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  • 1
    Electronic Resource
    Electronic Resource
    Calculations on the competition between association and reaction for C3H++H2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2812-2820 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A potential energy surface has been calculated for the competing associative and reactive ion–molecule processes involving the reactants C3H++H2. Our ab initio results show that the linear ion C3H+ and H2 can directly access the deep potential well of the propargyl ion H2CCCH+, which is calculated to lie 390 kJ mol−1 below the zero-point energy of the reactants. Isomerization between the propargyl ion and the lower energy, cyclic C3H3+ ion, calculated to lie 501 kJ mol−1 below the zero-point energy of reactants, can subsequently occur via two pathways. One of these pathways involves a transition state lying 22 kJ mol−1 below the energy of the reactants while the other, which occurs at much lower energies, involves two transition states and an intermediate. The dissociation of c-C3H3+ into c-C3H2++H is calculated to occur directly, without any intermediate potential energy maximum, but the energy of the products lies 7.3 kJ mol−1 above the energy of the reactants. Using the minimum energy potential pathway and properties of the stationary point structures determined via ab initio methods, we have calculated both the association rate coefficient to produce C3H3+ as a function of density and the branching ratio between the propargyl and cyclic structures of the ion. Our results are in good agreement with some experimental results and in conflict with others. Specifically, we agree with the 1:1 branching ratio measured for the propargyl and cyclic isomers of C3H3+ at 80 and 300 K and we agree with the rate coefficient for radiative association measured at 80 K. We cannot reproduce reported measurements that the reactive channel (C3H2++H) is the dominant channel at 80 K and at low gas densities, or that the association channel at high densities saturates at an effective rate coefficient well below the Langevin value −2×10−11 cm3 s−1 at 300 K and 1×10−10 cm3 s−1 at 80 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465190
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical prediction of the vibrational spectrum of naphthalene in the first excited singlet state (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 974-987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Complete harmonic force fields have been calculated for the ground state (S0) and the first excited singlet state (S1) of naphthalene using the multiconfiguration self-consistent field (MCSCF) approach. Identical calculations were performed for benzene to test the methodology with already available theoretical and empirical force fields. Two different basis sets were applied (STO-3G and near double-zeta) and all π-orbitals included in the active space. The geometries of ground and excited states were separately optimized. Following the ideas of Pulay, the force constants were scaled before calculating frequencies and normal modes. For the ground states the influence of correlation is discussed by comparison with Pulay's results. Except for special vibrations where correlation effects turn out to be important, the use of Pulay's scaling factors leads to a satisfactory description of the in-plane-vibrations. In the case of benzene the calculated frequency shifts between S0 and S1 are in complete qualitative agreement with experimental observations. In the case of naphthalene the new theoretical results suggest several revisions of earlier empirical assignments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464261
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  • 3
    Electronic Resource
    Electronic Resource
    Small oscillations: A new solution based on non-Noetherian symmetries (1993)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 2968-2974 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A new (non-Noetherian) symmetry transformation for the small oscillations problem is exhibited. A novel way to solve this classical problem, based on conservation laws constructed using the new symmetry, is presented. Applications of these results to other fields of physics are outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.530109
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  • 4
    Electronic Resource
    Electronic Resource
    Comparable levels of trace metal contamination in two semienclosed embayments: San Diego Bay and south San Francisco Bay (1993)
    s.l. : American Chemical Society
    Environmental science & technology 27 (1993), S. 1934-1936 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es00046a025
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  • 5
    Electronic Resource
    Electronic Resource
    Relationship between growth conditions, nitrogen profile, and charge to breakdown of gate oxynitrides grown from pure N2O (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 194-196 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the relationship between the growth conditions, the nitrogen profile, and the charge to breakdown of N2O oxynitrides grown in a RTP and in a conventional furnace. RTP oxynitride shows nitrogen accumulation at the Si/SiO2 interface. On the other hand, furnace oxynitride shows almost uniform nitrogen distribution in the bulk, resulting in poor charge to breakdown characteristics. We find that two-step oxynitridation processes provide nitrogen accumulation at the Si/SiO2 interface and result in better electrical properties than those of one-step oxynitrides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110400
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  • 6
    Electronic Resource
    Electronic Resource
    A case of periodic sweating associated with a subarachnoid cyst and multifocal dystonia (1993)
    Springer
    Clinical autonomic research 3 (1993), S. 299-301 
    Details
    ISSN: 1619-1560
    Keywords: Acetazolamide ; Multifocal dystonia ; Periodic sweating ; Suprasellar cyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Acase of periodic sweating with multifocal dystonia is reported in a 60-year-old woman. At the age of 48 years, she presented with involuntary twisting of the lower face on the right. Six months later she noticed similar movements in the head and right arm. Four years later she began having attacks of generalized sweating over the whole face, anterior region of the trunk and both arms. The attacks occurred hourly each and every day. They lasted for about 10 min and were followed by voluntary urinary voiding. The biochemical and laboratory investigations showed no abnormalities except for the luteinizing hormone and follicle-stimulating hormone values that were below normal. The computerized tomography and magnetic resonance imaging scans revealed a suprasellar cyst. Clonazepam was introduced with partial improvement of the dystonic movements but not of the sweating attacks. The patient refused surgery. Acetazolamide was added and reduced the sweating attacks. We speculate that the periodic sweating may be related to cerebrospinal fluid production and cyst enlargement, hence the ability of acetazoleamide, which reduces cerebrospinal fluid production, to reduce attacks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01827330
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  • 7
    Electronic Resource
    Electronic Resource
    cis-Acting DNA elements involved in oocyte-specific expression of mouse sperm receptor gene mZP3 are located close to the gene's transcription start site (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 36 (1993), S. 494-499 
    Details
    ISSN: 1040-452X
    Keywords: Luciferase gene ; 153-ZP3/LUC ; ZDT ; Transgene ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We report that cis-acting DNA elements involved in oocyte-specific expression of the mouse sperm receptor gene (mZP3) are located close to the gene's transcription start site. Mice bearing a transgene that consists of only 153 nt of mZP3 5′-flanking region fused to the firefly luciferase gene (153-ZP3/LUC) expressed the reporter gene in ovary not in a wide variety of tissues; although two of three lines carrying 153-ZP3/LUC also expressed the transgene in forebrain and hypothalamus. Within the ovaries of transgenic mice, luciferase activity was restricted to growing oocytes. However, levels of luciferase activity in these oocytes were lower than those in oocytes from mice bearing transgenes that contain a larger segment of mZP3 5′-flanking region (470-6,500 nt) fused to the firefly luciferase gene. Mice bearing a trans-gene that consists of 470 nt of mZP3 5′-flanking region and mZP3 intragenic sequences (ZDT) were also analyzed. The presence of mZP3 intragenic sequences did not result in significantly increased levels of firefly luciferase activity in oocytes of mice carrying the ZDT transgene. Overall, these results suggest that as little as 153 nt of mZP3 5′-flanking region is sufficient to target expression of the firefly luciferase gene to mouse oocytes and that the mZP3 intragenic sequences probably do not contain enhancer elements. Rather, enhancer elements are probably present between  -  153 and  -  470 nt of the mZP3 5′-flanking region. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080360414
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of calcium deficiency on chondrocyte hypertrophy and type X collagen expression in chick embryonic sternum (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Developmental Dynamics 198 (1993), S. 284-295 
    Details
    ISSN: 1058-8388
    Keywords: Skeletogenesis ; Endochondral ossification ; Shell-less chick embryo ; Hyaline cartilage ; Extracellular matrix ; Mineralization ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Maintenance of chick embryos in long-term culture without their calcareous eggshell is a useful method for studying the relationship between calcium homeostasis and cell differentiation during skeletogenesis. Previously, we have shown that in shell-less (SL) embryos, calcium deficiency induces a cartilage-like phenotype in osteogenic tissues, such as calvaria (Jacenko and Tuan [1986] Dev. Biol. 115:215). In this investigation, we have studied the relationship between cartilage calcification and hypertrophy, and the expression of type X collagen, a specific product of hypertrophic chondrocytes. For this study, the cephalic (calcifying) and caudal (permanently cartilaginous) regions of sterna from day 18 and day 20 normal (NL) and SL embryos were metabolically labeled with [14C]-proline. Analysis of the biosynthetic products revealed significant differences in type X collagen expression in the cephalic region of sternal cartilage. In NL tissues, type X collagen production increased from 13.1% of total collagen at day 18 to 43.7% at day 20. In contrast, in SL embryos, type X collagen was not detectable until day 20, when it represented only 1% of total collagen. Comparison of the NL and SL embryos with respect to their serum calcium level and sternal calcium content and histology revealed a direct relationship between low systemic calcium and limited cartilage hypertrophy, undermineralization, and decreased type X collagen production in the sternal cephalic cartilage. Supplementation of CaCO3 to SL embryos increased their serum and sternal calcium, and restored cartilage hypertrophy, mineralization, and type X collagen synthesis in the cephalic portion of the sterna. These findings confirm that a critical relationship exists between calcium homeostasis, chondrocyte hypertrophy, mineralization, and type X collagen synthesis in the cephalic region of sternal cartilage. These results further demonstrate the importance of calcium in the morphogenetic events of endochondral ossification, in particular the transition from hyaline cartilage to hypertrophic cartilage, and eventually to bone. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001980406
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