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At least 649 records · Page 36

All sources NASA NTRS DOE OSTI

DOE OSTI2013

Observation of plasma instabilities related to dust particle growth mechanisms in electron cyclotron resonance plasmas

Instabilities are observed in the self-bias voltage measured on a probe immersed in microwave plasma excited at Electron Cyclotron Resonance (ECR). Observed in the MHz range, they were systematically measured in dust-free or dusty plasmas (obtained for different conditions of applied microwave powers and acetylene flow rates). Two characteristic frequencies, well described as lower hybrid oscillations, can be defined. The first one, in the 60–70 MHz range, appears as a sharp peak in the frequency spectra and is observed in every case. Attributed to ions, its position shift observed with the output power highlights that nucleation process takes place in the dusty plasma. Attributed to lower hybrid oscillation of powders, the second broad peak in the 10–20 MHz range leads to the characterization of dust particles growth mechanisms: in the same way as in capacitively coupled plasmas, accumulation of nucleus confined near the probe in the magnetic field followed by aggregation takes place. Then, the measure of electrical instabilities on the self-bias voltage allows characterizing the discharge as well as the chemical processes that take place in the magnetic field region and their kinetics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Fermi-level shifts in graphene transistors with dual-cut channels scraped by atomic force microscope tips

We investigate the electronic properties of p-type graphene transistors on silicon dioxide with dual-cut channels that were scraped using atomic force microscope tips. In these devices, the current is forced to squeeze into the path between the two cuts rather than flow directly through the graphene sheet. We observe that the gate voltages with minimum current shift toward zero bias as the sizes of the dual-cut regions increase. These phenomena suggest that the Fermi levels in the dual-cut regions are shifted toward the Dirac points after the mechanical scraping process.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Electronic structure at transition metal phthalocyanine-transition metal oxide interfaces: Cobalt phthalocyanine on epitaxial MnO films

The electronic structure of the interface between cobalt phthalocyanine (CoPc) and epitaxially grown manganese oxide (MnO) thin films is studied by means of photoemission (PES) and X-ray absorption spectroscopy (XAS). Our results reveal a flat-lying adsorption geometry of the molecules on the oxide surface which allows a maximal interaction between the π-system and the substrate. A charge transfer from MnO, in particular, to the central metal atom of CoPc is observed by both PES and XAS. The change of the shape of N-K XAS spectra at the interface points, however, to the involvement of the Pc macrocycle in the charge transfer process. As a consequence of the charge transfer, energetic shifts of MnO related core levels were observed, which are discussed in terms of a Fermi level shift in the semiconducting MnO films due to interface charge redistribution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Restorative effect of oxygen annealing on device performance in HfIZO thin-film transistors

Metal-oxide based thin-film transistors (oxide-TFTs) are very promising for use in next generation electronics such as transparent displays requiring high switching and driving performance. In this study, we demonstrate an optimized process to secure excellent device performance with a favorable shift of the threshold voltage toward 0V in amorphous hafnium-indium-zinc-oxide (a-HfIZO) TFTs by using post-treatment with oxygen annealing. This enhancement results from the improved interfacial characteristics between gate dielectric and semiconductor layers due to the reduction in the density of interfacial states related to oxygen vacancies afforded by oxygen annealing. The device statistics confirm the improvement in the device-to-device and run-to-run uniformity. We also report on the photo-induced stability in such oxide-TFTs against long-term UV irradiation, which is significant for transparent displays.

36 MATERIALS SCIENCE↗

DOE OSTI2012

THE SPITZER SPECTROSCOPIC SURVEY OF THE SMALL MAGELLANIC CLOUD (S{sup 4}MC): PROBING THE PHYSICAL STATE OF POLYCYCLIC AROMATIC HYDROCARBONS IN A LOW-METALLICITY ENVIRONMENT

We present results of mid-infrared spectroscopic mapping observations of six star-forming regions in the Small Magellanic Cloud (SMC) from the Spitzer Spectroscopic Survey of the SMC (S{sup 4}MC). We detect the mid-IR emission from polycyclic aromatic hydrocarbons (PAHs) in all of the mapped regions, greatly increasing the range of environments where PAHs have been spectroscopically detected in the SMC. We investigate the variations of the mid-IR bands in each region and compare our results to studies of the PAH bands in the SINGS sample and in a sample of low-metallicity starburst galaxies. PAH emission in the SMC is characterized by low ratios of the 6-9 {mu}m features relative to the 11.3 {mu}m feature and weak 8.6 and 17.0 {mu}m features. Interpreting these band ratios in the light of laboratory and theoretical studies, we find that PAHs in the SMC tend to be smaller and less ionized than those in higher metallicity galaxies. Based on studies of PAH destruction, we argue that a size distribution shifted toward smaller PAHs cannot be the result of processing in the interstellar medium, but instead reflects differences in the formation of PAHs at low metallicity. Finally, we discuss the implications of our observations for our understanding of the PAH life-cycle in low-metallicity galaxies-namely that the observed deficit of PAHs may be a consequence of PAHs forming with smaller average sizes and therefore being more susceptible to destruction under typical interstellar medium conditions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Intensity-dependent interference effect in high-order harmonic generation from aligned H{sub 2}{sup +} molecules

Based on the nonperturbative quantum scattering theory of high-order harmonic generation (HHG) and using the linear combination of atomic orbitals theory of molecular orbitals, we derive the HHG rate formula for molecules. Employing the formula, we study the intensity dependence of the interference effect induced by the molecular structure. We find that the molecular HHG was modulated by the interference not only in the recombination process but also in the ionization process. The location of the interference minimum in HHG shifts to higher energy by a quantity of the ponderomotive energy as the laser intensity increases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Shift photocurrent induced by two-quantum transitions

A theory of the shift current induced by direct two-photon and indirect one-photon absorption is developed for noncentrosymmetric crystals. A formula is derived for the microscopic shifts of Bloch electrons induced by two-quantum processes. It is shown that the ratio of the two-photon photocurrent at the photon frequency {omega} to the photocurrent induced by direct one-photon transitions at the photon frequency 2{omega}, as compared to the corresponding absorption-rate ratio, contains a large factor {l_brace}ie152-1{r_brace}{omega}/(2{l_brace}ie152-2{r_brace}{omega} - E{sub g}), where E{sub g} is the bandgap; i.e., these photocurrent can be comparable in order of magnitude. For crystals of T{sub d} symmetry, the photocurrents induced by one- and two-photon absorption are compared in terms of polarization dependence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

On the effect of bias on the behavior of MOS structures subjected to ionizing radiation

Using a quantitative model [6], the analysis of published data on the effect of the gate bias on the behavior of MOS structure subjected to ionizing radiation is performed. It is shown that, along with hydrogen-containing traps, there are hydrogen-free hole traps in samples with a low content of hydrogen; traps of both types are distributed inhomogeneously over the thickness of the gate insulator. In addition to ionized hydrogen, neutral hydrogen is involved in the formation of surface states and provides the main contribution to this process at negative gate bias. A decrease in the shift of the threshold voltage in the case of high fields is caused by an increase in the drift component of the hole drain to the electrodes.

36 MATERIALS SCIENCE↗

DOE OSTI2016

A Closed-Loop Proportional-Integral (PI) Control Software for Fully Mechanically Controlled Automated Electron Microscopic Tomography

A closed-loop proportional-integral (PI) control software is provided for fully mechanically controlled automated electron microscopic tomography. The software is developed based on Gatan DigitalMicrograph, and is compatible with Zeiss LIBRA 120 transmission electron microscope. However, it can be expanded to other TEM instrument with modification. The software consists of a graphical user interface, a digital PI controller, an image analyzing unit, and other drive units (i.e.: image acquire unit and goniometer drive unit). During a tomography data collection process, the image analyzing unit analyzes both the accumulated shift and defocus value of the latest acquired image, and provides the results to the digital PI controller. The digital PI control compares the results with the preset values and determines the optimum adjustments of the goniometer. The goniometer drive unit adjusts the spatial position of the specimen according to the instructions given by the digital PI controller for the next tilt angle and image acquisition. The goniometer drive unit achieves high precision positioning by using a backlash elimination method. The major benefits of the software are: 1) the goniometer drive unit keeps pre-aligned/optimized beam conditions unchanged and achieves position tracking solely through mechanical control; 2) the image analyzing unit relies on only historical data and therefore does not require additional images/exposures; 3) the PI controller enables the system to dynamically track the imaging target with extremely low system error.

Ren, Gang↗

DOE OSTI2022

Corresponding Standard Reference Material Data used in Partial Least Squares Regression Models for Sugar Composition Estimates in Biomass in: Economic Impact of Yield and Composition Variation in Bioenergy Crops: Populus trichocarpa

Corresponding Standard Reference Material Data used in Partial Least Squares Regression Models for Sugar Composition Estimates in Biomass in: Economic Impact of Yield and Composition Variation in Bioenergy Crops: Populus trichocarpa (for corresponding manuscript: DOI: 10.1002/bbb.2148) PDF Files: Images of 1H NMR spectra for neutralized 2-stage acid hydrolysates of 4 NIST Standard Reference Material biomass samples (Monterey Pine 8493, Sugarcane Bagasse 8491, Wheat Straw 8494, and Eastern Cottonwood/Poplar 8492) and 2 Center for Bioenergy Innovation reference biomass samples (Poplar - Populus trichocarpa and Switchgrass - Panicum Virgatum). Suppression of the water peak was achieved using a NOESY-1D with presaturation, a recycle delay of 5 s, and a total of 64 scans. Spectra were acquired at 298 K and processed with automatic phase correction, baseline correction, and chemical shift referencing to TSP-d4. Images show all 1H data from 10 to 1ppm with inset spectra of region of interest (4.0 to 3.1 ppm). Text Files: Spectra for neutralized 2-stage acid hydrolysates of 4 NIST Standard Reference Material biomass samples (Monterey Pine 8493, Sugarcane Bagasse 8491, Wheat Straw 8494, and Eastern Cottonwood/Poplar 8492) and 2 Center for Bioenergy Innovation reference biomass samples (Poplar - Populus trichocarpa and Switchgrass - Panicum Virgatum) were converted into text files for plotting. Files contain 8192 points of raw spectral data from 12.23 to -2.78 ppm. The text file contains 4 columns of data and includes: Point number, Intensity, Hz, and ppm. Xcel Spreadsheet: HPLC measured monomeric sugar concentrations and bucketed 1H NMR data used to build monomeric sugar composition prediction models. Sugar composition in biomass determined from HPLC analyses are given in mg sugar/mg of biomass. Spectral bucketing was performed using Bruker’s AMIX software. Spectra were divided into 0.005 ppm buckets in the region of 3.10– 4.15 ppm for a total of 210 buckets. Headers for the bucketed data are the chemical shift in ppm of the center of the bucket. Bucketed data was used to build partial least squares models for subsequent predictions in The Unscrambler v. 10.5(CAMO A/S, Trondheim, Norway). The formation of methanol during hydrolysis interferes with the quantitative NMR analysis of sugars, so the methanol peak centered at 3.37 ppm and spanning four buckets (3.2925 – 3.2775 ppm) was set to zero for all spectra.

09 BIOMASS FUELS↗

NASA NTRS1978

A1 moonquakes - Source distribution and mechanism

Two novel analysis techniques have been used to study focal mechanisms of A1 moonquakes, which occur at the most active of the 80 deep-moonquake source regions identified to date. The first is the cross-spectral analysis of matching signal waveforms. Cross phase spectra clearly show relative polarity of signals and give precise time relationships between signals, thus enabling accurate detemination of relative source locations within the source region. The second is the analysis of amplitude ratios, which reveal the patterns of P- and S-wave radiations around the source region. A1 moonquake foci are found to be concentrated in a nearly horizontal planar region less than 1 km in diameter. Their focal mechanism may be described by slippages along a horizontal plane with the slip direction rotating with and predominantly controlled by the shifting tidal stress field. Thus, A1 moonquakes represent a process of simple storage and release of tidal energy with no evidence for a release of accumulated tectonic stress.

Nakamura, Y.↗

NASA NTRS1983

Some new results on irradiation characteristics of synthetic quartz crystals and their application to radiation hardening

The paper reports some new results on irradiation characteristics of synthetic quartz crystals and their application to radiation hardening. The present results show how the frequency shift in quartz crystals can be influenced by heat processing prior to irradiation and how this procedure can lead to radiation hardening for obtaining precise frequencies and time intervals from quartz oscillators in space.

Bahadur, H.↗

NASA NTRS1990

Hybrid vision activities at NASA Johnson Space Center

NASA's Johnson Space Center in Houston, Texas, is active in several aspects of hybrid image processing. (The term hybrid image processing refers to a system that combines digital and photonic processing). The major thrusts are autonomous space operations such as planetary landing, servicing, and rendezvous and docking. By processing images in non-Cartesian geometries to achieve shift invariance to canonical distortions, researchers use certain aspects of the human visual system for machine vision. That technology flow is bidirectional; researchers are investigating the possible utility of video-rate coordinate transformations for human low-vision patients. Man-in-the-loop teleoperations are also supported by the use of video-rate image-coordinate transformations, as researchers plan to use bandwidth compression tailored to the varying spatial acuity of the human operator. Technological elements being developed in the program include upgraded spatial light modulators, real-time coordinate transformations in video imagery, synthetic filters that robustly allow estimation of object pose parameters, convolutionally blurred filters that have continuously selectable invariance to such image changes as magnification and rotation, and optimization of optical correlation done with spatial light modulators that have limited range and couple both phase and amplitude in their response.

Juday, Richard D.↗

NASA NTRS1992

Microgravity effects on standardized cognitive performance measures

The purpose of this experiment, selected to fly on the International Microgravity Laboratory (IML-2) Spacelab mission, is to determine the effects of microgravity upon the cognitive skills which are critical to successful performance of many tasks on board the Space Shuttle. Six tests from the Unified Tri-service Cognitive Performance Assessment Battery (UTC-PAB) will be administered to the Mission Specialists to fulfill the goals of this experiment. These tests are based upon current theoretical models of human performance and the hypothesized effects of microgravity. The principle objective is the identification of the effects of microgravity upon specific information processing skills affecting performance from those of fatigue and shifts in work/rest cycles. Multiple measures of both short and long term fatigue will be obtained and used as a major independent variable for the analysis of these performance data. Scientific supporting studies will determine optimum practice and performance testing schedules for the astronauts. The same tests will be used post-flight to collect data on the recovery of any cognitive performance impairment compared with pre-flight, baseline levels.

Schiflett, Samuel G.↗

NASA NTRS1992

Stellar occultation experiment with the CASSINI VIMS instrument

The VIMS instrument (Visible and Infrared Mapping Spectrometer) will be flown in the late 1990s on the CASSINI mission to Saturn and its moons. VIMS is designed to generate two-dimensional multispectral images of planetary surfaces and their features in the visible and infrared spectra. Compared to earth-based instruments, the stellar occultation experiment will provide unprecedented thickness resolution and chemical composition of planetary atmospheres. It will also gather high SNR optical depth profiles and particle size distribution of the Saturnian rings. The stellar occultation mode ideally requires continuous data acquisition for periods of up to several hours as the instrument stares at a star. This presents a sizeable challenge to the instrument's operational mode: processes that normally occur during mirror retrace must be shifted to data acquisition cycles, thereby creating timing difficulties in the sequencing of these cycles. The presentation focuses on the analysis of the stellar occultation mode and presents solutions to the challenge of an uninterrupted data stream. Several options will be presented that minimize any possible degradation of the experiment's science content.

Walch, Marc↗

NASA NTRS1999

Trade Study of Five In-Situ Propellant Production Systems for a Mars Sample Return Mission

One of the goals of NASA's HEDS enterprise is to establish a long-term human presence on Mars at a fraction of the cost of employing today's technology. The most direct method of reducing mission cost is to reduce the launch mass of the spacecraft. If the propellants for the return phase of the mission are produced on Mars, the total spacecraft mass could be reduced significantly. An interim goal is a Mars Sample Return (MSR) mission, which is proposed to demonstrate the feasibility of in-situ propellant production (ISPP). Five candidate ISPP systems for producing two fuels and oxygen from the Martian atmosphere are considered in this design trade-off study: 1) Zirconia cell with methanol synthesis, 2) Reverse water gas shift with water electrolysis and methanol synthesis, 3) Sabatier process for methane product ion with water electrolysis, 4) Sabatier process with water electrolysis and partial methane pyrolysis, and 5) Sabatier/RWGS combination with water electrolysis.

Green, S. T.↗

NASA NTRS1999

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth

In a reported period in situ atomic force microscopy was utilized in our laboratory to study mechanisms of growth and kinetics of crystallization of ten protein and virus crystals. These included canavalin, thaumatin, apoferritin, lipase, catalase, t-RNA, lysozyme, xylanase, turnip yellow mosaic virus (TYMV) and satellite tobacco mosaic virus (STMV). We have also designed and constructed in our laboratory both in situ conventional two-beam Michelson and phase shift Mach-Zenhder interferometers. Computer software for the processing of the interferometric images was developed as well. Interferometric techniques were applied for studies of growth kinetics and transport phenomena in crystallization of several macromolecular crystals. As a result of this work we have published 21 papers and have given many presentations at international and national meetings. A list of these publications and conference presentations is attached.

Malkin, Alexander J.↗

NASA NTRS2014

OMPS Limb Profiler Instrument Performance Assessment

Following the successful launch of the Ozone Mapping and Profiler Suite (OMPS) aboard the Suomi National Polar-orbiting Partnership (SNPP) spacecraft, the NASA OMPS Limb team began an evaluation of instrument and data product performance. The focus of this paper is the instrument performance in relation to the original design criteria. Performance that is closer to expectations increases the likelihood that limb scatter measurements by SNPP OMPS and successor instruments can form the basis for accurate long-term monitoring of ozone vertical profiles. The team finds that the Limb instrument operates mostly as designed and basic performance meets or exceeds the original design criteria. Internally scattered stray light and sensor pointing knowledge are two design challenges with the potential to seriously degrade performance. A thorough prelaunch characterization of stray light supports software corrections that are accurate to within 1% in radiances up to 60 km for the wavelengths used in deriving ozone. Residual stray light errors at 1000nm, which is useful in retrievals of stratospheric aerosols, currently exceed 10%. Height registration errors in the range of 1 km to 2 km have been observed that cannot be fully explained by known error sources. An unexpected thermal sensitivity of the sensor also causes wavelengths and pointing to shift each orbit in the northern hemisphere. Spectral shifts of as much as 0.5nm in the ultraviolet and 5 nm in the visible, and up to 0.3 km shifts in registered height, must be corrected in ground processing.

ozone↗