laser fluence. Complex spectra for tD<0 show features characteristic of a perturbed free induction decay, which are expected based on multiple‐level density‐matrix models. For tD≥0, the CO/Pt absorption exhibits a shift to lower frequency and an asymmetric broadening which are strongly dependent on fluence (1.3–15 mJ/cm2 ). Spectra return to equilibrium (unexcited) values within a few picoseconds. These transient spectral shifts and the t...
TL;DR: The application of dry purple membrane films for nonlinear-optical filtering is described and a model describing the nonlinear transmission of PM films containing the wild-type form of BR or one of its mutated variants, e.g., BR(D96N), and examples of their application in spatial filtering are presented.
Abstract: The application of dry purple membrane films for nonlinear-optical filtering is described. The biological photo-chrome bacteriorhodopsin (BR) is contained in the purple membrane (PM) from Halobacterium halobium. BR has two dominant photoactive states, B and M, which have well-separated absorption bands with maxima at 570 nm (B) and 412 nm (M). Since the local transmission of a PM film depends on the ratio between the forward (B → M) and the backward (M → B) photoreactions, PM films can be used as light-controlled absorptive spatial light modulators. A model describing the nonlinear transmission of PM films containing the wild-type form of BR or one of its mutated variants, e.g., BRD96N, and examples of their application in spatial filtering, e.g., edge enhancement, are presented.
TL;DR: In this article, a review of the radiative recombination processes occurring in semiconductor quantum wells and superlattices under different excitation conditions is presented, including luminescence induced by multiphoton absorption, exciton and biexciton radiative decay, and electron-hole plasma recombination.
Abstract: In this paper we review the radiative recombination processes occurring in semiconductor quantum wells and superlattices under different excitation conditions. We consider processes whose radiative efficiency depends on the photogenerated density of elementary excitations and on the frequency of the exciting field, including luminescence induced by multiphoton absorption, exciton and biexciton radiative decay, luminescence arising from inelastic excitonic scattering, and electron-hole plasma recombination. Semiconductor quantum wells are ideal systems for the investigation of radiative recombination processes at different carrier densities owing to the peculiar wavefunction confinement which enhances the optical non-linearities and the bistable behaviour of the crystal. Radiative recombination processes induced by multi-photon absorption processes can be studied by exciting the crystal in the transparency region under an intense photon flux. The application of this non-linear spectroscopy gives d...
TL;DR: An infrared-transmitting chalcogenide fiber was used as an optical probe to analyze qualitatively and quantitatively various chemical substances in aqueous solutions and demonstrated that the same sensor design is capable of monitoring gaseous species such as dichlorodifluoromethane.
Abstract: An infrared-transmitting chalcogenide fiber was used as an optical probe to analyze qualitatively and quantitatively various chemical substances in aqueous solutions. An unclad fiber with 380-microm diameter was combined with a Fourier transform infrared spectrometer to monitor the concentration of the analytes in solutions by measuring the changes in the absorbance of their fundamental vibration peaks. A linear relationship was observed between the absorption by the vanescent field and concentrations of various analytes. For this study low concentrations of acetone, ethyl alcohol, and sulfuric acid were detected in aqueous solutions. The minimum detection limit for these three chemical substances was 5, 3, and 2 vol. %, respectively, with a sensor length of 15 cm. It was also demonstrated that the same sensor design is capable of monitoring gaseous species such as dichlorodifluoromethane.
TL;DR: The effects of steady state nitrogen limitation on the optical properties of Dunalielh tertiolecta were investigated in this article, where growth rate was varied in a continuous culture under constant irradiance and temperature with absorption, fluorescence and cellular characteristics including pigment contents determined at each steady state.
Abstract: The effects of steady state nitrogen limitation on the optical properties of Dunalielh tertiolecta were investigated. Growth rate was varied in a continuous culture under constant irradiance and temperature with absorption, fluorescence, and cellular characteristics including pigment contents determined at each steady state. The cellular concentration of Chl a increased with growth rate while Chl-a-specific absorption and fluorescence both decreased. In addition, the quantum yield for growth varied by more than a factor of 3.5 over the growth conditions examined, with the highest yield in the most rapidly growing cells. The decrease in magnitude of Chl-a-specific optical properties is caused by pigment package effects and changes in the abundance of accessory pigments relative to Chl a. Changes in absorption and fluorescence properties are consistent with theoretical predictions for discrete packages. In addition, pigment-based reconstruction techniques overestimate the magnitude ofboth in vivo and unpackaged absorption by D. tertiolecta under these growth conditions. The observed variability in Chl-a-specific absorption and quantum yield is a fundamental aspect of phytoplankton physiology that should be incorporated into models of oceanic primary production.