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41.
Effective exposure temperatures (Teff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The Teff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel Teff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (Ea) of 21 kJ/mol (5 kcal/mol). Teff was only weakly dependent on Ea over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have Teff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample Teff if the annual black panel Teff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor Teff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year. 相似文献
42.
Superconductivity of MgB2: covalent bonds driven metallic 总被引:3,自引:0,他引:3
A series of calculations on MgB2 and related isoelectronic systems indicates that the layer of Mg2+ ions lowers the nonbonding B pi ( p(z)) bands relative to the bonding sigma ( sp(x)p(y)) bands compared to graphite, causing sigma-->pi charge transfer and sigma band doping of 0.13 holes/cell. Because of their two dimensionality the sigma bands contribute strongly to the Fermi level density of states. Calculated deformation potentials of gamma point phonons identify the B bond stretching modes as dominating the electron-phonon coupling. Superconductivity driven by sigma band holes is consistent with the report of destruction of superconductivity by doping with Al. 相似文献
43.
Lee R. Webster Dr. Saad K. Ibrahim Dr. Joseph A. Wright Prof. Christopher J. Pickett 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(37):11798-11803
We show that a robust molybdenum hydride system can sustain photoelectrocatalysis of a hydrogen evolution reaction at boron‐doped, hydrogen‐terminated, p‐type silicon. The photovoltage for the system is about 600–650 mV and the current densities, which can be sustained at the photocathode in non‐catalytic and catalytic regimes, are similar to those at a photoinert vitreous carbon electrode. The kinetics of electrocatalysed hydrogen evolution at the photocathode are also very similar to those measured at vitreous carbon—evidently visible light does not significantly perturb the catalytic mechanism. Importantly, we show that the doped (1–10 Ω cm) p‐type Si can function perfectly well in the dark as an ohmic conductor and this has allowed direct comparison of the cyclic voltammetric behaviour of the response of the system under dark and illuminated conditions at the same electrode. The p‐type Si we have employed optimally harvests light energy in the 600–700 nm region and with 37 mW cm?2 illumination in this range; the light to electrochemical energy conversion is estimated to be 2.8 %. The current yield of hydrogen under broad tungsten halide lamp illumination at 90 mW cm?2 is (91±5) % with a corresponding chemical yield of (98±5) %. 相似文献
44.
James Chapman Nigel L. Pickett Gabriel Kolawole Majid Motevalli Paul O'Brien 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):e501-e502
The title copper complex, [Cu(dl ‐DAP)2(H2O)2]·2H2O or [Cu(C3H7N2O2)2(H2O)2]·2H2O, prepared from the non‐protein amino acid dl ‐2,3‐diaminopropionic acid (dl ‐HDAP), has a center of symmetry and a distorted octahedral coordination, with four N atoms in equatorial positions and two water molecules in apical sites. The water molecule of crystallization is hydrogen bonded to the deprotonated carboxylate group of the ligand. 相似文献
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Douglas Pickett 《Mathematical Methods in the Applied Sciences》1992,15(1):57-71
Given self-adjoint operators Hj, on Hilbert spaces ??j, j = 0,l, and J ∈ ?? (??0, ??1) (where ?? (??0 ??1) denotes the set of bounded linear operators from ??0to ??1), define the wave operators where P0 is the projection onto the subspace for absolute continuity for H0. We use (i) to study the scattering problem associated with a pair of equations each of the form where L is a positive, self-adjoint operator on a Hilbert space X, m is a positive integer and the αj are distinct positive constants. Methods patterned after those of Kato are used to study two equations (that is for L = L0 and L = Ll) each of the form (ii). We show that they are equivalent to equations of the form where each ?k is a self-adjoint operator on an associated Hilbert space ??k. Now suppose~he-wave operators W±,(L1 L0) exist and are complete. Then we can find a J ∈ ??(H1 H0) such that W+(?l, ?0,J) exists. In the case where Lo and L1 have the same domain, ??1 and ??0 are equal as vector spaces, and under certain conditions (on Li, i = 0, 1) ??0 and ??1 have equivalent norms. Assuming these conditions, let J'∈ ??(??1' ??0) be the identity map. We show that (with an additional assumption on L0 and L1) W+(?1?0,J) exists andisequal to W+(?l,?0, J). 相似文献
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D. J. Cousins M. P. Enrico S. N. Fisher A. M. Guénault S. L. Phillipson G. R. Pickett P. Thibault R. P. Turner 《Czechoslovak Journal of Physics》1996,46(1):155
We have measured the3He concentration dependence of the thermal boundary resistanceR B between3He?4He dilute mixtures and submicron sintered silver between 10 and 150 mK. For concentrations greater than one percent, the results for the boundary resistance per inverse volume are insensitive to the concentration and have a magnitude similar to that predicted by the acoustic mismatch theory. For concentrations less than one percent, we observe an increase ofR B for decreasing concentrations. 相似文献
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