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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud

A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.

Datta, Saswati↗
NASA NTRS1994

Quantum state transfer in double-quantum-well devices

A Monte Carlo simulation of double-quantum-well (DQW) devices is presented in view of analyzing the quantum state transfer (QST) effect. Different structures, based on the AlGaAs/GaAs system, were simulated at 77 and 300 K and optimized in terms of electron transfer and device speed. The analysis revealed the dominant role of the impurity scattering for the QST. Different approaches were used for the optimization of QST devices and basic physical limitations were found in the electron transfer between the QWs. The maximum transfer of electrons from a high to a low mobility well was at best 20%. Negative differential resistance is hampered by the almost linear rather than threshold dependent relation of electron transfer on electric field. By optimizing the doping profile the operation frequency limit could be extended to 260 GHz.

Jakumeit, Jurgen↗
NASA NTRS1974

Free-free absorption of infrared radiation in collisions of electrons with neutral rare-gas atoms

A relationship between the inverse bremsstrahlung absorption cross section and the electron neutral momentum transfer cross section has been utilized to determine the infrared free-free continuum absorption coefficient for the negative ions of helium, neon, argon, krypton, and xenon. The values of the momentum transfer cross section for this calculation have been obtained from experimental measurements. Analytical expressions for the absorption coefficient have also been developed. From the results of this calculation, it is possible to determine the absorption coefficient per unit electron density per neutral atom for temperatures in the range from 2500 to 25,000 K. The results are compared with those from tabulations of previous calculations and those computed from theoretical values of the phase shifts for the elastic scattering of electrons by neutral atoms.

Stallcop, J. R.↗
DOE OSTI2023

Structure of Rhizobium sp. 4-9 histamine dehydrogenase and analysis of the electron transfer pathway to an abiological electron acceptor

Histamine dehydrogenase from the gram-negative bacterium Rhizobium sp. 4-9 (HaDHR) is a member of a small family of dehydrogenases containing a covalently attached FMN, and the only member so far identified to date that does not exhibit substrate inhibition. Here, in this study, we present the 2.1 Å resolution crystal structure of HaDHR. This new structure allowed for the identification of the internal electron transfer pathway to abiological ferrocene-based mediators. Alanine 437 was identified as the exit point of electrons from the Fe 4 S 4 cluster. The enzyme was modified with a Ser436Cys mutation to facilitate covalent attachment of a ferrocene moiety. When modified with Fc-maleimide, this new construct demonstrated direct electron transfer from the enzyme to a gold electrode in a histamine concentration-dependent manner without the need for any additional electron mediators.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Observations Show Charge Density of Volcanic Plumes is Higher Than Thunderstorms

We analyze slow electric field change and lightning mapping measurements to provide insight into the characteristics of volcanic lightning and the associated implications on charging processes and the charge structure of a Vulcanian eruption plume. Data were obtained during a multi-instrumental field campaign at Sakurajima volcano in 2015 when the Showa crater was active. We combine the electric field change and lightning mapping data from one explosive eruption on June 6, 2015 to identify individual flashes. From this, we interpret the flash type and polarity. In addition, the long-time constant of the electric field change instrument allowed measurement of the quasi-static field associated with charge separation in the eruption plume. We find that both intracloud and cloud-to-ground discharges occurred, and the polarity of cloud-to-ground discharges were all negative. The quasi-static field measurement showed the plume carried a net negative charge. We calculate both the total charge transferred by cloud-to-ground discharges and the net charge density of the eruption plume. We find that cloud-to-ground discharges transfer an average of –0.41C per flash and the net charge density was –33C/ km 3 . Here, the percent error is at least 200%, due to uncertainty in the antenna gain. We show that these estimates are consistent with lightning that is 100 m in length. Further, the average flash rate during the first 8 s following the onset of eruption was five flashes per second. After that time, the flash rate abruptly decreased, which may be related to the end of gas-thrust forcing.

58 GEOSCIENCES↗
DOE OSTI2024

Imaging interfacial topography with coherent x-ray reflectivity

The use of coherent x-ray reflectivity to image interfaces is illustrated using model calculations for three cases: a thin film, a semi-infinite substrate, and a coherently strained epitaxial thin film. The intensities and phases of the coherent scattering signals are calculated based on a fully atomistic model (where the phases are assumed to have been recovered by a phasing algorithm). Here, we describe the characteristics of the effective density that are obtained by direct inverse Fourier transformation of the complex structure factors, using a window function to define the data range. These effective densities include significant artifacts like oscillations and negative values derived from the finite vertical momentum transfer of the window function. Two approaches are described to extract the surface topography from the effective densities for three-dimensional visualization: (i) multiplying the effective density by a phase factor and (ii) analyzing the data as a hybrid structure factor F(x, Q z ). The explicit surface sensitivity and specificity of measurements is illustrated when the film or substrate Bragg peaks are excluded. These considerations show that images of interfacial topography can be obtained using currently available experimental capabilities with parameters corresponding to epitaxial thin films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

On the magnetic mirroring as the basic cause of parallel electric fields

Among the different proposed mechanisms for generating parallel electric fields, magnetic mirroring of charged particles seems to be the most plausible. In the present paper, it is suggested that magnetic mirroring is the basic cause of parallel electric fields in the magnetosphere and that the magnetic mirroring effect may be able to form the basis of an auroral theory that can remove a major portion of the ambiguity of observations. In the model proposed, the parallel electric field is due to a magnetic confinement of a negatively charged hot collision-free plasma. A transfer of electron gyroenergy into wave energy tends to weaken this confinement; if this energy transfer becomes too strong, the parallel potential gradient will break down. Hence, from this model, in contrast to certain other models of parallel electric fields, only a small fraction of the total auroral particle energy may be expected to be transformed into electromagnetic wave energy during the acceleration process.

Lennartsson, W.↗
NASA NTRS1991

An observational and theoretical study of highly supercooled altocumulus

The microphysics of two altocumulus clouds sampled at a temperature of about -30 C through the NCAR King Air aircraft and coincident lidar has been characterized. The clouds are structurally similar to stratocumulus and have extensive cloudtop entrainment, a capping temperature inversion, and a dry layer above. Microphysical and radiative properties of both clouds have been modeled numerically. When entrainment effects are incorporated in the model, calculations of droplet concentration and mean diameter profiles compare favorably with the measurements. Radiative transfer calculations indicate that radiative cooling causes sufficient negative buoyancy in cloudtop parcels for producing convective instability and reproducing the observed downdraft velocities. It is shown that entrainment of warmer, drier air near a cloudtop counteracts the radiatively induced negative buoyancy in the downdrafts.

Heymsfield, Andrew J.↗
NASA NTRS2001

ISS And Space Environment Interactions Without Operating Plasma Contactor

The International Space Station (ISS) will be the largest, highest power spacecraft placed in orbit. Because of this the design of the electrical power system diverged markedly from previous systems. The solar arrays will operate at 160 V and the power distribution voltage will be 120 V. The structure is grounded to the negative side of the solar arrays so under the right circumstances it is possible to drive the ISS potential very negative. A plasma contactor has been added to the ISS to provide control of the ISS structure potential relative to the ambient plasma. The ISS requirement is that the ISS structure not be greater than 40 V positive or negative of local plasma. What are the ramifications of operating large structures with such high voltage power systems? The application of a plasma contactor on ISS controls the potential between the structure and the local plasma, preventing degrading effects. It is conceivable that there can be situations where the plasma contactor might be non-functional. This might be due to lack of power, the need to turn it off during some of the build-up sequences, the loss of functionality for both plasma contactors before a replacement can be installed, similar circumstances. A study was undertaken to understand how important it is to have the contactor functioning and how long it might be off before unacceptable degradation to ISS could occur. The details of interaction effects on spacecraft have not been addressed until driven by design. This was true for ISS. If the structure is allowed to float highly negative impinging ions can sputter exposed conductors which can degrade the primary surface and also generate contamination due to the sputtered material. Arcing has been known to occur on solar arrays that float negative of the ambient plasma. This can also generate electromagnetic interference and voltage transients. Much of the ISS structure and pressure module surfaces exposed to space is anodized aluminum. The anodization thickness is very thin to provide the required solar absorptance and emittance. For conditions where ISS structure can charge negative a large percentage of the array voltage, the dielectric strength of this layer is low, and dielectric breakdown (arcing) can occur. The energy stored capacitively in the structure can be delivered to the arc. The mechanisms by which this energy is delivered and how much of the energy is available hasn't been fully quantified. Questions have been raised regarding the possibility of whether a sustained arc might result due to current collected by the solar arrays from local plasma. It was postulated that even if dielectric breakdown didn't occur, impacts due to micrometeoroids and space debris could penetrate thin layers of dielectric on ISS and initiate an arc due to the coupling provided by the dense local plasma produced by the impact. This was proven in experiments conducted jointly by MSFC and Auburn University. A target chamber with a simulated ionospheric plasma and a biased, anodized aluminum plate and a 1-microfarad capacitor was used. The plate was then impacted by 75-micron particles accelerated to orbital velocity. Arc discharges were sustained for higher voltages but a threshold appears below which no discharge was initiated. Most items without an exposed power system will float electrically near the local plasma potential. This is true of the Space Shuttle, an Astronaut on EVA, and similar items. The structure of ISS might be at a large negative voltage. Therefore, capacitively stored energy can be transferred during docking, installing external boxes and equipment and Astronaut contact with ISS structure. The circumstances of when this can happen and the resulting effects are evaluated in this study. Also, a crewmember on EVA might be in the vicinity of an arc. All safety aspects of such an encounter including charging, molten particles from the arc site and EMI have been evaluated. This paper will report on the total results of this study focussed on the 4A configuration, scheduled to be complete in November, 2000. Interactions such as arcing, debris induced arcs, sustained arcs, sputtering, contamination from sputtering and arcing, docking interactions and Astronaut safety issues will all be addressed.

Carruth, M. R., Jr.↗
NASA NTRS2008

Solid-State Lighting Module (SSLM)

The project's goal was to build a light-emitting-diode (LED)-based light fixture that is identical in fit, form, and function to the existing International Space Station (ISS) General Luminaire Assembly (GLA) light fixture and fly it on the ISS in early FY 2008 as a Station Detailed Test Objective (SDTO). Our design offers the following strengths: proven component hardware: Our design uses components flown in other KSC-developed hardware; heat path thermal pad: LED array heat is transferred from the circuit board by silicon pad, negating the need for a cooling fan; variable colorimetry: The output light color can be changed by inserting different LED combinations.

Source record↗
DOE OSTI2023

Conductivity and Transference Numbers in Lithium Salt-Doped Block Copolymeric Ionic Liquid Electrolytes

We present multiscale molecular dynamics simulation results comparing the conductivity and transference numbers in lithium salt-doped polymeric ionic liquids (PolyILs) and the lamellar phases of block copolymeric ionic liquids (coPolyILs). In both systems, the anion mobilities decreased with salt loading. Lithium ions exhibited negative mobilities in both systems, but the magnitudes decreased with an increase in salt concentrations. More interestingly, the anion mobilities were lower in the lamellar systems compared to homopolymers in magnitude, but the lithium ion mobilities and transference numbers were less negative in such systems. We examine the anion–cation and lithium–anion interactions in terms of radial distribution functions, coordination characteristics, and ion-pair relaxation timescales. Based on such analyses, we rationalize the salt concentration dependencies as a result of the interfacial interactions in lamellar systems and the competition between anion–cation and lithium–anion interactions in both PolyILs and coPolyILs. Altogether, the findings presented in this study demonstrate that the modified anion–cation and lithium–anion interactions in the microphase-separated coPolyILs may provide a strategy for realizing higher lithium ion transference numbers relative to the homopolymeric counterparts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Enhancing CO Oxidation Activity via Tuning a Charge Transfer Between Gold Nanoparticles and Supports

Charge transfer from the supports to nanoparticles at the interface is one of the key factors to determine the catalytic performances of supported nanoparticles. In this work, we revealed that the charge transfer from semiconductor support to Au nanoparticle catalysts enhanced their activity toward CO oxidation. In this work, a novel Au/SiO 2 /Si composite system with precisely controllable SiO 2 layer thickness was fabricated to tune the magnitude of interfacial charge transfer. With the support of X-ray photoelectron spectroscopy and numerical simulations, it was demonstrated that the Schottoky barrier formed across the Au/SiO 2 /Si heterojunction led to negative charge accumulation at the surface of Au nanoparticles, which may be transferred to the antibonding orbitral of adsorbed O 2 molecules to the O-O bonds. This discovery highlights a new perspective in explaining the role of strong metal-support interactions for catalytic reactions and provides a fresh path for designing the next generation of nanocatalysts.

36 MATERIALS SCIENCE↗
NASA NTRS1988

The effects of turbulence and stator/rotor interactions on turbine heat transfer. II - Effects of Reynolds number and incidence

Part I of this paper presents airfoil heat transfer data obtained in a rotating turbine model at its design rotor incidence. This portion of the paper presents heat transfer data obtained in the same model for various combinations of Reynolds number and inlet turbulence and for a very wide range of rotor incidence. On the suction surfaces of the first stage airfoils the locations and lengths of transition were influenced by both the inlet turbulence level and the Reynolds number. In addition it was demonstrated that on the first stage pressure surfaces combinations of high Reynolds number and high turbulence can produce heat transfer rates well in excess of two-dimensional turbulent flow. Rotor heat transfer distributions indicate that for relatively small deviations from the design incidence, local changes to the heat transfer distributions were produced on both pressure and suction sides near the stagnation region. For extremely large negative incidence the flow was completely separated from the rotor pressure surface producing very high local heat transfer.

Blair, M. F.↗
DOE OSTI2024

Measurement of g 9/2 strength in the stretched 8 – state and other negative parity states via the 51 V (d,p) 52 V reaction

We performed a measurement of the 51 V (d,p) 52 V reaction at 16 MeV using the Florida State University Super-Enge Split-Pole Spectrograph (SE-SPS) to search for single-neutron transfer strength for the g 9/2 intruder orbit. Measurements of νg 9/2 strength with (d, p) reactions in the N = 29 isotones 49 Ca, 51 Ti, 53 Cr, and 55 Fe have concluded that much of the expected νg 9/2 strength is “missing”; that is, the summed strength is much smaller than the sum rule. In odd-odd N = 29 isotones, we expect a significant amount of νg 9/2 strength to be located in the “stretched” 8 – states with π $f$$^{n}_{7/2}$νg 9/2 structure that were systematically observed in the odd-odd N = 29 isotones via the (α,d) reaction. 52 V is the only one of these odd-odd isotones in which a stable target is available for single-neutron transfer reactions. We report on a determination of νg 9/2 strength for the stretched 8 – state and ten other negative parity states populated via L = 4 transfer in the 51 V(d, p) 52 V reaction. Furthermore, this is the first measurement of spectroscopic strength for L = 4 states in 52 V via (d, p). In total, the L = 4 strength observed here sums to only 28.9(11)% of the sum rule for g 9/2 neutron strength, a result that is consistent with the summed strengths observed in recent (d, p) measurements of the even-Z N = 29 isotones 51 Ti, 53 Cr, and 55 Fe. The (α,3 He) reaction and the use of particle-γ coincidences would provide more sensitivity to search for the missing g 9/2 strength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

Measurement of capsule heat transfer gaps using neutron radiography

A technique is described for measuring heat transfer gaps from neutron radiographs. The method involves scanning the radiograph negative with a recording microdensitometer to obtain a trace of the optical density variation across the diameter of the capsule. The optical density change representing the gap is measured from the microdensitometer trace and related to the physical measurement. Heat transfer gaps from 0.061 to 0.178 cm have been determined by this technique and agree with preassembly physical measurements to plus or minus 0.005 cm.

Thaler, L. A.↗
DOE OSTI2022

Genome‐wide CRISPR‐Cas9 screen reveals a persistent null‐hyphal phenotype that maintains high carotenoid production in Yarrowia lipolytica

Abstract Yarrowia lipolytica is a metabolic engineering host of growing industrial interest due to its ability to metabolize hydrocarbons, fatty acids, glycerol, and other renewable carbon sources. This dimorphic yeast undergoes a stress‐induced transition to a multicellular hyphal state, which can negatively impact biosynthetic activity, reduce oxygen and nutrient mass transfer in cell cultures, and increase culture viscosity. Identifying mutations that prevent the formation of hyphae would help alleviate the bioprocess challenges that they create. To this end, we conducted a genome‐wide CRISPR screen to identify genetic knockouts that prevent the transition to hyphal morphology. The screen identified five mutants with a null‐hyphal phenotype— ΔRAS2 , ΔRHO5 , ΔSFL1 , ΔSNF2 , and ΔPAXIP1 . Of these hits, only ΔRAS2 suppressed hyphal formation in an engineered lycopene production strain over a multiday culture. The RAS2 knockout was also the only genetic disruption characterized that did not affect lycopene production, producing more than 5 mg L −1 OD −1 from a heterologous pathway with enhanced carbon flux through the mevalonate pathway. These data suggest that a ΔRAS2 mutant of Y. lipolytica could prove useful in engineering a metabolic engineering host of the production of carotenoids and other biochemicals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Dynamical Correlations and Order in Magic-Angle Twisted Bilayer Graphene

The interplay of dynamical correlations and electronic ordering is pivotal in shaping phase diagrams of correlated quantum materials. In magic-angle twisted bilayer graphene, transport, thermodynamic, and spectroscopic experiments pinpoint a competition between distinct low-energy states with and without electronic order, as well as between localized and delocalized charge carriers. In this study, we utilize dynamical mean-field theory on the topological heavy fermion model of twisted bilayer graphene to investigate the emergence of electronic correlations and long-range order in the absence of strain. We contrast moment formation, Kondo screening, and ordering on a temperature basis and explain the nature of emergent correlated states based on three central phenomena: (i) the formation of local spin and valley isospin moments around 100 K, (ii) the ordering of the local isospin moments around 10 K preempting Kondo screening, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. At integer fillings, we find that low-energy spectral weight is depleted in the symmetric phase, while we find insulating states with gaps enhanced by exchange coupling in the zero-strain ordered phases. Doping away from integer filling results in distinct metallic states: a “bad metal” above the ordering temperature, where scattering off the disordered local moments suppresses electronic coherence, and a “good metal” in the ordered states with coherence of quasiparticles facilitated by isospin order. This finding reveals coherence from order as the microscopic mechanism behind the Pomeranchuk effect observed experimentally by Rozen [] and by Saito []. Upon doping, there is a periodic charge reshuffling between localized and delocalized electronic orbitals leading to cascades of doping-induced Lifshitz transitions, local spectral weight redistributions, and periodic variations of the electronic compressibility ranging from nearly incompressible to negative. Our findings highlight the essential role of charge transfer, hybridization, and ordering in shaping the electronic excitations and thermodynamic properties in twisted bilayer graphene and provide a unified understanding of the most puzzling aspects of scanning tunneling spectroscopy, transport, and compressibility experiments. Published by the American Physical Society 2024

Physics↗
DOE OSTI2023

Experimental and Numerical Investigation of Flow Boiling in Additive Manufactured Foam Structures With Vapor Pathways

Abstract The unique properties of metal foams make them potential candidates for a range of applications, including microsystem thermal management. Using additive manufacturing to create foam-type structures can improve upon prior thermal solutions by eliminating thermal interface materials and allowing for customization/local control of parameters. In the present investigation, flow boiling in additive-manufactured metal foams is investigated both experimentally and numerically. Two test samples, one with uniform structure and the other with pathways for vapor removal, are compared both experimentally and numerically. A conjugate computational fluid dynamics and heat transfer (CFD-HT) model utilizing a three-dimensional volume of fluid (VOF) model with accompanying evaporation/condensation model provided in-depth visualization of the boiling flow phenomena. The experiments generated the thermohydraulic performance over a range of heat fluxes, demonstrating that the sample incorporating dedicated vapor pathways performed better in both pressure and heat transfer performance metrics compared to the uniform foam. Additionally, negative system-level effects (i.e., hydraulic oscillations) were shown to be abated using the vapor removal structures. The numerical model yielded further insight into the factors contributing to the improved performance. Results indicated the pathways functioned as vapor removal channels, allowing the generated vapor to vent from the foam structure into the lanes. Further computational investigations demonstrated changes in flow regimes, where the addition of vapor channels caused the flow to change from churn to annular. Bubble behavior unique to the vapor pathway structure was studied, showing stagnant regions that eject vapor into the channel.

Engineering↗