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91.
The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using
the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative
morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted
for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating
the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated
by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the
observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc
tris(thiourea) ions and sulphate ions. 相似文献
92.
Chromophore for UV-induced Immunosuppression: DNA 总被引:1,自引:0,他引:1
By Arie A. Vink Daniel B. Yarosh Margaret L. Kripke 《Photochemistry and photobiology》1996,63(4):383-386
93.
The luminescence of powder samples of the well-known green-emitting Zn2SiO4:Mn and the red-emitting Mg4Ta2O9:Mn phosphor shows a considerable fine structure at 4° K in appropriately prepared samples containing a sufficiently low Mn concentration. For (Zn1-xMnx)2SiO4 (0.0005?x?0.05) two sharp lines were found which are interpreted as due to zero phonon transitions between the 4T1 and 6A1 levels of Mn2+ ions on the two crystallographically different zinc sites. The remaining structure is ascribed to vibronic sidebands. The decay times of the luminescence bands associated with the two sites differ; they are 12 and 15 ms for the high and low energy bands respectively. The experimental results of Vlam are confirmed by our data. In addition some (Zn1-yBey)2SiO4:Mn (0.025? y ?1) samples were investigated. In Mg4Ta2O9:Mn two zero phonon lines could be identified, indicating that in this material Mn2+ is distributed over two inequivalent Mg sites. Most of the phonon replicas were found at intervals of 15 meV. Raman scattering experiments showed that this energy corresponds to one of the lattice vibrations. The decay time of this luminescence band is 1.0 ms. 相似文献
94.
Wouter Vink Alex Kuiper Benjamin Kemper Sandjai Bhulai 《European Journal of Operational Research》2015
We study appointment scheduling problems in continuous time. A finite number of clients are scheduled such that a function of the waiting time of clients, the idle time of the server, and the lateness of the schedule is minimized. The optimal schedule is notoriously hard to derive within reasonable computation times. Therefore, we develop the lag order approximation method, that sets the client’s optimal appointment time based on only a part of his predecessors. We show that a lag order of two, i.e., taking two predecessors into account, results in nearly optimal schedules within reasonable computation times. We illustrate our approximation method with an appointment scheduling problem in a CT-scan area. 相似文献