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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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An authentication procedure utilizes multiple independent sources of data to determine whether usage of a device, such as a desktop computer, is authorized. When a comparison indicates an anomaly from the base-line usage data, the system, provides a notice that access of the first device is not authorized.
A hetero-junction device and fabrication method in which phase-separated n-type and p-type semiconductor pillars define vertically-oriented p-n junctions extending above a substrate. Semiconductor materials are selected for the p-type and n-type pillars that are thermodynamically stable and substantially insoluble in one another. An epitaxial deposition process is employed to form the pillars on a nucleation layer and the mutual insolubility drives phase separation of the materials. During the epitaxial deposition process, the orientation is such that the nucleation layer initiates propagation of vertical columns resulting in a substantially ordered, three-dimensional structure throughout the deposited material. An oxidation state of at least a portion of one of the p-type or the n-type semiconductor materials is altered relative to the other, such that the band-gap energy of the semiconductor materials differ with respect to stoichiometric compositions and the device preferentially absorbs particular selected bands of radiation.
Systems and methods described herein are directed to rotary heat exchangers configured to transfer heat to a heat transfer medium flowing in substantially axial direction within the heat exchangers. Exemplary heat exchangers include a heat conducting structure which is configured to be in thermal contact with a thermal load or a thermal sink, and a heat transfer structure rotatably coupled to the heat conducting structure to form a gap region between the heat conducting structure and the heat transfer structure, the heat transfer structure being configured to rotate during operation of the device. In example devices heat may be transferred across the gap region from a heated axial flow of the heat transfer medium to a cool stationary heat conducting structure, or from a heated stationary conducting structure to a cool axial flow of the heat transfer medium.
Systems and methods described herein are directed to rotary heat exchangers configured to transfer heat to a heat transfer medium flowing in substantially axial direction within the heat exchangers. Exemplary heat exchangers include a heat conducting structure which is configured to be in thermal contact with a thermal load or a thermal sink, and a heat transfer structure rotatably coupled to the heat conducting structure to form a gap region between the heat conducting structure and the heat transfer structure, the heat transfer structure being configured to rotate during operation of the device and flow a heat transfer medium in a substantially axial direction through the heat transfer structure. In example devices heat may be transferred across the gap region from a heated axial flow of the heat transfer medium to a cool stationary heat conducting structure, or from a heated stationary conducting structure to a cool axial flow of the heat transfer medium.
Accelerated life testing of GaAs complementary heterojunction field effect transistors (CHFET) was carried out. Temperature dependence of single and synchronous rectifier CHFET device characteristics were also obtained.
Bird strikes are a major safety and financial concern for modern aviation. Audible stimuli are common bird dispersal techniques, but their effectiveness is limited by the saliency and relevance of the stimulus. Furthermore, high ambient sound levels present at airfields might require that effective audible stimuli rely more on total volume (i.e., exceeding physiological tolerances) than ecological relevance. Acoustic hailing devices (AHD) are capable of sound output with a narrow beam width and at volumes high enough to cause physical discomfort at long distances. We tested the effectiveness of an AHD as a dispersal tool on free-ranging birds recognized as hazardous to aviation safety at the Savannah River Site and Phinizy Swamp Nature Park in South Carolina and Georgia, respectively. Our study design included experimental trials with timed-interval counts of birds directly before and after AHD treatment. For most species, counts of birds associated with treatment periods (use of AHD) and control periods (no use of AHD) occurred on different days. Sound treatments yielded variable success at dispersing birds. Specifically, AHD treatment was effective for dispersing vultures (Coragyps atratus and Cathartes aura) and gulls (Laridae), and ineffective for dispersing blackbirds (Icteridae), diving ducks (Aythya, Bucephala, Oxyura), and coots (Fulica americana). These trials were conducted in a relatively quiet environment with birds that were unhabituated to excessive noise, and thus we cannot unequivocally recommend an AHD as a universally effective avian dispersing tool. Furthermore, future research should consider AHD testing integrated with other methods, as well as investigation of treatments that might be salient to specific target species.
The theory of quadratic-flux-minimizing (QFM) surfaces is reviewed, and numerical techniques that allow high-order QFM surfaces to be efficiently constructed for experimentally relevant, non-integrable magnetic fields are described. As a practical example, the chaotic edge of the magnetic field in the Large Helical Device (LHD) is examined. A precise technique for finding the boundary surface is implemented, the hierarchy of partial barriers associated with the near-critical cantori is constructed, and a coordinate system, which we call chaotic coordinates, that is based on a selection of QFM surfaces is constructed that simplifies the description of the magnetic field, so that flux surfaces become “straight” and islands become “square.”.
The field of self-assembly has moved far beyond early work, where the focus was primarily the resultant beautiful two- and three-dimensional structures, to a focus on forming materials and devices with important properties either otherwise not available, or only available at great cost. Over the last few years, materials with unprecedented electronic, photonic, energy-storage, and chemical separation functionalities were created with self-assembly, while at the same time, the ability to form even more complex structures in two and three dimensions has only continued to advance. Self-assembly crosscuts all areas of materials. Functional structures have now been realized in polymer, ceramic, metallic, and semiconducting systems, as well as composites containing multiple classes of materials. Finally, as the field of self-assembly continues to advance, the number of highly functional systems will only continue to grow and make increasingly greater impacts in both the consumer and industrial space.
Abstract It is shown that the semiconducting performance of field‐effect transistors (FETs) with PDPP4T (poly(diketopyrrolopyrrole‐quaterthiophene)) can be reversibly tuned by UV light irradiation and thermal heating after blending with the photochromic hexaarylbiimidazole compound ( p ‐NO 2 ‐HABI). A photo‐/thermal‐responsive FET with a blend thin film of PDPP4T and p ‐NO 2 ‐HABI is successfully fabricated. The transfer characteristics are altered significantly with current enhanced up to 10 6 ‐fold at V G = 0 V after UV light irradiation. However, further heating results in the recovery of the transfer curve. This approach can be extended to other semiconducting polymers such as P3HT (poly(3‐hexyl thiophene)), PBTTT (poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b] thiophene)) and PDPPDTT (poly(diketopyrrolopyrrole‐dithienothiophene)). It is hypothesized that TPIRs (2,4,5‐triphenylimidazolyl radicals) formed from p ‐NO 2 ‐HABI after UV light irradiation can interact with charge defects at the gate dielectric–semiconductor interface and those in the semiconducting layer to induce more hole carriers in the semiconducting channel. The application of the blend thin film of PDPP4T and p ‐NO 2 ‐HABI is further demonstrated to fabricate the photonically programmable and thermally erasable FET‐based nonvolatile memory devices that are advantageous in terms of i) high ON/OFF current ratio, ii) nondestructive reading at low electrical bias, and iii) reasonably highly stable ON‐state and OFF‐state.
Highlights: • Development of a new spintronic device. • Development of spin anticrossing spectroscopy of nanolayers. • Development of theory of quantum spin-polarized filter. - Abstract: Presently we report measurements of the spin-anticrossing spectra in the Co–SiO{sub 2}–Fe and ZnO–SiO{sub 2}–CuO three-nanolayer sandwich structures. The spin-anticrossing spectra in these systems are quite specific, differing from those observed earlier in other similar structures built of different materials. The theoretical model developed earlier is extended and used to interpret the available experimental results. A detailed ab initio analysis of the magnetic-field dependence of the output magnetic moment is also performed. The model predicts a spin-anticrossing spectrum comprising a series of peaks, with the spectral structure determined by several factors, discussed in the paper.
InGaAs heterostructures have demonstrated the means to maintain hot carrier behavior under practical operating conditions via valley photovoltaics. However, enhancing the extraction to create a fully operational hot carrier solar cell requires an enhanced understanding of the barriers inside such devices. A set of four InGaAs heterostructures altering the n + top layer of the structure has been produced to enable comparative analysis of the current density-voltage characterization and the relationship to the band and valley alignments.
This work analyzes the differences between a ‘photoanode first’ and a ‘photocathode first’ 2-photon water splitting device.
Bayesian optimization (BO) was implemented to improve a membrane electrode assembly CO 2 electroreduction device undergoing pulsed operation.
Quantitative electroluminescence (EL) and luminescent coupling (LC) analysis, along with more conventional characterization techniques, are combined to completely characterize the subcell JV curves within a fourjunction (4J) inverted metamorphic solar cell (IMM). The 4J performance under arbitrary spectral conditions can be predicted from these subcell JV curves. The internal radiative efficiency (IRE) of each junction has been determined as a function of current density from the external radiative efficiency using optical modeling, but this required the accurate determination of the individual junction current densities during the EL measurement as affected by LC. These measurement and analysis techniques can be applied to any multijunction solar cell. The 4J IMM solar cell used to illustrate these techniques showed excellent junction quality as exhibited by high IRE and a one-sun AM1.5D efficiency of 36.3%. This device operates up to 1000 suns without limitations due to any of the three tunnel junctions.
A novel robotic plasma magnetron mole with a 50 cm long cathode was designed, fabricated, and operated. The reason for this endeavor is to alleviate the problems of unacceptable resistive heating of stainless steel vacuum tubes in the BNL Relativistic Heavy Ion Collider (RHIC). The magnetron mole was successfully operated to copper coat an assembly containing a full-size, stainless steel, cold bore, RHIC magnet tubing connected to two types of RHIC bellows, to which two additional pipes made of RHIC tubing were connected. To increase the cathode lifetime, a movable magnet package was developed, and the thickest possible cathode was made, with a rather challenging target to substrate (de facto anode) distance of less than 1.5 cm. Achieving reliable steady state magnetron discharges at such a short cathode to anode gap was rather challenging, when compared to commercial coating equipment, where the target to substrate distance is 10's cm; 6.3 cm is the lowest experimental target to substrate distance found in the literature. Additionally, the magnetron developed during this project provides unique omni-directional uniform coating. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system is driven by a motorized spool. Excellent coating adhesion was achieved. Measurements indicated that well-scrubbed copper coating reduced secondary electron yield to 1, i.e., the problem of electron clouds can be eliminated. Room temperature RF resistivity measurement indicated that a 10 μm copper coated stainless steel RHIC tube has a conductivity close to that of pure copper tubing. Excellent coating adhesion was achieved. The device details and experimental results are described.