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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Determination of Mercury Content in a Shallow Firn Core from Summit, Greenland by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

The total mercury Hg content was determined in 6 cm sections of a near-surface 7 m firn core and in surrounding surface snow from Summit, Greenland (elevation: 3238 m, 72.58 N, 38.53 W) in May 2001 by isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS). The focus of this research was to evaluate the capability of the ID-CV-ICPMS technique for measuring trace levels of Hg typical of polar snow and firn. Highly enriched Hg-201 isotopic spike is added to approximately 10 ml melted core and thoroughly mixed. The Hg(+2) in the sample is reduced on line with tin (II) chloride (SnCl2) and the elemental Hg (Hg(0)) vapor pre-concentrated on to gold gauze using a commercial amalgam system. The Hg is then thermally desorbed and introduced into a quadrupole ICP-MS. The blank corrected Hg concentrations determined for all samples ranged from 0.25 ng/L to 1.74 ng/L (ppt) (average 0.59 ng/L plus or minus 0.28 ng/L) and fall within the range of those previously determined by Boutron et al., 1998 (less than or equal to 0.05 ng/L to 2.0 ng/L) for the Summit site. The average blank value was 0.19 ng/L plus or minus 0.045 ng/L (n=6). The Hg values specifically for the firn core range from 0.25 ng/L to 0.87 ng/L (average 0.51 ng/L plus or minus 0.13 ng/L) and show both values declining with time and larger variability in concentration in the top 1.8 m.

Mann, Jacqueline L.↗
NASA NTRS2004

Metal-Silicate Segregation in Deforming Dunitic Rocks: Applications to Core Formation in Europa and Ganymede

Core formation is an important event in the evolution of a planetary body, affecting both the geochemical and geophysical properties of the body. Metal-silicate segregation could have proceeded either by settling of liquid metal through a magma ocean or by percolation of liquid metal through a solid silicate mantle. Percolation of metallic melt had previously been excluded as a viable segregation mechanism because metallic melts do not form an interconnected network under hydrostatic conditions, except at high melt fraction (>5 vol%), due to the high dihedral angle between metals and silicates (>60 ). Without an interconnected network, porous flow of metallic melt is impossible, leaving the magma ocean scenario as the only mechanism to form the core. Moment-of-inertia measurements of Europa and Ganymede from the Galileo probe indicate that they are differentiated. This evidence suggests that a method for segregating metals and silicates at temperatures low enough to retain volatile compounds must exist. We have investigated the effect of deformation on the distribution of metallic melts in silicates. We have deformed samples of olivine + 5-9 vol% Fe-S to strains of 2.5 in simple shear and find that the metallic melt segregates into melt-rich planes oriented at 20 to the shear plane. These metallic melt-rich bands are similar in structure to the silicate melt-rich bands reported by Holtzman, indicating that deformation can interconnect isolated metallic melt pockets and allow porous flow of non-wetting melts. Such a core formation process could have occurred in the jovian satellites.

Hustoft, J. W.↗
NASA NTRS2004

Core Formation in the Earth: Constraints from Ni and Co

Due to their metal-loving nature, Ni and Co were strongly partitioned into the metallic core and were left depleted in the silicate mantle during core formation in the Earth. Based on experimental liquid metal- liquid silicate partition coefficients (D), studies have suggested that core formation in an early magma Ocean can explain the observed mantle depletions of Ni and Co [l-51. However, the conditions proposed by the magma ocean models have ranged from pressures of 24 to 59 GPa and temperatures of 2200 to < 4000 K. Furthermore, the proposed magma Ocean oxygen fugacities have differed by nearly two orders of magnitude.Chabot and Agee noted that the different models predicted contradictory behaviors for D(Ni) and D(Co) as a function of temperature. With the hope of resolving the discrepancies between the magma ocean models, we conducted a systematic experimental study to constrain the effects of temperature on D(Ni) and D(Co).

Chabot, N. L.↗
NASA NTRS2000

Chemistry of the organic-rich hot core G327.3-0.6

We present gas-phase abundances of species found in the organic-rich hot core G327.3-0.6. The data were taken with the Swedish-ESO Submillimetre Telescope (SEST). The 1-3 mm spectrum of this source is dominated by emission features of nitrile species and saturated organics, with abundances greater than those found in many other hot cores, including Sgr B2 and OMC-1. Population diagram analysis indicates that many species (CH3CN, C2H3CN, C2H5CN, CH3OH, etc.) have hot components that originate in a compact (~2") region. Gas-phase chemical models cannot reproduce the high abundances of these molecules found in hot cores, and we suggest that they originate from processing and evaporation of icy grain mantle material. In addition, we report the first detection of vibrationally excited ethyl cyanide and the first detection of methyl mercaptan (CH3SH) outside the Galactic center.

NASA Discipline Exobiology↗
NASA NTRS1995

Geochemical characteristics of organic compounds in a permafrost sediment core sample from northeast Siberia, Russia

We studied total organic carbon (TOC), hydrocarbons and fatty acids in a permafrost sediment core sample (well 6-90, length 32.0 m, 1.5-2.5 Ma BP) from northeast Siberia (approximately 70 degrees N, 158 degrees E), Russia, to elucidate their geochemical features in relation to source organisms and paleoenvironmental conditions. Long-chain n-alkanes and n-alkanoic acids (>C19) were most predominant hydrocarbons and fatty acids, respectively, so organic matter in the sediment core was derived mainly from vascular plants and, to a much smaller extent, from bacteria. Low concentrations of unsaturated fatty acids revealed that organic matter in the sediment core was considerably degraded during and/or after sedimentation. The predominance of vascular plant components, the major ionic components of nonmarine sources, and geological data strongly implied that the sediment layers were formed in shallow lacustrine environments, such as swamp with large influences of tundra or forest-tundra vegetation. Also, no drastic changes in paleoenvironmental conditions for biological activity or geological events, such as sea transgressions or ice-sheet influences, occurred at the sampling site approximately 100 km from the coast of the East Siberian Sea during the late Pliocene an early Pleistocene periods.

NASA Discipline Exobiology↗
NASA NTRS2003

Phylogenetic analysis of anaerobic psychrophilic enrichment cultures obtained from a greenland glacier ice core

The examination of microorganisms in glacial ice cores allows the phylogenetic relationships of organisms frozen for thousands of years to be compared with those of current isolates. We developed a method for aseptically sampling a sediment-containing portion of a Greenland ice core that had remained at -9 degrees C for over 100,000 years. Epifluorescence microscopy and flow cytometry results showed that the ice sample contained over 6 x 10(7) cells/ml. Anaerobic enrichment cultures inoculated with melted ice were grown and maintained at -2 degrees C. Genomic DNA extracted from these enrichments was used for the PCR amplification of 16S rRNA genes with bacterial and archaeal primers and the preparation of clone libraries. Approximately 60 bacterial inserts were screened by restriction endonuclease analysis and grouped into 27 unique restriction fragment length polymorphism types, and 24 representative sequences were compared phylogenetically. Diverse sequences representing major phylogenetic groups including alpha, beta, and gamma Proteobacteria as well as relatives of the Thermus, Bacteroides, Eubacterium, and Clostridium groups were found. Sixteen clone sequences were closely related to those from known organisms, with four possibly representing new species. Seven sequences may reflect new genera and were most closely related to sequences obtained only by PCR amplification. One sequence was over 12% distant from its closest relative and may represent a novel order or family. These results show that phylogenetically diverse microorganisms have remained viable within the Greenland ice core for at least 100,000 years.

Evaluation Studies↗
NASA NTRS1998

Effects of Heat Treatment on the Magnetic Properties of Polymer-Bound Iron Particle Cores

Spherical iron particles of three different size distributions, 6-10 microns in diameter, 100 mesh and 30-80 mesh, were mixed with 2.0 wt. % of soluble imide and compression molded at 300 C under 131 MPa. Post fabrication heat treatments were performed at 960 C for 6 hours resulting in a significant enhancement of the permeability in low field region for all the specimens except for the one made of 30-80 mesh particles. The rate of core loss of these specimens at a magnetic induction of 5 kG measured up to 1 kHz shows a noticeable increase after heat treatment which, along with the permeability enhancement, can be explained by the coalescence of particles forming a network of conductivity paths in the specimens. The scanning electron micrographs taken for the 6-10 micron particle specimens show no evidence of heat treatment-induced grain growth. The untreated specimens show a very weak f(sup 2) dependence of the core loss which clearly indicates a negligible contribution from the eddy current loss. In particular, an almost perfect linearity was found in the frequency dependence of the core loss of the untreated specimen made of 100 mesh iron particles.

Namkung, M.↗
NASA NTRS2004

Analysis of Stainless Steel Sandwich Panels with a Metal Foam Core for Lightweight Fan Blade Design

The quest for cheap, low density and high performance materials in the design of aircraft and rotorcraft engine fan and propeller blades poses immense challenges to the materials and structural design engineers. The present study investigates the use of a sandwich foam fan blade mae up of solid face sheets and a metal foam core. The face sheets and the metal foam core material were an aerospace grade precipitation hardened 17-4 PH stainless steel with high strength and high toughness. The resulting structures possesses a high stiffness while being lighter than a similar solid construction. The material properties of 17-4 PH metal foam are reviewed briefly to describe the characteristics of sandwich structure for a fan blade application. A vibration analysis for natural frequencies and a detailed stress analysis on the 17-4 PH sandwich foam blade design for different combinations of kin thickness and core volume are presented with a comparison to a solid titanium blade.

Min, James B.↗
NASA NTRS2000

The timing of the human circadian clock is accurately represented by the core body temperature rhythm following phase shifts to a three-cycle light stimulus near the critical zone

A double-stimulus experiment was conducted to evaluate the phase of the underlying circadian clock following light-induced phase shifts of the human circadian system. Circadian phase was assayed by constant routine from the rhythm in core body temperature before and after a three-cycle bright-light stimulus applied near the estimated minimum of the core body temperature rhythm. An identical, consecutive three-cycle light stimulus was then applied, and phase was reassessed. Phase shifts to these consecutive stimuli were no different from those obtained in a previous study following light stimuli applied under steady-state conditions over a range of circadian phases similar to those at which the consecutive stimuli were applied. These data suggest that circadian phase shifts of the core body temperature rhythm in response to a three-cycle stimulus occur within 24 h following the end of the 3-day light stimulus and that this poststimulus temperature rhythm accurately reflects the timing of the underlying circadian clock.

Non-NASA Center↗
NASA NTRS2004

Discovery of Extremely Embedded X-ray Sources in the R Coronae Australis Star Forming Core

We detected three extremely embedded X-ray sources in the R Corona Australis (R CrA) star forming core, IRS 7 region. Two weak X-ray sources are associated with the VLA centimeter radio sources 10E & W, whereas the third brightest source detected in the two XMM-Newton observations on March 2003 has no counterpart at any wavelengths. The large K-band upper-limit (19.4m) measured with the University of Hawaii 88-inch Telescope and strong absorption derived in X-rays (N(sub H) approx. 2.8 x 10(exp 23)/sq cm equivalent to A(sub v) approx. 180 m) indicate that the source is younger than typical Class I protostars, i.e. a Class 0 protostar or an intermittent phase between Class 0 and Class I protostars. The X-ray luminosity was less than one thirtieth (log L(sub x) less than or approx. equals 29.3 ergs/s) in the former Chandra observation in October 2000, which suggests that the X-ray activity, probably generated by magnetic activity, is triggered by an intermittent mass accretion episode such as FU Ori type outbursts. Because the source was detected at high significance in the XMM-Newton observations (approx. 2,000 cnts), X-ray properties of such young protostars can be well investigated for the first time. The light curves were constant in the 1st observation and increased linearly by a factor of two during 30 ksec in the 2nd observation. Both spectra showed iron K lines originated in hot thin-thermal plasma and fluorescence by cold gas. They can be reproduced by an absorbed thin-thermal plasma model with a Gaussian component at 6.4 keV (kT approx. 3-4 keV, L(sub x) approx. 7-20 x 10(exp 30) ergs/s). The rising timescale of the light curves in the 2nd observation was too slow for magnetically generated X-ray flares, whereas large equivalent width of the fluorescence iron K line in the 1st observation (approx. 810 eV) requires strong partial covering of the X-ray source. These results suggest that a confined hot (perhaps accretion) spot on the protostellar core was behind the star in the 1st observation and just appeared in the 2nd observation due to the core rotation with period of greater than or approx. 22.8 days, which is much slower than the break-up velocity previously assumed for young protostars. This means that the source had quiescent X-ray activity during the observations with an order of magnitude stronger level than Class I (older) protostars. We also consider whether the X-ray source associated with 10E could be shock heated plasma by a collision of a jet emanating from the tentative Class 0 object.

Hamaguchi, Ken-Ji↗
NASA NTRS2005

The Core of the Moon - Molten or Solid?

While several studies beginning in the Apollo era and continuing up to the present have tried to detect the lunar core, either geochemically, geophysically or geologically [e.g. 1, 2, 3, 4], it has so far proven somewhat elusive. The unambiguous detection of the lunar core is of prime importance as it holds the potential of distinguishing between the various theories for the formation of the Moon. The theory which currently enjoys the greatest success is the giant impact model, which has the Moon forming about 4.5 Gyr ago from the debris produced when a Mars sized proto planet collided with the proto Earth [e.g. 5, 6]. Simulations reveal that the material from which the Moon is made up contains very little iron and consequently a lunar core, if it exists, should be small.

Khan, A.↗
NASA NTRS2007

Clinical Core Competency Training for NASA Flight Surgeons

Introduction: The cohort of NASA flight surgeons (FS) is a very accomplished group with varied clinical backgrounds; however, the NASA Flight Surgeon Office has identified that the extremely demanding schedule of this cohort prevents many of these physicians from practicing clinical medicine on a regular basis. In an effort to improve clinical competency, the NASA FS Office has dedicated one day a week for the FS to receive clinical training. Each week, an FS is assigned to one of five clinical settings, one being medical patient simulation. The Medical Operations Support Team (MOST) was tasked to develop curricula using medical patient simulation that would meet the clinical and operational needs of the NASA FS Office. Methods: The MOST met with the Lead FS and Training Lead FS to identify those core competencies most important to the FS cohort. The MOST presented core competency standards from the American Colleges of Emergency Medicine and Internal Medicine as a basis for developing the training. Results: The MOST identified those clinical areas that could be best demonstrated and taught using medical patient simulation, in particular, using high fidelity human patient simulators. Curricula are currently being developed and additional classes will be implemented to instruct the FS cohort. The curricula will incorporate several environments for instruction, including lab-based and simulated microgravity-based environments. Discussion: The response from the NASA FS cohort to the initial introductory class has been positive. As a result of this effort, the MOST has identified three types of training to meet the clinical needs of the FS Office; clinical core competency training, individual clinical refresher training, and just-in-time training (specific for post-ISS Expedition landings). The MOST is continuing to work with the FS Office to augment the clinical training for the FS cohort, including the integration of Web-based learning.

Polk, J. D.↗
NASA NTRS1997

Measurement of Vortex Strength and Core Diameter in the Wake of a Hovering Rotor

Detailed hot wire measurements have been acquired in the tip vortex of a three-bladed model tilt rotor in hover. Testing was conducted at a rotor tip speed of 752 ft/sec, a Reynolds number (based on blade tip chord) of 1.77 x 10(exp 6), for thrust coefficients up to 0.0160. A figure shows the hot wire mounted above the inverted rotor at the Outside Aerodynamic Rotor Facility (OARF) at NASA Ames Research Center. Strobed shadowgraph flow visualization was used to define the vortex trajectory as an aid in hot wire positioning. Considerable variations in tip vortex structure with time were observed, even from the same blade, under essentially uniform test conditions. The only velocity signatures analyzed were those corresponding to passage of the probe directly through the center of the vortex. These time histories were ensemble averaged after compensating for jitter in the vortex arrival time at the probe, thereby retaining the core structure with minimal smearing. An example of a mean velocity signature, after ensemble averaging, is shown. The mean velocity signature was analyzed under the assumption of constant (unknown) translation speed of the vortex filament past the fixed probe. The translation speed of the vortex is deduced and the vortex strength and core diameter inferred. The results were highly unexpected. The indicated vortex strength is seen to decrease rapidly after first blade passage. In addition, the core radius is seen to decrease with increasing wake age, not increase as might be expected from simple diffusion.

Wadcock, Alan J.↗
NASA NTRS2006

Turbofan Engine Core Compartment Vent Aerodynamic Configuration Development Methodology

This paper presents an overview of the design methodology used in the development of the aerodynamic configuration of the nacelle core compartment vent for a typical Boeing commercial airplane together with design challenges for future design efforts. Core compartment vents exhaust engine subsystem flows from the space contained between the engine case and the nacelle of an airplane propulsion system. These subsystem flows typically consist of precooler, oil cooler, turbine case cooling, compartment cooling and nacelle leakage air. The design of core compartment vents is challenging due to stringent design requirements, mass flow sensitivity of the system to small changes in vent exit pressure ratio, and the need to maximize overall exhaust system performance at cruise conditions.

Hebert, Leonard J.↗
NASA NTRS2008

Siderophile Element Depletion in the Angrite Parent Body (APB) Mantle: Due to Core Formation?

The origin of angrites has evaded scientists due in part to unusual mineralogy, oxidized character, and small numbers of samples. Increased interest in the origin of angrites has stemmed from the recovery of approximately 10 new angrites in the past decade. These new samples have allowed meteoriticists to recognize that angrites are compositionally diverse, old, and record very early differentiation. Also, a magma ocean has been proposed to have been involved in APB early differentiation, but this remains untested for siderophile elements which are commonly cited as one of the main lines of evidence for magma oceans on the early Earth, Moon, Mars and eucrite parent body (e.g., [6]). And recent suggestions that angrites may or may not be from Mercury have also peaked interest in these achondrites. Given all of this background, a detailed understanding of the early differentiation process is desired. Previous efforts at examining siderophile element (SE) concentrations with respect to core formation processes in the APB have not resulted in any definite conclusions regarding segregation of a metallic core. The goal of this study is to summarize what is known about SE concentrations in the suite, estimate depletions of SE compared to chondrites, and apply metal/silicate experimental partition coefficients to assess whether the APB had a core.

Righter, K.↗
NASA NTRS2007

Foam Core Shielding for Spacecraft

A foam core shield (FCS) system is now being developed to supplant multilayer insulation (MLI) systems heretofore installed on spacecraft for thermal management and protection against meteoroid impacts. A typical FCS system consists of a core sandwiched between a face sheet and a back sheet. The core can consist of any of a variety of low-to-medium-density polymeric or inorganic foams chosen to satisfy application-specific requirements regarding heat transfer and temperature. The face sheet serves to shock and thereby shatter incident meteoroids, and is coated on its outer surface to optimize its absorptance and emittance for regulation of temperature. The back sheet can be dimpled to minimize undesired thermal contact with the underlying spacecraft component and can be metallized on the surface facing the component to optimize its absorptance and emittance. The FCS systems can perform better than do MLI systems, at lower mass and lower cost and with greater volumetric efficiency.

Adams, Marc↗
NASA NTRS2011

Response of Honeycomb Core Sandwich Panel with Minimum Gage GFRP Face-Sheets to Compression Loading After Impact

A compression after impact study has been conducted to determine the residual strength of three sandwich panel constructions with two types of thin glass fiber reinforced polymer face-sheets and two hexagonal honeycomb Nomex core densities. Impact testing is conducted to first determine the characteristics of damage resulting from various impact energy levels. Two modes of failure are found during compression after impact tests with the density of the core precipitating the failure mode present for a given specimen. A finite element analysis is presented for prediction of the residual compressive strength of the impacted specimens. The analysis includes progressive damage modeling in the face-sheets. Preliminary analysis results were similar to the experimental results; however, a higher fidelity core material model is expected to improve the correlation.

McQuigg, Thomas D.↗
NASA NTRS2011

Observations of Nitrogen Isotope Fractionation in Prestellar Cores

Isotopically fractionated material is found in many solar system objects, including meteorites and comets [1]. It is considered, in some cases, to trace interstellar material that was incorporated into the solar system without undergoing significant processing, thus preserving the fractionation. In interstellar molecular clouds, ion-molecule chemistry continually cycles nitrogen between the two main reservoirs - Nand N2 - leading to only minor N-15 enrichments [2]. Charnley and Rodgers [3,4] showed that depletion of CO removes oxygen from the gas and weakens this cycle such that significant N-15 fractionation can occur for N2 and other N-bearing species in such cores. Observations are being conducted at millimeter and submillimeter wavelengths employing various facilities in order to both spatially and spectrally, resolve emission from these cores. A preliminary study to obtain the N-14/N-15 ratio in nitriles was conducted at the Arizona Radio Observatory's 12m telescope on Kitt Peak, AZ. Spectra were obtained at high resolution (0.08 km/s) in order to resolve dynamic properties of each source as well as to resolve hyperfine structure present in certain isotopologues. This study included four dark cloud cores, observed to have varying levels of molecular depletion: Ll521E, Ll498, Ll544, and Ll521F. Previous studies of the N-14/N-15 ratio towards Ll544 were obtained with N2H(+) and NH3 yielding ratios of 446 and greater than 700, respectively [5,6]. The discrepancy observed in these two measurements suggests a strong chemical dependence on the fractionation of nitrogen. Ratios (C,N, and D) obtained from isotopologues for a particular molecule are likely tracing the same chemical heritage and are directly comparable within a given source. Results and comparisons between the protostellar evolutionary state and isomer isotope fractionation as well as between other N-bearing species will be presented.

Milam, Stefanie N.↗