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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Heterogeneous conversion of N2O5 to HNO3 on background stratospheric aerosols - Comparisons of model results with data

The effects of heterogeneous processing by a parameterized lower stratospheric sulfate aerosol layer on model calculations were examined using a 2D photochemical model. Model results were compared with zonally averaged LIMS data on HNO3 and NO2 and in situ measurements of NO, NO(y), and ClO, taken by the ER-2 aircraft. The results obtained are contradictory: some comparisons favor heterogeneous chemistry, and some do not. It is suggested that the assumptions made to parameterize the sulfate aerosol chemistry result in a rate of heterogeneous processing that is too vigorous.

Considine, David B.↗
NASA NTRS1994

Effects of a polar stratosphere cloud parameterization on ozone depletion due to stratospheric aircraft in a two-dimensional model

A parameterization of Type 1 and 2 polar stratospheric cloud (PSC) formation is presented which is appropriate for use in two-dimensional (2-D) photochemical models of the stratosphere. The calculations of PSC frequency of occurrence and surface area density uses climatological temperature probability distributions obtained from National Meteorological Center data to avoid using zonal mean temperatures, which are not good predictors of PSC behavior. The parameterization does not attempt to model the microphysics of PSCs. The parameterization predicts changes in PSC formation and heterogeneous processing due to perturbations of stratospheric trace constituents. It is therefore useful in assessing the potential effects of a fleet of stratospheric aircraft (high speed civil transports, or HSCTs) on stratospheric composition. the model calculated frequency of PSC occurrence agrees well with a climatology based on stratospheric aerosol measurement (SAM) 2 observations. PSCs are predicted to occur in the tropics. Their vertical range is narrow, however, and their impact on model O3 fields is small. When PSC and sulfate aerosol heterogeneous processes are included in the model calculations, the O3 change for 1980 - 1990 is in substantially better agreement with the total ozone mapping spectrometer (TOMS)-derived O3 trend than otherwise. The overall changes in model O3 response to standard HSCT perturbation scenarios produced by the parameterization are small and tend to decrease the model sensitivity to the HSCT perturbation. However, in the southern hemisphere spring a significant increase in O3 sensitivity to HSCT perturbations is found. At this location and time, increased PSC formation leads to increased levels of active chlorine, which produce the O3 decreases.

Considine, David B.↗
NASA NTRS1990

Effects of atmospheric transport on column abundances of nitrogen and chlorine compounds in the arctic stratosphere

In the absence of heterogeneous processes, distributions of NO(y), HNO3, Cl(x) and HCl in the polar winter stratosphere should be determined by transport. A model simulating distributions of these species in the arctic for January and February 1989 is developed using observed fields of potential vorticity and potential temperature. Comparison of model results with column measurements from the DC-8 indicates conversion of NO(x) to HNO3, condensation of HNO3, conversion of HCl to CINO3, and conversion of HCl plus CINO3 to an unmeasured species. Heterogeneous processes strongly affect abundances of NO(y) and Cl(x) species in the winter arctic stratosphere.

Yatteau, John H.↗
DOE OSTI2022

Liquid-Phase Effects on Adsorption Processes in Heterogeneous Catalysis

Aqueous solvation free energies of adsorption have recently been measured for phenol adsorption on Pt(111). Endergonic solvent effects of ~1 eV suggest solvents dramatically influence a metal catalyst’s activity with significant implications for the catalyst design. However, measurements are indirect and involve adsorption isotherm models, which potentially reduces the reliability of the extracted energy values. Computational, implicit solvation models predict exergonic solvation effects for phenol adsorption, failing to agree with measurements even qualitatively. In this study, an explicit, hybrid quantum mechanical/molecular mechanical approach for computing solvation free energies of adsorption is developed, solvation free energies of phenol adsorption are computed, and experimental data for solvation free energies of phenol adsorption are reanalyzed using multiple adsorption isotherm models. Explicit solvation calculations predict an endergonic solvation free energy for phenol adsorption that agrees well with measurements to within the experimental and force field uncertainties. Computed adsorption free energies of solvation of carbon monoxide, ethylene glycol, benzene, and phenol over the (111) facet of Pt and Cu suggest that liquid water destabilizes all adsorbed species, with the largest impact on the largest adsorbates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

Transport phenomena of reactive fluid flow in heterogeneous combustion processes.

A previously developed computer program was used to model two transient hybrid combustion processes involving tubes of solid Plexiglas. In the first study, representing combustion of a hybrid rocket, the oxidizing gas was oxygen, and calculations were continued sufficiently long to obtain steady-state values. Systematic variations were made in reaction rate constant, mass flow rate, and pressure, alternatively using constant and temperature dependent regression rate models for the fuel surface. Consistent results were obtained, as is evidenced by the values for the mass function of the reaction product and the flame temperature, for which plots are supplied. In the second study, fire initiation in a duct was studied, with an air mixture as the oxidizing gas. It was demonstrated that a satisfactory flame spread mechanism could be reproduced on the computer. In both of the above applications, the general, transient, two-dimensional conservation equations were represented, together with chemical reactions, solid-fuel interface conditions, and heat conduction in the solid fuel.

Hung, W. S. Y.↗
NASA NTRS1993

A model for heterogeneous chemical processes on the surfaces of ice and nitric acid trihydrate particles

The study presents a model that incorporates the physics and physical chemistry of ice surfaces relevant to polar stratospheric clouds. Surface concentrations of H2O, HCl, HOCl, ClONO2, and N2O5 on ice and nitric acid trihydrate (NAT) crystals are computed, and surface reaction rates and reaction probabilities (sticking coefficients) are determined. For gas pressures of about 10 exp -7 torr and temperatures in the range of 180-200 K, HCl completely coats ice and water-rich NAT surfaces, while HOCl, ClOHO2, and N2O5 may cover 0.01-1 percent of these surfaces. The energy parameters are used to calculate surface temperatures such as adsorption and desorption constants, surface coverages, reaction rate coefficients, surface diffusion coefficients, and reaction probabilities for various species and chemical interactions on ice and NAT surfaces. Implications for chemical processing on polar stratospheric clouds are discussed.

Tabazadeh, Azadeh↗
DOE OSTI2020

Heterogeneous graphics processing unit for scheduling thread groups for execution on variable width SIMD units

A compute unit configured to execute multiple threads in parallel is presented. The compute unit includes one or more single instruction multiple data (SIMD) units and a fetch and decode logic. The SIMD units have differing numbers of arithmetic logic units (ALUs), such that each SIMD unit can execute a different number of threads. The fetch and decode logic is in communication with each of the SIMD units, and is configured to assign the threads to the SIMD units for execution based on such differing numbers of ALUs.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1988

Heterogeneous physicochemistry of the winter polar stratosphere

Present chemical theories of the Antarctic ozone hole assume that heterogeneous reactions involving polar stratospheric clouds (PSCs) are the precursor of springtime ozone depletions. However, none of the theories quantify the rates of proposed heterogeneous processed, and none utilize the extensive data base on PSC's. Thus, all of the theories must be considered incomplete until the heterogeneous mechanisms are properly defined. A unified treatment developed of the cloud related processes, both physical and chemical, and the importance of these processes using observation data is calibrated. The rates are compared competitive heterogeneous processes to place reasonable limits on critical mechanisms such as the denitrification and dechlorination of the polar winter stratosphere. Among the subjects addressed here are the physical/chemical properties of PSC's including their relevant microphysical, optical and compositional characteristics, mass transfer rates of gaseous constituents to cloud particles, adsorption, accommodation and sticking coefficients on cloud particles, time constants for condensation, absorption and other microphysical processes, effects of solubility and vapor pressure on cloud composition, the statistics of cloud processing of chemically active condensible species, rate limiting steps in heterogeneous chemical reactions, and the nonlinear dependence of ozone loss on physical and chemical parameters.

Turco, R. P.↗
NASA NTRS1994

The chemical and radiative effects of the Mount Pinatubo eruption

To clarify the mechanisms leading to effects on stratospheric ozone, time-dependent stratospheric aerosol and gas experiment II (SAGE II) and cryogenic limb array elaton spectrometer (CLAES) aerosol optical extinction data and SAGE II surface area density are used as parameters in a two-dimensional (2-D) zonally averaged chemical radiative transport model. The model was integrated with time from before the eruption through December 1993. The modeled impact on global ozone results from increased rates of heterogeneous reactions on sulfate aerosols and from the increased radiative heating and scattering caused by these aerosols. When the aerosol heating is allowed to modify the temperature distribution, the maximum change calculated in equatorial column ozone is -1.6%. The calculated equatorial temperature change and peak local ozone change in October 1991 are +6K and -4%, respectively. When aerosol heating perturbs the circulation in the model, the maximum change in equatorial column ozone is -6%. Increased heterogeneous processing on sulfate aerosols is calculated to have changed equatorial column ozone in late 1991 by -1.5%. Global column ozone in the model in 1992 and 1993 changed by -2.8% and -2.4%, respectively. The relationship of ozone-controlling processes in the lower stratosphere is altered as well; HO(x) becomes the most important catalytic cycle, followed by ClO(x) and NO(x). This is driven by significant changes in trace gas concentrations. In October 1991, lower stratospheric, equatorial NO(x) decreased by 40%, ClO(x) increased by 60%, and HO(x) increased by 25%. When the effect of heterogeneous chemical processing on sulfate aerosols is combined with aerosol heating, modifying either circulation or temperature, dramatically different ozone fingerprints with time and latitude are predicted. Model-derived changes in the equatorial region in column ozone best represented the observed data when perturbed circulation was combined with heterogeneous chemical effects. However, at high latitudes, the increased ozone production from the strengthening of the mean circulation tends to cancel the heterogeneous reduction of ozone. This is not in good agreement with observed data, especially in 1992 and 1993. When the circulation is held fixed and the temperature allowed to change, and heterogeneous chemical effects are included, the equatorial ozone decrease predicted was too small for 1991. However, the mid- to high-latitude decrease in 1992 and 1993 is in better agreement with observed data.

Kinneson, Douglas E.↗
NASA NTRS1990

Heterogeneous conversion of COF2 to HF in polar stratospheric clouds

It is argued that the reaction COF2 + H2O - 2HF + CO2 should proceed on surfaces of polar stratospheric clouds, based on laboratory evidence for this reaction in condensed phase and on analysis of column observations of HF during the Airborne Arctic Stratospheric Expedition. If the hypothesis is confirmed, observations of COF2 and HF could provide unambiguous indication of heterogeneous processing of polar air, and could help elucidate the influence of heterogeneous chemistry on concentrations of HCl, ClNO3, and chlorine oxide radicals.

Wofsy, Steven C.↗
DOE OSTI2024

Recent Advances in Immobilizing and Benchmarking Molecular Catalysts for Artificial Photosynthesis

Transition metal complexes have been widely used as catalysts or chromophores in artificial photosynthesis. Traditionally, they are employed in homogeneous settings. Despite their functional versatility and structural tunability, broad industrial applications of these catalysts are impeded by the limitations of homogeneous catalysis such as poor catalyst recyclability, solvent constraints (mostly organic solvents), and catalyst durability. Over the past few decades, researchers have developed various methods for molecular catalyst heterogenization to overcome these limitations. Here, in this review, we summarize recent developments in heterogenization strategies, with a focus on describing methods employed in the heterogenization process and their effects on catalytic performances. Alongside the in-depth discussion of heterogenization strategies, this review aims to provide a concise overview of the key metrics associated with heterogenized systems. We hope this review will aid researchers who are new to this research field in gaining a better understanding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Photochemical partitioning of the reactive nitrogen and chlorine reservoirs in the high-latitude stratosphere

The correlated set of measurements in the lower stratosphere from polar missions of the NASA ER-2 is used to derive partitioning of the major components of the reactive nitrogen and inorganic chlorine reservoirs. The results provide a consistent method for comparing distributions, and hence the controlling processes, between different areas of the near-polar regions. Clear evidence of the effects of heterogeneous processes in the atmosphere is found. Values for NO2, ClONO2, N2O5, and Cl2O2 are derived in a simplified steady-state model based on in situ NO, ClO, O3, temperature, and pressure measurements, laboratory-measured reaction rates; and modeled photodissociation rates. Values for the reservoir totals are independently derived from measurements of N2O, organic chlorine, and total reactive nitrogen. The relative abundances of the measured and derived species within the reservoirs are calculated, and the longer-lived species HCl and HNO3 are estimated as the residuals of their respective reservoirs.

Kawa, S. R.↗
DOE OSTI2024

Area-selective deposition of germanium on patterned graphene/monolayer molybdenum disulfide stacks via dipole engineering

Heterogeneous integration of two-dimensional materials and the conventional semiconductor has opened opportunities for next-generation semiconductor devices and their processing. Heterogeneous integration has been studied for economical manufacturing by substrate recycling and novel functionalities by a combination of incommensurate materials. However, utilizing the integration requires controlling locations of the integrated architectures. Here, we show area-selective deposition (ASD) of germanium on the graphene/MoS 2 stack. Ge nucleation precisely occurred on the surfaces of the patterned graphene/MoS 2 stack via dipole engineering. In this study, the growth temperature of ASD of Ge was significantly lower than that based on precursor desorption on SiO 2 . The first-principles calculations revealed that Ge deposited by ASD on the graphene/MoS 2 stack was not affected by charge transfer. This work provides a viable way to utilize atomically thin materials for next-generation semiconductor devices, which can be applicable for “Beyond Moore” and “More Moore” approaches.

2D materials↗
NASA NTRS1977

The nucleation of H2SO4-H2O solution aerosol particles in the stratosphere

The homogeneous- and heterogeneous-heteromolecular nucleation of H2SO4-H2O solution droplets in the stratosphere is investigated and order-of-magnitude nucleation rates are evaluated. The heterogeneous processes considered are nucleation onto soluble particles, flat insoluble surfaces, spherical insoluble particles, and ions. The relative importance of the various nucleation mechanisms is determined for conditions assumed to correspond to 18 km altitude. Under the assumed conditions, the heterogeneous nucleation rate onto insoluble particles is shown to be about 10 to the 69th times larger than the homogeneous nucleation rate and 10 to the 57th times larger than nucleation onto ions.

Hamill, P.↗
NASA NTRS1993

Some aspects of the interaction between chemical and dynamic processes relating to the Antarctic ozone hole

Observational and modeling studies have been conducted to examine the interaction between the chemical and dynamical processes that occur during springtime in the lower stratosphere of the Southern Hemisphere. The temporal evolution of the ozone distribution and the circulation during 1987 is contrasted with that for 1988 as an illustrative example of how dynamical processes and the resulting meteorological conditions modulate the ozone depletion. Concurrently with the observational analysis, an effort was initiated to simulate the ozone depletion during austral spring using a 3D chemical/transport model. The model includes a parameterized representation of the heterogeneous processes thought to be important in this region. The simulation indicates that the inclusion of this additional chemistry, which results in the release of free chlorine and the redistribution of odd nitrogen into reservoir species, reproduces many aspects of the observations.

Eckman, R. S.↗
NASA NTRS1994

Global ozone observations from the UARS MLS: An overview of zonal-mean results

Global ozone observations from the Microwave Limb Sounder (MLS) aboard the Upper Atmosphere Research Satellite (UARS) are presented, in both vertically resolved and column abundance formats. The authors review the zonal-mean ozone variations measured over the two and a half years since launch in September 1991. Well-known features such as the annual and semiannual variations are ubiquitous. In the equatorial regions, longer-term changes are believed to be related to the quasi-biennial oscillation (QBO), with a strong semiannual signal above 20 hPa. Ozone values near 50 hPa exhibit an equatorial low from October 1991 to June 1992, after which the low ozone pattern splits into two subtropical lows (possibly in connection with residual circulation changes tied to the QBO) and returns to an equatorial low in September 1993. The ozone hole development at high southern latitudes is apparent in MLS column data integrated down to 100 hPa, the MLS data reinforce current knowledge of this lower-stratospheric phenomenon by providing a height-dependent view of the variations. The region from 30 deg S to 30 deg N (an area equal to half the global area) shows very little change in the ozone column from year to year and within each year. The most striking ozone changes have occurred at northern midlatitudes, with the October 1992 to July 1993 column values significantly lower than during the prior year. The zonal-mean changes manifest themselves as a slower rate of increase during the 1992/93 winter, and there is some evidence for a lower fall minimum. A recovery occurs during late summer of 1993; early 1994 values are significantly larger than during the two previous winters. The timing and latitudinal extent of the northern midlatitude decreases appear to rule out observed ClO enhancements in the Arctic vortex, with related chemical processing and ozone dilution effects, as a unique cause. Local depletion from ClO-related chemical mechanisms alone is also not sufficient, based on MLS ClO data. The puzzling asymmetric nature of the changes probably requires a dynamical component as an explanation. A combination of effects (including chemical destruction via heterogeneous processes and QBO phasing) apparently needs to be invoked. This dataset will place constraints on future modeling studies, which are required to better understand the source of the observed changes.

Froidevaux, Lucien↗
NASA NTRS1990

Wintertime nitric acid chemistry - Implications from three-dimensional model calculations

A three-dimensional simulation of the evolution of HNO3 has been run for the winter of 1979. Winds and temperatures are taken from a stratospheric data assimilation analysis, and the chemistry is based on Limb Infrared Monitor of the Stratosphere (LIMS) observations. The model is compared to LIMS observations to investigate the problem of 'missing' nitric acid chemistry in the winter hemisphere. Both the model and observations support the contention that a nitric acid source is needed outside of the polar vortex and north of the subtropics. Observations suggest that HNO3 is not dynamically controlled in middle latitudes. The model shows that given the time scales of conventional chemistry, dynamical control is expected. Therefore, an error exists in the conventional chemistry or additional processes are needed to bring the model and data into agreement. Since the polar vortex is dynamically isolated from the middle latitudes, and since the highest HNO3 values are observed in October and November, a source associated solely with polar stratospheric clouds cannot explain the deficiencies in the chemistry. The role of heterogeneous processes on background aerosols is reviewed in light of these results.

Rood, Richard B.↗