Surfaces of controlled spectral absorptance
Calculation of film thickness in two and three layer systems required to achieve high absorption for solar radiation and low thermal emission
THERMAL EMISSION↗
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High-Energy Hybridized States Enable Long-Lived Hot Electrons in Cobaloxime-Silicon Nanocrystal System
Strong electronic coupling is achieved between the molecular catalyst cobaloxime ([Co]) and silicon nanocrystals (Si NCs) bridged by an ethylenepyridine group derived from vinylpyridine (vpy) covalently bound to the Si NC surface (Si-vpy-[Co]). The ethylenepyridine tether in Si-vpy-[Co] is key to dramatic changes to the system’s physical properties which are not observed in the corresponding formylpyridine (fpy) system (Si-fpy-[Co]) consistent with strong electronic coupling previously observed only in dark electrochemical systems. UV−vis absorption spectroscopy reveals new [Co]-centered electronic states in Si-vpy-[Co], and transient absorption spectroscopy finds a strong absorption feature appearing within 250 fs and persisting for at least 5 ns. Astoundingly, spectroelectrochemical measurements reveal that this absorption feature is consistent with both the singly reduced [Co] − and doubly reduced [Co] 2− complexes, leading to the conclusion that these long-lived charges are derived from high-energy “hot” electrons residing in [Co]-centered states. Detailed analysis using cyclic voltammetry, spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and density functional theory (DFT) calculations provides insight into the unique electronic structure created in Si-vpy-[Co]. DFT reveals that the new electronic states arise from hybridization between deep Si NC band states and high-energy molecular orbitals of the ethylenepyridine tether and the [Co] catalyst and are facilitated by σ-bonding character at the ethylenepyridine linkage. This study demonstrates that strong electronic coupling achieved through precise molecular chemistry can change the paradigm of otherwise fixed energy levels in hybrid photoelectrochemical systems for artificial photosynthesis and related applications.
14 SOLAR ENERGY↗
Rocket measurements of Faraday rotation and differential absorption.
Differential absorption and Faraday rotation in D region, using closed loop feedback system and two signals of different frequencies
D LAYER↗
Quantifying Trapped Powder in Electron Beam Powder Bed Fusion
Abstract Electron beam powder bed fusion (PBF-EB) shows great potential for manufacturing complex parts including those with internal cavities for heat exchanger, manifold systems, or energy absorption purposes. PBF-EB allows for the manufacture of channel geometries without the need for support structures. Due to the nature of the powder spreading process, powder feedstock is often trapped in intentionally manufactured cavities. This trapped powder can often be difficult to remove and can disturb the intended flow of fluid through the cavity or damage downstream components in its use case. These trapped powder particles present a risk of contamination and component failure if not completely evacuated. Ti6Al4V is a choice material for aerospace applications due to its high strength to weight ratio and its composition as a nonferrous metal; however, in weight sensitive applications excess entrapped powders or powders loosely attached to the surface could cause undesirable weight increases. The inherent spreading process of PBF-EB is different than laser powder bed fusion (PBF-LB) in its operational temperature, sintering. In addition, PBF-EB is less commonly studied in literature compared to its PBF-LB counterpart, and as a result the complexity of the semi-sintered powder and its spreading behavior are not well understood. Prior work has investigated the difficulty in removing trapped powder from PBF-EB, but these studies do not address how to quantify the amount of trapped powder in the cavity. Thus, an accurate method to measure the amount of trapped powder in the cavity must be investigated. In this work, Ti6Al4V coupons were manufactured with horizontal and vertical cavities of three different sizes. Archimedes testing allows for the determination of density differences caused by porosity and trapped powders by measuring mass and volumetric dispersion. Computed tomography (CT) is well suited for segmenting the internal structure and features of a part and has been studied for applications including voids, porosity, and dross. Thus, CT was explored as a method for evaluating trapped powder content in this work. The volumetric representation of the segmentation of the reconstructed CT volume can vary greatly depending on the input filter and thresholding methods. In this study, four different types of segmentation approaches were evaluated to determine the best approach for segmenting the volume as compared to an operator labeled ground truth. The percentage density results from the Archimedes testing were compared to the volumetric percent density from the computed tomography approach. Differences in packing density between two different internal channel features were investigated. Overall, this work sought to validate the use of computed tomography for the detection of trapped powders and present a framework for volumetric segmentation.
Johnstone, Brian↗
Water hyacinths for removal of cadmium and nickel from polluted waters
Removal of cadmium and nickel from static water systems utilizing water hyacinths (Eichhornia crassipes (Mart.) Solms) was investigated. This aquatic plant demonstrated the ability to rapidly remove heavy metals from aqueous systems by root absorption and concentration. Water hyacinths demonstrated the ability to absorb and concentrate up to 0.67 mg of cadmium and 0.50 mg of nickel per gram of dry plant material when exposed for a 24-hour period to waters polluted with from 0.578 to 2.00 ppm of these toxic metals. It is found that one hectare of water hyacinths has the potential of removing 300 g of cadmium or nickel from 240,000 liters of water polluted with these metals during a 24-hour period.
Wolverton, B. C.↗
Water hyacinths and alligator weeds for removal of silver, cobalt, and strontium from polluted waters
Water hyacinths and alligator weeds demonstrated the ability to rapidly remove heavy metals from an aqueous system by root absorption and concentration. Water hyacinths demonstrated the ability to remove 0.439 mg of silver, 0.568 mg of cobalt, and 0.544 mg of strontium in an ionized form per gram of dry plant material in a 24-hour period. Alligator weeds removed a maximum of 0.439 mg of silver, 0.130 mg of cobalt, and 0.161 mg of strontium per gram of dry plant material per day.
Wolverton, B. C.↗
Empirical evidence concerning absorption lines and radiation pressure in quasi-stellar objects
Empirical spectroscopic evidence is examined for the hypothesis that radiation pressure having large gradients with wavelength plays a crucial role in maintaining patterns of redshift differences in quasars. Seventy-four absorption-line redshift systems in 32 quasars and two Seyfert galaxies are analyzed and discussed in terms of the radiation-pressure line-locking hypothesis. Redshift line ratios greater than unity are computed for each quasar and plotted as histograms. Ratios which may indicate line and edge locking are identified, including those of the C IV and Mg II doublets and those of the N III/C III, He II/O III, C II/He I, Ly-beta/H I, and H I/He I ionization edges.
Burbidge, E. M.↗
Characterization of iron-doped lithium niobate for holographic storage applications
A comprehensive characterization of chemical and holographic properties of eight systematically chosen Fe:LiNbO3 crystals is performed in order to determine optimum performance of the crystals in holographic storage and display applications. The discussion covers determination of Fe(2+) and Fe(3+) ion concentrations in Fe:LiNbO3 system from optical absorption and EPR measurements; establishment of the relation between the photorefractive sensitivity of Fe(2+) and Fe(3+) concentrations; study of the spectral dependence, the effect of oxygen annealing, and of other impurities on the photorefractive sensitivity; analysis of the diffraction efficiency curves for different crystals and corresponding sensitivities with the dynamic theory of hologram formation; and determination of the bulk photovoltaic fields as a function of Fe(2+) concentrations. In addition to the absolute Fe(2+) concentration, the relative concentrations of Fe(2+) and Fe(3+) ions are also important in determining the photorefractive sensitivity. There exists an optimal set of crystal characteristics for which the photorefractive sensitivity is most favorable.
Shah, R. R.↗
Investigation of potential of differential absorption Lidar techniques for remote sensing of atmospheric pollutants
The NASA multipurpose differential absorption lidar (DIAL) system uses two high conversion efficiency dye lasers which are optically pumped by two frequency-doubled Nd:YAG lasers mounted rigidly on a supporting structure that also contains the transmitter, receiver, and data system. The DIAL system hardware design and data acquisition system are described. Timing diagrams, logic diagrams, and schematics, and the theory of operation of the control electronics are presented. Success in obtaining remote measurements of ozone profiles with an airborne systems is reported and results are analyzed.
Butler, C. F.↗
Collisional redistribution of radiation. II - The effects of degeneracy on the equations of motion for the density matrix. III - The equation of motion for the correlation function and the scattered spectrum
The effect of correlations between an absorber atom and perturbers in the binary-collision approximation are applied to degenerate atomic systems. A generalized absorption profile which specifies the final state of the atom after an absorption event is related to the total intensities of Rayleigh scattering and fluorescence from the atom. It is suggested that additional dynamical information to that obtainable from ordinary absorption experiments is required in order to describe redistributed atomic radiation. The scattering of monochromatic radiation by a degenerate atom is computed in a binary-collision approximation; an equation of motion is derived for the correlation function which is valid outside the quantum-regression regime. Solutions are given for the weak-field conditions in terms of generalized absorption and emission profiles that depend on the indices of the atomic multipoles.
Burnett, K.↗
Temporal correlation measurements of pulsed dual CO2 lidar returns
A pulsed dual-laser direct-detection differential-absorption lidar DIAL system, operating near 10.6 microns, is used to measure the temporal correlation and statistical properties of backscattered returns from specular and diffuse topographic targets. Results show that atmospheric-turbulence fluctuations can effectively be frozen for pulse separation times on the order of 1-3 msec or less. The diffuse target returns, however, yielded a much lower correlation than that obtained with the specular targets; this being due to uncorrelated system noise effects and different statistics for the two types of target returns.
Menyuk, N.↗
Temperature dependence of the self-reaction of CH3O2 radicals
The rate constants for the reaction CH3O2 + CH3O2 yields products (1) were measured in the temperature range from 248 to 417 K, taking into consideration pressures in the range from 60 to 700 torr of N2. The experimental investigation was carried out in a Pyrex flash photolysis system employing ultraviolet absorption detection. Methylperoxy radicals (CH3O2) were produced by the photolysis of Cl2-CH4-O2 mixtures. Rate constants were measured by observing the second-order disappearance of CH3O2 radicals. Plots of 1/(CH3O2 optical density) vs. time were observed to be linear over a concentration change of a factor of 10-50. Results of the kinetic runs at each temperature are summarized in a table, and an Arrhenius plot of the data is shown in a graph.
Sander, S. P.↗
Airborne lidar investigations of ozone and aerosols in the nonurban troposphere
A description is presented of the first application of an airborne optical radar (lidar) to measurements of ozone and aerosol profiles in regional and global tropospheric investigations. It is pointed out that high spatial resolution measurements of ozone and aerosols are important in studying the relative contribution of chemistry and transport in large scale atmospheric processes. The investigation makes use of an airborne differential absorption optical radar system, which has been developed for the remote profiling of O3 and aerosols in the troposphere. Attention is given to lower tropospheric measurements and upper tropospheric measurements. The obtained results demonstrate the capability of the considered system to measure O3 and aerosol profiles in the troposphere and lower stratosphere.
Browell, E. V.↗
Limitations of signal averaging due to temporal correlation in laser remote-sensing measurements
Laser remote sensing involves the measurement of laser-beam transmission through the atmosphere and is subject to uncertainties caused by strong fluctuations due primarily to speckle, glint, and atmospheric-turbulence effects. These uncertainties are generally reduced by taking average values of increasing numbers of measurements. An experiment was carried out to directly measure the effect of signal averaging on back-scattered laser return signals from a diffusely reflecting target using a direct-detection differential-absorption lidar (DIAL) system. The improvement in accuracy obtained by averaging over increasing numbers of data points was found to be smaller than that predicted for independent measurements. The experimental results are shown to be in excellent agreement with a theoretical analysis which considers the effect of temporal correlation. The analysis indicates that small but long-term temporal correlation severely limits the improvement available through signal averaging.
Menyuk, N.↗
Experimental comparison of heterodyne and direct detection for pulsed differential absorption CO2 lidar
A pulsed dual-wavelength dual-CO2-laser differential-absorption lidar (DIAL) system has been developed which permits simultaneous heterodyne and direct detection of the same lidar returns. This system has been used to make an experimental comparison of the SNRs and statistical and temporal characteristics of the DIAL returns from several topographic targets. These results were found to be in general agreement with theory and were used to quantify the relative merits of the two detection techniques. The measured parameter values were applied to an analytical treatment to predict system trade-offs for the remote sensing of atmospheric species, with application to both path-averaged and range-resolved measurements.
Killinger, D. K.↗
LaNi5 hydride cryogenic refrigerator test results
A complete LaNi5 hydrogen absorption cryogenic refrigerator system was developed. The system uses low temperature waste heat of approximately 100 C as a power source, and has no moving parts other than self operating valves. The cycle continues automatically by an electronic sequencing timing mechanism for the three compressors which are phased such that a constant supply of high pressure hydrogen gas is provided. It is indicated that with a fully clean hydrogen system, hundreds of thousand cycles should be attainable, even though some degradation may eventually occur. Simple vacuum reactivation of the hydride of moving parts, other than self operating, long life valves, the refrigerators predicted life is extremely long.
Jones, J. A.↗
Gating characteristics of photomultiplier tubes for Lidar applications
A detector test facility was developed and applied in the evaluation and characterization of lidar detectors in support of the multipurpose airborne differential absorption lidar (DIAL) system based at the Langley Research Center (LaRC). A performance data base of various detector configurations available to the DIAL system was obtained for optimum lidar detector selection. Photomultiplier tubes (PMT's) with multialkaline and bialkaline photocathodes were evaluated in voltage-divider networks (bases) by using either the focusing electrode or dynodes as a gating mechanism. Characteristics used for detector evaluation included gain stability, signal rise time, and the ability to block unwanted high light levels.
Barrick, J. D. W.↗
Flight tests of a range-resolved airborne dial with two min-tea CO2 lasers
It is important to measure regional distributions of ozone concentrations in a short time for understanding a mechanism of photo-chemical smog development. An airborne Differential Absorption Lidar (DIAL) system with two low-power mini-TEA CO2 lasers was developed for measuring three-dimensional distributions of ozone in the lower troposphere. The CO2 DIAL is a nadir-looking system and is designed to measure ozone profiles between ground and airplane by using atmospheric aerosols as a distributed radar target. First flight test with a single laser were conducted in February 1985 over the Tokyo area. The system was operated at an altitude of 5000 ft. Results of the first flight tests show that the height profiles of the received power in the boundary layer were different between over land and ocean. The received power has to be inverted to an expression of a single optical parameter to see real aerosol distributions. Inversion of the lidar signal to the aerosol extinction was performed by using Klett's solution.
Itabe, T.↗