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Interação de Íons de manganês, em diferentes estados de oxidação, com íon azoteto; On the interaction between azide and manganese ions at several oxidation states

Moya, Horacio Dorigan
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/06/1998 PT
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Realizaram-se estudos potenciométricos, em combinação com medições espectrofotométricas, para caracterizar a espécie de íon manganês obtida a partir de oxidação coulométrica a corrente constante utilizando-se solução de Mn(II) (0,050 mol.L-1) em N3- (0,50 a 2,0 mol.L-1) e H+ (0,01 mol.L-1). Graficamente foi possível concluir que a espécie gerada é Mn(III) e obter os valores dos potenciais condicionais de redução, E0'x, do par Mn(III)/Mn(II), em soluções tampão N3-/HN3, de concentração de N3- 0,50; 1,0; 1,5; 2,0 e 4,0 mol.L-1 e H+ 0,010 mol.L-1, sendo 0,468, 0,421, 0,396, 0,377 e 0,336 V (vs. ECS), respectivamente. Esses valores de E0'x permitiram o cálculo das constantes de equilíbrio para os complexos no sistema Mn(III)/N3-, sendo: β1 = 1,23.105 M-1, β2 = 6,03.108 M-2, β3 = 2,37.1011 M-3, β4 = 1,54.1011 M-4 e β5 = 9,57.1011 M-5 (T = 25,0 ± 0,1 ºC, I = 2,0 mol.L-1 com NaClO4). Os valores calculados para as absortividades molares, em 430 nm, para as espécies [Mn(N3)3], [Mn(N3)4]- e [Mn(N3)5]2- foram 226, 3.680 e 6560 mol-1.L.cm-1, respectivamente. Para o estudo do cátion Co(II), foram efetuadas oxidações coulométricas da mesma forma e nas mesmas condições que para o cátion Mn(II). Os valores de E0'x encontrados para o par Co(III)/Co(II) foram 0...

STABILITY OF OILS HEATED BY MICROWAVE: UV - SPECTROPHOTOMETRIC EVALUATION

VIEIRA,Thais M. F. S.; REGITANO-D’ARCE,Marisa A. B.
Fonte: Sociedade Brasileira de Ciência e Tecnologia de Alimentos Publicador: Sociedade Brasileira de Ciência e Tecnologia de Alimentos
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/1998 EN
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The effects of microwave heating on the oxidative stability of refined canola, corn and soybean oils were determined by absorptivity in the UV spectrum and by chemical analysis (peroxide and acid values). Samples were heated in a microwave oven (800 W, 2,450 MHz) for 0 to 36 min. Microwave heating produced oxidative degradation in the three oils. Absorptivity at 232 and 270 nm increased gradually with an increase in microwave exposure time (0-36 min) for canola, corn and soybean oils. Values of absorptivity at 232 nm increased from 4.812, 3.568 and 4.183 to 10.579, 12.874 and 15.950 after 36 min of heating canola, corn and soybean oil, respectively. The absorptivity at 232nm, due to the formation of conjugated dienes, was a good index for measuring the degradation of microwaved samples. UV scanning (220 - 320 nm) detected alterations in the spectrum of microwaved samples. Acid value also increased within 36 min of heating for all oils. Peroxide value showed a significant difference (P<0.05) in the initial stage of heating (0-6 min) for all oils. After this period it could not be correlated with absorptivity at 232 nm, due to the instability of hydroperoxides at high temperatures.

Evaluation of a kinetic uricase method for serum uric acid assay by predicting background absorbance of uricase reaction solution with an integrated method*

Liao, Fei; Zhao, Yun-sheng; Zhao, Li-na; Tao, Jia; Zhu, Xiao-yun; Liu, Lan
Fonte: Zhejiang University Press Publicador: Zhejiang University Press
Tipo: Artigo de Revista Científica
EN
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A patented kinetic uricase method was evaluated for serum uric acid assay. Initial absorbance of the reaction mixture before uricase action (A 0) was obtained by correcting the absorbance at 293 nm measured before the addition of uricase solution, and background absorbance (A b) was predicted by an integrated method. Uric acid concentration in reaction solution was calculated from ΔA, the difference between A 0 and A b, using the absorptivity preset for uric acid. This kinetic uricase method exhibited CV<4.3% and recovery of 100%. Lipids, bilirubin, hemoglobin, ascorbic acid, reduced glutathione and xanthine <0.32 mmol/L in serum had no significant effects. ΔA linearly responded to 1.2 to 37.5 μmol/L uric acid in reaction solution containing 15 μl serum. The slope of linear response was consistent with the absorptivity preset for uric acid while the intercept was consistent with that for serum alone. Uric acid concentrations in clinic sera by different uricase methods positively correlated to each other. By Bland-Altman analysis, this kinetic uricase method accorded with that by quantifying the total change of UV absorbance on the completion of uricase reaction. These results demonstrated that this kinetic uricase method is reliable for serum uric acid assay with enhanced resistance to both xanthine and other common errors...

Investigations on the Q and CT Bands of Cytochrome c Submonolayer Adsorbed on an Alumina Surface Using Broadband Spectroscopy with Single-Mode Integrated Optical Waveguides

Wiederkehr, Rodrigo S.; Hoops, Geoffrey C.; Aslan, Mustafa M.; Byard, Courtney L.; Mendes, Sergio B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 14/05/2009 EN
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In this work, we report experimental results on the molar absorptivity of cytochrome c adsorbed at different submonolayer levels onto an aluminum oxide waveguide surface; our data show a clear dependence of the protein optical properties on its surface density. The measurements were performed using the broadband, single-mode, integrated optical waveguide spectroscopic technique, which is an extremely sensitive tool able to reach submonolayer levels of detection required for this type of studies. This investigation focuses on the molar absorptivity at the Q-band (centered at 525 nm) and, for the first time to our knowledge, the weak charge transfer (CT) band (centered at 695 nm) of surface-adsorbed cyt c. Polarized light in the spectral region from 450 to 775 nm was all-coupled into an alumina thin film, which functioned as a single-mode planar optical waveguide. The alumina thin-film waveguide used for this work had a thickness of 180 nm and was deposited on a glass substrate by the atomic layer deposition process. The protein submonolayer was formed on the alumina waveguide surface through electrostatic adsorption from an aqueous buffer solution at neutral pH. The optical properties of the surface-adsorbed cyt c were investigated for bulk protein concentrations ranging from 5 nM to 8200 nM in the aqueous buffer solution. For a protein surface density of 2.3 pmol/cm2...

The Effect of Varying Short-Chain Alkyl Substitution on the Molar Absorptivity and Quantum Yield of Cyanine Dyes

Chapman, Gala; Henary, Maged; Patonay, Gabor
Fonte: Libertas Academica Publicador: Libertas Academica
Tipo: Artigo de Revista Científica
Publicado em 23/03/2011 EN
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The effect of varying short-chain alkyl substitution of the indole nitrogens on the spectroscopic properties of cyanine dyes was examined. Molar absorptivities and fluorescence quantum yields were determined for a set of pentamethine dyes and a set of heptamethine dyes for which the substitution of the indole nitrogen was varied. For both sets of dyes, increasing alkyl chain length resulted in no significant change in quantum yield or molar absorptivity. These results may be useful in designing new cyanine dyes for analytical applications and predicting their spectroscopic properties.

Determination of Spectrophotometric Absorptivity by Analytical Ultracentrifugation

Senthilraja, M.
Fonte: Medknow Publications & Media Pvt Ltd Publicador: Medknow Publications & Media Pvt Ltd
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
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Rapid determination of the absorptivity for a recombinant IgG monoclonal antibody using the Beckman equipped with both Raleigh interference and UV absorbance optical systems. The analytical ultracentrifuge data for determining spectrophotometric absorptivities is compared to experimental data from quantitative amino acid analysis and an enzymatic digestion method.

Thermal oxidation of rice bran oil during oven test and microwave heating

Mishra, Richa; Sharma, Harish K.; Sarkar, Bhavesh C.; Singh, Charanjiv
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
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The purpose of the present study was to evaluate the oxidative stability of physically refined rice bran oil (RBO) under oven heating at 63 °C and microwave heating conditions by absorptivity. Oil samples with tertiary-butylhydroquinone (TBHQ) (100 ppm and 200 ppm), citric acid (CA), butylhydroxyanisole/butylhydroxytoluene (BHA/BHT) and in other combination, BHA/BHT+CA were submitted to oven test for 6 days, and the linear coefficient of correlation between peroxide value and absorptivity at 232 nm was determined. The gradual increase in peroxide value and absorptivity at 232 nm was observed in all the RBO samples, control and antioxidant added. RBO samples added with tertiary-butylhydroquinone (TBHQ) had shown the least peroxide value and absorptivity as 6.10 and 5.8 respectively, when added at a concentration of 200 ppm whereas; the control RBO samples had shown the maximum values. The peroxide values obtained from the correlations during the oven test were found closely correlated with the peroxide values obtained during the microwave oven heating experimentally. The effect of microwave heating on the oryzanol content and p-anisidine value was also observed and the correlation to the oven test was established. The oryzanol content and p-anisidine values obtained after oven heating when correlated to the microwave heating data showed the oryzanol content 13...

Spectrophotometric Methods for the Determination of Cefprozil in Bulk and Dosage Form

Gadkariem, Elrasheed A.; Mutasim, Mohammed M.; Ibrahim, Kamal E. E.; El-Obeid, Humeida A.
Fonte: Master Publishing Group Publicador: Master Publishing Group
Tipo: Artigo de Revista Científica
Publicado em /09/2009 EN
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Two simple spectrophotometric methods were developed for the determination of cefprozil in pure bulk and in tablets forms. The first is a colorimetric method based on the coupling of cefprozil, after being hydrolyzed by sodium hydroxide (0.1N), with ascorbic acid as a chromogen (method A). It has been established that cefprozil reacts with ascorbic acid to form a 1:1 water soluble colored product with maximum absorbance (λmax) at 408 nm and molar absorptivity of 7.2 × 103L mol−1 cm−1. The second method (Method B) utilizes a direct reaction between cefprozil and sodium hydroxide (1N). A colored product with λmax at 486 nm and molar absorptivity of 7.4 × 103 L mol−1 cm−1 is formed after heating cefprozil with sodium hydroxide (1N). The absorbance-concentration plot was rectilinear over the range 5–25 µg/ml in both methods with correlation coefficient values not less than 0.999. The detection limits (L.O.D.) were 0.96 µg/ml and 0.93 µg/ml for method A and method B respectively. The methods were validated using the USP liquid chromatography method for cefprozil assay. The results obtained by the USP liquid chromatography method for the tablets dosage form were statistically compared with those of the developed methods and evaluated at 95% confidence limits.

Sequence-specific determination of protein and peptide concentrations by absorbance at 205 nm

Anthis, Nicholas J; Clore, G Marius
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
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Quantitative studies in molecular and structural biology generally require accurate and precise determination of protein concentrations, preferably via a method that is both quick and straightforward to perform. The measurement of ultraviolet absorbance at 280 nm has proven especially useful, since the molar absorptivity (extinction coefficient) at 280 nm can be predicted directly from a protein sequence. This method, however, is only applicable to proteins that contain tryptophan or tyrosine residues. Absorbance at 205 nm, among other wavelengths, has been used as an alternative, although generally using absorptivity values that have to be uniquely calibrated for each protein, or otherwise only roughly estimated. Here, we propose and validate a method for predicting the molar absorptivity of a protein or peptide at 205 nm directly from its amino acid sequence, allowing one to accurately determine the concentrations of proteins that do not contain tyrosine or tryptophan residues. This method is simple to implement, requires no calibration, and should be suitable for a wide range of proteins and peptides.

Structure-dependent lipid peroxidation by photoirradiation of pyrene and its mono-substituted derivatives

Fullove, Tracie Perkins; Johnson, Britney; Yu, Hongtao
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Pyrene, one of the most studied polycyclic aromatic hydrocarbons can damage biological macromolecules and cause toxicity when irradiated by light. The effect of substituents, 1-amino, 1-hydroxy, 1-nitro, and 1-bromo, on light-induced lipid peroxidation is studied. Degradation kinetics and photoproduct analyses were conducted to test how these substituents affect the photoreaction. All five compounds have different photodegradation rates, and these rates parallel their light absorptivity. Four out of the five compounds induce lipid peroxidation when irradiated with UVA light; whereas, 1-aminopyrene causes minimum or no lipid peroxidation. The relative amount of lipid peroxidation caused is: 1-Bromopyrene > Pyrene > 1-Nitropyrene ≈ 1-Hydroxypyrene > 1-Aminopyrene. This relative lipid peroxidation is dependent on structure due to the following factors: light absorptivity, relative rates of the competing processes in the excited states, nature of the photoreaction, and nature of the photoproducts.

Metodologias para verificação da estabilidade térmica e fotoelétrica de estruturas absorvedoras de radiação UV.; Methodologies for thermal and photoelectric stability verification of UV radiation on absorbing structures

Luzin, Rangel Magalhães
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Química (IQ); Instituto de Química - IQ (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Química (IQ); Instituto de Química - IQ (RG)
Tipo: Dissertação Formato: application/pdf
POR
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This work describes the thermal and photoelectric stability investigation of commercial sunscreens benzophenone-3, octyl methoxycinnamate and octyl salicylate. The purpose was determining thermal and photoelectric (resistance to sunlight) stability. For thermal stability evaluation, thermal ramp was set up in attempt to get closer to conditions which sunscreen could be submitted in manufacture or in people using. In this test each filter was exposed to temperature variations from 30 to 65 °C, in times and speeds of heating, under synthetic air atmosphere. A solar simulator was used for photoelectric stability evaluation. The measures were not performed with samples irradiated at a specific wavelength, but exposed to all wavelengths emitted by the sun, extending from the ultraviolet to infrared, with high reproducibility. The samples were exposed to simulated solar light in five different times, ranging from 30 to 120 minutes. This change aims to understand how the filter behaves with the increased exposure time. Infrared, ultraviolet and NMR spectroscopies were used on structural characterization of the compounds submitted to thermal and photoelectrical evaluation. This study has demonstrated that sunscreens evaluated are thermally stable but photoelectrically unstable. This instability was observed by formation of minor compounds derivative of sunscreens studied. The shift in the chemical equilibrium producing higher concentrations of minor compounds was also observed. These factors change the absorptive capacity of the sunscreens...

Characteristics and application of road absorbing solar energy

Zhou, Z.; Hu, S.; Zhang, X.; Zuo, J.
Fonte: Springer Berlin Heidelberg Publicador: Springer Berlin Heidelberg
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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If the heat of road surface can be stored in summer, the road surface temperature will be decreased to prevent permanent deformation of pavement. Besides, if the heat stored is released, it can supply heat for buildings or raise the road surface temperature for snow melting in winter. A road-solar energy system was built in this study, and the heat transfer mechanism and effect of the system were analyzed according to the monitored solar radiant heat, the solar energy absorbed by road and the heat stored by soil. The results showed that the road surface temperature was mainly affected by solar radiation, but the effect is hysteretic in nature. The temperature of the solar road surface was 3°C–6°C lower than that of the ordinary road surface. The temperature of the solar road along the vertical direction was 2°C–5°C lower than that of the ordinary road. The temperature difference increased as the distance to the heat transfer tubes decreased. The average solar collector efficiency of the system was 14.4%, and the average solar absorptivity of road surface was 36%.; Zhihua Zhou, Shan Hu, Xiaoyan Zhang, Jian Zuo

Determination of Molar Absorptivity Coefficients for Major Type-B Trichothecenes and Certification of Calibrators for Deoxynivalenol and Nivalenol

KRSKA Rudolf; SCHUBERT-ULLRICH Patricia; JOSEPHS Ralf; EMTEBORG HAKAN; BUTTINGER GERHARD; PETTERSSON Hans; VAN EGMOND Hans; SCHOTHORST Ronald C.; MACDONALD Susan; CHAN Danny
Fonte: SPRINGER HEIDELBERG Publicador: SPRINGER HEIDELBERG
Tipo: Articles in Journals Formato: Printed
ENG
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This paper presents the results of the European Commission funded project DONCALIBRANT which aimed to produce calibrators with certified mass fractions of the Fusarium toxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-Ac-DON), 15- acetyldeoxynivalenol (15-Ac-DON) and nivalenol (NIV) in acetonitrile. The ampouled calibrators showed sufficient homogeneity with between-bottle variations (sbb) of less than 2 %. The short- and long-term stability studies performed at four different temperatures between -18 °C and 40 °C showed no significant negative trends (at a confidence level of 95 %). Molar absorptivity coefficients (in L.mol-1 .cm-1) were determined for all four toxins (DON: 6805 ± 205, 3-Ac-DON: 6983 ± 141, 15-Ac-DON: 6935 ± 142) on the basis of a mini-interlaboratory exercise. The overall uncertainty of the calibrators' target values for DON and NIV were evaluated on the basis of the gravimetrical preparation data and including uncertainty contributions of possible heterogeneity, storage and transport. The DONCALIBRANT project resulted in the production of calibrators for DON (IRMM-315) and NIV (IRMM-316) with certified mass fractions of 25.1 ± 1.2 µg/g and 24.0 ± 1.1 µg/g, respectively. Both CRMs became commercially available from the Institute for Reference Materials and Measurements (IRMM...

Measurement of laser absorptivity for operating parameters characteristic of laser drilling regime

SCHNEIDER, Matthieu; BERTHE, Laurent; FABBRO, Rémy; MULLER, Maryse
Fonte: IOP Publicador: IOP
EN
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Publisher version : http://iopscience.iop.org/0022-3727/41/15/155502/; Laser drilling in the percussion regime is commonly used in the aircraft industry to drill sub-millimetre holes in metallic targets. Characteristic laser intensities in the range of 10 MW cm−2 are typically employed for drilling metallic targets. With these intensities the temperature of the irradiated matter is above the vaporization temperature and the drilling process is led by hydrodynamic effects. Although the main physical processes involved are identified, this process is not correctly understood or completely controlled. A major characteristic coefficient of laser–matter interaction for this regime, which is the absorptivity of the laser on the irradiated surface, is still unknown, because of the perturbing effects due to laser beam geometrical trapping inside the drilled hole. So, by using time resolved experiments, this study deals with the direct measurement of the variation of the intrinsic absorption of aluminium, nickel and steel materials, as a function of the incident laser intensity up to 20 MW cm−2. We observe that for this incident intensity, the absorptivity can reach up to 80%. This very high and unexpected value is discussed by considering the microscopic behaviour of the heated matter near the vapour–liquid interface that undergoes possible Rayleigh–Taylor instability or volume absorption

Qualidade do óleo de fritura de mandioca: correlação entre dados analíticos e sensoriais para determinação do ponto de descarte; Quality of cassava frying oil: correlation between analytical and sensory data for determining oil disposal point.

Matsuoka, Carla Romero
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/08/2009 PT
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A fritura é um procedimento que confere aos alimentos características sensoriais de cor, aroma, textura e sabor diferentes. Neste processo a matéria graxa é exposta a agentes de deterioração que promovem a quebra dos triglicerídeos, a oxidação e a polimerização em função do tempo de uso, provocando perdas sensoriais e nutricionais nos alimentos fritos e no próprio óleo. A falta de regulamentação no Brasil que defina o ponto de descarte dos óleos de fritura faz com que este seja realizado de forma subjetiva. O presente trabalho teve o objetivo de avaliar óleo de soja em fritura de mandioca em toletes em diferentes períodos e correlacionar resultados de análise sensorial aos analíticos para determinar o ponto de descarte. As operações de fritura com óleo de soja refinado foram realizadas a 170ºC por períodos de 1h06min, 2h, 3h05min, 6h54min e 15h40min. As determinações analíticas realizadas nos óleos foram de ácidos graxos livres (em porcentagem de ácido oléico), teor de compostos polares totais (CPT), absortividade em 232nm e 270nm, período de indução (PI) em Rancimat e composição em ácidos graxos. Nas mandiocas cozidas e fritas foram determinados a umidade e o teor lipídico. Os índices de deterioração indicaram incidência maior de deterioração com o aumento do uso do óleo na fritura. Verificou-se que nos períodos de 1h06min...

Wavy-roughness effect to thermal explosion of materials with power-law thermal absorptivity in microannuli

Chu, Zotin K. -H.; Qin, Chen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We obtain the approximate solutions for the steady temperature profiles of materials with a temperature-dependent thermal absorptivity inside a microannulus with wavy-rough surfaces considering a quasilinear partial differential equation by the boundary perturbation approach. We found the critical Frank-Kamanestkii parameter will depend on the small amplitude wavy-roughness.; Comment: two figures

Preparation of a clay based superabsorbent polymer composite of copolymer poly(acrylate-co-acrylamide) with bentonite via microwave radiation

Kalaleh, Hussam-Aldeen; Tally, Mohammad; Atassi, Yomen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/11/2013
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In this paper we present a fast, new and easy method for the preparation of bentonite-g-poly(acrylate-co-acrylamide) composite material using microwave radiation. The composite has water absorptivity of 1002 g/g while the corresponding copolymer is tacky and has poor gel texture. The relative thermal stability of the composite in comparison with the copolymer was proved via thermogravimetric analysis These results indicate the synergistic effect of the bentonite with the copolymer by increasing water absorptivity and enhancing thermal and mechanical properties of the final gel. The composite was characterized by X-ray and FTIR. The influence of the environmental parameters on water absorptivity such as the pH and the ionic force was investigated; Comment: 9 pages, 6 figures

Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid

Gramotnev, Dmitri K.; Mather, Melissa L.; Nieminen, Timo A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/09/2005
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It is demonstrated theoretically that the absorptivity of bulk shear sagittal waves by an ultra-thin layer of viscous fluid between two different elastic media has a strong maximum (in some cases as good as 100%) at an optimal layer thickness. This thickness is usually much smaller than the penetration depths and lengths of transverse and longitudinal waves in the fluid. The angular dependencies of the absorptivity are demonstrated to have significant and unusual structure near critical angles of incidence. The effect of non-Newtonian properties and non-uniformities of the fluid layer on the absorptivity is also investigated. In particular, it is shown that the absorption in a thin layer of viscous fluid is much more sensitive to non-zero relaxation time(s) in the fluid layer than the absorption at an isolated solid-fluid interface.; Comment: 14 pages, 8 figures

Optical Absorptivity versus Molecular Composition of Model Organic Aerosol Matter

Rincón, Angela G.; Guzmán, Marcelo I.; Hoffmann, Michael R.; Colussi, A. J.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/10/2009
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Aerosol particles affect the Earth’s energy balance by absorbing and scattering radiation according to their chemical composition, size, and shape. It is generally believed that their optical properties could be deduced from the molecular composition of the complex organic matter contained in these particles, a goal pursued by many groups via high-resolution mass spectrometry, although: (1) absorptivity is associated with structural chromophores rather than with molecular formulas, (2) compositional space is a small projection of structural space, and (3) mixtures of polar polyfunctional species usually exhibit supramolecular interactions. Here we report a suite of experiments showing that the photolysis of aqueous pyruvic acid (a proxy for aerosol α-dicarbonyls absorbing at λ > 300 nm) generates mixtures of identifiable aliphatic polyfunctional oligomers that develop absorptions in the visible upon standing in the dark. These absorptions and their induced fluorescence emissions can be repeatedly bleached and retrieved without carbon loss or ostensible changes in the electrospray mass spectra of the corresponding mixtures and display unambiguous signatures of supramolecular effects. The nonlinear additivity of the properties of the components of these mixtures supports the notion that full structural speciation is insufficient and possibly unnecessary for understanding the optical properties of aerosol particles and their responses to changing ambient conditions.

The interaction of acoustic radiation with turbulence

Goldreich, Peter; Kumar, Pawan
Fonte: American Astronomical Society Publicador: American Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/03/1988
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We derive expressions for the spectral emissivity and absorptivity of acoustic radiation by low Mach number (M ≪ 1) turbulent fluids. The emissivity and absorptivity depend on the manner in which the turbulence is excited. We consider three types of turbulence. The first is free turbulence, that is, turbulence which is not subject to external forces. The second and third examples are special cases of forced turbulence, turbulence maintained by stirring with spoons and turbulent pseudoconvection. Acoustic quadrupoles are the lowest order acoustic multipoles present in free turbulence, and they control both its emissivity and absorptivity. Acoustic dipoles are created in forced turbulence, and they enhance the acoustic emissivity by M^(-2) compared to that of free turbulence. The acoustic absorptivity of forced turbulence is quite subtle. The absorptivity of turbulence which is maintained by stirring is dominated by acoustic dipoles and exceeds that of free turbulence by M^(-2). The dipole absorptivity of turbulent pseudoconvection is reduced by M^2 below that of turbulence maintained by stirring. Thus, the absorptivity of turbulent pseudoconvection is no larger than that of free turbulence. We apply our results to estimate the equilibrium energies of the acoustic modes in a box filled with fluid some of which is turbulent. For both free turbulence and turbulence maintained by stirring...