Accurate Absorption Research Articles

Algorithms for three-dimensional chemical analysis via multi-energy synchrotron X-ray tomography

The conversion of X-ray tomography images into three-dimensional chemical composition requires accurate mass absorption values, high-quality images, and a robust fitting algorithm. The least-squares fits of the images to a three-dimensional chemical composition can proceed with several different options such as minimal vs. over-determined and/or constrained parameters. This project has investigated the impact of XAFS features and a limited CCD dynamic range. These simulated results are compared to a recent experimental project in which synchrotron X-ray tomography was used to image a polymer blend, and from those images, calculated three-dimensional chemical composition maps of the two-component flame retardant, a brominated phthalimide dimer, Saytex ™ BT-93 and a synergist, antimony(III) oxide (Sb 2O 3).

Measurements of spectral parameters of water-vapour transitions near 1388 and 1345 nm for accurate simulation of high-pressure absorption spectra

Quantitative near-infrared absorption spectroscopy of water-vapour overtone and combination bands at high pressures is complicated by pressure broadening and shifting of individual lines and the blending of neighbouring transitions. An experimental and computational methodology is developed to determine accurate high-pressure absorption spectra. This case study investigates two water-vapour transitions, one near 1388 nm (7203.9 cm−1) and the other near 1345 nm (7435.6 cm−1), for potential two-line absorption measurements of temperature in the range of 400–1050 K with a pressure varying from 5–25 atm. The required quantitative spectroscopy data (line strength, collisional broadening, and pressure-induced frequency shift) of the target transitions and their neighbours (a total of four H2O vapour transitions near 1388 nm and six transitions near 1345 nm) are measured in neat H2O vapour, H2O–air and H2O–CO2 mixtures as a function of temperature (296–1000 K) at low pressures (<800 Torr). Precise values of the line strength S(T), pressure-broadening coefficients γair(T) and , and pressure-shift coefficients δair(T) and for the ten transitions were inferred from the measured spectra and compared with data from HITRAN 2004. A hybrid spectroscopic database was constructed by modifying HITRAN 2004 to incorporate these values for simulation of water-vapour-absorption spectra at high pressures. Simulations using this hybrid database are in good agreement with high pressure experiments and demonstrate that data collected at modest pressures can be used to simulate high-pressure absorption spectra.

Simplified procedure for computing the absorption of sound by the atmosphere

This paper describes a study that resulted in the development of a simplified method for calculating attenuation by atmospheric-absorption for wide-band sounds analyzed by one-third octave-band filters. The new method [referred to herein as the Volpe Method] utilizes the accurate pure-tone sound absorption algorithms of two published standards, the International Standard, Acoustics-Attenuation of Sound During Propagation Outdoors-Part 1: Calculation of the Absorption of Sound by the Atmosphere, ISO 9613-1 and, the American National Standard, for Calculation of the Absorption of Sound by the Atmosphere, ANSI S1.26-1995. The purpose of the study was to extend the useful attenuation range of the Approximate Method outlined in the ANSI document, and provide a basis for replacing the current Society of Automotive Engineers Aerospace Recommended Practice 866A, Standard Values of Atmospheric Absorption as a Function of Temperature and Humidity (SAE ARP 866A). The Volpe Method was found to be useable to mid-band absorption levels up to 500 dB with errors of less than ±0.5 dB or ±5% (of mid-band attenuation levels) to 100 dB, and ±7% to 500 dB.

Horizontal radiation transport in 3-D forest canopies at multiple spatial resolutions: Simulated impact on canopy absorption

The divergence of horizontal radiation in vegetation canopies is generally considered to be of negligible consequence to 1) algorithms designed for the physically-based interpretation of space borne observations, and 2) field campaigns aiming at the validation of derived surface products, like FAPAR and albedo. However, non-zero horizontal radiation balances are likely to occur if the internal variability of the vegetation target and the typical distances that photons may travel horizontally within such 3-D media extend to spatial scales that are similar to or larger than those of the measuring sensor. Detailed radiative transfer simulations in 3-D coniferous forest environments are presented to show how the magnitude of local net horizontal fluxes (for spatial resolutions ranging from 1 × 1 m 2 to 500 × 500 m 2 forest areas) can reach multiple times the incident solar radiation at the top-of-canopy level. Furthermore, the PDFs of these local net horizontal fluxes ( H) are skewed toward negative values (meaning that most local canopy volumes have more radiation exiting than entering via their lateral sides), in particular when the radiative regime is dominated by single-scattering interactions and geometric shading is prominent. In order to maintain the energy balance of the overall forest domain, however, local canopy volumes with rather large positive net horizontal fluxes must also exist, thus underscoring the importance of properly locating local flux measurement equipment. Irrespective of the sign of H, it is shown that the local canopy absorption ( A) falls within the A = H (perfect shadowing of the forest floor) and A = H + 1 (perfect illumination of the forest floor) domain in the red spectral band. This correlation between A and H implies that the range of local canopy absorption values is far larger than unity which reduces its potential to serve as a proxy in delivering accurate domain-averaged absorption estimates on the basis of spatially incomplete sampling schemes. Instead, it is shown that, for a spatial sampling of 1% of the forest area of interest, local absorption estimates – derived from vertical fluxes only – are sufficient for delivering domain-averaged canopy estimates that lie, on average, within 0.05 of the truth. For forest domains that are smaller than about 30 × 30 m 2, however, horizontal radiation transport will still affect the domain-averaged canopy absorption values and thus a spatially exhaustive sampling of the true local absorption may be more appropriate.

DETERMINATION OF DILTIAZEM HCI AND DOTHIEPIN HCI THROUGH COMPLEX FORMATION

Simple, sensitive and accurate spectrophotometric and atomic absorption spectrometric procedures were developed for the determination of both diltiazem and dothiepin hydrochlorides in pure forms and in pharmaceutical preparations. The first method was based on the formation of ion-pair complexes between the two drugs and tropeolin oo using extractive procedures. The complex showed absorption maxima at 477 nm. Beer's Law was obeyed in the concentration range of (4-20) and (1.6-16) µgml-1 for diltiazem and dothiepin hydrochlorides respectively. The second method was based on formation of a ternary complex between (copper (II), rose bengal and drug). This complex was extracted with methylene chloride and measured at 555 nm. Beer's Law was obeyed in concentration range (24-80) and (16-32) µgml-1 for diltiazem and dothiepin hydrochlorides, respectively. The third method depends on determination of copper content of the formed complex using atomic absorption procedure, Beer's Law was obeyed in concentration range (16-24) and (32-68) µg ml-1 for dothiepin and diltiazem hydrochlorides respectively. The proposed methods hold their accuracy and precision welt when applied to the determination of diltiazem and dothiepin in their dosage forms.

Excited state geometry optimizations by analytical energy gradient of long-range corrected time-dependent density functional theory

An analytical excitation energy gradient of long-range corrected time-dependent density functional theory (LC-TDDFT) is presented. This is based on a previous analytical TDDFT gradient formalism, which avoids solving the coupled-perturbed Kohn-Sham equation for each nuclear degree of freedom. In LC-TDDFT, exchange interactions are evaluated by combining the short-range part of a DFT exchange functional with the long-range part of the Hartree-Fock exchange integral. This LC-TDDFT gradient was first examined by calculating the excited state geometries and adiabatic excitation energies of small typical molecules and a small protonated Schiff base. As a result, we found that long-range interactions play a significant role even in valence excited states of small systems. This analytical LC-TDDFT gradient was also applied to the investigations of small twisted intramolecular charge transfer (TICT) systems. By comparing with calculated ab initio multireference perturbation theory and experimental results, we found that LC-TDDFT gave much more accurate absorption and fluorescence energies of these systems than those of conventional TDDFTs using pure and hybrid functionals. For optimized excited state geometries, LC-TDDFT provided fairly different twisting and wagging angles of these small TICT systems in comparison with conventional TDDFT results.

The role of iron in reactive oxygen species generation from diesel exhaust particles

Diesel exhaust particles (DEP) are known to produce reactive oxygen species (ROS), which induce oxidative stress and inflammation in the lung and respiratory tract. DEP are composed of polycyclic aromatic hydrocarbons (PAH) and their derivatives, redox active semi-quinones, and trace amounts of heavy metals. ROS production was measured by thiobarbituric acid-reactive substances of deoxyribose (TBARS) formation from DEP samples obtained from Korea (DEP-KO), and the Standard Reference Material (SRM) 2975 to explore the role of transition metals. Both DEP-KO and SRM2975 had similar amounts of transition metals, whereas DEP-KO contained more iron, but less copper and zinc, than SRM2975. The water-soluble fraction from SRM2975, but not that from DEP-KO, had a broad absorption in the visible region, but not from DEP-KO, obscuring an accurate absorption measurement of TBARS. Fluorescence measurements of TBARS generation in a water-soluble extract showed that SRM2975 produces more TBARS, but the addition of hydrogen peroxide (H 2O 2) generated more TBARS in DEP-KO than in SRM2975, consistent with the higher amounts of iron in DEP-KO. The incubation of DEP with iron chelators inhibited the production of TBARS. Finally, a novel use of the fluorogenic spin trap probe, proxyl fluorescamine, enabled the detection of the ROS production from both DEP-KO and SRM2975. Our findings suggested that careful consideration is needed to measure TBARS production in DEP, and that iron in DEP seems to be more important than other transition metals in H 2O 2-induced ROS generation.

Comparison of Drug Transporter Levels in Normal Colon, Colon Cancer, and Caco-2 Cells: Impact on Drug Disposition and Discovery

A critical step in early phase drug development is the determination of oral bioavailability. In part, the ability to predict whether a drug will be effectively transported across the gastrointestinal mucosa can be estimated from the physicochemical properties of the compound. Although advancements through rational drug design have more correctly predicted bioavailability, considerable variability remains to be explained. Transporter expression throughout the gastrointestinal tract may explain much of this variation. ATP-binding cassette (ABC) transporters were the first family of transporters identified to modify bioavailability. More recently, the solute carrier family has also been shown to alter the pharmacokinetic profile of drugs. Currently, the Caco-2 human colon carcinoma cell line is often used by the pharmaceutical industry to evaluate intestinal absorption of drugs; however, in vivo/in vitro permeabilities with carrier mediated drugs do not correlate well, suggesting that Caco-2 transporter expression varies from that of the small intestine. With this is mind, we integrated U133A GeneChip expression data from the NCBIs Gene Expression Omnibus (GEO) collection and then compared the expression pattern of Caco-2 cells to normal colon to determine if the Caco-2 cell line is a reliable model for colonic delivery. Furthermore, transporter expression of Caco-2 cells was compared to that of human colon tumors to assess whether this cell line could be useful to predict drug absorption for colon cancer. Our analysis shows that the expression pattern for Caco-2 cells closely resembles the gene expression profile of transporters within the normal colon, suggesting that this cell line may serve as an in vitro model of colonic drug adsorption. However, the molecular "fingerprint" of Caco-2 was distinctly different from tumor samples, indicating that the Caco-2 model would unlikely predict accurate drug absorption for colon cancer sites.

Study on absorption coefficients of dual-energy γ-rays in determining phase fractions of multiphase flows

This paper discusses the principle and mathematical method to measure the phase fractions of multiphase flows by using a dual-energy gamma-ray system. The dual-energy gamma-ray device is composed of radioactive isotopes of241Am and137Cs with emission energies of 59.5 keV and 662 keV respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The statistical error has been analyzed on the basis of the accurate absorption coefficient which enables determination phrase fractions almost independent of the flow regime. Improvement has been achieved on the measurement accuracy of phase fractions.

Investigation of two-dimensional numerical shock propagation using a weighted essentially non-oscillatory scheme

This work is focused on the computational simulation of realistic jet noise propagation in air. Consequently, in addition to accurate absorption, dispersion, wave steepening, etc., propagation of multidimensional shocks is necessary. Time-domain propagation of shocks requires some special technique to ensure stability and this is usually accomplished using artificial viscosity. In this investigation, instead of using artificial viscosity, a weighted essentially non-oscillatory (WENO) scheme is used. The WENO scheme is unique in that it uses a combination of multiple stencils to calculate derivatives. Shock propagation is achieved in this method through its use of smoothness indicators, which work to leave out any candidate stencils that contain a discontinuity in the calculation of derivatives. Its ability to handle a wide variety of acoustical conditions and the future potential of such a model is shown. [Work supported by ONR and the Pennsylvania State University Applied Research Laboratory Exploratory and Foundational Program.]

SAC–CI theoretical investigation on electronic structure of fluorene–thiophene oligomers

The excited states of the fluorene–thiophene compounds whose polymers are useful as a light-emitting diode were studied by SAC–CI method. The effect of the torsional angle on the excited state was examined for the FT and FMT monomers in details. The first three excited states were calculated for the conformers of several torsional angles. These three excited states were found to change their characters by varying the torsional angle from 0 to 90°. The accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angle from 0 to 90°. The absorption spectra of dimer and trimer were also calculated at the equilibrium structure. It was found that the oscillator strength of S1 states of the dimer and trimer was very high and the red shift occurs due to the π-conjugation. The equilibrium structures are planar for both FT and FMT, and the calculated emission energies are in consistent agreement with the experiment. The effect of applying the electric fields to these molecules was examined.

Inferring black carbon content and specific absorption from Aerosol Robotic Network (AERONET) aerosol retrievals

Black carbon is ubiquitous in the atmosphere and is the main anthropogenic absorbing particulate. Absorption by black carbon is thought to be comparable to the cooling associated with sulfate aerosols, although present‐day satellites are incapable of obtaining this measurement, and model estimates are highly uncertain. More measurements of black carbon concentration are necessary for improving and validating transport and general circulation models. The Aerosol Robotics Network (AERONET) of 180 worldwide radiometers offers an opportunity to obtain these measurements. We use the Maxwell Garnett effective medium approximation to infer the column‐averaged black carbon concentration and specific absorption of AERONET retrievals at 46 locations. The yearly averaged black carbon column concentrations exhibit the expected regional dependence, with remote island locations having values about an order of magnitude lower than the continental biomass burning locations. The yearly averaged black carbon specific absorption cross section is consistent with other measured values, 9.9 m2 g−1 for 19,591 retrievals, but varies from 7.7 to 12.5 m2 g−1. We attribute this variability to the details of the size distributions and the fraction of black carbon contained in the aerosol mixture. We also used the Maxwell Garnett equations to parameterize the imaginary refractive index with respect to the black carbon volume fraction, enabling simple but accurate absorption estimates for aerosol mixtures when the black carbon fraction and size distribution is known. The black carbon concentrations that we derive from AERONET measurements correctly describe the radiance field and represent an alternative to absorption optical thickness in the link between models and AERONET measurements.

Determination of visible near-IR absorption coefficients of mammalian fat using time- and spatially resolved diffuse reflectance and transmission spectroscopy

In-vivo optical spectroscopy and the determination of tissue absorption and scattering properties have a central role in the development of novel optical diagnostic and therapeutic modalities in medicine. A number of techniques are available for the optical characterization of tissue in the visible near-IR region of the spectrum. An important consideration for many of these techniques is the reliability of the absorption spectrum of the various constituents of tissue. The availability of accurate absorption spectra in the range 600 to 1100 nm may allow for the determination of the concentration of key tissue constituents such as oxy- and deoxy-hemoglobin, water, and lipids. The objective of the current study is the determination of a reliable absorption spectrum of lipid(s) that can be used for component analysis of in-vivo spectra. We report the absorption spectrum of a clear purified oil obtained from pig lard. In the liquid phase above 36 degrees C, the oil is transparent and thus suitable for collimated transmission measurements. At room temperature, the oil is a solid grease that is highly scattering. The absorption and scattering properties in this solid phase are measured using time- and spatially resolved diffuse reflectance spectroscopy. Using these three independent measurement techniques, we have determined an accurate estimate for the absorption spectrum of mammalian fat.

Detection of Nitrogen Dioxide by Cavity Attenuated Phase Shift Spectroscopy

We present initial results obtained from an optical absorption sensor for the monitoring of ambient atmospheric nitrogen dioxide concentrations (0-200 ppb). This sensor utilizes cavity attenuated phase shift spectroscopy, a technology related to cavity ringdown spectroscopy. A modulated broadband incoherent light source (a 430-nm LED) is coupled to an optically resonant cavity formed by two high-reflectivity mirrors. The presence of NO(2) in the cell causes a phase shift in the signal received by a photodetector that is proportional to the NO(2) concentration. The sensor, which employed a 0.5-m cell, was shown to have a sensitivity of 0.3 ppb in the photon (shot) noise limit. Improvements in the optical coupling of the LED to the resonant cavity would allow the sensor to reach this limit with integration times of 10 s or less (corresponding to a noise equivalent absorption coefficient of <1 x 10(-8) cm(-1) Hz(-1/2)). Over a 2-day-long period of ambient atmospheric monitoring, a comparison of the sensor with an extremely accurate and precise tunable diode laser-based absorption spectrometer showed that the CAPS-based instrument was able to reliably and quantitatively measure both large and small fluctuations in the ambient nitrogen dioxide concentration.

Influence of driving frequency on oxygen atom density in O2 radio frequency capacitively coupled plasma

The influence of the driving frequency on the absolute oxygen atom density in an O2 radio frequency (RF) capacitively coupled plasma (CCP) was investigated using vacuum ultraviolet absorption spectroscopy with pulse modulation of the main plasma. A low-power operation of a compact inductively coupled plasma light source was enabled to avoid the significant measurement errors caused by self-absorption in the light source. The pulse modulation of the main plasma enabled accurate absorption measurement for high plasma density conditions by eliminating background signals due to light emission from the main plasma. As for the effects of the driving frequency, the effect of VHF (100 MHz) drive on oxygen atom production was small because of the modest increase in plasma density of electronegative O2 in contrast to the significant increase in electron density previously observed for electropositive Ar. The recombination coefficient of oxygen atoms on the electrode surface was obtained from a decay rate in the afterglow by comparison with a diffusion model, and it showed agreement with previously reported values for several electrode materials.

A Long Look at NGC 3783 with theXMM‐NewtonReflection Grating Spectrometer

A long 280 ks observation of the Seyfert 1 galaxy NGC 3783 with XMM-Newton is reported. We focus on the oxygen line complex between 17 and 24 A as measured with the Reflection Grating Spectrometer. Accurate absorption column densities and emission-line fluxes are obtained. We explore several options for the geometry and physical form of the emitting and absorbing gas. The lack of change in ionization in the absorber despite an increase in continuum flux during the observation restricts the high-ionization (O-K) and the low-ionization (Fe-M) gas to distances of at least 0.5 and 2.8 pc, respectively, away from the central source. Given the P Cygni type profiles in the resonance spectral lines and the similar velocity widths, column densities, and ionization structure inferred separately from the emission and absorption lines, it is tempting to relate the X-ray narrow-line emitting plasma with the X-ray-absorbing gas. Under this assumption, the scenario of dense clumped clouds can be ruled out. Conversely, extended ionization cones (r 10 pc) are consistent with the observation independent of this assumption. These findings are in stark contrast to the picture of numerous clumpy (ne 109 cm-3) clouds drawn recently from UV spectra, but they are consistent with the extended X-ray emission cones observed directly in Seyfert 2 galaxies.

Atomic absorption spectroscopic, conductometric and colorimetric methods for determination of fluoroquinolone antibiotics using ammonium reineckate ion-pair complex formation

Three accurate, rapid and simple atomic absorption spectrometric, conductometric and colorimetric methods were developed for the determination of norfloxacin (NRF), ciprofloxacin (CIP), ofloxacin (OFL) and enrofloxacin (ENF). The proposed methods depend upon the reaction of ammonium reineckate with the studied drugs to form stable precipitate of ion-pair complexes, which was dissolved in acetone. The pink coloured complexes were determined either by AAS or colorimetrically at λ max 525 nm directly using the dissolved complex. Using conductometric titration, the studied drugs could be evaluated in 50% (v/v) acetone in the range 5.0–65, 4.0–48, 5.0–56 and 6.0–72 μg ml −1 of NRF, CPF, OFL and ENF, respectively. The optimizations of various experimental conditions were described. The results obtained showed good recoveries of 99.15±1.15, 99.30±1.40, 99.60±1.50, and 99.00±1.25% with relative standard deviations of 0.81, 1.06, 0.97, and 0.69% for NRF, CPF, OFL, and ENF, respectively. Applications of the proposed methods to representative pharmaceutical formulations are successfully presented.

Preconcentration and speciation of chromium in water samples by atomic absorption spectrometry after cloud-point extraction.

A rapid, sensitive and accurate atomic absorption method for Cr(III) and Cr(VI) ions was developed based on the cloud-point extraction (CPE) technique. Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of concentrated H2SO4 and ethanol to the sample solution. The condensed surfactant phase containing the metal chelates is introduced into an atomic absorption spectrometer. The relative standard deviations were 2.1% for both species and the limits of detection were around 0.17 microg l(-1).

Transient hygrothermal stresses in fiber reinforced composites: a heterogeneous characterization approach

Transient hygrothermal stresses induced in fiber-reinforced composites are studied in detail by adopting a novel heterogeneous characterization approach. This approach incorporates two distinct features: transient moisture absorption analysis of actual composite materials exposed to a humid environment, and highly detailed computational analyses that capture the actual heterogeneous microstructure of the composite. The latter feature is carried out by modeling a uniaxial laminate having more than one thousand individual carbon fibers that are randomly distributed within an epoxy matrix. Results indicate that these computational models are essential in capturing the accurate moisture absorption process of the actual specimen. In the analysis, the evolutions of thermal residual stresses and moisture-induced stresses within the humidity and thermal exposed composites have been analyzed. It was observed that high stress concentration develops in the epoxy phase where high fiber density or fiber clustering exists and its magnitude increases as the moisture content saturates. Large stresses can potentially initiate epoxy damage or delamination of epoxy and fibers. Furthermore, due to opposing effects of thermal and moisture exposure, lower stresses are found in the laminate when both are considered simultaneously.

Hyperfine Structure Emission and Absorption Lines in Hot Gas

ABSTRACTSyunyaev & Churazov originally pointed out that there is a large set of hyperfine structure lines that are produced by isotopes of the abundant elements. They occur with the H‐like (1 electron), Li‐like, and Na‐like ions by the same process as the hydrogen 21 cm line. Most are highly charged ions, so they will be present in hot X‐ray–emitting gas. More recently, Zhang & Sampson computed collision strengths for some of these lines, making it possible to compute accurate level populations, emission, and absorption for the first time. We have incorporated the full set of Syunyaev & Churazov lines into the spectra simulation code Cloudy. We use the Zhang & Sampson calculations as a guide for estimating the order of magnitude of the collision strengths for the lines that do not have collision data. We also calculate a visibility function that predicts which lines will be most easily seen in absorption. The column densities needed to produce strong absorption are greater than those found in even the most massive galaxy clusters, suggesting that these lines will be very hard to detect.