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排序方式: 共有132条查询结果,搜索用时 15 毫秒
21.
O. Werzer B. Stadlober A. Haase M. Oehzelt R. Resel 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):455-459
Pentacene thin films with thicknesses ranging from 10 nm to
180 nm are investigated by specular X-ray diffraction in the
reflectivity regime and in the wide angular regime. The results of
the reflectivity measurements show a clear shift of the 001
reflection of the thin film phase depending on the layer thickness.
It is shown that this shift can be explained by the dynamical
scattering theory. The wide angular regime measurements show the 00L
of the thin film phase. Williams-Hall plots are used to extract
information on the crystallite size and mean micro strain of the
thin film phase. The crystallite size is in good agreement with the
results obtained by the reflectivity measurements. From this it can
be concluded that the thin film phase crystallites are extended over
the entire film thickness down to the substrate. Additionally an
increase of the micro strain with increasing film thickness is
observed. 相似文献
22.
During the preparation of 1-tributylstannyl glucals from 1-phenylsulfinyl glycosides an unexpected side reaction was observed for 2,3,4,6-tetra-O-methoxyethoxy (MEM) protected 1-phenylsulfinyl glucoside. Treatment of the latter with lithium diisopropylamide (LDA) afforded the expected, fully MEM protected 1-phenylsulfinyl glucal accompanied by variable amounts of an unexpected 1-phenylsulfinyl 2-hydroxymethyl-3,4,6-tri-O-methoxyethoxyglucal. The amount of the side product rose with increasing concentration of the starting material. 相似文献
23.
For evaluating the microstructure evolution and mechanical property of Ni-based Hastelloy C-276 weld joint by the pulsed laser welding, the influence of pulsed laser welding on the microstructure and mechanical property of the weld joint is investigated by the analysis of the microstructure morphology, microhardness, phase structure and tensile property. The results indicate that, in the fusion zone three sections are divided on the basis of the patterns of grain structures. In the weld joint, the element segregation is found, but the trend of brittle phase׳s formation is weakened. The weld microhardness presents just a little higher than that of base metal, and there is no obvious the softened heat affected zone. Meanwhile in the weld joint, the phase structure is still the face-center cubic with the tiny shift of peak positions and widened Full Width at Half-Maximum. The yield strength of weld joint is the same as that of base metal, and the tensile strength is nearly 90% of that of base metal. The decreased tensile strength is mainly attributed to the dislocation piling-up. 相似文献
24.
After the appearance of W. Arendt's result that “Gaussian estimate of a semigroup implies the Lp-spectral independence of the generator,” various generalizations have been obtained. This paper shows that a certain kernel estimate of a semigroup implies the Lp-spectral independence of the generator, generalizing the case of upper Gaussian estimate and “Gaussian estimate of order α(0,1] [S. Miyajima, H. Shindoh, Gaussian estimates of order α and Lp-spectral independence of generators of C0-semigroups, Positivity 11 (1) (2007) 15–39], Definition 3.1.” The proof uses S. Karrmann's result about the Lp-spectral independence and B.A. Barnes' theorem about the spectrum of integral operators. As an application, the Lp-spectral independence of −[(−Δ)α+V] (α(0,1]) for a suitable V is proved with the help of a recent result by V. Liskevich, H. Vogt and J. Voigt [V. Liskevich, H. Vogt, J. Voigt, Gaussian bounds for propagators perturbed by potentials, J. Funct. Anal. 238 (2006) 245–277]. 相似文献
25.
Alexander Perjssy Du
an Loos Erkki Kolehmainen Pavol Hrn
iar 《Journal of organometallic chemistry》1999,590(2):1-264
The IR, 13C- and 17O-NMR spectral characteristics of the Cr(CO)3 group in a series of eight chromium, tricarbonyl[3-[(η6-aryl)methylene]-Z-1(3H)-isobenzofuranones] were correlated mutually as well as with theoretical data obtained by optimized MMX force-field and EHT calculations. The net charges on the carbon and oxygen atoms of the CO group and their differences were found as the most appropriate quantitative characteristics for the electronic properties of the Cr(CO)3 group. Using the results of the previously reported linear correlations, the electron-withdrawing effect of the PhCr(CO)3 moiety, weakened by the back-donation effect, was estimated as σ0.45 on the scale of Hammett substituent constants. 相似文献
26.
Hanene Zemmouri Sonda Ammar Amel Boumendjel Mahfoud Messarah Abdelfattah El Feki Mohamed Bouaziz 《Arabian Journal of Chemistry》2019,12(8):1954-1963
The aqueous and hydroalcoholic extracts of borage (Borago officinalis) leaves from Annaba region (Algeria) were preliminary analyzed for their phenolic profile (total phenolics, total flavonoids, total flavonols, total tannins and total anthocyanins). These extracts were evaluated for their antioxidant properties by different methods such as DPPH radical scavenging, test NBT and total antioxidant activity. The two extracts have exhibited a high antiradical capacity. Indeed, the ethanolic extract showed the lower IC50 values and the highest amount of phenolics (94.09 ± 1.72 mg gallic acid/g dry extract). Using LC-MS/MS analysis, it was possible to identify phenolic acids, flavonoids, sterol and for the first time oleuropein was identified in the aqueous extract of the plant. The obtained results have demonstrated that phenolic compounds are the major contributor to the antioxidant activity of plants. 相似文献
27.
A.V. Plyukhin 《Physics letters. A》2009,373(25):2122-2124
In a simple model of a continuous random walk a particle moves in one dimension with the velocity fluctuating between +v and −v. If v is associated with the thermal velocity of a Brownian particle and allowed to be position dependent, the model accounts readily for the particle's drift along the temperature gradient and recovers basic results of the conventional thermophoresis theory. 相似文献
28.
M.?Braun C.?Root F.?J.?Lederer T.?E.?Schrader W.?Zinth C.?von?Korff?Schmising M.?Bargheer T.?Elsaesser M.?Woerner 《Applied Physics A: Materials Science & Processing》2009,96(1):107-115
Intramolecular charge transfer in aminobenzonitrile (DIABN) single crystals is studied by a combination of ultrafast techniques.
The intramolecular dynamics is probed by time-resolved spectroscopy in the UV/Vis and mid-IR. The intermolecular structural
response is investigated by transient X-ray scattering and transmission experiments. A theoretical analysis shows that diffuse
scattering and dipole solvation determine the X-ray data. The observed dynamics results from charge transfer reaction leading
to strong local changes of molecular dipole moments and related structural rearrangements in the crystal. 相似文献
29.
Current dynamic processes in realistic magnetotail geometry simulations under various driven conditions and Hall effects. are studied by Hall magnetohydrodynamic (MHD) Associated with the external driving force, a thin current sheet with a broad extent is built up in the near-Earth magnetotail. The time evolution for the formation of the current sheet comprises two phases: slow growth and a fast impulsive phase before the near-Earth disruption of the current sheet resulting from the fast magnetic reconnection. The simulation results indicate that as the external driving force increases, the site and the tailward speed of the near-Earth current disruption region are closer to the Earth and faster, respectively. Whether the near-Earth disruption of the current sheet takes place or not is mainly controlled by Hall effects. It is found that there is no sudden disruption of the current sheet in the near-Earth region if the ion inertial length is below di= 0.04. 相似文献
30.