Browsing by Tema "Absorption (acoustics)"

Now showing 1 - 14 of 14

2D XAFS-XEOL Spectroscopy – Some recent developments
(IOP Publishing, 2013) Matthew J. Ward; Jeremy G. Smith; Tom Regier; Tsun‐Kong Sham
The use of optical photons to measure the modulation of the absorption coefficient upon X-ray excitation, or optical XAFS, is of particular interest for application to the study of light emitting semiconducting nanomaterials due to the additional information that may be gained. The potential for site-selectivity, elemental and excitation energy specific luminescence decay channels, and surface vs. bulk effects all make the use of X-ray excited optical luminescence (XEOL) desirable as a detection method. Previous experiments have made use of a monochromator to select the optical emission wavelength used to monitor optical XAFS. This method of detection suffers from the primary limitation of only being able to monitor the optical response at one emission wavelength. By combining the high resolution soft X-ray Spherical Grating Monochromator beam-line at the Canadian Light Source with an Ocean Optics QE 65000 fast CCD spectrophotometer and custom integration software we have developed a technique for collecting 2D XAFS-XEOL spectra, in which the excitation energy is scanned and a XEOL spectra is collected for every energy value. Herein we report the development of this technique and its capabilities using the study of the luminescence emitted from single crystal zinc oxide as an example.
A comparative study of methods for determining selenium in biological materials.
(National Institutes of Health, 1990) Burguera Jl; M Burguera; Máximo Gallignani; Alarcón Om
A comparative study of the analytical performance of fluorimetric spectrophotometric, atomic absorption spectrometric, flow injection analysis with atomic absorption spectrometric, flow injection analysis with atomic absorption spectrometric detection, hydride generation with atomic absorption spectrometric detection and hydride generation with molecular emission cavity analysis detection methods has been carried out for the determination of selenium in biological materials. Based on results concerning detection limit, linearity and sensitivity, only the fluorimetric and hydride generation with atomic absorption spectrometric detection methods were suitable for the determination of selenium in biological materials. Whereas, the spectrophotometric, flame absorption spectrometric flow injection-atomic absorption spectrometric and hydride generation with molecular emission cavity detection, due to its worse detection limits and poorer sensitivities, were found to be unsuitable for the determination of selenium in such matrices. The accuracy of the fluorimetric and hydride generation with atomic absorption spectrometric detection methods were tested by using NBS standard reference materials.
Arsenic adsorption by iron–aluminium hydroxide coated onto macroporous supports: Insights from X-ray absorption spectroscopy and comparison with granular ferric hydroxides
(Elsevier BV, 2015) Prashanth Suresh Kumar; Roxana Quiroga-Flores; Carin Sjöstedt; Linda Önnby
Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)
(Copernicus Publications, 2019) Aurélien Chauvigné; Diego Aliaga; Karine Sellegri; Nadège Montoux; Radovan Krejčí; Griša Močnik; Isabel Moreno; Thomas Müller; Marco Pandolfi; Fernando Velarde
Abstract. This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz–El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multi-year record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm−1 respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz–El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.
Chromatographic and spectroscopic properties of regioisomers of some 1H‐1,5‐benzodiazepines
(Wiley, 1994) S. Vianna‐Rodrigues; L. Martins‐Viana; Jairo Quiroga; Braulio Insuasty; Rodrigo Abonı́a; W. Baumann
Abstract The separation of the two regioisomeric derivatives of 1 H ‐1,5‐benzodiazepine yielded from the reaction of 1,2‐diamino‐4‐methylbenzene with 4‐substituted acetophenones was performed by reversed phase high performance liquid chromatography, and the absorption spectra of the separated isomers have been determined for three isomer pairs which have been obtained starting from acetophenones with substituents of different electronegativity. The isomer ratio then could be estimated as well from the ratio of the peak areas as from the absorption spectra. They agree well with the known ratio determined from nmr intensities.
Determination of trace lead in feed-grade dicalcium phosphate by hydride generation atomic absorption spectrometry
(2009) Chuanhua Wang
A method is described for determination of trace lead in feed-grade dicalcium phosphate with the correlation coefficient r = 0.9987,and within the range of marking average recovery rate 98.45% ～ 100.75%. The sample is dissolved with hydrochloric acid solution,and its lead content is determined in a reaction system of HCl-K3Fe(CN)6-NaBH4 by hydride generation atomic absorption spectrometry.
Impacts of brown carbon from biomass burning on surface UV and ozone photochemistry in the Amazon Basin
(Nature Portfolio, 2016) Jungbin Mok; N. A. Krotkov; Antti Arola; Omar Torres; Hiren Jethva; Marcos Andrade; G. J. Labow; T. F. Eck; Zhanqing Li; Russell R. Dickerson
Low organic content hybrid perovskite (Cs1-xDMAx)Pb(Br1-xIx)3 with increased stability for solar cell fabrication
(National University of Colombia, 2023) Juan J. Patiño; Juan Felipe Montoya; Edwin Alexander Ramírez; Franklin Jaramillo; Daniel Ramírez
Hybrid perovskites with reduced organic content have brought great interest for solar cells applications. Particularly, adding inorganic cations increase material stability, by providing an adequate tolerance factor. However, these cations lead to lower absorption coefficient than using only organic cations, therefore it is necessary to implement strategies for having films with appropriate thickness and good light absorption properties. In this work, several experiments were performed with ((Cs1-xDMAx)Pb(Br1-xIx)3 perovskite films of different thicknesses, resulting in devices with photovoltaic conversion efficiency (PCE) near 80% of the reference MAPbI3 cell, high purity phase, appropriate morphology, and higher stability. The perovskite successfully maintained integrity for 12 days in air with relative humidity between 30 and 40%, indicating the fulfillment of the study's objectives.
Optical Absorption and Raman Scattering Measurements in CuAlSe2 at High Pressure
(Wiley, 1996) L. Roa; J. C. Chervin; A. Chévy; M. E. Dávila; P. Grima; J. Gonzáez
Abstract The ternary compound CuAlSe 2 is a direct energy gap semiconductor ( E g = 2.6 eV at 300 K) crystallizing in the tetragonal chalcopyrite structure. In this work the optical absorption edge and the Raman active modes of CuAlSe 2 were measured as a function of pressure up to 30 GPa. The measurements were performed in a membrane diamond‐anvil cell at ambient temperature using neon gas as pressure transmitting medium. The direct energy gap (Γ → Γ ) increases linearly with pressure at the rate of 4.7 × 10 −2 eV GPa −1 . At 6.7 GPa the character of the fundamental gap changes to pseudodirect (Γ → Γ ). This gap decreases with pressure at a rate of −2.9 × 10 −2 eV GPa −1 . The effect of pressure on the phonon frequencies is discussed in terms of the Grüneisen parameters. A first‐order structural phase transition was observed at 12 GPa in the upstroke and at 2 GPa in the downstroke.
Problems existing in operation of 600 kt/a SA plant from sulfur burning and its modification
(2008) Shu Shi-tao
The operation troubles are described,including turbine fault,failure of circulating acid pump of dry absorption,primary reforming of catalyst caking in a 600 kt/a sulfur-based sulfuric acid plant.The countermeasures are presented after analyzing the representation and reason.Application effect shows the operation ratio increased in the plant.
Reply on RC1
(2024) Valeria Mardoñez
Abstract. Black carbon (BC) is a major component of sub-micron particulate matter (PM) with significant health and climate impacts. Many cities in emerging countries lack comprehensive knowledge about BC emissions and exposure levels. This study investigates BC concentration levels, identify its emission sources, and characterize the optical properties of BC at urban background sites of the two largest high-altitude Bolivian cities: La Paz (LP) (3600 m above sea level) and El Alto (EA) (4050 m a.s.l.) where atmospheric oxygen levels and intense radiation may affect BC production. The study relies on concurrent measurements of equivalent black carbon (eBC), elemental carbon (EC), and refractory black carbon (rBC), and their comparison with analogous data collected at the nearby Global Atmosphere Watch-Chacaltaya station (5240 m a.s.l). The performance of two independent source-apportionment techniques was compared: a bilinear model and a least squares multilinear regression (MLR). Maximum eBC concentrations were observed during the local dry season (LP: eBC=1.5±1.6 μg m-3; EA: 1.9±2.0 μg m-3). While eBC concentrations are lower at the mountain station, daily transport from urban areas is evident. Average mass absorption cross sections of 6.6-8.2 m2 g-1 were found in the urban area at 637 nm. Both source apportionment methods exhibited a reasonable level of agreement in the contribution of biomass burning (BB) to absorption. The MLR method allowed the estimation of the contribution and the source-specific optical properties for multiple sources including open waste burning.
Reply on RC2
(2024) Valeria Mardoñez
Abstract. Black carbon (BC) is a major component of sub-micron particulate matter (PM) with significant health and climate impacts. Many cities in emerging countries lack comprehensive knowledge about BC emissions and exposure levels. This study investigates BC concentration levels, identify its emission sources, and characterize the optical properties of BC at urban background sites of the two largest high-altitude Bolivian cities: La Paz (LP) (3600 m above sea level) and El Alto (EA) (4050 m a.s.l.) where atmospheric oxygen levels and intense radiation may affect BC production. The study relies on concurrent measurements of equivalent black carbon (eBC), elemental carbon (EC), and refractory black carbon (rBC), and their comparison with analogous data collected at the nearby Global Atmosphere Watch-Chacaltaya station (5240 m a.s.l). The performance of two independent source-apportionment techniques was compared: a bilinear model and a least squares multilinear regression (MLR). Maximum eBC concentrations were observed during the local dry season (LP: eBC=1.5±1.6 μg m-3; EA: 1.9±2.0 μg m-3). While eBC concentrations are lower at the mountain station, daily transport from urban areas is evident. Average mass absorption cross sections of 6.6-8.2 m2 g-1 were found in the urban area at 637 nm. Both source apportionment methods exhibited a reasonable level of agreement in the contribution of biomass burning (BB) to absorption. The MLR method allowed the estimation of the contribution and the source-specific optical properties for multiple sources including open waste burning.
Scattering and absorption of massless scalar waves by a ModMax black hole
(American Physical Society, 2025) Arturo Quispe Baptista; M. L. Peñafiel
ModMax electrodynamics is a remarkable example of nonlinear electrodynamics that preserves both conformal and duality invariance. When coupled to General Relativity, the resulting black hole solutions introduce a tunable nonlinearity parameter that effectively screens the electromagnetic charge. We study the scattering and absorption of massless scalar waves by a ModMax black hole by applying the partial waves method. We also compute some well-known analytical approximations for the scattering and absorption cross sections and contrast them with the full numerical solution. Our results adequately reproduce those of Maxwell electrodynamics in the appropriate limit and illustrate the effect of the charge screening in ModMax electrodynamics.
Theory of the Compensation-Induced Parity-Forbidden Excitation Spectra of Shallow Impurities in Semiconductors
(1974) Timothy Gonzalez; Luis R. González; J. Trylski
An approximate formula for the line shape for the compensation-induced parity-forbidden 1s–2s optical absorption of shallow hydrogen-like impurities in semiconductors is given in the limit of small compensations. The unusual “camel-back” structure of the absorption peak is predicted.