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At least 415 records · Page 23

All sources NASA NTRS DOE OSTI

DOE OSTI2025

Nonpyrophoric alternative to trimethylaluminum for the atomic layer deposition of Al 2 O 3

We have examined the atomic layer deposition (ALD) of Al 2 O 3 using a nonpyrophoric precursor, which possesses only Al–N bonds and no Al–C bonds: Al(N(CH 3 ) 2 ) 2 (–N(C 2 H 5 )–C 2 H 4 –N(C 2 H 5 ) 2 ), which we refer to as bis-dimethylamino-diamino-aluminum (BDMADA-Al). We employed a quartz crystal microbalance (QCM) to monitor ALD in situ and in real time, and the deposited thin films have been characterized using x-ray photoelectron spectroscopy, spectroscopic ellipsometry, x-ray reflectivity, and atomic force microscopy. Films deposited with BDMADA-Al result in near-stoichiometric Al2O3 at temperatures ranging from T = 120 to 285 °C using H 2 O as the coreactant and at T = 285 °C using t-BuOH as the coreactant. The properties of the films (density, C incorporation, stoichiometry, growth rates) are comparable using either BDMADA-Al or trimethylaluminum (TMA) as the precursor under similar reaction conditions. The N content in the films deposited with BDMADA-Al as the precursor is <1% at both T = 120 and 285 °C. Additionally, both BDMADA-Al|t-BuOH and TMA|t-BuOH processes deposit near-stoichiometric Al 2 O 3 at T = 285 °C, while neither process chemistry produces a constant growth rate per cycle at T = 120 °C. Close examination of single cycle QCM data from BDMADA-Al ALD indicates unique ligand exchange reaction mechanisms during each of the half-reactions. Experimentally, we have evidence supporting the mechanism in which upon the chemisorption of BDMADA-Al, the species on the surface retains the –N(CH 3 ) 2 ligands, while the diamine ligand is mostly lost on dissociative adsorption, except possibly at the higher temperature (285 °C). As a result, our work demonstrates that BDMADA-Al can be used as an effective alternative precursor to TMA for the ALD of Al 2 O 3 .

36 MATERIALS SCIENCE↗

NASA NTRS1984

Strain analysis of the Leoville chondrite and conditions in asteroidal interiors

Deformed chondrules in the Leoville carbonaceous chondrite define a preferred orientation, also recognized previously in other CV3 chondrites. Identifying the strain mechanism is necessary for understanding the conditions which caused this compressional shortening. Luckly, the major mineralogical constituent of CV3 meteorites is olivine, for which experimental data on strain mechanisms exist. The conditions that caused strain in the olivine were obviously applicable to the whole meteorite. Possible mechanisms of olivine deformation are cataclasis, low temperature plasticity, power low creep, and diffusional flow, each of which occurs under different combinations of temperature and deviatoric stress. Cataclasis can be ruled out on the basis of its high deviatoric stress requirements; some fractures occur in chondrule olivines, but these may have formed during excavation or impact. Low temperature plasticity and power low creep occur by means of various types of lattice dislocations. However, methods of thermal decoration and chemical etching of dislocations failed to indicate evidence for either mechanism. Thus, the inference is that diffusional flow, characteristic of low to moderately high temperatures and low deviatoric stress, was the major deformation mechanism.

Cain, P. M.↗

NASA NTRS1993

A combined experimental and finite element study to predict the failure mechanisms in SiC coated carbon/carbon composites at room and elevated temperatures under flexural loading

Response of quasi-isotropic laminates of SiC coated Carbon/Carbon (C/C) composites have been investigated under flexural loading at various temperatures. Variation of load-deflection behavior with temperatures are studied. Increase in flexural strength and stiffness are observed with the rise in temperature. Extensive analyses through Optical Microscope (OM) and Non-Destructive Evaluation (NDE) have been performed to understand the failure mechanisms. Damage zone is found only within the neighborhood of the loading plane. Isoparametric layered shell elements developed on the basis of the first order shear deformation theory have been used to model the thin laminates of C/C under flexural loading. Large deformation behavior has been considered in the finite element analysis to account for the non-linearities encountered during the actual test. Data generated using finite element analysis are presented to corroborate the experimental findings, and a comparison in respect of displacement and stress-strain behavior are given to check the accuracy of the finite element analysis. Reasonable correlation between the experimental and finite element results have been established.

Mahfuz, Hassan↗

NASA NTRS1987

The carbon dioxide chaperon efficiency for the reaction H + O2 + M yields HO2 + M from ignition delay times behind reflected shock waves

Ignition delay times for stoichiometric hydrogen-oxygen in argon with and without carbon dioxide were measured behind reflected shock waves. A 20-reaction kinetic mechanism models the measured hydrogen-oxygen delay times over the temperature range 950 to 1300 K. The chaperon efficiency for carbon dioxide determined for the hydrogen-oxygen carbon dioxide mixture was 7.0. This value is in agreement with literature values but much less than a recent value obtained from flow tube experiments. Delay times measured behind a reflected shock wave were about 20% longer than those measured behind incident shock waves. The kinetic mechanism successfully modeled the high-pressure data of Skinner and the hydrogen-air data of Stack. It is suggested that the lowest temperature points for the hydrogen-air data of Slack are unreliable and that the 0.27-atm data may illustrate a case where vibrational relaxation of nitrogen is important. The reaction pathway HO2 yields H2O2 yields OH yields H was required to model the high-pressure data of Skinner. The successful modeling of the stoichiometric hydrogen-air data demonstrates the appropriateness of deriving kinetic models from data for gas mixtures highly diluted with argon. The technique of reducing a detailed kinetic mechanism to only the important reactions for a limited range of experimental data may render the mechanism useless for other test conditions.

Brabbs, Theodore A.↗

NASA NTRS1984

Aerodynamic features of flames in premixed gases

A variety of experimentally established flame phenomena in premixed gases are interpreted by relating them to basic aerodynamic properties of the flow field. On this basis the essential mechanism of some well known characteristic features of flames stabilized in the wake of a bluff-body or propagating in ducts are revealed. Elementary components of the flame propagation process are shown to be: rotary motion, self-advancement, and expansion. Their consequences are analyzed under a most strict set of idealizations that permit the flow field to be treated as potential in character, while the flame is modelled as a Stefan-like interface capable of exerting a feed-back effect upon the flow field. The results provide an insight into the fundamental fluid-mechanical reasons for the experimentally observed distortions of the flame front, rationalizing in particular its ability to sustain relatively high flow velocities at amazingly low normal burning speeds.

Oppenheim, A. K.↗

NASA NTRS1985

Long-delayed radio echoes - Mechanisms and observations

Experiments carried out in Alaska with the object of observing long-delayed radio echoes (LDE) are described. The results are subjected to critical sonogram analysis, together with data form previous experiments carried out at Stanford and elsewhere. It is concluded that, although strong supporting evidence for sporadic LDE phenomena has accumulated over the late 50 years, and a variety of plausible mechanisms have been proposed, stringent analysis of records such as those discussed in the paper almost invariably reveal alternative possible explanations for them. Further detailed experimentation is required on mechanisms, for which the phenomenon seems best established, e.g., round-the-world echoes and other forms of guided propagation.

Vidmar, R. J.↗

NASA NTRS1975

Experimental and analytical investigation of 0 G condensation in a mechanical refrigeration system application

Basic equations of momentum and energy are presented and discussed with respect to heat transfer and pressure drop for forced flow condensation in horizontal tubes under 1-g and 0-g conditions. Some experimental results are presented for condensing refrigerant-12 in a system of three parallel-connected quartz tubes (3-mm inside diameter, G = 1.037 to 3.456 x 105 lbm/hr-sq. ft). From high speed photographs, measurements were obtained of film thickness, phase velocities, disturbance wavelengths, and flow regimes and their transitions. Based upon these measurements various dimensionless force ratios (flow and instability parameters) were calculated. Under 0-g conditions a uniformly thick redistribution of liquid condensate about the tube walls was found to result in a lowered heat transfer coefficient as compared with 1-g conditions, based upon fundamental heat transfer theory. A model is proposed that takes into account the difference in heat transfer due to condensate distribution under 1-g and 0-g conditions.

Keshock, E. G.↗

DOE OSTI2025

Studying Open Quantum Systems Relevant to Chemistry on a Trapped-Ion Quantum Simulator (Final Technical Report)

This project advances the trapped-ion quantum simulator as a versatile platform for studying open quantum system phenomena. We aim to contribute to the emerging quantum simulation toolkits and enable simulation of nanoscale energy processes. Trapped-ion platforms offer unique capabilities: their vibrational motion can be precisely manipulated, measured, and coherently coupled to auxiliary qubits. The vibrational mode can function both as a highly sensitive quantum sensor and a programmable environment bath. Using this platform, we achieved three major outcomes. First, we demonstrated using the vibrational mode as an ultrasensitive probe for testing fundamental physics, including possible nonlinear quantum mechanics effects. Second, we established that these modes can act as controllable baths in which tunable noise and loss can enhance or modify energy-transfer dynamics, providing the experimental preparation toward studying mechanisms relevant to chemical reactions and light-harvesting systems. Third, by introducing controllable nonlinear gain and loss, we showed theoretically how simulations using trapped ions can model vibrationally-assisted energy transport in a non‐Hermitian quantum system comprising a chromophore dimer weakly coupled to a vibrational mode. Exploring the non‐Hermitian dynamics of the whole system including vibrations, we found that energy transfer accompanied by absorption of phonons from a vibrational mode can be significantly enhanced near an exceptional point. This theoretical work on simulation of energy transfer processes in driven non‐Hermitian quantum systems revealed an interesting novel path to study open quantum systems dynamics under conditions of gain and loss. We then further explored the benefits of controllable gain and loss with an experimental realization of quantum analogs of nonlinear oscillators, namely, the van der Pol oscillator. Here we observed mutual synchronization mediated by collective dissipation between two oscillators. In parallel, we explored related quantum networking protocols using the same trapped-ion platform, developing fast, high-fidelity schemes for distributing entanglement. Together, these achievements show that trapped-ion vibrational modes provide a highly programmable and high-fidelity platform for investigating complex dissipative quantum behavior, while enabling new approaches to remote quantum sensing, energy science, and nonlinear quantum dynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

Gear Test Assembly – Report Experimental Testing and Gear Analysis (FY2021 Midyear Report)

The Gear Test Assembly (GTA) has completed three experimental campaigns at the Mechanisms Engineering Test Loop (METL) facility. The most recent campaign tested Inconel 718 spur gears, tapered roller bearings of 52100 bearing steel with no heat treatment, and a lantern ring shaft seal with spring-loaded fasteners. Testing was performed in Test Vessel 1 (TV1) with 250°C sodium that had an oxide concentration of <10ppm. Testing began in February 2021 and was ended in March 2021 when a thrust bearing assembly failed, requiring shutdown and maintenance. The third experimental campaign completed 1,568 simulated fuel assembly maneuvers before the thrust bearing failure. The GTA was removed from TV1 and cleaned in the Carbonation System. The GTA is currently being prepared for the next experimental campaign. Nondestructive examination methods have been developed at Argonne to monitor the health of the GTA spur gears. Eddy current testing (ECT) and ultrasonic testing (UT) were performed prior to sodium testing and after each experimental campaign. The NDE has shown that the primary damage mechanism is mechanical wear on the gear tooth surface. Several larger nicks are observable on the gear faces, with additional large nicks present on the edges of the gear teeth. While this damage is observable, the overall health of the gears is adequate for more in-sodium testing. A total of 12,752 simulated fuel assembly maneuvers have been completed using this set of gears.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2024

Finding a common ground for RCM experiments. Part B: Benchmark study on ethanol ignition

Rapid compression machines (RCMs) are widely used to investigate gas phase reaction kinetics of various kind of fuels at application relevant conditions. In principle, the operation of an RCM is based on the idea of compressing a homogenous pre-mixed fuel-air mixture by a piston. Usually creviced pistons ensure a homogenous adiabatic core in the center of the reaction chamber which permits the assumption of an isentropic relation between the measured pressure and gas temperature. Despite the ideal core gas compression, non-ideal effects such as heat loss, differences in the compression behavior, and ultimately non-standardized design and operation of rapid compression machines lead to different experimental results in different facilities at nominally the same end of compression conditions. In this study ignition delay times of ethanol are investigated at four different conditions in five independent RCMs. As expected, the raw results of the different facilities indeed show notable differences at the same end of compression conditions. However, according to the adiabatic core hypothesis the agreement between kinetic simulations and experiments should be consistent for all facilities provided that the facility effects are correctly accounted for. To elaborate upon this hypothesis, a kinetic mechanism is optimized to reflect the experimental results of all facilities. In the end, the optimized mechanism predicts all experimental data within the expected uncertainty. This confirms the reliability of RCM experiments for kinetic investigations and the validity of the effective volume approach in simulating RCM data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Recent progress toward catalyst properties, performance, and prediction with data-driven methods

Herein, data-driven approaches are currently renovating the field of heterogenous catalysis and open a door to advance catalyst design. Their success depends heavily on the synergy among machine learning (ML), experimental data, and quantum mechanical (QM) calculations. In this brief survey of recent progress, we examine catalysis informatics in the context of (1) ML-aided catalyst characterizations, (2) knowledge extractions from experimental data, (3) predictions of catalytic properties and constructions of reaction networks, and (4) ML-enabled large-scale QM simulations. An outlook on the current challenges of this rapidly evolving field is also provided.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRSDate not supplied

Conclusions of a Mini Technical Interchange Meeting on Mechanisms and Pathways Common Between Adverse Health Outcomes from Exposures to Space Radiation

To enable deep space exploration and sustained human presence in space, the NASA Human Research Program’s (HRP) Space Radiation Element (SRE) funds research to characterize and mitigate adverse health outcomes from exposure to space radiation that include risks of carcinogenesis, cardiovascular disease (CVD) and central nervous system (CNS) decrements. Over the past decade, a growing body of compelling experimental evidence suggests shared mechanisms and pathophysiological processes for CVD, neurodegenerative effects, and cancer development and progression, which are traditionally managed as separate disease processes. Additionally, epidemiological studies have identified cross-sectional and longitudinal associations between some specific types of cancer and CVD, and accumulating evidence indicates that the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease may overlap with CVD and cancer pathogenesis. Identifying the mechanisms and pathways common to these important health decrements will not only accelerate development of effective countermeasures and improve management of spaceflight-induced risk, it will also help to develop new treatment strategies for patients on Earth. To identify common pathways and mechanisms of disease induction and progression from current SR-funded studies and to inform future work and solicitations, the SRE organizes themed sessions at annual HRP Investigators’ Workshops (IWS). These technical interchange meetings (TIMs) provide a venue for the scientific community to present ongoing work and engage in open discussion on results, limitations of current approaches, and incorporation of novel experimental strategies, model systems, and other innovative techniques. Here a summary and lessons learned from the SRE-sponsored mini-TIM titled “mechanisms and pathways common between adverse health outcomes” held at HRP IWS 2023 will be communicated. The 90-min TIM had 30-min dedicated to discussing and developing potential collaboration and tissue sharing opportunities among investigators. The SRE facilitated the discussion using a set of pressing questions and gaps in knowledge that need to be addressed by the scientific community. This poster presents the outcomes of the session along with proposed future workshops and other SRE initiatives.

Janapriya Saha↗

NASA NTRSDate not supplied

Conclusions of a Mini Technical Interchange Meeting on Mechanisms and Pathways Common Between Adverse Health Outcomes from Exposures to Space Radiation

Janapriya Saha↗

DOE OSTI2023

Porosity modeling in a TiNbTaZrMo high-entropy alloy for biomedical applications

High-entropy alloys (HEAs) have attracted great attention for many biomedical applications. However, the nature of interatomic interactions in this class of complex multicomponent alloys is not fully understood. We report, for the first time, the results of theoretical modeling for porosity in a large biocompatible HEA TiNbTaZrMo using an atomistic supercell of 1024 atoms that provides new insights and understanding. Our results demonstrated the deficiency of using the valence electron count, quantification of large lattice distortion, validation of mechanical properties with available experimental data to reduce Young's modulus. We utilized the novel concepts of the total bond order density (TBOD) and partial bond order density (PBOD) via ab initio quantum mechanical calculations as an effective theoretical means to chart a road map for the rational design of complex multicomponent HEAs for biomedical applications.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Investigation of δ zirconium hydride morphology in a single crystal using quantitative phase field simulations supported by experiments

In light water nuclear reactors, waterside corrosion of the cladding material leads to the production of hydrogen, a fraction of which is picked up by the zirconium cladding and precipitates into brittle hydride particles. These nanoscale hydride particles aggregate into mesoscale hydride clusters. The principal stacking direction of the nanoscale hydrides precipitated in the cladding tube changes from circumferential in the absence of applied stress to radial under circumferential applied stress. A quantitative phase field model has been developed to predict the hydride morphology observed experimentally and identify the mechanisms responsible for nanoscale hydride stacking. The model focuses on nanoscale hydride precipitation in a single zirconium grain with a detailed description of the anisotropic elastic contribution. The model predictions concerning the shape, orientation, and stacking behavior of nanoscale hydride are analyzed and compared with experimental observations. The model accurately accounts for the experimentally observed elongated nanoscale hydride shape and the stacking of hydrides along the basal plane of the hexagonal zirconium matrix. When investigating the role of applied stress in hydride morphology, the model challenges some of the mechanisms previously proposed to explain hydride reorientation. Finally, although hydride reorientation has been hypothesized to be caused by a change in nanoscale hydride shape, the current study shows that these mechanisms are unlikely to occur.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2021

Metalloprotein catalysis: structural and mechanistic insights into oxidoreductases from neutron protein crystallography

Metalloproteins catalyze a range of reactions, with enhanced chemical functionality due to their metal cofactor. The reaction mechanisms of metalloproteins have been experimentally characterized by spectroscopy, macromolecular crystallography and cryo-electron microscopy. An important caveat in structural studies of metalloproteins remains the artefacts that can be introduced by radiation damage. Photoreduction, radiolysis and ionization deriving from the electromagnetic beam used to probe the structure complicate structural and mechanistic interpretation. Neutron protein diffraction remains the only structural probe that leaves protein samples devoid of radiation damage, even when data are collected at room temperature. Additionally, neutron protein crystallography provides information on the positions of light atoms such as hydrogen and deuterium, allowing the characterization of protonation states and hydrogen-bonding networks. Neutron protein crystallography has further been used in conjunction with experimental and computational techniques to gain insight into the structures and reaction mechanisms of several transition-state metal oxidoreductases with iron, copper and manganese cofactors. Here, the contribution of neutron protein crystallography towards elucidating the reaction mechanism of metalloproteins is reviewed.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1984

Liquid crystal polyester-carbon fiber composites

Liquid crystal polymers (LCP) have been developed as a thermoplastic matrix for high performance composites. A successful melt impregnation method has been developed which results in the production of continuous carbon fiber (CF) reinforced LCP prepreg tape. Subsequent layup and molding of prepreg into laminates has yielded composites of good quality. Tensile and flexural properties of LCP/CF composites are comparable to those of epoxy/CF composites. The LCP/CF composites have better impact resistance than the latter, although epoxy/CF composites possess superior compression and shear strength. The LCP/CF composites have good property retention until 200 F (67 % of room temperature value). Above 200 F, mechanical properties decrease significantly. Experimental results indicate that the poor compression and shear strength may be due to the poor interfacial adhesion between the matrix and carbon fiber as adequate toughness of the LCP matrix. Low mechanical property retention at high temperatures may be attributable to the low beta-transition temperature (around 80 C) of the LCP matrix material.

Chung, T. S.↗

NASA NTRS2003

Sound Generation by Aircraft Wake Vortices

This report provides an extensive analysis of potential wake vortex noise sources that might be utilized to aid in their tracking. Several possible mechanisms of aircraft vortex sound generation are examined on the basis of discrete vortex dynamic models and characteristic acoustic signatures calculated by application of vortex sound theory. It is shown that the most robust mechanisms result in very low frequency infrasound. An instability of the vortex core structure is discussed and shown to be a possible mechanism for generating higher frequency sound bordering the audible frequency range. However, the frequencies produced are still low and cannot explain the reasonably high-pitched sound that has occasionally been observed experimentally. Since the robust mechanisms appear to generate only very low frequency sound, infrasonic tracking of the vortices may be warranted.

Hardin, Jay C.↗