Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “generative diffusion”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Injection mechanisms in a III -nitride light-emitting diode as seen by self-emissive electron microscopy

Here, we report on the investigation of an electrically biased high efficiency green III-nitride light-emitting diode (LED) by electron emission microscopy (EEM) using a low-energy electron microscope (LEEM). The surface of the LED was activated to negative electron affinity via deposition of a submonolayer of Cs. With the illumination column of the LEEM turned off, upon electrical injection of the LED, we directly image the hot electrons generated by eeh Auger-Meitner nonradiative processes that diffuse through the top p-Ga N layer and emit out the surface of the biased LED. By determining the source of emitted electrons using complementary electron emission spectroscopy measurements, EEM allows us to effectively map the carrier density within the LED. Using EEM, we observed nonelectron emitting regions with a density of approximately 3 × 10 8 cm -2 , identified as V-shaped defects (V-defects). This is confirmed through the corresponding dark spots of panchromatic cathodoluminescence measurements of the same sample and by plan-view transmission electron microscopy. The absence of electron emission at the sidewall of the V-defects can be attributed to several factors, including reduced carrier density in the sidewall quantum wells due to carriers traveling fast through the semipolar sidewalls before being injected into the planar quantum wells, the reduced population of hot electrons surviving diffusion through the thicker p-GaN filling in the V-defect before emission onto vacuum, and a smaller Auger-Meitner coefficient for the low In content semipolar sidewall quantum wells. The stronger electron emission observed at the ridges of most V-defects compared to the planar quantum well regions indicates larger local injected carrier densities, confirming that V-defect sidewalls allow for strong lateral carrier injection when compared to the weaker vertical injection away from the V-defect as evidenced by the weaker electron emission intensity away from the V-defects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

SU-E-T-333: Towards Customizable Radiotherapy Enhancement (CuRE) for Prostate Cancer Using Cisplatin Nanoparticles

Purpose: Replacing routinely used brachytherapy spacers with multifunctional ones loaded with cisplatin nanoparticles (CNP), which can be released into the tumor after implantation, could enable customizable radiation boosting to the prostate tumor in addition to chemotherapy effect. This study investigates the feasibility of customizing the intra-tumor biodistribution and corresponding dose enhancement (DEF) over time for the released CNP as a function of nanoparticle size. Methods: Dose enhancement factors (DEF) due to photon-induced emission of photo-/Auger electrons from CNPs were calculated as a function of concentration using previously published analytical calculation method. An experimentally determined diffusion coefficient (D) for 10 nm nanoparticles in mouse tumor model was employed to estimate D for other sizes using the Stoke- Einstein equation. The error function diffusion model in the experimental study was applied to generate the intra-tumor concentration profile for a burst release of CNPs from the spacer over time. The corresponding DEF profiles were then determined for brachytherapy using Pd-103 and I-125 sources. Results: As expected, the generated profiles showed greater DEF over time for smaller CNP sizes at sample distances from the spacer. For example, for a centrally located spacer, clinically significant DEF (> 20%) could be achieved near the tumor periphery (ca. 0.85 cm distance from the spacer for average PCa tumor size) after 20, and 100 days, respectively for CNPs sizes of 2 nm, and 10 nm, using I-125. Meanwhile for Pd-103, clinically significant DEF could be achieved at the same position after 22 and 108 days, respectively, for same size particles. Conclusion: Our preliminary results demonstrate the feasibility of customizing dose enhancement to prostate tumors as a function of spacer location, brachytherapy source type or size of CNPs released from multifunctional spacers. Such an approach could enable customizable radiation boosting to tumor sub-volumes, while minimizing dose to healthy tissues.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Multi-omic Analyses of Extensively Decayed Pinus contorta Reveal Expression of a Diverse Array of Lignocellulose-Degrading Enzymes

Fungi play a key role cycling nutrients in forest ecosystems, but the mechanisms remain uncertain. To clarify the enzymatic processes involved in wood decomposition, the metatranscriptomics and metaproteomics of extensively decayed lodgepole pine were examined by RNA sequencing (RNA-seq) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), respectively. Following de novo metatranscriptome assembly, 52,011 contigs were searched for functional domains and homology to database entries. Contigs similar to basidiomycete transcripts dominated, and many of these were most closely related to ligninolytic white rot fungi or cellulolytic brown rot fungi. A diverse array of carbohydrate-active enzymes (CAZymes) representing a total of 132 families or subfamilies were identified. Among these were 672 glycoside hydrolases, including highly expressed cellulases or hemicellulases. The CAZymes also included 162 predicted redox enzymes classified within auxiliary activity (AA) families. Eighteen of these were manganese peroxidases, which are key components of ligninolytic white rot fungi. The expression of other redox enzymes supported the working of hydroquinone reduction cycles capable of generating reactive hydroxyl radicals. These have been implicated as diffusible oxidants responsible for cellulose depolymerization by brown rot fungi. Finally, enzyme diversity and the coexistence of brown and white rot fungi suggest complex interactions of fungal species and degradative strategies during the decay of lodgepole pine.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Minimizing Cr-Evaporation from Balance Of Plant Components By Utilizing Cost-Effective Alumina-Forming Austenitic Steels

A solid oxide fuel cell (SOFC) is a clean and efficient energy conversion device. The development of intermediate-temperature SOFCs has made it preferable to use metallic interconnects (MICs) to greatly reduce the cost and significantly increase the efficiency compared to ceramic interconnect materials. However, gaseous chromium species will evaporate from the chromium-containing layer formed on the surface of commonly used MICs and balance of plant (BoP) components. Volatile chromium species have been shown to form solid deposits which poison the cathodes of SOFCs, causing drastic cell performance degradation and thereby limiting commercialization. In order to alleviate the Cr poisoning and achieve long-term high performance of SOFC stacks, various Al 2 O 3 -forming austenitic (AFA) stainless steels applied at different temperatures are evaluated in this project. Based on our Phase I results (500 h operation), it is shown that on the AFAs, an alumina-based protective layer forms under high temperature that is invulnerable to water vapor effects and suppresses the diffusion of chromium and manganese which can prevent the generation of spinels on the alloy surface. Therefore, 310S, OC4 and OC5 at 800 °C and 625, OC11 and OC11LZ at 900 °C are selected to be tested in the Phase II long-term operation. From the results, we find that besides the lower Cr evaporation rates and better oxidation resistance of AFAs than benchmark alloys after short-term (500 h) operation, AFAs also possess the sturdy and compact alumina layer after a long-term operation (5000 h). A protective oxide layer is of great importance for the long-term high-temperature operation of structural materials. The high-temperature oxidation behavior of AFAs and commercial 310S and 625 alloys in Air + 10% H 2 O at 800 °C and 900 °C is systematically investigated. Severe breakaway oxidation and minor spallation are observed for the 310S and 625 after the long-term operation, while the AFAs show high oxidation resistance. It is found that the formation of a continuous alumina layer could greatly prevent the volatilization of chromium vapors. In addition, the corresponding evolving models are discussed. Chromium evaporation from BoP components in high-temperature environment could severely deteriorate the electrochemical performance of SOFC. Several methods were applied to evaluate the Cr evaporation rates of BoP after 500 h exposure at 800 °C to 900 °C in air with 10% H 2 O. An optimal method was designed to exclude the effect of silicon (Si) deposits from quartz tube and sodium (Na) deposits from the sodium carbonate on the oxidation process and the chemical interaction between Cr gaseous species and alumina tube which could provide further quantitative correlation of the evaporated Cr species quantities and degradation rates of SOFC. Based on the great performance of AFAs after long-term operation, AFAs are assembled with Anode-supported cells (ASC) to investigate the the Cr deposition of anode-supported cell under a constant current density of 0.5 A cm -2 at 800 °C with AFA alloys compared with commercial alloys. In addition, the anodic and cathodic processes are deconvoluted by distribution of relaxation times (DRT) method which are comprehensively discussed. It is found out that the voltage exhibited a slight decrease of 5.09 % and 1.54 % in the presence of OC11 and OC11LZA alloy, respectively. However, a considerable decrease of 22.14 % and 12.06 % was determined in the presence of 310S and 625 alloy, respectively. AFAs possessing the low-cost, low Cr evaporation rates and the high oxidation resistance will make it of great potential to replace the existing BoP components.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2025

Templates for Risk Informed Assurance with Curvature Embeddings (TRACE)

We investigate recovery of geometric structure from networks embedded in manifolds with spatially varying curvature, extending the constant-curvature framework of Lubold et al. (2023). Our work supports cascade risk assessment in critical infrastructure through the Templates for Risk-informed Assurance with Curvature Embeddings (TRACE) framework. Simulations on a bi-modal Gaussian surface show that constant-curvature methods yield weighted averages shaped by clique patterns, while hierarchical clustering identifies distinct regimes. Localized estimation, however, reveals boundary contamination in transitional regions. To address heterogeneity, we develop distance metrics for graphs with edge and node features, proving their metric validity, and validate them via deterministic graph generation from canonical tilings. We further propose a diffusion-based anomaly detection approach that treats networks as glued manifolds, using curvature discontinuities to detect structural anomalies. Employing the carré-du-champ operator and scalar curvature, we achieve robust anomaly discrimination, demonstrated on the Singapore Water Treatment (SWaT) dataset with joint network-traffic and sensor features. Integration with TRACE reveals how curvature shapes cascade dynamics: positive curvature impedes, while negative curvature accelerates propagation. This geometric perspective provides interpretable risk metrics and visualization tools for critical infrastructure managers. While full validation remains ongoing, our contributions establish a rigorous foundation for geometric analysis of network resilience and cascade vulnerability.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

GALAXY OUTFLOWS WITHOUT SUPERNOVAE

High surface density, rapidly star-forming galaxies are observed to have ≈50–100 km s{sup −1} line of sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae. We find that such motions lead to strong global outflows in the highly compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds ≈35 km s{sup −1}, as occurs in the dense disks that have star-formation rate (SFR) densities above ≈0.1 M{sub ⊙} yr{sup −1} kpc{sup −2}. These outflows are triggered by a thermal runaway, arising from the inefficient cooling of hot material coupled with successive heating from turbulent driving. Thus, even in the absence of stellar feedback, a critical value of the SFR density for outflow generation can arise due to a turbulent heating instability. This suggests that in strongly self-gravitating disks, outflows may be enhanced by, but need not caused by, energy input from supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Investigation of the Ignition and Burning of Materials in Space Cabin Atmospheres. Part 2: Ignition of a Combustible Mixture by a Hot Body with the Effects of Gravity

The ignition of a combustible gas mixture by a hot cylinder under the effect of a gravity field for steady state conditions is examined. For this purpose a horizontal cylinder is considered with gravity as a parameter together with a finite chemical reacting flow generated by free convection with the additional effect of diffusion. Both mass transfer and zero mass transfer cases are considered. By defining an ignition criterion the surface temperature and species are obtained from the analysis as a function of the gravity field. It is supposed that at the point of ignition the heat evolved in the gas is sufficiently high to attain a sustained combustion without any energy from the hot cylinder.

Lew, H. G.↗
NASA NTRS1972

Thermal property measurements on lunar material returned by Apollo 11 and 12 missions.

Measurement of thermal diffusivity on Apollo 11 type A and type C samples in the temperature range between 150 and 440 K under atmospheric pressure. Thermal diffusivity of type C material is lower and less temperature-dependent than type A material. Both types of samples exhibit lower thermal diffusivities than nonporous terrestrial basalt. The rate of heat generation of Apollo 11 and 12 samples was calculated from the concentrations of radioactive elements: potassium, thorium, and uranium. Apollo 11 crystalline rocks show an average rate of heat generation which is not significantly different from terrestrial basalt. The Th/U ratio does not differ greatly from chondritic and terrestrial averages.

Horai, K.-I.↗
NASA NTRS1975

Radiative equilibrium in a rectangular enclosure bounded by gray walls

Two-dimensional temperature and heat-flux distributions are calculated for an absorbing-emitting gray medium at radiative equilibrium in a rectangular enclosure. The bounding walls are gray and diffuse with arbitrary surface-temperature distributions, and heat generation may take place inside the medium. As a first approximation, the problem is solved for optically thick systems (differential approximation). These results are subsequently improved by the introduction of a number of geometrical parameters to yield good accuracy for all optical thicknesses. As examples, two cases are discussed in detail: (1) uniform heat generation in a black enclosure, and (2) an enclosure with one gray surface at constant temperature. Comparison with some numerical solutions generated by Hottel's /Hottel and Cohen (1958) and Einstein (1963)/ zonal method shows excellent agreement.

Modest, M. F.↗
NASA NTRS1981

Elemental composition of aerosols in fourteen experiments of the Cloud Condensation Nuclei Workshop

Aeosols were collected with two Ci impactors and analyzed with proton induced X-ray emission (PIXE) for chemical composition and to detect if contamination was present. One of the impactors sampled the generated aerosols; the other impactor sampled droplets from a diffusion cloud chamber. The purpose of the experiments was to test the feasibility of a study of the transfer of chemical elements from the fine particle sizes to the coarse particle sizes, after CCN are activated and cloud droplets are formed. The data indicated that sulfur-containing aerosols did exhibit the expected transfer.

Mach, W. H.↗
NASA NTRS1987

Electric discharge synthesis of HCN in simulated Jovian atmospheres

Corona discharge is presently considered as a possible source of the HCN detected in the Jovian atmosphere at 2.2 x 10 to the -7th moles/sq cm column density, for the cases of gas mixtures containing H2, CH4, and NH3, with H2/CH4 ratios from 4.4 to 1585. A 3:1 ratio of corona discharge to lightning energy similar to that of the earth is applied to Jupiter. Depending on the lightning energy available on Jupiter and the eddy diffusion coefficients in the synthesis region, HCN column densities generated by corona discharge could account for about 10 percent of the HCN observed.

Stribling, Roscoe↗
NASA NTRS1989

Hydrogen line and continuum emission in young stellar objects. II - Theoretical results and observational constraints

Theoretical results for H I emission from YSOs are compared with available observations. IR line and radio continuum properties have been gathered for 29 objects that include a number of T Tau stars, several emission-line stars with IR excesses, and many heavily obscured luminous YSOs. The present excitation model can account for the observed Brackett line and radio continuum fluxes of YSOs with luminosities of 20-100,000 solar luminosities. It is argued that the observed Br-alpha line and 6-cm free-free continuum emissions are best explained in terms of a core-halo structure. The small core (ranging from r less than about 30 AU for a 10,000-solar luminosity YSO to r less than about 0.2 AU for a 10-solar luminosity YSO) is responsible for generating the strong IR line fluxes, while the surrounding diffuse halo dominates the 6-cm emission.

Alonso-Costa, Jose L.↗
NASA NTRS1993

The effect of Na vapor on the Na content of chondrules

Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasibility. The Knippa basalt, a MgO-rich alkali olivine basalt with a melting temperature of 1325 +/- 5 C and a Na2O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas-mixing furnace with the fO2 controlled by a CO/CO2 gas mixture and fixed at the I-W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 C - 1350 C) for duration of up to 72 h without a Na-rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 C for 16 h in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry analysis of NaCl determined the P(sub Na) for these experimental conditions to be in the 10(exp -6) atm range. This value is considered high for nebula conditions but is still plausible for non-canonical environments. In these trials the Na2O content of the glass was maintained or in some cases increased; Na2O values ranged from 2.62% wt to 4.37% wt. The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatile Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the P(sub Na) generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.

Lewis, R. Dean↗
NASA NTRS1978

Polycrystalline or amorphous semiconductor photovoltaic device having improved collection efficiency

A body of semiconductor material having a first surface and a second surface spaced from the first surface includes a first layer along the first surface, a second layer along the second surface, a third layer between and contiguous to the first and second layers. The third layer is of a conductivity type opposite that of the first and second layers so as to form first and second P-N junctions respectively therebetween. The thickness of the third layer is at least twice the minority carrier diffusion length of the semiconductor material, so that carriers generated within the third layer have a high probability of being collected by one of the P-N junctions. The body includes means for electrically connecting the first and second P-N junctions and means for transferring the carriers collected at the first P-N junction to a portion of the first surface.

Kressel, Henry↗
NASA NTRS2008

The Foggy EUV Corona and Coronal Heating by MHD Waves from Explosive Reconnection Events

In 0.5 arcsec/pixel TRACE coronal EUV images, the corona rooted in active regions that are at the limb and are not flaring is seen to consist of (1) a complex array of discrete loops and plumes embedded in (2) a diffuse ambient component that shows no fine structure and gradually fades with height. For each of two not-flaring active regions, found that the diffuse component is (1) approximately isothermal and hydrostatic and (2) emits well over half of the total EUV luminosity of the active-region corona. Here, from a TRACE Fe XII coronal image of another not-flaring active region, the large sunspot active region AR 10652 when it was at the west limb on 30 July 2004, we separate the diffuse component from the discrete loop component by spatial filtering, and find that the diffuse component has about 60% of the total luminosity. If under much higher spatial resolution than that of TRACE (e. g., the 0.1 arcsec/pixel resolution of the Hi-C sounding-rocket experiment proposed by J. W. Cirtain et al), most of the diffuse component remains diffuse rather being resolved into very narrow loops and plumes, this will raise the possibility that the EUV corona in active regions consists of two basically different but comparably luminous components: one being the set of discrete bright loops and plumes and the other being a truly diffuse component filling the space between the discrete loops and plumes. This dichotomy would imply that there are two different but comparably powerful coronal heating mechanisms operating in active regions, one for the distinct loops and plumes and another for the diffuse component. We present a scenario in which (1) each discrete bright loop or plume is a flux tube that was recently reconnected in a burst of reconnection, and (2) the diffuse component is heated by MHD waves that are generated by these reconnection events and by other fine-scale explosive reconnection events, most of which occur in and below the base of the corona where they are seen as UV explosive events, EUV blinkers, and type II spicules. These MHD waves propagate across field lines and dissipate, heating the plasma in the field between the bright loops and plumes.

Moore, Ron L.↗
NASA NTRS2008

Precipitation Model Validation in 3rd Generation Aeroturbine Disc Alloys

In support of application of the DARPA-AIM methodology to the accelerated hybrid thermal process optimization of 3rd generation aeroturbine disc alloys with quantified uncertainty, equilibrium and diffusion couple experiments have identified available fundamental thermodynamic and mobility databases of sufficient accuracy. Using coherent interfacial energies quantified by Single-Sensor DTA nucleation undercooling measurements, PrecipiCalc(TM) simulations of nonisothermal precipitation in both supersolvus and subsolvus treated samples show good agreement with measured gamma particle sizes and compositions. Observed longterm isothermal coarsening behavior defines requirements for further refinement of elastic misfit energy and treatment of the parallel evolution of incoherent precipitation at grain boundaries.

Olson, G. B.↗