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At least 469 records · Page 26

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NASA NTRS2012

Space Weathering Products Found on the Surfaces of the Itokawa Dust Particles: A Summary of the Initial Analysis

Surfaces of airless bodies exposed to interplanetary space gradually have their structures, optical properties, chemical compositions, and mineralogy changed by solar wind implantation and sputtering, irradiation by galactic and solar cosmic rays, and micrometeorite bombardment. These alteration processes and the resultant optical changes are known as space weathering [1, 2, 3]. Our knowledge of space weathering has depended almost entirely on studies of the surface materials returned from the Moon and regolith breccia meteorites [1, 4, 5, 6] until the surface material of the asteroid Itokawa was returned to the Earth by the Hayabusa spacecraft [7]. Lunar soil studies show that space weathering darkens the albedo of lunar soil and regolith, reddens the slopes of their reflectance spectra, and attenuates the characteristic absorption bands of their reflectance spectra [1, 2, 3]. These changes are caused by vapor deposition of small (<40 nm) metallic Fe nanoparticles within the grain rims of lunar soils and agglutinates [5, 6, 8]. The initial analysis of the Itokawa dust particles revealed that 5 out of 10 particles have nanoparticle-bearing rims, whose structure varies depending on mineral species. Sulfur-bearing Fe-rich nanoparticles (npFe) exist in a thin (5-15 nm) surface layer (zone I) on olivine, low-Ca pyroxene, and plagioclase, suggestive of vapor deposition. Sulfur-free npFe exist deeper inside (<60 nm) ferromagnesian silicates (zone II). Their texture suggests formation by amorphization and in-situ reduction of Fe2+ in ferromagnesian silicates [7]. On the other hand, nanophase metallic iron (npFe0) in the lunar samples is embedded in amorphous silicate [5, 6, 8]. These textural differences indicate that the major formation mechanisms of the npFe0 are different between the Itokawa and the lunar samples. Here we report a summary of the initial analysis of space weathering of the Itokawa dust particles.

Noguchi, T.↗

NASA NTRS1976

A hybrid computer program for rapidly solving flowing or static chemical kinetic problems involving many chemical species

A hybrid chemical kinetic computer program was assembled which provides a rapid solution to problems involving flowing or static, chemically reacting, gas mixtures. The computer program uses existing subroutines for problem setup, initialization, and preliminary calculations and incorporates a stiff ordinary differential equation solution technique. A number of check cases were recomputed with the hybrid program and the results were almost identical to those previously obtained. The computational time saving was demonstrated with a propane-oxygen-argon shock tube combustion problem involving 31 chemical species and 64 reactions. Information is presented to enable potential users to prepare an input data deck for the calculation of a problem.

Mclain, A. G.↗

DOE OSTI2020

Crack nucleation and growth during dynamic indentation of chemically-strengthened glass

Dynamic point impact loading is a primary cause of fracture of glass screens on mobile devices. An improved understanding of crack initiation and evolution under high-speed indentation could contribute to the development of materials with better performance, but experimental observations are challenging due to the short timescales and limited depth-of-field of optical microscopy. To address this need, we have observed fracture of a chemically-strengthened glass during dynamic indentation using in situ x-ray phase-contrast imaging (XPCI). Median cracks initiate below the surface of the glass, at a depth approximately corresponding to the depth at which the surface residual compressive stress diminishes to zero. These cracks initially propagate at ~10ms –1 , rapidly accelerating to > 100ms –1 . We also observe some evidence for rate-dependent behavior, in that indentation at the lowest rates studied here (below about ~0.15ms –1 ) fails to initiate cracks regardless of the depth of the indentation (up to 18μm), while indentation at higher rates produces median cracks that either arrest or cause complete fracture, depending on the depth of indentation.

36 MATERIALS SCIENCE↗

NASA NTRS1991

Mixing and non-equilibrium chemical reaction in a compressible mixing layer

The effects of compressibility, chemical reaction exothermicity, and non-equilibrium chemical modeling in a reacting plane mixing layer were investigated by means of two dimensional direct numerical simulations. The chemical reaction was irreversible and second order of the type A + B yields Products + Heat. The general governing fluid equations of a compressible reacting flow field were solved by means of high order finite difference methods. Physical effects were then determined by examining the response of the mixing layer to variation of the relevant non-dimensionalized parameters. The simulations show that increased compressibility generally results in a suppressed mixing, and consequently a reduced chemical reaction conversion rate. Reaction heat release was found to enhance mixing at the initial stages of the layer growth, but had a stabilizing effect at later times. The increased stability manifested itself in the suppression or delay of the formation of large coherent structures within the flow. Calculations were performed for a constant rate chemical kinetics model and an Arrhenius type kinetic prototype. The choice of the model was shown to have an effect on the development of the flow. The Arrhenius model caused a greater temperature increase due to reaction than the constant kinetic model. This had the same effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

Steinberger, Craig J.↗

DOE OSTI2024

High-resolution chemical patterns from negative tone resists for the integration of extreme ultraviolet patterns of metal-oxide resists with directed self-assembly of block copolymers

Extreme ultraviolet (EUV) lithography faces significant challenges in designing suitable resist materials that can provide adequate precision, while maintaining economically viable throughput. These challenges in resist materials have led to printing failures and high roughness in EUV patterns, compromising the performance of semiconductor devices. Integrating directed self-assembly (DSA) of block copolymers (BCPs) with EUV lithography offers a promising solution because, while the BCPs register to the EUV-defined chemical guiding pattern, the thermodynamically determined structures of the BCPs automatically rectify defects and roughness in the EUV pattern. Despite the superior resolution of metal-oxide EUV resists (MORs), their application to DSA is limited by the difficulty in converting them into chemical patterns that allow effective transfer of the rectified patterns of DSA films into inorganic materials. To address this challenge, this study introduces a novel strategy for fabricating chemical patterns using hydrogen silsesquioxane (HSQ), a high-resolution negative tone inorganic resist, as a model system for MORs. Initially, a sacrificial Cr pattern is generated from HSQ patterns via reactive ion etching. The sacrificial Cr pattern is converted into a chemical pattern by first grafting a water-soluble polyethylene oxide brush onto the substrate, then wet etching the Cr, and finally grafting nonpolar polystyrene brushes. Assembling polystyrene-block-poly(methyl methacrylate) on these patterns results in structures oriented and registered with the underlying pattern, achieving 24 nm full-pitch resolutions. In conclusion, this approach has the potential to integrate MOR patterns into the DSA process, thereby enabling the generation of high-quality sub-10 nm patterns with high-χ BCPs.

Atomic force microscopy↗

DOE OSTI2021

Fourier-like Thermal Relaxation of Nanoscale Explosive Hot Spots

Hot spots are local regions of high temperature that are widely considered to govern explosive initiation. Hot spot dynamics rests on a delicate balance between heat generation due to chemical reactions and heat loss through thermal conduction, making accurate determinations of the conductivity under extreme conditions a key component of predictive explosive models. We develop here an approach to directly determine the thermal transport properties of explosive hot spots with realistic initial structures through a combination of molecular dynamics (MD) and diffusive heat equation (HEq) modeling. Effective thermal conductivity values are determined by fitting HEq models to MD predictions of long timescale hot spot relaxation. The approach is applied to model hot spots in the molecular crystalline explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) for a range of shock strengths and two limiting cases for impact orientation. Isotropic and anisotropic HEq models yield similar results, despite TATB exhibiting some of the largest and most anisotropic thermal conductivity values for explosive near normal conditions. The conductivity is found to be a strong function of density, which parametrically captures dependence on temperature, pressure, and material state. The associated root-mean-square errors of the fitted HEq models are approximately 5% of MD predicted final equilibrium temperatures. Here, the conductivity values determined here for TATB hot spots are considerably larger than those used in a prior hot spot criticality study, which may significantly impact predictions for critical hot spot sizes. The approach provides a convenient foundation for determining the effective thermal conductivity for hot spot problems in other explosives and directly yields information on reasonable approximations that might be taken in higher-level models for those materials.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Next-generation sequencing dataset of genome-scale CRISPRi in Synechococcus sp. PCC 7002 across seven conditions

A 33,298-member sgRNA library developed for Synechococus sp. PCC 7002 was screened with two replicates across seven growth conditions and sequenced with Illumina NextSeq (paired end, 2x150 bp) for a total of ~700M reads. The original plasmid library and the library after transformation into a dCas9-containing and dCas9-absent strain were also sequenced as a reference for initial sgRNA abundance.

genome- wide screens environmental acclimation spe↗

NASA NTRS1994

On the Dynamics of Computing a Chemically Relaxed Nonequilibrium Flow

In order to gain insights into the strong dependence of numerical solutions on initial data for finite time steps, a set of nonlinear test problems rich enough to capture the behavior of difference schemes were recently identified and the numerical basins of attraction for these problems were computed using commonly used time discretizations in CFD. Our study revealed a wealth of surprisingly nonlinear behavior of numerical schemes that were not observed before, in particular for the implicit time discretizations that are commonly used in CFD. The goal of this work is to apply these tools to study a practical model from non-equilibrium flowfield relaxation. This type of problem arises in chemically nonequilibrium hypersonic flows such as in a shock tube experiment or an expanding nozzle. Here we consider a reacting mixture of (N2, N) for an inviscid one-dimensional steady model. Preliminary numerical results indicate that, aside from the possibility of spurious numerical solutions being introduced by the time discretizations, limitations on the model for physical or accurate solutions may also play a part in the dynamics observed.

Sweby, P. K.↗

DOE OSTI2021

Insight into the Solid Electrolyte Interphase Formation in Bis(fluorosulfonyl)Imide Based Ionic Liquid Electrolytes

The formation of the solid electrolyte interphase (SEI) in an ionic liquid electrolyte of 0.5 m lithium bis(fluorosulfonyl)imide (LiFSI) in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide at high cell voltages (1.7–1.9 V) is investigated in ordered mesoporous carbon (OMC) based Li metal cells using an operando small-angle neutron scattering (SANS) technique coupled with electrochemical impedance spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS). It is demonstrated that discharging the OMC Li metal cells to ≈2 V and holding the cell voltage constant induces a rapid current increase with time, confirming extensive reduction and SEI formation. XPS analysis reveals that LiF is formed at open cell voltage (OCV), which is attributed to the carbenes generated at the lithium negative electrode because of its reaction with EMIm cation diffusing to and initiating the reaction with FSI - anions at the carbon positive electrode. It is confirmed that the chemical reaction at OCV and electrochemical reduction at high cell voltage of the FSI - anion plays a protective role against EMIm cation co-intercalation into the carbon positive electrode during the initial discharge. Operando SANS studies also suggest that slight differences occur in the surface composition and reaction mechanism as a function of cell voltage.

1-ethyl-3- methylimidazolium bis(fluorosulfonyl)im↗

DOE OSTI2020

The “Hole” Story in Ionized Water from the Perspective of Ehrenfest Dynamics

The radiolysis of liquid water and the radiation-matter interactions that happen in aqueous environments are important to the elds of chemistry, materials, and environmental sciences, as well as biological and physiological response to extreme conditions and medical treatments. The initial stage of radiolysis is the ultrafast response, or hole dynamics, that trigger chemical processes within complex energetic landscapes that may include reactivity. A fundamental understanding necessitates the use of theoretical methods that are capable of simulating both ultrafast coherence and non-adiabatic energy transfer pathways. In this work, we carry out an ab initio Ehrenfest dynamic study in order to provide a more complete description of the ultrafast dynamics and reactive events initiated by photoionization of water. Furthermore, after sudden ionization, the range of processes that include hole trapping and transfer, large OH oscillations, proton transfer and subsequent relay, formation of the metastable Zundel complex, and long-lived coherence, are identied and new insight into their driving forces are elucidated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1994

LSENS: A General Chemical Kinetics and Sensitivity Analysis Code for homogeneous gas-phase reactions. Part 1: Theory and numerical solution procedures

LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 1 of a series of three reference publications that describe LENS, provide a detailed guide to its usage, and present many example problems. Part 1 derives the governing equations and describes the numerical solution procedures for the types of problems that can be solved. The accuracy and efficiency of LSENS are examined by means of various test problems, and comparisons with other methods and codes are presented. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions.

Radhakrishnan, Krishnan↗

NASA NTRS1994

LSENS: A General Chemical Kinetics and Sensitivity Analysis Code for homogeneous gas-phase reactions. Part 3: Illustrative test problems

LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 3 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 3 explains the kinetics and kinetics-plus-sensitivity analysis problems supplied with LSENS and presents sample results. These problems illustrate the various capabilities of, and reaction models that can be solved by, the code and may provide a convenient starting point for the user to construct the problem data file required to execute LSENS. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions.

Bittker, David A.↗

NASA NTRS1994

LSENS, a general chemical kinetics and sensitivity analysis code for homogeneous gas-phase reactions. 2: Code description and usage

LSENS, the Lewis General Chemical Kinetics Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 2 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 2 describes the code, how to modify it, and its usage, including preparation of the problem data file required to execute LSENS. Code usage is illustrated by several example problems, which further explain preparation of the problem data file and show how to obtain desired accuracy in the computed results. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions. Part 1 (NASA RP-1328) derives the governing equations describes the numerical solution procedures for the types of problems that can be solved by lSENS. Part 3 (NASA RP-1330) explains the kinetics and kinetics-plus-sensitivity-analysis problems supplied with LSENS and presents sample results.

Radhakrishnan, Krishnan↗

NASA NTRS1994

LSENS, A General Chemical Kinetics and Sensitivity Analysis Code for Homogeneous Gas-Phase Reactions: Code Description and Usage - Part 2

LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part II of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part II describes the code, how to modify it, and its usage, including preparation of the problem data file required to execute LSENS. Code usage is illustrated by several example problems, which further explain preparation of the problem data file and show how to obtain desired accuracy in the computed results. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions. Part I (NASA RP-1328) derives the governing equations and describes the numerical solution procedures for the types of problems that can be solved by LSENS. Part III (NASA RP-1330) explains the kinetics and kinetics-plus-sensitivity-analysis problems supplied with LSENS and presents sample results.

Radhakrishnan, Krishnan↗

NASA NTRS1994

Theoretical Basis for Estimated Test Times and Conditions for Drop Tower and Space-Based Droplet Burning Experiments With Methanol and N-Heptane

In order to develop an extensive envelope of test conditions for NASA's space-based Droplet Combustion Experiment (DCE) as well those droplet experiments which can be performed using a drop tower, the transient vaporization and combustion of methanol and n-heptane droplets were simulated using a recently developed fully time-dependent, spherically symmetric droplet combustion model. The transient vaporization of methanol and n-heptane was modeled to characterize the instantaneous gas phase composition surrounding the droplet prior to the introduction of an ignition source. The results for methanol/air showed that the entire gas phase surrounding a 2 mm methanol droplet deployed in zero-g .quickly falls outside the lean flammability limit. The gas phase surrounding an identically-sized n-heptane droplet, on the other hand, remains flammable. The combustion of methanol was then modeled considering a detailed gas phase chemical kinetic mechanism (168 steps, 26 species) and the effect of the dissolution of flame-generated water into the liquid droplet. These results were used to determine the critical ignition diameter required to achieve quasi-steady droplet combustion in a given oxidizing environment. For droplet diameters greater than the critical ignition diameter, the model predicted a finite diameter at which the flame would extinguish. These extinction diameters were found to vary significantly with initial droplet diameter. This phenomenon appears to be unique to the transient heat transfer, mass transfer and chemical kinetics of the system and thus has not been reported elsewhere to date. The extinction diameter was also shown to vary significantly with the liquid phase Lewis number since the amount of water present in the droplet at extinction is largely governed by the rate at which water is transported into the droplet via mass diffusion. Finally, the numerical results for n-heptane combustion were obtained using both 2 step and 96 step semi-emperical chemical kinetic mechanisms. Neither mechanism exhibited the variation of extinction diameter with initial diameter.

Marchese, Anthony J.↗

NASA NTRS1980

Numerical simulation of advection fog formation on multi-disperse aerosols due to combustion-related pollutants

The effects of multi-disperse distribution of the aerosol population are presented. Single component and multi-component aerosol species on the condensation/nucleation processes which affect the reduction in visibility are described. The aerosol population with a high particle concentration provided more favorable conditions for the formation of a denser fog than the aerosol population with a greater particle size distribution when the value of the mass concentration of the aerosols was kept constant. The results were used as numerical predictions of fog formation. Two dimensional observations in horizontal and vertical coordinates, together with time-dependent measurements were needed as initial values for the following physical parameters: (1)wind profiles; (2) temperature profiles; (3) humidity profiles; (4) mass concentration of aerosol particles; (5) particle size distribution of aerosols; and (6) chemical composition of aerosols. Formation and dissipation of advection fog, thus, can be forecasted numerically by introducing initial values obtained from the observations.

Hung, R. J.↗

DOE OSTI2021

Cellular remains in a ~3.42-billion-year-old subseafloor hydrothermal environment

Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth’s earliest microbial habitats. Though the site of life’s emergence continues to be debated, evidence of early life provides insights into its early evolution1. Here we present our discovery of exceptionally well-preserved ~3.40-billion-years-old carbonaceous filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt (BGB) in South Africa. The distribution of the microfossils in growth position on the walls of the initial conduits created by low- temperature hydrothermal fluid and their morphological and chemical characteristics as investigated over a range of scales, are consistent with an assemblage of methanogens that thrived in an ultramafic volcanic substrate.

Cavalazzi, Barbara↗

NASA NTRS2004

Environmental Remediation Technologies Derived from Space Industry Research

Beginning in the 1950s and 1960s, an abundance of effort and initiative was focused on propelling the space industry outward for planetary exploration and habitation. During these early years, the push to take space science to new levels indirectly contributed to the evolution of another science field that would not fully surface until the early 1980s, environmental remediation. This field is associated with the remediation or cleanup of environmental resources such as groundwater, soil, and sediment. Because the space-exploration initiative began prior to the establishment of the U.S. Environmental Protection Agency (EPA) in December of 1970, many NASA Centers as well as space-related support contractors allowed for the release of spent chemicals into the environment. Subsequently, these land owners have been directed by the EPA to responsibly initiate cleanup of their impacted sites. This paper will focus on the processes and lessons learned with the development, testing, and commercialization initiatives associated with four remediation technologies. The technologies include installation techniques for permeable reactive barriers (PRBs), the use of ultrasound to improve long-term performance of PRBs, emulsified zero-valent iron for product-level solvent degradation, and emulsion technologies for application to metal and polychlorinated biphenyl contaminated media. Details of the paper cover technology research, evaluation, and testing; contracts and grants; and technology transfer strategies including patenting, marketing, and licensing.

Quinn, Jacqueline↗