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991.
Monique Biesemans Hassan Dalil Loc Thanh Nguyen Bart Haelterman Ghislain Decadt Francis Verpoort Rudolph Willem Paul Geerlings 《Tetrahedron》2002,58(52):10447-10453
The regio- and stereoisomeric composition of the product mixture in the Diels–Alder reaction between dicyclopentadiene and bicyclononadiene is determined by 2D 1H–13C HMQC and HMBC and 1H 2D DQF COSY and NOESY NMR techniques. The absence in the experimental mixture of one of the expected products is explained by high-level quantum chemical density functional theory calculations. 相似文献
992.
Zirconium oxide (ZrO2) thin films deposited at room temperature by the filtered cathodic vacuum arc (FCVA) technique are detailed in terms of the film structure, composition, morphology, and optical and mechanical properties, which are tailored by the oxygen (O2) flow rate during deposition. The relationships between the film structure, composition, morphology, and properties are emphasized. With an increasing O2 flow rate, the film evolves in structure from amorphous, through a pure monoclinic phase with varying preferential orientation, to amorphous again, accompanied by an increase in the O/Zr atomic ratio and a conversion of Zr ions from low oxidation states into Zr4+. Such a structural trend arises from the change in composition, and influences the film morphology and mechanical properties so that the amorphous films exhibit small clusters on the surface and smoother morphology as well as lower hardness compared with the polycrystalline films. The film composition rather than the density dominates the optical properties, where the transmittance and the optical band gap increase with increasing O/Zr values, while the refractive index and extinction coefficients behave conversely with the lowest refractive index (2.16 at 550 nm) approaching the bulk value (2.2) . PACS 68.55.Jk; 78.66.Nk; 68.37.Ps 相似文献
993.
Ch. W. Francis M. E. Timpson S. Y. Lee M. P. Elless J. H. Wilson 《Journal of Radioanalytical and Nuclear Chemistry》1998,228(1-2):15-21
The objective of this research was to design an extraction media and procedure that would selectively remove uranium without adversely affecting the soils' physicochemical characteristics or generating secondary waste forms difficult to manage or dispose of. Investigations centered around determining the best lixiviant and how the various factors such as pH, time, and temperature influenced extraction efficiency. Other factors investigated included the influence of attrition scrubbing, the effect of oxidants and reductants, and the recycling of lixiviants. Experimental data obtained at the bench-and pilot-scale levels indicated 80% to 95% of the uranium could be removed from the uranium-contaminated soils by using a carbonate lixiviant. The best treatment was three successive extractions with 0.25M carbonate-bicarbonate (in presence of KMnO4 as an oxidant) at 40°C followed with two water rinses. 相似文献
994.
Y.H. Cheng B.K. Tay S.P. Lau X.L. Qiao J.G. Chen Z.H. Sun C.S. Xie 《Applied Physics A: Materials Science & Processing》2002,75(3):375-380
Super-hard and elastic carbon nitride films have been synthesized by using an off-plane double-bend filtered cathodic vacuum
arc combined with a radio-frequency nitrogen-ion beam source. A nanoindenter was used to determine the micromechanical properties
of the deposited films. X-ray photoelectron spectroscopy was used to study the composition and bonding structure of the deposited
films. The influence of nitrogen ion energy on the structure and micromechanical properties of the deposited films was systematically
studied. As the nitrogen ion energy is increased, the microhardness, Young’s modulus and elastic recovery also increase, reaching
a maximum of 47 GPa, 400 GPa, and 87.5%, respectively, at a nitrogen ion energy of 100 eV. Further increase in nitrogen ion
energy results in a decrease in microhardness, Young’s modulus and elastic recovery of the deposited films. The formation
of five-membered rings, as indicated by XPS, which causes bending of the basal planes and forms a three-dimensional rigid
covalent bond network, contributes to the super-hardness, Young’ s modulus and high elastic recovery of the films deposited
at a nitrogen ion energy of 100 eV.
Revised version: 29 October 2001 / Accepted: 7 November 2001 / Published online: 2 May 2002 相似文献
995.
Eric F. Bernstein Francis P. Gasparro Douglas B. Brown Tsunemichi Takeuchi Sung K. Kong Jouni Uitto 《Photochemistry and photobiology》1996,64(2):369-374
Treatment of skin diseases with the combination of 8-methoxypsoralen and ultraviolet A radiation (PUVA) results in clinical alterations in treated skin that resemble those observed in chronically photodamaged skin. The PUVA-treated patients develop nonmelanoma skin cancers, pigmentary alterations and wrinkling characteristic of sun-induced changes. The major alteration in the dermis of sun-damaged skin is the deposition of abnormal elastic fibers, termed solar elastosis. Up-regulation of elastin promoter activity in dermal fibroblasts explains the excess elastic tissue but not the reason for the aberrant morphology of the elastotic material. In order to study photoaging in an experimental system, we utilized a transgenic mouse line that expresses the human elastin promoter/chloramphenicol acetyltransferase construct in a tissue-specific and developmentally regulated manner. Although UVB radiation has been demonstrated to increase promoter activity in vitro, UVA fails to demonstrate a similar effect at the doses utilized. In this study, we demonstrate the ability of PUVA treatment to up-re-gulate elastin promoter activity both in vitro and in vivo. These data help to explain the development of photoaging in sun-protected PUVA-treated skin. We attribute the up-regulation of elastin promoter activity in response to PUVA to the formation of DNA photoadducts, which do not occur in response to UVA radiation alone. 相似文献
996.
997.
Francis Micheli Gilles Losfeld Myriam Protto Didier Soulevant 《Particle & Particle Systems Characterization》2002,19(6):401-409
This study deals with re‐entry vehicles passing through high‐altitude clouds of ice particles. The particles disturb the flow field and are erosive, thereby increasing the turbulent heat flux considerably. Measurements were performed in a blow‐down wind tunnel to analyze the effects of a particle field on the flow. The wind tunnel flow was seeded by two aerosols. The first was used for LDV flow velocity measurements. Its size was checked by the analysis of its passage through a plane shock wave. The second aerosol was made of uniform micro‐spheres of 200 μm diameter, used to simulated the water droplets. The velocity, feeding and scattering of the latter aerosol need to be accurately measured. The velocities of the flow field and of the micro‐spheres were measured simultaneously by laser velocimetry. This paper describes the instruments used to seed, ascertain and measure this flow with two aerosols. 相似文献
998.
Francis A. Carey William C. Hutton James C. Schmidt 《Magnetic resonance in chemistry : MRC》1980,14(2):141-144
The 13C NMR spectra were determined and signals assigned to the various carbons of the alkamines veracevine, germine and zygacine derived from steroidal alkaloids of the ceveratrum class. Assignment of signals was aided by analysis of the partially relaxed spectrum of cervagenine 9,12,14-orthoacetate-3, 16-diacetate. 相似文献
999.
Varieties of idempotent semirings with commutative addition 总被引:3,自引:0,他引:3
The multiplicative reduct of an idempotent semiring with commutative addition is a regular band. Accordingly there are 13
distinct varieties consisting of idempotent semirings with commutative addition corresponding to the 13 subvarieties of the
variety of regular bands. The lattice generated by the these 13 semiring varieties is described and models for the semirings
free in these varieties are given.
Received April 22, 2004; accepted in final form June 3, 2005. 相似文献
1000.
Reaction of AlCl3 with {Me2SiO}n (Dow‐Corning high‐vacuum grease) at an Al : Si ratio of 1 : 1 in hexane at room temperature yielded a large crop of colorless crystals of [{ClSiMe2OAlCl2}2], which were characterized by single‐crystal X‐ray diffraction and NMR. These crystals hydrolyzed on an aluminum surface to give a coating of silicone oil interspersed with particles of [Al(OH2)6]Cl3, as determined by powder X‐ray diffraction and X‐ray photoelectron spectrometry. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献