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Absorption Coefficient (absorption + coefficient)
Kinds of Absorption Coefficient Selected AbstractsDetermination of Scattering and Absorption Coefficients for Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008Jeffrey I. Eldridge Prediction of radiative transport through translucent thermal barrier coatings (TBCs) can only be performed if the scattering and absorption coefficients and index of refraction of the TBC are known. To date, very limited information on these coefficients, which depend on both the coating composition and the microstructure, has been available for the very commonly utilized plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) TBCs. In this work, the scattering and absorption coefficients of freestanding plasma-sprayed 8YSZ coatings were determined from room-temperature normal-incidence directional-hemispherical reflectance and transmittance spectra over the wavelength range from 0.8 to 7.5 ,m. Spectra were collected over a wide range of coating thickness from 60 to almost 900 ,m. From the reflectance and transmittance spectra, the scattering and absorption coefficients as a function of wavelength were obtained by fitting the reflectance and transmittance values predicted by a four flux model to the experimentally measured values at all measured 8YSZ thicknesses. While the combined effects of absorption and scattering were shown in general to exhibit a nonexponential dependence of transmittance on specimen thickness, it was shown that for sufficiently high absorption and optical thickness, an exponential dependence becomes a good approximation. In addition, the implications of the wavelength dependence of the plasma-sprayed 8YSZ scattering and absorption coefficients on (1) obtaining accurate surface-temperature pyrometer measurements and on (2) applying mid-infrared reflectance to monitor TBC delamination are discussed. [source] Growth, etching morphology and spectra of LiAlO2 crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2008Taohua Huang Abstract ,-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×103 cm,2. The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of optical band gap in potassium acid phthalate single crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2008S. Krishnan Abstract Optical absorption in photonic crystals of potassium acid phthalate has been measured at room temperature, from which the band gap has been determined and the optical band gap was calculated by using absorption spectrum. The analysis of absorption coefficient in the absorption region reveals a direct band gap of 3.70 eV. Further this study includes the theoretical calculations to determine the optical constant of the material and a technique for photonic band gap tuning which is minimally required to develop the optoelectronic device. It was confirmed that potassium acid phthalate crystal has maximum transparency in the entire visible region and hence it exhibits industrial application oriented properties. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical investigations on the existence of phase transition in ZnO:Li thin films prepared by DC sputtering methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2008A. Abu EL-Fadl Abstract We investigated the effect of temperature on the absorption spectra of Zn0.8Li0.2O thin films (ZnO:Li), deposited at 573 K, in the wavelength range 190-800 nm. The films were deposited on sapphire, MgO or quartz substrates by DC sputtering method. The results show a shift of the optical energy gap (Eg), with direct allowed transition type near the fundamental edge, to lower wavelengths as the temperature increases. The temperature rate of Eg changes considerably showing an anomaly around 320 K depending on type of substrate. The founded results indicated that replacement of Zn ions with Li ions induces a ferroelectric phase in the ZnO wurtzite-type semiconductor. The exponential dependence of the absorption coefficient on the incident photon energy suggests the validity of the Urbach rule. (© 2007 WILEY -VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Separation of Nile Blue-labelled fatty acids by CE with absorbance detection using a red light-emitting diodeELECTROPHORESIS, Issue 8 2007Michael C. Breadmore Dr. Abstract The separation of fatty acids derivatised with Nile Blue (NB) by CE with detection using a red light-emitting diode (LED) was examined. NB was selected as the derivatisation agent due to its high molar absorption coefficient of 76,000,M,1cm,1 at 633,nm, making it well suited for sensitive absorbance detection using a red 635,nm LED. NB-labelled fatty acids were separated by both MEKC using SDS micelles, i -PrOH and n -BuOH and by NACE in a number of solvents including MeOH, EtOH and ACN. The sensitivity of NACE was superior to MEKC, with detection limits of 5×10,7,7×10,7,M obtained for each acid, approximately 20 times lower than the MEKC method. The NACE detection limits are approximately 100 times lower than previous reports on the separation of fatty acids by CE using indirect absorbance detection, ten times lower than using indirect fluorescence detection and are inferior only to those obtained using precapillary derivatisation and direct fluorescence detection. The efficiency of the NACE method was also superior to MEKC and allowed the separation of unsaturated fatty acids to be examined, although it was not possible to baseline-resolve linoleic (C18:2) and linolenic (C18:3) acids in a reasonable time. The method was used to analyse the fatty acid profile of two edible oils, namely sunflower and sesame oils, after alkali hydrolysis, where it was possible to identify both the saturated and unsaturated fatty acids in each sample. [source] Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experimentGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Ulrich Wegler SUMMARY The seismic structure of the stratovolcano Merapi (Java, Indonesia) was studied using an active seismic experiment. Three 3 km long seismic profiles each consisting of up to 30 three-component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level. The detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting. The seismic experiment at Merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome, where the sources of most of the natural volcanic seismic events are located. The cone of Merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material. Additionally, the topography of the erosion valleys leads to an irregular deposition, which cannot be described by a simple 1-D layering. These inhomogeneities have a strong influence on seismic signals. The direct P and S waves are attenuated quickly and show only small amplitudes on seismograms. The energy lost from the direct waves, however, is not changed into heat but scattered and can be observed as seismic coda following the direct waves. The observed seismograms show a spindle-like amplitude increase after the direct P phase. This shape of the envelope can be explained by the diffusion model. According to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves. Besides the envelope, the coherence and polarization properties of the wavefield also indicate strong scattering. Only the first onset shows coherence over a station spacing of 100 m, whereas the late phases carrying the major part of the energy are mainly incoherent. The horizontal components of the seismograms have larger amplitudes than the vertical component, but within the horizontal plane the polarization is almost arbitrary, corresponding to waves arriving from scatterers located arbitrarily in space. As a result of the inversion using the diffusion model we obtain values of the S -wave scattering attenuation coefficient, ,s, and the S -wave intrinsic absorption coefficient, ,i. In the frequency range of 4,20 Hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption (,s,,i). The mean free path of S waves is as low as 100 m (,s,1,100 m). The scattering coefficient is independent of frequency (,s,f0.0), whereas the coefficient of intrinsic attenuation increases with increasing frequency (,i,f1.6). The natural seismic signals at Merapi volcano show similar characteristics to the artificial shots. The first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves. Therefore, these signals appear to be strongly affected by multiple scattering also. [source] Modelling of GPR waves for lossy media obeying a complex power law of frequency for dielectric permittivityGEOPHYSICAL PROSPECTING, Issue 1 2004Maksim Bano ABSTRACT The attenuation of ground-penetrating radar (GPR) energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies (absorption) with increasing traveltime and causes also a distortion of wavelet phase (dispersion). The attenuation is often expressed by the quality factor Q. For GPR studies, Q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity. We consider a complex power function of frequency for the dielectric permittivity, and show that this dielectric response corresponds to a frequency-independent- Q or simply a constant- Q model. The phase velocity (dispersion relationship) and the absorption coefficient of electromagnetic waves also obey a frequency power law. This approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only, for example Q and the phase velocity at an arbitrary reference frequency. This simplicity makes it practical for any inversion technique. Furthermore, by using the Hilbert transform relating the velocity and the absorption coefficient (which obeys a frequency power law), we find the same dispersion relationship for the phase velocity. Both approaches are valid for a constant value of Q over a restricted frequency-bandwidth, and are applicable in a material that is assumed to have no instantaneous dielectric response. Many GPR profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes. Changes in water content are believed to be the origin of this reflectivity. We model the radar reflections from the bottom of a dry aeolian dune using the 1D wavelet modelling method. We discuss the choice of the reference wavelet in this modelling approach. A trial-and-error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site. Additionally, by combining the complex refractive index method (CRIM) and/or Topp equations for the bulk permittivity (dielectric constant) of moist sandy soils with a frequency power law for the dielectric response, we introduce them into the expression for the reflection coefficient. Using this method, we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling. [source] New Ruthenium Complexes Containing Oligoalkylthiophene-Substituted 1,10-Phenanthroline for Nanocrystalline Dye-Sensitized Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2007C.-Y. Chen Abstract Two new ruthenium complexes [Ru(dcbpy)(L)(NCS)2], where dcbpy is 4,4,-dicarboxylic acid-2,2,-bipyridine and L is 3,8-bis(4-octylthiophen-2-yl)-1,10-phenanthroline (CYC-P1) or 3,8-bis(4-octyl-5-(4-octylthiophen-2-yl)thiophen-2-yl)-1,10-phenanthroline (CYC-P2), are synthesized, characterized by physicochemical and semiempirical computational methods, and used as photosensitizers in nanocrystalline dye-sensitized solar cells. It was found that the difference in light-harvesting ability between CYC-P1 and CYC-P2 is associated mainly with the location of the frontier orbitals, in particular the highest occupied molecular orbital (HOMO). Increasing the conjugation length of the ancillary ligand decreases the energy of the metal-to-ligand charge transfer (MLCT) transition, but at the same time reduces the molar absorption coefficient, owing to the HOMO located partially on the ancillary ligand of the ruthenium complex. The incident photon-to-current conversion efficiency curves of the devices are consistent with the MLCT band of the complexes. Therefore, the overall efficiencies of CYC-P1 and CYC-P2 sensitized cells are 6.01 and 3.42,%, respectively, compared to a cis- di(thiocyanato)-bis(2,2,-bipyridyl)-4,4,-dicarboxylate ruthenium(II)-sensitized device, which is 7.70,% using the same device-fabrication process and measuring parameters. [source] Linear and Nonlinear Optical Properties of Ag Nanowire Polarizing Glass,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2006Q.-Q. Wang Abstract An R2O,B2O3,SiO2 (R,=,Li, Na, K) polarizing glass containing Ag nanorods is prepared by thermal elongation,reduction technology. The transverse and longitudinal plasmon absorption peaks of the embedded Ag nanorods are near 460 and 720,nm, respectively. When the polarization of the laser is parallel to the long axis of the Ag nanorods, the nonlinear absorption coefficient ,,=,0.82,cm,GW,1 and the nonlinear refractive index n2,=,,1.5,×,10,4,cm2,GW,1. When the polarization of light is perpendicular to the long axis of the Ag nanorods ,,=,0.12,cm,GW,1 and n2,=,,7.2,×,10,5,cm2,GW,1 and the appropriate one- and two-photon figures of merit (FOM), W,=,1.6 and T,=,0.16, respectively, are obtained, which satisfies the demand, W,>,1 and T,<,1, for applications in all optical switching, where W is a one-photon FOM, and T is a two-photon FOM. [source] Noncontact measurement of deep tissue absorption coefficient using Spatially Resolved Near-Infrared SpectroscopyIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2007Masatsugu Niwayama Member Abstract We examined the influence of probe-tissue distance on the relationship between the deep tissue absorption coefficient and the spatial profile of light intensity by Monte Carlo simulation and in vivo experiments, using noncontact spatially resolved near-infrared spectroscopy (SRS). These results suggest that noncontact SRS can be reliably used for noncontact measurement of the absorption coefficient and oxygen saturation of deep tissues. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] An inverse radiation problem of simultaneous estimation of heat transfer coefficient and absorption coefficient in participating mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2003H. M. Park Abstract An inverse radiation problem is investigated where the spatially varying heat transfer coefficient h(z) and the absorption coefficient , in the radiant cooler are estimated simultaneously from temperature measurements. The inverse radiation problem is solved through the minimization of a performance function, which is expressed by the sum of square residuals between calculated and observed temperature, using the conjugate gradient method. The gradient of the performance function is evaluated by means of the improved adjoint variable method that can take care of both the function estimation and the parameter estimation efficiently. The present method is found to estimate h(z) and , with reasonable accuracy even with noisy temperature measurements. Copyright © 2002 John Wiley & Sons, Ltd. [source] Kinetics and mechanism for the formation of o -carboxy(N -methyl)-benzohydroxamic acid in the cleavage of ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)-benzoyl]carbamate in N -methylhydroxylamine, acetate, and phosphate buffersINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2003M. Niyaz Khan The rate of cleavage of ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)benzoyl]- carbamate (ENMBC) in the buffer solutions containing N -methylhydroxylamine, acetate + N -methylhydroxylamine, and phosphate + N -methylhydroxylamine followed an irreversible consecutive reaction path: ENMBC where A and B represent N -hydroxyl group cyclized product of ENMBC and o -(N -methyl- N -hydroxycarbamoyl)benzoic acid, respectively. Both rate constants k1 obs and k2 obs showed the presence of buffer catalysis, but buffer catalysis turned out to be weak in the presence N -methylhydroxylamine buffer, while it was strong in the presence of acetate and phosphate ones. Buffer-independent rate constants k10 and k20 increased linearly with the increase in aOH with definite intercepts. The values of molar absorption coefficient of A, obtained under varying total buffer concentrations at a constant pH, showed the presence of a fast equilibrium: A + CH3NHOH , C, where C represents N -[o -(N -methyl- N -hydroxycarbamoyl)methyl]benzohydroxamic acid. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 427,437, 2003 [source] Strong Optical Limiting of Soluble Axially Substituted Gallium and Indium Phthalocyanines,ADVANCED MATERIALS, Issue 11 2003Y. Chen Optical limiting in In- and Ga-phthalocyanines exhibits a range of saturation densities and absorption cross-section ratios. Substitution of the p -trifluoromethylphenyl group at the central metal in tBu4PcGaCl and tBu4PcInCl reduces the saturation energy density by a factor of >3. Tailorable optical limiting properties are shown in the Figure, which plots the nonlinear absorption coefficient as a function of intensity for the five compounds studied. [source] Radiation model of a TiO2 -coated, quartz wool, packed-bed photocatalytic reactorAICHE JOURNAL, Issue 4 2010G. E. Imoberdorf Abstract The radiation field of a packed-bed photocatalytic reactor filled with quartz wool coated with titanium dioxide was modeled using the Monte Carlo technique and the following information: the radiation flux emitted by the lamps, the diameter size distribution of the quartz fiber cloth, the mass of quartz fibers and of TiO2 that was immobilized on the fiber surface as well as the refractive index, and the spectral absorption coefficient of the materials of the system. Modeling predictions were validated with radiometer measurements of the transmitted radiation through the reactor, the root mean square error being <9.7%. Finally, by means of a parametric study, the validated model was used to analyze the effect of the design variables, such as the radii of the quartz fibers, thickness of the TiO2 coatings, and amount of TiO2 -coated quartz wool, on the distribution and nonuniformity of the radiative energy distribution inside the reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Radiative heat exchange modeling inside an ovenAICHE JOURNAL, Issue 9 2009Ashish Dhall Abstract The 3D nongray radiative heat exchange in a near-infrared commercial oven is modeled. The spectrum is divided into into four gray bands to model the narrow wavelength range in which the halogen heat source radiates, the wavelength dependence of the food surface emittance, and the absorption coefficient of the heat source cover glass. The model is used to estimate the heating of a cuboidal food sample for 1 min at different cyclic settings of a halogen radiant heat source. The model predictions agree with the experimental data, and capture the cover-glass and the food-surface temperature and heat flux histories very well. The band-wise distribution of energy absorption by the food reveals the separate contributions from the source and the oven walls. Comparison of the heating rates between the measured non-gray food-surface and the different gray food-surface emittance values establishes the necessity of the nongray treatment. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Optical and physicochemical properties of silica-supported TiO2 photocatalystsAICHE JOURNAL, Issue 8 2006Javier Marugán Abstract Commercial applications of photocatalysis in slurry reactors employing titanium dioxide particles present the disadvantage of the additional cost associated with the downstream catalyst separation. In past years a significant effort has been made to develop supported titania photocatalysts on particles of larger size in order to facilitate the sedimentation recovery process. In this work, two different silica materials have been used for preparing immobilized catalysts. Their physicochemical characteristics have been compared with those corresponding to two commercially available unsupported titanium dioxide catalysts. However, for reaction kinetics and reactor design purposes, three additional properties must be known: (i) the spectral specific radiation absorption coefficient, (ii) the spectral specific radiation scattering coefficient, and (iii) the asymmetry factor of a model for the angular distribution of the scattered photons (the phase function). They have been determined with specially designed spectrophotometer transmission, diffuse transmittance, and diffuse reflectance experiments and constitute the most significant addition to this contribution. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Modeling of transmitted X-ray intensity variation with sample thickness and solid fraction in glycine compactsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2003Wenjin Cao Abstract The previous paper in this series introduced an X-ray diffraction quantitation method for the polymorphic content in tablets made of pure components. Before the method could be transferred, further studies were required to explain the commonly observed X-ray intensity variation in analyzing compacts. The literature typically attributes the variation to partial amorphization under compression and/or to preferred orientation, without much viable explanation or compelling evidence. In this study, changes in intensity in compacts analyzed in transmission geometry were found to be primarily a function of sample thickness and solid fraction. A theoretical model was developed to describe the X-ray powder diffraction (XRPD) intensity as a function of solid fraction, mass absorption coefficient, and thickness. The model was tested on two sets of glycine compacts: one with varying thickness at constant solid fraction, and the other with various solid fractions at a given thickness. The results show that the model predicts the XRPD intensity at any given sample thickness and solid fraction. With this model, the intensity variation of compacts made under different compression conditions can be normalized, making the method transferable to various tablet geometries and facilitating the analysis over expected ranges of formulation and process variation. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2345,2353, 2003 [source] Synthesis and characterization of cyclopentadithiophene-based low bandgap copolymers containing electron-deficient benzoselenadiazole derivatives for photovoltaic devicesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2010In Hwan Jung Abstract We have synthesized two cyclopentadithiophene (CDT)-based low bandgap copolymers, poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(benzo[c][1,2,5]selenadiazole-4,7-diyl)] (PCBSe) and poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(4,7-dithiophen-2-yl-benzo[c][1,2,5]selenadiazole-5,5,-diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron-donating CDT unit and the electron-accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37,1.46 eV. The UV,vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor,acceptor (D,A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D,A complex using the ab initio Hartree-Fock method with a split-valence 6-31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]-phenyl-C61 -butyric acid methyl ester (PC61BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC71BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short-circuit current of 6.63 mA/cm2, and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423,1432, 2010 [source] Fabrication and Luminescent Properties of Nd3+ -Doped Lu2O3 Transparent Ceramics by Pressureless SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Ding Zhou The fabrication of transparent Nd3+ ion-doped Lu2O3 ceramics is investigated by pressureless sintering under a flowing H2 atmosphere. The starting Nd-doped Lu2O3 nanocrystalline powder is synthesized by a modified coprecipitant processing using a NH4OH+NH4HCO3 mixed solution as the precipitant. The thermal decomposition behavior of the precipitate precursor is studied by thermogravimetric analysis and differential thermal analysis. After calcination at 1000°C for 2 h, monodispersed Nd3+:Lu2O3 powder is obtained with a primary particle size of about 40 nm and a specific surface area of 13.7 m2/g. Green compacts, free of additives, are formed from the as-synthesized powder by dry pressing followed by cold isostatic pressing. Highly transparent Nd3+:Lu2O3 ceramics are obtained after being sintered under a dry H2 atmosphere at 1880°C for 8 h. The linear optical transmittance of the polished transparent samples with a 1.4 mm thickness reaches 75.5% at the wavelength of 1080 nm. High-resolution transmission electron microscopy observations demonstrate a "clear" grain boundary between adjacent grains. The luminescent spectra showed that the absorption coefficient of the 3 at.% Nd-doped Lu2O3 ceramic at 807 nm reached 14 cm,1, while the emission cross section at 1079 nm was 6.5 × 10,20 cm2. [source] Spectroscopic and Thermal Properties of Ga2S3,Na2S,CsCl GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Luiz C. Barbosa The synthesis and properties of the vitreous system (0.75,x)Ga2S3,0.25Na2S,xCsCl, with x varying from 0.1 to 0.2, are presented. Thermal, optical, and structural properties such as density, viscosity, thermal expansion coefficient, glass transition temperature, softening point temperature, refractive index, and absorption coefficient were measured using several techniques: X-ray diffraction, Raman scattering, differential thermal analysis, thermal mechanical analysis, and absorption spectroscopy. This glass system presents a high third-order non-linear optical susceptibility that can be significantly increased by increasing the CsCl content without affecting the low phonon frequency. [source] Extraction of pure lycopene from industrial tomato by-products in water using a new high-pressure processJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 14 2008Daniele Naviglio Abstract BACKGROUND: Lycopene, a precursor of ,-carotene with a well-known antioxidant activity, contained in many natural products such as tomato (Lycopersicon esculentum Mill.), watermelon, red pepper and papaya, is usually recovered from natural vegetal sources using organic solvents and a purification step. In this paper an innovative process for the extraction of pure lycopene from tomato waste in water that uses the Naviglio® extractor and water as extracting phase is presented. RESULTS: Lycopene was obtained in the all- trans form at a very high grade of purity, not less than 98% (w/w), with an average recovery of 14% (w/w). The availability of high-purity trans -lycopene allowed measurement of the molar absorption coefficient. An alternative procedure for high-performance liquid chromatographic analysis using a phenyl-hexyl silicone phase as inverse phase and a linear gradient in water and acetonitrile is also described. CONCLUSIONS: The use of water as extracting phase considerably reduces the cost of the entire process when compared with the commonly used solvent-based procedure or with the newer supercritical extraction process of lycopene from tomato waste. Lycopene, not soluble in water, was recovered in a quasi-crystalline solid form and purified by solid-phase extraction using a small amount of organic solvent. Copyright © 2008 Society of Chemical Industry This article was published online on September 15, 2008. Errors in Figures 2 - 4 were subsequently identified. The publishers wish to apologise for these errors. This notice is included in the online and print versions to indicate that both have been corrected [September 19, 2008] [source] Hydrogen generation from photoelectrochemical water splitting based on nanomaterialsLASER & PHOTONICS REVIEWS, Issue 4 2010Y. Li Abstract Hydrogen is potentially one of the most attractive and environmentally friendly fuels for energy applications. Safe and efficient generation, storage, and utilization of hydrogen present major challenges in its widespread use. Hydrogen generation from water splitting represents a holy grail in energy science and technology, as water is the most abundant hydrogen source on the Earth. Among different methods, hydrogen generation from photoelectrochemical (PEC) water splitting using semiconductors as photoelectrodes is one of the most scalable and cost-effective approaches. Compared to bulk materials, nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy, and reduced carrier-scattering rate. This article provides a brief overview of some recent research activities in the area of hydrogen generation from PEC water splitting based on nanostructured semiconductor materials, with a particular emphasis on metal oxides. Both scientific and technical issues are critically analyzed and reviewed. [source] Vascular response to laser photothermolysis as a function of pulse duration, vessel type, and diameter: Implications for port wine stain laser therapyLASERS IN SURGERY AND MEDICINE, Issue 2 2002Sol Kimel PhD Abstract Background and Objective Treatment of port wine stains (PWS) by photothermolysis can be improved by optimizing laser parameters on an individual patient basis. We have studied the critical role of pulse duration (tp) on the treatment efficacy. Study Design/Materials and Methods The V-beam laser (Candela) allowed changing tp over user-specified discrete values between 1.5 and 40 milliseconds by delivering a series of 100 microsecond spikes. For the 1.5 and 3 millisecond pulses, three spikes were observed at intervals tp/2 and for tp,,,6 milliseconds, four spikes separated by tp/3. The ScleroPlus laser (Candela) has a smooth output over its fixed 1.5 milliseconds duration. Blood vessels in the chick chorioallantoic membrane (CAM) were irradiated at fixed wavelength (595 nm), spot size (7 mm), radiant exposure (15 Jcm,2), and at variable tp. The CAM contains an extensive microvascular network ranging from capillaries with diameter D,<,30 ,m to blood vessels of D,,,120 ,m. The CAM assay allows real-time video documentation, and observation of blood flow in pre-capillary arterioles (A) and post-capillary venules (V). Vessel injury was graded from recorded videotapes. Mathematical modeling was developed to interpret results of vessel injury when varying tp and D. A modified thermal relaxation time was introduced to calculate vessel wall temperature following laser exposure. Results Arterioles. For increasing tp, overall damage was found to decrease. For fixed tp, damage decreased with vessel size. Venules. For all D, damage was smaller than for corresponding arterioles. There was no dependence of damage on tp. For given tp, no variation of damage with D was observed. Photothermolysis due to spiked (V-beam) vs. smooth (Scleroplus) delivery of laser energy at fixed tp (1.5 milliseconds), showed similar vessel injuries for al values of D (P>0.05). Conclusions The difference between initial arteriole and venule damage could be explained by the threefold higher absorption coefficient at 595 nm in (oxygen-poor!) arterioles. In human patients, PWS consist of ectatic venules (characterized by higher absorption), so that these considerations favor the use of 595-nm irradiation for laser photothermolysis. For optimal treatment of PWS it is proposed that tp be between 0.1 and 1.5 milliseconds. This is based on a modified relaxation time ,d,, defined as the time required for heat conduction into the full thickness of the vessel wall, which is assumed to have a thickness ,D ,,0.1D. The corresponding ,d, will be a factor of about six smaller than given in the literature. For vessels with D between 30 and 300 ,m, ,d, ranges from 0.1 to 1.5 milliseconds. Lasers Surg. Med. 30:160,169, 2002. © 2002 Wiley-Liss, Inc. [source] Continuous changes in the optical properties of liver tissue during laser-induced interstitial thermotherapyLASERS IN SURGERY AND MEDICINE, Issue 4 2001Joerg P. Ritz MD Abstract Background and Objective Laser-induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. To predict the effects of laser applications and to optimize treatment planning in LITT, it is essential to gain knowledge about light distribution in tissue, tissue optical properties (absorption, scattering, anisotropy, penetration depth), and their continuous changes during therapy. Study Design/Materials and Methods Measurements of optical properties were performed with a double integrating-sphere system and a laser diode (830 nm). Porcine liver tissue samples were examined in a native state (35°C) and after exposure to different temperatures (45°C to 80°C). Results Rising temperature was accompanied by a decrease in the absorption coefficient and anisotropy factor and an increase in the scattering coefficient. These changes were only significant in the temperature range of 50° to 65°C (P,<,0.01). The optical penetration depth decreased from 3.1mm in the native state to 1.7mm at 65°C (P,<,0.01). Above 65°, there was no significant change in the tissue optical properties. Conclusions The optical properties of liver tissue change significantly under the influence of tissue heating, resulting in a decreased optical penetration depth. These changes occur mainly in the temperature range of 50°C to 65°C, corresponding to protein denaturation. To ensure a safe and effective procedure, an adjustment of the laser power to the actual penetration depth is recommended during therapy. Lasers Surg. Lasers Surg. Med. 28:307,312, 2001. © 2001 Wiley-Liss, Inc. [source] Dielectric properties of silicon in terahertz wave regionMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2008JiuSheng Li Abstract By using backward-wave oscillator system, the terahertz dielectric properties of p-type silicon were tested in the frequency range extending from 0.68 to 0.85 THz. The refractive indices, the power absorption coefficient, and the dielectric functions of various resistivity p-type silicons were measured and compared. The variation of the refractive index of the ultra-resistivity silicon was less than 3%, ranging from 3.037 to 3.125, but the absorption coefficient of the ultra-resistivity silicon showed very different frequency-dependent behaviors, ranging from 3.25 × 10,3 cm,1 to 2.90 × 10,5 cm,1, within the investigated frequency range. The ultra-resistivity silicon will be a good candidate material for terahertz transmission waveguide with ultra-low loss. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1143,1146, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23313 [source] Light-emission potential of Si-based nanostructures from calculated absorption coefficientMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2001Sumitra Ghosh Abstract The values of the absorption coefficient in coupled Si/SiGe and Si/SiGeC nanostructures are calculated for quasidirect no-phonon transition due to the momentum spread of electrons spatially confined in ultrathin layers. The values in quantum dots are found to be as large as that in bulk GaAs. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 352,355, 2001. [source] Mira variables in the Galactic bulge with OGLE-II dataMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005Noriyuki Matsunaga ABSTRACT We have extracted a total of 1968 Mira variables from the Optical Gravitational Lensing Experiment II (OGLE-II) data base in the Galactic bulge region. Among them, 1960 are associated with 2 Micron All-sky Survey (2MASS) sources, and 1541 are further identified with Midcourse Space Exploration (MSX) point sources. Their photometric properties are compared with those of Mira variables in the Large and Small Magellanic Clouds. We have found that mass-losing stars with circumstellar matter are reddened such that the colour dependence of the absorption coefficient is similar to that of interstellar matter. We also discuss the structure of the bulge. The surface number density of the bulge Mira variables is well correlated with the 2.2-,m surface brightness obtained by the Cosmic Background Explorer (COBE) satellite. Using this relation, the total number of Mira variables in the bulge is estimated to be about 6 × 105. The log P,K relation of the Mira variables gives their space distribution which supports the well-known asymmetry of the bar-like bulge. [source] Primary Photoprocesses in a Fluoroquinolone Antibiotic Sarafloxacin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Fernando Lorenzo The photophysical properties of the fluoroquinolone antibiotic sarafloxacin (SFX) were investigated in aqueous media. SFX in water, at pH 7.4, shows intense absorption with peaks at 272, 322 and 335 nm, (, = 36800 and 17000 dm3 mol,1 cm,1, respectively). Both the absorption and emission properties of SFX are pH-dependent; pKa values for the protonation equilibria of both the ground (5.8 and 9.1) and excited singlet states (5.7 and 9.0) of SFX were determined spectroscopically. SFX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Laser flash photolysis and pulse radiolysis studies have been carried out in order to characterize the transient species of SFX in aqueous solution. Triplet,triplet absorption has a maximum at 610 nm with a molar absorption coefficient of 17,000 ± 1000 dm3 mol,1 cm,1. The quantum yield of triplet formation has been determined to be 0.35 ± 0.05. In the presence of oxygen, the triplet reacts to form excited singlet oxygen with quantum yield of 0.10. The initial triplet (3A*) was found to react with phosphate buffer to form triplet 3B* with lower energy and longer lifetime and having an absorption band centered at 700 nm. SFX triplet was also found to oxidize tryptophan to its radical with concomitant formation of the anion radical of SFX. Hence the photosensitivity of SFX could be initiated by the oxygen radicals and/or by SFX radicals acting as haptens. [source] Determination of the Minimum Temperature Required for Selective Photothermal Destruction of Cancer Cells with the Use of Immunotargeted Gold NanoparticlesPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2006Xiaohua Huang ABSTRACT Laser photothermal therapy of cancer with the use of gold nanoparticles immunotargeted to molecular markers on the cell surface has been shown to he an effective modality to selectively kill cancer cells at much lower laser powers than those needed for healthy cells. To elucidate the minimum light dosimetry required to induce cell death, photothermal destruction of two cancerous cell lines and a noncancerous cell line treated with antiepidermal growth factor receptor (anti-EGFR) antibody-conjugated gold nanoparticles is studied, and a numerical heat transport model is used to estimate the local temperature rise within the cells as a result of the laser heating of the gold nanoparticles. It is found that cell samples with higher nanoparticle loading require a lower incident laser power to achieve a certain temperature rise. Numerically estimated temperatures of 70,80°C achieved by heating the gold particles agree well with the measured threshold temperature for destruction of the cell lines by oven heating and those measured in an earlier nanoshell method. Specific binding of anti-EGFR antibody to cancerous cells overexpressing EGFR selectively increases the gold nanoparticle loading within cancerous cells, thus allowing the cancerous cells to be destroyed at lower laser power thresholds than needed for the noncancerous cells. in addition, photothermal therapy using gold nanoparticles requires lower laser power thresholds than therapies using conventional dyes due to the much higher absorption coefficient of the gold nanoparticles. [source] Influence of Nd co-doping on the Cr4+ content in PWO single crystalPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2004Weifeng Li Abstract The formation mechanism of Cr4+ in PbWO4 (PWO) crystals is studied by optical absorption and X-ray excited luminescence (XEL) spectra. It is found that the concentration of Cr4+ depends not only on the initial amount of Cr3+ but more importantly on the coaddition of Nd3+. This material may be used as a new passive Q-switched laser in view of its high absorption coefficient in the NIR region. For Cr-containing sample, Cr3+ primarily replaces Pb2+ and results in large relaxation of lattice. In order to keep the scheelite structure, some Cr3+ ions are oxidized into Cr4+ and occupy W6+ sites. In the codoping case, Nd3+ preferentially substitute for Pb2+ and Cr is forced into W6+ sites in the form of Cr4+ to keep charge neutrality and structural integrity. This view is strongly supported by FT-IR spectra. The origin of the decrease and even extinction of XEL is also discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||||||||