70,064 research outputs found
M. J. Tricart, Quelques caractéristiques générales des villes latino-américaines
No full textPradilla Cobos Emilio. M. J. Tricart, Quelques caractéristiques générales des villes latino-américaines. In: Tiers-Monde, tome 8, n°32, 1967. L'Espagne à l'heure du développement. pp. 1203-1204
Experimental and modeling study of the reaction C2F4 (+M) = CF2 + CF2 (+M)
No full textThe thermal dissociation reaction C2F4(+ M) → 2CF2(+ M) was studied in shock waves monitoring CF2 radicals by their UV absorption. The absorption coefficients as functions of wavelength and temperature were redetermined and are represented in analytical form. Dissociation rate constants as functions of bath gas concentration [M] and temperature, from previous and the present work, are presented analytically employing falloff expressions from unimolecular rate theory. Equilibrium constants are determined between 1200 and 1500 K. The data are shown to be consistent, with a C–C bond energy of 67.5 (±0.5) kcal mol–1. High-pressure limiting rate constants for dissociation and recombination are found to be unusually small. This phenomenon can be attributed to an unusually pronounced anisotropy of the potential energy surface, such as demonstrated by quantum-chemical calculations of the potential energy surface.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Croce, Adela Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Luther, K.. Universität Göttingen. Institut für Physikalische Chemie; AlemaniaFil: Sölter, L.. Universität Göttingen. Institut für Physikalische Chemie; AlemaniaFil: Tellbach, E.. Universität Göttingen. Institut für Physikalische Chemie; AlemaniaFil: Troe, J.. Universität Göttingen. Institut für Physikalische Chemie; Alemania. Max-Planck-Institut für Biophysikalische Chemie; Alemani
Agrilaxia (Agrilaxia) simillima Cobos 1972
No full textAgrilaxia (Agrilaxia) simillima (Cobos, 1972) (Fig. 4) Anthaxia (Agrilaxia) simillima Cobos, 1972: 109. Anthaxia (Agrilaxia) simillima: Bílý, 1997: 36, 115 (catalogue). Agrilaxia simillima: Bellamy, 2008: 1507 (catalogue). Type specimen studied. Holotype by monotypy (male, NHMB): “ 2176 [blue, h] // Costa Rica Schmidt S. [p, framed] // cum typo comp. Dr. Hoscheck [p, framed] // Museum Frey Tutzing [green, p] // schmidti Obb. sec. Hoscheck [h, Cobos] // Holotypus [p, red]// Anthaxia (Agrilaxia) simillima nov. sp. Holotypus [h] A. Cobos det. 1968 [p]” Further specimens studied. COSTA RICA: Puntarenas, Manuel Antonio, 20.iii. 1996, Dr. D. Dauber leg. (1 male, NMPC); VENEZUELA: Aragua, Rancho Grande, 700 m, 14.ix. 1970, J. & B. Bechyně leg. (1 male—Fig. 4, MIZA); Barinas, Soledad, Carretera I, 1100 m, 22.viii. 1974, B. Bechyně leg. (1 male, NMPC). Note. This species was described for a single male from Costa Rica in the genus Anthaxia (Cobos, 1972); the female is unknown. Distribution. Costa Rica, Venezuela (new country record).Published as part of Bílý, Svatopluk, 2015, A study on the genus Agrilaxia Kerremans, 1903 from Venezuela (Coleoptera: Buprestidae: Buprestinae: Anthaxiini), pp. 173-182 in Zootaxa 4039 (1) on page 175, DOI: 10.11646/zootaxa.4039.1.8, http://zenodo.org/record/23984
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
Re-evaluation of rate constants for the reaction N2H4 (+ M) ⇄ NH2 + NH2 (+ M)
No full textArticle describes how rate constants for the dissociation/recombination reaction N2H4 (+ M) ⇄ NH2 + NH2 (+ M) are determined by a combination of quantum-chemical calculations and statistical unimolecular rate theory. Implications of the present re-evaluated rate constants for the modeling of high temperature ammonia oxidation kinetics are discussed, showing an only small influence of their precise values on the overall properties of the process
Shock wave study of the thermal decomposition of CF3 and CF2 radicals.
No full textThe thermal dissociation reactions CF3 + M -> CF2 + F + M (reaction 1) and CF2 + M -> CF + F + M (reaction 3) were studied behind shock waves. CF.) radicals were monitored through their UV absorption. By working at very low reactant concentrations, the rate coefficients of the unimolecular processes could be derived. Reaction 1 was investigated between 1600 and 2300 K in the intermediate range of the falloff curves, at similar to 10 times larger bath gas pressures than employed in earlier work (Srinivasan, N. K.; Su, M.-C.; Michael, J. V.; Jasper, A. W.; Klippenstein, S. J.; Harding, L. B. J. Phys. Chem. A 2008, 112, 31). The combination of the two sets of data, together with theoretical modeling, allows one to construct falloff curves and to provide complete representations of the temperature and pressure dependences of the rate coefficients. Reaction 3 was studied in the limiting low-pressure range and, over the range 2900-3800 K, a rate coefficient k(3) = [Ar] 1.6 x 10(15) exp(-48 040 K/T) cm(3) molecule(-1) s(-1) was obtained. Representations of the rate coefficients over the full falloff curves were again derived by theoretical modeling
Temperature and pressure dependence of the reaction 2CF(3) (+ M) double left right arrow C2F6 (+ M).
No full textLimiting low- and high-pressure rate coefficients as well as full falloff curves have been modeled by unimolecular rate theory for the recombination reaction 2CF(3) (+ M) -> C2F6 (+ M) and the reverse dissociation of C2F6. The results are compared with experimental data from the literature. Although there are considerable discrepancies (up to a factor of 5) between various experimental data near 300 K and the database for high temperatures is still limited, we try to conclude on the temperature dependence of the high-pressure rate coefficient. We suggest that there is only a small and probably positive temperature coefficient of the latter quantity. The present theoretical modeling seems to be in agreement with this experimental result, but it is in disagreement with conclusions from earlier theoretical work. The difference is attributed to different empirical assumptions about the anisotropy of the potential. It is shown that nearly all previous experiments (except high-temperature shock wave and very low pressure pyrolysis/photolysis experiments) correspond to nearly limiting high-pressure conditions
Letter from Carl Hayden to M. J. Riordan
No full textLetter from Carl Hayden to M. J. Riordan expressing his support for Coconino County in turning over the Bright Angel Trail to the federal government
Letter from M. J. Riordan, Arizona Lumber and Timber Company, to Carl Hayden
No full textLetter from M. J. Riordan to Carl Hayden expressing his opposition to the federal government's takeover of Bright Angel Trail
Falloff curves of the reaction CF<sub>3</sub> (+M) → CF<sub>2</sub> + F (+M).
No full textThe thermal dissociation reaction CF3 (+ Ar) → CF2 + F (+ Ar) was studied in incident and reflected shock waves by monitoring UV absorption signals of the primary dissociation product CF2. CF3 radicals were produced by thermal decomposition of CF3I. Accounting for secondary reactions of F atoms, rate constants for the unimolecular dissociation were derived. Experimental parts of the falloff curves were obtained over the ranges 1544 - 2106 K and 1.0×〖10〗^(-5)≤["Ar" ]≤9.3×〖10〗^(-5 ) "mol " 〖"cm" 〗^"-3" . Theoretical modelling allowed for a construction of the full falloff curves connecting the limiting low pressure rate constants k_0=["Ar" ] 2.5×〖10〗^18 (T⁄(2000 "K" ))^(-5.1) " exp" ((-42450 "K" )⁄T) 〖"cm" 〗^"3" 〖"mol" 〗^(-1) "s" ^(-1) with the limiting high pressure rate constants k_∞= 1.6×〖10〗^16 (T⁄(2000 "K" ))^(-1.3) "exp" ((-43250 "K" )⁄T) "s" ^(-1) (center broadening factors of F_cent= 0.25, 0.22, and 0.20 at 1500, 2000, and 2500 K, respectively, were used). The influence of simplifications of falloff expressions and of limiting rate constants on the representation of experimental data is discussed
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