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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Afterpulsing in Silicon Photomultipliers: Impact on the Photodetectors Characterization

Novel generation of silicon-based photodetectors are attractive alternatives to the traditional phototubes. They offer significant advantages but they present new challenges too. Presence of afterpulses may affect many characteristics of the photodetectors. Simple statistical model of afterpulsing is used to evaluate the contribution to the observed dark count rates, to examine the contribution to the pulse height resolution and to demonstrate the modification of the observed timing properties of the SiPMs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

TIMING AND SPECTRAL PROPERTIES OF Be/X-RAY PULSAR EXO 2030+375 DURING A TYPE I OUTBURST

We present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy-dependent pulse profiles were clearly detected up to 100 keV. Narrow dips are seen in the profiles up to {approx}70 keV. The presence of prominent dips at several phases in the profiles up to such high energy ranges was not seen before. At higher energies, these dips gradually disappeared and the profile appeared to be single-peaked. The 1.0-200.0 keV broadband spectrum is found to be well described by a partial covering high-energy cutoff power-law model. Several low-energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with the above continuum model yielding similar parameter values. The partial covering with a partially ionized absorber resulted in a marginally better fit. The spectral fitting did not require any cyclotron feature in the best-fit model. To investigate the changes in spectral parameters at dips, we carried out pulse-phase-resolved spectroscopy. During the dips, the value of the additional column density was estimated to be high compared to other pulse phases. While using a partially ionized absorber, the value of the ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRSDate not supplied

Successive Convexification for Powered Descent Guidance with Time-Varying Mass Properties

This paper extends the 6 degree-of-freedom successive convexification (SCvx) algorithm discussed in literature to account for time-varying mass properties in the representation of the attitude dynamics. Simulation results of a notional large-size lander performing the last minutes of Lunar powered descent with significant variations in the center-of-mass and moments of inertia over the duration of the trajectory are shown. Differences in the final optimal trajectories generated via SCvx are presented between the constant vs. variable mass property formulations for an in-plane and out-of-plane example.

Alex Hayes↗
NASA NTRSDate not supplied

Successive Convexification for Powered Descent Guidance with Time-Varying Mass Properties

This paper extends the 6 degree-of-freedom successive convexification (SCvx) algorithm discussed in literature to account for time-varying mass properties in the representation of the attitude dynamics. Simulation results of a notional large-size lander performing the last minutes of Lunar powered descent with significant variations in the center-of-mass and moments of inertia over the duration of the trajectory are shown. Differences in the final optimal trajectories generated via SCvx are presented between the constant vs. variable mass property formulations for an in-plane and out-of-plane example.

Alex Hayes↗
DOE OSTI2025

Report on Preliminary Detailed Experimental Plan for Neutron Irradiation of A709 at ATR and HFIR

Advanced nuclear power technologies will use higher temperatures as a means to extract energy at a higher efficiency than current plants and therefore put a larger demand on the structural materials. Improved performance of structural materials could enable greater safety margins, longer plant lifetimes, and reduce maintenance costs. Alloy 709 is championed as the next generation of austenitic alloys for advanced nuclear reactors. In parallel to the ASME code case pursued, the AMMT program is initiating a neutron irradiation campaign to provide first-of-a-kind engineering data to establish operational design parameters and how the mechanical response is modified by environmental factors. This document refines the AMMT neutron irradiation campaign to a 4 year program to support the generation of creep knockdown factors for Alloy 709 and welded Alloy 709. The campaign is divided among two national laboratories, Oak Ridge National Laboratory and Idaho National Laboratory, to use the strengths of each laboratory. Through a cooperative plan, time-independent properties and time-dependent properties will be obtained across a large temperature window, nominally 300°C to 800°C, damage levels up to 10 dpa, and with and without the impacts of transmutation produced helium.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2026

Report on Preliminary Detailed Experimental Plan for Neutron Irradiation of A709 at ATR and HFIR

Advanced nuclear power technologies will use higher temperatures as a means to extract energy at a higher efficiency than current plants and therefore put a larger demand on the structural materials. Improved performance of structural materials could enable greater safety margins, longer plant lifetimes, and reduce maintenance costs. Alloy 709 is championed as the next generation of austenitic alloys for advanced nuclear reactors. In parallel to the ASME code case pursued, the AMMT program is initiating a neutron irradiation campaign to provide first-of-a-kind engineering data to establish operational design parameters and how the mechanical response is modified by environmental factors. This document refines the AMMT neutron irradiation campaign to a 4 year program to support the generation of creep knockdown factors for Alloy 709 and welded Alloy 709. The campaign is divided among two national laboratories, Oak Ridge National Laboratory and Idaho National Laboratory, to use the strengths of each laboratory. Through a cooperative plan, time-independent properties and time-dependent properties will be obtained across a large temperature window, nominally 300°C to 800°C, damage levels up to 10 dpa, and with and without the impacts of transmutation produced helium.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Photophysical and Time‐resolved Infrared Properties of Long‐Lived Rhenium(I) 4,5‐Diazafluorene Tricarbonyl Chromophores

This report investigates the synthesis, structural characterization, fundamental molecular photophysics, electrochemistry, UV-Vis spectroelectrochemistry, and time-resolved infrared spectroscopic properties of eight [fac-Re(dafR)(CO) 3 L] 0/+ complexes, where R=ethyl [(dedaf); 1, 3, 5, 7] or H [(dafH); 2, 4, 6, 8] and L=Cl− (1, 2), imidazole [(Im); 3, 4], 4-ethylpyridine [(4-Etpy); 5, 6], or pyridine [(py); 7, 8]. Universally, 1–8 yield higher energy photoluminescence (PL) emission bands and higher PL quantum yields (up to 53 %) than the classic 2,2’-bipyridine (bpy) and 1,10-phenanthroline (phen) ligated Re(I) tricarbonyl complexes. The excited state lifetimes of 1–8 lie between those corresponding to the bpy and phen derivatives, ranging from 120 and 1300 ns at room temperature. Combinations of reductive UV-Vis spectroelectrochemistry, transient absorption spectroscopy, and time-resolved infrared spectroscopy consistently assigned the lowest excited states in 1–8 being of metal-to-ligand charge transfer (MLCT) character. These new ReI MLCT chromophores follow classic energy gap law behavior and possess the characteristics necessary for serving as valuable photosensitizers suitable to energize excited state electron and energy transfer photochemistry.

Charge transfer↗
DOE OSTI2019

Structural origins of the electronic properties of materials via time-resolved infrared spectroscopy

Time-resolved mid-infrared (TRIR) spectroscopy offers new opportunities to investigate how the molecular and structural properties of optoelectronic materials influence their electronic and transport states. This capability emerges from the ability to measure low energy electronic transitions in the mid-infrared that are related to delocalized states in materials and to simultaneously detect the vibrational properties of the materials that influence those states. Furthermore, the ability to simultaneously measure electronic and vibrational transitions in materials offers unprecedented opportunities to correlate structural dynamics of materials with their electronic and transport properties. Here, these capabilities are introduced by first describing the basic principles of TRIR spectroscopy used to examine electronic processes in materials. Then, several applications of TRIR spectroscopy are described in which measurements of the vibrational spectra of electronic excited states are probed as a means to correlate the structural properties of materials with the delocalization of their electronic states. In one example, exciton localization mechanisms in organic semiconductors are probed through vibrational spectra of the molecules in their excited states and correlated with their crystalline packing arrangements. Another example highlights the use of TRIR spectroscopy to examine singlet fission reaction dynamics through a combination of low energy electronic transitions and the vibrational spectra that are unique to the electronic states involved in the reaction. Finally, the use of TRIR spectroscopy to investigate charge carrier localization mechanisms in lead-halide perovskites is described, followed by an outlook of future applications of the technique in optoelectronic materials research.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Effect of milling time on magnetic properties and structures of bulk Sm-Co/{alpha}-(Fe, Co) nanocomposite magnets

Bulk Sm-Co/{alpha}-(Fe,Co) nanocomposite magnets were fabricated by hot pressing composite powders prepared by high-energy ball milling of magnetically hard SmCo{sub 5} powder and magnetically soft Fe powder. The bulk magnets had a nanocomposite structure consisting of Sm-Co matrix (1:5 H and 1:7 H phases) and {alpha}-(Fe,Co) phases. The Fe-Co particles were distributed uniformly in the Sm-Co matrix. The milling time strongly affects the structures and the magnetic properties of the bulk magnets. Increasing milling time led to a decrease of the amount of 1:5 H phase, an increase in the phase fraction of the 1:7 H phase, and a decrease in the amount of soft phase, which resulted in an increase in magnetization and a decrease in coercivity. Scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) analyses revealed that inter-diffusion took place between the Sm-Co matrix and Fe particles during the processing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Time-dependent THMC properties and microstructural evolution of damaged rocks in excavation damage zone

Modeling coupled thermo-hydro-mechanical-chemical (THMC) processes in host rocks near high-level nuclear waste (HLW) repositories at various time scales is an extremely challenging task. The current study integrates experimental, theoretical, and numerical methods in assessing the evolution of excavation damage zone (EDZ) over time and its implication on the long-term migration of hazardous species. Argillite and rock salt and are the focus of this study. The first part of the report presents a novel time-dependent directional microcrack damage theory for generic brittle rocks. It features detailed statistical description of the microcracks within a damaged solid, permitting a direct upscaling of microscale processes such as crack growth kinetics, crack closure/opening, sliding friction to explain the macroscopic creep, nonlinear elasticity, shear dilation, and loading-unloading hysteresis. This provides a basic platform for describing the anisotropic mechanical and transport properties of damaged rocks during excavation and subsequent THMC loadings. The model is validated and numerically implemented to Finite Element (FE) package ABAQUS through the user-defined material (UMAT) interface and have demonstrated great potential in resolving the time-dependent and anisotropic evolution of damage in the EDZ. The second part of the report presents a multi-scale experimental effort in characterizing the thermal, hydraulic, and mechanical properties of Mancos shale and Avery Island salt. For the Mancos shale, triaxial compression tests are performed at different confining pressures and temperatures to probe its thermomechanical properties relevant to HLW repositories. The obtained stress-strain data are interpreted using the proposed directional damage theory. Post-test specimens are subjected to gas permeability tests to reveal the correlation between permeability and the degree of microcracking. At microscale, temperature-controlled nanoindentation tests are performed and found a linear correlation between fracture toughness and elastic modulus from 25°C to 300°C. For Avery Island salt, we have designed and manufactured a novel relative-humidity controlled uniaxial creep device. Long-term creep tests at low stresses (< 5 MPa) are performed at different levels of relative humidity (RH). Besides confirming the much higher creep rates as one would expect through extrapolating the high-stress creep data, the results reveal that the steady-state creep rate of rock salt is strongly dependent on the ambient RH, an aspect that is often neglected in the literature. Both behaviors can be attributed to the pressure-solution creep mechanism which dominates at low stress and high RH levels. The third part of the report explores a set of numerical strategies in modeling the THMC behavior of porous geomaterials. A fully implicit, monolithic FE solution that can flexibly interface with different material models and coupling mechanisms for THMC problems is developed and verified through the ABAQUS user-defined element (UEL) interface. The scheme is used to study the THM response of a hypothetical HLW storage site with reference to an existing in-situ heater test. Strategies for integrating the UEL and the microcrack UMAT are suggested. Another numerical endeavor of this study is to implement a higher-order asymptotic homogenization method to account for the heterogeneous porous structures. The same method is then extended to perform microstructure-informed thermo-mechanical modeling of generalized continua. The above outcomes of this project provide a strong thrust towards enhancing the fundamental understanding and modeling capability of the long-term evolution of host rocks in EDZ, thus helping achieve the design goal of 1-million-year isolation of high-level nuclear wastes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Investigation of properties of time-dependent bell inequalities in Wigner’s form for nonstationary and open quantum systems

A radically new class of Bell inequalities in Wigner’s form was obtained on the basis of Kolmorov’s axiomatization of probability theory and the hypothesis of locality. These inequalities take explicitly into account the dependence on time (time-dependent Bell inequalities in Wigner’s form). By using these inequalities, one can propose a means for experimentally testing Bohr’ complementarity principle in the relativistic region. The inequalities in question open broad possibilities for studying correlations of nonrelativistic and relativistic quantum systems in external fields. The violation of the time-dependent inequalities in quantum mechanics was studied by considering the behavior of a pair of anticorrelated spins in a constant external magnetic field and oscillations of neutral pseudoscalar mesons. The decay of a pseudoscalar particle to a fermion–antifermion pair is considered within quantum field theory. In order to test experimentally the inequalities proposed in the present study, it is not necessary to perform dedicated noninvasive measurements required in the Leggett–Garg approach, for example.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1979

Robustness properties of discrete time regulators, LOG regulators and hybrid systems

Robustness properites of sample-data LQ regulators are derived which show that these regulators have fundamentally inferior uncertainty tolerances when compared to their continuous-time counterparts. Results are also presented in stability theory, multivariable frequency domain analysis, LQG robustness, and mathematical representations of hybrid systems.

Stein, G.↗