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At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

DOE OSTI2023

The role of stress and fluid saturation on the acoustic response of fractured rock

Standard rock physics models are formulated to describe the behavior of porous sedimentary reservoirs, with clean sandstones being the archetypal system; however, many situations demand geophysical monitoring of rocks with significantly different structures, such as low porosity, fractured reservoirs. Conventional models also suggest that these “stiff” reservoirs can be challenging to monitor seismically due to small fluid substitution effects, but the presence of fractures leads to stress dependence which may be leveraged for remote monitoring purposes. Using samples from the Duperow Formation (dolostone) obtained from the Danielson test well in Kevin Dome, MT, we conducted ultrasonic and multi-scale structural (profilometry, synchrotron micro-tomography, pressure sensitive film) measurements on naturally fractured core in order to characterize the effects of fluid substitution and effective stress on the acoustic response of fractured reservoir rock with a focus in particular on the textural and seismic characteristics of natural fractures. We find that changes in effective stress can yield changes in velocity of up to 20% and changes in attenuation up to 200%. Measured fluid substitution effects are resolvable, but stress effects dominate. These measurements provide insight into the physical processes controlling acoustic response of fractured rocks in general and can also be used to inform monitoring efforts in fractured reservoirs.

58 GEOSCIENCES↗

DOE OSTI2022

Crystal Chemistry and Thermodynamics of HREE (Er, Yb) Mixing in a Xenotime Solid Solution

Rare earth elements (REEs), the 15 naturally occurring lanthanides plus yttrium and scandium, are ubiquitously used in modern life as they are critical components of many advanced devices and technologies. However, the demand for REEs is not equal, with the heavy rare earth elements (HREEs) having a higher demand. Xenotime (HREEPO 4 ) is an important HREE ore mineral and globally is an economical source of HREE. Most of the crystallographic and thermodynamic properties of xenotime endmembers have been elucidated by calorimetric, solubility, and high-pressure studies. Yet, in natural systems, endmembers are rarely encountered, and instead, REE solid solutions are more commonly observed. Here, we characterize the crystal chemistry, thermodynamics of HREE mixing, and high-temperature material behaviors and thermochemistry of a synthetic erbium (Er)-ytterbium (Yb) binary xenotime solid solution (Er (x) Yb (1-x) PO 4 ) using a suite of experimental techniques, including X-ray fluorescence spectroscopy, synchrotron X-ray powder diffraction implemented with Rietveld analysis, Fourier transform infrared spectroscopy coupled with attenuated total reflectance, Raman spectroscopy, thermogravimetric analysis coupled with differential scanning calorimetry, and high-temperature oxide melt drop solution calorimetry. Our results shed light on the formation of natural xenotimes and lay the foundation for their industrial applications as thermal coating materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Simulated Aquifer Heterogeneity Leads to Enhanced Attenuation and Multiple Retention Processes of Zinc

Alluvial aquifers serve as one of the main water sources for domestic, agricultural, and industrial purposes globally. Groundwater quality, however, can be threatened by naturally occurring and anthropogenic metal contaminants. Differing hydrologic and biogeochemical conditions between predominantly coarse-grained aquifer sediments and embedded layers or lenses of fine-grained materials lead to variation in metal behavior. Here, we examine processes controlling Zn partitioning within a dual-pore domain-reconstructed alluvial aquifer. Natural coarse aquifer sediments from the Wind River-Little Wind River floodplain near Riverton, WY, were used in columns with or without fine-grained lenses to examine biogeochemical controls on Zn concentrations, retention mechanisms, and transport. Furthermore, following the introduction of Zn to the groundwater source, Zn preferentially accumulated in the fine-grained lenses, despite their small volumetric contributions. While the clay fraction dominated Zn retention in the sandy aquifer, the lenses supported additional reaction pathways of retention—the reducing conditions within the lenses resulted in ZnS precipitation, overriding the contribution of organic matter. Zinc concentration in the groundwater controlled the formation of Zn-clays and Zn-layered double hydroxides, whereas the extent of sulfide production controlled precipitation of ZnS. Our findings illustrate how both spatial and compositional heterogeneities govern the extent and mechanisms of Zn retention in intricate groundwater systems, with implications for plume behavior and groundwater quality.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1973

Digital interactive image analysis by array processing

An attempt is made to draw a parallel between the existing geophysical data processing service industries and the emerging earth resources data support requirements. The relationship of seismic data analysis to ERTS data analysis is natural because in either case data is digitally recorded in the same format, resulting from remotely sensed energy which has been reflected, attenuated, shifted and degraded on its path from the source to the receiver. In the seismic case the energy is acoustic, ranging in frequencies from 10 to 75 cps, for which the lithosphere appears semi-transparent. In earth survey remote sensing through the atmosphere, visible and infrared frequency bands are being used. Yet the hardware and software required to process the magnetically recorded data from the two realms of inquiry are identical and similar, respectively. The resulting data products are similar.

Sabels, B. E.↗

NASA NTRS2004

Forward and Backscattering Measurements of Rainfall using the NASA Microwave Link

This paper will present results from a study on the feasibility of making backscatter measurements from rainfall with the NASA/Microwave Link system at Wallops Island, VA. The study entails the implementation of an FMCW radar at the Link frequencies to enable simultaneous forward and backscatter measurements from rain. The Microwave Link system has been successfully employed in the development and testing of rainfall retrieval techniques. As presently configured, the Microwave Link measures attenuation and phase-shift due to rain over a 2.3 km path between the transmitting and receiving antennas. By their very nature, these measured quantities are averaged over the propagation path. As a result, the rainfall estimates obtained from the Link data are also averaged over the propagation path. However, rainfall is a highly variable process in space (as well as time). In order to gain a more detailed knowledge of its microphysics finer spatial resolutions are required. The backscatter measurements would enable range profiling over the Link path permitting a detailed study of the rainfall process. The backscatter measurements will be used in conjunction with the forward measurements and the measurements from a ground-based network of disdrometers and rain gauges located under the propagation path to develop new microwave retrieval techniques, and to test established single-frequency and dual-frequency radar retrieval algorithms relevant to the ongoing TRMM and up coming GPM missions.

Rincon, Rafael F.↗

DOE OSTI2025

In Situ MOF Pyrolysis Construction of Hierarchical Porous Co‐Nanoparticles/Carbon Cloth Composites for Enhanced Electromagnetic Wave Shielding and Absorption

The development of high-performance electromagnetic protection materials integrating broadband absorption and effective shielding capabilities is hindered by challenges in simultaneously optimizing multiple electromagnetic properties through conventional material designs. This study pioneers a hierarchical porous Co nanoparticle/carbon cloth (Co/CC) composite via controlled annealing of a Co-MOF precursor on carbon cloth. The Co-MOF served a dual role as both magnetic source and pore-forming agent, enabling in situ generation of uniformly dispersed Co nanoparticles and creation of abundant pores/interfaces on the CC fibers during pyrolysis. This unique architecture synergistically enhanced dielectric loss (via interfacial/dipolar polarization) and magnetic loss (via natural resonance, exchange interactions, and eddy currents), significantly improving impedance matching. The hierarchical pores further functioned as integrated “absorption–reflection” units for efficient electromagnetic energy attenuation. Consequently, the Co/CC composite annealed at 800°C (Co/CC-800) achieves minimum reflection loss (−40.69 dB) and 120% effective absorption bandwidth extension (6.16 GHz) as a filler, and exhibits superior electromagnetic interference shielding effectiveness (46.66 dB) as an integrated component. Significantly, Co/CC-800 demonstrated robust photothermal and electrothermal conversion capabilities, ensuring operational stability in ice-covered and humid harsh environments. This work pioneers a pore-structure-mediated strategy to harmonize dielectric–magnetic synergy, providing a new paradigm for designing advanced multifunctional electromagnetic protection materials.

dielectric‐magnetic synergy↗

DOE OSTI2020

Quantifying CTFE content in FK-800 using ATR-FTIR and time to peak crystallization

The chlorotrifluoroethylene (CTFE) content in vinylidene fluoride (VDF)-CTFE copolymers greatly influences the chemical and physical properties and ultimately determines the application. The copolymer known as FK-800 has a VDF:CTFE ratio of ~1:3 and is used almost exclusively as the binder in the insensitive high explosive (HE) formulation PBX 9502. Due to the dangerous nature of HE work and the effect CTFE content variations have, the ability to quickly and easily quantify CTFE content is of interest. Two techniques, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and time to peak crystallization measured by heat flow calorimetry, were evaluated here as potential means for quantifying CTFE content. Based on the certificate of analyses (COAs), FK-800 lots with varied CTFE content encompassing the range historically used in HE applications were used as standards for both methodologies. For FTIR, a linear regression was performed on the peak area of the C-Cl IR stretch and the CTFE content; the methodology was then demonstrated on four samples, two lots of unadulterated material and material recovered from two HE samples. The calculated CTFE content and COAs were in good agreement for all four samples. Heat flow calorimetry revealed the relationship between time to peak crystallization and CTFE content was best fit by a power regression; the methodology was then tested on two different FK-800 lots. Only one sample showed good agreement between the calculated CTFE content and the COA. This discrepancy indicates the method developed is not suitable for quantifying CTFE, but provides valuable insight regarding the crystallization behavior of VDF-CTFE copolymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1980

Absorption coefficient instrument for turbid natural waters

The paper presents an instrument that directly measures multispectral absorption coefficient of turbid natural water. Attention is given to the design, which is shown to incorporate methods for the compensation of variation in the internal light source intensity, correction of the spectrally dependent nature of the optical elements, and correction for variation in the background light level. In addition, when used in conjunction with a spectrally matched total attenuation instrument, the spectrally dependent scattering coefficient can also be derived. Finally, it is reported that systematic errors associated with multiple scattering have been estimated using Monte Carlo techniques.

Friedman, E.↗

NASA NTRS1994

The H(sub infinity) optimal controller design and reduction for the inertial hold mode of the attitude control system of the XTE spacecraft

The Inertial Hold Mode (IHM) is one mode of the attitude control system of the X-ray Timing Explorer spacecraft that is disturbed by both parametric uncertainties and external torque disturbance. The IHM model is modified into a typical H-infinity mixed-sensitivity problem through choosing suitable weighting functions W(sub 1)(s) and W(sub 3)(s). The controller is designed by the H-infinity optimization technique with the transformation of shifting the imaginary axis. It can stabilize the plant with uncertainties from the natural frequencies of the flexible body. The gain margin and phase margin of the system are 24.03 db and 55.04 deg, respectively. The step response attenuates to zero within 150 seconds. These show that the controller satisfies the specified requirements. Since the order of the controller appears high, it is reduced to fourth order one. The results show that the stability and the performance of the system with the reduced controller are retained perfectly.

Xu, Zhong Ling↗

NASA NTRS2007

On the Evolution of Localized Disturbances and their Spanwise Interactions Leading to Breakdown

Localized disturbances in a laminar boundary layer represent a more realistic model of transition than the extensively studies, two or quasi three-dimensional perturbations regardless of the fact if they evolve in a linear manner or not. Localized disturbances can originate by surface imperfections, insects or dust. The disturbances can be harmonic (i.e. containing a single frequency and a complete set of spanwise wave numbers) or Pulsed (i.e. containing a band of streamwise and spanwise wave numbers). At sufficiently low amplitudes localized disturbances behave according to a linear stability model. It is highly probably that in a natural transition process such localized disturbances will overslap and interact. These interactions could either delay transition because of a partial wave cancellation resulting in an attenuation of the disturbance, or adversely enhance it by promoting nonlinear interactions. The nonlinearity could be simply amplitude dependent or cause a triad resonance. Nonlinear processes in a wave packet lead to breakdown and to the formation of turbulent spots. When the amplitude of the harmonic disturbance saturates, nonlinear processes widen the band of the lower amplified frequencies adjacent to the frequency of excitation. Experimental results describing the spanwise interactions of harmonic and pulsed localized disturbances leading to breakdown will be presented and discussed. A comparison to the evolution and breakdown of a single localized disturbance will be provided.

Seifert, Avi↗

DOE OSTI2020

Experimental evidence for low-lying quadrupole isovector excitation of 208 Po

In this study, we present the results from an experiment dedicated to measure the lifetime of the \(2^+_2\) state, candidate for the one-phonon mixed-symmetry state, of \(^{208}\) Po. This nucleus was studied in the \(\alpha \) -transfer reaction \(^{204}\) Pb( \(^{12}\) C, \(^{8}\) Be) \(^{208}\) Po and the lifetime of the \(2^+_2\) state was determined by utilizing the Doppler-shift attenuation method. The experimental data show that the \(2^+_2\) state decays with a sizable M 1 transition to the \(2^+_1\) state revealing its isovector nature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1977

Terrestrial environment (Climatic) criteria guidelines for use in aerospace vehicle development, 1977 revision

Guidelines are provided on terrestrial environment data specifically applicable for NASA aerospace vehicles and associated equipment development. Information is included on the general distribution of natural environment extremes in the conterminous United States that may be needed to specify design criteria in the transportation of space vehicle subsystems and components. Atmospheric attenuation was investigated since certain earth orbital experiment missions are influenced by the earth's atmosphere. A summary of climatic extremes for worldwide operational needs is also included. The latest available information on probable climatic extremes is presented with information on atmospheric chemistry, seismic criteria, and on a mathematical model to predict atmospheric dispersion of aerospace engine exhaust cloud rise and growth. Cloud phenomena are also considered.

Kaufman, J. W.↗

NASA NTRS1972

Techniques in balloon X-ray astronomy.

Since the first balloon observation of the Crab Nebula balloon data have provided much information on the positions, spectra, time variability and pulsed nature of localized sources, and on the spectrum and isotropy of diffuse galactic and universal components. Measurements are limited to energies above about 20 keV by atmospheric attenuation at 2 to 3 g/sq cm depth and to below several hundred keV by detector sensitivity. Detectors usually consist of large-area Na I or Cs I scintillation counters with anticoincidence collimators for rejection of charged particles and scattered X-rays. Proportional counters are occasionally used at lower energies and solid-state detectors are used where extreme energy resolution is important. The instruments require a pointing capability on the order of 1.0 to 0.1 deg, depending on the collimator aperture. Digital data is either recorded on board or telemetered using a PCM technique.

Peterson, L. E.↗

NASA NTRS1980

Simple method for prediction of aircraft noise contours

A method for generating noise contours more rapidly and more simply than previously used programs is discussed. The method gives the area, the noise contour, and its extremities for an arbitrarily complex flight path for both takeoffs and landings with relative ease. The analysis reveals the fundamental nature of the contours and how the various factors that influence its size and shape enter into the analysis. It is noted that the effects of ground attenuation and shielding are omitted as they are important only on the initial portion of flight and are highly dependent upon aircraft configuration. However, the analysis shows that these effects could be included. It is emphasized the the single-event contour is an obvious choice for purposes of minimizing noise impact.

Stewart, E. C.↗

NASA NTRS2000

Optimized Shielding for Space Radiation Protection

Abstract. Future deep space mission and International Space Station exposures will be dominated by the high-charge and -energy (HZE) ions of the Galactic Cosmic Rays (GCR). A few mammalian systems have been extensively tested over a broad range of ion types and energies. For example, C3H10T1/2 cells, V79 cells, and Harderian gland tumors have been described by various track-structure dependent response models. The attenuation of GCR induced biological effects depends strongly on the biological endpoint, response model used, and material composition. Optimization of space shielding is then driven by the nature of the response model and the transmission characteristics of the given material.

Wilson, J. W.↗

NASA NTRS2001

Optimized shielding for space radiation protection

Future deep space mission and International Space Station exposures will be dominated by the high-charge and -energy (HZE) ions of the Galactic Cosmic Rays (GCR). A few mammalian systems have been extensively tested over a broad range of ion types and energies. For example, C3H10T1/2 cells, V79 cells, and Harderian gland tumors have been described by various track-structure dependent response models. The attenuation of GCR induced biological effects depends strongly on the biological endpoint, response model used, and material composition. Optimization of space shielding is then driven by the nature of the response model and the transmission characteristics of the given material.

NASA Discipline Radiation Health↗

NASA NTRS1983

The attenuation of sound in a randomly lined duct

The kinetic theory of wave propagation in random media is applied to assess the relative merits of the peripherally segmented, axially segmented and 'checkerboard' configured acoustic duct treatments proposed by Mani (1976). It is argued that, in a first approximation, a multisegmented liner involving many discrete and distinct sections may be modelled as a liner whose impedance varies randomly with position. This results in a relatively simple analytical description of the acoustic properties of the liner in terms of a system of linear, first order ordinary differential equations, whose solution gives the distribution with axial distance of the acoustic modal intensities. The theory is expected to be valid provided that the variation in the impedance from segment to segment is small, so that the conclusions obtained here are of a preliminary nature, and must be regarded as giving a general indication of features which should be incorporated into the design of efficient acoustic liners. The principal such conclusion is that a checkerboard liner offers the best means of increasing the attenuation over and above that of a uniformly lined duct. On the other hand, only minimal gains are to be derived from the use of strictly peripherally segmented liners.

Howe, M. S.↗

NASA NTRS1971

Metabolic effects of artificial environments

The mechanisms by which inert gases influence metabolism were investigated from several viewpoints. Groups of rats were exposed at the thermal neutral temperature of the respective mixtures, to normoxic (P sub A 02 = 100 mm Hq) environments with argon, helium or nitrogen as the diluent at a total pressure of one atmosphere. The possible influence of diluent gases on oxygen transport to the cell was examined with hypoxic (P sub A O2 = 70 mm Hg) mixtures of the same diluent gases. Metabolic measurements included food, water, and oxygen consumption, CO2 production, hematocrit and the rate C-14O2 of expiration subsequent to intraperitoneal injection of acetate-1-C-14 or glucose UL-C-14. Argon-exposed animals showed a consistently decreased metabolic rate while, on the other hand, helium-exposed rats did not significantly alter metabolic rate relative to nitrogen. Certain indices, including acetate and glucose utilization, suggested that helium attenuated the imposed hypoxia at the cellular level while argon facilitated it as compared with nitrogen. These results suggest that metabolic influence of helium is largely thermal in nature while argon has a significant direct metabolic effect and that diluent gases may selectively influence oxygen availability to the interior of the cell.

Jordan, J. P.↗