Variation Of Absorption Coefficient Research Articles

Effects of temperature-dependent material properties and shielding gas on molten pool formation during continuous laser welding of AZ91 magnesium alloy

Laser welding processes are widely used for fabrications in many engineering applications such as aerospace and automotives. In this paper, a moving distributed heat source model based on Goldak's method [1] has been implemented into finite volume thermal simulations in order to predict temperature distributions during the welding process of a magnesium alloy and to study the effects of variations in thermal properties, absorption coefficient and gas shielding on the computed temperature distributions and weld pool dimensions. The main conclusion is the significant effects of varying the thermal conductivity and absorption coefficient of magnesium. Also, it has been seen that the shielding gas, besides its main role of protection against oxidation, has a significant effect on the width of the weld pool. Finally, the obtained results have been compared to the experimental ones and a satisfactory correlation has been observed, indicating the reliability of the model developed in this study.

The Effect of Thermal Oxidation on the Luminescence Properties of Nanostructured Silicon

Herein is reported a detailed study of the luminescence properties of nanostructured Si using X-ray excited optical luminescence (XEOL) in combination with X-ray absorption near-edge structures (XANES). P-type Si nanowires synthesized via electroless chemical etching from Si wafers of different doping levels and porous Si synthesized using electrochemical method are examined under X-ray excitation across the Si K-, L(3,2) -, and O K-edges. It is found that while as-prepared Si nanostructures are weak light emitters, intense visible luminescence is observed from thermally oxidized Si nanowires and porous Si. The luminescence mechanism of Si upon oxidation is investigated by oxidizing nanostructured Si at different temperatures. Interestingly, the two luminescence bands observed show different response with the variation of absorption coefficient upon Si and O core-electron excitation in elemental silicon and silicon oxide. A correlation between luminescence properties and electronic structures is thus established. The implications of the finding are discussed in terms of the behavior of the oxygen deficient center (OCD) and non-bridging oxygen hole center (NBOHC).

OH in natural orthopyroxene: an in situ FTIR investigation at varying temperatures

In situ unpolarized and polarized Fourier transform infrared spectra of a natural orthopyroxene at varying temperatures were obtained using a heating stage attached on an Infrared microscope. The three main bands (3,595, 3,520 and 3,410 cm−1) at room temperature are ascribed to OH fundamental stretching bands. With increasing temperature from room temperature to 500 °C, the 3,595 cm−1 band shifts 20 cm−1 to lower frequency. The total integral absorbance decreases with increasing temperature. These changes are reversible. Excluding the influences of dehydration, proton migration, thermal expansion, and changes in OH dipole direction, the change of integral absorbance with temperature reflects the temperature dependence of absorption coefficient due to the anharmonicity of OH vibration. Based on the integral absorption coefficient at room temperature (14.84 ppm−1 cm−2) from Bell et al. (Am Mineral 80:463–474, 1995), the integral absorption coefficients at other temperatures are calculated. The variation of integral absorption coefficient between room temperature and 500 °C obtained in this study is about 18.5 % and may be greater at higher temperature according to the proposed linear relationship.

Photoacoustic optical properties at UV, VIS, and near IR wavelengths for laboratory generated and winter time ambient urban aerosols

Abstract. We present the laboratory and ambient photoacoustic (PA) measurement of aerosol light absorption coefficients at ultraviolet wavelength (i.e., 355 nm) and compare with measurements at 405, 532, 870, and 1047 nm. Simultaneous measurements of aerosol light scattering coefficients were achieved by the integrating reciprocal nephelometer within the PA's acoustic resonator. Absorption and scattering measurements were carried out for various laboratory-generated aerosols, including salt, incense, and kerosene soot to evaluate the instrument calibration and gain insight on the spectral dependence of aerosol light absorption and scattering. Ambient measurements were obtained in Reno, Nevada, between 18 December 2009 and 18 January 2010. The measurement period included days with and without strong ground level temperature inversions, corresponding to highly polluted (freshly emitted aerosols) and relatively clean (aged aerosols) conditions. Particulate matter (PM) concentrations were measured and analyzed with other tracers of traffic emissions. The temperature inversion episodes caused very high concentration of PM2.5 and PM10 (particulate matter with aerodynamic diameters less than 2.5 μm and 10 μm, respectively) and gaseous pollutants: carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxide (NO2). The diurnal change of absorption and scattering coefficients during the polluted (inversion) days increased approximately by a factor of two for all wavelengths compared to the clean days. The spectral variation in aerosol absorption coefficients indicated a significant amount of absorbing aerosol from traffic emissions and residential wood burning. The analysis of single scattering albedo (SSA), Ångström exponent of absorption (AEA), and Ångström exponent of scattering (AES) for clean and polluted days provides evidences that the aerosol aging and coating process is suppressed by strong temperature inversion under cloudy conditions. In general, measured UV absorption coefficients were found to be much larger for biomass burning aerosol than for typical ambient aerosols.

Tuning the photovoltaic parameters of thiophene-linked donor–acceptor liquid crystalline copolymers for organic photovoltaics

Three new donor–acceptor copolymers containing the electron acceptor di-2-thienyl-2′,1′,3′-benzothiadiazole (DTBT) linked to the electron donors 9,9-bis[6-(4′-hexyloxy-terphenyloxy)-hexyl]-fluorene (Ftp) with terphenyl mesogen side chain viathiophene units are synthesized to study polymer structure–properties relationships in organic photovoltaic devices. All the random copolymers (PFtpTDTBT-a, b, c) were prepared via Stille polycondensations based on variable contents of DTBT and Ftp. The results of absorption spectra, fluorescence spectra and electrochemistry shows that increasing the ratio of fluorine units and decreasing the electron withdrawing groups of DTBT not only control the bandgaps but also the liquid crystallinity of the copolymers. The structural variation of mesomorphism behaviors induced by terphenyl pendants is characterized by POM, DSC, XRD and polarized absorption. When the polymers were blended with fullerene derivative as an electron acceptor, the photovoltaic performance reveals the good correlation between the Ftp and DTBT ratio in the main chain of the copolymers with desirable HOMO levels and the open circuit voltage (Voc). Therefore, the deepest HOMO energy level of polymer PFtpTDTBT-a leads to the highest Voc of 0.86 V, while the polymer PFtpTDTBT-c possesses a superior absorption coefficient resulting in the largest short current density (Jsc = 4.58 mA cm−2). Additionally, the packing alignments of the three polymers guided by the orientation of mesogenic pendants pose a significantly effect on the morphology with different microphase separation after annealing treatment. Nevertheless, the solar cell based on PFtpTDTBT-b shows the best performance among the thiophene incorporated polymers, which demonstrated the importance of designing materials with a balance in the properties of HOMO/LUMO energy levels, the absorption coefficient and morphological variations.

Effects of edge screens on the absorption of blocks of theatre chairs

This paper reports new measurement results investigating the use of screens around samples of theatre chairs to minimize edge effects when measuring theatre chair absorption in reverberation chambers. The absorption measurements included both full scale and scale model measurements in reverberation chambers and a model recital hall. The use of screens has been proposed to better approximate the sound absorption of the larger blocks of chairs in auditoria. The method of measuring the absorption of blocks of chairs with screens around their edges and located in the corner of a reverberation chamber did not give results indicative of the values obtained for larger areas in auditoria. The addition of screens around samples of chairs did not eliminate the variation of absorption coefficients with perimeter/area ratio. The results of extrapolations from measurements of blocks of screened chairs to infinite samples gave lower absorption coefficients than found for blocks of unscreened chairs. The absorption of chairs in large performance halls can best be predicted using the P/A method to extrapolate from reverberation chamber measurements of smaller samples of unscreened chairs, with a range of P/A values, to the larger samples and lower P/A ratios of blocks of chairs typical of performance spaces.

Study on the Sound Absorption Properties of Several Kinds of Fibers

In this paper, four kinds of natural fibers (cotton, wool, silk and ramie) are studied. Three experimental programs are designed, and influence factors of sound absorption properties of porous sound absorption material are discussed. With the change of material thickness and cavity length, the variation of sound absorption coefficient is obtained in different noise frequency.

Effects of Indole-3 acetic acid and turnip peroxidase and Indole-3 acetic acid and horseradish peroxidase systems on human colon cancer HT2G cells

The addition of cholesterol into the AOT/isooctane/H2O system makes the surfactant monolayer of the reverse micellar droplets rigid with concomitant decrease of interdroplet interactions. So a peroxidase molecule hosted by some of these droplets experiences a completely different atmosphere than that without the additive. The change of composition of the reverse micelles results in enhancing the catalytic activity of the enzyme at various temperatures and pH values. A different trend of variation of molar absorption coefficient (ϵ) is also found Wo ≅ 10, where ϵ gradually decreases with a rise in Wo value till Wo ≅ 10 and above which it remains more or less constant. There is no shift of pH profile in the micellar system by the introduction of the cholesterol into it. By measuring the catalytic constant (kcat) it is found that the critical Wo shifts from 12 to a value 10.

Optical Properties of Undoped and Indium-doped Tin Oxide Thin Films

Thin films of Tin Oxide (SnO2), having thickness of 200 nm, were formed on to glass substrates by thermal evaporation of high-purity SnO2 powder in vacuum at various substrate temperatures (TS), ranging between 25 and 200°C. SnO2 films with varying thickness were also prepared for a fixed TS = 100°C. Further, doping of SnO2 films with Indium (In) was accomplished through solid state diffusion process by successive deposition of SnO2 and In films and subsequent annealing at 200°C for 10 minutes. Both undoped and doped films were characterized optically by UV-VIS-NIR spectrophotometry in the photon wavelength ranging from 300 to 2500 nm. In the visible photon wavelength range, the average optical transmittance (T%) of the films with varying TS was found to be 85%. The maximum value of T % was found to be 89 % around the wavelength of 700nm. The variation of absorption coefficient with photon energy in the fundamental absorption region is the steepest for TS = 100°C. The sub-band gap (SBG) absorption is also minimum for this Ts. A fluctuating behavior of the band gap energy (Eg) with Ts is observed attaining the highest value of 3.59 eV for Ts = 100°C. The band gap energy increases with thickness but T% in the visible range decreases. The T% in the visible range varies inversely with indium doping, being highest for undoped films. The Eg increases upto 2 wt% In doping and gradually decreases for enhanced doping. It seems reasonable to conclude that In doping does not bring favorable optical characteristics. Undoped SnO2 films having thickness of 200 nm and formed at substrate temperature of 100°C yield essential acceptable properties for photovoltaic applications.DOI: http://dx.doi.org/10.3329/jbas.v35i1.7975Journal of Bangladesh Academy of Sciences, Vol.35, No.1, 99-111, 2011

Sulphide oxidation in ornamental slates: protective treatment with siloxanes

In this work, we present the results of the measurement of the effectiveness of two silanes-siloxanes based products applied on roofing slates with the aim of slowing down the oxidation of the iron sulphide inclusions. The products were applied by immersion and spraying and also at different dilutions. The effectiveness of the treatments were evaluated by means of static contact angle measurements and water absorption coefficient variations; also, the durability under thermal cycles and the colour variations before treatment and before UVA exposition were tested. In all the cases, a very low product consumptions were obtained, due to the particular porous system of these rocks; also, any of the treatments increased the static angle. Nevertheless, the products tested remarkably increased the resistance of sulphides to the oxidation during thermal cycles without producing important changes in rock colour and also they have shown a good durability under UVA exposition

Simulation and modeling of laser-tissue interactions based on a liposome-dye system.

This work presents an overview of the use of liposomes for targeted delivery of photosensitizers to tumors for Photodynamic Therapy (PDT). It assesses the results of a quantitative model to explain the interaction of short-pulsed lasers (in the nanosecond and picosecond domains) with a liposome-dye complex in terms of a localized photo-induced thermal mechanism. Incorporation of an organic dye (sulforhodamine) within lipid vesicles has been investigated in conjunction with the effect of laser irradiation on the integrity of the liposome-dye complex. The variation of the absorption coefficient as a function of wavelength for dye-encapsulated liposomes before and after laser-induced release of dye was studied and modeled. The commercial software Mathematica was used to develop a Gaussian model for the energy absorption by the liposome-dye complex. Dye release from 3 microm - liposome encapsulating 25 mM aqueous solution of sulforhodamine dye was studied using 8 ns laser pulses at the second harmonic of the Nd:YAG laser (at 532 nm) and compared with dye release employing 25 ps - laser pulses. In addition, the temperature-dependence of the dye release has been included in the photo-thermal model.

Variation of Absorption Coefficient of Glucose Water in Consideration of Water Displacement

Adding glucose in water will cause two influences on the aqueous solution: one is absorption coefficient addition of glucose; the other is absorption coefficient decrease of water because of water displacement. So the total absorption effect is the result of the absorption coefficient increase of glucose and absorption coefficient decrease of water. In this paper the absorption coefficient of glucose water is analyzed in consideration of water displacement. By data of handbook, we deduce a relationship between the glucose absorption coefficient addition and water absorption coefficient decrease. When one molar glucose is added into water, 6.15 molars water molecular is displaced. The wavelength selection in glucose detection should be at the place where the combined absorption is maximum. The wavelength of widely used in blood glucose concentration detection, e.g. 1.6μm, is selected as an example for analysis. When glucose is added into water, the linear relationship between glucose concentration and absorption coefficient is hold on. On the other hand, when the water molecular is decreased, the water absorption coefficient will decreased, too, which will decrease the total absorption coefficient compared to the situation without water displacement. In general, water displacement will decrease the sensitivity of absorption coefficient to glucose concentration.

Pulsed photothermal profiling of water-based samples using a spectrally composite reconstruction approach

Pulsed photothermal profiling involves reconstruction of temperature depth profile induced in a layered sample by single-pulse laser exposure, based on transient change in mid-infrared (IR) emission from its surface. Earlier studies have indicated that in watery tissues, featuring a pronounced spectral variation of mid-IR absorption coefficient, analysis of broadband radiometric signals within the customary monochromatic approximation adversely affects profiling accuracy. We present here an experimental comparison of pulsed photothermal profiling in layered agar gel samples utilizing a spectrally composite kernel matrix vs. the customary approach. By utilizing a custom reconstruction code, the augmented approach reduces broadening of individual temperature peaks to 14% of the absorber depth, in contrast to 21% obtained with the customary approach.

Investigation of optical properties of the sulfosalt new absorber Sn2Sb2S5 thin films using photothermal deflection spectroscopy

The thin Sn2Sb2S5 films which are new absorber material useful for photovoltaic cells are studied in this paper by the photothermal deflection spectroscopic method. Our study consists to draw the experimental normalized amplitude and phase of the photothermal signal versus wavelength at a fixed modulated monochromatic light pump beam frequency. The phase curves are independent of wavelength which is predicted theoretically. However the amplitude ones show saturated regions for high and low absorption coefficient and great variations in the vicinity of the energy gap. These curves show two energy gaps which may be explained by the coexistence of two phases. By comparison of the experimental and theoretical normalized amplitude of the PDS signal one can deduce the optical absorption coefficient and then the energy gaps. The obtained values of the energy gaps are in good agreement with those obtained by reflectivity and transmission measurements.

Site-specific infrared O-H absorption coefficients for water substitution into olivine

There are four ways by which OH - commonly substitutes into olivine, namely those associated with (1) Si vacancies, (2) Mg vacancies, (3) Ti, or (4) trivalent cations. The four mechanisms, which we label [Si], [Mg], [Ti], and [triv], respectively, may each be fingerprinted by their characteristic O-H stretching modes in the infrared spectrum. We show by comparing the integrated intensities of these characteristic infrared peaks against total water content analyzed by secondary ion mass spectrometry, obtained for a suite of synthetic olivines plus one natural olivine, that the different substitution mechanisms require different absorption coefficients (k). For [Ti], we find k = 0.18 ± 0.07, identical to the value previously obtained from natural olivines in which the water was mainly associated with [Ti] defects. Values of k for [Si] and [triv] are 0.57 ± 0.04 and 0.18 ± 0.05, respectively; that for [Mg] is too small to be accurately determined (0.03 ± 0.03). The values of k for [Ti] and [Si] defects differ by a factor of three even though their average wavenumbers are virtually the same. The [Ti] and [triv] defects, on the other hand, have very similar absorption coefficients at significantly different wavenumbers. This highlights the inadequacy of using wavenumber-dependent calibrations for olivine and presumably for NAMs in general. Different substitution mechanisms have their own crystallographic environments that determine their absorption coefficients. The large variation in absorption coefficients within a single mineral emphasizes the importance of distinguishing the substitution mechanism if meaningful quantitative results are to be obtained from infrared spectroscopy.

Donor/acceptor effects on the nonlinear optical properties of 1,3 diphenyl propenones

Employing the single beam Z-scan technique with nanosecond laser pulses at 532 nm, the refractive and absorptive nonlinearities of donor and acceptor substituted (2E)-1-(3,4-dimethoxyphenyl)-3-phenylprop-2-en-1-one have been studied. The sign of the nonlinear index of refraction (n 2) is found to be negative and the magnitude of n 2 is in the order of 10−11 esu. The second-order molecular hyperpolarizability (γh) is calculated to be in the order of 10−32 esu. The variation of nonlinear absorption coefficient (βeff) with input intensity (I 0) is studied and the nonlinear absorption mechanism is found to be reverse saturable absorption (RSA). The enhancement of nonlinearity due to the donor and acceptor substitution is in accordance with the variation in π electron delocalization in the molecules. The compounds exhibit good optical limiting as well.

Effects of the physical and optical properties of urban aerosols measured during the CAPITOUL summer campaign on the local direct radiative forcing

Measurements of aerosol optical and physical properties, and chemical composition were conducted at Toulouse, an urban site of southwest France, as part of the CAPITOUL experiment. A period of intensive observations was held over 10 days during the summer campaign in June–July, 2004. During this period, PM2.5 concentrations ranged between 1 and 50 µg m−3. Aerosol size distributions exhibit the presence of three distinct modes which could be fitted by lognormal functions. Diurnal variations of aerosol concentration, size distribution, BC concentration, scattering and absorption coefficients, and single scattering albedo show the presence of two maxima corresponding to rush hours due to various urban activities such as vehicle traffic. Over the period of study, the single scattering albedo at 0.52 µm is found to be 0.7 ± 0.1, indicating the dominance of absorbing aerosols over Toulouse. Airborne measurements observed the vertical distribution of aerosols in the atmosphere. These observations clearly show that aerosol is mostly contained within the UBL which contributes significantly to the aerosol optical depth. The GAME radiative transfer model (RTM) has been used to carry out the radiative transfer computations. A synergetic approach was applied to generate spectral values of aerosol parameters required as input for the radiative transfer calculations. Vertical radio soundings and airborne measurements provided in-situ parameters required for the RTM. Simulations indicate that aerosols over Toulouse reduce significantly (−30 W m−2) the solar energy reaching the surface, mainly by absorption of the solar radiation into the atmosphere. At the TOA, aerosol forcing is even found to be positive (+0.8 W m−2). These results confirm that local direct aerosol forcing in urban atmosphere is mainly driven by the absorbing black carbon aerosols. The mean heating rate within the UBL is considerably enhanced, by 4.57 K day−1, due to the presence of absorbing aerosols.

Design and Sensing Properties of an Integrated Optical Gas Sensor Based on a Multilayer Structure

In this paper, a new multilayer integrated optical sensor (MIOS) for ammonia detection at room temperature is proposed and characterized. The sensor is integrated on a single-mode TE0-TM0 planar polymer waveguide and based on polyaniline (PANI) sensitive material. A polymethyl methacrylate (PMMA) passive layer is deposited between the waveguide core and PANI sensitive layer in order to decrease optical losses induced by evanescent wave/sensitive material coupling. The design of this new sensor is discussed. Moreover, in order to investigate the feasibility of this sensor, the sensing properties to ammonia at room temperature are studied. A significant change is observed in the guided light output power after the sensor is exposed to ammonia gas, due to PANI absorption coefficient variation. This new ammonia sensor shows fast response and recovery times, good reversibility and repeatability. The metrological parameters (sensitivity, response time and recovery time) of the sensor are strongly influenced by the interaction length (length of sensing region) and the PANI forms (doped and dedoped). The sensor has a logarithmic linear optical response within the ammonia concentration range between 92 to 4618 ppm. These experimental results demonstrate that the MIOS structure presents a potential innovation to elaborate integrated optical sensor based on non transparent (opaque) sensitive material.

Implementation of a phase array diffuse optical tomographic imager

Diffuse optical tomography (DOT) using near-infrared (NIR) light is a promising tool for noninvasive imaging of deep tissue. This technique is capable of quantitative reconstructions of absorption coefficient inhomogeneities of tissue. The motivation for reconstructing the optical property variation is that it, and, in particular, the absorption coefficient variation, can be used to diagnose different metabolic and disease states of tissue. In DOT, like any other medical imaging modality, the aim is to produce a reconstruction with good spatial resolution and accuracy from noisy measurements. We study the performance of a phase array system for detection of optical inhomogeneities in tissue. The light transport through a tissue is diffusive in nature and can be modeled using diffusion equation if the optical parameters of the inhomogeneity are close to the optical properties of the background. The amplitude cancellation method that uses dual out-of-phase sources (phase array) can detect and locate small objects in turbid medium. The inverse problem is solved using model based iterative image reconstruction. Diffusion equation is solved using finite element method for providing the forward model for photon transport. The solution of the forward problem is used for computing the Jacobian and the simultaneous equation is solved using conjugate gradient search. The simulation studies have been carried out and the results show that a phase array system can resolve inhomogeneities with sizes of 5 mm when the absorption coefficient of the inhomogeneity is twice that of the background tissue. To validate this result, a prototype model for performing a dual-source system has been developed. Experiments are carried out by inserting an inhomogeneity of high optical absorption coefficient in an otherwise homogeneous phantom while keeping the scattering coefficient same. The high frequency (100 MHz) modulated dual out-of-phase laser source light is propagated through the phantom. The interference of these sources creates an amplitude null and a phase shift of 180 degrees along a plane between the two sources with a homogeneous object. A solid resin phantom with inhomogeneities simulating the tumor is used in our experiment. The amplitude and phase changes are found to be disturbed by the presence of the inhomogeneity in the object. The experimental data (amplitude and the phase measured at the detector) are used for reconstruction. The results show that the method is able to detect multiple inhomogeneities with sizes of 4 mm. The localization error for a 5 mm inhomogeneity is found to be approximately 1 mm.

Thermal acoustic radiation from multilamellar vesicles in lipid phase transition

A new acoustical method for the investigation of lipid phase transition is introduced based on the measurement of the thermal acoustic radiation (TAR) inherent in lipids. The TAR of multilamellar vesicles from dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) was measured in the megahertz range and the variations in the radiation intensity during the lipid phase transition were recorded. Two types of variations are possible: if the temperature of the vesicles decreases (in the process of transition from the liquid crystalline state to the gel state) then the TAR intensity increases, and if the temperature increases (in the reverse transition) then the TAR intensity decreases. These effects are connected with an increase in the ultrasonic absorption in the vesicles under lipid phase transition. Basing on the results of the TAR investigation, a new theoretical estimate has been developed of the variation in the absorption coefficient during the lipid phase transition. In this estimate, the variation is equated to the ratio of the phase transition entropy to the gas constant.