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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Intrinsic Kinetics Fluctuations as Cause of Growth Inhomogeneity in Protein Crystals

Intrinsic kinetics instabilities in the form of growth step bunching during the crystallization of the protein lysozyme from solution were characterized by in situ high-resolution optical interferometry. Compositional variations (striations) in the crystal, which potentially decrease its utility, e.g., for molecular structure studies by diffraction methods, were visualized by polarized light reflection microscopy. A spatiotemporal correlation was established between the sequence of moving step bunches and the striations.

Vekilov, Peter G.↗
NASA NTRS1998

Effects of Convective Solute and Impurity Transport in Protein Crystal Growth

High-resolution optical interferometry was used to investigate the effects of forced solution convection on the crystal growth kinetics of the model protein lysozyme. Most experiments were conducted with 99.99% pure protein solutions. To study impurity effects, approx. 1% of lysozyme dimer (covalently bound) was added in some cases. We show that the unsteady kinetics, corresponding to bunching of growth steps, can be characterized by the Fourier components of time traces of the growth rate. Specific Fourier spectra are uniquely determined by the solution conditions (composition, temperature, and flow rate) and the growth layer source activity. We found that the average step velocity and growth rate increase by approx. I0% with increasing flow rate, as a result of the enhanced solute supply to the interface. More importantly, faster convective transport results in lower fluctuation amplitudes. This observation supports our rationale for system-dependent effects of transport on the structural perfection of protein crystals. We also found that solution flow rates greater than 500 microns/s result in stronger fluctuations while the average growth rate is decreased. This can lead to growth cessation at low supersaturations. With the intentionally contaminated solutions, these undesirable phenomena occurred at about half the flow rates required in pure solutions. Thus, we conclude that they are due to enhanced convective supply of impurities that are incorporated into the crystal during growth. Furthermore, we found that the impurity effects are reduced at higher crystal growth rates. Since the exposure time of terraces is inversely proportional to the growth rate, this observation suggests that the increased kinetics instability results from impurity adsorption on the interface. Finally, we provide evidence relating earlier observations of "slow protein crystal growth kinetics" to step bunch formation in response to nonsteady step generation.

Vekilov, Peter G.↗
NASA NTRS2001

The Role of Bearing and Scan Mechanism Life Testing in Flight Qualification of the MODIS Instrument

The Moderate Resolution Imaging Spectroradiometer (MODIS) is an instrument aboard the Terra (EOS AM-11) satellite and has been operating successfully since December 1999. MODIS has been viewing the entire Earth's surface and gathering data to better understand the global dynamics and processes occurring on land, in the oceans, and in the lower atmosphere. All observations are made through an extremely high resolution, optically and mechanically precise, scan mirror motor/encoder assembly. The reliable performance of this assembly depends on two duplex bearing pairs lubricated with Pennzane, a synthetic hydrocarbon, formulated with lead napthanate. This paper describes the results of accelerated and operational life tests. It also describes the post-test analyses of the disassembled bearings. Analyses were performed using micro-Raman, micro-FTIR, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Size Exclusion Chromatography (SEC). In general, the three sets of bearings in each of the test stations were in very good condition after accumulating 68, 144, and 209 million revolutions, respectively. Some of the bearings exhibited lubricant degradation, indicated by viscous lubricant deposits on the cage and raceways.

VanDyk, Steven G.↗
NASA NTRS2001

The Role of Bearing and Scan Mechanism Life Testing in Flight Qualification of the MODIS Instrument

The Moderate Resolution Imaging Spectroradiometer (MODIS) is an instrument aboard the Terra (EOS AM-1) satellite and has been operating successfully since December 1999. MODIS has been viewing the entire Earth's surface and gathering data to better understand the global dynamics and processes occurring on land, in the oceans, and in the lower atmosphere. All observations are made through an extremely high resolution, optically and mechanically precise, scan mirror motor/encoder assembly. The reliable performance of this assembly depends on two duplex bearing pairs lubricated with Pennzane, a synthetic hydrocarbon, formulated with lead napthanate. This paper describes the results of accelerated and operational life tests. It also describes the post-test analyses of the disassembled bearings. Analyses were performed using micro-Raman, micro-FTIR, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Size Exclusion Chromatography (SEC). In general, the three sets of bearings in each of the test stations were in very good condition after accumulating 68, 144, and 209 million revolutions, respectively. Some of the bearings exhibited lubricant degradation, indicated by viscous lubricant deposits on the cage and raceways.

VanDyk, Steven G.↗
NASA NTRS2001

Abundances in the Planetary Nebula IC 5217

High resolution optical wavelength spectroscopic data were secured in the optical wavelengths, 3700A - 10,050A, for the planetary nebula IC 5217 with the Hamilton Echelle Spectrograph at Lick Observatory. These optical spectra have been analyzed along with the near-UV and UV archive data. Diagnostic analyses indicate a nebular physical condition with electron temperature of about 10,700 K (from the [O III] lines) and the density of N(sub epsilon) = 5000/cm. Ionic concentrations have been derived with the representative diagnostics, and with the aid of a photoionization model construction, we derived the elemental abundances. Contrary to the previous studies found in the literature, He and C appear to be depleted compared to the average planetary nebula and to the Sun (and S marginally so), while the remaining elements appear to be close to the average value. IC 5217 may have evolved from an O-rich progenitor and the central star temperature of IC 5217 is likely to be 92,000 K.

Hyung, Siek↗
NASA NTRS1986

A simple fiber-optic microprobe for high resolution light measurements: application in marine sediment

A fiber-optic microphobe is described which is inexpensive and simple to build and use. It consists of an 80-micrometers optical fiber which at the end is tapered down to a rounded sensing tip of 20-30-micrometers diameter. The detector is a hybrid photodiode/amplifier. The probe has a sensitivity of 0.01 microEinst m-2 s-1 and a spectral range of 300-1,100 nm. Spectral light gradients were measured in fine-grained San Francisco Bay sediment that had an undisturbed diatom coating on the surface. The photic zone of the mud was only 0.4 mm deep. Measured in situ spectra showed extinction maxima at 430-520, 620-630, 670, and 825-850 nm due to absorption by chlorophyll a, carotenoids, phycocyanin, and bacterio-chlorophyll a. Maximum light penetration in the visible range was found in both the violet and the red < or = 400 and > or = 700 nm.

NASA Center ARC↗
NASA NTRS2004

Steps in Solution Growth: Revised Gibbs-Thomson Law, Turbulence and Morphological Stability

Two groups of new phenomena revealed by AFM and high resolution optical interferometry on crystal faces growing from solutions will be discussed. 1. Spacing between strongly polygonized spiral steps with low less than 10(exp -2) kink density on lysozyme and K- biphtalate do not follow the Burton-cabrera-Frank theory. The critical length of the yet immobile first Short step segment adjacent to a pinning defect (dislocation, stacking fault) is many times longer than that following from the step free energy. The low-kink density steps are typical of many growth conditions and materials, including low temperature gas phase epitaxy and MBE. 2. The step bunching pattern on the approx. 1 cm long { 110) KDP face growing from the turbulent solution flow (Re (triple bonds) 10(exp 4), solution flow rate approx. 1 m/s) suggests that the step bunch height does not increase infinitely as the bunch path on the crystal face rises, as is usually observed on large KDP crystals. The mechanism controlling the maximal bunch width and height is based on the drag of the solution depleted by the step bunch down thc solution stream. It includes splitting, coagulation and interlacing of bunches

Chernov, A. A.↗
NASA NTRS2004

The mass and speed dependence of meteor air plasma temperatures

The speed and mass dependence of meteor air plasma temperatures is perhaps the most important data needed to understand how small meteoroids chemically change the ambient atmosphere in their path and enrich the ablated meteoric organic matter with oxygen. Such chemistry can play an important role in creating prebiotic compounds. The excitation conditions in various air plasma emissions were measured from high-resolution optical spectra of Leonid storm meteors during NASA's Leonid Multi-Instrument Aircraft Campaign. This was the first time a sufficient number and range of temperature measurements were obtained to search for meteoroid mass and speed dependencies. We found slight increases in temperature with decreasing altitude, but otherwise nearly constant values for meteoroids with speeds between 35 and 72 km/s and masses between 10(-5) g and 1 g. We conclude that faster and more massive meteoroids produce a larger emission volume, but not a higher air plasma temperature. We speculate that the meteoric plasma may be in multiphase equilibrium with the ambient atmosphere, which could mean lower plasma temperatures in a CO(2)-rich early Earth atmosphere.

Temperature↗
NASA NTRS2005

Tomography of a Gamma-ray Burst Progenitor and its Host Galaxy

We have obtained near-infrared and high-resolution optical spectroscopy of the bright afterglow of the very intense gamma-ray burst recorded on 2002, October 4 (GRB 021004). Besides of line emission in the near-IR allowing an independent measurement of the systemic redshift (z = 2.3304 plus or minus 0.0005), we find several absorption line groups spanning a range of about 3,000 kilometers per second in velocity relative to the redshift of the host galaxy. The absorption profiles are very complex with both velocity-broadened components extending over several 100 kilometers per second and narrow lines with velocity widths of only approximately 20 kilometers per second. By analogy with QSO absorption line studies, the relative velocities, widths, and degrees of ionization of the lines ("line-locking", "ionization-velocity correlation") show that the progenitor had both an extremely strong radiation field and several distinct mass loss phases (winds). These results are consistent with GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or Wolf-Rayet stars, providing a detailed picture of the spatial and velocity structure of the GRB progenitor star at the time of explosion. The host galaxy is a prolific star-forming galaxy with a SFR of approximately 10 solar mass yr(sup -l).

Castro-Tirado, Alberto J.↗
NASA NTRS2013

Reference Images from Thin Sections of Lunar Regolith

The specialist literature about the lunar regolith is massive. It is also highly focused on specific topics and effectively impenetrable to most non-geologists. Both characteristics of the literature present substantial hurdles to scientists and engineers interested in the regolith In the author's experience it neither surprising or unusual to find serious misconceptions about lunar-type materials outside of the lunar research community. Education of professionals who are non-geologists but interested in the regolith is impeded by a lack of some basic resources. One asset that has been missing is simply detailed images of the regolith "soil". While a few websites offer imagery of specific features, these are of course selected to illustrate specific features. It is almost impossible for a non-specialist to reason from these what "normal" or "typical" regolith looks like. Further, access to lunar material is highly restricted. And as publications rarely do not provide other than highly focused and narrowly tailored data, there is little potential for workers without personal access to sample to do any work with lunar material. To address both problems the authors have begun to make high resolution optical micrographs of entire thin sections of lunar regolith.

Rickman Doug↗
NASA NTRS2014

Comet C2012 S1 (ISON)s Carbon-rich and Micron-size-dominated Coma Dust

Comet C/2012 S1 (ISON) was unique in that it was a dynamically new comet derived from the Nearly Isotropic Oort cloud reservoir of comets with a sun-grazing orbit. We present thermal models for comet ISON (rh approx.1.15 AU, 2013-Oct-25 11:30 UT) that reveal comet ISON's dust was carbon-rich and dominated by a narrow size distribution dominated by approx. micron-sized grains. We constrained the models by our SOFIA FORCAST photometry at 11.1, 19.7 and 31.5 microns and by a silicate feature strength of approx.1.1 and an 8-13microns continuum greybody color temperature of approx. 275-280 K (using Tbb ∝ r−0.5 h and Tbb approx. 260-265 K from Subaru COMICS, 2013-Oct-19 UT)[1,2]. N-band spectra of comet ISON with the BASS instrument on the NASA IRTF (2013-Nov-11-12 UT) show a silicate feature strength of approx. 1.1 and an 11.2microns forsterite peak.[3] Our thermal models yield constraints the dust composition as well as grain size distribution parameters: slope, peak grain size, porosity. Specifically, ISON's dust has a low silicate-to- amorphous carbon ratio (approx. 1:9), and the coma size distribution has a steep slope (N4.5) such that the coma is dominated by micron-sized, moderately porous, carbon-rich dust grains. The N-band continuum color temperature implies submicronto micron-size grains and the steep fall off of the SOFIA far-IR photometry requires the size distribution to have fewer relative numbers of larger and cooler grains compared to smaller and hotter grains. A proxy for the dust production rate is fρ approx.1500 cm, akin to Afρ. ISON has a moderate-to-low dust-to-gas ratio. Comet ISON's dust grain size distribution does not appear similar to the few well-studied long-period Nearly Isotropic Comets (NICs), namely C/1995 O1 (Hale-Bopp) and C/2001 Q4 (NEAT) that had smaller and/or more highly porous grains and larger sizes, or C/2007 N4 (Lulin) and C/2006 P1 (McNaught) that had large and/or compact grains. Radial transport to comet-forming disk distances (≥ 20 AU) is easier for smaller grains (≤1 micron) than for larger grains (approx. 20 microns like Stardust terminal particles). The presence of predominantly micron-sized and smaller grains suggests comet ISON may have formed either earlier in disk evolution whereby larger grains did not have the time to be transported to distances beyond Neptune, or the comet formed so far out in the disk that larger grains did not traverse such large radial distances. The high carbon-content of ISON's refractory dust appears to be complimented by the presence of limitedlifetime organic (CHON-like) grain materials: preliminary analyses of near-IR and high-resolution optical spectra indicate that gas-phase daughter molecules C2, CN, and CH were more abundant than their parent molecules (C2H2, C2H6, measured in the near- IR). Dust composition as well as grain size distribution parameters (slope, peak grain size, and porosity) give clues to comet origins.

NASA/DLR Stratospheric Observatory↗
NASA NTRS2014

Investigation into the Use of the Concept Laser QM System as an In-Situ Research and Evaluation Tool

The NASA Marshall Space Flight Center (MSFC) is using a Concept Laser Fusing (Cusing) M2 powder bed additive manufacturing system for the build of space flight prototypes and hardware. NASA MSFC is collecting and analyzing data from the M2 QM Meltpool and QM Coating systems for builds. This data is intended to aide in understanding of the powder-bed additive manufacturing process, and in the development of a thermal model for the process. The QM systems are marketed by Concept Laser GmbH as in-situ quality management modules. The QM Meltpool system uses both a high-speed near-IR camera and a photodiode to monitor the melt pool generated by the laser. The software determines from the camera images the size of the melt pool. The camera also measures the integrated intensity of the IR radiation, and the photodiode gives an intensity value based on the brightness of the melt pool. The QM coating system uses a high resolution optical camera to image the surface after each layer has been formed. The objective of this investigation was to determine the adequacy of the QM Meltpool system as a research instrument for in-situ measurement of melt pool size and temperature and its applicability to NASA's objectives in (1) Developing a process thermal model and (2) Quantifying feedback measurements with the intent of meeting quality requirements or specifications. Note that Concept Laser markets the system only as capable of giving an indication of changes between builds, not as an in-situ research and evaluation tool. A secondary objective of the investigation is to determine the adequacy of the QM Coating system as an in-situ layer-wise geometry and layer quality evaluation tool.

Bagg, Stacey↗
NASA NTRS2021

Landslide Mapping Using Object-Based Image Analysis and Open Source Tools

Availability of high-resolution optical imagery and advances in image processing technologies have significantly improved our ability to map landslides. In recent years object-based image analysis (OBIA) has been gaining in popularity for landslide mapping due to its ability to incorporate spectral, textural, morphological and topographical properties. Many studies have been conducted based on commercial software. In this study, we create an open source Semi-Automatic Landslide Detection (SALaD) system utilizing OBIA and machine learning. Configured to run in Linux environment, it uses various opensource Python packages and modules. This system was tested in 575 km2 area along the Pasang Lhamu Highway, Nepal where large numbers of landslides were triggered by the 2015 Gorkha earthquake. Comparison with a manual inventory highlighted that this system was able to detect 70% of the landslide area. The speed and efficiency with which this system was able to detect landslides makes it a viable alternative to manual techniques for landslide mapping over large areas, when establishing approximate landslide locations is of prime importance.

Open source↗
NASA NTRS2021

Target Prioritization and Observing Strategies for the NEID Earth Twin Survey

NEID is a high-resolution optical spectrograph on the WIYN 3.5 m telescope at Kitt Peak National Observatory and will soon join the new generation of extreme precision radial velocity instruments in operation around the world. We plan to use the instrument to conduct the NEID Earth Twin Survey (NETS) over the course of the next 5 years, collecting hundreds of observations of some of the nearest and brightest stars in an effort to probe the regime of Earth-mass exoplanets. Even if we take advantage of the extreme instrumental precision conferred by NEID, it will be difficult to disentangle the weak (~10 cm/s) signals induced by such low-mass, long-period exoplanets from stellar noise for all but the quietest host stars. In this work, we present a set of quantitative selection metrics which we use to identify an initial NETS target list consisting of stars conducive to the detection of exoplanets in the regime of interest. We also outline a set of observing strategies with which we aim to mitigate uncertainty contributions from intrinsic stellar variability and other sources of noise.

Arvind F. Gupta↗
NASA NTRS2021

TESS Hunt for Young and Maturing Exoplanets (THYME). V. A Sub-Neptune Transiting a Young Star in a Newly Discovered 250 Myr Association

The detection and characterization of young planetary systems offer a direct path to study the processes that shape planet evolution. We report on the discovery of a sub-Neptune-sized planet orbiting the young star HD 110082 (TOI-1098). Transit events we initially detected during TESS Cycle 1 are validated with time-series photometry from Spitzer. High-contrast imaging and high-resolution, optical spectra are also obtained to characterize the stellar host and confirm the planetary nature of the transits. The host star is a late-F dwarf (M⁎ = 1.2Mꙩ) with a low-mass, M dwarf binary companion (M⁎ = 0.26Mꙩ) separated by nearly one arcminute (∼6200 au). Based on its rapid rotation and Lithium absorption, HD 110082 is young, but is not a member of any known group of young stars (despite proximity to the Octans association). To measure the age of the system, we search for coeval, phase-space neighbors and compile a sample of candidate siblings to compare with the empirical sequences of young clusters and to apply quantitative age-dating techniques. In doing so, we find that HD 110082 resides in a new young stellar association we designate MELANGE-1, with an age of 250(+50, -70) Myr. Jointly modeling the TESS and Spitzer light curves, we measure a planetary orbital period of 10.1827 days and radius of R(p) = 3.2 ± 0.1Rꚛ. HD 110082 b’s radius falls in the largest 12% of field-age systems with similar host-star mass and orbital period. This finding supports previous studies indicating that young planets have larger radii than their field-age counterparts.

TESS↗
NASA NTRS2021

TESS Hunt for Young and Maturing Exoplanets (THYME). V. A Sub-Neptune Transiting a Young Star in a Newly Discovered 250 Myr Association

The detection and characterization of young planetary systems offer a direct path to study the processes that shape planet evolution. We report on the discovery of a sub-Neptune-sized planet orbiting the young star HD 110082(TOI-1098). Transit events we initially detected during TESS Cycle 1 are validated with time-series photometry from Spitzer. High-contrast imaging and high-resolution, optical spectra are also obtained to characterize the stellar host and confirm the planetary nature of the transits. The host star is a late-F dwarf(Må=1.2Me)with a low-mass,M dwarf binary companion(Må=0.26Me)separated by nearly one arc minute(∼6200 au). Based on its rapid rotation and Lithium absorption, HD 110082 is young, but is not a member of any known group of young stars(despite proximity to the Octans association). To measure the age of the system, we search for coeval, phase-space neighbors and compile a sample of candidate siblings to compare with the empirical sequences of young clusters and to apply quantitative age-dating techniques. In doing so, we find that HD 110082 resides in a new young stellar association we designate MELANGE-1, with an age of -+ 2507050 Myr. Jointly modeling the TESS and Spitzer light curves, we measure a planetary orbital period of 10.1827 days and radius of Rp=3.2±0.1R⊕. HD 110082 b’s radius falls in the largest 12% of field age systems with similar host-star mass and orbital period. This finding supports previous studies indicating that young planets have larger radii than their field-age counterparts

Benjamin M. Tofflemire↗
NASA NTRS2022

A Dynamic Landslide Hazard Monitoring Framework for the Lower Mekong Region

The Lower Mekong region is one of the most landslide-prone areas of the world. Despite the need for dynamic characterization of landslide hazard zones within the region, it is largely understudied for several reasons. Dynamic and integrated understanding of landslide processes requires landslide inventories across the region, which have not been available previously. Computational limitations also hamper regional landslide hazard assessment, including accessing and processing remotely sensed information. Finally, open-source software and modelling packages are required to address regional landslide hazard analysis. Leveraging an open-source data-driven global Landslide Hazard Assessment for Situational Awareness model framework, this study develops a region-specific dynamic landslide hazard system leveraging satellite-based Earth observation data to assess landslide hazards across the lower Mekong region. A set of landslide inventories were prepared from high-resolution optical imagery using advanced image-processing techniques. Several static and dynamic explanatory variables (i.e., rainfall, soil moisture, slope, relief, distance to roads, distance to faults, distance to rivers) were considered during the model development phase. An extreme gradient boosting decision tree model was trained for the monsoon period of 2015–2019 and the model was evaluated with independent inventory information for the 2020 monsoon period. The model performance demonstrated considerable skill using receiver operating characteristic curve statistics, with Area Under the Curve values exceeding 0.95. The model architecture was designed to use near-real-time data, and it can be implemented in a cloud computing environment (i.e., Google Cloud Platform) for the routine assessment of landslide hazards in the Lower Mekong region. This work was developed in collaboration with scientists at the Asian Disaster Preparedness Center as part of the NASA SERVIR Program’s Mekong hub. The goal of this work is to develop a suite of tools and services on accessible open-source platforms that support and enable stakeholder communities to better assess landslide hazard and exposure at local to regional scales for decision making and planning.

Nishan Kumar Biswas↗
NASA NTRS2024

South Africa Ecological Conservation: Identifying and Mapping Riparian Areas in South Africa with Earth Observations

Riparian zones are thin strips of wetland that occur along the edges of rivers, lakes, and other water bodies. They provide many ecosystem and societal benefits such as stream bank stabilization, flood control, and habitat stability, making these zones very important areas to preserve and protect. Recognizing the need to accurately map these ecosystems in a cost-effective way, we partnered with the South African National Biodiversity Institute (SANBI) and the Biodiversity Survey of the Cape(BioSCape) to develop a GI methodology using Esri's ArcGIS Pro and data from Landsat 9 Operational Land Imager-2, Sentinel-2 Multispectral Instrument, and the Shuttle Radar Topography Mission to identify potential riparian zones (PRZ) and observed riparian vegetation(ORV) in the Southern Cape and the North West Province of South Africa to estimate the actual riparian vegetation (ARV) within those areas. Potential riparian ecosystems were calculated by utilizing a Topographic Wetness Index (TWI) and a water feature layer, while observed riparian vegetation were calculated by overlaying a Normalized Difference Vegetation Index (NDVI) and TWI. Actual Riparian Vegetation is determined by the overlap of ORV with PRZ and is done with conditional statements; ORV within PRZ is ARV. This method significantly improved a current riparian land cover classification since it combined high resolution optical imagery and topographic data. We anticipate such maps will be used by conservationists and practitioners interested in riparian monitoring and management.

Remote Sensing↗