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At least 1,315 records · Page 73

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DOE OSTI2026

Beta-Decay Half-Lives beyond 54 Ca: A Systematic Survey of Decay Properties Approaching the Neutron Dripline

In an experiment performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator, 15 new half-lives of isotopes near 54 Ca were measured. A new method of extracting lifetimes from experimental data, taking into account the unknown 𝛽-delayed neutron emission branches of very neutron-rich nuclei, was developed to enable systematic uncertainty analysis. The experiment observed a dramatic change in the half-life systematics for the isotopes with neutron number 𝑁 = 34. Beyond 𝑁 = 34, the decline of nuclear lifetime is much slower, leading to longer than anticipated lifetimes for near-dripline nuclei. State-of-the-art shell-model calculations can explain the experimental results, revealing the imprint of shell effects and the need for modification of single-particle neutron states. In conclusion, the results from a newly developed quasiparticle random phase approximation model with potential for making global predictions were also tested against the experimental results and good agreement was found.

Physics - Nuclear physics and radiation physics↗

DOE OSTI2021

Compressive Neural Representations of Volumetric Scalar Fields

Here, we present an approach for compressing volumetric scalar fields using implicit neural representations. Our approach represents a scalar field as a learned function, wherein a neural network maps a point in the domain to an output scalar value. By setting the number of weights of the neural network to be smaller than the input size, we achieve compressed representations of scalar fields, thus framing compression as a type of function approximation. Combined with carefully quantizing network weights, we show that this approach yields highly compact representations that outperform state-of-the-art volume compression approaches. The conceptual simplicity of our approach enables a number of benefits, such as support for time-varying scalar fields, optimizing to preserve spatial gradients, and random-access field evaluation. We study the impact of network design choices on compression performance, highlighting how simple network architectures are effective for a broad range of volumes.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2022

Effects of high concentrate rations on ruminal fermentation and microbiota of yaks

Ruminal microflora is closely correlated with the ruminant’s diet. However, information regarding the effect of high concentrate diets on rumen microflora in yaks is lacking. In the current study, 24 healthy male yaks were randomly assigned to two groups, each fed with different diets: less concentrate (LC; concentrate: coarse = 40: 60) and high concentrate (HC; concentrate: coarse = 80: 20) diets. Subsequently, a 21-day feeding trial was performed with the yaks, and rumen fluid samples were collected and compared using 16 s rRNA sequencing. The results showed that NH 3 -N, total VFA, acetate, butyrate, isobutyrate, and isovalerate were significantly higher in the HC group than that in the LC group ( p < 0.05), while microbial diversity and richness were significantly lower in the HC group ( p < 0.05). Principal coordinate analysis indicated that rumen microflora was significantly different in LC and HC groups ( p < 0.05). In the rumen, phyla Firmicutes and Bacteroidota were the most abundant bacteria, with Firmicutes being more abundant, and Bacteroidota being less abundant in the HC group than those found in the LC group. Christensenellaceae_R-7_group and Prevotella are the highest abundant ones at the genus level. The relative abundance of Acetitomaculum , Ruminococcus , and Candidatus_Saccharimonas were significantly higher in the HC group than that in the LC group ( p < 0.05), while the relative abundance of Olsenella was significantly lower in the HC group than in the LC group ( p < 0.05). Compared to the LC group, the relative abundance of Prevotella , Ruminococcus , and Candidatus_Saccharimonas was significantly higher in the HC group. The relative abundances of Prevotella , Prevotellaceae_UCG-003 , Olsenella , Ruminococcus , Acetitomaculum , Candidatus_Saccharimonas , and NK4A214_group were correlated with ruminal fermentation parameters ( p < 0.05). Furthermore, PICRUSt 2 estimation indicated that microbial genes associated with valine, leucine, and isoleucine biosynthesis were overexpressed in the rumen microflora of yaks in the HC group ( p < 0.05). Conclusively, our results suggest that high concentrate diets affect the microflora composition and fermentation function in yak rumen. The present findings would provide new insights into the health of yaks under high concentrate feeding conditions and serve as a potent reference for the short-term fattening processes of yaks.

Pang, Kaiyue↗

NASA NTRS1966

Inexpensive insulation is effective for cryogenic transfer lines

Matting cover thermally insulates cryogenic-liquid transfer pipelines. The matting consists of layers of commercially available fiber glass tape in which the fibers are randomly oriented in parallel planes.

Lindgren, A. R.↗

NASA NTRS1966

Launch booster gust alleviation.

Design of gust alleviation controls for boost phase flight of missiles incorporating random winds, time-varying missile dynamics, control problem, etc

WIND EFFECT↗

NASA NTRS1981

Analysis of coherent satellite communication systems in the presence of interference and noise

The general analysis presented can be used to evaluate the performance of M-ary phase shift keying (MPSK) used over a nonlinear satellite channel in the presence of interference (CW tone and ISI) and channel noise. The numerical evaluation is based on the classical moment technique for approximating the probability distribution from moments of a random variable. The mathematical formulation of error probabilities of MPSK signals transmitted over nonlinear satellite repeaters is presented to include the effect of CW tone interference as well as the intersymbol interference. The approach is general and can be extended to include the effect of the synchronization.

Huang, T.-C.↗

NASA NTRS1984

Relative Radiometric Calibration of LANDSAT TM Reflective Bands

The characterization of the relative radiometric calibration of the protoflight Thematic Mapper sensor (TM/PF) is considered with focus on the variability and uncertainty of TM relative radiometry, including total variability as well as its systematic and random components. Emphasis is placed on identifying the magnitude and types of systematic errors, since these have the potential for being reduced during ground processing. Estimates of innate random variability, such as the standard deviation of a signal or its signal to noise ratio, are also important. The processing effects of radiometry are explored. Recommendations are given for engineering characterization, flight segment operations and ground processing.

Barker, J. L.↗

NASA NTRS1986

A synchronization technique for optical PPM signals

A technique for maintaining synchronization between optical PPM (pulse-position modulation) pulses and a receiver clock by means of a delay-tracking loop is described and analyzed. The tracking loop is driven by a doubly stochastic Poisson process that contains information about the location of the desired slot boundaries. The slot boundaries are subject to slowly varying random delays that are ultimately tracked by the loop. The concept of fractional rms delay error is introduced to quantify the effects of signal and background induced shot noise on the performance of the delay-tracking loop.

Vilnrotter, V. A.↗

NASA NTRS1986

A synchronization technique for optical PPM signals

Vilnrotter, V. A.↗

NASA NTRS1988

The collective emission of electromagnetic waves from astrophysical jets - Luminosity gaps, BL Lacertae objects, and efficient energy transport

A model of the inner portions of astrophysical jets is constructed in which a relativistic electron beam is injected from the central engine into the jet plasma. This beam drives electrostatic plasma wave turbulence, which leads to the collective emission of electromagnetic waves. The emitted waves are beamed in the direction of the jet axis, so that end-on viewing of the jet yields an extremely bright source (BL Lacertae object). The relativistic electron beam may also drive long-wavelength electromagnetic plasma instabilities (firehose and Kelvin-Helmholtz) that jumble the jet magnetic field lines. After a sufficient distance from the core source, these instabilities will cause the beamed emission to point in random directions and the jet emission can then be observed from any direction relative to the jet axis. This combination of effects may lead to the gap turn-on of astrophysical jets. The collective emission model leads to different estimates for energy transport and the interpretation of radio spectra than the conventional incoherent synchrotron theory.

Baker, D. N.↗

NASA NTRS1989

Linear digital imaging system fidelity analysis

The combined effects of imaging gathering, sampling and reconstruction are analyzed in terms of image fidelity. The analysis is based upon a standard end-to-end linear system model which is sufficiently general so that the results apply to most line-scan and sensor-array imaging systems. Shift-variant sampling effects are accounted for with an expected value analysis based upon the use of a fixed deterministic input scene which is randomly shifted (mathematically) relative to the sampling grid. This random sample-scene phase approach has been used successfully by the author and associates in several previous related papers.

Park, Stephen K.↗

NASA NTRS1989

Simultaneous stochastic inversion for geomagnetic main field and secular variation. II - 1820-1980

With the aim of producing readable time-dependent maps of the geomagnetic field at the core-mantle boundary, the method of simultaneous stochastic inversion for the geomagnetic main field and secular variation, described by Bloxham (1987), was applied to survey data from the period 1820-1980 to yield two time-dependent geomagnetic-field models, one for the period 1900-1980 and the other for 1820-1900. Particular consideration was given to the effect of crustal fields on observations. It was found that the existing methods of accounting for these fields as sources of random noise are inadequate in two circumstances: (1) when sequences of measurements are made at one particular site, and (2) for measurements made at satellite altitude. The present model shows many of the features in the earth's magnetic field at the core-mantle boundary described by Bloxham and Gubbins (1985) and supports many of their earlier conclusions.

Bloxham, Jeremy↗

NASA NTRS1991

Probabilistic lifetime strength of aerospace materials via computational simulation

The results of a second year effort of a research program are presented. The research included development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic phenomenological constitutive relationship, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subjected to a number of effects of primitive variables. These primitive variables often originate in the environment and may include stress from loading, temperature, chemical, or radiation attack. This multifactor interaction constitutive equation is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the constitutive equation using actual experimental materials data together with the multiple linear regression of that data.

Boyce, Lola↗

NASA NTRS1992

Space environmental effects on the integrity of chromic acid anodized coatings

The Long Duration Exposure Facility (LDEF) tray clamps used to hold the experiment trays in place on the LDEF were analyzed to determine the effects of long term space exposure on the performance of the chromic acid anodized coating. Spectroscopic anomalies observed appeared to be random and related to application techniques as opposed to exposure or position on LDEF. Thickness measurements indicated that the coating was less than 1u and was probably not degraded by space exposure. Metallurgical analysis revealed that leading edge exposure may have increased the porosity of the coating. Emittance values for the coating decreased uniformly by an average of 6.8 percent while solar absorptance values increased for trailing edge and decreased for leading edge specimens. The a/e ratio for the coating also increased as a result of long term space exposure.

Plagemann, Walter L.↗

NASA NTRS1991

Initial performance improvements due to design modifications for the Pointing Control System on the Hubble Space Telescope

Shortly after Hubble Space Telescope was deployed on orbit it became apparent that the Pointing Control System was experiencing unexpectedly large disturbances during certain portions of the orbit. While these disturbances were most pronounced during transitions of the Earth's shadow, significant disruptions to the pointing occurred at other times in the orbit. Careful analysis of the flight data has lead to the conclusion that the disturbances are caused by a combination of rapid thermal deformations of the Solar Arrays together with striction-friction mechanisms within the array that randomly release stored thermal/mechanical energy. This paper describes the baseline pointing control system design and the flight data that characterized the effects of the extraneous disturbances. The paper goes on to describe the procedure for modifying the onboard controller to attenuate the disturbances to levels consistent with the science operations. Flight data demonstrating the improved performance are shown and are tabulated to compare performance prior to and after phase I of the redesign.

Nurre, G. S.↗

NASA NTRS1993

Flight-path estimation in passive low-altitude flight by visual cues

A series of experiments was conducted, in which subjects had to estimate the flight path while passively being flown in straight or in curved motion over several types of nominally flat, textured terrain. Three computer-generated terrain types were investigated: (1) a random 'pole' field, (2) a flat field consisting of random rectangular patches, and (3) a field of random parallelepipeds. Experimental parameters were the velocity-to-height (V/h) ratio, the viewing distance, and the terrain type. Furthermore, the effect of obscuring parts of the visual field was investigated. Assumptions were made about the basic visual-field information by analyzing the pattern of line-of-sight (LOS) rate vectors in the visual field. The experimental results support these assumptions and show that, for both a straight as well as a curved flight path, the estimation accuracy and estimation times improve with the V/h ratio. Error scores for the curved flight path are found to be about 3 deg in visual angle higher than for the straight flight path, and the sensitivity to the V/h ratio is found to be considerably larger. For the straight motion, the flight path could be estimated successfully from local areas in the far field. Curved flight-path estimates have to rely on the entire LOS rate pattern.

Grunwald, Arthur J.↗

NASA NTRS1994

The dynamical evolution of poor clusters of galaxies: Growth and properties of the first-ranked galaxy

We report N-body simulations of the dynamical evolution of isolated clusters of 50 galaxies containing a dark matter component that comprises 90% of the cluster mass. For our adopted physical scaling, the line-of-sight velocity dispersion of the cluster is 310 km/s and the initial core radius is 250 kpc. Our results are applicable to (1) present-day poor clusters, (2) the small systems that may have merged to produce present-day rich clusters, and (3) virialized subclumps within larger systems, in between major substructure merger events. We have evolved a total of 10 cluster models, using N = 40,000 particles per model. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the gravitational potential arises from the particles alone. Dark matter is apportioned between the galaxy halos and a smoothly distributed common group halo, the intracluster background (ICB). The percentage of cluster mass initially in the ICB, Beta, is chosen to be 50, 75, or 90. Increasing Beta has the effect of removing mass from dark halos around galaxies and distributing it throughout the cluster. The initial conditions were constructed by randomly sampling a King distribution with W(sub 0) = 6. The galaxies are also King models; the masses of the galaxies follow a Schechter distribution function.

Bode, Paul W.↗

NASA NTRS2004

Flows in the Solar Convection Zone

Flows within the solar convection zone are the primary drivers of the Sun's magnetic activity cycle. Differential rotation stretches out the magnetic field and converts poloidal fields into toroidal fields. Zones of strong radial shear are found at both the surface and at the base of the convection zone (the tachocline). The poleward meridional flow near the surface transports magnetic flux that is observed to reverse the magnetic poles near the time of cycle maxima. The deeper (and as yet unobserved), equatorward meridional flow should carry magnetic flux toward the equator where it reconnects with oppositely directed fields in the other hemisphere. The non-axisymmetric flows (granules, supergranules, and giant cells) also transport magnetic flux but in a more random, diffusive, manner. Supergranules and giant cells also play significant roles in driving the large-scale, axisymmetric flows themselves. The effect of solar rotation on supergranulation produces the shear layer near the surface and enhances the meridional flow. The effect of solar rotation on giant cells should produce the latitudinal differential rotation, the shear in the tachocline, and the meridional circulation. In this presentation I will describe the observed and theorized characteristics of the flows in the solar convection zone and discuss their connections to the solar activity cycle.

Hathaway, D. H.↗