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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.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Observations of Pc5 micropulsation-related electric field oscillations in equatorial ionosphere

A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5 deg N, 77 deg E, 0.5 deg N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (A(sub p) = 161). Simultaneous 100-n T-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6 deg N gm) and at Narsarsuaq, Greenland (70.6 deg N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730-1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV/m and it increases with height, while it is about 1.0 mV/m in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brofelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the assoicated ionospheric electric field penetrating from high latitudes to the magnetic equator.

Reddy, C. A.↗
DOE OSTI2024

Terahertz electric-field-driven dynamical multiferroicity in SrTiO 3

The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO 3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein–de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Probing BSM Oscillatory Signals with the DUNE Detectors and the LBNF Neutrino Beam: NSI and Sterile Neutrino Sensitivities

The Deep Underground Neutrino Experiment (DUNE) is a flagship long-baseline accelerator neutrino experiment under construction in the U.S. With a 1,300 km distance between its Near Detector (ND) and Far Detector (FD), the world’s most intense LBNF (Long-Baseline Neutrino Facility) neutrino beam, and high-resolution LArTPC (Liquid Argon Time Projection Chamber) detectors, DUNE will measure the neutrino oscillation parameters with unprecedented precision. In addition to the determination of the neutrino mass ordering and the potential discovery of Charge-Parity violation in the leptonic sector, DUNE's capabilities present a unique opportunity for probing Beyond the Standard Model (BSM) physics signals with neutrinos. Examples of BSM physics manifestations include the presence of Non-Standard Interactions (NSI) of neutrinos with matter, or the existence of sterile neutrinos that mix with 3-Flavor neutrinos. In this study, we present a joint ND+FD fit to simulated data assessing DUNE's sensitivity to probing neutrino NSI, as well as scenarios including sterile neutrino mixing.

Prais, Luiz [Cincinnati U.] (ORCID:000000018224947↗
NASA NTRS1972

Space and time variations of the solar Na D line profiles.

Preliminary results are presented of observations of the solar Na D lines obtained with high space and time resolution. The line profiles vary strongly with space and time implying that time averaging over a long period and large area will not produce the 'true' profile. The centre-limb increase in apparent Doppler width in the D lines is intrinsic. It is not due to space or time averaging. The amplitude of the 300-sec oscillation may range up to 1.5 km/sec in the region of formation of the D lines. The variation of the D line profile caused by the 300-sec oscillation may be described as follows: (1) the core is raised and lowered without change of shape, and (2) the wings broaden as the central intensity rises and narrow as it falls. Doppler width values derived from pairs of D line profiles are strongly correlated with the motion of the element observed. Indications of running waves have been found in the time variation of the core line bisectors.

Slaughter, C. D.↗
NASA NTRS1974

Beading and spiking phenomena in the M551 metals melting experiment

A study was made regarding the beading and spiking phenomena observed in the M551 metals melting experiment conducted during the Skylab I mission in June 1973. An analysis was made of the beading phenomenon based on the Karman vortex shedding theory. The results tend to support the hypothesis that beading which occurred in the stainless and tantalum samples was a Karman vortex street formation. A dynamic model of cavity oscillation is discussed to explain the spiking phenomenon which was observed in the stainless steel and tantalum samples. Calculations of spiking frequency indicate that the intensity of spiking depends primarily on the vapor pressure and surface tension properties of the material, and is only slightly affected by the level of gravitation acceleration.

Fan, C.↗
NASA NTRS1975

Isotopic abundance ratios for carbon and nitrogen in Nova Herculis 1934

Spectra of Nova Herculis 1934 taken during an episode of intense CN absorption are analyzed to determine the isotopic abundance ratios of C12/C13 and N14/N15. Synthetic spectrum analysis, based on the wavelengths, excitation potentials, and oscillator strengths for the CN lines, and radial velocity measurements indicate that C(12)N(14) was the dominant species in the Nova, and that the minimum abundance limit for C12/C13 is about 1.5, while the minimum for N14/N15 is about 2. The results are compared with predictions based on models of thermonuclear runaways in hydrogen-rich envelopes of white dwarfs. It is noted that the nova material may have been contaminated with C13-rich material prior to or during the eruption. Possible causes of this isotope enrichment are presented.

Sneden, C.↗
NASA NTRS1989

A search for quasi-periodic oscillations in 4U/MXB 1735-44

A search for quasi-periodic oscillations (QPOs) in 4U/MXB 1735-44 was performed using Exosat observations during which the source was in a horizontal branch of the spectral hardness-intensity diagram for about 8 hr and in a normal branch type of behavior for about 46 hr. No QPOs or low-frequency noise was found in the horizontal branch state. It is suggested that this absence is due to either low luminosity or the fact that the companion in 1735-44 is a main-sequence star.

Penninx, Wim↗
NASA NTRS1994

Comparison of new experimental and atrophysical f-values for some Ru II lines, observed in HST spectra of chi Lupi

We report an experimental absolute oscillator strengths for 18 UV lines of Ru II, obtained by combining laser-induced flourescence measurements of radiative lifetimes and branching fractions from line intensities in a calibrated Fourier-transform spectrum Hubble Space Telescope/Goddard High Resolution Spectrograph (HST/GHRS) observations of the spectrum of the sharp-lined B star chi Lupi contain six of these lines, for which 'astrophysical' relative f-values have been determined. The agreement is within 0.10 dex for a Ru abundance of log N(Ru)/N(H) = -7.90, which is 2.3 dex above the solar abundance.

Johansson, Sveneric G.↗
NASA NTRS2000

Wintertime East Asian Jet Stream and Its Association with the Asian-Pacific Climate

Interannual variability of the wintertime East Asian westerly jet stream and the linkage between this variability and the Asian-Pacific climate are investigated. The study emphasizes on the variability of the jet core and its association with the Asian winter monsoon, tropical convection, upper tropospheric wave patterns, and the teleconnection of the jet with other climate systems. The relationship between the jet and North Pacific sea surface temperature pattern (SST) is also explored. NCEP/NCAR reanalysis, NASA GISS surface temperature, NASA GEOS reanalysis, NOAA reconstructed SST, GPCP precipitation, and NOAA snow cover data sets are analyzed in this study. An index of the East Asian jet has been defined by the December-February means of the 200 mb zonal winds that are averaged within a box enclosing the jet maximum, which shifts only moderately from one year to another especially in the south-north direction. The jet links to a teleconnection pattern whose major climate anomalies appear over the Asian continent and western Pacific (west of the dateline). This pattern differs distinctly from the teleconnection pattern associated with El Nino/Southern Oscillation (ENSO), which causes the Pacific/North American pattern to the east of the dateline. A strong jet is accompanied clearly by an increase in the intensity of the atmospheric circulation over Asia and the Pacific. In particular, the winter monsoon strengthens over East Asia, leading to cold climate in the region, and convection intensifies over the tropical Asia-Australia sector. Changes in the jet are associated with broad-scale modification in the upper tropospheric wave patterns that leads to downstream climate anomalies over the eastern Pacific. Through this downstream influence, the East Asian jet causes climate signals in North America as well. A strong jet gives rise to warming and less snow cover in the western United States but reverse climate anomalies in the eastern part of the country, although these signals are relatively weaker than the jet-related anomalies in East Asia. There is a strong association between the East Asian jet and the North Pacific SST (NPSST). A strong jet is accompanied by a cooling in the extratropical Pacific and a warming in the tropical-subtropical Pacific. Evidence also indicates that the extratropical NPSST pattern plays a role in modulating the intensity of the jet stream. ENSO, the jet, and the NPSST are mutually interactive on certain time scales and such an interaction links closely to the climate anomalies in the Asian-Pacific-American regions.

Yang, Song↗
NASA NTRS2010

Free-Free Transitions in the Presence of Laser Fields at Very Low Incident Electron Energy

We study the free-free transition in electron-hydrogenic systems in ground state in presence of an external laser field at very loud incident energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen to be monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser in a nonperturbative manner by choosing a Volkov wave function for it. The scattering weave function for the electron is solved numerically by taking into account the effect of the electron exchange, short-range as well as of the long-range interactions to get the S and P wave phase shifts while for the higher angular momentum phase shifts the exchange approximation has only been considered. We calculate the laser assisted differential cross sections (LADCS) for the aforesaid free-free transition process for single photon absorption/emission. The laser intensity is chosen to be much less than the atomic field intensity. A strong suppression is noted in the LADCS as compared to the field free (FF) cross sections. Unlike the FF ones, the LADCS exhibit some oscillations having a distinct maximum at a low value of the scattering angle depending on the laser parameters as well as on the incident energies.

Bhatia, A. K.↗
NASA NTRS2009

Free-Free Transitions in the Presence of Laser Fields at Very Low Incident Electron Energy

We study the free-free transition in electron-hydrogenic systems in ground state in presence of an external laser field at very low incident energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen to be monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser in a nonperturbative manner by choosing a Volkov wave function for it The scattering wave function for the electron is solved numerically by taking into account the effect of the electron exchange, short-range as well as of the long-range interactions to get the S and P wave phase shifts while for the higher angular momentum phase shifts, the exchange approximation has only been considered. We calculate the laser-assisted differential cross sections (LADCS) for the aforesaid free-free transition process for single photon absorption/emission. The laser intensity is chosen to be much less than the atomic field intensity. A strong suppression is noted in the LADCS as compared to the field free (FF) cross sections. Unlike the FF ones, the LADCS exhibit some oscillations having a distinct maximum at a low value of the scattering angle depending on the laser parameters as well as on the incident energies.

Bhatia, Anand K.↗
NASA NTRSDate not supplied

Comparison of Ring Diagrams Based on the Doppler Shifts of Synthetic Data Obtained with Bisector Method and SDO/HMI Pipeline

Ring diagrams are cross-sections of three-dimensional spatiotemporal power spectra of solar oscillations. The rings reveal information about sub-surface flows and represent an important tool for helioseismology. Ring diagrams can be constructed using Doppler velocity or intensity maps of spectral lines. How the velocities are computed is an important factor for accuracy of information we can retrieve on subsurface flows. In our work, the ring diagrams are generated from Doppler shift data of synthesized Fe I 6173 Å line. We compare ring diagrams computed by two methods–HMI line-of-sight pipeline and the bisector of Fe line. Fe I line is synthesized for StellarBox 3D Radiative hydrodynamic simulations under LTE assumption. We aim to answer the following questions: 1.How do power spectra obtained from velocities computed with the HMI pipeline and bisector of the Fe I 6173Å compare? 2.How do the power spectral density retrieved with each method vary with heliocentric angle? 3.What is the effect of changing resolution on the power spectral density in ring diagrams obtained with the two methods?

SMD↗
DOE OSTI2021

Oscillations of the thermal conductivity in the spin-liquid state of α-RuCl 3

In the class of materials called spin liquids a magnetically ordered state cannot be attained even at millikelvin temperatures because of conflicting constraints on each spin; for example, from geometric or exchange frustration. The resulting quantum spin-liquid state is currently of intense interest because it exhibits unusual excitations as well as wave-function entanglement. The layered insulator α-RuCl 3 orders as a zigzag antiferromagnet at low temperature in zero magnetic field. The zigzag order is destroyed when a magnetic field is applied parallel to the zigzag axis. At moderate magnetic field strength, there is growing evidence that a quantum spin-liquid state exists. Here we report the observation of oscillations in its thermal conductivity in that field range. The oscillations, whose amplitude is very large within this field range and strongly suppressed on either side, are periodic. This is analogous to quantum oscillations in metals, even though α-RuCl 3 is an excellent insulator with a large gap. As the temperature is raised above 0.5 K, the oscillation amplitude decreases exponentially, anticorrelating with the emergence of an anomalous planar thermal Hall conductivity above approximately 2 K.

36 MATERIALS SCIENCE↗
NASA NTRS1998

Advanced High Brilliance X-Ray Source

The possibility to dramatically increase the efficiency of laboratory based protein structure measurements through the use of polycapillary X-ray optics was investigated. This project initiated April 1, 1993 and concluded December 31, 1996 (including a no cost extension from June 31, 1996). This is a final report of the project. The basis for the project is the ability to collect X-rays from divergent electron bombardment laboratory X-ray sources and redirect them into quasiparallel or convergent (focused) beams. For example, a 0.1 radian (approx. 6 deg) portion of a divergent beam collected by a polycapillary collimator and transformed into a quasiparallel beam of 3 millradian (0.2 deg) could give a gain of 6(exp 2)/0.2(exp 2) x T for the intensity of a diffracted beam from a crystal with a 0.2 deg diffraction width. T is the transmission efficiency of the polycapillary diffraction optic, and for T=0.5, the gain would be 36/0.04 x O.5=45. In practice, the effective collection angle will depend on the source spot size, the input focal length of the optic (usually limited by the source spot-to-window distance on the x-ray tube) and the size of the crystal relative to the output diameter of the optic. The transmission efficiency, T, depends on the characteristics (fractional open area, surface roughness, shape and channel diameter) of the polycapillary optic and is typically in the range 0.2-0.4. These effects could substantially reduce the expected efficiency gain. During the course of this study, the possibility to use a weakly focused beam (0.5 deg convergence) was suggested which could give an additional 10-20 X efficiency gain for small samples . Weakly focused beams from double focusing mirrors are frequently used for macromolecular crystallography studies. Furthermore the crystals are typically oscillated by as much as 2 deg during each X-ray exposure in order to increase the reciprocal space (number of crystal planes) sampled and use of a slightly convergent beam could, in principle, provide a similar sampling benefit without oscillation. Although more problematic, because of complications in analyzing the diffraction patterns, it was also suggested that even more extreme beam convergence might be used to give another order of magnitude intensity gain and even smaller focused spot size which could make it possible to study smaller protein crystals than can be studied using standard laboratory based X-ray diffraction systems. This project represents the first systematic investigation of these possibilities. As initially proposed, the contract included requirements for design, purchase, evaluation and delivery of three polycapillary lenses to the Laboratory for Structural Biology at MSFC and demonstration of such optics at MSFC for selected protein crystal diffraction applications.

Gibson, Walter M.↗
DOE OSTI2023

Online real-time learning of dynamical systems from noisy streaming data

Abstract Recent advancements in sensing and communication facilitate obtaining high-frequency real-time data from various physical systems like power networks, climate systems, biological networks, etc. However, since the data are recorded by physical sensors, it is natural that the obtained data is corrupted by measurement noise. In this paper, we present a novel algorithm for online real-time learning of dynamical systems from noisy time-series data, which employs the Robust Koopman operator framework to mitigate the effect of measurement noise. The proposed algorithm has three main advantages: (a) it allows for online real-time monitoring of a dynamical system; (b) it obtains a linear representation of the underlying dynamical system, thus enabling the user to use linear systems theory for analysis and control of the system; (c) it is computationally fast and less intensive than the popular extended dynamic mode decomposition (EDMD) algorithm. We illustrate the efficiency of the proposed algorithm by applying it to identify the Van der Pol oscillator, the chaotic attractor of the Henon map, the IEEE 68 bus system, and a ring network of Van der Pol oscillators.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1971

Lighting factors affecting the visibility of a moving display.

Compensatory tracking performance was shown to be substantially degraded by oscillation of the visual display at both 1.0 and 2.0 Hz. The severity of this decrement was altered significantly by changes in both the color and the intensity of the display illumination. Performance was significantly better with red light illuminating the display at 0.05 mL than with blue light at the equivalent luminance. This improvement in performance was similar in magnitude to that found for an increase in broad-band illumination of the display where luminance was increased from 1/2 log unit below to 1/2 log unit above 0.05 mL. Visual mechanisms that may have been responsible for these findings are suggested.

Gilson, R. D.↗
NASA NTRS1979

The physical basis for absorption of light

The effects of light absorption on the wave functions of gas-phase molecules and atoms are investigated by high resolution spectral measurements of radiation emerging from a sample. A Stark-modulated sample of methyl fluoride was irradiated at the 102 GHz rotational transition and the emergent radiation was resolved by means of a spectrum analyzer. For signal oscillator frequencies below or above the molecular resonance by one modulation frequency, the amplitudes of the upper and lower modulation sidebands are found to be of nonuniform intensity, which is inconsistent with amplitude modulation. Emission due to polarization is, however, calculated to be consistent with the results observed, indicating that light absorption should be considered as a subtractive stimulated emission.

Pickett, H. M.↗
NASA NTRS1997

Modeling the Effect of Optical System Aberrations on Coherent Lidar Heterodyne Efficiency

Signal-to-noise ratio of a coherent lidar is directly proportional to heterodyne efficiency, which is a measure of the mixing of the local oscillator and signal beams. Formulation of heterodyne efficiency is presented and then extended to include the primary, or Seidel, aberrations arising from optical systems. Animations of the intensity pattern for mixing of truncated Gaussian beams in the presence of Seidel aberrations are shown to illustrate the effect on heterodyne efficiency. Results showing the degradation of heterodyne efficiency with an increasing amount of Seidel aberration are given for the same Gaussian beams. This is further extended to predict the change in heterodyne efficiency of a coherent lidar as a result of its optical components by including aberration data derived from optical testing.

Chambers, Diana M.↗