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Noble Gases (noble + gase)

Distribution by Scientific Domains

Chemistry	16%
Medical Sciences	12%
Engineering	8%

Selected Abstracts

Spectacular fall of the Kendrapara H5 chondrite

METEORITICS & PLANETARY SCIENCE, Issue S8 2004
D. Dhingra
In a rare observation, the fireball was seen by two airline pilots, providing direction of the trail with reasonable accuracy, consistent with ground-based observations. A few fragments of the meteorite were subsequently recovered along the end of the trail in different parts of Kendrapara district (20°30, N; 86°26, E) of Orissa. Based on petrography and chemical composition, the meteorite is classified as H5 chondrite. The cosmogenic radionuclides54Mn,22Na,60Co, and26Al and tracks have been studied in this stony meteorite. Two of the fragments show an unusually high activity of60Co (,160 dpm/kg) indicating a meteoroid radius of 50,150 cm. Assuming that less than 10% (by weight) of the fragments could be recovered because of difficult terrain, an atmospheric mass ablation of >95% is estimated. Based on the observations of the trail and the estimated mass ablation, orbital parameters of the meteoroid have been calculated. The aphelion is found to lie in the asteroidal belt (1.8,2.4 AU), but the inclination of the orbit is large (22°,26°) with respect to the ecliptic. Noble gases have been analysed in two samples of this meteorite. He and Ne are dominantly cosmogenic. Using production rates based on the sample depth derived from60Co content,21Ne-based exposure age of 4.50 ± 0.45 Ma is derived for Kendrapara. One of the samples, known to be more deeply shielded based on high60Co activity, shows the presence of80Kr,82Kr, and128Xe produced by (n, ,) reaction on79Br,81Br, and127I, respectively. The (80Kr/82Kr)n ratio of 3.5 ± 0.9 is consistent with neutrons being mostly thermal. Trapped84Kr and132Xe are in the expected range for metamorphic grade H5. [source]

Noble gases in geochemistry and cosmochemistry edited by Donald P. Porcelli, Chris J. Ballentine, and Rainer Wieler

METEORITICS & PLANETARY SCIENCE, Issue 3 2003
Marc W. Caffee
No abstract is available for this article. [source]

Combined noble gas and trace element measurements on individual stratospheric interplanetary dust particles

METEORITICS & PLANETARY SCIENCE, Issue 10 2002
K. Kehm
Trace element compositions are generally similar to CI meteorites, with occasional depletions in Zn/Fe with respect to CI. Noble gases were detected in all but one of the IDPs. Noble gas elemental compositions are consistent with the presence of fractionated solar wind. A rough correlation between surface-normalized He abundances and Zn/Fe ratios is observed; Zn-poor particles generally have lower He contents than the other IDPs. This suggests that both elements were lost by frictional heating during atmospheric entry and confirms the view that Zn can serve as an entry-heating indicator in IDPs. [source]

Noble gas compositions of Antarctic micrometeorites collected at the Dome Fuji Station in 1996 and 1997

METEORITICS & PLANETARY SCIENCE, Issue 7 2002
Takahito Osawa
Eleven of the AMMs were collected in 1996 (F96 series) and 16 were collected in 1997 (F97 series). One of the F97 AMMs is a totally melted spherule, whereas all other particles are irregular in shape. Noble gases were extracted using a Nd-YAG continuous wave laser with an output power of 2.5-3.5 W for ,5 min. Most particles released measurable amounts of noble gases. 3He/4He ratios are determined for 26 AMMs ((0.85-9.65) × 10,4). Solar energetic particles (SEP) are the dominant source of helium in most AMMs rather than solar wind (SW) and cosmogenic He. Three samples had higher 3He/4He ratios compared to that of SW, showing the presence of spallogenic 3He. The Ne isotopic composition of most AMMs resembled that of SEP as in the case of helium. Spallogenic 21Ne was detected in three samples, two of which had extremely long cosmic-ray exposure ages (> 100 Ma), calculated by assuming solar cosmic-ray (SCR) + galactic cosmic-ray (GCR) production. These two particles may have come to Earth directly from the Kuiper Belt. Most AMMs had negligible amounts of cosmogenic 21 Ne and exposure ages of <1 Ma. 40Ar/36Ar ratios for all particles (3.9,289) were lower than that of the terrestrial atmosphere (296), indicating an extraterrestrial origin of part of the Ar with a very low 40Ar/36Ar ratio plus some atmospheric contamination. Indeed, 40Ar/36Ar ratios for the AMMs are higher than SW, SEP, and Q-Ar values, which is explained by the presence of atmospheric 40Ar. The average 38Ar/36Ar ratio of 24 AMMs (0.194) is slightly higher than the value of atmospheric or Q-Ar, suggesting the presence of SEP-Ar which has a relatively high 38Ar/36Ar ratio. According to the elemental compositions of the heavy noble gases, Dome Fuji AMMs can be classified into three groups: chondritic (eight particles), air-affected (nine particles), and solar-affected (eight particles). The eight AMMs classified as chondritic preserve the heavy noble gas composition of primordial trapped component due to lack of atmospheric adsorption and solar implantation. The average of 129Xe/132Xe ratio for the 16 AMMs not affected by atmospheric contamination (1.05) corresponds to the values in matrices of carbonaceous chondrites (,1.04). One AMM, F96DK038, has high 129Xe/132Xe in excess of this ratio. Our results imply that most Dome Fuji AMMs originally had chondritic heavy noble gas compositions, and carbonaceous chondrite-like objects are appropriate candidate sources for most AMMs. [source]

Pseudomonas fluorescens' view of the periodic table

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2008
Matthew L. Workentine
Summary Growth in a biofilm modulates microbial metal susceptibility, sometimes increasing the ability of microorganisms to withstand toxic metal species by several orders of magnitude. In this study, a high-throughput metal toxicity screen was initiated with the aim of correlating biological toxicity data in planktonic and biofilm cells to the physiochemical properties of metal ions. To this end, Pseudomonas fluorescens ATCC 13525 was grown in the Calgary Biofilm Device (CBD) and biofilms and planktonic cells of this microorganism were exposed to gradient arrays of different metal ions. These arrays included 44 different metals with representative compounds that spanned every group of the periodic table (except for the halogens and noble gases). The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum biofilm eradication concentration (MBEC) values were obtained after exposing the biofilms to metal ions for 4 h. Using these values, metal ion toxicity was correlated to the following ion-specific physicochemical parameters: standard reduction-oxidation potential, electronegativity, the solubility product of the corresponding metal,sulfide complex, the Pearson softness index, electron density and the covalent index. When the ions were grouped according to outer shell electron structure, we found that heavy metal ions gave the strongest correlations to these parameters and were more toxic on average than the other classes of the ions. Correlations were different for biofilms than for planktonic cells, indicating that chemical mechanisms of metal ion toxicity differ between the two modes of growth. We suggest that biofilms can specifically counter the toxic effects of certain physicochemical parameters, which may contribute to the increased ability of biofilms to withstand metal toxicity. [source]

Laser Ablation (193 nm), Purification and Determination of Very Low Concentrations of Solar Wind Nitrogen Implanted in Targets from the GENESIS Spacecraft

GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2009
Laurent Zimmermann
azote; ablation laser; purification; spectrométrie de masse; mission GENESIS The GENESIS space mission recovered ions emitted by the Sun during a 27 month period. In order to extract, purify and determine the very low quantities of solar nitrogen implanted in the GENESIS targets, a new installation was developed and constructed at the CRPG (Nancy, France). It permitted the simultaneous determination of nitrogen and noble gases extracted from the target by laser ablation. The extraction procedure used a 193 nm excimer laser that allowed for surface contamination in the outer 5 nm to be removed, followed by a step that removed 50 nm of the target material, extracting the solar nitrogen and noble gases implanted in the target. Following purification using Ti and Zr getters for noble gases and a Cu-CuO oxidation cycle for N2, the extracted gases were analysed by static mode (pumps closed) mass spectrometry using electron multiplier and Faraday cup detectors. The nitrogen blanks from the purification section and the static line (30 minutes) were only 0.46 picomole and 0.47 picomole, respectively. La mission GENESIS a récupéré des ions émis par le soleil pendant une période de 27 mois. Afin d'extraire, purifier et analyser de très faibles quantités d'azote solaire implantés dans des cibles GENESIS, une nouvelle installation a été développée et construite au CRPG. Elle a permis l'analyse simultanée de l'azote et des gaz nobles extraits de la couche d'or par ablation. La procédure d'extraction a utilisé un laser Excimer 193 nm qui a permis une étape d'extraction à 5 nm pour éliminer la pollution à la surface, suivie d'une étape qui a extrait jusqu'à une profondeur de 50 nm l'azote et les gaz rares solaires implantés dans la cible. Après une purification à l'aide de getters Ti et Zr pour les gaz rares et un cycle d'oxydation Cu-CuO pour N2, les gaz extraits ont été analysés en mode statique (pompage fermé) par spectrométrie de masse à l'aide d'un multiplicateur d'électrons et d'une cage de Faraday. Les blancs d'azote provenant de la partie purification et de la ligne en statique (30 minutes) étaient de seulement 0.46 et 0.47 picomole, respectivement. [source]

Isotope Methods for Management of Shared Aquifers in Northern Africa

GROUND WATER, Issue 5 2005
Bill Wallin
Access to fresh water is one of the major issues of northern and sub-Saharan Africa. The majority of the fresh water used for drinking and irrigation is obtained from large ground water basins where there is minor contemporary recharge and the aquifers cross national borders. These aquifers include the Nubian Aquifer System shared by Chad, Egypt, Libya, and Sudan; the Iullemeden Aquifer System, extending over Niger, Nigeria, Mali, Benin, and Algeria; and the Northwest Sahara Aquifer System shared by Algeria, Libya, and Tunisia. These resources are subject to increased exploitation and may be severely stressed if not managed properly as witnessed already by declining water levels. In order to make appropriate decisions for the sustainable management of these shared water resources, planners and managers in different countries need an improved knowledge base of hydrological information. Three technical cooperation projects related to aquifer systems will be implemented by the International Atomic Energy Agency, in collaboration with the United Nations Educational, Scientific and Cultural Organization and United Nations Development Programme/Global Environmental Facility. These projects focus on isotope hydrology studies to better quantify ground water recharge and dynamics. The multiple isotope approach combining commonly used isotopes 18O and 2H together with more recently developed techniques (chlorofluorocarbons, 36Cl, noble gases) will be applied to improve the conceptual model to study stratification and ground water flows. Moreover, the isotopes will be an important indicator of changes in the aquifer due to water abstraction, and therefore they will assist in the effort to establish a sustainable ground water management. [source]

Direct computation of thermodynamic properties of chemically reacting air with consideration to CFD

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2003
Joe IannelliArticle first published online: 2 SEP 200
Abstract This paper details a two-equation procedure to calculate exactly mass and mole fractions, pressure, temperature, specific heats, speed of sound and the thermodynamic and jacobian partial derivatives of pressure and temperature for a five-species chemically reacting equilibrium air. The procedure generates these thermodynamic properties using as independent variables either pressure and temperature or density and internal energy, for CFD applications. An original element in this procedure consists in the exact physically meaningful solution of the mass-fraction and mass-action equations. Air-equivalent molecular masses for oxygen and nitrogen are then developed to account, within a mixture of only oxygen and nitrogen, for the presence of carbon dioxide, argon and the other noble gases within atmospheric air. The mathematical formulation also introduces a versatile system non-dimensionalization that makes the procedure uniformly applicable to flows ranging from shock-tube flows with zero initial velocity to aerothermodynamic flows with supersonic/hypersonic free-stream Mach numbers. Over a temperature range of more than 10000 K and pressure and density ranges corresponding to an increase in altitude in standard atmosphere of 30000 m above sea level, the predicted distributions of mole fractions, constant-volume specific heat, and speed of sound for the model five species agree with independently published results, and all the calculated thermodynamic properties, including their partial derivatives, remain continuous, smooth, and physically meaningful. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Calculations of frequency-dependent molecular magnetizabilities with quasi-relativistic time-dependent generalized unrestricted Hartree,Fock method

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2007
Terutaka Yoshizawa
Abstract The time-dependent generalized unrestricted Hartree,Fock (TDGUHF) method combined with a two-component quasi-relativistic Hamiltonian generated from the Douglas,Kroll,Hess (DKH) transformation was developed to calculate frequency-dependent molecular magnetizabilities, which are the linear response quantity of a molecule to an external magnetic field. By calculating the magnetizabilities of H2X (X = O, S, Se, and Te), the noble gases (He, Ne, Ar, Kr, and Xe) and small open shell molecules (CH2, CH3, and O2), we found that scalar relativistic terms affect mainly the diamagnetic magnetizability and spin-orbit (SO) interaction affects the paramagnetic magnetizability. © 2007 Wiley Periodicals, Inc. J Comput Chem 28: 740,747, 2007 [source]

Proton affinities of maingroup-element hydrides and noble gases: Trends across the periodic table, structural effects, and DFT validation

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2006
Marcel Swart
Abstract We have carried out an extensive exploration of the gas-phase basicity of archetypal neutral bases across the periodic system using the generalized gradient approximation (GGA) of the density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. First, we validate DFT as a reliable tool for computing proton affinities and related thermochemical quantities: BP86/QZ4P//BP86/TZ2P is shown to yield a mean absolute deviation of 2.0 kcal/mol for the proton affinity at 298 K with respect to experiment, and 1.2 kcal/mol with high-level ab initio benchmark data. The main purpose of this work is to provide the proton affinities (and corresponding entropies) at 298 K of the neutral bases constituted by all maingroup-element hydrides of groups 15,17 and the noble gases, that is, group 18, and periods 1,6. We have also studied the effect of step-wise methylation of the protophilic center of the second- and third-period bases. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1486,1493, 2006 [source]

MRI of the lungs using hyperpolarized noble gases

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2002
Harald E. Möller
Abstract The nuclear spin polarization of the noble gas isotopes 3He and 129Xe can be increased using optical pumping methods by four to five orders of magnitude. This extraordinary gain in polarization translates directly into a gain in signal strength for MRI. The new technology of hyperpolarized (HP) gas MRI holds enormous potential for enhancing sensitivity and contrast in pulmonary imaging. This review outlines the physics underlying the optical pumping process, imaging strategies coping with the nonequilibrium polarization, and effects of the alveolar microstructure on relaxation and diffusion of the noble gases. It presents recent progress in HP gas MRI and applications ranging from MR microscopy of airspaces to imaging pulmonary function in patients and suggests potential directions for future developments. Magn Reson Med 47:1029,1051, 2002. © 2002 Wiley-Liss, Inc. [source]

Noble gas study of the Saratov L4 chondrite

METEORITICS & PLANETARY SCIENCE, Issue 3 2010
Jun-ichi MATSUDA
The Ar, Kr, and Xe concentrations in the HF/HCl residue are two orders of magnitude higher than those in the bulk sample, while He and Ne concentrations from both are comparable. The residue contains only a portion of the trapped heavy noble gases in Saratov; 40 ± 9% for 36Ar, 58 ± 12% for 84Kr, and 48 ± 10% for 132Xe, respectively. The heavy noble gas elemental pattern in the dissolved fraction is similar to that in the residue but has high release temperatures. Xenon isotopic ratios of the HF/HCl residue indicate that there is no Xe-HL in Saratov, but Ne isotopic ratios in the HF/HCl residue lie on a straight line connecting the cosmogenic component and a composition between Ne-Q and Ne-HL. This implies that the Ne isotopic composition of Q has been changed by incorporating Ne-HL (Huss et al. 1996) or by being mass fractionated during the thermal metamorphism. However, it is most likely that the Ne-Q in Saratov is intrinsically different from this component in other meteorites. The evidence of this is a lack of correlation between the isotopic ratio of Ne-Q and petrologic types of meteorites (Busemann et al. 2000). A neutron capture effect was observed in the Kr isotopes, and this process also affected the 128Xe/132Xe ratio. The 3He and 21Ne exposure ages for the bulk sample are 33 and 35 Ma, respectively. [source]

Cosmic-ray exposure age and heliocentric distance of the parent bodies of enstatite chondrites ALH 85119 and MAC 88136

METEORITICS & PLANETARY SCIENCE, Issue 6 2006
D. Nakashima
These two meteorites contain solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated heliocentric distances, parent body exposure ages, and space exposure ages of the two meteorites. The parent body exposure ages are longer than 6.7 Ma for ALH 85119 and longer than 8.7 Ma for MAC 88136. The space exposure ages are shorter than 2.2 Ma for ALH 85119 and shorter than 3.9 Ma for MAC 88136. The estimated heliocentric distances are more than 1.1 AU for ALH 85119 and 1.3 AU for MAC 88136. Derived heliocentric distances indicate the locations of parent bodies in the past when constituents of the meteorites were exposed to the Sun. From the mineralogy and chemistry of E chondrites, it is believed that E chondrites formed in regions within 1.4 AU from the Sun. The heliocentric distances of the two E chondrite parent bodies are not different from the formation regions of E chondrites. This may imply that heliocentric distances of E chondrites have been relatively constant from their formation stage to the stage of exposure to the solar wind. [source]

Opportunities for the stratospheric collection of dust from short-period comets

METEORITICS & PLANETARY SCIENCE, Issue 11 2002
Scott MESSENGER
These comets have had the rare characteristics of low eccentricity, low inclination orbits with nodes very close to 1 AU. Dust from these comets is directly injected into Earth-crossing orbits by radiation pressure, unlike the great majority of interplanetary dust particles collected in the stratosphere which spend millennia in space prior to Earth-encounter. Complete dust streams from these comets form within a few decades, and appreciable amounts of dust are accreted by the Earth each year regardless of the positions of the parent comets. Dust from these comets could be collected in the stratosphere and identified by its short space exposure age, as indicated by low abundances of implanted solar-wind noble gases and/or lack of solar flare tracks. Dust from Grigg-Skjellerup probably has the highest concentration at Earth orbit. We estimate that the proportion of dust from this comet will reach at least several percent of the background interplanetary dust flux in the >40 ,m size range during April 23,24 of 2003. [source]

Nitrogen in diamond-free ureilite Allan Hills 78019: Clues to the origin of diamond in ureilites

METEORITICS & PLANETARY SCIENCE, Issue 8 2002
V. K. Rai
A small amount of amorphous carbon combusting at ,500 °C carries most of the noble gases, while the major carbon phase consisting of large crystals of graphite combusts at ,800 °C, and is almost noble-gas free. Nitrogen on the other hand is present in both amorphous carbon and graphite, with different ,15N signatures of ,21%o and +19%o, respectively, distinctly different from the very light nitrogen (about ,100%o) of ureilite diamond. Amorphous carbon in ALH 78019 behaves similar to phase Q of chondrites with respect to noble gas release pattern, behavior towards oxidizing acids as well as nitrogen isotopic composition. In situ conversion of amorphous carbon or graphite to diamond through shock would require an isotopic fractionation of 8 to 12% for nitrogen favoring the light isotope, an unlikely proposition, posing a severe problem for the widely accepted shock origin of ureilite diamond. [source]

Noble gas compositions of Antarctic micrometeorites collected at the Dome Fuji Station in 1996 and 1997

About noble gases in E chondrites

METEORITICS & PLANETARY SCIENCE, Issue 4 2002
Henner Busemann
[source]

The irradiation history of the Ghubara (L5) regolith breccia

METEORITICS & PLANETARY SCIENCE, Issue 3 2002
T. E. Ferko
The xenoliths, like the host, have high concentrations of trapped solar gases and are heavily shocked. While contents of noble gases and degree of shock-loading in this individual and three others differ somewhat, the data indicate that Ghubara is a two-generation regolith breccia. Contents of cosmogenic 26Al and 10Be and low track densities indicate that the Ghubara individuals were located more than 15 cm below the surface of an 85 cm meteoroid. Because of its large size, Ghubara's cosmic-ray exposure age is poorly defined to be 15,20 Ma from cosmogenic nuclides. Ghubara's terrestrial age, based on 14C data, is 2,3 ka. Not only is Ghubara the first known case of a two-generation regolith breccia on the macroscale, it also has a complicated thermal and irradiation history. [source]

Heavy noble gases in solar system matter

METEORITICS & PLANETARY SCIENCE, Issue 2 2002
Kurt Marti
[source]

Nanoscale lead and noble gas inclusions in aluminum: Structures and properties

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 5-6 2004
Erik Johnson
Abstract Transmission electron microscopy has been used for structural and physical characterization of nanoscale inclusions of lead and noble gases in aluminum. When the inclusion sizes approach nanoscale dimensions, many of their properties are seen to deviate from similar properties in bulk and in most cases the deviations will increase as the inclusion sizes decrease. Binary alloys of lead and noble gases with aluminum are characterized by extremely low mutual solubilities and inclusions will, therefore, exist as practically pure components embedded in the aluminum matrix. Furthermore, the thermal vacancy mobility in aluminum at and above room temperature is sufficiently high to accommodate volume strains associated with the inclusions thus leading to virtually strain free crystals. The inclusions grow in parallel cube alignment with the aluminum matrix and have a cuboctahedral shape, which reflects directly the anisotropy of the interfacial energies. Inclusions in grain boundaries can have single crystalline or bicrystalline morphology that can be explained from a generalized Wulff analysis such as the ,-vector construction. The inclusions have been found to display a variety of nanoscale features such as high Laplace pressure, size-dependent superheating during melting, deviations from the Wulff shape displaying magic size effects, a shape dependence of edge energy, and so on. All these effects have been observed and monitored by TEM using conventional imaging conditions and high-resolution conditions in combination with in-situ analysis at elevated temperatures. Microsc. Res. Tech. 64:356,372, 2004. © 2004 Wiley-Liss, Inc. [source]

Solution of protein crystallographic structures by high-pressure cryocooling and noble-gas phasing

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2006
Chae Un Kim
Room-pressure flash-cryocooling of protein crystals is the standard way to reduce radiation damage during data collection. Typically, it is necessary to find cryoprotection conditions by trial and error, a process that is not always successful. Recently, a new method, high-pressure cryocooling, was developed that does not require penetrative cryoprotectants and typically yields very high quality diffraction. Since this method involves helium gas as a pressurizing medium, it was of great interest to see whether the method could be extended to diffraction phasing by the incorporation of heavy noble gases such as krypton. A modified Kr,He high-pressure cyrocooling procedure is described wherein crystals are first pressurized with krypton gas to 10,MPa for 1,h. The krypton pressure is then released and the crystals are repressurized with helium over 150,MPa and cooled to liquid-nitrogen temperatures. Porcine pancreas elastase (PPE; 240 residues, 26,kDa) was selected as a test case for this study. Excellent diffraction was achieved by high-pressure cryocooling without penetrating cryoprotectants. A single 0.31 occupied krypton site in a PPE molecule [Bijvoet amplitude ratio (,|,F|,/,F,) of 0.53%] was successfully used for SAD phasing at 1.3,Å. This method has the potential to greatly simplify obtaining protein structures. [source]