Extinction Coefficient Values Research Articles

Effects of cloud and humidity on atmospheric extinction coefficient derived from visual range observations in Iranian major airports

ABSTRACTVisibility impairment, one of the restricting phenomena for aviation, results from light scattering and absorption. In this study, the historical visibility database for the period of 1981–2010 is used to obtain extinction coefficient according to the Koschmieder theory in the four busiest airports in Iran, including Tehran‐Mehrabad, Mashhad, Shiraz and Isfahan. The long‐term trend of extinction coefficient and its seasonal variations are investigated using 10th and 90th percentiles of extinction data to show the visual range in each airport. Correlation of the long‐term visibility trend with relative humidity (RH) and cloudiness is also examined. The comparison of seasonal mean extinctions shows the noticeable effect of local climate. The highest extinction coefficient value in each airport is seen during winter, while the lowest value occurs in summer. The seasonal mean extinction coefficient level in winter is about 0.1 km−1 higher than those of the other seasons. This is likely due to pollutants trapped by the stagnant cold air that partly obstruct visibility and increase the extinction in wintertime. There is not an outstanding variation of the tenth percentile of the extinction coefficient in the four airports. The low variation may relate to the definition of the upper threshold in visibility. Analysis shows that there is a positive correlation between extinction and humidity in all the airports that indicates the increase of scattering by hygroscopic particles with increasing humidity, such effect would be accentuated in high RH. The same result is seen for different percentages of cloudiness. To minimize the effects of humidity and cloudiness on the long‐term visibility trend, the days with the relative humidity values more than 70% and cloudiness of more than 5/8 of the sky are removed from the visibility trend analysis. The trends of the screened days are nearly parallel to the trends of raw data, but with a slight difference in each airport. The overall filtered long‐term trends show the increase of extinction coefficient at all the airports that emphasize the effect of pollution on the trend of light extinction within the whole period of this study. Eliminating the meteorological factors from the raw data does not change the overall increasing trend of extinction at Tehran and Isfahan airports. It suggests that the changes in air quality are responsible for the long‐term visibility degradation at these two stations that are located in the two most highly industrialized and polluted cities in Iran.

Multifrequency lidar sounding of air pollution by particulate matter with separation into respirable fractions

A technique is considered for retrieving the spatial distributions of respirable fractions of aerosol in the lower atmosphere on the basis of multifrequency lidar sounding data without the use of additional aerosol optical and microphysical parameters along a sounding path. For this purpose, it is suggested to replace the spectral values of the aerosol extinction coefficient involved in lidar equations with the linearly independent parameters of their approximation, and retrieve the spatial distributions of these parameters from the numerical solution of the set of equations composed of all wavelength-time lidar signal samples. As a result, the number of unknowns in the set of equations to be solved is significantly reduced, and its matrix becomes overdetermined, which can be used for selection of physically reasonable values of the aerosol backscattering phase function at the lidar operating wavelengths. An assumption that there are two segments at the sounding path with similar aerosol extinction coefficient profiles is used to determine the lidar calibration constants. An algorithm is suggested for the search for these segments by the wavelength-time structure of a lidar signal. The inverse problem of aerosol light scattering is solved on the basis of stable regression relations between the concentrations of respirable aerosol fractions and approximation parameters of the aerosol extinction spectrum. The stability of the technique developed to the calibration errors and spatial variations in the aerosol backscattering phase function is shown in numerical experiments on laser sounding of aerosol.

Effect of Red-to-Near Infrared Light on the Reaction of Isolated Cytochrome c Oxidase with Cytochrome c.

Our primary hypothesis was that red-to-near infrared (R-NIR) irradiation would have an effect on the kinetics parameters of the reaction of cytochrome c with isolated cytochrome c oxidase (CCO), and that the magnitude and direction of these changes could be interpreted in the context of the reaction schemes proposed by other authors. New values for the milimolar extinction coefficients of cytochrome c were also determined. Definitive answers to the fundamental processes involved in red-to-near infrared photobiomodulation (R-NIR-PBM) have not been obtained. The consensus is that the electron transport chain enzyme CCO is the target for R-NIR-PBM. This work was undertaken to explore the effect of R-NIR on the activity of isolated CCO. Scans for cytochrome c were obtained in both reduced and oxidized states, and values for the extinction coefficients were calculated. Activity assays were performed by following the oxidation state of cytochrome c at 550 or 415 nm. R-NIR effects on CCO activity were evaluated by pre-irradiating the enzyme at 670 or 830 nm, or by irradiating the reaction mixture with 660 nm light. Milimolar extinction coefficients (L-1 cm-1) were: ɛ550red = 29.1 ± 0.4, ɛ550ox = 8.60 ± 0.15, ɛ415red = 140 ± 2, and ɛ415ox = 89.0 ± 1.1. Reduced-oxidized extinction coefficients were: δɛ550red-ox = 20.5 ± 0.2, and δɛ415red-ox = 51.0 ± 2.0. The second order rate constants k' for irradiated CCO did not show a statistically significant difference from controls. The oxidation of cytochrome c by isolated CCO has not been shown to be affected by R-NIR irradiation, whether applied prior to or concurrently with the enzymatic assays. This lack of effect by R-NIR calls into question the CCO activity model of R-NIR photobiomodulation.

Influence of annealing treatment on phase transformation of Ga15Se77Tl8 thin films

The present work describes the first order phase transformation in chalcogenide Ga15Se77Tl8 thin films. Simple melt quenching method was applied to prepare the bulk Ga15Se77Tl8 samples. Ga15Se77Tl8 thin films were prepared by the thermal evaporation on glass and silicon wafer substrates under the vacuum condition of 10−5 Torr. The amorphous and glassy nature of synthesized sample was verified by differential scanning calorimeter. The phase transformation was studied at different temperatures of 343, 358 and 373 K for 2 h. The crystalline, morphological and optical properties were analysed to explain the phase transformation in as grown and thermally annealed films at different temperatures. It was found that as grown film revealed the amorphous nature, while the annealed films possessed the polycrystalline nature. From optical properties, the values of extinction (k) and absorption (α) coefficient for Ga15Se77Tl8 thin films enhanced with the increase of the incident photon energy as well as annealed temperature. The decrease in the optical band gap with respect to annealed temperatures was described on the basis of phase transformation from amorphous to polycrystalline state.

Influence of sprayed nanocrystalline Zn-doped TiO2 photoelectrode with the dye extracted from Hibiscus Surattensis as sensitizer in dye-sensitized solar cell

Highly oriented Zn doped TiO2 thin films (0, 2, 4, 6 and 8at%) were deposited by spray pyrolysis technique. X-ray diffraction analysis showed a strong orientation along (101) direction for 6at% Zn with polycrystalline tetragonal anatase phase. Scanning electron microscopy observations revealed uniform distribution of spherical-shaped grains, whereas columnar arrangement of tetragonal-shaped grains with porous nature was revealed from atomic force microscopy. Transmittance spectra indicated a decrease in the energy band gap with increasing doping concentration; i.e. 3.55 up to 3.21eV, attributed to grain refinement to the nanoscale regime. The optical constants such as refractive index and extinction coefficient as a function of wavelength, were determined; the low extinction coefficient values confirmed the good quality of the thin films. Photoluminescence spectra showed strong emissions at 423 and 437nm with a weak emission at 505nm, which confirmed the lesser defect density in 6at% Zn film. The electrical properties studied by Hall Effect measurements revealed that the 6at% Zn led to an increase in the carrier concentration, as well as an increase in the mobility with a least resistivity. The efficiency of dye sensitized solar cells, assembled by using natural dye extracted from Hibiscus Surattensis as sensitizer and Zn-doped TiO2 nanocrystalline thin films as a photoelectrode, was found to be around 1.22%.

Influence of Cu dopant on the optical and electrical properties of spray deposited tin sulphide thin films

Copper doped tin sulphide (SnS: Cu) thin films have been prepared by the spray pyrolysis technique at the substrate temperature of 350 °C. The optical and electrical properties of the films were studied as a function of copper dopant concentration (up to 10 at.%). The optical measurements showed the energy band gap, refractive index and extinction co-efficient values varied with increase in Cu concentration and the PL spectra showed the strong emission peak around at 765 nm. The film has the lowest resistivity while higher carrier concentration and mobility were obtained at 8 at.% of Cu.

Preparation and Optical Characterization of Polymer Composites Reinforced by Natural Materials

Three groups of composite materials were prepared by using casting method from Unsaturated Polyester with volume fraction (70%) reinforced by Rice Husks with volume fraction (30%) (first group), the second group was prepared from Unsaturated Polyester with volume fraction (70%) reinforced by Rice Husks with volume fraction (15%) and by Palm Fibers with volume fraction (15%) (hybird composite) and the third group consist also of Unsaturated Polyester with volume fraction (70%) reinforced by Palm Fibers with volume fraction (30%), the length of palm fibers was (2-3) mm. Parameters such as absorbance (A), transmittance (T), reflectance(R), refractive index (n), extinction coefficient (k) , real (er) and imaginary parts (ei) of dielectric constants, were studied in the spectral range (200-800) nm. The results show that the absorbance increases with increasing the ratio of Palm Fibers while the transmittance decreases, the hybrid composite has the best values of reflectance and the higher values of extinction coefficient, Refractive index, real and imaginary parts of dielectric constants were for samples containing ratios of Palm Fibers and the lower values were for those contain Rice Husks only.

Surface plasmon resonance for characterization of large-area atomic-layer graphene film

Characterization of large-area thin films with atomic-scale resolution is challenging but in great demand for diverse applications (e.g., nanotechnology and sensing). Here, we use the Surface Plasmon Resonance (SPR) method to characterize both the thickness and refractive index of chemical-vapor-deposition (CVD)-grown graphene films. The measured refractive index and extinction coefficient values of the CVD-grown graphene monolayer at 670 nm wavelength are 3.135 and 0.897, respectively. Our results demonstrate that SPR shifts generated by graphene films are large (i.e., ∼1°/nm), almost tenfold larger than that observed in SPR measurements of organic monolayers. We find that this significantly large SPR shift easily enables the thickness of a large area sample (i.e., ∼mm2) to be determined with subnanometer-scale resolution. We show that the SPR method can identify thickness of different graphene layers and give an estimate of ∼0.37 nm for the thickness of the CVD-grown graphene layer, which agrees extremely well with the 0.335 nm reported for layer-to-layer carbon atom distance of graphite crystals. Our results open the avenue to fast and cost-effective simultaneous characterization of various parameters (including thickness and optical constants) of thin films at the atomic-scale resolution. The presented characterization method can be applied both to physical characterizations of various two-dimensional layered materials as well as to the use of these layered materials for biosensing applications as shown earlier, due to the favorable properties of graphene plasmons.

Anisotropic optical distribution of powder phosphor materials applied in medical imaging instrumentation

Image quality for medical purposes is related to the useful diagnostic information that can be extracted from an image. The performance of indirect X-ray detectors, which in turn affects the quality of the medical image, can be significantly influenced by the characteristics of the phosphor, employed to convert incident radiation into emitted light. Given the technological and medical importance of phosphor materials, understanding the fundamental effects of optical anisotropy is crucial. The purpose of the present paper was to examine the influence of optical anisotropy in optical diffusion within the powder phosphor-based X-ray detectors. The present investigation was based on Mie scattering theory and Monte Carlo simulation techniques. The variation of the anisotropy factor was examined for: (1) light wavelengths in the range 400–700 nm, (2) particle refractive index between 1.5 and 2 and (3) three regions of particle sizes: nanoscale (from 10 up to 100 nm), submicron scale (from 100 nm up to 1 μm), and microscale (from 1 up to 10 μm). In addition, optical diffusion performance was carried out considering: (a) anisotropy factor values 0.2, 0.5, 0.8 which represent different aspects of light propagation after scattering and (b) phosphors of different layer thickness, 100 (thin layer) and 300 μm (thick layer), respectively. Results showed that the highest variation on the anisotropy factor was observed in the submicron scale, and, in particular, for grain diameters between 100 and 600 nm (increase from 0.1 up to 0.8). In addition, Monte Carlo simulations showed that the spread of light photons decreases (i.e., high spatial resolution) with the decrease in the anisotropy factor. In particular, the FWHM was found to decrease with the anisotropy factor: (1) 11.4 % at 100 μm and 4.2 %, at 300 μm layer thickness, for light extinction coefficient 0.217 μm−1 and (2) 1.9 % at 100 μm and 2.0 %, at 300 μm layer thickness, for light extinction coefficient 3 μm−1. The present work indicated that lateral spreading is affected by the anisotropy factor. However, this effect is more dominant for low values of light extinction coefficient of the material.

Substituent Effect at the C4-Position of 1,3a,6a-Triazapentalene.

Various 2,4-disubstituted-1,3a,6a-triazapentalenes possessing methyl and phenyl groups at the C4-position were synthesized. Fluorescence observation of the synthetic 4-methyl- and 4-phenyl-1,3a,6a-triazapentalenes revealed that the introduction of a substituent at the C4-position allowed a long-wavelength shift of the fluorescence maximum. Furthermore, the phenyl group at the C4-position was found to induce a substantial increase in the extinction coefficient value.

Impact of lake surface temperatures simulated by the FLake scheme in the CNRM-CM5 climate model

The impact of lakes on climate is investigated in a set of global simulations performed with the CNRM-CM5 climate model coupled to the FLake lake scheme. First, offline simulations driven by ERA-Interim (ERA-I hereafter) reanalysis are performed on a limited set of lakes to find the best FLake parameters setting. Optimal values of lake depth, ice albedo and light extinction coefficient are defined by evaluating the model's performance in different climates for surface temperature and lake ice duration. Second, global simulations are performed with and without FLake to assess the impact of lake representation on the surface energy balance and the boundary layer characteristics. Results indicate that FLake simulates the lake surface temperature satisfactorily in an offline mode and that the use of FLake coupled to CNRM-CM5 improves some of the global biases found in the climate model. It is also shown that lakes impact the surface energy budget significantly at a regional scale; however, the impact on climate is rather limited. Finally, future developments related to the implementation of a more physical snow model and a water balance in FLake are discussed.

On Depolarization Lidar-Based Method for The Determination of Liquid-Cloud Microphysical Properties

Abstract : Under single scattering conditions, water droplets clouds do not depolarize the backscattered light. However, backscattered light from multiple scattering will be depolarized. The level of depolarization is a function of the droplets size, the cloud extinction coefficient value and profile; it has also an important dependency on the lidar field-of-view (FOV). The use of depolarization information to retrieve cloud microphysical properties, using Multiple-FOV has been the object of studies, [1], [2]. Recently the use of the depolarization, at a single FOV, has been studied for cloud with linear liquid water content profiles, [3], [4]. In this paper we present the mechanism leading to depolarization and identify the FOV values for which the information on particle size is high. Also Monte Carlo simulations for cloud with constant and ramp up profiles are presented. The degree of linear depolarization as a function of cloud penetration is significantly different for both cloud profiles. This suggests that the use of the degree of linear depolarization at a single FOV should be used with caution to determine clouds micro-physical parameters.

Observation of Clouds Using the CSIR Transportable LIDAR: A Case Study over Durban, South Africa

The Council for Scientific and Industrial Research (CSIR) transportable Light Detection And Ranging (LIDAR) was used to collect data over Durban (29.9°S, 30.9°E) during 20–23 November 2012. Aerosol measurements have been carried out in the past over Durban; however, no cloud measurements using LIDAR have ever been performed. Therefore, this study further motivates the continuation of LIDAR for atmospheric research over Durban. Low level clouds were observed on 20–22 November 2012 and high level clouds were observed on 23 November 2012. The low level cloud could be classified as stratocumulus clouds, whereas the high level clouds could be classified as cirrus clouds. Low level cloud layers showed high extinction coefficients values ranging between 0.0009 and 0.0044 m−1, whereas low extinction coefficients for high level clouds were observed at values ranging between 0.000001 and 0.000002 m−1. Optical depth showed a high variability for 20 and 21 November 2012. This indicates a change in the composition and/or thickness of the cloud. For 22 and 23 November 2012, almost similar values of optical depth were observed. Cloud-Aerosol LIDAR and Infrared Pathfinder Satellite Observations (CALIPSO) revealed high level clouds while the CSIR LIDAR could not. However, the two instruments complement each other well to describe the cloudy condition.

Theoretical approximations and experimental extinction coefficients of biopharmaceuticals.

UV spectrophotometric measurement is a widely accepted and standardized routine analysis for quantitation of highly purified proteins; however, the reliability of the results strictly depends on the accuracy of the employed extinction coefficients. In this work, an experimental estimation of the differential refractive index (dn/dc), based on dry weight measurements, was performed in order to determine accurate extinction coefficients for four biotherapeutic proteins and one synthetic copolymer after separation in a size-exclusion ultra-performance liquid chromatograph coupled to an ultraviolet, multiangle light scattering and refractive index (SE-UPLC-UV-MALS-RI) multidetection system. The results showed small deviations with respect to theoretical values, calculated from the specific amino acid sequences, for all the studied immunoglobulins. Nevertheless, for proteins like etanercept and glatiramer acetate, several considerations, such as glycan content, partial specific volume, polarizability, and higher order structure, should be considered to properly calculate theoretical extinction coefficient values. Herein, these values were assessed with simple approximations. The precision of the experimentally obtained extinction coefficients, and its convergence towards the theoretical values, makes them useful for characterization and comparability exercises. Also, these values provide insight into the absorbance and scattering properties of the evaluated proteins. Overall, this methodology is capable of providing accurate extinction coefficients useful for development studies.

Functionalization of poly(amidoamine) dendrimer-based nano-architectures using a naphthalimide derivative and their fluorescent, dyeing and antimicrobial properties on wool fibers.

Novel naphthalimide-poly(amidoamine) dendrimer fluorescent dyes were synthesized, and their structures were identified and confirmed using different characterization methods such as Fourier transform infrared, (1) H NMR, (13) C NMR, differential scanning calorimetry, elemental analysis and UV-vis spectroscopy. The spectrophotometric studies demonstrated absorption maxima (λmax ) and extinction coefficient (εmax ) values in the ranges of 429-438 nm and 25,635-88,618 L/mol/cm, respectively. The dyeing, fastness and antimicrobial properties of dyed wool fibers were examined. Colorimetric measurements demonstrated a greenish-yellow hue with remarkable fluorescence intensity on dyed wool. Although the fastness properties of naphthalimide dye on wool fibers were poor/moderate, color fastness was appreciably improved through modification of the dye using dendrimers. The results revealed that the newly synthesized dyes are potent antimicrobial agents on wool fibers. Overall, it was deduced that poly(amidoamine) (PAMAM) dendrimers could be exploited as a promising tool in tailoring the different properties of naphthalimide dyes, being suitable for dyeing and antimicrobial finishing agents for wool fibers. Copyright © 2015 John Wiley & Sons, Ltd.

Spectroscopic ellipsometry investigation on the excimer laser annealed indium thin oxide sol–gel films

We report on the effect of the excimer laser annealing on the electronic properties of indium tin oxide (ITO) sol–gel films by using spectroscopic ellipsometric technique. We found that the excimer laser annealing effectively induces the crystallization as well as condensation of the sol–gel film. As the laser power increased, the carrier concentration and the relaxation time of photo-annealed films increased, with the bandgap shifting to higher energies. Simultaneously, the extinction coefficient values in the visible region were reduced significantly. We suggest that the excimer laser annealing should be a promising method for low temperature preparation of the ITO film on heat-sensitive substrates via the sol–gel process.

Optical absorption characteristics in the assessment of powder phosphor-based x-ray detectors: from nano- to micro-scale

X-ray phosphor-based detectors have enormously improved the quality of medical imaging examinations through the optimization of optical diffusion. In recent years, with the development of science and technology in the field of materials, improved powder phosphors require structural and optical properties that contribute to better optical signal propagation. The purpose of this paper was to provide a quantitative and qualitative understanding of the optical absorption characteristics in the assessment of powder phosphor-based detectors (from nano- scale up to micro-scale). Variations on the optical absorption parameters (i.e. the light extinction coefficient and the percentage probability of light absorption p%) were evaluated based on Mie calculations examining a wide range of light wavelengths, particle refractive indices and sizes. To model and assess the effects of the aforementioned parameters on optical diffusion, Monte Carlo simulation techniques were employed considering: (i) phosphors of different layer thickness, 100 μm (thin layer) and 300 μm (thick layer), respectively, (ii) light extinction coefficient values, 1, 3 and 6 μm−1, and (iii) percentage probability of light absorption p% in the range 10−4–10−2. Results showed that the coefficient is high for phosphor grains in the submicron scale and for low light wavelengths. At higher wavelengths (above 650 nm), optical quanta follow approximately similar depths until interaction for grain diameter 500 nm and 1 μm. Regarding the variability of the refractive index, high variations of the coefficient occurred above 1.6. Furthermore, results derived from Monte Carlo modeling showed that high spatial resolution phosphors can be accomplished by increasing the parameter. More specifically, the FWHM was found to decrease (i.e. higher resolution): (i) 4.8% at 100 μm and (ii) 9.5%, at 300 μm layer thickness. This study attempted to examine the role of the optical absorption parameters on optical diffusion studies. A significant outcome of the present investigation was that the improvement of phosphor spatial resolution without decreasing the light collection efficiency too much can be better achieved by increasing the parameter rather than the parameter p%.

TRACK--A new method for the evaluation of low-level extinction coefficient in optical films.

We develop a rigorous methodology named TRACK based on the collection of multi-angle spectrophotometric transmission and reflection data in order to assess the extinction coefficient of quasi-transparent optical films. The accuracy of extinction coefficient values obtained by this method is not affected by sample non-idealities (thickness non-uniformity, refractive index inhomogeneities, anisotropy, interfaces, etc.) and therefore a simple two-layer (substrate/film) optical model can be used. The method requires the acquisition of transmission and reflection data at two angles of incidence: 10° and 65° in p polarization. Data acquired at 10° provide information about the film thickness and the refractive index, while data collected at 65° are used for absorption evaluation and extinction coefficient computation. We test this method on three types of samples: (i) a CR-39 plastic substrate coated with a thick protective coating; (ii) the same substrate coated with a thin TiO(2) film; (iii) and a thick Si(3)N(4) film deposited on Gorilla glass that presents thickness non-uniformity and refractive index gradient non-idealities. We also compare absorption and extinction coefficient values obtained at 410 and 550 nm by both TRACK and Laser Induced Deflection techniques in the case of a 1 micron thick TiO(2) coating. Both methods display consistent extinction coefficient values in the 10(-4) and 10(-5) ranges at 410 and 550 nm, respectively, which proves the validity of the methodology and provides an estimate of its accuracy limit.

Synthesis and characterization of conjugated polymers containing phenyl and bithiophene: controlling of optical properties with molarity

Conjugated polymers containing phenyl and bithiophene units are synthesized by conventional polycondensation and crossing-coupling method of carboxylic acids with halides. The structure of both polymers formed by adding the ester group to the first polymer was confirmed by means of Fourier transform infrared (FTIR), nuclear magnetic resonance techniques, differential scanning calorimetry, and thermogravimetry and elemental analysis. The molecular weight distribution values of polymers were determined with a gel permeation chromatography (GPC) system. The optical properties of these different polymers with synthesis methods and structures were investigated for different molarities. The molar extinction coefficient values of the polymers decrease with increasing molarity. Transmittance (T) values of the polymers are increased with ester group addition and decreasing molarity. We obtained two types (direct and indirect allowed band gaps) of band gaps. The direct allowed optical band gap (E gd) values of poly(2,2′ bithiophene terephthalate) (polyBTTP) are lower than the indirect allowed optical band gap (E gid) values of poly(5-phenyl-2,2′ bithiophene) (polyPBT). The direct and indirect allowed band gap values of the polymers can be decreased with ester group addition and increasing molarity. The refractive index of the polymers can be decreased with decreasing molarity, increasing wavelength, and ester group addition.

UV-visible Absorption Study of the Self-association of Non-ionic Chromonic Triphenylenes TP6EOnM (n = 2, 3, 4) in Dilute Aqueous Solutions: Impact of Chain Length on Aggregation.

A series of triphenylenes with oligoethoxy chains of various length, TP6EOnM with n = 2, 3, 4, has been synthesised and purified by HPLC. The self-association of these disc-shaped molecules in dilute aqueous solutions (∼10(-7) to ∼4 × 10(-4) M) has been studied by UV-visible absorption spectroscopy. The free energy of association decreases as the length of the chains increases. As a result, for a given concentration, the average size of aggregate diminishes as the chain length increases. While the absorption properties of the monomer are identical for the three molecules, the extinction coefficients of solutions of the three triphenylenes at a given concentration are significantly different and are directly linked to the average size of the aggregates. The change of epsilon values upon aggregation could explain the trend generally observed with dyes for solar cells substituted with chains of increasing length showing increasing extinction coefficient values.