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AbstractAbstract

[en] Many important classes of surface reactions exhibit both high heats of reaction and large, positive activation energies. In addition, many surface reactions often occur in thermally isolated environments. As a result, significant autothermic effects are possible. In part I of this article, a generalized model of these effects is presented which describes the enhancement in reaction rate as a function of activation energy, bulk temperature, and a parameter termed the characteristic temperature. Reactant concentration and reaction order effects are also considered. Part II of this work presents the application of this model to numerous experimental plasma etching data

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[en] Different factors affecting the accuracy of the computed energy surfaces of the ground and first excited state of He

_{2}^{+}have been examined, including the choice of the one-and many-particle bases, the configurational space in the MRCI (multi-reference configuration interaction) calculations and other corrections such as the Davidson and the full counterpoise (CP) correction. From basis-variation studies, it was concluded that multi-reference direct-CI calculations (MRDCI) using CASSCF MOs and/or natural orbitals (NOs) from a smaller CISD calculation, gave results close to full CI. The computed dissociation energies, D_{e}, for the ground and first excited state of He_{2}^{+}were 2.4670 (2.4659) eV and 17.2 (17.1) cm^{-1}, respectively, at the highest level [without and with CP correction for basis-set superposition errors (BSSE)] of calculation with an [11s8p3d1f] GTO contraction, in reasonably good agreement with previous calculations, and estimated correct values, where available. It is believed that the computed D_{e}, and the energy surface for the first excited state should be reasonably accurate. However, for the ground state, the effects of multiple f functions and/or functions of higher angular momentum have not been investigated owing to limitation of the available computing resources. This is probably the only weakness is the present study. (Author)Primary Subject

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Journal of the Chemical Society. Faraday Transactions; ISSN 0956-5000; ; CODEN JCFTEV; v. 89(4); p. 645-653

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[en] Starting from the complete anisotropic Eliashberg equations valid for a layered compound, we compute the temperature variation of the London penetration depth λ

_{L}(T) parallel and perpendicular to the planes. In our model we use a free-electron approximation in the planes with a hopping probability for interplane motion. The anisotropy in the pairing is expanded in Fermi-surface harmonics. It is found that anisotropy can strongly influence the temperature dependence of λ_{L}(T) but that its effect is suppressed with increasing coupling strengthRecord Type

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Kuz'menko, N.K.; Nesterenko, V.O.; Pashkevich, V.V.; Frauendorf, S.

Joint Inst. for Nuclear Research, Dubna (Russian Federation). Lab. of Theoretical Physics

Joint Inst. for Nuclear Research, Dubna (Russian Federation). Lab. of Theoretical Physics

AbstractAbstract

[en] The pairing between valence electrons is considered as a possible origin of the odd-even staggering (OES) in the ionization potentials (IP) of sodium clusters with 20 ≤ N ≤ 80. For the first time, both effects of pairing and shape deformation are taken into account simultaneously. On the average, quite a reasonable description of the IP is achieved. It is shown that in sodium clusters only a weak pairing can exist (if the pairing exists at all). In this case, it is not correct to use the Bardin-Cooper-Shriffer (BCS) method. Only the particle-number projecting methods can be applied. It is shown that competition between pairing and deformation effects is small and does not change the equilibrium deformations. Pairing leads to systematic and pronounced OES and destroys the so-called quartets in the IP. This improves the agreement with experimental data in some size regions. On the other hand, the pairing worsens the agreement in the size regions where the OES has not been observed at all. Finally, the existence of the pairing in sodium clusters seems to be very questionable. 35 refs., 3 figs

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1994; 16 p; Submitted to Zeitschrift fuer Physik. D, Atoms, Molecules and Clusters.

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[en] We have analyzed the possible superconducting states of a model layered superconductor with N conducting layers in a unit cell, for N=3 and 4, in the presence of both intralayer and interlayer pairing interactions. In case all layers are identical, the system has the same behavior as one-layer and two-layer systems, namely that pure intralayer pairing interaction stabilizes an s-wave state with equal and isotropic gaps in all N quasiparticle bands, while interlayer pairing produces both singlet and triplet paired states with anisotropic gap functions. The singlet state is always energetically more stable than the triplet state. The analysis can be easily extended to nonidentical layers. As one example, a model for YBa

_{2}Cu_{3}O_{7-δ}consisting of two CuO_{2}layers in a unit cell separated by a layer of CuO chains is discussed. It is shown that the system reduces to an effective two-layer model, due to the large difference in electronic energy states between the planes and the chains. The chains are most likely nonsuperconducting. In another example, we show that Bi_{2}Sr_{2}CaCu_{2}O_{8}can be reduced to an effective three-layer system. Recent tunneling data can be understood on the basis of this modelSecondary Subject

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[en] The leading asymptotic term (for large impact parameters) of the charge-exchange amplitude for 1s

_{1/2}→1s_{1/2}transitions is calculated in a modified relativistic eikonal approximation. Relativistic effects are taken into account in the kinematics of electron capture and in the description of the bound states. A study is made of the effects of the long-range interaction due to the Coulomb interaction between the particles in the entrance and exit reaction channels. The analytic results obtained in the nonrelativistic limit (c→∞) for the charge-exchange amplitude in the asymptotic region of large impact parameters are valid for all velocities, going over the adiabatic limit into the well-known expressions of Firsov and in the limit of high velocities into the expressions of the Born approximation. 25 refs., 1 fig., 2 tabsPrimary Subject

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Cover-to-cover Translation of Teoreticheskaia I Matematicheskaia Fizika (USSR); Translated from Teoreticheskaya i Matematicheskaya Fizika; 95: No. 3, 451-477(Jun 1993).

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AbstractAbstract

[en] Results of spin--orbit interaction calculations on the three lowest triplet states of ozone,

^{3}B_{2},^{3}A_{2}, and^{3}B_{1}, are presented. These calculations use a one-electron, one-center approximation of the spin--orbit operator and a modest number of configurations within a 3s2p1d basis to estimate the amount of singlet character in these predominantly triplet states and triplet character in the predominantly singlet ground state. The results are given in the context of recent studies which predict that one of these triplet states gives rise to the Wulf optical absorption bands of ozone, a series of weak diffuse peaks in the near infrared, just above the O_{2}+O dissociation threshold. Without spin--orbit coupling, these triplet states are spin forbidden from the singlet ozone ground state,^{1}A_{1}. The present results point to the^{3}A_{2}and^{3}B_{1}states as playing a possible role in the Wulf bands, but more complete calculations will be needed to confirm thisPrimary Subject

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[en] Relativistic effects on the Thomas-Fermi model for atoms in a very strong magnetic field are considered. A general calculation of the binding energy is given which does not refer to any specific solution of the equation governing the self-consistent electrostatic potential. (orig.)

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Cha, Y.S.; Niemann, R.C.; Hull, J.R.; Youngdahl, C.A.; Lanagan, M.T.; Nakade, M.; Hara, T.

Argonne National Lab., IL (United States). Funding organisation: USDOE, Washington, DC (United States)

Argonne National Lab., IL (United States). Funding organisation: USDOE, Washington, DC (United States)

AbstractAbstract

[en] Liquid helium boil-off experiments are conducted to determine the heat leakage rate of a pair of BSCCO 2223 high-temperature superconductor current leads made by sinter forging. The experiments are carried out in both DC and AC conditions and with and without an intermediate heat intercept. Current ranges are from 0-500 A for DC tests and 0-1,000 A

_{rms}for AC tests. The leads are self-cooled. Results show that magnetic hysteresis (AC) losses for both the BSCCO leads and the low-temperature superconductor current jumper are small for the current range. It is shown that significant reduction in heat leakage rate (liquid helium boil-off rate) is realized by using the BSCCO superconductor leads. At 100 A, the heat leakage rate of the BSCCO/copper binary lead is approximately 29% of that of the conventional copper lead. Further reduction in liquid helium boil-off rate can be achieved by using an intermediate heat intercept. For example, at 500 K, the heat leakage rate of the BSCCO/copper binary lead is only 7% of that of the conventional copper lead when an intermediate heat intercept is usedSource

Jun 1995; 22 p; Cryogenic engineering conference and international cryogenic materials conference; Columbus, OH (United States); 17-21 Jul 1995; CONF-950722--1; CONTRACT W-31109-ENG-38; Also available from OSTI as DE95014227; NTIS; US Govt. Printing Office Dep

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[en] The Born-Oppenheimer (BO) potential energy curves for several of the lowest

^{3}Σ_{g}^{+}and^{3}Σ_{u}^{+}of H_{2}at internuclear distances R ≤ 5 au are calculated using large elliptical orbital sets and full configuration interaction (CI) expansions. The resulting energies are shown to be surprisingly accurate compared with those obtained by using explicitly correlated basis functions of the generalized James-Coolidge or Hylleraas type. Accurate BO potential energy curves for the first three excited^{3}Σ_{u}^{+}states and the second up through fifth excited^{3}Σ_{g}^{+}states are given. It is concluded that for the triplet Rydberg states of H_{2}the CI method is as effective at describing electron correlation as are the methods that include the interelectron distance explicitly. (author)Primary Subject

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Journal of Physics. B, Atomic, Molecular and Optical Physics; ISSN 0953-4075; ; CODEN JPAPEH; v. 27(22); p. L729-L734

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