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At least 289 records · Page 16

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NASA NTRS1982

On the distribution of orbits among long-period comets

The distribution of the axes defining the planes and orientations of the orbits of 542 long-period comets are analyzed. The directions of the perihelia and of the oriented plane normals show significant nonuniformity in their distributions. The preferred direction of perihelia near the apex of solar motion is refined to an (1 sigma) error circle of 20.6 deg, and possible concentrations of the plane normals and the directions of perihelion velocity along roughly orthogonal directions are noted, although the error circles extend to nearly full hemispheres. Planes of preference (and avoidance) are found from the distribution ellipsoids of the three orbital axes, with the perihelion directions lying preferentially along the galactic plane. The distribution ellipsoids of all three sets of orbital axes exhibit anisotropies roughly twice those expected for random distributions.

Bogart, R. S.↗

DOE OSTI2022

Is Jet Re-orientation the Elusive Trigger for Star Formation Suppression in Radio Galaxies?

Abstract Jet re-orientation associated with the time evolution of radio quasars explains the formation of X-shaped radio galaxies and their preference for isolated environments. But since X-shaped radio galaxies are generally not found in dense environments (e.g., groups/clusters), the jet re-orientation phenomenon for radio galaxies in groups and clusters has been ignored. We take a closer look at the re-orientation of FRI jets with respect to FRII jets, and find that it may constitute the as-yet unidentified trigger for star formation suppression in radio galaxies. We show how the recently explored radio “red geyser” galaxies can be interpreted in this context and ultimately reveal a deeper understanding of why FRII radio galaxies are on one side of the star formation enhancement/suppression divide compared to FRI radio galaxies.

Astronomy & Astrophysics↗

NASA NTRS1989

Functional decor in the International Space Station: Body orientation cues and picture perception

Subjective reports of American astronauts and their Soviet counterparts suggest that homogeneous, often symmetrical, spacecraft interiors can contribute to motion sickness during the earliest phase of a mission and can also engender boredom. Two studies investigated the functional aspects of Space Station interior aesthetics. One experiment examined differential color brightnesses as body orientation cues; the other involved a large survey of photographs and paintings that might enhance the interior aesthetics of the proposed International Space Station. Ninety male and female college students reclining on their backs in the dark were disoriented by a rotating platform and inserted under a slowly rotating disk that filled their entire visual field. The entire disk was painted the same color but one half had a brightness value that was about 69 percent higher than the other. The effects of red, blue, and yellow were examined. Subjects wearing frosted goggles opened their eyes to view the rotating, illuminated disk, which was stopped when they felt that they were right-side up. For all three colors, significant numbers of subjects said they felt right-side up when the brighter side of the disk filled their upper visual field. These results suggest that color brightness could provide Space Station crew members with body orientation cues as they move about. It was found that subjects preferred photographs and paintings with the greatest depths of field, irrespective of picture topic.

Coss, Richard G.↗

NASA NTRS2011

Toward Realistic Dynamics of Rotating Orbital Debris, and Implications for Lightcurve Interpretation

Optical observations of rotating space debris near GEO contain important information on size, shape, composition, and rotational states, but these aspects are difficult to extract due to data limitations and the high number of degrees of freedom in the modeling process. For tri-axial rigid debris objects created by satellite fragmentations, the most likely initial rotation state has a large component of initial angular velocity directed along the intermediate axis of inertia, leading to large angular reorientations of the body on the timescale of the rotation period. This lends some support to the simplest possible interpretation of light curves -- that they represent sets of random orientations of the objects of study. However, effects of internal friction and solar radiation are likely to cause significant modification of rotation states within a time as short as a few orbital periods. In order to examine the rotational dynamics of debris objects under the influences of these effects, a set of seven first-order coupled equations of motion were assembled in state form: three are Euler equations describing the rates of change of the components of angular velocity in the body frame, and four describe the rates of change of the components of the unit quaternion. Quaternions are a four-dimensional extension of complex numbers that form a seamless, singularity-free representation of body orientation on S3. The Euler equations contain explicit terms describing torque from solar radiation in terms of spherical harmonics, and terms representing effects of a prescribed rate of internal friction. Numerical integrations of these equations of motion are being performed, and results will be presented. Initial tests show that internal friction without solar radiation torque leads to rotation about the maximum principal axis of inertia, as required, and solar radiation torque is expected to lead to spin-up of objects. Because the axis of maximum rotational inertia tends to be roughly coincident with the normal to the largest projected cross-sectional area, internal friction is expected to lead to reduced variation of light curve amplitudes at a given phase angle, but a large dependence of the same on phase angle. At a given phase angle, databases are generated which contain reflected intensities for comprehensive sets of equally-likely orientations, represented as unit quaternions. When projected onto three dimensions (S2) and color-coded by intensity, the set is depicted as points within a solid, semi-transparent unit sphere, within which all possible reflected intensities for an object at a given phase angle may be inspected simultaneously. Rotational sequences are represented by trajectories through the sphere. Databases are generated for each of a set of phase angles separately, forming a comprehensive dataset of reflected intensities spanning all object orientations and solar phase angles. Symmetries in the problem suggest that preferred rotation states are likely, defined relative to the object-sun direction in inertial space and relative to the maximum principal axis of inertia in the body coordinate system. Such rotation states may greatly simplify the problem of light curve interpretation by reducing the number of degrees of freedom in the problem.

Ojakangas, Gregory W.↗

DOE OSTI2025

Facet-Dependent Cold Welding of Au Nanorods Revealed by Liquid Cell Transmission Electron Microscopy

Cold welding of metals at the nanoscale has been demonstrated to play a significant role in bottom-up manufacturing and self-healing processes of nanostructures and nanodevices. However, the welding mechanism at the nanoscale is not well understood. In this study, a comprehensive demonstration of the cold welding process of gold nanorods with different modes is presented through in situ liquid cell transmission electron microscopy. The experimental results and molecular dynamics simulations reveal that the nanorods are welded through the facet-dependent atomic surface diffusion and rearrangement along {100} facets. The density functional theory calculations indicate that the preferred coalescence of two {100} surfaces is thermodynamically favorable. Unlike the prevalent “oriented attachment” in the nanoparticle coalescence, the misalignment of nanorod orientations and local stresses can induce grain boundaries and stacking faults in the welded interface.

42 ENGINEERING↗

DOE OSTI2024

Structure and Dynamics of Aqueous Electrolytes at Quartz (001) and (101) Surfaces

Here, understanding and describing reactivity at mineral-water interfaces such as ion adsorption, the kinetics of dissolution, or surface charge development depends on our ability to improve the accuracy of electrical double layer (EDL) models. While molecular dynamics (MD) simulations are routinely used to investigate the structure and energetics of adsorbed ions comprising the EDL, less attention is paid to their self-diffusion dynamics, which can uniquely inform on coupling to interfacial reactions. Here we use MD to investigate both the organization and diffusion dynamics of water and electrolyte ions (NaCl, KCl, CaCl 2 ) at hydroxylated quartz (001) and (101) surfaces, a comparison which allowed us to assess surface structural effects of corrugation and silanol density. We found that inner- versus outer-sphere complex formation depends on cation size and charge but not necessarily hydration energies. Participation of surface silanols in the hydration spheres of Na + and K + generally indicated their preference for inner-sphere complexation, but this depends strongly on the orientation of the surface considered through its influence over the organization and dynamics of adsorbed water layers. In particular, surface orientation substantially affects the diffusive behavior of the near-surface water. Na + was found to decrease the mobility of water in the first layer, consistent with an increasing frequency of hydrolysis implied by faster quartz dissolution rates observed in experiments via the well known salt effect. Our results are also in good agreement with the observed dissolution rate of quartz vs. surface adsorption strength measure by Dove and Nix. This study sets the stage for a forthcoming paper examining how the dynamics at quartz/electrolyte interfaces are influenced by externally applied electric fields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1993

Lunar lander configuration study and parametric performance analysis

Future Lunar exploration plans will call for delivery of significant mounts or cargo to provide for crew habitation, surface tansportation, and scientific exploration activities. Minimization of costly surface based infrastructure is in large part directly related to the design of the cargo delivery/landing craft. This study focused on evaluating Lunar lander concepts from a logistics oriented perspective, and outlines the approach used in the development of a preferred configuration, sets forth the benefits derived from its utilization and describes the missions and system considered. Results indicate that only direct-to-surface downloading of payloads provides for unassisted cargo removal operations imperative to efficient and low risk site buildup, including the emplacement of Space Station derivative surface habitat modules, immediate cargo jettison for both descent abort and emergency surface ascent essential to piloted missions carrying cargo, and short habitat egress/ingress paths necessary to productive surface work tours for crew members carrying hand held experiments, tools and other bulky articles. Accommodating cargo in a position underneath the vehicles structural frame, landing craft described herein eliminate altogether the necessity for dedicated surface based off-loading vehicles, the operations and maintenance associated with their operation, and the precipitous ladder climbs to and from the surface that are inherent to traditional designs. Parametric evaluations illustrate performance and mass variation with respect to mission requirements.

Donahue, Benjamin B.↗

NASA NTRS2011

Influence of Sensory Dependence on Postural Control

The current project is part of an NSBRI funded project, "Development of Countermeasures to Aid Functional Egress from the Crew Exploration Vehicle Following Long-Duration Spaceflight." The development of this countermeasure is based on the use of imperceptible levels of electrical stimulation to the balance organs of the inner ear to assist and enhance the response of a person s sensorimotor function. These countermeasures could be used to increase an astronaut s re-adaptation rate to Earth s gravity following long-duration space flight. The focus of my project is to evaluate and examine the correlation of sensory preferences for vision and vestibular systems. Disruption of the sensorimotor functions following space flight affects posture, locomotion and spatial orientation tasks in astronauts. The Group Embedded Figures Test (GEFT), the Rod and Frame Test (RFT) and the Computerized Dynamic Posturography Test (CDP) are measurements used to examine subjects visual and vestibular sensory preferences. The analysis of data from these tasks will assist in relating the visual dependence measures recognized in the GEFT and RFT with vestibular dependence measures recognized in the stability measures obtained during CDP. Studying the impact of sensory dependence on the performance in varied tasks will help in the development of targeted countermeasures to help astronauts readapt to gravitational changes after long duration space flight.

Santana, Patricia A.↗

NASA NTRS1993

Viewpoint 9--molecular structure of aqueous interfaces

In this review we summarize recent progress in our understanding of the structure of aqueous interfaces emerging from molecular level computer simulations. It is emphasized that the presence of the interface induces specific structural effects which, in turn, influence a wide variety of phenomena occurring near the phase boundaries. At the liquid-vapor interface, the most probable orientations of a water molecule is such that its dipole moment lies parallel to the interface, one O-H bond points toward the vapor and the other O-H bond is directed toward the liquid. The orientational distributions are broad and slightly asymmetric, resulting in an excess dipole moment pointing toward the liquid. These structural preferences persist at interfaces between water and nonpolar liquids, indicating that the interactions between the two liquids in contact are weak. It was found that liquid-liquid interfaces are locally sharp but broadened by capillary waves. One consequence of anisotropic orientations of interfacial water molecules is asymmetric interactions, with respect to the sign of the charge, of ions with the water surface. It was found that even very close to the surface ions retain their hydration shells. New features of aqueous interfaces have been revealed in studies of water-membrane and water-monolayer systems. In particular, water molecules are strongly oriented by the polar head groups of the amphiphilic phase, and they penetrate the hydrophilic head-group region, but not the hydrophobic core. At infinite dilution near interfaces, amphiphilic molecules exhibit behavior different from that in the gas phase or in bulk water. This result sheds new light on the nature of hydrophobic effect in the interfacial regions. The presence of interfaces was also shown to affect both equilibrium and dynamic components of rates of chemical reactions. Applications of continuum models to interfacial problems have been, so far, unsuccessful. This, again, underscores the importance of molecular-level information about interfaces.

Review, Tutorial↗

DOE OSTI2026

Atomic‐Scale Surface Imaging of Bulk Epitaxial CsPbBr 3 Perovskite Single Crystals on Mica Using Light Assisted Scanning Tunneling Microscopy at Low‐Temperature (80 K)

Epitaxial single-crystalline CsPbBr 3 perovskite films on mica, prepared ex situ, are explored using a low-temperature scanning tunneling microscope (STM) by probing the unoccupied electronic states of their surface in ultra-high vacuum (UHV) at 80 K. Light-assisted STM measurements under a broadband illumination with visible light were employed to enhance and stabilize surface conductivity. STM imaging across the surface of macroscopic bulk CsPbBr 3 films reveals large flat terraces characterized by a specific type of surface reconstruction, consisting of parallel rows of U-shaped atomic nanostructures. These structures are spaced by 12 Å and exhibit an internal feature size of 5.1 Å. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr 3 (110) surface reconstructions: a Cs-rich structure, identified as the most energetically stable, and three alternative Pb–Br-rich reconstructions, which are slightly higher in energy yet remain consistent with the STM data. Additional analyses that explicitly account for the mica substrate exclude the cubic CsPbBr 3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr 3 (110) reconstruction. In conclusion, this combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr 3 .

36 MATERIALS SCIENCE↗

DOE OSTI2022

A treatment-effect model to quantify human dimensions of disaster impacts: the case of Hurricane Maria in Puerto Rico

Here, we propose a supervised learning approach using publicly available panel data to statistically quantify the specific manifestations of human impacts of an extreme event, such as changes number of suicides, substance abuse, excess mortality, and unemployment. This allows us to conceptually focus our framework on human impacts and how by attributing them to disaster events along widely accepted psychological, economic, and social dimensions. Our modified treatment-effect model allows counterfactual baseline conditions to be posited for each manifestation from which an aggregated quantitative multi-faceted measure of human impacts can be determined. The developed statistical methodology could be beneficial to policymakers who must allocate scarce resources to those communities in greater need. We illustrate the applicability of our approach using annual and monthly panel data from 2012 to 2018 encompassing the 2017 Hurricane Maria event across various municipalities in Puerto Rico. Our statistical modeling methodology stands apart since (i) it explicitly and more realistically captures the effect of different human-oriented manifestations of an actual event and (ii) it is flexible enough to accommodate individual preferences of various stakeholders in how they assign importance to multiple manifestations of human impacts.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1980

Future lunar gravity measurements

Future missions to the moon should include a detailed high-resolution global gravity survey from a low (15-30 km) polar orbiting spacecraft. The use of gravity gradiometer instruments on board the spacecraft will give higher-resolution data at lower total mission cost than the present Doppler tracking technique. Simulations show that although a three axis gradiometer system is preferred, and can even be used to estimate spacecraft attitude and altitude variation, a properly oriented single rotating gravity gradiometer can be used to resolve closely spaced mascons in both the along-track and cross-track directions.

Forward, R. L.↗

NASA NTRS1981

Whys and hows of in-house writing

The combining of requisite technical knowledge with requisite writing ability is addressed. Considerations in the development of in-house writing courses, in-plant training, are presented and evaluated. Specific problems in past methodology are also detailed. It is suggested that teachers of technical writing should be technical people themselves, preferably with working experience in industry or business; the training provided should be user-oriented, not theory oriented.

Lane, J. C.↗

NASA NTRS1987

On the noncoplanarity of the magnetic field within a fast collisionless shock

Within the magnetic ramp of fast collisionless plasma shocks observed with spacecraft instruments and simulated numerically, the magnetic field undergoes an excursion out of the plane of coplanarity. This rotation is consistently in the direction such that the electrostatic potential jump across the shock, as measured in the de Hoffman-Teller frame of the reference (HTF), is about 2-6 times smaller than the electrostatic potential jump measured in the normal incidence frame. The preferred direction is consistent with a basic whistler mode transition between the upstream and downstream orientations. The potential jump in the HTF is considerably smaller than the change in bulk flow energy across the shock, confirming the recent suggestion that magnetic forces contribute importantly to the slowing of the plasma in that frame. A further consequence is that suprathermal particles leaking back into the upstream region across the shock do not gain much energy from the cross-shock electric field.

Thomsen, M. F.↗

NASA NTRS2007

Coupled Groups of g-Modes in a Sun with Mixed Core

Groups of linear g-modes can sum to create long-lived nonlinear oscillations in small "hot volumes" very deep in the Sun that help drive the modes. In these volumes (dimensions -10 Mm), the time average rate of He-3 burning doubles as temperature fluctuations exceed 10% and rises by an order of magnitude for fluctuations of 25%. To be consistent with locally large motions, we impose a mixed shell on an otherwise standard solar model before computing g-mode solutions. Mixing in the assumed shell r = (0.10+/-0.03) R(sub sun) is rapid (<<10(exp 6) yr) with slower mixing somewhat beyond. If l is the principal spherical harmonic index, a set of g-modes for any single l less than or equal to 15 with five consecutive radial harmonics can be excited with nearly linear thermal amplitudes, A(sub T) less than or equal to 0.053, throughout the star and a fractional temperature fluctuation in its hot volume of (Delta)T/T less than or equal to 0.18. These thresholds for excitation will become smaller when sets for several values of l are computed simultaneously. There is some evidence for the rotation of g-mode sets in the long solar activity record and g-mode upward wave flux has been suggested to explain the 1.3 yr reversing flows tentatively detected below the Sun's convective envelope (CE). The large local amplitudes needed for excitation implies that g-modes may transport a non-negligible fraction of the solar luminosity, yet their near linear amplitudes outside the hot volume suggests amplitudes over most of the solar surface that would be barely detectable for l > 3. A formalism is presented for summing the g-modes and estimating growth rates under the approximation that modes are strictly linear except in a hot volume which holds only a few percent of mode kinetic energy. Finally over the range 2 less than or equal to l less than or equal to 30, we summed all zonal harmonics, m, for a given l and computed the relative angular orientations that would release the most nuclear energy. This should be close to the physically preferred angular state of such a family and a few examples were displayed.

Wolff, Charles L.↗

NASA NTRS1981

Anisotropic tribological properties of silicon carbide

The effects of crystallographic orientation on the tribological properties of single-crystal silicon carbide surfaces in contact with various solids are investigated for adhesive and abrasive wear processes. In the adhesive wear process, the adhesion and wear of silicon carbide is found to be markedly dependent on crystallographic orientation. The force resisting shearing fracture of the adhesive bonds at the interface is lower in preferred crystallographic direction of slip. In the abrasive wear process, the 1 0 -1 0 direction on the basal plane of silicon carbide exhibits the lowest coefficient of friction and the greatest resistance to abrasion.

Miyoshi, K.↗

NASA NTRS1991

S-R compatibility effects with orthogonal stimulus and response dimensions

An experiment was conducted to assess the relative influence of several factors on performance with orthogonal stimulus-response arrays. Subjects responded to the onset of one of three aligned light circles with a press of one of three aligned response keys. The response array was aligned parallel, angled, or orthogonal to the stimulus array. The results indicated that performance with orthogonal arrays is worse than with parallel or angled S-R arrays. For the orthogonal arrangements, the results also indicate that each hand prefers a mapping directly opposite to the other hand, and that this mapping reverses when the orientation of the stimulus and response arrays are transposed. In addition, the results also revealed that the relative costs of orthogonal S-R arrangements are somewhat attenuated when the assigned mapping associates (i.e., colocates) a given display with its closest control.

Andre, Anthony D.↗

NASA NTRS1995

Laser-Directed Ranging System Implementing Single Camera System for Telerobotics Applications

The invention relates generally to systems for determining the range of an object from a reference point and, in one embodiment, to laser-directed ranging systems useful in telerobotics applications. Digital processing techniques are employed which minimize the complexity and cost of the hardware and software for processing range calculations, thereby enhancing the commercial attractiveness of the system for use in relatively low-cost robotic systems. The system includes a video camera for generating images of the target, image digitizing circuitry, and an associated frame grabber circuit. The circuit first captures one of the pairs of stereo video images of the target, and then captures a second video image of the target as it is partly illuminated by the light beam, suitably generated by a laser. The two video images, taken sufficiently close together in time to minimize camera and scene motion, are converted to digital images and then compared. Common pixels are eliminated, leaving only a digital image of the laser-illuminated spot on the target. Mw centroid of the laser illuminated spot is dm obtained and compared with a predetermined reference point, predetermined by design or calibration, which represents the coordinate at the focal plane of the laser illumination at infinite range. Preferably, the laser and camera are mounted on a servo-driven platform which can be oriented to direct the camera and the laser toward the target. In one embodiment the platform is positioned in response to movement of the operator's head. Position and orientation sensors are used to monitor head movement. The disparity between the digital image of the laser spot and the reference point is calculated for determining range to the target. Commercial applications for the system relate to active range-determination systems, such as those used with robotic systems in which it is necessary to determine the, range to a workpiece or object to be grasped or acted upon by a robot arm end-effector in response to commands generated by an operator. In one embodiment, the system provides a real-time image of the target for the operator as the robot approaches the object. The system is also adapted for use in virtual reality systems in which a remote object or workpiece is to be acted upon by a remote robot arm or other mechanism controlled by an operator.

Wells, Dennis L.↗