Search NASA⌕ Search

SEARCH · Search NASA

Results for “Complex scattering”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The soft gamma-ray spectrum of A0535+26: Detection of an absorption feature at 110 keV by OSSE

We present soft gamma-ray observations by the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (GRO) of the transient X-ray binary pulsar A0535+26. The observations were made 1994 February 8-17, immediately prior to the peak of a giant outburst. The phase averaged spectrum is complex and cannot be described by a single-component model. We find that structure in the spectrum above 100 keV can best be modeled by an absorption feature near 110 keV, which we interepret as the signature of cyclotron resonant scattering. Because of OSSE's 45 keV threshold, we are unable to make a definitive statement on the presence of a 55 keV absorption line; however, we can conclude that if this line does exist, it must have a smaller optical depth than the line at 110 keV. A first harmonic (=fundamental) cyclotron resonance at 110 keV corresponds to a magnetic field strength at the surface of the neutron star of approximately 1 x 10(exp 13) G (approximately 5 x 10(exp 12) G if the first harmonic is at 55 keV).

Grove, J. E.↗
NASA NTRS2013

Analysis of the Impedance Resonance of Piezoelectric Multi-Fiber Composite Stacks

Multi-Fiber CompositesTM (MFC's) produced by Smart Materials Corp behave essentially like thin planar stacks where each piezoelectric layer is composed of a multitude of fibers. We investigate the suitability of using previously published inversion techniques for the impedance resonances of monolithic co-fired piezoelectric stacks to the MFCTM to determine the complex material constants from the impedance data. The impedance equations examined in this paper are those based on the derivation. The utility of resonance techniques to invert the impedance data to determine the small signal complex material constants are presented for a series of MFC's. The technique was applied to actuators with different geometries and the real coefficients were determined to be similar within changes of the boundary conditions due to change of geometry. The scatter in the imaginary coefficient was found to be larger. The technique was also applied to the same actuator type but manufactured in different batches with some design changes in the non active portion of the actuator and differences in the dielectric and the electromechanical coupling between the two batches were easily measureable. It is interesting to note that strain predicted by small signal impedance analysis is much lower than high field stains. Since the model is based on material properties rather than circuit constants, it could be used for the direct evaluation of specific aging or degradation mechanisms in the actuator as well as batch sorting and adjustment of manufacturing processes.

Multi-fiber composites↗
DOE OSTI2026

Nonadiabatic strong-field photoionization revisited: Detailed analysis

We develop a theoretical framework to interpret “bump-like” enhancements in the energy distribution of electrons emitted from cesium atoms subjected to intense infrared laser fields, as observed in a recent experiment. These emissions, detected at energies approaching twice the ponderomotive energy (2⁢𝑈 p ), indicate a mechanism where electrons are nonadiabatically ejected with substantial inward velocity following ionization. The bump-like features arise from returning trajectories that scatter off the residual ion. We interpret these experimental results classically using a periodically driven version of the Bohr model and quantum mechanically through Keldysh's adiabaticity parameter (𝛾 K ) and Reiss's continuum-state intensity parameter 𝒵 in a Coulomb-corrected version of the strong-field approximation (SFA) that incorporates “complex” electronic trajectories. Notably, our theoretical analysis shows that these emissions are independent of the specific short-range form of the atomic potential.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Structural and Spectroscopic Characterization of Plutonium and Other Tetravalent Metals Complexed to a Keggin Ion

Here, we report the isolation of the first plutonium(IV) complex with a Keggin ion chelator: Cs 20 [Pu(PW 11 O 39 ) 2 ] 2 ·13H 2 O. Single crystal XRD and solid-state UV–vis absorbance analysis demonstrate the stabilization of Pu 4+ by the Keggin ligand. The unit cell contains two [Pu(PW 11 O 39 ) 2 ] 10– complexes (Pu(PW 11 ) 2 ) bridged by Cs + . Raman and 31 P NMR spectra of Pu(PW 11 ) 2 are consistent with the analogous Zr 4+ , Hf 4+ , Ce 4+ , and Th 4+ complexes. The Pu–O bond distances at the two Pu sites are 2.35(3) and 2.34(3) Å, matching the value extrapolated from the bonding trend built with the other 8-coordinated tetravalent cations. However, the long-range arrangement of the Pu(PW 11 ) 2 complexes within the lattice is unique in the series of M IV (PW 11 ) 2 compounds: pairs of Pu(PW 11 ) 2 are organized perpendicular to each other. Based on solution-state UV–visible absorbance, small-angle X-ray scattering (SAXS), and 31 P NMR, the tetravalent cations quantitatively form the 1:2 species in solution ([Pu(PW 11 O 39 ) 2 ] 10– (aq) ) and no 1:1 species ([Pu(PW 11 O 39 )(H 2 O) x ] 3– (aq) ). Finally, a linear correlation exists between the metal–oxygen distances in the M IV (PW 11 ) 2 compounds and the corresponding metal dioxides, allowing for extrapolation for Pa 4+ , Am 4+ , and Bk 4+ . The results indicate that our microscale POM approach represents a viable pathway to probe properties of rare actinide ions in discrete molecules, beyond the traditional oxide extended solids.

and nuclear chemistry↗
NASA NTRS1980

Determination of the complex refractive index and size distribution of atmospheric particulates from bistatic-monostatic lidar and solar radiometer measurements

A method is presented for inferring both the size distribution and the complex refractive index of atmospheric particulates from combined bistatic-monostatic lidar and solar radiometer observations. The basic input measurements are spectral optical depths at several visible and near-infrared wavelengths as obtained with a solar radiometer and backscatter and angular scatter coefficients as obtained from a biostatic-monostatic lidar. The spectral optical depth measurements obtained from the radiometer are mathematically inverted to infer a columnar particulate size distribution. Advantage is taken of the fact that the shape of the size distribution obtained by inverting the particulate optical depth is relatively insensitive to the particle refractive index assumed in the inversion. Bistatic-monostatic angular scatter and backscatter lidar data are then processed to extract an optimum value for the particle refractive index subject to the constraint that the shape of the particulate size distribution be the same as that inferred from the solar radiometer data. Specifically, the scattering parameters obtained from the bistatic-monostatic lidar data are compared with corresponding theoretical computations made for various assumed refractive index values. That value which yields best agreement, in a weighted least squares sense, is selected as the optimal refractive index estimate. The results of this procedure applied to a set of simulated measurements as well as to measurements collected on two separate days are presented and discussed.

Reagan, J. A.↗
NASA NTRS1998

Molecular Processes in Comets

The research focused on molecular hydrogen and its response to ultraviolet radiation, photoelectron impact excitation and X-ray radiation and on the interpretation of the ultraviolet spectra of the Jupiter dayglow and auroras. A systematic effort was made to obtain reliable rate coefficients for rovibrational energy transfer of H2, particularly in collisions with hydrogen atoms. We carried out elaborate quantum-mechanical calculations of the scattering of H and H2 on what had been characterized as a reliable potential energy surface of the H3 molecular system. These calculations took into account reactive channels and rate coefficients for ortho-para transitions were obtained. Quantal calculations are too complex to be applied to all the possible rovibrational transitions and we turned to a semi-classical method. With it we calculated rate coefficients for transitions, reactive and non-reactive, for all the rovibrational levels. We carried out the calculations for three of the available H3 potential energy surfaces. We discovered an unexpected sensitivity of the rate coefficients for the non-reactive channels to the potential energy surface. This discovery stimulated more thorough investigations of the potential energy surface elsewhere and to the construction of a new surface. We have used it in further semi-classical calculations in work that will shortly be 2 completed and which, together with new quantum-mechanical calculations should comprise a set of reliable rate coefficients that can be used in discussions of H2 on the Jovian planets. We carried out a detailed study of the Jovian ultraviolet dayglow. There has been a long-running argument about the dayglow on Jupiter. There are two sources of excitation: fluorescence and photoelectron impact excitation. It had been argued that a third source "the electron glow" was needed to bring theory and observation into agreement. We believe we have shown conclusively that the third source is unnecessary. We have achieved a close quantitative agreement between the predicted spectrum arising from fluorescence and photoelectrons and the measured spectrum. We also demonstrated a method by which the presence of HD could be established observationary. Similar calculations were carried out of the ultraviolet spectra of the Jovian auroras. We again found close agreement. Indeed, the agreement was so detailed we were able to derive the temperature of the atmosphere. We found, contrary to the standard model of the time, a high temperature between 400 K and 600 K and established the presence of a significant temperature gradient. A large temperature gradient was indeed found by direct sampling with the Jupiter probe.

Dalgarno, A.↗
NASA NTRS2016

Polarbrdf: A General Purpose Python Package for Visualization Quantitative Analysis of Multi-Angular Remote Sensing Measurements

The Bidirectional Reflectance Distribution Function (BRDF) is a fundamental concept for characterizing the reflectance property of a surface, and helps in the analysis of remote sensing data from satellite, airborne and surface platforms. Multi-angular remote sensing measurements are required for the development and evaluation of BRDF models for improved characterization of surface properties. However, multi-angular data and the associated BRDF models are typically multidimensional involving multi-angular and multi-wavelength information. Effective visualization of such complex multidimensional measurements for different wavelength combinations is presently somewhat lacking in the literature, and could serve as a potentially useful research and teaching tool in aiding both interpretation and analysis of BRDF measurements. This article describes a newly developed software package in Python (PolarBRDF) to help visualize and analyze multi-angular data in polar and False Color Composite (FCC) forms. PolarBRDF also includes functionalities for computing important multi-angular reflectance/albedo parameters including spectral albedo, principal plane reflectance and spectral reflectance slope. Application of PolarBRDF is demonstrated using various case studies obtained from airborne multi-angular remote sensing measurements using NASA's Cloud Absorption Radiometer (CAR). Our visualization program also provides functionalities for untangling complex surface/atmosphere features embedded in pixel-based remote sensing measurements, such as the FCC imagery generation of BRDF measurements of grasslands in the presence of wild fire smoke and clouds. Furthermore, PolarBRDF also provides quantitative information of the angular distribution of scattered surface/atmosphere radiation, in the form of relevant BRDF variables such as sunglint, hotspot and scattering statistics.

CAR↗
DOE OSTI2026

Mechanisms of Metal Additive-Induced Ordering During SNIPS Membrane Formation

Isoporous membranes can be fabricated by combining self-assembly with nonsolvent induced phase separation (SNIPS) using an amphiphilic block copolymer like polystyrene-b-poly(4-vinylpyridine) (SV). Poly(4-vinylpyridine) (V) is known to complex with metal salts, which are hypothesized to stabilize solution ordering and preserve structure during casting. We explored how the molar ratio of metal additive to the poly(4-vinylpyridine) block affected the final membrane morphology via scanning electron microscopy (SEM). Dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and in situ grazing-incidence SAXS were used to track changes in solution ordering and chain conformation as a function of the molar ratio of the additive to the V block. Additives induced aggregation, promoted the formation of more compact conformations in solution, and facilitated micelle ordering onto lattices at optimal ratios. Furthermore, these experimental results were supported by random phase approximation calculations, which helped explain how the thermodynamic order–disorder transition shifts with additive binding strength. Stronger additive–polymer interactions reduced the block copolymer volume fraction required for ordering in solution, allowing ordered domains to form at lower polymer concentrations.

Additives↗
NASA NTRS1979

Diffusion approximation for large absorption in radiative transfer

A new diffusion model is developed for radiative transfer in particulate media. It includes the effects of higher Legendre moments while avoiding the mathematical complexities of solving multiple coupled differential moment equations and satisfying higher-order boundary conditions. The method accurately extrapolates the conventional Eddington approximation to problems involving large absorption. Although the simplifying assumptions limit the model to nonbeam incidence and spatial homogeneity of the scattering material, they are nonrestrictive with regard to the size and shape of the medium, the character of background reflections, and the type of phase function.

Meador, W. E.↗
NASA NTRS1989

Data acquisition and processing

Fundamental methods of signal processing used in normal mesosphere stratosphere troposphere (MST) radar observations are described. Complex time series of received signals obtained in each range gate are converted into Doppler spectra, from which the mean Doppler shift, spectral width and signal-to-noise ratio (SNR) are estimated. These spectral parameters are further utilized to study characteristics of scatterers and atmospheric motions.

Tsuda, Toshitaka↗
NASA NTRS2000

Potential Applications of Satellite Based Low Frequency Microwave Measurements of Snow and Ice

In this presentation we will examine some potential applications of low frequency microwave radar and radiometer data to remote sensing of snow and ice conditions over land. We focus on the following low frequency bands; L-band (1.28 GHz), S-band (2.69 GHz), and C-band (5.0 GHz). To predict the effect of snow cover on microwave emission, we need to characterize the dielectric properties of the snow in terms of important physical parameters such as snow density, temperature, and wetness. For the case of dry snow, we use an empirical mixing formula which gives the effective complex permittivity of snow as a function of density, temperature, and frequency. For wet snow, we use another mixing formula which gives the effective complex permittivity as a function of snow wetness. With dry snow, the loss at low microwave frequencies is very small so the corresponding penetration depths are very large (eg., 100 m). Clearly seasonal snow covers are far too thin to have a direct scattering or emission effect on these low frequency bands. There are, however, indirect effects introduced because of altered reflection at the snow/soil boundary, and an extra reflecting interface at the snow/air boundary. For C-band, layers of snow with different densities can have an impact if the number of layers grows sufficiently large. (eg., many meters of snow pack with cm-scale density layering.) Wet snow poses a more difficult problem. Liquid water is much more effective than ice at scattering and absorbing L-band radiation, so even a small amount of wetness will greatly reduce penetration. For example, with a snow wetness of 1 percent (volume fraction), and a density of 300 kg/cu. m, the penetration depths for L-band, S-band, and C-band are about 1.6 m, 0.3 m, and 0.15 m respectively. Very wet snow has more than 10 percent liquid water, and the corresponding L-band penetration is less than 0.2 m. Because the penetration distance is a strong function of frequency, it may be possible to identify a particular class of snow where the wetness is a few percent, and the depth is around one meter by looking at the frequency gradient.

West, Richard D.↗
NASA NTRS2007

The Variable X-Ray Spectrum of Markarian 766. II. Time-resolved Spectroscopy

Time-resolved spectroscopy, slicing XMM and Suzaku data down to 25 ks elements was used to investigate whether absorption or scattering components dominate the spectral variations in Mrk 766. Results: Time-resolved spectroscopy confirmed that spectral variability in Mrk 766 can be explained by either of two interpretations of principal components analysis. Detailed investigation confirmed that rapid changes in the relative strengths of scattered and direct emission or rapid changes in absorber covering fraction provide good explanations of most of the spectral variability. However, a strong correlation between the 6.97 keV absorption line and primary continuum together with rapid opacity changes showed that variations in a complex and multi-layered absorber, most likely a disk wind, are the dominant source of spectral variability in Mrk 766.

Turner, T. J.↗
NASA NTRS1998

A Hybrid SBR/MoM Technique for Analysis of Scattering from Small Protrusions on a Large Conducting Body

For analysis of large-scale electromagnetic scattering problems, high-frequency asymptotic methods are fast but approximate, whereas low-frequency numerical methods are accurate but slow. Neither can produce an efficient and accurate solution to scattering by large bodies containing small structures. A promising approach is to combine the best features of both types of methods to produce a hybrid technique that is sufficiently fast, reasonably accurate, and applicable to a class of unsolvable problems such as the scatterers mentioned above. There are two extremes for this type of hybridization. One is simply to superimpose solutions from asymptotic and numerical methods. While this approach is most widely used in practical applications, it neglects the interactions between the two solutions, which can be significant in many problems. The other extreme is to combine an asymptotic and a numerical method in an exact manner. In this approach, the effect of a large body is included by incorporating its diffraction into the Green's function in the integral equation for the small structures, which accounts for all interactions. While this approach is accurate, it is difficult to be implemented in a general-purpose computer code because of its complex nature. A more practical approach is to develop a technique that can include all significant interactions and neglect all trivial interactions. The resulting hybrid technique can produce sufficient accuracy and can be implemented in a general-purpose computer code. In this paper, we develop a technique that combines the shooting and- bouncing-ray (SBR) method and the method of moments (MoM) to solve for the scattering by large conducting bodies with small structures mounted on their surfaces.

Jin, J. M.↗
DOE OSTI2025

Optimizing the impacts of solid additives on the operational stability and processing reliability of organic solar cells

Previous reports have revealed that by leveraging solid additives, organic solar cells (OSCs) can surpass the device’s performance beyond the intrinsic limitations of host photoactive molecules, a remarkable advancement. However, the impacts of more complex interactions introduced by solid additives are not yet well understood. Herein, optimizing the fabrication process based on the traditional efficiency-guided approach fails to represent the ideal and most practical devices. In particular, achieving superior operational stability while minimizing the device performance scattering was found to require processing solvent evaporation to be synchronized with the volatility of the chosen solid additive. However, this may be challenging since most organic photoactive materials display excellent efficiencies only with selected solvents. Accordingly, this work also demonstrates the potential of dual and complementary solvents selection, consisting of low boiling point (primary) and high boiling point (secondary). This strategy allows for the suppression of any potential trade-offs in efficiency. Meanwhile, the operational stability and precision of device performance are substantially enhanced. Additionally, solid additives have demonstrated that the singlet exciton dissociation rate does not limit the free charge generation yield. Finally, these findings are expected to reformulate OSC device fabrication strategies towards more practical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The Polarity of Co-solvents Regulates the Charge Storage Mechanisms in Supercapacitors with Concentrated Electrolytes

Developing better energy storage devices depends on comprehending the underlying mechanisms involved in charge storage. With the continuous conception of new electrolytes, this task becomes progressively more urgent and complex. An example is the utilization of co-solvated concentrated solutions. While these show promising electrochemical responses, their dynamic properties (especially under confinement) and their relationships with performance are not fully understood. Here, we combined modified step potential electrochemical spectroscopy and quasielastic neutron scattering to investigate systems composed of activated mesoporous carbon (AMC) and concentrated solutions of lithium bis(trifluoromethanesulfonyl)imide in acetonitrile co-solvated with either toluene or acetone. Further, we report that acetone does not impair surface-controlled mechanisms, contrary to the case with toluene, which competes with charged species to populate the AMC’s pores without contributing to charge storage. In turn, toluene promotes a greater overall capacitance owing to Faradaic processes, which may be related to changes in the solvation structures under confinement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Structural, biophysical, and biochemical insights into C–S bond cleavage by dimethylsulfone monooxygenase

Sulfur is an essential element for life. Bacteria can obtain sulfur from inorganic sulfate; but in the sulfur starvation–induced response,Pseudomonadsemploy two-component flavin-dependent monooxygenases (TC-FMOs) from themsuandsfnoperons to assimilate sulfur from environmental compounds including alkanesulfonates and dialkylsulfones. Here, we report binding studies of oxidized FMN to enzymes involved within theP. fluorescensenzymatic pathway responsible for converting dimethylsulfone (DMSO 2 ) to sulfite. In this catabolic pathway, SfnG serves as the initial TC-FMO for sulfur assimilation, which is investigated in detail by solving the 2.6-Å resolution crystal structure of unliganded SfnG and the 1.75-Å resolution crystal structure of the SfnG ternary complex containing FMN and DMSO 2 . We find that SfnG adopts a (β/α) 8 barrel fold with a distinct quaternary configuration from other tetrameric class C TC-FMOs. To probe the unexpected tetramer arrangement, structural heterogeneity is assessed by chromatography and light scattering to confirm ligand binding correlates with a tetramer. Binding of FMN and DMSO 2 accompanies ordering of the active site, with DMSO 2 bound on thesi-face of the flavin. A previously unobserved protein backbone conformation is found within the oxygen-binding site on there-face of the flavin. Functional assays and the positioning of ligands with respect to the oxygen-binding site are consistent with use of an N5-(hydro)peroxyflavin pathway. Biochemical endpoint assays and docking studies reveal SfnG breaks the C–S bond of a range of dialkylsulfones.

Science & Technology - Other Topics↗
DOE OSTI2025

Dynamics of Thermally Driven Domain Transformation in Ferroelectric Thin Films

An important feature in ultrathin ferroelectric films is the spontaneous formation of nanoscale polarization domain patterns. Epitaxial strain can greatly increase the ferroelectric transition temperature such that films can be in the ferroelectric state during growth. On the other hand, depolarization fields compete with ferroelectricity in ultrathin films, and, consequently, the optimal domain configuration during growth is a moving target. Under these conditions it is readily possible for a grown film to be in a nonequilibrium domain configuration. As the energy landscape in the system is quite complex, the relaxation dynamics by which a system can evolve towards the true equilibrium configuration are also quite interesting. Here, to capture the details of this process we used Bragg-geometry x-ray photon correlation spectroscopy (XPCS), in which x-ray scattering speckle patterns contain the information from the domain arrangements inside the film. With modest heating (∼15⁢0 °C) domain relaxation from 𝑇 (tetragonal) to 𝑀 𝐶 (monoclinic) was observed in BaTiO 3 films grown on ultrathin ferroelectric PbTiO 3 layers. Two-time correlation analysis reveals fascinating details associated with sticking points and reversals in the process.

36 MATERIALS SCIENCE↗