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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

An alternative analysis of low- and high-altitude observations of ring current ions during a storm recovery phase

Explorer 45 equatorial observations of ring current ions during a storm recovery phase have shown pitch angle distributions and decay rates inconsistent with proton charge exchange with neutral hydrogen. This inconsistency has led to the suggestion that recovery phase ring current ions at L less than or equal to 4 and energies not greater than 50 keV are dominated by He(+) rather than protons. The absence of He(+) on flux tubes from which H(+) and O(+) were precipitating in ion mass spectrometer measurements made during the same period by the low-altitude polar-orbiting satellite 1971-089A led Sharp et al. to suggest a source of H(+) and O(+) to L = 3 during this period. An alternative explanation, in which the magnetic field lines labeled L = 3 at the earth's surface near local midnight were mapped to about 3.7 earth radii in the equatorial plane during the storm recovery phase and during the period of enhanced activity, is proposed. If the proposed explanation is correct, the observations of Sharp et al. are not incompatible with the conclusion that the recovery phase ions at less than 50 keV were dominated by He(+) for L not greater than 3.7.

Lyons, L. R.↗
NASA NTRS1982

Impact of uniform electrode current distribution on ETF

The design impacts on the ETF electrode consolidation network associated with uniform channel electrode current distribution are examined and the alternate consolidation design which occur are presented compared to the baseline (non-uniform current) design with respect to performance, and hardware requirements. A rational basis is given for comparing the requirements for the different designs and the savings that result from uniform current distribution. Performance and cost impacts upon the combined cycle plant are discussed.

Bents, D. J.↗
NASA NTRSDate not supplied

Engine Cycle Comparison for Alternative Propellant Nuclear Thermal Propulsion Engines

A modular Nuclear Thermal Propulsion (NTP) engine modeling suite was coded in Simulink to analyze various engine cycle configurations and propellants. This model was validated and used for previous studies involving alternative propellants for NTP engines. The current study compared hydrogen-based NTP (H-NTP) with ammonia-based Alternative propellant NTP (A-NTP) engines with expander and bleed cycle configurations. Based on prior work, the bleed cycle configuration was modified to yield a feasible result. The assumption that was made was that the Testing Reference Design (TRD) reactor will be used for all cases and that the difference in fuel loading fractions will be enough to offset any differences in the neutronics caused by switching the propellant. This work provided and compared propellant state points throughout the cycles as well as the key performance parameters. The conclusion was that bleed cycles for H-NTP engines are advantageous over expander cycles in terms of maximum system pressure, cycle simplicity, and potentially engine mass. Conversely, expander cycles are more advantageous for A-NTP engines according to the same scope of parameters. Future work will analyze reactor designs that are different from the TRD and use neutronics software integrated with the X-NTP model to provide higher fidelity results.

Nuclear↗
NASA NTRS2013

Conductance of Ion Channels - Theory vs. Experiment

Transmembrane ion channels mediate a number of essential physiological processes in a cell ranging from regulating osmotic pressure to transmission of neural signals. Kinetics and selectivity of ion transport is of critical importance to a cell and, not surprisingly, it is a subject of numerous experimental and theoretical studies. In this presentation we will analyze in detail computer simulations of two simple channels from fungi - antiamoebin and trichotoxin. Each of these channels is made of an alpha-helical bundle of small, nongenomically synthesized peptides containing a number of rare amino acids and exhibits strong antimicrobial activity. We will focus on calculating ionic conductance defined as the ratio of ionic current through the channel to applied voltage. From molecular dynamics simulations, conductance can be calculated in at least two ways, each involving different approximations. Specifically, the current, given as the number of charges transferred through the channel per unit of time, can be obtained from the number of events in which ions cross the channel during the simulation. This method works well for large currents (high conductance values and/or applied voltages). If the number of crossing events is small, reliable estimates of current are difficult to achieve. Alternatively, conductance can be estimated assuming that ion transport can be well approximated as diffusion in the external potential given by the free energy profile. Then, the current can be calculated by solving the one-dimensional diffusion equation in this external potential and applied voltage (the generalized Nernst-Planck equation). To do so three ingredients are needed: the free energy profile, the position-dependent diffusion coefficient and the diffusive flux of ions into the channel. All these quantities can be obtained from molecular dynamics simulations. An important advantage of this method is that it can be used equally well to estimating large and small currents. In addition, once the free energy profile becomes available the full current-voltage dependence can be readily obtained. For both channels we carried out calculations using both approaches. We also tested the main assumptions underlying the diffusive model, such as uncorrelated nature of individual crossing events and Fickian diffusion. The accuracy and consistency of different methods will be discussed. Finally we will discuss how comparisons between calculated and measured ionic conductance and selectivity of transport can be used for determining structural models of the channels.

Pohorille, Andrew↗
NASA NTRS2007

MEMS Micro-Translation Device with Improved Linear Travel Capability

A microscopic translation device for a microelectromechanical system includes a pair of linear stator assemblies disposed in spaced relation to define an elongate channel. Each assembly is formed by a plurality of stators arranged in a row along the channel. A shuttle member is disposed between the stator assemblies for translating movement along the channel. The shuttle member includes a plurality of rotors extending outwardly from opposite sides. The shuttle is grounded through the stator assemblies and includes a mounting area for an object to be translated. Electrical lines are individually connected to alternate stators of a plurality of groups of the stators. A current supply sequentially supplies current through the electrical lines to the alternate stators so as to effect charging of the stators in a predetermined sequence. This produces a tangential capacitive force that causes translation of the shuttle.

Abushagur, Mustafa A. G.↗
DOE OSTI2021

Method for heat-treating metal materials

A method for heat treating metal materials by passing electrical current through a metallic workpiece to heat the workpiece via Joule heating to a preselected temperature for a preselected period of time, based upon the formula I2×R×t, wherein I is current, R is resistance and t is time. The current may be a direct or an alternating one. Various configurations of the method are envisioned wherein multiple current inputs and outputs are attached to the metal material so as to selectively heat specific portions of the piece including irregular shapes and differing diameters.

Rohatgi, Aashish↗
DOE OSTI2024

The Realistic Potential of Soil Carbon Sequestration in U.S. Croplands for Climate Mitigation

Existing estimates of the climate mitigation potential from cropland carbon sequestration (C-sequestration) are limited because they tend to assume constant rates of soil organic carbon change over all available cropland area, use relatively coarse land delineations, and often fail to adequately consider the agronomic and socioeconomic dimensions of agricultural land use. This results in an inflated estimate of the C-sequestration potential. We address this gap by defining a more appropriate land base for cover cropping in the United States for C-sequestration purposes: stable croplands in annual production systems that can integrate cover cropping without irrigation. Our baseline estimate of this suitable stable cropland area is 32% of current U.S. cropland extent. Even an alternative, less restrictive definition of stability results in a large reduction in area (44% of current U.S. croplands). Focusing cover crop implementation to this constrained land base would increase durability of associated C-sequestration and limit soil carbon loss from land conversion to qualify for carbon-specific incentives. Applying spatially-variable C-sequestration rates from the literature to our baseline area yields a technical potential of 19.4 Tg CO 2 e yr –1 annually, about one-fifth of previous estimates. We also find the cost of realizing about half (10 Tg CO 2 e yr –1 ) of this potential could exceed 100 USD Mg CO 2 e –1 , an order of magnitude higher than previously thought. While our economic analyses suggest that financial incentives are necessary for large-scale adoption of cover cropping in the U.S., they also imply any C-sequestration realized under such incentives is likely to be additional.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Increased fracture depth range in controlled spalling of (100)-oriented germanium via electroplating

Controlled spalling in (100)-oriented germanium using a nickel stressor layer shows promise for semiconductor device exfoliation and kerfless wafering. Demonstrated spall depths of 7-60 um using DC sputtering to deposit the stressor layer are appropriate for the latter application but spall depths < 5 um may be required to minimize waste for device applications. This work investigates the effect of tuning both electroplating current density and electrolyte chemistry on the residual stress in the nickel and on the achievable spall depth range for the Ni/Ge system as a lower-cost, higher-throughput alternative to sputtering. By tuning current density and electrolyte phosphorous concentration, it is shown that electroplating can successfully span the same range of spalled thicknesses as has previously been demonstrated by sputtering and can reach sufficiently high stresses to enter a regime of thickness (<7 um) appropriate to minimize substrate consumption for device applications.

14 SOLAR ENERGY↗
NASA NTRS1983

An Assessment of Potential Detectors to Monitor the Man-made Orbital Debris Environment

Observations using NORAD radar showed that man made debris exceeds the natural environment for large objects. For short times (a few days to a few weeks) after solid rocket motor (SRM) firings in LEO, man made debris in the microparticle size range also appears to exceed the meteoroid environment. The properties of the debris population between these size regimes is currently unknown as there has been no detector system able to perform the required observations. The alternatives for obtaining data on this currently unobserved segment of the population are assessed.

Reynolds, R. C.↗
NASA NTRS1981

Transportation systems evaluation methodology development and applications, phase 3

Transportation systems or proposed changes in current systems are evaluated. Four principal evaluation criteria are incorporated in the process, operating performance characteristics as viewed by potential users, decisions based on the perceived impacts of the system, estimating what is required to reduce the system to practice; and predicting the ability of the concept to attract financial support. A series of matrix multiplications in which the various matrices represent evaluations in a logical sequence of the various discrete steps in a management decision process is used. One or more alternatives are compared with the current situation, and the result provides a numerical rating which determines the desirability of each alternative relative to the norm and to each other. The steps in the decision process are isolated so that contributions of each to the final result are readily analyzed. The ability to protect against bias on the part of the evaluators, and the fact that system parameters which are basically qualitative in nature can be easily included are advantageous.

Kuhlthau, A. R.↗
NASA NTRS1984

End effects of a bifilar magnetic wiggler

The magnetic field at the entrance of a wiggler magnet in a free-electron laser (FEL) determines the character of the electron orbits and influences the FEL gain. To obtain the desired adiabatic entrance conditions, it is necessary to investigate different methods of connecting leads to the wiggler as well as methods of gradually reducing the wiggler field. The field of a current-driven, finite-length bifilar helical wiggler magnet is derived and is used to investigate the magnetic field end perturbations. For a limited range of wiggler parameters, flaring the wiggler end produces an adiabatic entrance region. Alternatively, gradually terminating the wiggler current at the wiggler entrance is shown to produce an adiabatic entrance for a large range of parameters.

Fajans, J.↗
DOE OSTI2025

An overview of switchgrass phenotypes variability across diverse populations and their implications for conversion to fuels

There have been substantial changes to the human lifestyle over the past two centuries, which are reflected in the amount of fuel we consume to power our day-to-day needs. The way we use these resources has indeed manifested in an overdependence on non-renewable energy sources, such as coal and petroleum, for generating electricity and powering our transportation needs. There is a pressing need to explore alternative ways of fueling our current lifestyle without impacting the environment. Biofuels have long been touted as a sustainable solution for use as drop-in fuels in aviation and maritime applications. Still, they have yet to establish themselves as a competitive commercial alternative, necessitating further research and development. Lignocellulosic biomass is an underutilized resource that is widely accessible for the commercial processing of renewable biofuels. Bioenergy crops, such as switchgrass (Panicum virgatum L.), which can be cultivated on marginal lands with minimal competition for agricultural land, are an ideal and promising candidate for bulk-scale biofuel synthesis. Over the past 30 years, significant progress has been made in breeding and genetically modifying these grasses to enhance their drought resilience and subsequent yields. However, discrepancies in biomass composition can lead to irregular feedstocks for downstream operations, which in turn affect overall production targets for biofuels. Here, this review examines the variability in switchgrass (P. virgatum L.) biomass phenotypes across diverse populations and plant components, and their implications for biofuel conversion. The study highlights significant variations in biomass yield, composition, and cell wall chemistry both between switchgrass genotypes and within individual cultivars. Key findings include differences in cellulose, hemicellulose, and lignin content between leaves and stems, which affect biomass digestibility and ethanol yield. The review also discusses the impact of lignin chemistry, particularly the syringyl/guaicyl (S/G) ratio, on the efficiency of biomass saccharification. Furthermore, it explores how these variations respond differently to various pretreatment techniques, affecting overall biofuel production. We conclude that understanding and quantifying this variability is crucial for optimizing switchgrass as a feedstock for commercial biofuel production, thereby potentially addressing the pressing need for sustainable energy sources in sectors such as aviation.

Kousika, Rohit [Univ. of Tennessee, Knoxville, TN ↗
NASA NTRS2021

Electrolytic Co-deposition Neutron Production Evaluation

Co-deposition electrochemical cells are a simple means to examine novel nuclear reactions. In this study, palladium and deuterium atoms were co-deposited on a cathode at stoichiometric densities, forming dendritic morphologies. Bubble detector neutron dosimeters were used to measure equivalent dose levels during electrolytic deposition. Standard configuration cells expected to produce excess neutrons were denoted as experimental cells and contained an electrolyte consisting of palladium(II) chloride, lithium chloride, and heavy water. The control cells used copper(II) chloride, lithium chloride, and heavy water electrolyte. Experimental and control cells were supplied current, increasing from 0.1 to 100.0 mA over a period of 20 days. For test days 9 through 20, the standard configuration experimental cells exhibited significantly higher average neutron radiation than the controls at a 99% confidence level. Alternative configurations involving more increasing current over a shortened time scale, substitutions of water in place of heavy water or potassium chloride for lithium chloride, as well as inclusion of depleted uranium near the cell cathodes all resulted in inconclusive evidence for promoting neutron production.

neutron↗
DOE OSTI2018

The Role of Proton Transport in Gating Current in a Voltage Gated Ion Channel, as Shown by Quantum Calculations

Over two-thirds of a century ago, Hodgkin and Huxley proposed the existence of voltage gated ion channels (VGICs) to carry Na + and K + ions across the cell membrane to create the nerve impulse, in response to depolarization of the membrane. The channels have multiple physiological roles, and play a central role in a wide variety of diseases when they malfunction. The first channel structure was found by MacKinnon and coworkers in 1998. Subsequently, the structure of a number of VGICs was determined in the open (ion conducting) state. This type of channel consists of four voltage sensing domains (VSDs), each formed from four transmembrane (TM) segments, plus a pore domain through which ions move. Understanding the gating mechanism (how the channel opens and closes) requires structures. One TM segment (S4) has an arginine in every third position, with one such segment per domain. It is usually assumed that these arginines are all ionized, and in the resting state are held toward the intracellular side of the membrane by voltage across the membrane. They are assumed to move outward (extracellular direction) when released by depolarization of this voltage, producing a capacitive gating current and opening the channel. We suggest alternate interpretations of the evidence that led to these models. Measured gating current is the total charge displacement of all atoms in the VSD; we propose that the prime, but not sole, contributor is proton motion, not displacement of the charges on the arginines of S4. It is known that the VSD can conduct protons. Quantum calculations on the K v 1.2 potassium channel VSD show how; the key is the amphoteric nature of the arginine side chain, which allows it to transfer a proton. This appears to be the first time the arginine side chain has had its amphoteric character considered. We have calculated one such proton transfer in detail: this proton starts from a tyrosine that can ionize, transferring to the NE of the third arginine on S4; that arginine’s NH then transfers a proton to a glutamate. The backbone remains static. A mutation predicted to affect the proton transfer has been qualitatively confirmed experimentally, from the change in the gating current-voltage curve. The total charge displacement in going from a normal closed potential of -70 mV across the membrane to 0 mV (open), is calculated to be approximately consistent with measured values, although the error limits on the calculation require caution in interpretation.

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

A Roadmap to Low-Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers

Hydrogen is an ideal alternative energy carrier to generate power for all of society's energy demands including grid, industrial, and transportation sectors. Among the hydrogen production methods, water electrolysis is a promising method because of its zero greenhouse gas emission and its compatibility with all types of electricity sources. Alkaline electrolyzers (AELs) and proton exchange membrane electrolyzers (PEMELs) are currently used to produce hydrogen. AELs are commercially mature and are used in a variety of industrial applications, while PEMELs are still being developed and find limited application. In comparison with AELs, PEMELs have more compact structure and can achieve higher current densities. Recently, however, an alternative technology to PEMELs, hydroxide exchange membrane electrolyzers (HEMELs), has gained considerable attention due to the possibility to use platinum group metal (PGM)-free electrocatalysts and cheaper membranes, ionomers, and construction materials and its potential to achieve performance parity with PEMELs. Here, the state-of-the-art AELs and PEMELs along with the current status of HEMELs are discussed in terms of their positive and negative aspects. Additionally discussed are electrocatalyst, membrane, and ionomer development needs for HEMELs and benchmark electrocatalysts in terms of the cost-performance tradeoff.

08 HYDROGEN↗
NASA NTRS2002

Modeling of InGaAsSb-Based Avalanche Photodetectors for 2-Micron Wavelengths

The main focus of this research is to study and evaluate the potential of InGaAsSb-AlGaAsSb based 2 micron avalanche photo-detectors. The photodetector contains a separate absorption and multiplication region (SAM) structure. The analysis has mainly been done to understand the electrical response characteristics of the devices existing at NASA, and to evaluate alternate structures proposed. Calculating the current flow for the existing detector structure, on the basis of its energy band diagram, is important. This analysis also helps to find shortcomings in the existing detector structure. It is shown that, unfortunately, the existing structure cannot lead to strong multiplication or voltage dependent gain. Two alternate structures are suggested, that could overcome the inherent flaws, and help achieve improved performance. These devices are obtained through modifications of the original structure, which include varying the doping levels, and changing the thicknesses of detector sub-regions. The results of our study are presented and discussed.

Joshi, Ravindra P.↗
DOE OSTI2018

Direct AFM-based nanoscale mapping and tomography of open-circuit voltages for photovoltaics

The nanoscale optoelectronic properties of materials can be especially important for polycrystalline photovoltaics including many sensor and solar cell designs. For thin film solar cells such as CdTe, the open-circuit voltage and short-circuit current are especially critical performance indicators, often varying between and even within individual grains. A new method for directly mapping the open-circuit voltage leverages photo-conducting AFM, along with an additional proportional-integral-derivative feedback loop configured to maintain open-circuit conditions while scanning. Alternating with short-circuit current mapping efficiently provides complementary insight into the highly microstructurally sensitive local and ensemble photovoltaic performance. Furthermore, direct open-circuit voltage mapping is compatible with tomographic AFM, which additionally leverages gradual nanoscale milling by the AFM probe essentially for serial sectioning. The two-dimensional and three-dimensional results for CdTe solar cells during in situ illumination reveal local to mesoscale contributions to PV performance based on the order of magnitude variations in photovoltaic properties with distinct grains, at grain boundaries, and for sub-granular planar defects.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Horizontal Splitter Design For FFA@CEBAF Energy Upgrade: Current Status

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is currently studying the feasibility of an energy upgrade based upon Fixed-Field Alternating Gradient (FFA) permanent magnet technology. The current plan is to replace the highest-energy recirculation arcs with FFA arcs, increasing the total number of beam recirculations, thus the energy. In order to accommodate multiple passes in the FFA arcs, horizontal splitters are being designed to control the beam parameters entering the FFA arcs, as well as the time of flight and R_56. In the current design, six passes will recirculate through the FFA arcs, necessitating the design of six independent beamlines to control the optics and beam dynamics matching into the arcs. These beamlines must fit into the current CEBAF tunnel, while allowing for personnel and equipment access. They must also be flexible enough to accommodate the beam under realistic operational conditions and fluctuations. The constraints on the system are highly restrictive, complicating the design. This document will describe the current state of the design, and indicate the work remaining for a complete conceptual design.

Benesch, Jay↗