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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 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The Effective Velocity of the Domain Wall Motion in the Quasi-One-Dimensional Nanosystem at a Multiple Nucleation of Domains of the New Phase

The process of switching a metastable state into an energetically preferable state in extended quasione- dimensional systems often occurs through the motion of domains walls of new phase. Usually considered limit cases are the propagation of the edge domains over the whole system or multiple nucleation and coalescence of domains in the volume of the material. This paper deals with the more general situation of front propagation of the switching state from the sample edge at a multiple nucleation of domains of a new phase on randomly located defects in the volume. The corresponding statistically-kinetic problem is solved with the calculation of the average magnitude and dispersion of path lengths, as well as the full generating function for finding higher moments of distribution of “the relay” run lengths of the boundary of the edge domain.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1989

Formation of Fourier phase shifts in the solar Ni I 6768 A line

A formalism is developed to understand better how Doppler shifts of spectrum lines as inferred from phase shifts in the Fourier transforms of line profiles are related to the underlying velocity structures which they are intended to measure. With a standard model atmosphere and a simplified, quasi-LTE treatment of line formation, the formalism is applied to the Ni I 6768 A line, which has been selected for use with a network of imaging interferometers under development by the Global Oscillations Network Group for research in helioseismology. Fourier phase shifts are found to be a remarkably linear measure of velocity even in the presence of gradients and unresolved lateral variations in the assumed velocity field. An assumed outward increase in amplitude of a model oscillatory velocity is noticeably reflected in the center-to-limb behavior of the simulated velocity measure, and a sample model of solar granulation is found to have a strong influence on the formation of the Fourier phase.

Jones, Harrison P.↗
NASA NTRS2005

Magnetohydrodynamic Power Generation in the Laboratory Simulated Martian Entry Plasma

This paper addresses the magnetohydrodynamic (MHD) conversion of the energy released during the planetary entry phase of an interplanetary vehicle trajectory. The effect of MHD conversion is multi-fold. It reduces and redirects heat transferred to the vehicle, and regenerates the dissipated energy in reusable and transportable form. A vehicle on an interplanetary mission carries about 10,000 kWh of kinetic energy per ton of its mass. This energy is dissipated into heat during the planetary atmospheric entry phase. For instance, the kinetic energy of Mars Pathfinder was about 4220 kWh. Based on the loss in velocity, Mars Pathfinder lost about 92.5% of that energy during the plasma-sustaining entry phase that is approximately 3900 kWh. An ideal MHD generator, distributed over the probe surface of Mars Pathfinder could convert more than 2000 kWh of this energy loss into electrical energy, which correspond to more than 50% of the kinetic energy loss. That means that the heat transferred to the probe surface can be reduced by at least 50% if the converted energy is adequately stored, or re-radiated, or directly used. Therefore, MHD conversion could act not only as the power generating, but also as the cooling process. In this paper we describe results of preliminary experiments with light and microwave emitters powered by model magnetohydrodynamic generators and discuss method for direct use of converted energy.

Vuskovic, L.↗
DOE OSTI2025

XRISM/Resolve view of Abell 2319: Turbulence, sloshing, and ICM dynamics

Here, we present results from XRISM/Resolve observations of the core of the galaxy cluster Abell 2319, focusing on its kinematic properties. The intracluster medium (ICM) exhibits temperatures of approximately 8 keV across the core, with a prominent cold front and a high-temperature region (⁠~11 keV) in the north-west. The average gas velocity in the 3' x 4' region around the brightest cluster galaxy (BCG) covered by two Resolve pointings is consistent with that of the BCG to within 40 km s -1 ⁠ and we found modest average velocity dispersion of 230–250 km s -1 ⁠. On the other hand, spatially resolved spectroscopy reveals interesting variations. A blueshift of up to ~230 km s -1 ⁠ is observed around the east edge of the cold front, where the gas with the lowest specific entropy is found. The region further south inside the cold front shows only a small velocity difference from the BCG; however, its velocity dispersion is enhanced to ~400 km s -1 ⁠, implying the development of turbulence. These characteristics indicate that we are observing sloshing motion with some inclination angle following BCG and that gas phases with different specific entropy participate in sloshing with their own velocities, as expected from simulations. No significant evidence for a high-redshift ICM component associated with the subcluster Abell 2319B was found in the region covered by the current Resolve pointings. These results highlight the importance of sloshing and turbulence in shaping the internal structure of Abell 2319. Further deep observations are necessary to better understand the mixing and turbulent processes within the cluster.

Astronomy and AstroPhysics↗
NASA NTRS1977

An experimental investigation of a three-dimensional wall jet

An experimental investigation of the effects of a curved and flat wall surface on the flow development of an axisymmetric jet exhausting into a moving airstream has been made. Of primary concern was the comparison of the one-point statistical properties of the unconfined jet to the quantities measured in the flows over a flat plate and a curved wall surface. Quantities measured in this investigation included mean velocities in all three directions, turbulent intensities, autocorrelations, power spectral densities, and intermittencies. The investigation was confined to the near field of the turbulent jet. The curved wall (flap) was found to have a very large effect on both the mean velocity and the turbulent velocity components of the flowfield. The potential core region of the jet was found to break up most rapidly for the flow over the flap. A laser-Doppler velocimeter, using a phase locked-loop processor, was used to make the desired velocity field measurements. To determine the intermittency profiles, a laser light scattering technique was employed.

Catalano, G. D.↗
DOE OSTI2014

Three moving groups detected in the LAMOST DR1 archive

We analyze the kinematics of thick disk and halo stars observed by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. We have constructed a sample of 7993 F, G, and K nearby main-sequence stars (d < 2 kpc) with estimates of position (x, y, z) and space velocity (U, V, W) based on color and proper motion from the Sloan Digital Sky Survey DR9 catalog. Three 'phase-space overdensities' are identified in (V, √(U{sup 2}+2V{sup 2})) with significance levels of σ > 3. Two of them (the Hyades-Pleiades stream and the Arcturus-AF06 stream) have been identified previously. We also find evidence for a new stream (centered at V ∼ –180 km s{sup –1}) in the halo. The formation mechanisms of these three streams are analyzed. Our results support the hypothesis that the Arcturus-AF06 stream and the new stream originated from the debris of a disrupted satellite, while the Hyades-Pleiades stream has a dynamical origin.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Dynamic evolution of the transition zone plasma in solar flares and active region transients

The dynamic evolution of flares and of transient brightenings in active regions observed during the Solar Maximum Mission (SMM) in the UV lines of Si IV and O IV were studied. Transient brightenings in active regions and in flares occur in small points or kernels, not necessarily the initially bright regions. There is no apparent velocity pattern in which flaring or transient brightenings preferentially occur. At the flaring point, the velocity of the transition zone plasma tends to show larger downflow in the rise phase, and after the peak UV emission the downflow decreases or may even reverse and become upflow. This anticorrelation between velocity and UV intensity holds for some of the transient bright points but is more apparent for the flaring points.

Cheng, Chung-Chieh↗
NASA NTRS1997

Coupling of fingertip somatosensory information to head and body sway

Light touch contact of a fingertip with a stationary surface can provide orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip provide sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, we asked to which extent somatosensory cues are part of the postural control system, that is, which sensory signal supports this coupling? We investigated postural control not only when the contact surface was stationary, but also when it was moving rhythmically (from 0.1 to 0.5 Hz). In doing so, we brought somatosensory cues from the hand into conflict with other parts of the postural control system. Our focus was the temporal relationship between body sway and the contact surface. Postural sway was highly coherent with contact surface motion. Head and body sway assumed the frequency of the moving contact surface at all test frequencies. To account for these results, a simple model was formulated by approximating the postural control system as a second-order linear dynamical system. The influence of the touch stimulus was captured as the difference between the velocity of the contact surface and the velocity of body sway, multiplied by a coupling constant. Comparison of empirical results (relative phase, coherence, and gain) with model predictions supports the hypothesis of coupling between body sway and touch cues through the velocity of the somatosensory stimulus at the fingertip. One subject, who perceived movement of the touch surface, demonstrated weaker coupling than other subjects, suggesting that cognitive mechanisms introduce flexibility into the postural control scheme.

NASA Discipline Neuroscience↗
DOE OSTI2016

Magnus-induced dynamics of driven skyrmions on a quasi-one-dimensional periodic substrate

Here we numerically examine driven skyrmions interacting with a periodic quasi-one-dimensional substrate where the driving force is applied either parallel or perpendicular to the substrate periodicity direction. For perpendicular driving, the particles in a purely overdamped system simply slide along the substrate minima; however, for skyrmions where the Magnus force is relevant, we find that a rich variety of dynamics can arise. In the single skyrmion limit, the skyrmion motion is locked along the driving or longitudinal direction for low drives, while at higher drives a transition occurs to a state in which the skyrmion moves both transverse and longitudinal to the driving direction. Within the longitudinally locked phase we find a pronounced speedup effect that occurs when the Magnus force aligns with the external driving force, while at the transition to transverse and longitudinal motion, the skyrmion velocity drops, producing negative differential conductivity. For collectively interacting skyrmion assemblies, the speedup effect is still present and we observe a number of distinct dynamical phases, including a sliding smectic phase, a disordered or moving liquid phase, a moving hexatic phase, and a moving crystal phase. The transitions between the dynamic phases produce distinct features in the structure of the skyrmion lattice and in the velocity-force curves. Lastly, we map these different phases as a function of the ratio of the Magnus term to the dissipative term, the substrate strength, the commensurability ratio, and the magnitude of the driving force.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A UNIVERSAL POWER-LAW PROFILE OF PSEUDO-PHASE-SPACE DENSITY-LIKE QUANTITIES IN ELLIPTICAL GALAXIES

We study profiles of mass density, velocity dispersion (VD), and a combination of both using ∼2000 nearly spherical and rotation-free Sloan Digital Sky Survey galaxies. For observational stellar mass density ρ{sub *}(r), we consider a range of dark matter (DM) distribution ρ{sub DM}(r) and VD anisotropy β(r) to investigate radial stellar VD σ{sub *r}(r) using the spherical Jeans equation. While mass and VD profiles vary appreciably depending on DM distribution and anisotropy, the pseudo-phase-space density-like combination ρ(r)/σ{sub ⋆r}{sup 3}(r) with total density ρ(r) = ρ{sub *}(r) + ρ{sub DM}(r) is nearly universal. In the optical region, the negative logarithmic slope has a mean value of (χ) ≈ 1.86-1.90 with a galaxy-to-galaxy rms scatter of ≈0.04-0.06, which is a few times smaller than that of ρ(r) profiles. The scatter of χ can be increased by invoking wildly varying anisotropies that are, however, less likely because they would produce too large a scatter of line of sight VD profiles. As an independent check of this universality, we analyze stellar orbit-based dynamical models of 15 early-type galaxies (ETGs) of the Coma cluster provided by J. Thomas. Coma ETGs, with σ{sub *r}(r) replaced by the rms velocity of stars v {sub *rms}(r) including net rotation, exhibit a similar universality with a slope of χ = 1.93 ± 0.06. Remarkably, the inferred values of χ for ETGs match well the slope ≈1.9 predicted by N-body simulations of DM halos. We argue that the inferred universal nature of ρ(r)/σ{sub ⋆r}{sup 3}(r) cannot be fully explained by equilibrium alone, implying that some astrophysical factors conspire and/or it reflects a fundamental principle in collisionless formation processes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Detailed space–time variations of the seismic response of the shallow crust to small earthquakes from analysis of dense array data

SUMMARY We compute high-resolution space–time variations of subsurface seismic properties from autocorrelation functions (ACF’s) of noise and local earthquakes, recorded by the Sage Brush Flat dense array deployed around the Clark branch of the San Jacinto fault. The resolved temporal changes are referred to as apparent velocity changes because they reflect both nonlinear response and variations of material properties such as cracking and damage. Apparent velocity changes are estimated at four frequency bands (10–15, 10–20, 15–30 and 20–40 Hz) for two local earthquake data sets. In one analysis, ACF’s from P- and S-wave windows of 31 small events with magnitudes below 3.1 are used to compute the apparent velocity variations with respect to the mean ACF of each phase, and we also use the mean ACF of noise data as reference to estimate the changes. In a further analysis, the temporal evolution of properties is computed using moving time windows in continuous waveform over one-hour long data with noise and earthquake signals. The apparent velocity changes and recovery times are frequency dependent and present a strong spatial variability across the array. The resolved changes are larger and recovery time shorter with data associated with higher frequencies. At frequencies larger than 15 Hz, and using the mean ACF of noise data as a reference, the apparent average velocity changes across the array during the passage of the P and S waves from the small local events are 2.5 per cent and 6 per cent, respectively. The apparent velocity changes decrease by one order of magnitude when the earthquake data are used as a reference. The relatively large changes in response to very low ground motion have important implications on nonlinear processes involving degradation and healing of the subsurface material during common earthquake shaking.

Geochemistry & Geophysics↗
NASA NTRS2009

Meridional Flow Variations Over Three Solar Cycles - What Happened in Cycle 23?

The meridional flow speed determines the strength of the Sun s polar fields in both surface flux transport models and in flux transport dynamos. The polar fields produced during cycle 23 were half as strong as those produced in the previous two cycles. Helioseismic measurements of the meridional flow over the rising phase of cycle 23 indicated a decrease in flow velocity. This observation was used in flux transport dynamo models to predict a delayed start for cycle 24 and was consistent with weak polar fields and a slower equatorward drift of the active latitudes during cycle 23. On the other hand, the surface flux transport models require a faster meridional flow to produce the weak polar fields. We have begun measurements of the surface meridional flow by tracking the motions of weak (outside active regions) magnetic field elements in magnetograms from SOHO/MDI over cycle 23 and from NSO/Kitt Peak over cycles 21 to 23. We confirm the slowdown of the meridional flow over the rising phase of cycle 23 but find that the flow speed returned to its previous level during the declining phase of cycle 23. Furthermore, this appears to be a normal feature of the meridional flow during sunspot cycles. The flow is fast at minima and slow at maxima. The lack of a significantly different meridional flow during cycle 23 is very problematic for both surface flux transport models and flux transport dynamos.

Hathaway, David H.↗
NASA NTRS1993

A spectroscopic and photometric study of FK Comae in 1989

Results of an observational campaign, coordinated between visual photometry, optical spectroscopy, and UV spectroscopy, to elucidate the characteristics of FK Comae are presented. The photometry showed complicated but systematic behavior. Photospheric absorption lines were distorted by a Doppler-shifted bump caused by dark starspots resulting in small apparent radial velocity variations. No radial velocity variations characteristic of orbital motion were seen to a level of 3 km/s. Broad emission in H-alpha was modulated at the photospheric rotational amplitude, implying an origin no farther from the rotational axis than 1 stellar radius. The strengths of Ca II lines are modulated in phase with H-alpha but do not have velocity-modulated wings like H-alpha.

Huenemoerder, David P.↗
DOE OSTI2022

Li2[SeC2Se] · 2 NH3: A Crystalline Ammoniate with a-Se-C=C-Se- Dianion

Reaction of Li2C2 with elemental selenium in a molar ratio of 1:2 in liquid ammonia led to the formation of the ammoniate Li2[SeC2Se] ? 2 NH3. Its crystal structure was solved and refined from high-resolution synchrotron powder diffraction data (P21/c, Z = 4). It contains the ?Se-C?C-Se? anion, unprecedented in a crystalline material, whose existence was corroborated by IR/Raman spectra and electronic-structure theory, showing an almost perfect agreement with calculated spectra. Elaborated magnetic-bottle and velocity-map imaging photoelectron spectroscopic investigations show that the ?Se-C?C-Se? radical anion can be transferred to the gas phase, where it was analyzed by NIPE (Negative Ion Photoelectron) and VMI (Velocity-Map Imaging) spectra, which correlate nicely with simulated spectra based on 2?u ? 3Sg – and 2?u ?1Sg + transitions including spin-orbit couplings

Hetzert, Marc↗
NASA NTRS1991

Jetting and the origin of tektites

The scientific consensus is that tektites were produced by impacts on the Earth, but the exact mechanism by impacts might form tektites is still unclear. The most widely cited mechanism is jetting, which results from the extremely high pressures generated at the intersection of two bodies whose surfaces converge obliquely at high speed. Theory of jetting for thin plates is extended to the case of the impact of the sphere onto a half-space. The calculations are done for the impact of a silicate sphere onto a silicate target for impact speeds of 15, 20, and 25 km/sec, spanning the range of reasonable impact speeds for asteroids. The angle of impact is varied from 0 to 75 deg. The mass jetted, the jet velocity, projectile fraction in the jet, azimuthal distribution of the jet, and the phase of the jetted material are calculated as functions of time. The total mass jetted and the overall mass-averages of jet velocity, etc. are also calculated.

Vickery, A. M.↗
NASA NTRS1997

Kinematic principles of primate rotational vestibulo-ocular reflex. II. Gravity-dependent modulation of primary eye position

The kinematic constraints of three-dimensional eye positions were investigated in rhesus monkeys during passive head and body rotations relative to gravity. We studied fast and slow phase components of the vestibulo-ocular reflex (VOR) elicited by constant-velocity yaw rotations and sinusoidal oscillations about an earth-horizontal axis. We found that the spatial orientation of both fast and slow phase eye positions could be described locally by a planar surface with torsional variation of <2.0 +/- 0.4 degrees (displacement planes) that systematically rotated and/or shifted relative to Listing's plane. In supine/prone positions, displacement planes pitched forward/backward; in left/right ear-down positions, displacement planes were parallel shifted along the positive/negative torsional axis. Dynamically changing primary eye positions were computed from displacement planes. Torsional and vertical components of primary eye position modulated as a sinusoidal function of head orientation in space. The torsional component was maximal in ear-down positions and approximately zero in supine/prone orientations. The opposite was observed for the vertical component. Modulation of the horizontal component of primary eye position exhibited a more complex dependence. In contrast to the torsional component, which was relatively independent of rotational speed, modulation of the vertical and horizontal components of primary position depended strongly on the speed of head rotation (i.e., on the frequency of oscillation of the gravity vector component): the faster the head rotated relative to gravity, the larger was the modulation. Corresponding results were obtained when a model based on a sinusoidal dependence of instantaneous displacement planes (and primary eye position) on head orientation relative to gravity was fitted to VOR fast phase positions. When VOR fast phase positions were expressed relative to primary eye position estimated from the model fits, they were confined approximately to a single plane with a small torsional standard deviation ( approximately 1.4-2.6 degrees). This reduced torsional variation was in contrast to the large torsional spread (well >10-15 degrees ) of fast phase positions when expressed relative to Listing's plane. We conclude that primary eye position depends dynamically on head orientation relative to space rather than being fixed to the head. It defines a gravity-dependent coordinate system relative to which the torsional variability of eye positions is minimized even when the head is moved passively and vestibulo-ocular reflexes are evoked. In this general sense, Listing's law is preserved with respect to an otolith-controlled reference system that is defined dynamically by gravity.

NASA Discipline Neuroscience↗
NASA NTRS1979

Evaluation of a locally homogeneous model of spray evaporation

A model of spray evaporation which employs a second-order turbulence model in conjunction with the locally homogeneous flow approximation, which implies infinitely fast interphase transport rates is presented. Measurements to test the model were completed for single phase constant and variable density jets, as well as an evaporating spray in stagnant air. Profiles of mean velocity, composition, temperature and drop size distribution as well as velocity fluctuations and Reynolds stress, were measured within the spray. Predictions were in agreement with measurements in single phase flows and also with many characteristics of the spray, e.g. flow width, radial profiles of mean and turbulent quantities, and the axial rate of decay of mean velocity and mixture fraction.

Shearer, A. J.↗
NASA NTRS1994

Experiment K-7-30: Effects of Spaceflight in the Cosmos Biosatellite 2044 on the Vestibular-Ocular Reflex (VOR) of Rhesus Monkeys

This technical paper discusses the following: (1) The VOR of two rhesus monkeys was studied before and after 14 days of spaceflight to determine effects of microgravity on the VOR. Horizontal, vertical and roll eye movements were recorded in these and six other monkeys implanted with scleral search coils. Animals were rotated about a vertical axis to determine the gain of the horizontal, vertical and roll VOR. They were rotated about axes tilted from the vertical (off-vertical axis rotation, OVAR) to determine steady state gains and effects of gravity on modulations in eye position and eye velocity. They were also tested for tilt dumping of post-rotatory nystagmus. (2) The gain of the horizontal VOR was close to unity when animals were tested 15 and 18 hours after flight. VOR gain values were similar to those registered before flight. If the gain of the horizontal VOR changes in microgravity, it must revert to normal soon after landing. (3) Steady state velocities of nystagmus induced by off-vertical axis rotation (OVAR) were unchanged by adaptation to microgravity, and the phase of the modulations was similar before and after flight. However, modulations in horizontal eye velocity had more variation after landing and were on mean about 50% larger for angles of tilt of the axis of rotation between 50 and 90?/s after flight. This difference was similar in both animals and was significant. (4) A striking finding was that tilt dumping was lost in the one animal tested for this function. This loss persisted for several days after return. This is reminiscent of the loss of response to pitch while rotating in the M-131 experiments of Skylab, and must be studied in detail in future spaceflights. (5) Thus, two major findings emerged from these studies: after spaceflight the modulation of horizontal eye velocity was larger during OVAR, and one animal lost its ability to tilt-dump its nystagmus. Both findings are consistent with the postulate that adaptation to microgravity causes alterations in the way that otolith information is processed in the central nervous system. The experiments lay the groundwork for studying the vertical and roll VOR before and after future space flights, as well as for studying modulations in vertical and roll eye position during OVAR and tilt dumping.

Cohen, B.↗