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At least 1,171 records · Page 65

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NASA NTRS2000

Neural processing of gravito-inertial cues in humans. I. Influence of the semicircular canals following post-rotatory tilt

Sensory systems often provide ambiguous information. Integration of various sensory cues is required for the CNS to resolve sensory ambiguity and elicit appropriate responses. The vestibular system includes two types of sensors: the semicircular canals, which measure head rotation, and the otolith organs, which measure gravito-inertial force (GIF), the sum of gravitational force and inertial force due to linear acceleration. According to Einstein's equivalence principle, gravitational force is indistinguishable from inertial force due to linear acceleration. As a consequence, otolith measurements must be supplemented with other sensory information for the CNS to distinguish tilt from translation. The GIF resolution hypothesis states that the CNS estimates gravity and linear acceleration, so that the difference between estimates of gravity and linear acceleration matches the measured GIF. Both otolith and semicircular canal cues influence this estimation of gravity and linear acceleration. The GIF resolution hypothesis predicts that inaccurate estimates of both gravity and linear acceleration can occur due to central interactions of sensory cues. The existence of specific patterns of vestibuloocular reflexes (VOR) related to these inaccurate estimates can be used to test the GIF resolution hypothesis. To investigate this hypothesis, we measured eye movements during two different protocols. In one experiment, eight subjects were rotated at a constant velocity about an earth-vertical axis and then tilted 90 degrees in darkness to one of eight different evenly spaced final orientations, a so-called "dumping" protocol. Three speeds (200, 100, and 50 degrees /s) and two directions, clockwise (CW) and counterclockwise (CCW), of rotation were tested. In another experiment, four subjects were rotated at a constant velocity (200 degrees /s, CW and CCW) about an earth-horizontal axis and stopped in two different final orientations (nose-up and nose-down), a so-called "barbecue" protocol. The GIF resolution hypothesis predicts that post-rotatory horizontal VOR eye movements for both protocols should include an "induced" VOR component, compensatory to an interaural estimate of linear acceleration, even though no true interaural linear acceleration is present. The GIF resolution hypothesis accurately predicted VOR and induced VOR dependence on rotation direction, rotation speed, and head orientation. Alternative hypotheses stating that frequency segregation may discriminate tilt from translation or that the post-rotatory VOR time constant is dependent on head orientation with respect to the GIF direction did not predict the observed VOR for either experimental protocol.

Non-NASA Center↗

NASA NTRS1973

The evolution of galaxies. III - Metal-enhanced star formation

The problem of the paucity of low-metal-abundance low-mass stars is discussed. One alternative to the variable-initial-mass-function (VIMF) solution is proposed. It is shown that this solution - metal-enhanced star formation - satisfies the classical test which prompted the VIMF hypothesis. Furthermore, with no additional parameters it provides improved fits to other tests - e.g., inhomogeneities in the abundances in young stars, concordance of all nucleo-cosmochronologies, and a required yield of heavy-element production which is consistent with current stellar evolution theory. In this model the age of the Galaxy is 18.6 plus or minus 5.7 b.y.

Talbot, R. J., Jr.↗

NASA NTRS1984

Reaction times to weak test lights

Maloney and Wandell (1984) describe a model of the response of a single visual channel to weak test lights. The initial channel response is a linearly filtered version of the stimulus. The filter output is randomly sampled over time. Each time a sample occurs there is some probability increasing with the magnitude of the sampled response - that a discrete detection event is generated. Maloney and Wandell derive the statistics of the detection events. In this paper a test is conducted of the hypothesis that the reaction time responses to the presence of a weak test light are initiated at the first detection event. This makes it possible to extend the application of the model to lights that are slightly above threshold, but still within the linear operating range of the visual system. A parameter-free prediction of the model proposed by Maloney and Wandell for lights detected by this statistic is tested. The data are in agreement with the prediction.

Wandell, B. A.↗

NASA NTRS1983

Covariance hypotheses for LANDSAT data

Two covariance hypotheses are considered for LANDSAT data acquired by sampling fields, one an autoregressive covariance structure and the other the hypothesis of exchangeability. A minimum entropy approximation of the first structure by the second is derived and shown to have desirable properties for incorporation into a mixture density estimation procedure. Results of a rough test of the exchangeability hypothesis are presented.

Decell, H. P.↗

NASA NTRS1994

Markarian 315: A test case for the active galactic nucleus-merger hypothesis?

Using the Hubble Space Telescope (HST) Wide Field/Planetary Camera, (WF/PC) we have detected a diffuse continuum knot in the inner regions of the Seyfert galaxy Markarian 315. This knot may be a remnant nucleus. It is associated with a complex, ringlike structure in both the continuum and ionized gas emission. We have measured the kinematics of the ionized gas in two position angles and find velocities which are consistent with a nonaxisymmetric gravitational disturbance. The galaxy is associated with an extended ionized filament, or tidal tail, and our measurements show that the ionized gas in this feature is redshifted by up to 500 km/s in the line of sight relative to the Seyfert nucleus. This combination of morphological and kinematic features suggests that Mrk 315 has suffered a disruptive, tidal interaction which has significantly influenced regions within 1 kpc of its nucleus.

Mackenty, John W.↗

NASA NTRS1995

Notes on the diversity of the properties of radio bursts observed on the nightside of Venus

We report on further studies of radio wave bursts detected by the Orbiting Electric Field Detector (OEFD) on the Pioneer Venus Orbiter (PVO) in the nightside ionosphere of Venus. We have tested a total of 25 cases of wave burst activity for evidence of whistler-mode propagation to the spacecraft from impulsive subionospheric sources. As in a previous study of 11 of these cases (Sonwalkar et al., 1991) we find at least two distinct classes of events, one, mostly involving bursts at 100 Hz only, that passes certain tests for whistler-mode propagation, and another, mostly involving bursts in two or more of the four PVO narrowband channels (at 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz), that fails to pass the tests. The subionospheric lightning hypothesis continues to be tenable as a candidate explanation for many of the 100 Hz-only events, but its number of 100 Hz-only cases that do no pass all the applicable whistler-mode tests, as well as the existence at a wide range of altitudes of multichannel cases that are clearly not propagating whistler-mode waves. The wideband bursts are often observed at altitudes above 1000 km and frequently occur in regions of locally reduced electron density. Those observed at high altitude (and possibly low altitude as well) are believed to be generated near the spacecraft, possibly by an as yet unknown mechanism responsible for similar burst observations made near Earth and other planets.

Sonwalkar, Vikas S.↗

NASA NTRS2003

Influence of Solutocapillary Convection on Macrovoid Defect Formation in Polymeric Membranes

The focus of this research project involved the dry-cast process for polymeric membrane formation, whereby evaporation of solvent from an initially homogeneous polymer/solvent/ nonsolvent solution results in phase separation and the formation of polymer-rich and polymer-lean phases. Under certain conditions the polymer-lean phase gives rise to very large and usually undesirable, tear-drop-shaped pores (size approx. 10 - 50 microns) termed macrovoids (MVs). Although in many cases the presence of MV pores has deleterious effects on membrane performance, there are a number of innovative applications where the presence of such pores is highly desirable. Although researchers have proposed a variety of mechanisms for MV formation over the past three decades, two main hypotheses are currently favored: one asserts that MV growth can be attributed solely to diffusion (the diffusive growth hypothesis), whereas the other states that solutocapillary convection (the SC hypothesis) at the MV interface contributes to growth. The overall goal of this research was to obtain a more comprehensive understanding of the fundamental mechanism of MV growth. This research incorporates a coupled modeling and experimental approach to test a solutocapillary convection hypothesis for the growth of macrovoid pores in polymeric membranes. Specifically, we utilized a modification of the first principles model developed by two of the PIs (ARG and WBK) for dry-cast CA membranes. For the experimental component, two separate and mutually complementary approaches were used to study MV growth. In the first, membranes cast in a zero-g environment aboard the NASA KC-135 aircraft were compared with those cast on the ground to assess the effect of the buoyancy force on membrane morphology and MV size and shape. In the second approach, videomicroscopy flow visualization (VMFV) was utilized to observe MV formation and growth in real time and to assess the effect of surface tension on the MV growth dynamics. As a result of these fundamental studies, our research group advanced a new hypothesis for MV pore development in polymeric membranes.

Greenberg, Alan R.↗

NASA NTRS1981

OSO 8 observational limits to the acoustic coronal heating mechanism

An improved analysis of time-resolved line profiles of the C IV resonance line at 1548 A has been used to test the acoustic wave hypothesis of solar coronal heating. It is shown that the observed motions and brightness fluctuations are consistent with the existence of acoustic waves. Specific account is taken of the effect of photon statistics on the observed velocities, and a test is devised to determine whether the motions represent propagating or evanescent waves. It is found that on the average about as much energy is carried upward as downward such that the net acoustic flux density is statistically consistent with zero. The statistical uncertainty in this null result is three orders of magnitue lower than the flux level needed to heat the corona.

Bruner, E. C., Jr.↗

NASA NTRS1982

Tropical cyclone track and genesis forecasting using satellite microwave sounder data

Although many dynamical and statistical prediction schemes are available to forecasters, tropical cyclone track errors are still large. One primary difficulty is that tropical cyclones exist over the data-sparse tropical oceans. Satellite sounders, however, routinely provide numerous data over these areas. Mean layer temperatures from the Scanning Microwave Spectrometer on board the Nimbus 6 satellite are decomposed using empirical orthogonal functions, and the expansion coefficients are related to deviations from the persistence forecast location, to speed change, to direction change and to intensity change. The significance of the regression equations is tested by a null hypothesis of zero correlation coefficient. It appears that significant information about tropical cyclone motion exists in the satellite-estimated mean layer temperatures, especially at upper levels. A physical interpretation of the statistical results is offered, and a one-storm-out independent test is used to test the stability of the equations. Finally, some further work is suggested.

Kidder, S. Q.↗

NASA NTRS1981

Ground photography for improvved image interpretation training

Systematic sets of ground based color and color infrared photography were presented to students in remote sensing classes to enhance their ability to interpret satellite images. Features readily apparent on computer enhanced LANDSAT images were presented simultaneously with ground based photography in the format of slide triplicates. It was hypothesized that this instructional approach would improve the students' abilities to recognize, understand and interpret ground phenomena present on remotely sensed imagery. Tests conducted in undergraduate remote sensing classes substantially upheld this hypothesis. Student image interpretive abilities were tested before and after being exposed to the ground level photography. In general, image interpretive skills of the class improved by 25%. Also, the performance of students having different academic majors varied greatly for differing types of image subjects.

Lougeay, R.↗

DOE OSTI2025

Initial assessment of alternative carbon fiber geometries for design of cost-effective compressive performance: Size effect studies

Carbon fiber provides opportunity to reduce weight in structural composites, including wind turbine blades, due to the material's superior specific stiffness and specific strength compared to alternatives. Despite these advantages, cost and compressive performance are considered weaknesses for carbon fiber products available today. Studies to produce low-cost carbon fiber alternatives, including the use of textile-derived precursor systems, have shown progress and merit through the DOE/ORNL low-cost carbon fiber initiatives. Here, this work focuses on enabling increases in compressive strength through design of the carbon fiber geometry, applicable to both textile and conventional precursor systems, while also providing opportunities to reduce carbon fiber processing costs. Fiber-resin interface and fiber alignment are among the most frequently cited factors controlling composite compressive performance. However, it is believed that there is opportunity in traditionally unexplored routes to increasing compressive strength through alteration of the carbon fiber geometry by increasing the fiber area moment of inertia and/or the fiber perimeter and interfacial area. This paper presents initial results from manufacturing carbon fiber materials to assess the impacts of carbon fiber size on tested composite compressive performance with projected neutral or even beneficial impact on fiber and composite manufacturing economics. Carbon fiber systems with increasing size illustrate a favorable correlation for compressive performance greater than predicted from a micromechanical failure model. The manufacturing and mechanical test results support the hypothesis of this work that alterations to fiber geometry can be used to produce improvements of the compressive strength of carbon fiber reinforced polymers and provide incentive for related work in designing alternative shapes to further enhance compressive performance.

42 ENGINEERING↗

DOE OSTI2026

Optimizing aluminum oxide passivation layers—Laser-induced plasmas for layer formation, real-time diagnostics, and layer evaluation

Molten salts have beneficial thermophysical and electrolytic properties, but the aggressive nature of molten salts requires corrosion mitigation strategies, such as structural material surface treatment. In this study, a laser-induced breakdown spectroscopy (LIBS) system was used to simultaneously ablate and monitor de-excitation spectra to form and identify dense alumina passivation layers. Additionally, high-frequency (kHz) LIBS imaging allowed rapid elemental mapping and depth profiling for surface O/Al ratios via minimally destructive analysis. The paired t-test rejected the null hypothesis that air and Ar cover gases were equivalent (p = 0.00012), and the analysis of variance (ANOVA) showed that overlap between shots (p = 0.03112) and cover gas flow rate (p = 0.02729) were statistically significant. At 75% overlap, the O/Al ratio increased to 10% ± 2%, and 90% overlap rose further to 31% ± 2%. Regardless of overlap, tuning the gas flow from 0.5 to 2.5 L min −1 enhanced the O/Al ratio by 24% ± 4%. LIBS depth profiling showed a 3× increase in layer thickness from 75% to 90% overlap. Molecular band peaks of AlO, a precursor to Al 2 O 3 found during treatment, suggest that band intensity could be used for real-time Al 2 O 3 optimization. Ultimately, by adjusting laser spot overlap and cover gas flow rate, a 266 nm laser was shown to form Al 2 O 3 layers on an Al6061 sample, with cover gas flow rate primarily affecting the O/Al ratio and layer thickness correlating with laser spot overlap. This combination of molecular spectra collection, imaging, and depth profiling demonstrated the robust layer analysis capabilities of LIBS.

Corrosion↗

DOE OSTI2020

Suppression of superconductivity by anisotropic strain near a nematic quantum critical point

In most unconventional and high-temperature superconductors, superconductivity emerges as a nearby symmetry-breaking phase is suppressed by chemical doping or pressure. This has led to the belief that the fluctuations associated with the symmetry-breaking phase are beneficial, if not responsible, for the superconducting pairing. A direct test to verify this hypothesis is to observe a decrease of the superconducting critical temperature (T c ) by applying the symmetry-breaking conjugate field that suppresses the dynamic fluctuations of the competing order. However, most of the competing phases in unconventional superconductors break translational symmetry, requiring a spatially modulated conjugate field that is difficult to realize experimentally. Here, we show that anisotropic strain, the conjugate field of nematicity, reduces the T c of an iron pnictide. For optimally doped samples we show a fivefold reduction of T c with less than one per cent of strain. For underdoped samples, T c becomes zero yielding a fully metallic ground state. In addition to providing direct evidence of the role played by the nematic fluctuations in the formation of the superconducting state, these results demonstrate tunable mechanical control of a high-temperature superconductor, an important step forward for technological applications of superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Light detection and cosmic rejection in the ICARUS LArTPC at Fermilab

Abstract The ICARUS-T600 detector is a 760-ton Liquid Argon Time Projection Chamber (LArTPC) currently operating at Fermilab as the Far Detector in the Short Baseline Neutrino (SBN) program. The SBN program is composed of three LArTPCs with a central goal of testing the sterile neutrino hypothesis. After operating for 3-years in the Gran Sasso Underground Laboratory, the ICARUS detector was shipped to CERN where it was outfitted with 360 8” Photomultiplier Tubes (PMTs) for a new optical detection system. The PMT system detects fast scintillation light from charged particles interacting in the Liquid Argon, generating the trigger signal for the full detector and allows 3D reconstruction of events. Now operating at shallow depth, the detector is exposed to a high flux of cosmic rays that can fake neutrino interactions. To mitigate this effect a Cosmic Ray Tagger (CRT) and a 3-meter-thick concrete were installed. Precise timing information from both the PMT and CRT subsystems can help to identify whether an interaction originated from inside or outside of the ICARUS cryostat. This paper reviews a method for cosmogenic background reduction and timing calibration of the CRT and PMT light detection systems in ICARUS.

Instruments & Instrumentation↗

DOE OSTI2025

Acceptance dependence of factorial cumulants, long-range correlations, and the antiproton puzzle

We analyze joint factorial cumulants of protons and antiprotons in relativistic heavy-ion collisions and point out that they obey the scaling Ĉnmp,p¯∝〈Np〉n〈Np¯〉m as a function of acceptance when only long-range correlations are present in the system, such as global baryon conservation and volume fluctuations. This hypothesis can be directly tested experimentally without the need for corrections for volume fluctuations. We show that if correlations among protons and antiprotons are driven by global baryon conservation and volume fluctuations only, the equality Ĉ2p/〈Np〉2=Ĉ2p¯/〈Np¯〉2 holds for large systems created in central collisions. We point out that the experimental data of the STAR Collaboration from phase I of the Relativistic Heavy Ion Collider (RHIC) beam energy scan (BES) are approximately consistent with the scaling Ĉnmp,p¯∝〈Np〉n〈Np¯〉m, but the normalized antiproton correlations are stronger than those of protons, −Ĉ2p¯/〈Np¯〉2>−Ĉ2p/〈Np〉2. Existing theoretical baselines, based on global baryon conservation and volume fluctuations, cannot explain the data, which we refer to as the antiproton puzzle. We also discuss high-order factorial cumulants which can be measured with sufficient precision within phase II of RHIC-BES.

Bzdak, Adam↗

DOE OSTI2021

Molecular phylogenetic analysis of the Paguristes tortugae Schmitt, 1933 complex and selected other Paguroidea (Crustacea: Decapoda: Anomura)

Morphological characters, as presently applied to describe members of the Paguristes tortugae Schmitt, 1933 species complex, appear to be of limited value in inferring phylogenetic relationships within the genus, and may have similarly misinformed understanding of relationships between members of this complex and those presently assigned to the related genera Areopaguristes Rahayu & McLaughlin, 2010 and Pseudopaguristes McLaughlin, 2002. Previously undocumented observations of similarities and differences in color patterns among populations additionally suggest genetic divergences within some species, or alternatively seem to support phylogenetic groupings of some species. In the present study, a Maximum Likelihood (ML) phylogenetic analysis was undertaken based on the H3, 12S mtDNA, and 16S mtDNA sequences of 148 individuals, primarily representatives of paguroid species from the western Atlantic. This molecular analysis supported a polyphyletic Diogenidae Ortmann, 1892, although incomplete taxonomic sampling among the genera of Diogenidae limits the utility of this finding for resolving family level relationships. Several hypotheses regarding the evolutionary relationships among hermit crab genera were refuted by the Kishino-Hasegawa (KH). ShimodairaHasegawa (SH) and Approximately Unbiased (AU) tree topology tests, among them the hypothesis that Areopaguristes is monophyletic. A lack of support for the monophyly of Areopaguristes calls into question the phylogenetic validity of gill number for the differentiation of Paguristes, Areopaguristes, and Pseudopaguristes. The study was inconclusive with regard to the relationships among these three genera, but previously unknown diversity within both Paguristes and Areopaguristes was demonstrated. Existence of an undescribed species confounded under the name Paguristes tortugae Schmitt, 1933 was supported by genetics, morphology, and coloration. A second undescribed species with remarkable similarity to Areopaguristes hummi Wass, 1955 was discovered based on genetics and coloration.

12S↗

DOE OSTI2020

Characterization of Urbix Resources Natural Flake Graphite Material for Nuclear Applications (CRADA NFE-18-07340 Final Report)

Urbix Resources is a company specializing in graphite powder processing and purification. Urbix is looking to become the first domestic supplier of nuclear-grade graphite in the United States. This has led to a Cooperative Research and Development Agreement (CRADA) being established between the Oak Ridge National Laboratory (ORNL) and Urbix Resources, with the goal of characterizing a purified graphite feedstock supplied by Urbix Resources. The resulting data will then be used to determine the viability of a large-scale nuclear graphite production and qualification campaign. These characterization methods have been performed on the as-received graphite feedstock, a heat-treated batch of the feedstock, a milled batch of the feedstock, and a nuclear-grade graphite powder historically used in fuel production. The data from the heat-treated and milled feedstock will determine how different processing methods affect the powder’s physical properties, whereas the data from the nuclear grade graphite will provide information about the characteristics of a graphite previously accepted for nuclear applications. All of these powders have been characterized individually and as part of a resin-graphite blend (herein referred to as matrix) that has been used in past fuel experiments. The results of these experiments show that the Urbix powder and nuclear-grade graphite powder display notably different properties from one another in many cases, but this discrepancy may have been the result of the typical particle size of each powder. This hypothesis is supported by tests conducted on the milled powder, which showed a closer resemblance in properties to the nuclear-grade graphite than the as-received powder. The method for pressing the graphite matrix also had a noticeable effect on the measured properties.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2021

Compensation Between Poleward Energy Transports in the Ocean and Atmosphere

The goal of our project is to investigate the degree of compensation in poleward energy transports by the atmosphere and ocean and its dependence on the time scale, latitude and background climate primarily based on a large suite of the Community Earth System Model version 1 (CESM1) simulations to test the Bjerknes compensation hypothesis. Our particular emphases are to understand: (1) robustness of the degree of the compensation across the various simulations with differing parameterizations and initial conditions, (2) the competing role of atmosphere-ocean couplings through the momentum flux and buoyancy flux in enabling or deterring the compensation, and (3) the role of compensation in the leading modes of variability in the atmosphere and ocean.

58 GEOSCIENCES↗