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At least 235 records · Page 13

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NASA NTRS1986

Use of a 35mm camera for remote surface cleanliness verification

Non-contact or remote monitoring of surfaces for both particle and molecular contaminants is required for verification of surface cleanliness on many program subsystems. The capability of a 35mm camera to satisfy this need is presented. The many limitations imposed by standard available lens systems are compared to actual required sensitivities. Methods of optimizing camera systems for specific applications and descriptions of support systems for extending the range of usefulness of the recorded data are also provided. Although this general concept is not new, significant improvements in the technique involving the use of polarized light and diffraction effects have resulted in a more efficient utilization of information recorded on the film.

Crutcher, E. R.↗

NASA NTRS1977

Outer Space Research Helps Color Habitability in Earth Interiors

Color is one of the most important elements in making an environment habitable. Both color and light level combine to create comfortable and efficient work areas and satisfying leisure time environments. Indeed, without light, color cannot even be experienced. It is vitally important for the designer to understand the subject of habitability and to know how to make a positive impact upon the habitability of spaces through the application of proven principles of color-design developed by the scientific community. Consider some of these possibilities and pitfalls: A color chosen in broad daylight will not appear the same under dim lighting conditions. If a designer were creating a dimly lit cocktail lounge, for example, there is little sense in using dark colors, which also tend to be more expensive. When the eyes have dark-adapted for even five minutes, any color reflecting 20 percent or less will appear black, and the color experience will be lost. Therefore, surface reflectances should be kept at least above 20 to 25 percent to maintain color where illumination is at low levels. In effect, for lower reflectance surfaces, higher levels of illumination are required to produce the most accurate color discriminability.

Haines, Richard F.↗

NASA NTRS2007

Gratings and Random Reflectors for Near-Infrared PIN Diodes

Crossed diffraction gratings and random reflectors have been proposed as means to increase the quantum efficiencies of InGaAs/InP positive/intrinsic/ negative (PIN) diodes designed to operate as near-infrared photodetectors. The proposal is meant especially to apply to focal-plane imaging arrays of such photodetectors to be used for near-infrared imaging. A further increase in quantum efficiency near the short-wavelength limit of the near-infrared spectrum of such a photodetector array could be effected by removing the InP substrate of the array. The use of crossed diffraction gratings and random reflectors as optical devices for increasing the quantum efficiencies of quantum-well infrared photodetectors (QWIPs) was discussed in several prior NASA Tech Briefs articles. While the optical effects of crossed gratings and random reflectors as applied to PIN photodiodes would be similar to those of crossed gratings and random reflectors as applied to QWIPs, the physical mechanisms by which these optical effects would enhance efficiency differ between the PIN-photodiode and QWIP cases: In a QWIP, the multiple-quantum-well layers are typically oriented parallel to the focal plane and therefore perpendicular or nearly perpendicular to the direction of incidence of infrared light. By virtue of the applicable quantum selection rules, light polarized parallel to the focal plane (as normally incident light is) cannot excite charge carriers and, hence, cannot be detected. A pair of crossed gratings or a random reflector scatters normally or nearly normally incident light so that a significant portion of it attains a component of polarization normal to the focal plane and, hence, can excite charge carriers. A pair of crossed gratings or a random reflector on a PIN photodiode would also scatter light into directions away from the perpendicular to the focal plane. However, in this case, the reason for redirecting light away from the perpendicular is to increase the length of the optical path through the detector to increase the probability of absorption of photons and thereby increase the resulting excitation of charge carriers. A pair of crossed gratings or a random reflector according to the proposal would be fabricated as an integral part of photodetector structure on the face opposite the focal plane (see figure). In the presence of crossed gratings, light would make four passes through the device before departing. In the presence of a random reflector, a significant portion of the light would make more than four passes: After each bounce, light would be scattered at a different random angle, and would have a chance to escape only when it was reflected, relative to the normal, at an angle less than the critical angle for total internal reflection. Given the indices of refraction of the photodiode materials, this angle would be about 17 . This amounts to a very narrow cone for escape of trapped light.

Gunapala, Sarath↗

NASA NTRS2013

The Sensitive Infrared Signal Detection by Sum Frequency Generation

An up-conversion device that converts 2.05-micron light to 700 nm signal by sum frequency generation using a periodically poled lithium niobate crystal is demonstrated. The achieved 92% up-conversion efficiency paves the path to detect extremely weak 2.05-micron signal with well established silicon avalanche photodiode detector for sensitive lidar applications.

Wong, Teh-Hwa↗

NASA NTRS2004

Thin Film Solar Cells: Organic, Inorganic and Hybrid

Thin film solar cells are an important developing resource for hundreds of applications including space travel. In addition to being more cost effective than traditional single crystal silicon cells, thin film multi-crystaline cells are plastic and light weight. The plasticity of the cells allows for whole solar panels to be rolled out from reams. Organic layers are being investigated in order to increase the efficiency of the cells to create an organic / inorganic hybrid cell. The main focus of the group is a thin film inorganic cell made with the absorber CuInS2. So far the group has been successful in creating the layer from a single-source precursor. They also use a unique method of film deposition called chemical vapor deposition for this. The general makeup of the cell is a molybdenum back contact with the CuInS2 layer, then CdS, ZnO and aluminum top contacts. While working cells have been produced, the efficiency so far has been low. Along with quantum dot fabrication the side project of this that is currently being studied is adding a polymer layer to increase efficiency. The polymer that we are using is P3OT (Poly(3-octylthiopene-2,5-diyll), retroregular). Before (and if) it is added to the cell, it must be understood in itself. To do this simple diodes are being constructed to begin to look at its behavior. The P3OT is spin coated onto indium tin oxide and silver or aluminum contacts are added. This method is being studied in order to find the optimal thickness of the layer as well as other important considerations that may later affect the composition of the finished solar cell. Because the sun is the most abundant renewable, energy source that we have, it is important to learn how to harness that energy and begin to move away from our other depleted non-renewable energy sources. While traditional silicon cells currently create electricity at relatively high efficiencies, they have drawbacks such as weight and rigidness that make them unattractive especially for space applications. Thin film photovoltaics have the potential to alleviate these problems and create a cheap and efficient way to harness the power of the sun.

Dankovich, John↗

DOE OSTI2024

1 kV 150 A Bidirectional Isolated DC/DC Converter With Full Range ZVS For Charger Application

This paper focusses on the development of a bidirectional DC/DC converter based on dual active bridge (DAB) converter for 1 kV class fast charger applications. A novel modulation technique is proposed to achieve zero voltage switching across the entire operating range of a vehicle battery system. The topology includes a tap changer to support multiple class of vehicles. The full range ZVS operation will allow high efficiency operation even at light load, reduced dv/dt to improve transformer insulation lifetime and mitigate EMI impact. A 1 kV class, 150 A prototype was developed to validate the proposed concepts.

Kandula, Prasad↗

NASA NTRS1994

Use of diffusive optical fibers for plant lighting

Lighting is one of the most critical aspects in plant production and environmental research with plants. Much research has been repeated on the effect of light intensity, spectral distribution of light and lighting cycle, but comparatively little research done on the effect of lighting direction on the growth, development and morphology of plants. When plants are grown with lamps above, light is directed downward to the plants. Downward or overhead lighting is utilized in almost all cases. However, downward lighting does not always give the best result in terms of lighting efficiency, growth, development and morphology of plants. In the present study, a sideward lighting system was developed using diffusive optical fiber belts. More higher quality tissue-cultured transplants could be produced in a reduced space with the sideward lighting system than with a downward lighting system. An application of the sideward lighting system using diffusive optical fiber belts is described and the advantages and disadvantages are discussed.

Kozai, T.↗

NASA NTRS2021

NASA High Efficiency, High OPR Capable Small Core Compressor

As future aircraft become lighter and more aerodynamically efficient, thrust requirements will decrease, reducing the core size of the engine. Furthermore, in the pursuit of improved fuel burn, engine overall pressure ratio and bypass ratio will increase, further driving down engine core size (core size being defined as high-pressure compressor [HPC] exit-corrected flow). These drivers together mean that the core size for future single-aisle aircraft applications will shrink below 3.0 lb/s. Traditionally, this small core compressor size is in the domain of axi-centrifugal designs, machines that are typically less efficient and limited to pressure ratios of ~25 due to stress and thermomechanical fatigue in the centrifugal impeller. In this light, NASA and Pratt & Whtiney (P&W) embarked upon a program to develop technologies to enable an all-axial high-pressure compressor with a core size below 3.0 lb/s and an overall pressure ratio greater than 50. The challenge with an all-axial high-pressure compressor at this core size is the small span at the rear of the compressor. As core size is scaled down, the rotor tip clearances, stator hub seal clearances, fillet sizes and leading edge thicknesses do not scale, leading to significant efficiency penalties. The goal of this program is to recover this lapse and realize the cycle benefits of small core size and high overall pressure ratio. The small core challenges described are mitigated through design optimization and technology insertion, enabling an estimated 5 to 10% fuel burn reduction relative to 2020 best-in-class. Three test rigs run at NASA Glenn Research Center evolved the small core design: a low-speed rig to vet technology and validate tools, and two high speeds rigs, the first to demonstrate an optimized meanline design and the second to validate technology to manage large rotor tip gaps. The efficiency improvement validated with these rigs has unlocked the small core design space, demonstrating that small core compressors can maintain a similar efficiency to current best-in-class large core size compressors. In addition to advancing the state-of-the-art of technology, the program has also advanced the modeling standards for multistage compressors with large clearance-to-span ratios. A best practice modeling standard was developed over the course of the program, incorporating learning from all three rig programs.

Axial Compressors↗

DOE OSTI2024

Bright and durable scintillation from colloidal quantum shells

Abstract Efficient, fast, and robust scintillators for ionizing radiation detection are crucial in various fields, including medical diagnostics, defense, and particle physics. However, traditional scintillator technologies face challenges in simultaneously achieving optimal performance and high-speed operation. Herein we introduce colloidal quantum shell heterostructures as X-ray and electron scintillators, combining efficiency, speed, and durability. Quantum shells exhibit light yields up to 70,000 photons MeV −1 at room temperature, enabled by their high multiexciton radiative efficiency thanks to long Auger-Meitner lifetimes (>10 ns). Radioluminescence is fast, with lifetimes of 2.5 ns and sub-100 ps rise times. Additionally, quantum shells do not exhibit afterglow and maintain stable scintillation even under high X-ray doses (>10 9 Gy). Furthermore, we showcase quantum shells for X-ray imaging achieving a spatial resolution as high as 28 line pairs per millimeter. Overall, efficient, fast, and durable scintillation make quantum shells appealing in applications ranging from ultrafast radiation detection to high-resolution imaging.

47 OTHER INSTRUMENTATION↗

NASA NTRS1980

High efficiency epitaxial GaAs/GaAs and GaAs/Ge solar cell technology using OM/CVD

A technology for fabricating high efficiency, thin film GaAs solar cells on substrates appropriate for space and/or terrestrial applications was developed. The approach adopted utilizes organometallic chemical vapor deposition (OM-CVD) to form a GaAs layer epitaxially on a suitably prepared Ge epi-interlayer deposited on a substrate, especially a light weight silicon substrate which can lead to a 300 watt per kilogram array technology for space. The proposed cell structure is described. The GaAs epilayer growth on single crystal GaAs and Ge wafer substrates were investigated.

Wang, K. L.↗

NASA NTRS2012

Overview of Photocatalysis, Photocatalytic Surface Materials Studies, and Demonstration of Self-Cleaning Materials for Space and Terrestrial Based Applications at the Infinity Science Center at NASA Stennis Space Center

Research into photocatalytic technology has been progressing for over three decades in the early 1990s Japanese and European companies initiate research into photocatalytic technology. In the 1996 specific focus on the technology with the first large-scale application: the construction of a church in Rome (Jubilee Church). And in 2000 Europe and Japan research into the benefits of photocatalytic technology. Currently, photocatalytic technology continues to improve, and with time development is becoming more efficient and effective. What is Photocatalysis? Photo: phenomenon induced by the light, having specifically a wavelength around 320-400 nm (artificial or natural sunlight). Catalyst: a material that induces a reaction but is not consumed or transformed by it. The catalyst remains constantly available. In this case, the catalyst is made with nano-particles of titanium oxide (Ti02).

Underwood, Lauren W.↗

NASA NTRS1947

Preliminary Tests of a Burner for Ram-Jet Applications

Preliminary tests have been made of a small burner to meet the requirements for application to supersonic ram jets. The principal requirements were taken as: (1) efficient combustion in a high-velocity air stream, (2) utilization for combustion of only a small fraction of the air passing through the unit, (3) low resistance to air flow, (4) simple construction, and (5) light weight. Tests of a small burner were carried to stream velocities of nearly 150 feet per second and fuel rates such that one-eighth to one-fourth of the total air was involved in combustion. Commercial propane was selected as the fuel since its low boiling point facilitated vaporization. Combustion which was 80 percent complete along with low aerodynamic losses was obtained by injecting the fuel evenly, prior to ignition, and allowing it to mix with the air without appreciably disturbing the stream. The pressure drop due to frictional losses around the burner and to the adjacent inside walls of the ram jet is small compared with the pressure drop due to combustion.

Huber, Paul W.↗

NASA NTRS2004

Programming an Experiment Control System

As NASA develops plans for more and more ambitious missions into space, it is the job of NASA's researchers to develop the technologies that will make those planed missions feasible. One such technology is energy conversion. Energy is all around us; it is in the light that we see in the chemical bonds that hold compounds together, and in mass itself.Energy is the fundamental building block of our universe, yet it has always been straggle for humans to convert this energy into useable forms, like electricity. For space-based applications, NASA requires efficient energy conversion method that require little or no fuel.

Lange, Stuart↗

NASA NTRS2009

Design and Manufacture of Structurally Efficient Tapered Struts

Composite materials offer the potential of weight savings for numerous spacecraft and aircraft applications. A composite strut is just one integral part of the node-to-node system and the optimization of the shut and node assembly is needed to take full advantage of the benefit of composites materials. Lockheed Martin designed and manufactured a very light weight one piece composite tapered strut that is fully representative of a full scale flight article. In addition, the team designed and built a prototype of the node and end fitting system that will effectively integrate and work with the full scale flight articles.

Brewster, Jebediah W.↗

DOE OSTI2025

Ultrawide bandgap semiconductor h-BN for direct detection of fast neutrons

III-nitride wide bandgap semiconductors have contributed on the grandest scale to many technological advances in lighting, displays, and power electronics. Among III-nitrides, BN has another unique application as a solid-state neutron detector material because the isotope B-10 is among a few elements that have an unusually large interaction cross section with thermal neutrons. A record high thermal neutron detection efficiency of 60% has been achieved by B-10 enriched h-BN detectors of 100 μm in thickness in our group. However, direct detection of fast neutrons with energies above 1 MeV is highly challenging due to the extremely low interaction cross section of fast neutrons with matter. We report the successful attainment of 0.4 mm thick freestanding h-BN 4"-diameter wafers, which enabled the demonstration of h-BN fast neutron detectors capable of delivering a detection efficiency of 2.2% in response to a bare AmBe neutron source. Furthermore, it was shown that the energy information of incoming fast neutrons is retained in the neutron pulse-height spectra. A comparison of characteristics between h-BN fast and thermal neutron detectors is summarized. Neutron detectors are vital diagnostic instruments for nuclear and fusion reactor power and safety monitoring, oil field exploration, neutron imaging and therapy, as well as for plasma and material science research. With the outstanding attributes resulting from its ultrawide bandgap (UWBG), including the ability to operate at extreme conditions of high power, voltage, and temperature, the availability of h-BN UWBG semiconductor detectors with the capability of simultaneously detecting thermal and fast neutrons with high efficiencies is expected to open unprecedented applications that are not possible to attain by any other types of neutron detectors.

36 MATERIALS SCIENCE↗

DOE OSTI2024

An Integrated Framework for Risk Assessment of Safety-related Digital Instrumentation and Control Systems in Nuclear Power Plants: Methodology Advancement and Application

This report documents activities performed by Idaho National Laboratory (INL) during fiscal year (FY) 2024 for the U.S. Department of Energy (DOE) Light Water Reactor Sustainability (LWRS) Program, Risk Informed Systems Analysis (RISA) Pathway, Digital Instrumentation and Control (DI&C) Risk Assessment project. The goal of the RISA Pathway is to optimize safety margins and minimize uncertainties to achieve economic efficiencies while maintaining high levels of safety. This is accomplished by providing scientific basis to better represent safety margins and factors that contribute to cost and safety, and by developing new technologies that reduce operating costs. The research efforts for FY 2024 encompass methodology refinement and exploration. The efforts include: (1) The implementation of a natural language processing tool to expedite key aspects of the reliability analysis methods developed by INL; (2) advances to support intersystem CCF analysis by providing guidance for and identification of coupling mechanisms that may contribute to CCF; (3) the investigation of how generative artificial intelligence tools can aid in hazard analysis and diversity and defense in depth (i.e., D3) assessments; (4) Industry collaboration, allowing the demonstration of and INL's risk assessment tools to support risk assessment of DI&C systems at early and late stages of development; (4) a roadmap for the development of a software for each of INL's risk assessment tools; (5) The development of a theory and methodology manual for a risk quantification methodology; (6) the development of a reliability analysis for machine learning (ML)-integrated control systems.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS2013

Nonlinear Analysis and Post-Test Correlation for a Curved PRSEUS Panel

The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept, developed by The Boeing Company, has been extensively studied as part of the National Aeronautics and Space Administration's (NASA s) Environmentally Responsible Aviation (ERA) Program. The PRSEUS concept provides a light-weight alternative to aluminum or traditional composite design concepts and is applicable to traditional-shaped fuselage barrels and wings, as well as advanced configurations such as a hybrid wing body or truss braced wings. Therefore, NASA, the Federal Aviation Administration (FAA) and The Boeing Company partnered in an effort to assess the performance and damage arrestments capabilities of a PRSEUS concept panel using a full-scale curved panel in the FAA Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility. Testing was conducted in the FASTER facility by subjecting the panel to axial tension loads applied to the ends of the panel, internal pressure, and combined axial tension and internal pressure loadings. Additionally, reactive hoop loads were applied to the skin and frames of the panel along its edges. The panel successfully supported the required design loads in the pristine condition and with a severed stiffener. The panel also demonstrated that the PRSEUS concept could arrest the progression of damage including crack arrestment and crack turning. This paper presents the nonlinear post-test analysis and correlation with test results for the curved PRSEUS panel. It is shown that nonlinear analysis can accurately calculate the behavior of a PRSEUS panel under tension, pressure and combined loading conditions.

Gould, Kevin↗

DOE OSTI2024

Förster Resonance Energy Transfer and Enhanced Emission in Cs 4 PbBr 6 Nanocrystals Encapsulated in Silicon Nano-Sheets for Perovskite Light Emitting Diode Applications

Encapsulating Cs 4 PbBr 6 quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs 4 PbBr 6 ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs 4 PbBr 6 pseudo-spherical quantum dots is quenched and is dominated with Pb 2+ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs 4 PbBr 6 ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb 2+ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs 4 PbBr 6 quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials.

36 MATERIALS SCIENCE↗