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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 1,423 records · Page 79

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NASA NTRS1990

A concatenated coded modulation scheme for error control

A concatenated coded modulation scheme for error control in data communications is presented. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary PSK modulation. Error performance of the scheme is analyzed for an AWGN channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner code and relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The proposed scheme is particularly effective for high speed satellite communications for large file transfer where high reliability is required. Also presented is a simple method for constructing block codes for M-ary PSK modulation. Some short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm.

Kasami, Tadao↗

NASA NTRS1991

Tiltrotor research aircraft composite blade repairs: Lessons learned

The XV-15, N703NA Tiltrotor Research Aircraft located at the NASA Ames Research Center, Moffett Field, California, currently uses a set of composite rotor blades of complex shape known as the advanced technology blades (ATBs). The main structural element of the blades is a D-spar constructed of unidirectional, angled fiberglass/graphite, with the aft fairing portion of the blades constructed of a fiberglass cross-ply skin bonded to a Nomex honeycomb core. The blade tip is a removable laminate shell that fits over the outboard section of the spar structure, which contains a cavity to retain balance weights. Two types of tip shells are used for research. One is highly twisted (more than a conventional helicopter blade) and has a hollow core constructed of a thin Nomex-honeycomb-and-fiberglass-skin sandwich; the other is untwisted with a solid Nomex honeycomb core and a fiberglass cross-ply skin. During initial flight testing of the blades, a number of problems in the composite structure were encountered. These problems included debonding between the fiberglass skin and the honeycomb core, failure of the honeycomb core, failures in fiberglass splices, cracks in fiberglass blocks, misalignment of mated composite parts, and failures of retention of metal fasteners. Substantial time was spent in identifying and repairing these problems. Discussed here are the types of problems encountered, the inspection procedures used to identify each problem, the repairs performed on the damaged or flawed areas, the level of criticality of the problems, and the monitoring of repaired areas. It is hoped that this discussion will help designers, analysts, and experimenters in the future as the use of composites becomes more prevalent.

Espinosa, Paul S.↗

NASA NTRS1992

Tiltrotor Research Aircraft composite blade repairs - Lessons learned

Espinosa, Paul S.↗

NASA NTRS1993

The formation and evolution of Alpha and Tellus tesserae on Venus

Although tesserae comprise at approximately 10 percent of the surface of Venus, the nature of their formation and evolution is not well understood. One important clue to elucidate this problem is tessera boundaries which are of two types: type 1 are generally embayed by plains; type 2 boundaries are characterized by being linear at the hundred kilometer scale and often associated with steep scarps or tectonic features. Previous study of a distinctive type 2 boundary at Alpha Regio was pursued in order to characterize and assess the implications for this style in general. A model of gravitational relaxation of the tessera block was presented to explain the specific style of type 2 feature seen at western Alpha; however, this model cannot account for the full range of interior structures of Alpha, namely widespread compressional features overprinted by extensional features and volcanism. In order to explain the features of Alpha, we have considered a three-stage model involving (1) mantle downwelling and compression of the lithosphere, (2) delamination of the thickened tessera root, and (3) gravitational relaxation and extension of the tessera plateau. We compare this to the characteristics of Tellus Regio in order to test its broader application.

Gilmore, M. S.↗

NASA NTRS1993

Propagation measurements for satellite radio reception inside buildings

Swept CW signals (from 700 to 1800 MHz) were received inside six buildings of brick, corrugated sheet-metal, wood-frame, mobile-home, and reinforced concrete-wall construction. A transmitter antenna was mounted outdoors on top of an 18 m tower to simulate a satellite, and a linearly scanned directional receiver antenna was used to probe the spatial, spectral, and temporal variability of the signal indoors. Levels were found to have much structure in the spatial and frequency domain, but were relatively stable in time. Typically, people moving nearby produced variations of less than 0.5 dB, whereas a person blocking the transmission path produced fades of 6 to 10 dB. Severe losses (17.5 dB) were observed in the concrete-wall building, which also exhibited the longest multipath delays (over 100 ns). Losses inside a mobile home were even larger (over 20 dB) and were independent of antenna orientation. The power-frequency distortion increased with the logarithm of the bandwidth, but could be reduced by moving to a position of higher power. Only the losses showed a clear frequency dependence, but they could be mitigated by moving the antenna.

Vogel, Wolfhard J.↗

NASA NTRS2004

Transformational Systems Concepts and Technologies for Our Future in Space

NASA is constantly searching for new ideas and approaches yielding opportunities for assuring maximum returns on space infrastructure investments. Perhaps the idea of transformational innovation in developing space systems is long overdue. However, the concept of utilizing modular space system designs combined with stepping-stone development processes has merit and promises to return several times the original investment since each new space system or component is not treated as a unique and/or discrete design and development challenge. New space systems can be planned and designed so that each builds on the technology of previous systems and provides capabilities to support future advanced systems. Subsystems can be designed to use common modular components and achieve economies of scale, production, and operation. Standards, interoperability, and "plug and play" capabilities, when implemented vigorously and consistently, will result in systems that can be upgraded effectively with new technologies. This workshop explored many building-block approaches via way of example across a broad spectrum of technology discipline areas for potentially transforming space systems and inspiring future innovation. Details describing the workshop structure, process, and results are contained in this Conference Publication.

Howell, J. T.↗

NASA NTRS2004

Nanoscale Bio-engineering Solutions for Space Exploration: The Nanopore Sequencer

Characterization of biological systems at the molecular level and extraction of essential information for nano-engineering design to guide the nano-fabrication of solid-state sensors and molecular identification devices is a computational challenge. The alpha hemolysin protein ion channel is used as a model system for structural analysis of nucleic acids like DNA. Applied voltage draws a DNA strand and surrounding ionic solution through the biological nanopore. The subunits in the DNA strand block ion flow by differing amounts. Atomistic scale simulations are employed using NASA supercomputers to study DNA translocation, with the aim to enhance single DNA subunit identification. Compared to protein channels, solid-state nanopores offer a better temporal control of the translocation of DNA and the possibility to easily tune its chemistry to increase the signal resolution. Potential applications for NASA missions, besides real-time genome sequencing include astronaut health, life detection and decoding of various genomes.

Stolc, Viktor↗

NASA NTRS2005

Nanoscale Bioengineering Solutions for Space Exploration the Nanopore Sequencer

Characterization of biological systems at the molecular level and extraction of essential information for nano-engineering design to guide the nano-fabrication of solid-state sensors and molecular identification devices is a computational challenge. The alpha hemolysin protein ion channel is used as a model system for structural analysis of nucleic acids like DNA. Applied voltage draws a DNA strand and surrounding ionic solution through the biological nanopore. The subunits in the DNA strand block ion flow by differing amounts. Atomistic scale simulations are employed using NASA supercomputers to study DNA translocation. with the aim to enhance single DNA subunit identification. Compared to protein channels, solid-state nanopores offer a better temporal control of the translocation of DNA and the possibility to easily tune its chemistry to increase the signal resolution. Potential applications for NASA missions, besides real-time genome sequencing include astronaut health, life detection and decoding of various genomes. http://phenomrph.arc.nasa.gov/index.php

Ioana, Cozmuta↗

NASA NTRS2006

Enhanced Surface Spray Cooling with Embedded and Compound Extended Surface Structures

Experiments were conducted to study the effects of enhanced surface structures on heat flux using spray cooling. The surface enhancements consisted of embedded structures (dimples, pores, and tunnels) and compound extended surface enhancements (straight fins, cubic pin fins and dimples) machined on and within the top surface of copper heater blocks. Each copper block had a projected cross-sectional area of 2.0 sq cm. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2x2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) and gassy conditions (chamber with N2 gas at 101 kPa) with a bulk fluid temperature of 20.5 C. Results for both the nominally degassed and gassy cases show that the highest critical heat flux (CHF) was attained using straight fins and porous tunnels. For the nominally degassed case, both had a CHF of approx.: 142 W/sq cm while for the gassy case their CHF values increased to 175 W/sq cm. This gave an enhancement relative to the nominally degassed flat surface case of approx. 77% and 119% respectively.

Silk, Erie A.↗

DOE OSTI2025

Si content in methacrylamide-containing A- b -(B- r -C) block copolymers and its impact on reactive ion etching properties

Block copolymers (BCPs) of an A-block-(B-random-C) architecture have been explored as materials for nanolithography because the composition and chemistry of the random block enables modification of thermodynamic and wetting properties to meet manufacturing criteria. Here, in this study, A-b-(B-r-C) BCPs created by an amidation reaction of polystyrene-block-poly(pentafluorophenyl methacrylate) (PS-b-PPFMA) with controlled amounts of Si add insight to previous conclusions about the dual contributions of BCP chemistry and reactive ion etch (RIE) gas chemistry on etch properties. We focus on two RIE etch characteristics: organosilicon etch resistance in H 2 /N 2 plasma etching and enhanced removal of non-styrenic structures in an Ar/O 2 etch. Consistent with previous studies, higher amounts of Si result in greater etch resistance under H 2 /N 2 RIE, where at least ∼10 wt. % Si is necessary to exhibit sufficient etch resistance. By contrast, Ar/O 2 etching resulted in etch rates independent of Si content. We observe previously unreported surface roughening aligned with morphological domains during the H 2 /N 2 etch of modified PS-b-PPFMA BCPs. Limited in the amount of allowable Si to attain equal surface energy between blocks, these BCPs are further disqualified in forming a Si-containing mask. However, in an Ar/O 2 etch, the same BCPs exhibit suitable etch contrast and smooth domain structures, forming a uniform PS mask. Ultimately, this study uses the chemical flexibility of these materials to demonstrate the mechanisms of interactions between BCP and etch chemistry that must be considered to design effective materials for pattern transfer applications.

Eom, Christopher J. [University of Chicago, IL (Un↗

DOE OSTI2021

Self-Assembly of 2D Gold Nanoparticle Superlattice in a Polymer Vesicle Layer Driven by Hydrophobic Interaction

We report self-assembly of gold nanoparticles (AuNPs) into highly ordered superstructures provides a promising route toward fabricating materials with new functionalities or enhanced physical properties. Although self-assembly of AuNPs has garnered significant research attention recently, a highly ordered superlattice of AuNPs under a low concentration in a confined geometry formed by nonfunctionalized materials has not been reported. Herein, we investigate the self-assembly of a 2D AuNPs superlattice in a polymer vesicle layer using hydrophobic interactions, which exhibits centered rectangular lattice symmetry. To create the highly ordered AuNPs superlattice, the P(EG x -b-iPGE y ) block copolymers that form the thickness of the hydrophobic vesicle layer comparable to the size of the AuNP are used as a template to control the AuNP degree of freedom. To the best of our knowledge, this study provides the first demonstration of a centered rectangular structure formation of AuNPs at the vesicle layer in 2D confined geometry.

self-assembly↗

DOE OSTI2021

Structural and Spectroscopic Comparison of Soft‐Se vs. Hard‐O Donor Bonding in Trivalent Americium/Neodymium Molecules

Covalency is often considered to be an influential factor in driving An 3+ vs. Ln 3+ selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An 3+ /Ln 3+ covalency differences prevail and manifest as the f-block is traversed, and the effects of periodic breaks beyond Pu. Herein, two Am complexes, [Am{N(E=PPh 2 ) 2 } 3 ] (1-Am, E=Se; 2-Am, E=O) are compared to isoradial [Nd{N(E=PPh 2 ) 2 } 3 ] (1-Nd, 2-Nd) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. In conclusion, through ab initio calculations grounded in UV-vis-NIR spectroscopy and single-crystal X-ray structures, we observe differences in f orbital involvement between Am–Se and Nd–Se bonds, which are not present in O-donor congeners.

Goodwin, Conrad A. P.↗

NASA NTRS1982

An intense, quasi-steady thunderstorm over mountainous terrain. II - Doppler radar observations of the storm morphological structure

The morphological characteristics of mean storm-scale airflow patterns of an intense quasi-steady storm formed in South Park, Colorado are described. Vertical transport of northerly low-level momentum within the updraft imparted a significant blocking on mid-level flow with southerly momentum. The blocking affected the movement and characteristics of adjacent, less organized storms, and additional storm-environment interactions produced an organized recirculation of precipitation particles from the mid-level updraft to the low-level updraft. The steadiness of the storm is found to have depended on the introduction of low-level flow directed opposite to mid-level flow, and on the formation of persistent downdrafts of sufficient magnitude to sustain an active gust front.

Knupp, K. R.↗

DOE OSTI2023

Gas phase synthesis of the C40 nano bowl C 40 H 10

Nanobowls represent vital molecular building blocks of end-capped nanotubes and fullerenes detected in combustion systems and in deep space such as toward the planetary nebula TC-1, but their fundamental formation mechanisms have remained elusive. By merging molecular beam experiments with electronic structure calculations, we reveal a complex chain of reactions initiated through the gas-phase preparation of benzocorannulene (C 24 H 12 ) via ring annulation of the corannulenyl radical (C 20 H 9 • ) by vinylacetylene (C 4 H 4 ) as identified isomer-selectively in situ via photoionization efficiency curves and photoion mass-selected threshold photoelectron spectra. In silico studies provided compelling evidence that the benzannulation mechanism can be expanded to pentabenzocorannulene (C 40 H 20 ) followed by successive cyclodehydrogenation to the C40 nanobowl (C 40 H 10 ) – a fundamental building block of buckminsterfullerene (C 60 ). This high-temperature pathway opens up isomer-selective routes to nanobowls via resonantly stabilized free-radical intermediates and ring annulation in circumstellar envelopes of carbon stars and planetary nebulae as their descendants eventually altering our insights of the complex chemistry of carbon in our Galaxy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Structural and Spectroscopic Comparison of Soft-Se vs. Hard-O Donor Bonding in Trivalent Americium/Neodymium Molecules

Covalency is often considered to be an influential factor in driving An 3+ vs. Ln 3+ selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An 3+ /Ln 3+ covalency differences prevail and manifest as the f-block is traversed, and the effects of periodic breaks beyond Pu. In this work, two Am complexes, [Am{N(E=PPh 2 ) 2 } 3 ] ( 1-Am , E=Se; 2-Am , E=O) are compared to isoradial [Nd{N(E=PPh 2 ) 2 } 3 ] ( 1-Nd , 2-Nd ) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. Through ab initio calculations grounded in UV-vis-NIR spectroscopy and single-crystal X-ray structures, we observe differences in f orbital involvement between Am–Se and Nd–Se bonds, which are not present in O-donor congeners.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Hierarchical, Self-Assembled Metasurfaces via Exposure-Controlled Reflow of Block Copolymer-Derived Nanopatterns

Here, nanopatterning for the fabrication of optical metasurfaces entails a need for high-resolution approaches like electron beam lithography that cannot be readily scaled beyond prototyping demonstrations. Block copolymer thin film self-assembly offers an attractive alternative for producing periodic nanopatterns across large areas, yet the pattern feature sizes are fixed by the polymer molecular weight and composition. Here, a general strategy is reported that overcomes the limitation of fixed feature size by treating the copolymer thin film as a hierarchical resist, in which the nanoscale pattern motif is defined by self-assembly. Feature sizes can then be tuned by thermal reflow controlled locally by irradiative crosslinking or chemical alteration using lithographic ultraviolet light or electron beam exposure. Using blends of polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) with PS and PMMA homopolymer, we demonstrate both self-assembled PS grating and hexagonal hole patterns; exposure-controlled reflow is then used to reduce hole diameter by as much as 50% or increase PS grating linewidth by more than 180%. Transferring these nanopatterns, or their inverse obtained by a lift-off approach, into silicon yields structural colors that may be prescriptively controlled based on nanoscale feature size. Furthermore, patterned exposure enables area-selective feature size control, yielding uniform structural color patterns across centimeter square areas. Electron beam lithography is also used to show that the lithographic resolution of this selective-area control can be extended to the nanoscale dimensions of the self-assembled features. The exposure-controlled reflow approach demonstrated here takes a pivotal step towards fabricating complex, hierarchical optical metasurfaces using scalable self-assembly methods.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1993

A new parallel-vector finite element analysis software on distributed-memory computers

A new parallel-vector finite element analysis software package MPFEA (Massively Parallel-vector Finite Element Analysis) is developed for large-scale structural analysis on massively parallel computers with distributed-memory. MPFEA is designed for parallel generation and assembly of the global finite element stiffness matrices as well as parallel solution of the simultaneous linear equations, since these are often the major time-consuming parts of a finite element analysis. Block-skyline storage scheme along with vector-unrolling techniques are used to enhance the vector performance. Communications among processors are carried out concurrently with arithmetic operations to reduce the total execution time. Numerical results on the Intel iPSC/860 computers (such as the Intel Gamma with 128 processors and the Intel Touchstone Delta with 512 processors) are presented, including an aircraft structure and some very large truss structures, to demonstrate the efficiency and accuracy of MPFEA.

Qin, Jiangning↗

DOE OSTI2020

Magnetic properties of γ-Fe 2 O 3 nanoparticles in a porous SiO 2 shell for drug delivery

A method is presented for synthesizing core–shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple γ -Fe 2 O 3 nanoparticles (~15 nm) enclosed in a SiO 2 (~100–200 nm) matrix using either methyl (denoted TMOS- γ -Fe 2 O 3 ) or ethyl (TEOS- γ -Fe 2 O 3 ) template groups. Low-temperature Mössbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, γ -Fe 2 O 3 , with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of γ -Fe 2 O 3 was greater in the TMOS- γ -Fe 2 O 3 nanoparticles than TEOS- γ -Fe 2 O 3 nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS- γ -Fe 2 O 3 and around 250 K for the TEOS- γ -Fe 2 O 3 . Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core–shell structure.

Physics↗