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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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All sources NASA NTRS DOE OSTI

DOE OSTI2018

Hexagonal Nanopyramidal Prisms of Nearly Intrinsic InN on Patterned GaN Nanowire Arrays

By using multiple growth steps that separate the nucleation and growth processes, we show that nearly intrinsic InN single nanocrystals of high optical quality can be formed on patterned GaN nanowire arrays by molecular beam epitaxy. The InN nanostructures form into well-defined hexagonal prisms with pyramidal tops. Micro-photoluminescence (μ-PL) is carried out at low temperature (LT: 28.2 K) and room temperature (RT: 285 K) to gauge the relative material quality of the InN nanostructures. Nanopyramidal prisms grown using a three-step growth method are found to show superior quantum efficiency. In conclusion, excitation and temperature dependent μ-PL demonstrates the very high quality and nearly intrinsic nature of the ordered InN nanostructure arrays.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides

Perovskite oxides can host various anion-vacancy orders, which greatly change their properties, but the order pattern is still difficult to manipulate. Separately, lattice strain between thin film oxides and a substrate induces improved functions and novel states of matter, while little attention has been paid to changes in chemical composition. Here we combine these two aspects to achieve strain-induced creation and switching of anion-vacancy patterns in perovskite films. Epitaxial SrVO 3 films are topochemically converted to anion-deficient oxynitrides by ammonia treatment, where the direction or periodicity of defect planes is altered depending on the substrate employed, unlike the known change in crystal orientation. First-principles calculations verified its biaxial strain effect. Like oxide heterostructures, the oxynitride has a superlattice of insulating and metallic blocks. Given the abundance of perovskite families, this study provides new opportunities to design superlattices by chemically modifying simple perovskite oxides with tunable anion-vacancy patterns through epitaxial lattice strain.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Typical hot water draw patterns based on field data

There is significant variation in hot water use and draw patterns among households. This report describes typical hot water use patterns in single-family residences in North America. We found that daily hot water use is highly variable both among residences and within the same residence. We compared the results of our analysis of the field data to the conditions and draw patterns established in the current U.S. Department of Energy (DOE) test procedure for residential water heaters. The results show a higher number of smaller draws at lower flow rates than used in the test procedure. The data from which the draw patterns were developed were obtained from 12 separate field studies. This report describes the ways in which we managed, cleaned, and analyzed the data and the results of our data analysis. After preparing the data, we used the complete data set to analyze inlet and outlet water temperatures. Then we divided the data into three clusters reflecting house configurations that demonstrated small, medium, or large median daily hot water use. We developed the three clusters partly to reflect efforts of the ASHRAE standard project committee (SPC) 118.2 to revise the test procedure for residential water heaters to incorporate a range of draw patterns. ASHRAE SPC 118.2 has identified the need to separately evaluate at least three, and perhaps as many as five, different water heater capacities. We analyzed the daily hot water use data within each cluster in terms of volume and number of hot water draws. The daily draw patterns in each cluster were characterized using distributions for volume of draws, duration of draws, time since previous draw, and flow rates.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2016

Observation of cosmic ray hadrons at the top of the Sierra Negra volcano in Mexico with the SciCRT prototype

In this work we report the flux of protons and neutral emission measured at the top of the Sierra Negra volcano at 4600 m.a.s.l. (575 g/cm2), in Eastern Mexico. As an example of the capability of the mini-SciCR as a cosmic ray detector we present the Forbush decrease recorded on March 7, 2012. These data were obtained with a cosmic ray detector prototype called mini-SciCR that was operating from October 2010 to July 2012. Our main aims were to measure the hadronic component flux of the secondary cosmic ray and to show the appropriate performance of all system of the detector. To separate the signals of protons from other charged particles we obtained the energy deposition pattern when they cross the detector using a Monte Carlo simulation, and to separate the signals of neutral emission we used an anticoincidence system between the edge bars and the internal bars of the detector. The mini-SciCR is a prototype of a new cosmic ray detector called SciBar Cosmic Ray Telescope (SciCRT) installed in the same place, which is in the process of calibration. The SciCRT will work mainly as a Solar Neutron and Muon Telescope, it is designed to achieve: (1) larger effective area than the current Solar Neutron Telescope, (2) higher energy resolution to determine the energy spectrum of solar neutrons, (3) lower energy threshold, and (4) higher particle identification ability.

58 GEOSCIENCES↗

DOE OSTI2011

SUBSURFACE MAGNETIC FIELD AND FLOW STRUCTURE OF SIMULATED SUNSPOTS

We present a series of numerical sunspot models addressing the subsurface field and flow structure in up to 16 Mm deep domains covering up to two days of temporal evolution. Changes in the photospheric appearance of the sunspots are driven by subsurface flows in several Mm depth. Most of magnetic field is pushed into a downflow vertex of the subsurface convection pattern, while some fraction of the flux separates from the main trunk of the spot. Flux separation in deeper layers is accompanied in the photosphere with light bridge formation in the early stages and formation of pores separating from the spot at later stages. Over a timescale of less than a day we see the development of a large-scale flow pattern surrounding the sunspots, which is dominated by a radial outflow reaching about 50% of the convective rms velocity in amplitude. Several components of the large scale flow are found to be independent from the presence of a penumbra and the associated Evershed flow. While the simulated sunspots lead to blockage of heat flux in the near surface layers, we do not see compelling evidence for a brightness enhancement in their periphery. We further demonstrate that the influence of the bottom boundary condition on the stability and long-term evolution of the sunspot is significantly reduced in a 16 Mm deep domain compared to the shallower domains considered previously.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1983

Stresses in a quasi-isotropic pin loaded connector using photoelasticity

Birefringent glass-epoxy and a numerical stress separation scheme are used to compute the stresses in the vicinity of a pin-loaded hole. The radial and circumferential stresses at the hole edge, and the net section and shear-out stresses are computed. The numerical and experimental results are compared with the computed stresses. The fixture used to load the connector is discussed and typical isochromatic and isoclinic fringe patterns are presented. The stress-separation scheme is briefly discussed.

Hyer, M. W.↗

NASA NTRS1984

Stresses in a quasi-isotropic pin-loaded connector using photoelasticity

Hyer, M. W.↗

NASA NTRS1988

Application of pattern recognition techniques to the identification of aerospace acoustic sources

A pattern recognition system was developed that successfully recognizes simulated spectra of five different types of transportation noise sources. The system generates hyperplanes during a training stage to separate the classes and correctly classify unknown patterns in classification mode. A feature selector in the system reduces a large number of features to a smaller optimal set, maximizing performance and minimizing computation.

Fuller, Chris R.↗

NASA NTRS1988

Observation of airplane flow fields by natural condensation effects

In-flight condensation patterns can illustrate a variety of airplane flow fields, such as attached and separated flows, vortex flows, and expansion and shock waves. These patterns are a unique source of flow visualization that has not been utilized previously. Condensation patterns at full-scale Reynolds number can provide useful information for researchers experimenting in subscale tunnels. It is also shown that computed values of relative humidity in the local flow field provide an inexpensive way to analyze the qualitative features of the condensation pattern, although a more complete theoretical modeling is necessary to obtain details of the condensation process. Furthermore, the analysis revealed that relative humidity is more sensitive to changes in local static temperature than to changes in pressure.

Campbell, James F.↗

NASA NTRS1974

Lee surface flow phenomena over space shuttle at large angles of attack at M sub infinity equal 6

Surface pressure and heat transfer, flow separation, flow field, and oil flow patterns on the leeward side of a space shuttle orbiter model are investigated at a free stream Mach number of 6. The free stream Reynolds numbers are between 1.64 times 10 to the 7th power and 1.31 times 10 to the 8th power per meter, and the angle of attack is varied between 0 deg and 40 deg for the present experiments. The stagnation temperatures for the tests are approximately 500 K and the wall temperature is maintained at 290 K. Existing numerical methods of three-dimensional inviscid supersonic flow theory and compressible boundary layer theory are used to predict the present experimental measurements. Results of the present tests indicate two distinct types of flow separation and surface peak heating depending on the angle of attack.

Zakkay, V.↗

DOE OSTI2019

Reconstruction of larval origins based on genetic relatedness and biophysical modeling

The assessment of the mechanisms and patterns of larval connectivity between geographically separated populations leads to a better understanding of benthic marine population dynamics, especially in commercially valuable species. This study investigated for the first time the fine-scale temporal genetic variability of new settlers and their origins in a benthic marine organism with one of the longest pelagic larval phases, the Caribbean spiny lobster (Panulirus argus). We genotyped newly settled postlarvae in the Florida Keys and adults of spiny lobster from the Florida Keys and throughout the Caribbean Sea. We identified strong larval connectivity between Dominican Republic, Belize, Nicaragua, the Florida Keys, and West-Florida. the larval dispersal modeling suggests that Florida’s lobster population could receive recruits from within and from other areas outside its state and national maritime boundaries. The genetic analyses refine the oceanographic model indicating that the connectivity patterns described could also result from unknown parental populations sourcing adults and postlarvae in different spawning seasons to the Florida Keys. We discuss the importance of small temporal scales to identify patterns in larval export. Our findings are significant on two levels. From the larval dispersal perspective, genetic results and biophysical modeling identify patterns of gene flow enhancing persistence of local populations. From an economic and fishery perspective, P. argus is the most important commercial species in the Caribbean and our results inform how considering larval source and sink dynamics across international boundaries could improve management plans at local, national, and regional levels.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2026

Magnon-Magnon Interaction Induced by Dynamic Coupling in a Hybrid Magnonic Crystal

We report a combined experimental and numerical investigation of spin-wave dynamics in a hybrid magnonic crystal consisting of a CoFeB artificial spin ice (ASI) of stadium-shaped nanoelements patterned atop a continuous NiFe film separated by a 5 nm Al 2 O 3 spacer. Using Brillouin light scattering spectroscopy, we probe the frequency dependence of thermal spin waves as functions of applied magnetic field and wavevector, revealing the decisive role of interlayer dipolar coupling in the magnetization dynamics. Micromagnetic simulations complement the experiments, showing a strong interplay between ASI edge modes and backward volume modes in the NiFe film. The contrast in saturation magnetization between CoFeB and NiFe enhances this coupling, leading to a pronounced hybridization manifested as a triplet of peaks in the BLS spectra predicted by simulations and observed experimentally. This magnon−magnon coupling persists over a wide magnetic field range, shaping both the spin-wave dispersion at fixed fields and the full frequency-field response throughout the magnetic hysteresis loop. Our findings establish how ASI geometry can selectively enhance specific spin-wave wavelengths in the underlying film, thereby boosting their amplitude and identifying them as preferential channels for spin wave transmission and manipulation.

Brillouin light scattering spectroscopy↗

DOE OSTI2021

Influence of turbulence intensity on vortex pattern for a rigid cylinder with turbulence stimulation in flow induced oscillations

The effect of ambient turbulence intensity on the flow induced oscillations of rigid circular cylinders with symmetric and asymmetric local turbulence stimulation is studied. Cylinders oscillate in one degree of freedom transversely to a steady uniform flow. Two-dimensional unsteady Reynolds-Average Navier-Stokes equations with the Spalart-Allmaras turbulence model are used to solve the problem numerically. Three freestream turbulence intensity values (0.2%, 1%, 5%) are used to study the influence of turbulence intensity on vortex pattern. Simulation results are compared with experimental data measured in the Marine Renewable Energy Laboratory of the University of Michigan in the range of 30,000 ≤ Re ≤ 110,000. The amplitude ratio, lift coefficient, vortex modes, and the interactions between vortices and cylinders are observed and discussed. In conclusion, major conclusions are: (a) Vortex patterns strongly depend on the freestream ambient turbulence intensity. (b) Low turbulence intensity can generate multi-vortex patterns at high Re. (c) High turbulence intensity results in fewer separations of a shed vortex into multiple vortices inducing emergence of elongated vortex patterns.

42 ENGINEERING↗

DOE OSTI2024

Human electromagnetic field exposure in wearable communications systems: A review

While wearable technologies have taken essential parts of our daily lives, concerns on human health are often overseen. Mainly due to extreme proximity or direct physical contact to human skin, wearable communications devices are prone to cause higher levels of electromagnetic field (EMF) exposure at human skin surface than any other type of wireless technologies. Nevertheless, while focusing on theoretical aspects of human EMF exposure in wearable communications, prior work paid little to no attention on exact exposure levels generated by commercial wearable devices that are already widely used by public consumers. In this context, this paper provides an extensive review of SAR from various commercial wearable devices that are currently sold in the market, as well as the analytical framework and the current measurement methodologies for standard compliance tests. To extend the discussion to general wearable communications, this paper presents simulation results adopting representative antenna patterns, which leads to suggestion of separation distances to keep the current safety guidelines. In particular, considering the increasing interest in millimeter wave (mmW), this paper sheds light on EMF exposure evaluated at 60 GHz and compares to results from 2.4 GHz.

42 ENGINEERING↗

DOE OSTI2016

Absolute Intra-Molecular Distance Measurements with Ångström-Resolution using Anomalous Small-Angle X-ray Scattering

Accurate determination of molecular distances is fundamental to understanding the structure, dynamics, and conformational ensembles of biological macromolecules. Here we present a method to determine the full,distance,distribution between small (~7 Å) gold labels attached to macromolecules with very high-precision(≤1 Å) and on an absolute distance scale. Our method uses anomalous small-angle X-ray scattering close to a gold absorption edge to separate the gold-gold interference pattern from other scattering contributions. Results for 10-30 bp DNA constructs achieve excellent signal-to-noise and are in good agreement with previous results obtained by single-energy,SAXS measurements without requiring the preparation and measurement of single labeled and unlabeled samples. Finally, the use of small gold labels in combination with ASAXS read out provides an attractive approach to determining molecular distance distributions that will be applicable to a broad range of macromolecular systems.

47 OTHER INSTRUMENTATION↗

DOE OSTI2013

Nexus between directionality of terahertz waves and structural parameters in groove patterned InAs

We performed terahertz (THz) time-domain spectroscopy in various geometries, for characterizing the directivity of THz waves emitted from groove patterned InAs structures. We first identified two transient transport processes as underlying THz emission mechanisms in InAs epilayers with different thicknesses. Carrier drift around the surface depletion region was predominant for the THz wave generation in the thin sample group (10-70 nm), whereas electronic diffusion overrode the drift currents in the thick sample group (370-900 nm) as revealed by the amplitude change and phase reversal. Through a combination of electron-beam lithography and inductively coupled plasma etching in 1 {mu}m-thick InAs epilayers, we could further periodically fabricate either asymmetric V-groove patterns or symmetric parabolic apertures. The THz amplitude was enhanced, particularly along the line-of-sight transmissive direction when the periodic groove patterns act as microscale reflective mirrors separated by a scale of the diffusion length.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Single photon energy dispersive x-ray diffraction

With the pressure range accessible to laser driven compression experiments on solid material rising rapidly, new challenges in the diagnosis of samples in harsh laser environments are emerging. When driving to TPa pressures (conditions highly relevant to planetary interiors), traditional x-ray diffraction techniques are plagued by increased sources of background and noise, as well as a potential reduction in signal. In this paper we present a new diffraction diagnostic designed to record x-ray diffraction in low signal-to-noise environments. By utilising single photon counting techniques we demonstrate the ability to record diffraction patterns on nanosecond timescales, and subsequently separate, photon-by-photon, signal from background. In doing this, we mitigate many of the issues surrounding the use of high intensity lasers to drive samples to extremes of pressure, allowing for structural information to be obtained in a regime which is currently largely unexplored.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Evaporation-driven clustering of microscale pillars and lamellae

As a liquid film covering an array of micro- or nanoscale pillars or lamellae evaporates, its meniscus pulls the elastic patterns together because of capillary effects, leading to clustering of the slender microstructures. While this elastocapillary coalescence may imply various useful applications, it is detrimental to a semiconductor manufacturing process called the spin drying, where a liquid film rinses patterned wafers until drying. To understand the transient mechanism underlying such self-organization during and after liquid evaporation, we visualize the clustering dynamics of polymer micropatterns. Our visualization experiments reveal that the patterns clumped during liquid evaporation can be re-separated when completely dried in some cases. This restoration behavior is explained by considering adhesion energy of the patterns as well as capillary forces, which leads to a regime map to predict whether permanent stiction would occur. This work does not only extend our understanding of micropattern stiction, but also suggests a novel path to control and prevent pattern clustering.

36 MATERIALS SCIENCE↗