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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effect of the preform fabrication process on the properties of all-silica optical fibres

In this paper, we present a detailed comparison of technical capabilities of processes for the fabrication of all-silica optical fibre preforms with the use of an atmospheric pressure radio frequency plasma (POVD process) and low-pressure microwave plasma (PCVD process) and analyse the origin of the difference in optical properties between fibres produced by these methods. It is shown that the higher temperature of the core material and the higher oxygen partial pressure in preform fabrication by the POVD process lead to an increase in optical losses in the visible and UV spectral regions in the silica fibres with low hydroxyl (OH) content and a decrease in the solarisation resistance of the fibres with high OH content, i.e. to a more rapid increase in background losses in response to UV irradiation. No such drawbacks are detected in the case of the growth of reflective layers by the PCVD process. (paper)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Implications of an internal dynamo for the thermal history of Mercury

Constraints placed on the thermal evolution of Mercury by the dynamo model of the planet's magnetic field are investigated. It is assumed that Mercury is a differentiated planet possessing an iron-nickel core with a radius approximately three-fourths of the planetary radius, that the mantle is made of silicates with thermal and rheological properties similar to those of earth's upper mantle, and that differentiation was a global process which resulted in the removal of radioactive heat sources from the core and the upward segregation of heat sources in the mantle. These assumptions are found to lead to the conclusion that the existence of a molten core requires the retention of a minimum concentration of heat sources throughout the mantle, the value being comparable to the mantle-wide average concentration for earth. Thus, it is suggested that the differentiation of Mercury could not have resulted in the complete removal of heat sources from the mantle into a crust near the planet's surface.

Cassen, P.↗
DOE OSTI2017

The impact of feedback during massive star formation by core accretion

We study feedback during massive star formation using semi-analytic methods, considering the effects of disk winds, radiation pressure, photoevaporation, and stellar winds, while following protostellar evolution in collapsing massive gas cores. We find that disk winds are the dominant feedback mechanism setting star formation efficiencies (SFEs) from initial cores of ∼0.3–0.5. However, radiation pressure is also significant to widen the outflow cavity causing reductions of SFE compared to the disk-wind only case, especially for >100 M{sub ⊙} star formation at clump mass surface densities Σ{sub cl}≲0.3 g cm{sup −2}. Photoevaporation is of relatively minor importance due to dust attenuation of ionizing photons. Stellar winds have even smaller effects during the accretion stage. For core masses M{sub c}≃10–1000 M{sub ⊙} and Σ{sub cl}≃0.1–3 g cm{sup −2}, we find the overall SFE to be ε-bar {sub ∗f}=0.31(R{sub c}/0.1pc){sup −0.39}, potentially a useful sub-grid star formation model in simulations that can resolve pre-stellar core radii, R{sub c}=0.057(M{sub c}/60M{sub ⊙}){sup 1/2}(Σ{sub cl}/gcm{sup −2}){sup −1/2} pc. The decline of SFE with M {sub c} is gradual with no evidence for a maximum stellar-mass set by feedback processes up to stellar masses of m{sub ∗}∼300 M{sub ⊙}. We thus conclude that the observed truncation of the high-mass end of the IMF is shaped mostly by the pre-stellar core mass function or internal stellar processes. To form massive stars with the observed maximum masses of ∼150–300M{sub ⊙}, initial core masses need to be ≳500–1000 M{sub ⊙}. We also apply our feedback model to zero-metallicity primordial star formation, showing that, in the absence of dust, photoevaporation staunches accretion at ∼50 M{sub ⊙}. Our model implies radiative feedback is most significant at metallicities ∼10{sup −2}Z{sub ⊙}, since both radiation pressure and photoevaporation are effective in this regime.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

IAEA Coordinated Research Project on HTGR Physics, Thermal Hydraulics, and Depletion Uncertainty Analysis: PHISICS/RELAP5-3D Results for the Phase III Coupled Core Exercises

This report details the Parallel and Highly Innovative Simulation for INL Code System (PHISICS)/Reactor Excursions and Leak Analysis Program (RELAP5)-3D results obtained for the neutronics stand-alone core exercises defined for Phase II of the International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on high-temperature gas cooled reactor (HTGR) uncertainty analysis in modeling (UAM). The Phase II models and results are linked to the earlier Standardized Computer Analyses for Licensing Evaluation (SCALE)/Sampler/New ESC-based Weighting Transport (NEWT) data generated for the lattice physics (lattice) stage Phase I of the CRP. The focus of this report is the propagation of cross-section uncertainties from the lattice to the core calculation (core) phase of the prismatic 350 megawatt (MW) General Atomics (GA) Modular HTGR (MHTGR). The Phase II neutronics exercises consist of two sub-cases (II-2a and II-2b) specified for the fresh and mixed core loading of the MHTGR-350 prismatic high-temperature reactor design. Exercises II-2a and II-2b are performed without temperature feedback using isothermal temperature profiles. For the nominal lattice physics (i.e., best-estimate) model, a series of fresh and depleted single block and super cell SCALE/KENO and SCALE/NEWT models were developed at Idaho National Laboratory (INL) to assess the impact of spectral effects on the few-group cross sections. A combination of these lattice cells were used in a super cell calculation to construct 8-group cross-section libraries for use in the INL-developed PHISICS/RELAP5-3D code suite. The block-level homogenized libraries were assigned to the 220 fuel zones utilized in the MHTGR-350 PHISICS core model, according to the fresh and mixed fresh/depleted core loading pattern. In order to evaluate the effect of uncertainty propagation, several sets consisting of 1,000 perturbed NEWT lattice and PHISICS/RELAP5-3D core calculations were performed using the SCALE 6.2 ENDF/B-VII.1 cross-section co-variance data and the stochastic sampling module Sampler in SCALE 6.2.0. The Figures of Merit (FOM) investigated include the mean and standard deviation uncertainty values obtained for the eigenvalues, control rod worth values, block-averaged power profiles, power axial offsets, and isothermal temperature feedback coefficients. A sensitivity study on the main nuclide reaction contributors to the FOM uncertainties has not yet been performed since the SCALE/PHISICS/RAVEN coupling with ENDF/B-VII co-variance data is still being developed. It was found that uncertainties in the cross sections lead to uncertainties in the local power values of up to 1.5%. The variances between the fresh and mixed/depleted core models are not as large as the axial variations between the top and bottom within each core model. The core eigenvalue uncertainty is approximately 0.5%, which is significant in comparison to typical eigenvalue difference targets (less than ~0.1% for LWRs). The power peaking and axial offset uncertainties are smaller (0.10% – 0.15%) and probably below the level of significance in typical core design metrics. The use of an 8-group energy structure slightly under-estimates some of the uncertainties, but in absolute terms, the uncertainty results are reasonably close to the 26-group results. The 26- and 8-group mean and nominal results differ by a larger degree, and if it can be afforded in terms of calculation resources, the 26-group structure should be used for HTGR calculations. The 8-group structure can, however, still be useful for reasonably accurate uncertainty assessments of transient cases where computational time is important. It was furthermore found that the use of a super cell during the cross-section generation process for better representation of the spectral environment at the core periphery did not lead to significant changes in the core eigenvalues, axial offset, and power peaking uncertainties. The impact of the super cell cross sections on the nominal and mean eigenvalues is, however, important enough (0.6% – 1.1% lower) to justify the use of these super cells for HTGR core simulation to represent the softer spectral environment in the core peripheral regions for nominal best-estimate calculations. The use of super cells for HTGR uncertainty studies is, therefore, not strictly necessary, but the improvements in nominal results could justify their use.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1984

Implications of lunar palaeomagnetism for the origin of the Moon

Three issues relating to the origin of the Moon are investigated: the early formation of a fluid iron core, the nature of primeval heat sources in the Moon and the existence of a primeval satellite systems. The remanent magnetization of the Apollo samples was interpreted as evidence for an internally generated lunar magnetic field. The three independent methods of determining paleointensities (the Thellier, ARM (2) and IRM methods (3) are now in general agreement that the field was about 1 G 3.9 b yr ago declining exponentially to .02 G 3.2 b yr ago. Paleomagnetic directions of crustal strata have been determined from the Apollo 15 and 16 subsatellite magnetometer observations. The question whether these are randomly directed such as would be expected from local magnetization processes or are proof of the existence of an early core dynamo field is one of the key issues of lunar science. Although the presence of a lunar core was long ago suggested and there are now various different, although individually not conclusive arguments, the fit of the paleomagnetic data to the dipole hypothesis is strong evidence for the existence of a molten lunar iron core and implies a powerful heat source present in the earliest history of the Moon.

Runcorn, S. K.↗
NASA NTRS1998

Study of a Wake Recovery Mechanism in a High-Speed Axial Compressor Stage

This work addresses the significant differences in compressor rotor wake mixing loss which exist in a stage environment relative to a rotor in isolation. The wake decay for a rotor in isolation is due solely to viscous dissipation which is an irreversible process and thus leads to a loss in both total pressure and efficiency. Rotor wake decay in the stage environment is due to both viscous mixing and the inviscid strain imposed on the wake fluid particles by the stator velocity field. This straining process, referred to by Smith (1993) as recovery, is reversible and for a 2D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated in isolation and in a stage configuration at near peak efficiency and near stall operating conditions. Additional insight is provided by a time-accurate 3D Navier-Stokes simulation of the compressor stator flow field at the corresponding stage loading levels. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model, laser anemometer measurements, and numerical simulations indicate that for the rotor/stator spacing used in this work, which is typical of core compressors, rotor wake straining (stretching) is the primary decay process in the stator passage with viscous mixing playing only a minor role. The implications of these results on compressor stage design are discussed.

VanZante, Dale E.↗
NASA NTRS2011

EOS MLS Level 1B Data Processing Software

This software is an improvement on Version 2, which was described in EOS MLS Level 1B Data Processing, Version 2.2, NASA Tech Briefs, Vol. 33, No. 5 (May 2009), p. 34. It accepts the EOS MLS Level 0 science/engineering data, and the EOS Aura spacecraft ephemeris/attitude data, and produces calibrated instrument radiances and associated engineering and diagnostic data. This version makes the code more robust, improves calibration, provides more diagnostics outputs, defines the Galactic core more finely, and fixes the equator crossing. The Level 1 processing software manages several different tasks. It qualifies each data quantity using instrument configuration and checksum data, as well as data transmission quality flags. Statistical tests are applied for data quality and reasonableness. The instrument engineering data (e.g., voltages, currents, temperatures, and encoder angles) is calibrated by the software, and the filter channel space reference measurements are interpolated onto the times of each limb measurement with the interpolates being differenced from the measurements. Filter channel calibration target measurements are interpolated onto the times of each limb measurement, and are used to compute radiometric gain. The total signal power is determined and analyzed by each digital autocorrelator spectrometer (DACS) during each data integration. The software converts each DACS data integration from an autocorrelation measurement in the time domain into a spectral measurement in the frequency domain, and estimates separately the spectrally, smoothly varying and spectrally averaged components of the limb port signal arising from antenna emission and scattering effects. Limb radiances are also calibrated.

Perun, Vincent S.↗
DOE OSTI2017

High-Performance Core–Shell Catalyst with Nitride Nanoparticles as a Core: Well-Defined Titanium Copper Nitride Coated with an Atomic Pt Layer for the Oxygen Reduction Reaction

A class of core–shell structured low-platinum catalysts with well-dispersed inexpensive titanium copper nitride nanoparticles as cores and atomic platinum layers as shells exhibiting high activity and stability for the oxygen reduction reaction is successfully developed. In using nitrided carbon nanotubes (NCNTs) as the support greatly improved the morphology and dispersion of the nitride nanoparticles, resulting in significant enhancement of the performance of the catalyst. The optimized catalyst, Ti 0.9 Cu 0.1 N@Pt/NCNTs, has a Pt mass activity 5 times higher than that of commercial Pt/C, comparable to that of core–shell catalysts with precious metal nanoparticles as the core, and much higher than that the latter if we take into account the mass activity of all platinum group metals. Furthermore, only a minimal loss of activity can be observed after 10000 potential cycles, demonstrating the catalyst’s high stability. After durability testing, atomic-scale elemental mapping confirmed that the core–shell structure of the catalyst remained intact. This approach may open a pathway for the design and preparation of high-performance inexpensive core–shell catalysts for a wide range of applications in energy conversion processes.

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

Low-Loss, High-Flux Saturation Magnetic Cores for Power Converters

As new and alternative energy sources are added to the energy grid, efficient and low-loss power converters are essential to the storage of energy from these intermittent power sources. Higher operating frequency can reduce the size and weight of transformers. However, current magnetic cores limit the operating frequency because core losses increase with frequency. Therefore, new magnetic core materials are needed with higher resistivity (lower eddy-current losses), lower coercivity (lower hysteresis losses), and higher permeability and flux density (higher power density). These new materials must be integrated into isolated power converters designed to optimize efficiency based on the transformer performance. To address this need, Mainstream pursued a two-pronged approach in Phase I to develop novel magnetic materials and model a planar transformer design. We irradiated silicon steel with a high-energy electron beam in an attempt to induce nanocrystalline grain formation. The nanocrystalline grains were expected to increase resistivity to reduce eddy-current losses and decrease coercivity to reduce hysteresis losses. We also modeled the transformer performance through Simulation Program with Integrated Circuit Emphasis (SPICE) and analytical models to establish the effect of magnetic properties of the core on the performance of the transformer. There still are hurdles to be overcome in Phase II. The electron beam processing was successful in increasing the resistivity and the flux saturation density. However, the resistivity is still too low for high-frequency magnetic cores, because the eddy-current losses would be prohibitively high. Additionally, the coercivity increased for the processed samples leading to higher hysteresis losses. In comparing our SPICE and analytical models to the planar transformer measured values and impedance plots, good agreement was seen for primary and secondary short-circuit impedance measurements and for primary-to-secondary capacitance measurements. The SPICE model deviated from measured values, though, when measuring the transformer open-circuit impedance, indicating that we might need to add more model complexity to the transformer model. Phase II research will continue to build on the transformer model and integrating novel magnetic materials into high-frequency transformers.

15 GEOTHERMAL ENERGY↗
DOE OSTI2017

Formation and mechanism of nanocrystalline AZ91 powders during HDDR processing

Grain sizes of AZ91 alloy powders were markedly refined to about 15 nm from 100 to 160 μm by an optimized hydrogenation-disproportionation-desorption-recombination (HDDR) process. The effect of temperature, hydrogen pressure and processing time on phase and microstructure evolution of AZ91 alloy powders during HDDR process was investigated systematically by X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy, respectively. The optimal HDDR process for preparing nanocrystalline Mg alloy powders is hydriding at temperature of 350 °C under 4 MPa hydrogen pressure for 12 h and dehydriding at 350 °C for 3 h in vacuum. A modified unreacted core model was introduced to describe the mechanism of grain refinement of during HDDR process. - Highlights: • Grain size of the AZ91 alloy powders was significantly refined from 100 μm to 15 nm. • The optimal HDDR technology for nano Mg alloy powders is obtained. • A modified unreacted core model of grain refinement mechanism was proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Recursive Use of the Short-Time Fast Fourier Transform for Signature Analysis in Continuous Processes

Although a nuclear reactor is a hostile environment for sensing and electrical communications, the reactor core is amenable to acoustic communication. An acoustic measurement infrastructure (AMI) has been installed in the Advanced Test Reactor (ATR) to record acoustic signals that can capture its different operating regimes. AMI uses coolant pumps as continuous signal sources, coolant and structural components as transmission lines, and accelerometers to capture system motion. A recursive signal processing technique based on the short-time fast Fourier transform (STFFT) for continuous processes provides unique signatures for diagnostic and prognostic analyses from the system motion data. Here this article presents a recursive STFFT methodology that processes acoustic signals from continuous industrial processes. The article first discusses the initial STFFT use with simulated data to elucidate the basic principles necessary to understand and interpret the STFFT results from actual pump vibration data. Each repetitive use of the STFFT on pump vibration data using the results from the prior STFFT processing will generate additional complimentary time-frequency-based signatures. These signatures are generated by the coolant pumps operating under different process conditions. After each use of the STFFT, the resulting signatures provide exemplary examples of the diversity and intuitive nature of recursively using the STFFT. This article focuses on recursively using the STFFT to provide numerous complimentary and diverse signatures that will ultimately be inputs for machine learning algorithms that provide predictive data analytics. The intuitive nature of the information and signatures from recursive STFFT processing will also bring intuitive interpretation capabilities to machine learning and predictive data analytic techniques.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1988

The rotational dynamics of Mercury and the state of its core

Data on the rotational dynamics of Mercury are examined together with possible events that could lead to the current state of rotation. It is shown that the dynamical evolution of Mercury's spin angular momentum controlled by the dissipative processes of tidal friction and relative motion between a solid mantle and a liquid core would lead naturally to the current state of rotation of the Mercury planet. To investigate the possibility that Mercury has a molten core, an experiment is designed for the measurement of the core properties of Mercury. It is shown that it is technically feasible to measure the four parameters necessary for the determination of the existence and the extent of a Mercurian molten core, including the amplitude of the physical vibration about the resonance spin rate, the obliquity, and the gravitational harmonic coefficients.

Peale, S. J.↗
DOE OSTI2018

Pathways towards Valid Data: Assessment of Optimized Packaging Strategies for Core Components - 18158

Every company that runs nuclear power plants needs a strategy for disposal of the radioactive waste and for decommissioning and dismantling of its nuclear reactors. The dismantling progress of several German NPPs is already in an advanced stage. Hence, particularly highly activated core components have to be disposed of as radioactive waste. Nevertheless, this is also an issue during the operating phase due to necessary replacements of highly activated core components such as PWR control elements or RPV heads. The conditioning of waste packages for final disposal in the German repository Konrad requires the core components to be dismantled, packaged and dried. Therefore, a qualified packaging strategy is needed to ensure a reliable compliance with the protection objectives of the repository and an optimized utilization of prescribed contingents. Exemplified by PWR control elements a pathway is drawn how to perform an optimized packaging strategy in compliance with the protection objectives of the repository based on only few relevant radionuclides derived from activation calculations. For these calculations, particularly the influence of trace impurities in the materials has to be considered and their amounts have to be verified or analyzed by sampling. Furthermore, low nuclide activities from contamination cannot simply be neglected because some of them are obliged to be declared or their radiological relevance has not been sufficiently determined. Due to various influence factors, qualified sampling strategies need carefully considered concepts. Therefore, detailed planning facilitates the qualification and approval process and reduces the costs for analyses and the number of containers. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Electron and ion spectroscopy of azobenzene in the valence and core shells

Azobenzene is a prototype and a building block of a class of molecules of extreme technological interest as molecular photo-switches. We present a joint experimental and theoretical study of its response to irradiation with light across the UV to x-ray spectrum. The study of valence and inner shell photo-ionization and excitation processes combined with measurement of valence photoelectron-photoion coincidence and mass spectra across the core thresholds provides a detailed insight into the site- and state-selected photo-induced processes. Photo-ionization and excitation measurements are interpreted via the multi-configurational restricted active space self-consistent field method corrected by second order perturbation theory. Using static modeling, we demonstrate that the carbon and nitrogen K edges of azobenzene are suitable candidates for exploring its photoinduced dynamics thanks to the transient signals appearing in background-free regions of the NEXAFS and XPS.

Chemistry↗
DOE OSTI2016

Asymmetric unwrapping of nucleosomal DNA propagates asymmetric opening and dissociation of the histone core

The nucleosome core particle (NCP) is the basic structural unit for genome packaging in eukaryotic cells and consists of DNA wound around a core of eight histone proteins. DNA access is modulated through dynamic processes of NCP disassembly. Partly disassembled structures, such as the hexasome (containing six histones) and the tetrasome (four histones), are important for transcription regulation in vivo. However, the pathways for their formation have been difficult to characterize. We combine time-resolved (TR) small-angle X-ray scattering and TR-FRET to correlate changes in the DNA conformations with composition of the histone core during salt-induced disassembly of canonical NCPs. We find that H2A–H2B histone dimers are released sequentially, with the first dimer being released after the DNA has formed an asymmetrically unwrapped, teardrop-shape DNA structure. This finding suggests that the octasome-to-hexasome transition is guided by the asymmetric unwrapping of the DNA. Furthermore, the link between DNA structure and histone composition suggests a potential mechanism for the action of proteins that alter nucleosome configurations such as histone chaperones and chromatin remodeling complexes.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1973

Trapped solar and cosmogenic noble gas abundances in Apollo 15 and 16 deep drill samples

Abundances and isotopic compositions of all the stable noble gases (He, Ne, Ar, Kr, Xe) were measured at different depths of the Apollo 15 and Apollo 16 deep drill cores, and in several surface fines and breccias. All samples analyzed from both drill cores were found to contain large concentrations of solar wind implanted gases. This means that even the deepest layers of both cores have experienced a lunar surface history. The Apollo 15 core data are consistent with a combined accretion plus static time of a few hundred million years, and also indicate variable pre-accretion irradiation of core material. Depth profiles of cosmogenic gases in the Apollo 16 core show considerably larger concentrations of cosmic gases below 65 cm depth than above. This pattern may be interpreted either as an accretionary process, or by a more recent deposition of regolith to the upper 70 cm of the core.

Bogard, D. D.↗
NASA NTRS2004

Biologically Derived Nanoparticle Arrays via a Site-Specific Reconstitution of Ferritin and their Electrochemistry

Nanoparticle arrays biologically derived from an electrochemically-controlled site-specific biomineralization were fabricated on a gold substrate through the immobilization process of biomolecules. The work reported herein includes the immobilization of ferritin with various surface modifications, the electrochemical biomineralization of ferritins with different inorganic cores, the fabrication of self-assembled arrays with the immobilized ferritin, and the electrochemical characterization of various core materials. Protein immobilization on the substrate is achieved by anchoring ferritins with dithiobis-N-succinimidyl propionate (DTSP). A reconstitution process of electrochemical site-specific biomineralization with a protein cage loads ferritins with different core materials such as Pt, Co, Mn, and Ni. The ferritin acts as a nano-scale template, a biocompatible cage, and a separator between the nanoparticles. The nano-sized metalcored ferritins on a gold substrate displayed a good electrochemical activity for the electron transport and storage, which is suitable for bioelectronics applications such as biofuel cell, bionanobattery, biosensors, etc. Keywords: Ferritin, immobilization, site-specific reconstitution, biomineralization, and bioelectronics

Kim, Jae-Woo↗