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  • ASTROPHYSICS  (7)
  • MECHANICAL ENGINEERING  (2)
  • formation clearance
  • 1990-1994  (3)
  • 1985-1989  (7)
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  • 1
    Digitale Medien
    Digitale Medien
    Inhibition of epoxidation of carbamazepine by valproic acid in the isolated perfused rat liver (1985)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 13 (1985), S. 453-466 
    Details
    ISSN: 1573-8744
    Schlagwort(e): carbamazepine ; valproic acid ; carbamazepine epoxide ; formation clearance ; perfused rat liver
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The effect of valproic acid on carbamazepine epoxidation in the perfused liver was investigated in two separate studies. In study I, significant decreases were observed both in the intrinsic clearance of carbamazepine and the intrinsic formation clearance of carbamazepineepoxide in the presence of therapeutic concentrations of valproate. The same inhibitory effect of valproate was also observed in liver preparations from a group of animals pretreated with carbamazepine. Study II focused on the effect of valproate and carbamazepine on the apparent Michaelis-Menten parameters (V max,m,Km,m)associated with the intrinsic formation clearance of carbamazepineepoxide in the perfused liver. Valproate had no statistically significant effect on either the V max,morthe Km,m of epoxidation, although the Km,m value was 43% higher in the presence of valproate. However, the ratio of V max,m and Km,m (intrinsic formation clearance) was significantly reduced by valproate. The V max,m and Km,m values obtained in study II predicted a significant decrease in the intrinsic formation clearance of carbamazepineepoxide, consistent with the results of study I. Carbamazepine pretreatment was associated with significant increases in apparent V max,m and Km,m of epoxide formation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01059329
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  • 2
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    Organic chemistry of Murchison meteorite: Carbon isotopic fractionation (1986)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA, Washington Second Symposium on Chemical Evolution and the Origin and Evolution of Life; p 40
    Format: text
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  • 3
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    Laser microprobe characterization of C species in Interplanetary Dust Particles (IDP) (1986)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Preliminary results of a study whose aim is the characterization of carbon (C) species in microvolumes of materials by means of laser ionization mass spectrometry (LIMS) are presented. The LIMS instrument employs a pulsed UV laser to produce nearly instantaneous vaporization and ionization of materials, followed by acceleration and time-of-flight analysis of the ions produced. LIMS provides a survey technique with nearly simultaneous acquisition of mass spectra covering the entire elemental range. The main limitation of the LIMS technique at present is its limited ability to perform quantitative analysis, due in part to insufficient knowledge of the mechanism of laser-solid interaction. However, considerable effort is now being directed at making LIMS a more quantitative technique. A variety of different C samples, both natural and man made were analyzed to establish the ability of LIMS to differentiate among the various C phases. The results of preliminary analyses performed on meteoritical and interplanetary dust samples are also presented. The C standards selected for the LIMS characterization range from essentially amorphous soot to diamond, which exhibits the highest degree of ordering.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Lunar and Planetary Inst. Trajectory Determinations and Collection of Micrometeoroids on the Space Station; p 77-79
    Format: application/pdf
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  • 4
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    The carbon chemistry of meteorites: Relationships to comets (1989)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The carbonaceous meteorites exhibiting alteration by liquid water bear a strong relationship to comets. Not only is their elemental composition closer to solar in relative abundances than other meteorites, they are water rich; and they contain isotopic compositions among refractory and volatile elements indicative of presolar components. Some of these isotopic anomalies occur in organic compounds and carbonaceous grains signifying the presence of discrete and identifiable carbon components derived from interstellar and circumstellar matter. Insofar as comets and meteorites are ultimately formed from interstellar gas and dust, and comets have been subjected to considerably less aqueous and thermal evolution than carbonaceous meteorites, the interstellar imprint should be much stronger and better preserved in comets.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Lunar and Planetary Inst., Workshop on Analysis of Returned Comet Nucleus Samples; p 13-14
    Format: application/pdf
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  • 5
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    Adsorption and recombination of hydrogen atoms on a model graphite surface (1985)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: The adsorption and recombination of atomic hydrogen on a model graphite grain have been examined in a series of calculations in which a modified, iterative, extended Hueckel program was used. The hydrogen atom is found to be chemisorbed at a site with a zero-point binding energy of 0.7 eV and at an equilibrium distance of 2.25 A above the site. Despite a barrier of about 0.4 eV between adjacent sites, calculations suggest that at temperatures as low as 10 K, an H atom will tunnel through to adjacent sites in less than one nanosecond. However, a potential barrier to the recombination of two hydrogen atoms has been found which displays high sensitivity to the mutual arrangement of the two hydrogen atoms with respect to the graphite surface. Results show that at very low temperatures, recombinations can occur only by tunneling. Consistent with experiment, the region in which H2 begins to form exhibits a repulsive potential with respect to possible chemisorption of the incipient H2 entity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 243-250
    Format: text
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  • 6
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    Evaluation of the Strecker synthesis as a source of amino acids on carbonaceous chondrites (1991)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The Strecker synthesis (SS) has been proposed as the source of amino acids (AA) formed during aqueous alteration of carbonaceous chondrites. It is postulated that the aldehyde and ketone precursors of the meteoritic AA originated in interstellar syntheses and accreted on the meteorite parent body along with other reactant species in cometesimal ices. The SS has been run with formaldehyde, acetyldehyde, propionaldehyde, acetone, and methyl ketone as starting materials. To study the effect of minerals on the reaction, the SS was run in the presence and absence of dust from the Allende meteorite using deuterated aldehydes and ketones as starting materials. The products were studied by GC/MS. With the exception of glycine, the retention of deuterium in the AA was greater than 90 pct. Some D exchange with water does occur, however, and determination of the rate of exchange as a function of pH and temperature may allow some bounds to be placed on the duration of parent body aqueous alteration. The retention of D by the AA under conditions studied thus far is consistent with the model that a SS starting from interstellar aldehydes and ketones led to the production of meteoritic AA.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Lunar and Planetary Inst., Abstracts for the 54th Annual Meeting of the Meteoritical Society; p 132
    Format: application/pdf
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  • 7
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    Carbon in Comet Halley dust particles (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: Comets are small bodies of the solar system containing primarily a mixture of frozen gases and carbonaceous and mineral grains. They are likely to preserve volatile mineral from cold regions of the protosolar nebula and remnants of interstellar dust and gas. More than 2500 mass spectra of cometary grains with masses in the range 5 x 10 exp -17 to 5 x 10 exp -12 g were measured in situ by PUMA1 and PUMA2 mass spectrometers on board the VEGA spacecraft during flyby missions to Comet Halley. In this paper, we discuss different organic and inorganic C-containing components discovered so far in Comet Halley dust particles, the nature and abundance of which provide information about possible astrophysical sources of C and constrain models of interstellar grains.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Lunar and Planetary Inst., Workshop on the Analysis of Interplanetary Dust Particles; p 22-24
    Format: text
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  • 8
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    Computer aided design and analysis of gear tooth geometry (1987)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A simulation method for gear hobbing and shaping of straight and spiral bevel gears is presented. The method is based upon an enveloping theory for gear tooth profile generation. The procedure is applicable in the computer aided design of standard and nonstandard tooth forms. An inverse procedure for finding a conjugate gear tooth profile is presented for arbitrary cutter geometry. The kinematic relations for the tooth surfaces of straight and spiral bevel gears are proposed. The tooth surface equations for these gears are formulated in a manner suitable for their automated numerical development and solution.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA-CR-179611 , NAS 1.26:179611 , AVSCOM-TR-87-C-13
    Format: application/pdf
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  • 9
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    Mass and spatial distribution of carbonaceous component in Comet Halley (1993)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: Cometary grains containing large amounts of carbon and/or organic matter were discovered by in situ measurements of cometary dust composition during VEGA and GIOTTO fly-by missions. In accordance with the classification for the data of PUMA-1 and PUMA-2 mass-spectrometers on board the VEGA spacecraft, particles with a ratio of C to any rock-forming element (Mg, Si, Fe, Ca etc.) greater than 10, were categorized as CHON. There are 464 such particles in PUMA-1 data and 51 in PUMA-2 data. Application of cluster analysis to these grains revealed several distinct compositional classes, namely: (H,C,N,O), (H,C,N), (H,C), (H,C,O), (C,N), (C,O), (C,N,O), and (C). Similar classes were identified among particles analyzed by PIA. Also, about a third of all particles fell into groups (H) and (O) characterized by abundances of these elements beyond chemically reasonable limits.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 501-502
    Format: text
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  • 10
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    Computer aided design of bevel gear tooth surfaces (1989)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: This paper presents a computer-aided design procedure for generating bevel gears. The development is based on examining a perfectly plastic, cone-shaped gear blank rolling over a cutting tooth on a plane crown rack. The resulting impression on the plastic gear blank is the envelope of the cutting tooth. This impression and envelope thus form a conjugate tooth surface. Equations are presented for the locus of points on the tooth surface. The same procedures are then extended to simulate the generation of a spiral bevel gear. The corresponding governing equations are presented.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: 1989 International Power Transmission and Gearing Conference; Apr 25, 1989 - Apr 28, 1989; Chicago, IL; United States
    Format: text
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