Search NASA⌕ Search

SEARCH · Search NASA

Results for “coherent group”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Uncertainty relations, zero point energy and the linear canonical group

The close relationship between the zero point energy, the uncertainty relations, coherent states, squeezed states, and correlated states for one mode is investigated. This group-theoretic perspective enables the parametrization and identification of their multimode generalization. In particular the generalized Schroedinger-Robertson uncertainty relations are analyzed. An elementary method of determining the canonical structure of the generalized correlated states is presented.

Sudarshan, E. C. G.↗
DOE OSTI2026

Understanding Electrochemical Alcohol Hydrogenolysis Enabled by Carbonyl Reduction in Lignocellulosic Biomass-Derived Aromatic Oxygenates

Molecules derived from lignocellulosic biomass are oxygenates with multiple oxygen-containing functional groups, such as hydroxyl and carbonyl groups. Therefore, the ability to selectively reduce a specific oxygenate group is essential for the reductive upgrading of such molecules. Previous studies on electrochemical biomass conversion have shown that alcohol hydrogenolysis, which involves cleavage of the σ(C–O alcohol ) bond, is extremely challenging for furfural and 5-hydroxymethylfurfural (HMF) derivatives, including furfuryl alcohol, 5-methylfurfuryl alcohol (MFA), and 2,5-bis(hydroxymethyl)furan (BHMF). In contrast, HMF itself undergoes alcohol hydrogenolysis relatively easily in acidic aqueous media. Considering that the only structural difference between HMF and BHMF or MFA is the presence of a carbonyl group, this observation raises the question of whether the carbonyl group in HMF facilitates alcohol hydrogenolysis. In this study, we designed systematic experiments to provide a coherent explanation of when and how a carbonyl group enables hydrogenolysis of a copresent alcohol group. Specifically, we show that alcohol hydrogenolysis in HMF proceeds via reduction of the carbonyl group to a ketyl radical, followed by a spin-center shift (SCS) through extended π conjugation. We also elucidate the effect of pH on the selectivity between carbonyl hydrogenation and alcohol hydrogenolysis, both of which share the ketyl radical intermediate. This mechanistic understanding enhances our ability to predict and control alcohol hydrogenolysis in the reductive upgrading of biomass-derived oxygenates.

alcohols↗
DOE OSTI2024

Theoretical examination of nuclear spin diffusion in light-induced spin coherences in photosystem I

Microsecond coherence times are predicted in spin dynamics calculations of a donor–acceptor electron spin pair P + A 1A - created upon light excitation of photosystem I (PSI). The effects of nuclear spin diffusion (NSD) due to the anisotropic protein environment on the predicted coherence times T M are studied. Closely positioned pairs and triples of protons located 5–8 Å from the electron spin are shown to largely control T M . Additionally, knowledge of the crystal structure of PSI allows for spin dynamics calculations where specific cofactors and amino acid residues are removed or replaced and the identification of anisotropic environmental features controlling electronic decoherence. Finally, we show that NSD alone cannot explain the >3× shorter experimentally observed coherence times and suggest that methyl groups at key protein sites may explain this discrepancy.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1998

Squeezed states as representations of symplectic groups

It is shown that the SU(1,1)-like and SU(2)-like two-photon coherent states can be combined to form a O(3,2)-like two-photon state. Since the O(3,2) group has many subgroups, there are also many new interesting new coherent and squeezed two-photon states. Among them is the two-photon sheared state whose symmetry property is like that for the two-dimensional Euclidean group. There are now two-phonon coherent states which may exhibit symmetries not yet observed for photons, including sheared states. Let us note that both SU(1,1) and S(3,2) are isomorphic to the symplectic groups Sp(2) and Sp(4) respectively, and that symplectic transformations consist of rotations and squeeze transformations.

Han, D.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-18834-DND

This presentation will give an overview of the 20-plus years of pulsed transmit laser development at NASA Langley Research Center (LaRC) to enable a coherent Doppler wind lidar to measure global winds from earth orbit. Our group at LaRC has been developing the pulsed laser and other coherent lidar technologies for the global wind mission since the late 1980s. The causal path followed has been from space mission requirements to coherent lidar requirements to component requirements to technology development and finally to ground and aircraft validation. We will describe the development and deployment of Doppler Aerosols Wind Lidar (DAWN) for airborne measurement of wind velocity and direction. The will also present the status of ongoing fully conductively-cooled 2-micron wind lidar transmitter for NASA 3-D winds mission.

Upendra N Singh↗
NASA NTRS2000

Decoherence Matrices

It is known that the Lorentz group is the natural language for a given two-beam system if there are no decoherence effects. This aspect of the twobeam system formulated in terms of the six-parameter representations of the Lorentz group. It is shown that these transformations do not alter the degree of coherence. Thus, the decoherence matrices do not come from the Lorentz group. It is shown therefore that a larger group is needed to accommodate the decoherence effects in the two-beam system. This larger group is isomorphic to O(3,3) or the Lorentz group with three space and three time dimensions.

Han, D.↗
DOE OSTI2024

Symmetry Protected Two-Photon Coherence Time

We report the observation of symmetry protected two-photon coherence time of biphotons generated from backward spontaneous four-wave mixing in laser-cooled 87 Rb atoms. When biphotons are nondegenerate, nonsymmetric photonic absorption loss results in exponential decay of the temporal waveform of the two-photon joint probability amplitude, leading to shortened coherence time. In contrast, in the case of degenerate biphotons, when both paired photons propagate with the same group velocity and absorption coefficient, the two-photon coherence time, protected by space-time symmetry, remains unaffected by medium absorptive losses. Furthermore, our experimental results validate these theoretical predictions. This outcome highlights the pivotal role of symmetry in manipulating and controlling photonic quantum states.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1998

Micro-Laser-Based Devices Allowing Optical Wavelength-Packing Densities

We examine theoretically and experimentally the space-time domain properties of high-speed electro-optically switched microlaser devices susceptible of construction at optical wavelength-packing densities. We address adjustable phase and group delays with wide dynamic range, coherent logic, temporal storage and reconfiguration of pulse arrays and applications to optical phased arrays.

Keys, Andrew S.↗
DOE OSTI2022

Slow light in a 2D semiconductor plasmonic structure

Spectrally narrow optical resonances can be used to generate slow light, i.e., a large reduction in the group velocity. In a previous work, we developed hybrid 2D semiconductor plasmonic structures, which consist of propagating optical frequency surface-plasmon polaritons interacting with excitons in a semiconductor monolayer. Here, we use coupled exciton-surface plasmon polaritons (E-SPPs) in monolayer WSe 2 to demonstrate slow light with a 1300 fold decrease of the SPP group velocity. Specifically, we use a high resolution two-color laser technique where the nonlinear E-SPP response gives rise to ultra-narrow coherent population oscillation (CPO) resonances, resulting in a group velocity on order of 105 m/s. Our work paves the way toward on-chip actively switched delay lines and optical buffers that utilize 2D semiconductors as active elements.

42 ENGINEERING↗
NASA NTRS2015

Open Rotor Noise Shielding by Blended-Wing-Body Aircraft

This paper presents an analysis of open rotor noise shielding by Blended Wing Body (BWB) aircraft by using model scale test data acquired in the Boeing Low Speed Aeroacoustic Facility (LSAF) with a legacy F7/A7 rotor model and a simplified BWB platform. The objective of the analysis is the understanding of the shielding features of the BWB and the method of application of the shielding data for noise studies of BWB aircraft with open rotor propulsion. By studying the directivity patterns of individual tones, it is shown that though the tonal energy distribution and the spectral content of the wind tunnel test model, and thus its total noise, may differ from those of more advanced rotor designs, the individual tones follow directivity patterns that characterize far field radiations of modern open rotors, ensuring the validity of the use of this shielding data. Thus, open rotor tonal noise shielding should be categorized into front rotor tones, aft rotor tones and interaction tones, not only because of the different directivities of the three groups of tones, but also due to the differences in their source locations and coherence features, which make the respective shielding characteristics of the three groups of tones distinctly different from each other. To reveal the parametric trends of the BWB shielding effects, results are presented with variations in frequency, far field emission angle, rotor operational condition, engine installation geometry, and local airframe features. These results prepare the way for the development of parametric models for the shielding effects in prediction tools.

Guo, Yueping↗
NASA NTRS2011

DAWN Coherent Wind Profiling Lidar Flights on NASA's DC-8 During GRIP

Almost from their invention, lasers have been used to measure the velocity of wind and objects; over distances of cm to 10s of km. Long distance (remote) sensing of wind has been accomplished with continuous-wave (CW), focused pulsed, and collimated pulsed lasers; with direct and coherent (heterodyne) optical detection; and with a multitude of laser wavelengths. Airborne measurement of wind with pulsed, coherent-detection lidar was first performed in 1971 with a CW CO2 laser1, in 1972 with a pulsed CO2 laser2, in 1993 with a pulsed 2-micron laser3, and in 1999 with a pulsed CO2 laser and nadir-centered conical scanning4. Of course there were many other firsts and many other groups doing lidar wind remote sensing with coherent and direct detection. A very large FOM coherent wind lidar has been built by LaRC and flown on a DC-8. However a burn on the telescope secondary mirror prevented the full demonstration of high FOM. Both the GRIP science product and the technology and technique demonstration from aircraft are important to NASA. The technology and technique demonstrations contribute to our readiness for the 3D Winds space mission. The data analysis is beginning and we hope to present results at the conference.

Kavaya, Michael J.↗
NASA NTRS1992

Apollo 15 green glass - Compositional distribution and petrogenesis

We have characterized a comprehensive suite of individual green-glass beads from Apollo 15 soil to determine interelement behavior and to constrain petrogenetic relationships. We analyzed 365 particles for trace elements by instrumental neutron activation analysis and analyzed 52 of them, selected to cover the compositional ranges observed for trace elements, for major elements by electron microprobe analysis. We confirm the observation of Delano (1979) that the beads comprise discrete compositional groups, although two of the groups he defined are further split on the basis of trace-element compositions. Each of the resulting seven groups has distinct average rare-earth abundances. The coherence between major- and trace-element data was masked in previous studies by imprecision, correlated error, and nonrepresentative sampling of the different groups. Most of the compositional characteristics of the green glasses can be explained by a model for batch equilibrium melting of a nearly homogeneous, ultramafic source region, when the complicating effects of high pressure and low oxygen fugacity are taken into account. The previously puzzling behavior of Ni and Co as apparently incompatible elements may arise from partial reduction of those elements to the zero oxidation state, resulting in low mineral/melt partition coefficients. The model also offers explanations for why the green glasses form boomerang-shaped trends on many two-element variation diagrams and why certain compositions (Groups A and D) are more abundant than glasses with other compositions.

Steele, Alison M.↗
NASA NTRS1999

The Multi-Center Airborne Coherent Atmospheric Wind Sensor: Recent Measurements and Future Applications

The atmospheric lidar remote sensing groups of NOAA Environmental Technology Laboratory, Jet Propulsion Laboratory and NASA Marshall Space Flight Center jointly developed an airborne scanning coherent Doppler Lidar. We describe the system, present recent measurement (including the first wind fields measured within a hurricane using Doppler lidar), and describe prospective instrument improvements and research applications.

Rothermel, Jeffry↗
NASA NTRS1993

The harmonic oscillator and nuclear physics

The three-dimensional harmonic oscillator plays a central role in nuclear physics. It provides the underlying structure of the independent-particle shell model and gives rise to the dynamical group structures on which models of nuclear collective motion are based. It is shown that the three-dimensional harmonic oscillator features a rich variety of coherent states, including vibrations of the monopole, dipole, and quadrupole types, and rotations of the rigid flow, vortex flow, and irrotational flow types. Nuclear collective states exhibit all of these flows. It is also shown that the coherent state representations, which have their origins in applications to the dynamical groups of the simple harmonic oscillator, can be extended to vector coherent state representations with a much wider range of applicability. As a result, coherent state theory and vector coherent state theory become powerful tools in the application of algebraic methods in physics.

Rowe, D. J.↗
DOE OSTI2024

Results from a multi-laboratory ocean metaproteomic intercomparison: effects of LC-MS acquisition and data analysis procedures

Metaproteomics is an increasingly popular methodology that provides information regarding the metabolic functions of specific microbial taxa and has potential for contributing to ocean ecology and biogeochemical studies. A blinded multi-laboratory intercomparison was conducted to assess comparability and reproducibility of taxonomic and functional results and their sensitivity to methodological variables. Euphotic zone samples from the Bermuda Atlantic Time-series Study (BATS) in the North Atlantic Ocean collected by in situ pumps and the autonomous underwater vehicle (AUV) Clio were distributed with a paired metagenome, and one-dimensional (1D) liquid chromatographic data-dependent acquisition mass spectrometry analysis was stipulated. Analysis of mass spectra from seven laboratories through a common bioinformatic pipeline identified a shared set of 1056 proteins from 1395 shared peptide constituents. Quantitative analyses showed good reproducibility: pairwise regressions of spectral counts between laboratories yielded R 2 values averaged 0.62±0.11, and a Sørensen similarity analysis of the top 1000 proteins revealed 70 %–80 % similarity between laboratory groups. Taxonomic and functional assignments showed good coherence between technical replicates and different laboratories. A bioinformatic intercomparison study, involving 10 laboratories using eight software packages, successfully identified thousands of peptides within the complex metaproteomic datasets, demonstrating the utility of these software tools for ocean metaproteomic research. Lessons learned and potential improvements in methods were described. Future efforts could examine reproducibility in deeper metaproteomes, examine accuracy in targeted absolute quantitation analyses, and develop standards for data output formats to improve data interoperability. Together, these results demonstrate the reproducibility of metaproteomic analyses and their suitability for microbial oceanography research, including integration into global-scale ocean surveys and ocean biogeochemical models.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1997

The Multi-Center Airborne Coherent Atmospheric Wind Sensor, MACAWS

In 1992 the atmospheric lidar remote sensing groups of the NASA Marshall Space Flight Center, NOAA Environmental Technology Laboratory, and Jet Propulsion Laboratory began a joint collaboration to develop an airborne high-energy Doppler laser radar (lidar) system for atmospheric research and satellite validation and simulation studies. The result is the Multi-center Airborne Coherent Atmospheric Wind Sensor, MACAWS, which has the capability to remotely sense the distribution of wind and absolute aerosol backscatter in the troposphere and lower stratosphere. A factor critical to the programmatic feasibility and technical success of this collaboration has been the utilization of existing components and expertise which were developed for previous atmospheric research by the respective institutions. The motivation for the MACAWS program Is three-fold: to obtain fundamental measurements of sub-synoptic scale processes and features which may be used as a basis to improve sub-grid scale parameterizations in large-scale models; to obtain similar datasets in order to improve the understanding and predictive capabilities on the mesoscale; and to validate (simulate) the performance of existing (planned) satellite-borne sensors. Examples of the latter include participation in the validation of the NASA Scatterometer and the assessment of prospective satellite Doppler lidar for global tropospheric wind measurement. Initial flight tests were made in September 1995; subsequent flights were made in June 1996 following improvements. This paper describes the MACAWS instrument, principles of operation, examples of measurements over the eastern Pacific Ocean and western United States, and future applications.

Rothermel, Jeffry↗
NASA NTRS1993

The q-harmonic oscillators, q-coherent states and the q-symplecton

The recently introduced notion of a quantum group is discussed conceptually and then related to deformed harmonic oscillators ('q-harmonic oscillators'). Two developments in applying q-harmonic oscillators are reviewed: q-coherent states and the q-symplecton.

Biedenharn, L. C.↗
NASA NTRS1994

Coherent-phase or random-phase acceleration of electron beams in solar flares

Time structures of electron beam signatures at radio wavelengths are investigated to probe correlated versus random behavior in solar flares. In particular we address the issue whether acceleration and injection of electron beams is coherently modulated by a single source, or whether the injection is driven by a stochastic (possibly spatially fragmented) process. We analyze a total of approximately = 6000 type III bursts observed by Ikarus (Zurich) in the frequency range of 100-500 MHz, during 359 solar flares with simultaneous greater than or = 25 keV hard X-ray emission, in the years 1890-1983. In 155 flares we find a total of 260 continuous type III groups, with an average number of 13 +/- 9 bursts per group, a mean duration of D = 12 +/- 14 s, a mean period of P = 2.0 +/- 1.2 s, with the highest burst rate at a frequency of nu = 310 +/- 120 MHz. Pulse periods have been measured between 0.5 and 10 s, and can be described by an exponential distribution, i.e., N(P) varies as e (exp -P/1.0s). The period shows a frequency dependence of P(nu)=46(exp-0.6)(sub MHz)s for different flares, but is invariant during a particular flare. We measure the mean period P and its standard deviation sigma (sub p) in each type III group, and quantify the degree of periodicity (or phase-coherence) by the dimensionless parameter sigma (sub p)P. The representative sample of 260 type III burst groups shows a mean periodicity of sigma (sub p/P) = 0.37 +/- 0.12, while Monte Carlo simulations of an equivalent set of truly random time series show a distinctly different value of sigma (sub p)P = 0.93 +/- 0.26. This result indicates that the injection of electron beams is coherently modulated by a particle acceleration source which is either compact or has a global organization on a timescale of seconds, in contrast to an incoherent acceleration source, which is stochastic either in time or space. We discuss the constraints on the size of the acceleration region resulting from electron beam propagation delays and from Alfvenic synchronization during a pulse period. We discuss two periodic preocesses in flares, which potentially control quasi-periodic particle acceleration: (1) MHD oscillations, and (2) current sheets with oscillatory dynamics.

Aschwanden, Markus J.↗