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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Factors affecting the open-circuit voltage and electrode kinetics of some iron/titanium redox flow cells

Performance of the iron-titanium redox flow cell was studied as a function of acid concentration. Anion permeable membranes separated the compartments. Electrodes were graphite cloth. Current densities ranged up to 25 mA/square centimeter. Open-circuit and load voltages decreased as the acidity was increased on the iron side as predicted. On the titanium side, open-circuit voltages decreased as the acidity was increased in agreement with theory, but load voltages increased due to decreased polarization with increasing acidity. High acidity on the titanium side coupled with low acidity on the iron side gives the best load voltage, but such cells show voltage losses as they are repeatedly cycled. Analyses show that the bulk of the voltage losses are due to diffusion of acid through the membrane.

Reid, M. A.↗
DOE OSTI2024

Use of Hydrogel Electrolyte in Zn-MnO2 Rechargeable Batteries: Characterization of Safety, Performance, and Cu2+ Ion Diffusion

Achieving commercially acceptable Zn-MnO2 rechargeable batteries depends on the reversibility of active zinc and manganese materials, and avoiding side reactions during the second electron reaction of MnO2. Typically, liquid electrolytes such as potassium hydroxide (KOH) are used for Zn-MnO2 rechargeable batteries. However, it is known that using liquid electrolytes causes the formation of electrochemically inactive materials, such as precipitation Mn3O4 or ZnMn2O4 resulting from the uncontrollable reaction of Mn3+ dissolved species with zincate ions. In this paper, hydrogel electrolytes are tested for MnO2 electrodes undergoing two-electron cycling. Improved cell safety is achieved because the hydrogel electrolyte is non-spillable, according to standards from the US Department of Transportation (DOT). The cycling of “half cells” with advanced-formulation MnO2 cathodes paired with commercial NiOOH electrodes is tested with hydrogel and a normal electrolyte, to detect changes to the zincate crossover and reaction from anode to cathode. These half cells achieved ≥700 cycles with 99% coulombic efficiency and 63% energy efficiency at C/3 rates based on the second electron capacity of MnO2. Other cycling tests with “full cells” of Zn anodes with the same MnO2 cathodes achieved ~300 cycles until reaching 50% capacity fade, a comparable performance to cells using liquid electrolyte. Electrodes dissected after cycling showed that the liquid electrolyte allowed Cu ions to migrate more than the hydrogel electrolyte. However, measurements of the Cu diffusion coefficient showed no difference between liquid and gel electrolytes; thus, it was hypothesized that the gel electrolytes reduced the occurrence of Cu short circuits by either (a) reducing electrode physical contact to the separator or (b) reducing electro-convective electrolyte transport that may be as important as diffusive transport.

25 ENERGY STORAGE↗
NASA NTRS1973

Heat treatment effects in Cu2S-CdS heterojunction photovoltaic cells

The optical and electronic properties of single crystal Cu2S-CdS photovoltaic cells were investigated. In these cells trapped charge near the interface which is manifested by a persistent increase in junction capacitance (the photocapacitance) plays a significant role in determining the carrier transport properties. It was found that the severe degradation in short-circuit current observed in heat-treated cells can be separated into two components: (1) a relatively small thermal component occurring on heat-treatment in the dark, and (2) a much larger degradation caused by exposure to light at room temperature. By a short additional heat-treatment above approximately 100 C the cell can be completely restored to its condition before the optically caused degradation with no effect on the depletion layer width.

Fahrenbruch, A. L.↗
NASA NTRS1975

Exploring the cell: Sodium (beta-alumina) cupric chloride - Aluminum chloride - Sodium chloride between 136 and 200 C

Experiments were done with a molten-salt catholyte (initially CuCl2 in AlCl3-NaCl) separated from molten Na by beta alumina. The open-circuit reduction potentials were 4.3 and 3 volts for Cu++ and Cu+, respectively. High polarization and nonrechargeability characterized the cell's operation. The cell's ohmic resistance during discharge was higher than what would be expected from only the ionic resistance of the beta-alumina.

Miller, R. O.↗
NASA NTRS1980

Electronic system for high power load control

Parallel current paths are divided into two groups, with control devices in the current paths of one group each having a current limiting resistor, and the control devices in the other group each having no limiting resistor, so that when the control devices of the second group are turned fully on, a short circuit is achieved by the arrangement of parallel current paths. Separate but coordinated control signals are provided to turn on the control devices of the first group and increase their conduction toward saturation as a function of control input, and when fully on, or shortly before, to turn on the control devices of the second group and increase their conduction toward saturation as a function of the control input as that input continues to increase. Electronic means may be used to generate signals. The system may be used for 1-V characteristic measurements of solar arrays as well as for other load control purposes.

Miller, E. L.↗
NASA NTRS1999

Interference of Backscatter from Two Droplets in a Focused Continuous Wave CO2 Doppler Lidar Beam

Interference due to the superposition of backscatter, beta, from two micron-sized droplets using a NASA/MSFC cw (continuous wave) CO2 Doppler lidar at 9.1 micrometer wavelength was detected for the first time. The resultant single beta signal from both droplets contained an interference structure with a well-defined periodicity which was accurately measured and compared with cw lidar theory. The agreement between measurements and theory is excellent, indicating that the interference arises because the droplets are moving at different speeds and, therefore, the relative droplet separation is not constant. This gives the superimposed beta signal from both droplets in the lidar beam moving in and out of constructive and destructive interference with a well-defined periodic structure. A measurement of a time-resolved signal pulse with an oscilloscope of the combined from two approx. 14.12 micrometers in diameter silicone oil droplets responding to the Gaussian lidar beam intensity at the lidar beam focus is shown. Full details of this laboratory experimental setup, particle generation method, measurement technique, and the cw lidar can be found elsewhere. The stream of silicone oil droplets resided at a Doppler-shift center frequency of f (sub D) approx. (3.4 plus or minus 0.2) MHz, giving droplet speed v approx.(21.9 plus or minus 1.3) ms (exp. -1). Also shown on a separate channel is the corresponding signature using an amplitude demodulator circuit designed to detect the amplitude envelope of f(sub D) within the pulse profile. beta from simultaneous droplet events show a complete cyclic interference structure of maximum and minimum. The average period T of the complete cycle of interference is 13.02 plus or minus.39 microseconds. Toward the right edge of the profile, the interference disappears because one of the droplets is leaving the lidar beam while the other one remains in the beam, thus, giving beta for a single droplet.

Jarzembski, Maurice A.↗
NASA NTRS1989

Four-terminal connector for measuring resistance of a pyrotechnic initiator

A four-terminal electrical connector device (40) for testing and measuring unknown resistances of initiators (11) used for starting pyrotechnic events aboard a Space Transportation System. The testing device minimizes contact resistance degradation effects and so improves the reliability of resistance measurement taken with the device. Separate and independent voltage sensing (19) and current supply (20) circuits each includes a pair of socket contacts (13-16) for mating engagement with the pins (17,18) of the initiator. The unknown resistance that is measured by the device is the resistance of the bridgewire (23) of the initiator which is required to be between 0.95 and 1.15 ohms.

Robinson, Robert L.↗
NASA NTRS2005

Hybrid Power Management

An engineering discipline denoted as hybrid power management (HPM) has emerged from continuing efforts to increase energy efficiency and reliability of hybrid power systems. HPM is oriented toward integration of diverse electric energy-generating, energy-storing, and energy-consuming devices in optimal configurations for both terrestrial and outer-space applications. The basic concepts of HPM are potentially applicable at power levels ranging from nanowatts to megawatts. Potential applications include terrestrial power-generation, terrestrial transportation, biotechnology, and outer-space power systems. Instances of this discipline at prior stages of development were reported (though not explicitly labeled as HPM) in three prior NASA Tech Briefs articles: "Ultracapacitors Store Energy in a Hybrid Electric Vehicle"(LEW-16876), Vol. 24, No. 4 (April 2000), page 63; "Photovoltaic Power Station With Ultracapacitors for Storage" (LEW-17177), Vol. 27, No. 8 (August 2003), page 38; and "Flasher Powered by Photovoltaic Cells and Ultracapacitors" (LEW-17246), Vol. 24, No. 10 (October 2003), page 37. As the titles of the cited articles indicate, the use of ultracapacitors as energy-storage devices lies at the heart of HPM. An ultracapacitor is an electrochemical energy-storage device, but unlike in a conventional rechargeable electrochemical cell or battery, chemical reactions do not take place during operation. Instead, energy is stored electrostatically at an electrode/electrolyte interface. The capacitance per unit volume of an ultracapacitor is much greater than that of a conventional capacitor because its electrodes have much greater surface area per unit volume and the separation between the electrodes is much smaller. Power-control circuits for ultracapacitors can be simpler than those for batteries, for two reasons: (1) Because of the absence of chemical reactions, charge and discharge currents can be greater than those in batteries, limited only by the electrical resistances of conductors; and (2) whereas the charge level of a battery depends on voltage, temperature, age, and load condition, the charge level of an ultracapacitor, like that of a conventional capacitor, depends only on voltage.

Eichenberg, Dennis↗
DOE OSTI2023

A Novel Spatial-Temporal Variational Quantum Circuit to Enable Deep Learning on NISQ Devices

Quantum computing presents a promising approach for machine learning with its capability for extremely parallel computation in high-dimension through superposition and entanglement. Despite its potential, existing quantum learning algorithms, such as Variational Quantum Circuits (VQCs), face challenges in handling more complex datasets, particularly those that are not linearly separable. What’s more, it encounters the deployability issue, making the learning models suffer a drastic accuracy drop after deploying them to the actual quantum devices. To overcome these limitations, this paper proposes a novel spatial-temporal design, namely “ST-VQC”, to integrate nonlinearity in quantum learning and improve the robustness of the learning model to noise. Specifically, ST-VQC can extract spatial features via a novel block-based encoding quantum sub-circuit coupled with a layer-wise computation quantum sub-circuit to enable temporal-wise deep learning. Additionally, a SWAP-Free physical circuit design is devised to improve robustness. These designs bring a number of hyperparameters. After a systematic analysis of the design space for each design component, an automated optimization framework is proposed to generate the ST-VQC quantum circuit. The proposed ST-VQC has been evaluated on two IBM quantum processors, ibm-cairo with 27 qubits and ibmq-lima with 7 qubits to assess its effectiveness. The results of the evaluation on the standard dataset for binary classification show that ST-VQC can achieve over 30% accuracy improvement compared with existing VQCs on actual quantum computers. Moreover, on a non-linear synthetic dataset, the STVQC outperforms a linear classifier by 27.9%, while the linear classifier using classical computing outperforms the existing VQC by 15.58%.

Li, Jinyang↗
NASA NTRS1984

The Rubidium-Crystal Oscillator Hybrid Development Program

The rubidium-crystal oscillator hybrid (RbXO) will make precise time available to systems that lack the power required by atomic frequency standards. The RbXO consists of two subassemblies in separate enclosures. One contains a small rubidium frequency standard (RFS) without its internal oven-controlled crystal oscillator (OCXO), plus interface circuits. The second contains a low-power OCXO, and additional interface circuits. The OCXO is on continuously. Periodically, e.g., once a week, the user system applies power to the RFS. After the few necessary for the warmup of the RFS, the interface circuits adjust the frequency of the OCXO to the RFS reference, then shut off the RFS. The OCXO enclosure is separable from the RFS enclosure so that manpacks will be able to operate with minimum size, weight, and power consumption, while having the accuracy of the RFS for the duration of a mission. A prototype RbXO's RFS has operated successfully for 4200 on-off cycles. Parallel efforts on a Phase 2 RbXO development are in progress. Two sources for the RbXO are scheduled to be available during 1986.

Vig, J. R.↗
DOE OSTI2023

Short-Depth QAOA circuits and Quantum Annealing on Higher-Order Ising Models (Rev.2)

The Quantum Alternating Operator Ansatz (QAOA) and Quantum Annealing (QA) are quantum algorithms that are both based on the adiabatic theorem and both have the goal of sampling the optimal solution(s) of combinatorial optimization problems. Quantum annealing has been physically instantiated on D-Wave devices using superconducting flux qubits, and QAOA can be programmed on digital gate-model quantum computers such as the programmable superconducting transmon qubits devices of the IBMQ series, for instance ibm washington. QAOA and QA address the same types of problems, but it is unclear how they will scale to large problem sizes and to larger and higher-fidelity quantum computers. In this article, we present a direct comparison between QAOA, one and two rounds, run on all 127 qubits of ibm washington and QA run on D-Wave Advantage system4.1 and Advantage system6.1. The problems which allow for this comparison are random Ising model problems whose connectivity matches the heavy hexagonal lattice topology of ibm washington and the Pegasus graph connectivity of the two D-Wave devices. We create two classes of problem instances for this comparison: one with higher order terms (ZZZ variable interactions), linear terms, and quadratic terms, and a separate problem type with only linear and quadratic terms. Our QAOA circuits are novel and extremely short depth, with a CNOT depth of 6 per round, which allows whole chip usage of ibm washington’s heavy hexagonal lattice and can be applied to future heavy-hex chips. We also test the effectiveness of the error suppression technique digital dynamical decoupling on the QAOA circuits. The QAOA circuits compiled to ibm washington are composed of several thousand circuit instructions, approximately 3, 000 depending on the details of the circuit, making these some the largest quantum circuits ever executed on a digital quantum processor. QAOA and QA are compared against the classical heuristic algorithm of simulated annealing and all problem instances are exactly solved using CPLEX in order to evaluate which samplers, if any, correctly found the ground state solution(s) of the problem instances. We find that (i) QA outperforms QAOA on all problem instances, (ii) QAOA samples the problems better than random sampling, and (iii) QAOA angle computation exhibits clear parameter concentration across the ensemble of Ising models.

127 Qubits↗
NASA NTRS1984

Analysis of the electron-beam-induced current of a polycrystalline p-n junction when the diffusion lengths of the material on either side of a grain boundary differ

The short circuit current generated by the electron beam of a scanning electron microscope in p-n junctions is reduced by enhanced recombination at grain boundaries in polycrystalline material. Frequently, grain boundaries separate the semiconductor into regions possessing different minority carrier life times. This markedly affects the short circuit current I(sc) as a function of scanning distance from the grain boundary. It will be shown theoretically that (1) the minimum of the I(sc) in crossing the grain boundary with the scanning electron beam is shifted away from the grain boundary toward the region with smaller life time (shorter diffusion length), (2) the magnitude of the minimum differs markedly from those calculated under the assumption of equal diffusion lengths on either side of the grain boundary, and (3) the minimum disappears altogether for small surface recombination velocities (s less than 10,000 cm/s). These effects become negligible, however, for large recombination velocities s at grain boundaries. For p-type silicon this happens for s not less than 100,000 cm/s.

Von Roos, O.↗
DOE OSTI2023

Changing Directions: Influence of Ligand Electronics on the Directionality and Kinetics of Photoinduced Charge Transfer in Cu(I)Diimine Complexes

A key challenge to the effective utilization of solar energy is to promote efficient photoinduced charge transfer, specifically avoiding unproductive, circuitous electron-transfer pathways and optimizing the kinetics of charge separation and recombination. We hypothesize that one way to address this challenge is to develop a fundamental understanding of how to initiate and control directional photoinduced charge transfer, particularly for earth-abundant first-row transition-metal coordination complexes, which typically suffer from relatively short excited-state lifetimes. Here, in this paper, we report a series of functionalized heteroleptic copper(I)bis(phenanthroline) complexes, which have allowed us to investigate the directionality of intramolecular photoinduced metal-to-ligand charge transfer (MLCT) as a function of the substituent Hammett parameter. Ultrafast transient absorption suggests a complicated interplay of MLCT localization and solvent interaction with the Cu(II) center of the MLCT state. This work provides a set of design principles for directional charge transfer in earth-abundant complexes and can be used to efficiently design pathways for connecting the molecular modules to catalysts or electrodes and integration into systems for light-driven catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Soft Coiled Pneumatic Actuator with Integrated Length-Sensing Function for Feedback Control

SPIRA Coil actuators are formed from thin sheets of PET plastic laminated into a coil shape that unfurls like a “party horn” when inflated, while many soft actuators require large pressures to create only modest strains, SPIRA Coils can easily be designed and fabricated to extend over dramatic distances with relatively low working pressures. Internal metalized PET strips separate in the extended portion of the actuator, creating an electrical circuit with a resistance that corresponds to the actuator length. This paper presents and experimentally validates easy-to-use design models for the actuators’ self-retracting spring stiffness, its pneumatic extension force, and its internal length-sensing electrical resistance. Testing of the self-sensing capabilities demonstrates that the embedded sensor can be used to determine the actuator length with virtually no hysteresis. Feedback control with the resistance-based sensing resulted in length-control errors within 5% of the extended actuator length (i.e., 3 cm of 60 cm).

Greenwood, Jacob R. (ORCID:0000000310897854)↗
NASA NTRS1995

Combining Video Memory Operations

Designs of video random-access memory (VRAM) integrated circuits operating under control by external logic circuits simplified according to concept of combining two memory operations performed separately heretofore. Eliminates need for DRAM-refresh timers and counters, reducing amount of circuitry needed to control VRAM thereby reducing time needed to design VRAM. Simplification also reduces time needed to redesign DRAM-refresh logic circuitry when adapting VRAM design to another VRAM for which timing specifications different. Concept can be applied to VRAM clocking data out to display unit continuously.

Kania, Michael J.↗
NASA NTRS2012

670-GHz Down- and Up-Converting HEMT-Based Mixers

A large category of scientific investigation takes advantage of the interactions of signals in the frequency range from 300 to 1,000 GHz and higher. This includes astronomy and atmospheric science, where spectral observations in this frequency range give information about molecular abundances, pressures, and temperatures of small-sized molecules such as water. Additionally, there is a minimum in the atmospheric absorption at around 670 GHz that makes this frequency useful for terrestrial imaging, radar, and possibly communications purposes. This is because 670 GHz is a good compromise for imaging and radar applications between spatial resolution (for a given antenna size) that favors higher frequencies, and atmospheric losses that favor lower frequencies. A similar trade-off applies to communications link budgets: higher frequencies allow smaller antennas, but incur a higher loss. All of these applications usually require converting the RF (radio frequency) signal at 670 GHz to a lower IF (intermediate frequency) for processing. Further, transmitting for communication and radar generally requires up-conversion from IF to the RF. The current state-of-the-art device for performing the frequency conversion is based on Schottky diode mixers for both up and down conversion in this frequency range for room-temperature operation. Devices that can operate at room temperature are generally required for terrestrial, military, and planetary applications that cannot tolerate the mass, bulk, and power consumption of cryogenic cooling. The technology has recently advanced to the point that amplifiers in the region up to nearly 1,000 GHz are feasible. Almost all of these have been based on indium phosphide pseudomorphic high-electron mobility transistors (pHEMTs), in the form of monolithic microwave integrated circuits (MMICs). Since the processing of HEMT amplifiers is quite differ en t from that of Schottky diodes, use of Schottky mixers requires separate MMICs for the mixers and amplifiers. Fabrication of all the down-/up-conversion circuitry on single MMICs, using a ll-HEMT circuits, would constitute a major advance in circuit simplicity.

Schlecht, Enrich T.↗
NASA NTRSDate not supplied

Evaluation of Contact Separation Force Testing as a Screening Methodology for Electrical Socket Contacts

During system level testing intermittent and permanent open circuit failures of mated, crimp removable, electrical contact pairs were experienced. The root cause of the failures was determined to be low (but not zero) contact forces applied by the socket contact tines against the engaging pin. The low contact force reduces the effectiveness of the wiping action of the socket tines against the pin. The observed failure mode may be produced when insufficient wiping during mate, demate and small relative movement in use allows for the accumulation of debris or insulating films that electrically separate the contact pair. The investigation identified at least three manufacturing process control problems associated with the socket contacts that enabled shipment of contacts susceptible to developing low contact forces: (1) Improper heat treatment of the socket tines resulting in plastic rather than elastic behavior; (2) Overly thinned socket tines at their base resulting in reduced pin retention forces; (3) Insufficient screening tests to identify parts susceptible to the aforementioned failure mechanisms. The results from an extensive screening program of socket contacts utilizing the industry standard contact separation force test procedures are described herein. The investigation shows this method to be capable of identifying initially weak sockets. However, sockets whose contact retention forces may degrade during use may not be screened out by pin retention testing alone. Further investigations are required to correlate low contact retention forces with increased electrical contact resistance in the presence of insulating films that may accumulate in the use environment.

Christopher Green↗