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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Quantification of fat and skeletal muscle tissue at abdominal computed tomography: associations between single-slice measurements and total compartment volumes

Purpose: Body composition is of great prognostic value in several severe diseases, including different types of cancer as well as cardiometabolic disorders. We aimed to investigate the correlations of skeletal muscle mass and abdominal adipose tissue compartments between volumetric and single-slice measurements to study the usefulness of several anatomical landmarks for estimation of total compartment volumes using abdominal CT-scans. Methods: In this retrospective study volumetric quantifications of paraspinal skeletal muscles (SM) and adipose tissue compartments (visceral adipose tissue, VAT; subcutaneous adipose tissue, SAT) were performed in 50 consecutive patients (26 male; mean age, 63 ± 15 years) who underwent abdominal multislice-CT for diagnostic purposes using an in-house software. Associations between total volumes of SM, VAT, and SAT with single-slice measurements at eight predefined anatomical landmarks (median intervertebral disk spaces T12/L1 to L5/S1; level of the umbilicus (U); level of the radix of the superior mesenteric artery (SMA)) were studied using correlation coefficients. Results: Statistical analysis revealed a strong association between single-slice measurements of adipose tissue compartments with total VAT and SAT volume (VAT: all r > 0.89, P < 0.001; SAT: all r > 0.95, P < 0.001). The strongest associations with total SM volume were found for single-slice measurements obtained at L3/4 (r = 0.94, P < 0.001) and were further improved by normalization to height (r = 0.98, P < 0.001). Conclusions: Single-slice measurements of SM, VAT, and SAT at several anatomical landmarks are strongly associated with total compartment volumes and therefore allow for easy and simultaneous assessment of skeletal muscle mass and adipose tissue compartment volumes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Open-Loop Control of Adjustable Tuned Mass Dampers for Floating Wind Turbine Platforms: Preprint

Floating offshore wind turbines have several advantages over their land-based counterparts, including access to stronger, more consistent winds and proximity to population centers. However, increased costs from the platform have been a challenge inhibiting their widespread adoption. New damping technologies with tunable target frequencies and damping ratios promise a greater degree of control over platform motions, allowing hulls to be designed smaller and reducing the overall cost of the turbines. In this work, a control strategy is proposed for these adjustable tuned mass dampers (TMDs). A frequency-domain model of the system is developed, from which response amplitude operators (RAOs) for the platform's rigid-body modes can be obtained for different natural frequencies and damping ratios of the dampers. Using these RAOs, and JONSWAP spectrums of operational and extreme sea states, the performance of the various damper settings are compared by evaluating the standard deviation of a rigid-body motion of interest (platform pitch or heave). By finding the optimal damper setting for a range of representative design load cases (DLCs), a lookup function is made to return the damper target frequency given the peak period of the sea state. To determine the current sea state, we propose a simple estimator that uses wave measurements (e.g., from a measurement buoy) to determine the peak period and significant wave height. The significant wave height is determined using the statistics of the past 100 seconds of wave elevation information and the peak period is computed using a frequency locked loop. Initial results show that we can use these estimated values to control the TMD natural frequency with an open loop controller. The controlled system is tested in a range of environmental conditions determined by the International Electrotechnical Commission design load cases (DLCs), which include normal and extreme wind and wave models. In these tests, we compare the performance of 4 cases: (1) no TMD, (2) a constant TMD based on the worst case DLC, (3) a controlled TMD based on known wind and wave environments, and (4) a real-time controlled TMD using estimated wind and wave environments. The effect of hull-based TMD control is also compared to changes in traditional wind turbine control via blade pitch.

control↗
DOE OSTI2011

The multi-stream flows and the dynamics of the cosmic web

A new numerical technique to identify the cosmic web is proposed. It is based on locating multi-stream flows, i.e. the places where the velocity field is multi-valued. The method is local in Eulerian space, simple and computationally efficient. This technique uses the velocities of particles and thus takes into account the dynamical information. This is in contrast with the majority of standard methods that use the coordinates of particles only. Two quantities are computed in every mesh cell: the mean and variance of the velocity field. Ideally in the cells where the velocity is single-valued the variance must be equal to zero exactly, therefore the cells with non-zero variance are identified as multi-stream flows. The technique has been tested in the Zel'dovich approximation and in the N-body simulation of the ΛCDM model. The effect of numerical noise is discussed. The web identified by the new method has been compared with the web identified by the standard technique using only the particle coordinates. The comparison has shown overall similarity of two webs as expected, however they by no means are identical. For example, the isocontours of the corresponding fields have significantly different shapes and some density peaks of similar heights exhibit significant differences in the velocity variance and vice versa. This suggests that the density and velocity variance have a significant degree of independence. The shape of the two-dimensional pdf of density and velocity variance confirms this proposition. Thus, we conclude that the dynamical information probed by this technique introduces an additional dimension into analysis of the web.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Responses to LBNP in men with varying profiles of strength and aerobic capacity: Implications for flight crews

Hemodynamic and hormonal responses to lower-body negative pressure (LBNP) were examined in 24 healthy men to test the hypothesis that responsiveness of reflex control of blood pressure during orthostatic stress is associated with strength and/or aerobic capacity. Subjects underwent treadmill tests to determine peak oxygen uptake (peak VO2) and isokinetic dynamo meter tests to determine leg strength. Based on predetermined criteria, the subjects were classified into one of four fitness profiles of six subjects each matched for age, height, and weight: (1) low strength/low aerobic fitness; (2) low strength/high aerobic fitness; (3) high strength/low aerobic fitness; and (4) high strength/high aerobic fitness. Following 90 min of 6 degree head-down tilt (HDT), each subject underwent graded LBNP through -50 mmHg or presyncope, with maximal duration 15 min. All groups exhibited typical hemodynamic, hormonal, and fluid shift responses during LBNP, with no intergroup differences except for catecholamines. Seven subjects, distributed among the four fitness profiles, became presyncopal. Subjects who showed greatest reduction in mean arterial pressure (MAP) during LBNP had greater elevations in vasopressin and lesser increases in heart rate and peripheral resistance. Peak VO2 nor leg strength were correlated with fall in MAP or with syncopal episodes. We conclude that neither aerobic nor strength fitness characteristics are good predictors of responses to LBNP stress.

Convertino, Victor A.↗
DOE OSTI2022

Effect of Heave Plate Hydrodynamic Force Parameterization on a Two-Body Wave Energy Converter

Heave plates are one approach to generating the reaction force necessary to harvest energy from ocean waves. In a Morison equation description of the hydrodynamic force, the components of drag and added mass depend primarily on the heave plate oscillation. These terms may be parameterized in three ways: (1) as a single coefficient invariant across sea state, most accurate at the reference sea state, (2) coefficients dependent on the oscillation amplitude, but invariant in phase, that are most accurate for relatively small amplitude motions, and (3) coefficients dependent on both oscillation amplitude and phase, which are accurate for all oscillation amplitudes. We validate a MATLAB model for a two-body point absorber wave energy converter against field data and a dynamical model constructed in ProteusDS. We then use the MATLAB model to evaluate the effect of these parameterizations on estimates of heave plate motion, tension between the float and heave plate, and wave energy converter electrical power output. We find that power predictions using amplitude-dependent coefficients differ by up to 30% from models using invariant coefficients for regular waves ranging in height from 0.5 to 1.9 m. Amplitude- and phase-dependent coefficients, however, yield less than a 5% change when compared with coefficients dependent on amplitude only. This suggests that amplitude-dependent coefficients can be important for accurate wave energy converter modeling, but the added complexity of phase-dependent coefficients yields little further benefit. We show similar, though less pronounced, trends in maximum tether tension, but note that heave plate motion has only a weak dependence on coefficient fidelity. Finally, we emphasize the importance of using experimentally derived added mass over that calculated from boundary element methods, which can lead to substantial under-prediction of power output and peak tether tension.

dynamical model↗
DOE OSTI2016

Evidence for a liquid-liquid critical point in supercooled water within the E3B3 model and a possible interpretation of the kink in the homogeneous nucleation line

Supercooled water exhibits many thermodynamic anomalies, and several scenarios have been proposed to interpret them, among which the liquid-liquid critical point (LLCP) hypothesis is the most commonly discussed. We investigated Widom lines and the LLCP of deeply supercooled water, by using molecular dynamics simulation with a newly reparameterized water model that explicitly includes three-body interactions. Seven isobars are studied from ambient pressure to 2.5 kbar, and Widom lines are identified by calculating maxima in the coefficient of thermal expansion and the isothermal compressibility (both with respect to temperature). From these data we estimate that the LLCP of the new water model is at 180 K and 2.1 kbar. The oxygen radial distribution function is calculated along the 2 kbar isobar. It shows a steep change in the height of its second peak between 180 and 185 K, which indicates a transition between the high-density liquid and low-density liquid phases and which is consistent with the ascribed location of the critical point. The good agreement of the height of the second peak of the radial distribution function between simulation and experiment at 1 bar, as a function of temperature, supports the validity of the model. The location of the LLCP within the model is close to the kink in the experimental homogeneous nucleation line. We use existing experimental data to argue that the experimental LLCP is at 168 K and 1.95 kbar and speculate how this LLCP and its Widom line might be responsible for the kink in the homogeneous nucleation line.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Peierls barrier characteristic and anomalous strain hardening provoked by dynamic-strain-aging strengthening in a body-centered-cubic high-entropy alloy

The temperature effect on the mechanical behavior of the HfNbTaTiZr high entropy alloy (HEA) was investigated at 77–673 K. The decrease of the yield strength with increasing the temperature was mechanistically analyzed by considering contributions from various strengthening mechanisms. An anomalous dependence of strain hardening on temperature was observed and was justified to be caused by dynamic strain aging (DSA) as an extra strengthening mechanism at elevated temperatures. A model was constructed to split the overall strain hardening into forest hardening and DSA hardening, both of which were theoretically quantified at all temperatures considered. The work quantifies the height of Peierls barriers in the bcc HfNbTaTiZr HEA, and reveals dynamic strain aging as the strengthening mechanism causing the anomalous strain hardening at elevated temperatures.

36 MATERIALS SCIENCE↗
NASA NTRS1998

Lasers in Earth and Planetary Exploration

For over 3 decades, lasers have been a tool of the space programs of the world for accomplishing a variety of engineering and scientific objectives. The majority of these uses have, however, been largely Earth-based and only a few lasers have actually been flown and operated in Earth orbit and even fewer on missions to the planets. However, in the last few years laser altimeters, lidars, and ranging systems have been part of space missions to the moon, an asteroid, and Mars; and more are planned and contemplated in the future exploration of the Earth and solar system. Early in 1994, the Clementine mission was launched to the moon and carried a laser altimeter that made the first systematic topographic survey of the moon during its 2-month observation period. This mission significantly improved our understanding of the shape and topography of the moon and along with gravity information obtained from the tracking data modified some of our thinking about the moon, the thickness of ice crust and the isostatic state of the highlands and basins. On September 11, 1997, the Mars Global Surveyor (MGS) entered into orbit around Mars and the Mars Orbiter Laser Altimeter (MOLA) started to map the topography of the planet to unprecedented accuracy. On its first pass across the planet, MOLA showed large areas of the northern hemisphere to be flatter than any other known surface on Earth or any other body explored to date. In January 1999, the NEAR spacecraft which carries a laser ranger (NLR), will arrive at the S-type asteroid, Eros, and during the following year the NLR will help determine the shape and rotational dynamics of this asteroid. In the Spring of 2000, the Vegetation Canopy Lidar (VCL) mission will be launched and employing a multi-beam laser altimeter (MBLA) will measure the Earth's tree canopy shapes and heights and begin to globally monitor the biomass. The following year, in 2001, the Geoscience Laser Altimeter System, which carries a 2 wavelength laser altimeter of a few centimeter accuracy, will begin a multi-year observation program of the Earth's icecaps, land mass, oceans and the clouds of the atmosphere. At the same time, laser ranging to satellites and the moon is likely to be poised to reach to the planets and track spacecraft throughout the inner solar system by applying optical transponder technology to increase its distance capability.

Smith, David E.↗
NASA NTRS2023

Compact Lightweight Aerial Sensor System (CLASSy)

In the wake of increasingly intense wildfires, innovative solutions are imperative to enhance wildfire mitigation strategies. Current technological integrations have hit a communicative limit. Between limited flight time, computational expenses as well as financial expenses, there is a hole in the market for an effective, low-tech, and disposable solution. The Compact Lightweight Aerial Sensor System (CLASSy) is designed to revolutionize active disaster operations through comprehensive decision support. CLASSy consists of a lightweight launch mechanism and a flight body equipped with a sensor package and parachute. The assembly integrates sensor networks with data analytics to provide real-time, high-resolution information to incident commanders, directly facilitating decision-making and resource allocation. Infrared imagery and temperature differentials are processed and analyzed throughout flight, offering valuable insights into fire behavior, hotspot detection, and fire spread trajectories. CLASSy is intended to meet a variety of natural disaster mitigation needs through its variable launch height and disposability. CLASSy’s goal is to assist wildfire fighting without taking up any human or material resources. As a result, CLASSy is as lightweight as possible, easily expendable, inexpensive to manufacture, and only requires one operator for effective use. CLASSy’s integrated sensor suite, real-time analytics, and closed loop active communications empower firefighting teams to proactively address wildfire challenges. As the frequency of wildfires continues to rise, technological innovations like CLASSy are crucial to effective wildfire management systems.

Kyleigh Anderson↗
NASA NTRS1980

Flow oscillations of spike-tipped bodies

The oscillating flow field around a spike-tipped body has been simulated by the numerical solution of the 3-D compressible Navier-Stokes equations at a Mach number of 3.0 and a nominal Reynolds number of 7.87 x 10 to the 6th/m. Computations were performed using a vectorized 3-D Navier-Stokes program on the STAR 100 computer. Numerical solutions confirmed the experimental result that the self-sustained oscillation occurs within a limited range of the protruded spike length to shoulder height ratio. The numerical result predicted correctly the discrete frequency range as well as the rms pressure intensity. The detailed flow structure is also presented and discussed.

Shang, J. S.↗
DOE OSTI2013

Computational Studies of Water Exchange around Aqueous Li+ with Polarizable Potential Models

To enhance our understanding of the mechanism of water-exchange around the aqueous Li+, we carried out a systematic study on this system using molecular dynamics simulations with many-body potential models. The mechanistic properties associated with the water-exchange process, such as potentials of mean force, time dependent transmission coefficients, and the corresponding rate constants, were examined using transition rate theory, the reactive flux method, and Grote-Hynes treatments of the dynamic response of the solvent. We compared the computed rate theory results with the results from previous corresponding studies in which classical non-polarizable force fields were used. Our computed barrier heights for water exchange are significantly larger than those obtained using classical non-polarizable force fields. We also studied the effect of pressure on water-exchange rates and the corresponding activation volume. Our computed rate results for water exchange increase with pressure; therefore, a small negative activation volume is observed. This work was funded by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences (BES), of the U.S. Department of Energy (DOE). Battelle operates Pacific Northwest National Laboratory for DOE. The calculations were carried out using computer resources provided by BES.

Dang, Liem X.↗
NASA NTRS1977

Optical Line Radiation from Uranium Plasmas

The radiative energy current due to line radiation is calculated in a U 235 plasma over a temperature range of 5000 K to 8000 K. Also a variation in the neutron flux of 2 x 10 to the 12th power neutrons/ (sq cm-sec) to 2 x 10 to the 16th power neutrons/(sq cm-sec) is considered. The plasma forms a cylinder with a diameter and height of one meter. To calculate the radiative-energy current, a rate equation formalism is developed to solve for the atomic state densities along with a model for the energy levels in neutral and singly ionized uranium. Because the electron states in uranium lie below 5eV, recombination is the principle excitation mechanism. At and above 6000 K, inversions were found, and at all temperatures the line radiation at line center was greater than the corresponding black-body radiation. There are negligible differences in the radiative-energy current at 6000 K for variations in the neutron flux. The average opacity, which varied from 100 to 100,000 gm/sq cm, over the frequency range of line radiation is calculated.

Maceda, E. L.↗
NASA NTRS1994

Impact of comet Shoemaker-Levy 9 on Jupiter

We have employed three-dimensional numerical simulations of the impact of Comet Shoemaker-Levy 9 (SL9) on Jupiter and the resulting vapor plume expansion using the smoothed particle hydrodynamics (SPH) method. An icy body with a diameter of 2 km can penetrate to an altitude of -350 km (0 km = 1 bar) and most of the incident kinetic energy is transferred to the atmosphere between -100 to -250 km. This energy is converted to potential energy of the resulting gas plume. The unconfined plume expands vertically and has a peak radiative power approximately equal to the total radiation from Jupiter's disc. The plume rises a few tens of atmospheric scale heights in approximately 10(exp 2) seconds. The rising plume reaches the altitude of approximately 3000 km; however, no atmospheric gas is accelerated to the escape velocity (approximately 60 km/s).

Takata, Toshiko↗
NASA NTRS1954

Wind-Tunnel Investigation at Subsonic and Supersonic Speeds of a Fighter Model Employing a Low-aspect-ratio Unswept Wing and a Horizontal Tail Mounted Well above the Wing Plane - Lateral and Directional Stability

The static lateral- and directional-stability characteristics of a high-speed fighter-type airplane, obtained from wind-tunnel tests of a model, are presented. The model consisted of a thin, unswept wing of aspect ratio 2.3 and taper ratio 0.385, a body, and a horizontal tail mounted in a high position on a vertical tail. Rolling-moment, yawing moment, and cross-wind-force coefficients are presented for a range of sideslip angles of -5 deg. to +5 deg, for Mach numbers of 0.90, 1.45, and 1.90. Data are presented which show the effects on the lateral and directional stability of: (1) component parts of the complete model, (2) modification of the empennage so as to provide different heights of the horizontal tail above the wing plane, (3) angle of attack, and (4) dihedral of the wing.

Wetzel, Benton E.↗
NASA NTRS2010

Relation Between Type II Bursts and CMEs Inferred from STEREO Observations

The inner coronagraph (COR1) of the Solar Terrestrial Relations Observatory (STEREO) mission has made it possible to observe coronal mass ejections (CMEs) a in the spatial domain overlapping with that of the metric type II radio bursts. The type II bursts were associated with generally weak flares (mostly B and C class soft X-ray flares), but the CMEs were quite energetic. Using CME data for a set of type II bursts during the declining phase of solar cycle 23, we determine the CME height when the type II bursts start, thus giving an estimate of the heliocentric distance at which CME-driven shocks form. This distance has been determined to be approximately 1.5Rs (solar radii), which coincides with the distance at which the Alfv?n speed profile has a minimum value. We also use type II radio observations from STEREO/WAVES and Wind/WAVES observations to show that CMEs with moderate speed drive either weak shocks or no shock at all when they attain a height where the Alfv?n speed peaks (?3Rs ? 4Rs). Thus the shocks seem to be most efficient in accelerating electrons in the heliocentric distance range of 1.5Rs to 4Rs. By combining the radial variation of the CME speed in the inner corona (CME speed increase) and interplanetary medium (speed decrease) we were able to correctly account for the deviations from the universal drift-rate spectrum of type II bursts, thus confirming the close physical connection between type II bursts and CMEs. The average height (approximately 1.5 Rs) of STEREO CMEs at the time of type II bursts is smaller than that (2.2 Rs) obtained for SOHO (Solar and Heliospheric Observatory) CMEs. We suggest that this may indicate, at least partly, the density reduction in the corona between the maximum and declining phases, so a given plasma level occurs closer to the Sun in the latter phase. In two cases, there was a diffuse shock-like feature ahead of the main body of the CME, indicating a standoff distance of 1Rs - 2Rs by the time the CME left the LASCO field of view.

Gopalswamy, N.↗
NASA NTRS2009

Relation Between Type II Bursts and CMEs Inferred from STEREO Observations

The inner coronagraph (COR1) of the Solar Terrestrial Relations Observatory (STEREO) mission has made it possible to observe CMEs in the spatial domain overlapping with that of the metric type II radio bursts. The type II bursts were associated with generally weak flares (mostly B and C class soft X-ray flares), but the CMEs were quite energetic. Using CME data for a set of type II bursts during the declining phase of solar cycle 23, we determine the CME height when the type II bursts start, thus giving an estimate of the heliocentric distance at which CME-driven shocks form. This distance has been determined to be approx. 1.5Rs (solar radii), which coincides with the distance at which the Alfven speed profile has a minimum value.We also use type II radio observations from STEREO/WAVES and Wind/WAVES observations to show that CMEs with moderate speed drive either weak shocks or no shock at all when they attain a height where the Alfven speed peaks (approx. 3Rs - 4Rs). Thus the shocks seem to be most efficient in accelerating electrons in the heliocentric distance range of 1.5Rs to 4Rs. By combining the radial variation of the CME speed in the inner corona (CME speed increase) and interplanetary medium (speed decrease) we were able to correctly account for the deviations from the universal drift-rate spectrum of type II bursts, thus confirming the close physical connection between type II bursts and CMEs. The average height (approx 1.5Rs) of STEREO CMEs at the time of type II bursts is smaller than that (2.2Rs) obtained for SOHO (Solar and Heliospheric Observatory) CMEs. We suggest that this may indicate, at least partly, the density reduction in the corona between the maximum and declining phases, so a given plasma level occurs closer to the Sun in the latter phase. In two cases, there was a diffuse shock-like feature ahead of the main body of the CME, indicating a standoff distance of 1Rs - 2Rs by the time the CME left the LASCO field of view.

Solar Energetic Particles↗
DOE OSTI2016

DUST AND GAS IN THE DISK OF HL TAURI: SURFACE DENSITY, DUST SETTLING, AND DUST-TO-GAS RATIO

The recent ALMA observations of the disk surrounding HL Tau reveal a very complex dust spatial distribution. We present a radiative transfer model accounting for the observed gaps and bright rings as well as radial changes of the emissivity index. We find that the dust density is depleted by at least a factor of 10 in the main gaps compared to the surrounding rings. Ring masses range from 10–100 M{sub ⊕} in dust, and we find that each of the deepest gaps is consistent with the removal of up to 40 M{sub ⊕} of dust. If this material has accumulated into rocky bodies, these would be close to the point of runaway gas accretion. Our model indicates that the outermost ring is depleted in millimeter grains compared to the central rings. This suggests faster grain growth in the central regions and/or radial migration of the larger grains. The morphology of the gaps observed by ALMA—well separated and showing a high degree of contrast with the bright rings over all azimuths—indicates that the millimeter dust disk is geometrically thin (scale height ≈1 AU at 100 AU) and that a large amount of settling of large grains has already occurred. Assuming a standard dust settling model, we find that the observations are consistent with a turbulent viscosity coefficient of a few 10{sup −4}. We estimate the gas/dust ratio in this thin layer to be of the order of 5 if the initial ratio is 100. The HCO{sup +} and CO emission is consistent with gas in Keplerian motion around a 1.7 M{sub ⊙} star at radii from ≤10–120 AU.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Impact on comet Shoemaker-Levy 9 on Jupiter

Three-dimensional numerical simulations of the impact of Comet Shoemaker - Levy 9 on Jupiter and the resulting vapor plume expansion were conducted using the Smoothed Particle Hydrodynamics (SPH) method. An icy body with a diameter of 2 km can penetrate to an altitude of -350 km (0 km = 1 bar) and most of the incident kinetic energy is transferred to the atmosphere between -100 km to -250 km. This energy is converted to potential energy of the resulting gas plume. The unconfined plume expands vertically and has a peak radiative power approximately equal to the total radiation from Jupiter's disk. The plume rises a few tens of atmospheric scale heights in approximately 10(exp 2) seconds. The rising plume reaches the altitude of approximately 3000 km, but no atmospheric gas is accelerated to the escape velocity (approximately 60 km/s).

Ahrens, Thomas J.↗