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61.
The influence of the location of the outflow computational boundary on the unsteady incompressible flow past a circular cylinder at Reynolds number 100 is examined. The vorticity-streamfunction formulation of the Navier-Stokes equations is used in all computations. Two types of outflow boundary conditions are subjected to a series of tests in which the domain length is gradually reduced. The traction-free condition performs well in most cases and allows the outflow boundary to be located as close as 6.5 cylinder diameters from the body. The other boundary condition type is not as forgiving, but has the advantage of being simpler to implement and can still provide reasonably accurate solutions. It is also observed that both condition types can influence the flow field strongly and globally when the boundary is brought closer than 2.5 diameters from the body. In such cases the temporal periodicity of the solution is lost. 相似文献
62.
Yow-Jon Lin Chia-Lung Tsai Chia-Jyi Liu Lance Horng Yu-Tai Shih Mu-Shan Wang Chuan-Sheng Jhang Chao-Shien Huang 《Journal of Sol-Gel Science and Technology》2009,52(1):109-112
Co0.2Mg
x
Zn0.8−x
O films prepared with different molar ratio of magnesium acetate to zinc acetate were deposited on substrates by the sol–gel
technique. X-ray diffraction, photoluminescence (PL) and ferromagnetism measurements were used to characterize the Co0.2Mg
x
Zn0.8−x
O diluted magnetic semiconductors. The acceptor-like defects were determined in the PL band and the intensity of the acceptor-related
PL increased with increasing Mg concentration. Therefore, an increase in the number of the acceptor-like defects (zinc vacancies
especially) in the Co0.2Mg
x
Zn0.8−x
O film may lead to the enhancement of the magnetic properties. It is worth noting that changes in Mg concentration and the
number of the acceptor-like defects are important issues for producing strong ferromagnetism Co0.2Mg
x
Zn0.8−x
O films prepared by the sol–gel method. 相似文献
63.
Yang-Je Cheng Cai-Wei Li Cing-Ling Kuo Tzenge-Lien Shih Jih-Jung Chen 《Molecules (Basel, Switzerland)》2022,27(8)
In this paper, the syntheses of twelve asymmetric curcumin analogs using Pabon’s method are reported. Generally, the previously reported yields of asymmetric curcuminoids, such as 9a (53%), 9c (38%), and 9k (38%), have been moderate or low. Herein, we propose that the low yields were due to the presence of water and n-BuNH2 in the reaction media. To prove this formulated hypothesis, we have demonstrated that the yields can be improved by adding molecular sieves (MS) (4 Å) to the reaction mixture, thus reducing the interference of water. Therefore, improved yields (41–76%) were obtained, except for 9b (36.7%), 9g (34%), and 9l (39.5%). Furthermore, compounds 9b, 9d, 9e, 9f, 9g, 9h, 9i, 9j, and 9l are reported herein for the first time. The structures of these synthetic compounds were determined by spectroscopic and mass spectrometry analyses. The free radical scavenging ability of these synthetic asymmetric curcuminoids was evaluated and compared to that of the positive control butylated hydroxytoluene (BHT). Among the synthesized asymmetric curcuminoids, compounds 9a (IC50 = 37.57 ± 0.89 μM) and 9e (IC50 = 37.17 ± 1.76 μM) possessed effective 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging abilities, and compounds 9h (IC50 = 11.36 ± 0.65 μM) and 9i (IC50 = 10.91 ± 0.77 μM) displayed potent 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical scavenging abilities comparable to that of curcumin (IC50 = 10.14 ± 1.04 μM). Furthermore, all the synthetic asymmetric curcuminoids were more active than BHT. 相似文献
64.
Local binary pattern (LBP) operators, which measure the local contrast within a pixel's neighborhood, have been successfully applied to texture analysis, visual inspection, and image retrieval. In the paper, we present a novel semi-fragile spatial watermarking method based on LBP operators by using the local pixel contrast for the embedding and extraction of watermarks. We also propose a general framework for multi-level image watermarking. Experimental results show that the proposed watermarking methods are robust against commonly-used image processing operations, such as additive noise, luminance change, contrast adjustment, color balance, and JPEG compression. At the same time, they achieve good invisibility, fragility, and image tamper detection and localization with less computational cost. 相似文献
65.
Chen Kai-Huang Cheng Chien-Min Shih Chia-Chi Tsai Jen-Hwan 《Applied Physics A: Materials Science & Processing》2011,103(4):1173-1177
In this study, the ferroelectricity of as-deposited Bi3.9La0.1Ti2.9V0.1O12 (BLTV), Bi3.9Ti2.9V0.1O12 (BTV), and Bi4Ti3O12 (BIT) thin films was prepared and compared by rf magnetron sputtering technology. For the BLTV, BTV, and BIT thin films deposited
on Pt/Ti/SiO2/Si and SiO2/Si substrate, the physical and electrical characteristics of lanthanum doped BTV (BLTV) were better than those of BIT and
BTV thin films. Regarding the physical properties, the micro-structure of as-deposited BTV and BLTV thin films were obtained
and compared by XRD patterns and SEM images. The BLTV and BTV thin films were also exhibited clear the ferroelectricity. The
remanent polarization (P
r
) of as-deposited BLTV thin films was 11 μC/cm2 as the measured frequency of 100 kHz. It was higher than those of BTV thin films. Finally, the polarization of BLTV thin
film capacitor decreased by 9%, while that of the BTV decreased by 15% after the fatigue test with 109 switching cycles. 相似文献
66.
Chia-Chi Shih Yu-Jen Chen Sean Wu Cheng-Che Tsai I-Min Jiang 《Optics Communications》2009,282(19):3977-3981
This study presents an integrated device that consists of a directional coupler and an electro-optic switch. The device is designed to include a nematic liquid crystal cell, comprising a grating-like electrode. Applying the appropriate voltage to the cell yields a periodically distributed refractive index. An incident polarized beam will couple to an adjacent channel if it is parallel to the channel. The coupling efficiency is controlled by applied voltage. An obliquely injected polarized beam will be reflected and refracted in the channel, and propagated along a curved path. The route of the beam can be controlled by applying the voltage. A multiport routing was achieved for voltage modulation. In addition, the distribution of refractive index is also investigated by employing conoscopic technique experimentally and numerically. 相似文献
67.
The disclination model of high angle grain boundaries proposed before is used to understand the energy-angle relations between cusp misorientations. It is found that the model predicts the correct relationship within experimental error with only one adjustable parameter which resembles the Burgers vector of dislocations at low angles. Experimental data for [100] symmetric tilt boundaries in Cu and Al and for [110] symmetric tilt boundaries in Al are used for illustration. 相似文献
68.
Electron Loss Spectroscopy (ELS), X-ray Photoemission (XPS), Secondary Emission Energy Distribution, and Secondary Electron yield data have been obtained on both evaporated films and sprayed-on coatings of BaO. Using the ELS correlated with the XPS data, bulk and surface plasmon losses as well as excitonic and interband transition electron loss mechanisms have been identified. It was found that at low primary beam energies (<100 eV), structure in the secondary emission energy distribution could be correlated with a conduction band energy structure. This structure was consistent with the model used to explain the loss transitions. The structure in the energy distribution curves shows little, if any, correlation with plasmon decay mechanisms and other two-step electron emission processes. On the contrary, for the case of BaO (at least at low primary energies), the energy distribution data and structure in the secondary yield vs. primary beam energy data indicate that most secondaries are produced by direct excitation of secondaries by the primary electrons. 相似文献
69.
In a semiconductor quantum dot, the IIx and IIy transitions to the polarization eigenstates, |x> and |y>, naturally form a three-level V-type system. Using low-temperature polarized photoluminescence spectroscopy, we have investigated the exciton dynamics arising under strong laser excitation. We also explicitly solved the density matrix equations for comparison with the experimental data. The polarization of the exciting field controls the coupling between the otherwise orthogonal states. In particular, when the system is initialized into \Y>, a polarization-tailored pulse can swap the population into |x>, and vice versa, effectively operating on the exciton spin. 相似文献
70.
Building Pb nanomesas with atomic-layer precision 总被引:1,自引:0,他引:1
Jiang CS Li SC Yu HB Eom D Wang XD Ebert P Jia JF Xue QK Shih CK 《Physical review letters》2004,92(10):106104
We demonstrate a novel scheme for manipulating metallic nanostructures involving a macroscopic number of atoms, yet with precise control in their local structures. The scheme entails a two-step process: (a) a triggering step using a scanning tunneling microscope, followed by (b) self-driven and self-limiting mass-transfer process. By using this scheme, we construct Pb nanomesas on Si(111) substrates whose thickness can be controlled with atomic-layer precision. The kinetic barrier for the mass transfer and the underlying mechanism behind this novel manipulation are determined. 相似文献