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We perform a detailed comparison study of Monte Carlo (MC) simulations and discrete-ordinate radiative-transfer (DISORT) calculations of spectral radiances in a 1D coupled air-tissue (CAT) system consisting of horizontal plane-parallel layers. The MC and DISORT models have the same physical basis, including coupling between the air and the tissue, and we use the same air and tissue input parameters for both codes. We find excellent agreement between radiances obtained with the two codes, both above and in the tissue. Our tests cover typical optical properties of skin tissue at the 280, 540, and 650 nm wavelengths. The normalized volume scattering function for internal structures in the skin is represented by the one-parameter Henyey-Greenstein function for large particles and the Rayleigh scattering function for small particles. The CAT-DISORT code is found to be approximately 1000 times faster than the CAT-MC code. We also show that the spectral radiance field is strongly dependent on the inherent optical properties of the skin tissue. OCIS codes: 170.3660, 170.5280, 290.4210.

The detection of vapors of dinitrobenzenes and dinitrotoluenes by UV cavity ringdown spectroscopy (CRDS) was investigated. Absorption cross sections at 248 nm were estimated by measurements on saturated vapors and compared with solution-phase values. The computed subparts per [10.sup.9] detection sensitivity with no effort at preconcentration was demonstrated through measurements on diluted flows. The factors affecting measurements on 1 atm total pressure were considered, and it was demonstrated that Rayleigh scattering by air will reduce the detection sensitivity by 5%-10%. The UV absorption spectra of these compounds are broad, resulting in a relatively poor selectivity for single-wavelength measurements with the UV CRDS technique. OCIS codes: 280.3420, 300.1030, 300.6390.

The phase function is an important parameter that affects the distribution of scattered radiation. In Rayleigh scattering, a scatterer is approximated by a dipole, and its phase function is analytically related to the scattering angle. For the Henyey-Greenstein (HG) approximation, the phase function preserves only the correct asymmetry factor (i.e., the first moment), which is essentially important for anisotropic scattering. When the HG function is applied to small particles, it produces a significant error in radiance. In addition, the HG function is applied only for an intensity radiative transfer. We develop a combined HG and Rayleigh (HG-Rayleigh) phase function. The HG phase function plays the role of modulator extending the application of the Rayleigh phase function for small asymmetry scattering. The HG-Rayleigh phase function guarantees the correct asymmetry factor and is valid for a polarization radiative transfer. It approaches the Rayleigh phase function for small particles. Thus the HG-Rayleigh phase function has wider applications for both intensity and polarimetric radiative transfers. For microwave radiative transfer modeling in this study, the largest errors in the brightness temperature calculations for weak asymmetry scattering are generally below 0.02 K by using the HG-Rayleigh phase function. The errors can be much larger, in the 1-3 K range, if the Rayleigh and HG functions are applied separately. OCIS codes: 010.0010, 010.1310, 200.0200.

Recent advancements in a molecular Rayleigh scattering based diagnostic technique allowed for simultaneous measurement of velocity and density fluctuations with high sampling rates. The technique was used to investigate unheated high subsonic and supersonic fully expanded free jets in the Mach number range from 0.8 to 1.8. The difference between the Favre-averaged and the Reynolds-averaged axial velocity and axial component of the turbulent kinetic energy is found to be small. On average, estimates based on Morkovin's strong Reynolds analogy are found to underpredict turbulent density fluctuations.

We measured fluorescence quantum yields of acetone and 3-pentanone as a pure gas and with nitrogen diluent at room temperature at 20, 507, and 1013 mbar using 248, 266, and 308 nm excitation by calibrating the optical collection system with Rayleigh scattering from nitrogen. At 20 mbar with 308-nm excitation, the fluorescence quantum yields for acetone and 3-pentanone are 7 [+ or -] 1 x [10.sup.-4] and 1.1 [+ or -] 0.2 x [10.sup.-3], respectively, and each decreases with decreasing excitation wavelength. These directly measured values are significantly lower than earlier ones that were based on a chain of relative measurements. The observed pressure and excitation wavelength dependence is in qualitative agreement with a previously developed fluorescence quantum yield model, but the absolute numbers disagree. Changing acetone's fluorescence rate constant to 3 x [10.sup.5] [s.sup.-1] from its previous value of 8 x [10.sup.5] [s.sup.-1] resulted in good agreement between our measurements and the model. OCIS codes: 300.2530, 140.3610, 120.5820.

Determination of the critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was done by hyper-Rayleigh scattering (HRS). The CMC is detected by an unprecedented drop in the HRS signal, which is believed to be due to the formation of smaller pre-micellar aggregates whose effective beta value is higher than that of the micellar aggregates.

We report the first gas temperature measurements in plasmas to our knowledge obtained by filtered Rayleigh scattering (FRS). A narrow-linewidth Ti:sapphire laser is used as the illumination source, and a mercury filter provides strong suppression of elastic background. We perform measurements in weakly ionized glow discharges in pure argon and in an argon-plus-1%-nitrogen mixture. Where possible, we verify the FRS technique by comparing filtered measurements with unfiltered measurements. We present point measurements of axial temperature with uncertainties of less than 5%. We use a planar scheme to obtain radial temperature profiles with uncertainties of 10%. OCIS Codes: 350.5400, 350.2450, 120.6780, 290.5870, 300.0300.

We present laser-ablation microprobe inductively coupled-mass spectrometry analyses of Y, Yb, Er, Dy, and Gd in garnet crystals from high-grade metamorphic and migmatitic rocks from the Sierras Pampeanas of Argentina. These rocks contain large garnet porphyroblasts ([greater than or equal to] 4 mm) that are compositionally zoned. Rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores. A notable feature of this zonation is the inversion of Yb/Er and Yb/Dy ratios, from >1 in the cores to Keywords: Rayleigh fractionation, garnet, heavy rare earth clements, melting.

Absolute number densities of nitrogen triple states were investigated using a laser induced fluorescence technique together with optical emission spectroscopy and Rayleigh scattering.

A study was conducted to analyze changes in the internal hydrogen bonding of methyl red during photoisomerization. Forced Rayleigh scattering (FRS) was utilized to carry out the analysis. Ab initio computations were then performed on the methyl red. In addition, the possible conformers of the cis and trans isomers of the methyl red were examined with and without internal hydrogen bonding. Results indicated that hydrogen bonding promotes the decay-growth-decay FRS signal of methyl red.

A study was conducted to obtain the average size of clusters formed in pulsed free-jet expansions of argon and N2O using Rayleigh scattering. An ion gauge linked to a digital oscilloscope was then utilized to determine relative flux measurements. Experimental results indicated the effectiveness of using Rayleigh light scattering to analyze the presence and size of both argon and N2O clusters generated in a pulsed free-jet expansion.

An experiment was performed to measure the mean density, turbulence quantities and mean velocities of a supersonic, high-temperature exhaust plume using Rayleigh scattering system and a two-dimensional laser Doppler velocimeter. Results showed that supersonic flow is maintained only up to 15 nozzle diameters while the potential core of the supersonic jet is estimated at 6 nozzle diameters.

The filtered Rayleigh scattering (FRS) method permits the simultaneous measurement of the pressure, velocity, and temperature in unseeded flows. The experimental total velocity uncertainties, in ambient room air and a Mach 2 freejet are greater than the predicted values. Velocity measurements differ due to a change in the spatial mode and vertical shift of the laser sheet. A theoretical model for velocity, temperature and pressure measurements, using the FRS method, is discussed.

Accurate temperature computations can be made even when the laser-line background intensity is double the Rayleigh signal. This applies to the novel laser-induced Rayleigh scattering technique for enhanced temperature studies on gas flows. Two lines of a copper vapor laser facilitate the derivation of spatially resolved temperature. The optical probe comprises a single set of optics to absorb the signal simultaneously from 510 nanometer and 578 nanometer lines.

Application of the two-dimensional laser Rayleigh technique to the investigation of a large-scale industrial combustor is reported for the first time to our knowledge. Two-dimensional laser Rayleigh scattering was used to perform quantitative measurements of the temperature fields in different downstream positions of a 150-kW industrial, premixed, turbulent low-emission swirl combustor. Because of the possible interferences of the Rayleigh signal with Mie scattering and laser reflections of the burner components, some minor modifications of the design of the combustor and its gas supply were necessary. This was done without changing the basic characteristics of the burner. The quantitative and instantaneous character of the collected data allows calculation of ensemble-averaged temperature distributions and analysis of the flame structure in the turbulent combustion field. The measured temperature distribution confirms that the flame is stabilized by a central recirculation zone.

Methods for estimating the optical properties of flame generated soot aggregates were studied employing computer simulations in the visible and near-infrared portions of the spectrum. The methods included the Rayleigh scattering approximation, Mie scattering for an equivalent sphere and the Rayleigh-Debye-Gans (R-D-G) scattering for both given and fractal aggregates. Available computer simulations and measurements of soot aggregate optical properties do not provide an accurate evaluation of the approximate prediction methods.

The detection of two-photon excited fluorescence is practically free from background caused by linear scattering because two-photon excited fluorescence occurs at a much shorter wavelength region than the excitation light. This property can be used to achieve ultrasensitive fluorescence detection. However, similar to linear scattering in the detection of one-photon excited fluorescence, the question arises whether background caused by nonlinear scattering may limit the detection sensitivity of two-photon excited fluorescence. In this work, quantitative comparisons between two-photon induced scattering of liquid water and two-photon excited dye fluorescence in a standard epifluorescence geometry show that the relative scattering background is typically reduced by orders of magnitude in two-photon excitation as compared to single-photon excitation with confocal detection. Hyper-Rayleigh and hyper-Raman (3400 [cm.sup.-1]) cross sections of liquid water have been measured to be 8 x [10.sup.-62] and 7 x [10.sup.-63] [cm.sup.4]s/photon, respectively, at 840 nm incident wavelength, with absolute values calibrated with respect to the known two-photon fluorescence excitation cross section of fluorescein.

The Rayleigh scattering method is employed to explain the generation of the hydrogen clusters taking place in the gas jet under liquid nitrogen temperature conditions. The number of expanded molecules is shown to be the main factor affecting the cluster formation in the system.

A flow visualization technique based on the filtered Rayleigh scattering method is used in the study of coompressible planar free shear layers. Experiments are conducted wherein the scattering phenomena associated with free streams are investigated at convective Mach numbers. An Nd:YAG laser is employed to generate the light source while the resulting images are recorded by means of an intensified computer-controlled display camera. Results reveal that there is a big variation in the structures of the low- and high-compressibility layers.

Byline: Flavio Buiochi, Oscar Martinez, Luis Gomez-Ullate, Francisco Montero De Espinosa This paper presents a computational method for determining the reflection and transmission of ultrasonic beams through plane interfaces between elastic media radiated from mono and multi element transducers. The ultrasonic field is calculated by the Rayleigh integral method, which is affected by reflection and/or transmission coefficients. In a first step, the velocity potential impulse response is calculated at the interface. In a second step, the reflected and transmitted pressure field is calculated by applying the Huygens' principle to the whole-extended interface. The method is valid for all field regions, may be performed for any excitation form, and can be easily applied in the case of arrays. In order to validate the method, the simulated field from a single piston-like transducer is compared to an experimentally measured field considering the wave evolution caused by planar interfaces between two media (water-acrylic). Finally, computation examples using phased arrays are also shown in the paper.

A 2835-MHz (10.6-cm wavelength) profiler and a 920-MHz (32.6-cm wavelength) profiler were collocated by the NOAA Aeronomy Laboratory at Garden Point, Australia, in the Tiwi Islands during the Maritime Continent Thunderstorm Experiment (MCTEX) field campaign in November and December 1995. The two profilers were directed vertically and observed vertical velocities in the clear atmosphere and hydrometeor fall velocities in deep precipitating cloud systems. In the absence of Rayleigh scatterers, the profilers obtain backscattering from the refractive index irregularities created from atmospheric turbulence acting upon refractive index gradients. This kind of scattering is commonly referred to as Bragg scattering and is only weakly dependent on the radar wavelength provided the radar half-wavelength lies within the inertial subrange of homogeneous, isotropic turbulence. In the presence of hydrometeors the profilers observe Rayleigh backscattering from hydrometeors much as weather radars do and this backscatter is very dependent upon radar wavelength, strongly favoring the shorter wavelength profiler resulting in a 20-dB enhancement of the ability of the 2835-MHz profiler to observe hydrometeors. This paper presents observations of equivalent reflectivity, Doppler velocity, and spectral width made by the collocated profilers during MCTEX. Differential reflectivity is used to diagnose the type of echo observed by the profilers in the spectral moment data. When precipitation or other particulate backscatter is dominant, the equivalent reflectivities are essentially the same for both profilers. When Bragg scattering is the dominant process, equivalent reflectivity observed by the 1-GHz profiler exceeds the equivalent reflectivity observed by the 3-GHz profiler by approximately 18 dBZe. However, when the 3-GHz profiler half-wavelength is smaller than the inner scale of turbulence, the equivalent reflectivity difference exceeds 18 dBZe, and when both Rayleigh scattering and Bragg scattering are observed simultaneously, the equivalent reflectivity difference is less than 18 dBZe. The results obtained confirm the capability of two collocated profilers to unambiguously identify the type of echo being observed and hence enable the segregation of 'clear air' and precipitation echoes for studies of atmospheric dynamics and precipitating cloud systems.