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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Molecular Dynamics Simulations of Adhesion at Epoxy Interfaces

The effect of moisture on adhesives used in aerospace applications can be modeled with chemically specific techniques such as molecular dynamics simulation. In the present study, the surface energy and work of adhesion are calculated for epoxy surfaces and interfaces, respectively, by using molecular dynamics simulation. Modifications are made to current theory to calculate the work of adhesion at the epoxy-epoxy interface with and without water. Quantitative agreement with experimental values is obtained for the surface energy and work of adhesion at the interface without water. The work of adhesion agrees qualitatively with the experimental values for the interface with water: the magnitude is reduced 15% with respect to the value for the interface without water. A variation of 26% in the magnitude is observed depending on the water configuration at a concentration of 1.6 wt%. The methods and modifications to the method that are employed to obtain these values are expected to be applicable for other epoxy adhesives to determine the effects of moisture uptake on their work of adhesion.

Frankland, Sarah-Jane V.↗
NASA NTRS1999

The Topography and Basin Deposits of the Equatorial Highlands: A MGS-Viking Synergistic Study

One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as: 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of: 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars. Additional information is contained in the original extended abstract.

Moore, J. M.↗
NASA NTRS1999

Topographic Evaluation of Mars 2001 Candidate Landing Sites: A MGS-Viking Synergistic Study

One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars.

Moore, J. M.↗
NASA NTRS1976

Correction factory techniques for improving aerodynamic prediction methods

A method for correcting discrete element lifting surface theory to reflect given experimental data is presented. Theoretical pressures are modified such that imposed constraints are satisfied while minimizing the changes to the pressures. Several types of correction procedures are presented and correlated; (1) scaling of pressures; (2) scaling of downwash values; and (3) addition of an increment to the downwash that is proportioned to pressure. Some special features are included in these methods and they include: (1) consideration of experimental data from multiple deflection modes, (2) limitation of the amplitudes of the correction factors, and (3) the use of correction factor mode shapes. These methods are correlated for cases involving all three Mach Number ranges using a FORTRAN IV computer program. Subsonically, a wing with an oscillating partial span control surface and a wing with a leading edge droop are presented. Transonically a two-dimensional airfoil with an oscillating flap is considered. Supersonically an arrow wing with and without camber is analyzed. In addition to correction factor methods an investigation is presented dealing with a new simplified transonic modification of the two-dimensional subsonic lifting surface theory. Correlations are presented for an airfoil with an oscillating flap.

Giesing, J. P.↗
DOE OSTI2023

Tuning the surface reactivity of oxides by peroxide species

The Mars–van Krevelen mechanism is the foundation for oxide-catalyzed oxidation reactions and relies on spatiotemporally separated redox steps. Herein, we demonstrate the tunability of this separation with peroxide species formed by excessively adsorbed oxygen, thereby modifying the catalytic activity and selectivity of the oxide. Using CuO as an example, we show that a surface layer of peroxide species acts as a promotor to significantly enhance CuO reducibility in favor of H 2 oxidation but conversely as an inhibitor to suppress CuO reduction against CO oxidation. Together with atomistic modeling, we identify that this opposite effect of the peroxide on the two oxidation reactions stems from its modification on coordinately unsaturated sites of the oxide surface. By differentiating the chemical functionality between lattice oxygen and peroxide, these results are closely relevant to a wide range of catalytic oxidation reactions using excessively adsorbed oxygen to activate lattice oxygen and tune the activity and selectivity of redox sites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hybrid Graphene Ribbon/Carbon Electrodes for High‐Performance Energy Storage

Abstract The utility of supercapacitors for both fixed and portable energy storage would be greatly enhanced if their energy density could be increased while maintaining their high power density, fast charging time, and low cost. This study describes a simple, solution‐phase, scalable modification of carbon materials by a covalently bonded “brush” of hydrogen‐terminated graphene ribbons (GRs) with layer thicknesses of 2–20 nm, resulting in a 20–100 times increase in the areal capacitance of the unmodified electrode surface. On a flat sp 2 carbon surface modified by GRs, the capacitance exceeds 1200 µF cm −2 in 0.1 m H 2 SO 4 due to a distinct type of pseudocapacitance during constant current charge/discharge cycling. Modification of high surface area carbon black electrodes with GRs yields capacitances of 950–1890 F g −1 , power densities >40 W g −1 , and minimal change in capacitance during 1500 charge/discharge cycles at 20 A g −1 . A capacitance of 1890 F g −1 affords an energy density of 318 Wh kg −1 operating at 1.1 V and 590 Wh kg −1 at 1.5 V. The projected energy density of a hybrid GR/carbon supercapacitor greatly exceeds the current 10 Wh kg −1 for commercial supercapacitors and approaches that of lithium ion batteries.

Farquhar, Anna K.↗
DOE OSTI2023

Chemical structure–property relationships in nanocelluloses

Abstract Nanocelluloses, nanoscale cellulosic particles or fibrils, are an appealing class of nanomaterials with enormous potential for sustainable development. They have great promise to target some of the 17 Sustainable Development Goals outlined by the United Nations. Nanocelluloses are derived from the most abundant biopolymer in the world, cellulose, which have multiple hydroxyl groups on their surface, enabling a vast range of chemical modifications. The interplay between the chemical structure and physicochemical properties of nanocelluloses is crucial to engineering the next generation of green, functional nanomaterials. In this review paper, we provide a comprehensive account of the structure–property relationships in nanocelluloses, which may establish the basis for the design of precision bio‐based materials. Chemical modifications of nanocelluloses, including hydrolysis, oxidation, esterification, amidation, and polymer grafting, provide an array of chemical and physical properties that open opportunities in a diverse spectrum of applications. We review how chemical modifications affect the physicochemical properties of nanocelluloses, such as thermal stability, hydrophobicity, and dispersibility in nonpolar media. Understanding nanocellulose chemical structure–property relationships is integral to the development of sustainable material platforms based on the most renewable biopolymer on earth.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Novel nucleocytoplasmic protein O -fucosylation by SPINDLY regulates diverse developmental processes in plants

Here, in metazoans, protein O-fucosylation of Ser/Thr residues was only found in secreted or cell surface proteins, and this post-translational modification is catalyzed by ER-localized protein O-fucosyltransferases (POFUTs) in the GT65 family. Recently, a novel nucleocytoplasmic POFUT, SPINDLY (SPY), was identified in the reference plant Arabidopsis thaliana to modify nuclear transcription regulators DELLAs, revealing a new regulatory mechanism for gene expression. The paralog of AtSPY, SECRET AGENT (SEC), is an O-link-N-acetylglucosamine (GlcNAc) transferase (OGT), which O-GlcNAcylates Ser/Thr residues of target proteins. Both AtSPY and AtSEC are tetratricopeptide repeat-domain-containing glycosyltransferases in the GT41 family. The discovery that AtSPY is a POFUT clarified decades of miss-classification of AtSPY as an OGT. SPY and SEC play pleiotropic roles in plant development, and the interactions between SPY and SEC are complex. SPY-like genes are conserved in diverse organisms, except in fungi and metazoans, suggesting that O-fucosylation is a common mechanism in modulating intracellular protein functions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

A family of tubular pili from harmful algal bloom forming cyanobacterium Microcystis aeruginosa

Cyanobacteria are vital photosynthetic prokaryotes, but some form harmful algal blooms (cyanoHABs) that disrupt ecosystems and produce toxins. The mechanisms by which these blooms form have yet to be fully understood, particularly the role of extracellular components. Here, we present a 2.4 Å cryo-EM structure of a pilus, termed the cyanobacterial tubular (CT) pilus, found in the cyanoHAB-forming Microcystis aeruginosa. The pilin exhibits a unique protein fold, forming a tubular pilus structure with tight, double-layer anti-parallel β-sheet interactions. We show that CT pili are essential for buoyancy by facilitating the formation of micro-colonies, which increases drag force and prevents sinking. The CT pilus surface is heavily glycosylated with ten monosaccharide modifications per pilin. Furthermore, CT pili can enrich microcystin, potentially enhancing cellular resilience, and co-localize with iron-enriched extracellular matrix components. Thus, we propose that this pilus plays an important role in the proliferation of cyanoHABs. This just discovered pilus family appears to be widely distributed across several cyanobacterial orders. Our structural and functional characterization of CT pili provide insights into cyanobacterial cell morphology, physiology, and toxin interactions, and identify potential targets for disrupting bloom formation.

Cryoelectron microscopy↗
DOE OSTI2019

A master equation simulation for the • OH + CH 3 OH reaction

A combined (fixed-J) two-dimensional master-equation / semi-classical transition state theory / variational Rice-Ramsperger-Kassel-Marcus (2DME/SCTST/vRRKM) approach has been used to compute reaction rate coefficients of •OH with CH 3 OH over a wide range of temperatures (10 - 2500 K) and pressures (10 -1 -10 4 Torr) based on a potential energy surface that has been constructed using a modification of the HEAT thermochemical protocol. The calculated results show that the title reaction is nearly pressure-independent when T > 250 K, but depends strongly on pressure at lower temperatures. Also, the preferred mechanism and rate constants are found to be very sensitive to temperature. The reaction pathway CH 3 OH + • OH → CH 3 O • + H 2 O proceeds exclusively through tunneling at exceedingly low temperatures (T ≤50 K) typical of those established in interstellar environments. In this regime, the rate constant is found to increase with decreasing temperature, which agrees with low-temperature experimental results. The thermodynamically favored reaction pathway CH 3 OH + • OH → • CH 2 OH + H 2 O becomes dominant at higher temperatures (T ≥ 200 K), such as those found in Earth’s atmosphere as well as combustion environments. By modifying the ab initio barrier heights slightly, experimental rate constants from 200 to 1250 K can be satisfactorily reproduced.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopy

The spatial distribution oftransition metal valence states is of broad interest in the microanalysis ofgeological and environmental samples. An example is rock varnish, a naturalmanganese (Mn)-rich rock coating, whose genesis mechanism remains a subjectof scientific debate. We conducted scanning transmission X-ray microscopywith near-edge X-ray absorption fine-structure spectroscopy (STXM-NEXAFS)measurements of the abundance and spatial distribution of different Mnoxidation states within the nano- to micrometer thick varnish crusts. Suchmicroanalytical measurements of thin and hard rock crusts require samplepreparation with minimal contamination risk. Focused ion beam (FIB) slicingwas used to obtain ~100–1000 nm thin wedge-shaped slices of thesamples for STXM, using standard parameters. Yet, while this preparationis suitable for investigating element distributions and structures in rocksamples, we observed artifactual modifications of the Mn oxidation states atthe surfaces of the FIB slices. Our results imply that the preparationcauses a reduction of Mn 4+ to Mn 2+ . We draw attention tothis issue, since FIB slicing, scanning electron microscopy (SEM) imaging,and other preparation and visualization techniques operating in thekilo-electron-volt range are well-established in geosciences, but researchersare often unaware of the potential for the reduction of Mn and possibly otherelements in the samples.

58 GEOSCIENCES↗
NASA NTRS1977

The clouds of Venus. II - An investigation of the influence of coagulation on the observed droplet size distribution

An approximate numerical technique is used to investigate the influence of coagulation, sedimentation and turbulent motions on the observed droplet size distribution in the upper layers of the Venus clouds. If the cloud mass mixing ratio is less than 0.000001 at 250 K or the eddy diffusivity throughout the cloud is greater than 1,000,000 sq cm per sec, then coagulation is unimportant. In this case, the observed droplet size distribution is the initial size distribution produced by the condensation of the droplets. It is found that all cloud models with droplet formation near the cloud top (e.g., a photochemical model) must produce the observed droplet size distribution by condensation without subsequent modification by coagulation. However, neither meteoritic or surface dust can supply sufficient nucleating particles to account for the observed droplet number density. If the cloud droplets are formed near the cloud bottom, the observed droplet size distribution can be produced solely by the interaction of coagulation and dynamics; all information about the initial size distribution is lost. If droplet formation occurs near the cloud bottom, the lower atmosphere of Venus is oxidizing rather than reducing.

Rossow, W. B.↗
NASA NTRS1979

Silicon Solar Cell Process Development, Fabrication and Analysis, Phase 1

Solar cells from RTR ribbons, EFG (RF and RH) ribbons, dendritic webs, Silso wafers, cast silicon by HEM, silicon on ceramic, and continuous Czochralski ingots were fabricated using a standard process typical of those used currently in the silicon solar cell industry. Back surface field (BSF) processing and other process modifications were included to give preliminary indications of possible improved performance. The parameters measured included open circuit voltage, short circuit current, curve fill factor, and conversion efficiency (all taken under AM0 illumination). Also measured for typical cells were spectral response, dark I-V characteristics, minority carrier diffusion length, and photoresponse by fine light spot scanning. the results were compared to the properties of cells made from conventional single crystalline Czochralski silicon with an emphasis on statistical evaluation. Limited efforts were made to identify growth defects which will influence solar cell performance.

Yoo, H. I.↗
NASA NTRS1980

Computerized three-dimensional aerodynamic design of a lifting rotor blade

A three-dimensional, inviscid, full-potential lifting rotor code was used to demonstrate that pressure distributions on both advancing and retreating blades could be significantly improved by perturbing local airfoil sections. The perturbations were described by simple geometric shape functions. To illustrate the procedure, an example calculation was made at a forward flight speed of 85 m/sec (165 knots) and an advance ratio of 0.385. It was found that a minimum of three shape functions was required to improve the pressures without producing undesirable secondary effects in high-speed forward flight on a hypothetical modern rotor blade initially having an NLR-1 supercritical airfoil. Reductions in the shock strength on the advancing blade could be achieved, while simultaneously lessening leading-edge pressure gradients on the retreating blade. The major blade section modifications required were blunting of the upper surface leading edge and some reshaping of the blade's upper surface resulting in moderately thicker airfoils.

Tauber, M. E.↗
NASA NTRS1981

Aerodynamic mission concepts for the Mars sample return mission

Future plans for the continued exploration of Mars call for a sample return mission. This plan proposes bringing a distributed, selected sample of Mars material from several locales on Mars back to earth. The mission options studied to date utilize an extensive number of aerodynamic concepts not previously planned in past planetary exploration programs. These include various modes of orbit modification using atmospheric braking, aeromaneuvering to effect precision surface landing, very low ballistic entry for a network of surface penetrators, low flying hydrazine powered airplanes, balloons, ascent vehicles and direct entry of the samples on return to earth. This paper will discuss the concepts and their feasibility along with technology problems associated with them as surveyed from the reference material. The paper focuses primarily on the aerocapture technique as it relates to Mars orbit modification. Remaining orbit modification techniques are also discussed briefly for comparison.

Cruz, M. I.↗
NASA NTRS1983

A case study of the energy dissipation of the gravity wave field based on satellite altimeter measurements

Wave breaking is proposed as the primary energy dissipation mechanism for the gravity wave field. The energy dissipation rate is calculated based on the statistical model proposed by Longuet-Higgins (1969) with a modification of the breaking criterion incorporating the surface stress according to Phillips and Banner (1974). From this modified model, an analytic expression is found for the wave attenuation rate and the half-life time of the wave field which depend only on the significant slope of the wave field and the ratio of friction velocity to initial wave phase velocity. These expressions explain why the freshly generated wave field does not last long, but why swells are capable of propagating long distances without substantial change in energy density. It is shown that breaking is many orders of magnitude more effective in dissipating wave energy than the molecular viscosity, if the significant slope is higher than 0.01. Limited observational data from satellite and laboratory are used to compare with the analytic results, and show good agreement.

Huang, N. E.↗
NASA NTRS1989

Fiber-Optic Sensor Would Detect Movements Of Shaft

Fiber-optic sensor senses both rotational speed and axial displacement of shaft in motor, pump, or other rotating machine. Does not require magnetic materials, notches, or grooves in shaft. Required modification of shaft is etching or plating surface to make ring black around half circumference and reflective around other half along short length at one end or some other convenient location. Triangular bundle of sending and receiving optical fibers aimed at black/reflective ring on shaft. Frequency and amplitude of output pulses of fiber-optic probe indicates rotational frequency and axial position of shaft.

Roschak, Edmund J.↗