Classification of particle effective shape ratios in cirrus clouds based on the lidar depolarization ratio

A shape classification technique for cirrus clouds that could be applied to future spaceborne lidars is presented. A ray-tracing code has been developed to simulate backscattered and depolarized lidar signals from cirrus clouds made of hexagonal-based crystals with various compositions and optical depth, taking into account multiple scattering. This code was used first to study the sensitivity of the linear depolarization rate to cloud optical and microphysical properties, then to classify particle shapes in cirrus clouds based on depolarization ratio measurements. As an example this technique has been applied to lidar measurements from 15 mid-latitude cirrus cloud cases taken in Palaiseau, France. Results show a majority of near-unity shape ratios as well as a strong correlation between shape ratios and temperature: The lowest temperatures lead to high shape ratios. The application of this technique to space-borne measurements would allow a large-scale classification of shape ratios in cirrus clouds, leading to better knowledge of the vertical variability of shapes, their dependence on temperature, and the formation processes of clouds.     

光照入射角对太阳能电池输出功率的影响

为了研究在自然条件下,光照入射角对太阳能电池实际输出功率的影响,对单晶硅、多晶硅和非晶硅太阳能电池进行了不同倾角和方位角的测试实验,得到了太阳能电池转换效率关于倾角和方位角的对应关系,并用转换效率的变化曲线分析和说明光照入射角对太阳能电池输出功率的影响.     

Fluorescence from airborne microparticles: dependence on size, concentration of fluorophores, and illumination intensity

We measured fluorescence from spherical water droplets containing tryptophan and from aggregates of bacterial cells and compared these measurements with calculations of fluorescence of dielectric spheres. The measured dependence of fluorescence on size, from both droplets and dry-particle aggregates of bacteria, is proportional to the absorption cross section calculated for homogeneous spheres containing the appropriate percentage of tryptophan. However, as the tryptophan concentration of the water droplets is increased, the measured fluorescence from droplets increases less than predicted, probably because of concentration quenching. We model the dependence of the fluorescence on input intensity by assuming that the average time between fluorescence emission events is the sum of the fluorescence lifetime and the excitation lifetime (the average time it takes for an illuminated molecule to be excited), which we calculated assuming that the intensity inside the particle is uniform. Even though the intensity inside the particles spatially varies, this assumption of uniform intensity still leads to results consistent with the measured intensity dependence.     

Field-of-view dependence of lidar signals by use of Newtonian and Cassegrainian telescopes

The dependence of lidar return signals on the aperture size of the field stop is examined. Observational results are presented for both Newtonian and Cassegrainian telescopes. Analytic expressions are derived for the lidar geometric form factors, in satisfactory agreement with the experiments.     

Guided transmission of Ne ions through nanocapillaries in PET: dependence on the tilt angle

We measured the transmission of 3 keV Ne⁷⁺ ions through nanocapillaries of 100 nm diameter and 10 μm length in a PET polymer foil. The capillaries were produced before the transmission experiments by etching tracks of fast xenon ions. The foils were tilted up to 15° for which the incident ions are forced to approach the capillary surface. After a characteristic time the majority of Ne⁷⁺ ions were found to be transmitted in their initial charge state. The angular distributions of the transmitted Ne⁷⁺ projectiles reveals a propagation of the ions parallel to the capillary axis. This indicates that the ions are guided through the capillaries. The capillary guiding is the result of deposit of charges in a self-organizing process. A non-linear model is presented to interpret the experimental observation. The analysis exhibits a significant dependence of the ion transmission on the tilt angle.     

Measurement of the azimuthal dependence of cross-polarized lidar returns and its relation to optical depth

We measure with a gated intensified CCD camera the cross-polarized backscattered light from a linearly polarized laser beam penetrating a cloud made of spherical particles. In accordance with previously published results we observe a clear azimuthal pattern in the recorded images. We show that the pattern is symmetrical, that it originates from second-order scattering, and that higher-order scattering causes blurring that increases with optical depth. We also find that the contrast in the symmetrical features can be related to measurement of the optical depth. Moreover, when the blurring contributions are identified and subtracted, the resulting pattern provides a pure second-order scattering measurement that can be used for retrieval of droplet size.     

Organic microcavity light-emitting diodes with metal mirrors: dependence of the emission wavelength on the viewing angle

Organic microcavity light-emitting diodes typically exhibit a blueshift of the emitting wavelength with increasing viewing angle. We have modeled the shift of the resonance wavelength for several metal mirrors. Eight metals (Al, Ag, Cr, Ti, Au, Ni, Pt, and Cu) have been considered top or bottom mirrors, depending on their work functions. The model fully take into account the dependence of thephase change that occurs on reflection on angle and wavelength for both s and p polarization, as well as on dispersion in the organic layers. Different contribution to the emission wavelength shift are discussed. The influence of the thickness of the bottom mirror and of the choice and thickness of the organic materials inside the cavity has been investigated. Based on the results obtained, guidelines for a choice of materials to reduce blueshift are given.     

The dependence of the texture of tellurium thin films on vacuum deposition angle

Vacuum-deposited tellurium thin films can show substantially different surface morphologies depending on the angle with which the vapor stream impinges on the substrate surface. These tellurium thin films have a tendency to grow as acicular crystallites but as the deposition angle is increased so that the vapor stream becomes tangetial to the substrate surface the spacing between crystallites increase and approaches, at stream angles of approximately 80° from the normal, dimensions roughly once or twice the average wavelength of visible light. Such films may have application in solar energy collector systems because of the high absorptivity of sunlight shown by such films. Mechanisms which describe the tendency for crystallite spacing to increase with increasing angle are discussed.     

Retrieval of droplet-size density distribution from multiple-field-of-view cross-polarized lidar signals: theory and experimental validation

Multiple-field-of-view (MFOV) secondary-polarization lidar signals are used to calculate the particle-size density distribution (PSD) at the base of a cloud. At the cloud base, multiple scattering is weak and single backscattering is predominant by many orders of magnitude. Because secondary polarization is a direct measure of multiple scattering, it is therefore advantageous to use secondary polarization. A mathematical relation among the PSD, the lidar fields of view, the scattering angles, and the angular depolarization is derived to facilitate use of secondary polarization. The model is supported by experimental MFOV lidar measurements carried out in a controlled environment, and its limitations and restrictions are discussed.     

Effects of source shape on the numerical aperture factor with a geometrical-optics model

We study the effects of an extended light source on the calibration of an interference microscope, also referred to as an optical profiler. Theoretical and experimental numerical aperture (NA) factors for circular and linear light sources along with collimated laser illumination demonstrate that the shape of the light source or effective aperture cone is critical for a correct NA factor calculation. In practice, more-accurate results for the NA factor are obtained when a linear approximation to the filament light source shape is used in a geometric model. We show that previously measured and derived NA factors show some discrepancies because a circular rather than linear approximation to the filament source was used in the modeling.     

The Faraday rotation angle of Ni nanowire arrays: its dependence on photon energy and nanowire size

The magneto-optical properties of Ni nanowire arrays embedded in anodic aluminum oxide templates are studied, for a selection of photon energies, as a function of their diameter and length for the first time. This was achieved by the determination of Stokes parameters of the transmitted light. The magneto-optical response is found to differ considerably from that of the bulk material. At all photon energies studied, a linear association of the Faraday rotation angle with nanowire length has been observed; moreover, a proportional relationship between rotation angle per unit length and nanowire diameter has also been also observed, consistent with our earlier work on Fe and Co nanowires. The relationship between the Faraday rotation angle per unit length with different nanowire diameters and photon energy has been found to exhibit clear spectroscopic structure.     

Contact angle measurement of SAC 305 solder: numerical and experimental approach

The solder process comprises the ability of a melted alloy to flow or spread on a substrate for the formation of a metallic bond driven by the physical–chemical properties of the system. Thus, the study of wetting behaviour is an important step in the characterisation of solder alloys and requires the discussion of different parameters that affect the solder junctions. The main objective of this work is to use a CFD study to determine the influence of several parameters in the melting shape obtained with a solder, of the SAC 305 type and compare the numerical results with experimental data. The computational model was implemented in ANSYS Fluent^® and the simulations were carried out involving the melting of a material using the volume of fluid method to capture the solidification/melting interfaces based on an enthalpy-porosity approach. The results show that shape of the melted solder is greatly influenced by the contact angle and, to a smaller extent, by the surface tension. It was also concluded that it is possible to accurately predict the shape of the melted solder using computational fluid dynamic tools in complement to the experimental validation.     

Aperture dependence of the mixing efficiency, the signal-to-noise ratio, and the speckle number in coherent lidar receivers

With the aid of the van Cittert-Zernike theorem we develop an analytical expression for the ensemble-averaged heterodyne mixing efficiency in coherent lidar receivers that are looking at a diffuse target that is in the receiver's far field. Our extremely simple and straightforward analysis shows that the dependence of the mixing efficiency on the receive aperture size d(R) first follows a parabolic decrease and later approaches a (d(R))(-2) function. As a consequence, the signal-to-noise ratio does not increase proportionally to the aperture area but saturates. For the system model chosen, the heterodyne mixing efficiency exhibits the same functional dependence on the lidar geometry as the reciprocal of the number of speckle cells within the receive aperture.     

Description and evaluation of a tropospheric ozone lidar implemented on an existing lidar in the southern subtropics

Rayleigh-Mie lidar measurements of stratospheric temperature and aerosol profiles have been carried out at Reunion Island (southern tropics) since 1993. Since June 1998, an operational extension of the system is permitting additional measurements of tropospheric ozone to be made by differential absorption lidar. The emission wavelengths (289 and 316 nm) are obtained by stimulated Raman shifting of the fourth harmonic of a Nd:YAG laser in a high-pressure deuterium cell. A mosaic of four parabolic mirrors collects the backscattered signal, and the transmission is processed by the multiple fiber collector method. The altitude range of ozone profiles obtained with this system is 3?17 km. Technical details of this lidar system working in the southern tropics, comparisons of ozone lidar profiles with radiosondes, and scientific perspectives are presented. The significant lack of tropospheric ozone measurements in the tropical and equatorial regions, the particular scientific interest in these regions, and the altitude range of the ozone measurements to 16?17 km make this lidar supplement useful and its adaptation technically conceivable at many Rayleigh-Mie lidar stations.     

The dependence of ultrasonic backscatter on trabecular thickness in human calcaneus: theoretical and experimental results

Trabecular thickness within cancellous bone is an important determinant of osteoporotic fracture risk. Noninvasive assessment of trabecular thickness potentially could yield useful diagnostic information. Faran's theory of elastic scattering from a cylindrical object immersed in a fluid has been used to predict the dependence of ultrasonic backscatter on trabecular thickness. The theory predicts that, in the range of morphological and material properties expected for trabecular bone, the backscatter coefficient at 500 kHz should be approximately proportional to trabecular thickness to the power of 2.9. Experimental measurements of backscatter coefficient were performed on 43 human calcaneus samples in vitro. Mean trabecular thicknesses on the 43 samples were assessed using micro computed tomography (CT). A power law fit to the data showed that the backscatter coefficient empirically varied as trabecular thickness to the 2.8 power. The 95% confidence interval for this exponent was 1.7 to 3.9. The square of the correlation coefficient for the linear regression to the log transformed data was 0.40. This suggests that 40% of variations in backscatter may be attributed to variations in trabecular thickness. These results reinforce previous studies that offered validation for the Faran cylinder model for prediction of scattering properties of cancellous bone, and provide added evidence for the potential diagnostic utility of the backscatter measurement.     

Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba

The tropospheric particle extinction-to-backscatter ratio, the depolarization ratio, and the water-vapor mixing ratio were measured by use of a Raman lidar and a polarization lidar during the Asian dust seasons in 2001 and 2002 in Tsukuba, Japan. The apparent (not corrected for multiple-scattering effects) extinction-to-backscatter ratios (Sp) showed a dependence on the relative humidity with respect to ice (RHice) obtained from the lidar-derived water-vapor mixing ratio and radiosonde-derived temperature; they were mostly higher than 30 sr in dry air (RHice < 50%), whereas they were mostly lower than 30 sr in ice-supersaturated air (RHice > or = 100%), where the apparent extinction coefficients were larger than 0.036 km(-1). Both regions showed mean particle depolarization ratios of 20%-22%. Comparisons with theoretical calculations and the previous experiments suggest that the observed dependence of Sp on RHice is attributed to the difference in the predominant particles: nonspherical aerosols (mainly the Asian dust) in dry air and cloud particles in ice-supersaturated air.