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排序方式: 共有520条查询结果,搜索用时 31 毫秒
211.
Ali Moradi Vahid Mojarradi Mehrnoush Sarcheshmehpour 《Research on Chemical Intermediates》2013,39(7):3235-3249
Some mathematical models have properly predicted the RO membrane performances. The equations of these models which were usually complex and time consuming were solved algebraically and numerically. The modified surface force-pore flow model is one of the best models which has predicted the RO membrane performances, for example separation factor (f), pure solvent flux (N P) and total flux (N T), better than the others. In this study, these performances were computed by use of an artificial neural networks technique by applying the parameters of this model and the physical properties of the membrane. A back-propagation feed-forward network with three layers including 9 neurons in the first layer and one neuron in the output layer was used. Minimum error was found with 20 neurons in the second layer, by trial and error. Some experimental data were used for simulating the network. The network was trained in two subsequent steps including feed-forward and error back-propagation. The datasets were randomly divided into three parts: 70 % of them were applied for training, 15 % were used for validating, and the remaining 15 % were applied for testing. The predicted values of the network were compared with experimental data existing for RO membrane performances (f, N P, and N T). A mean square error less than 0.0007 was achieved and a correlation coefficient with more than 0.99 was derived for the test datasets. 相似文献
212.
The recently improved finite order BFT Hamiltonian embedding method is applied to the two dimensional chiral bosons in non-commutative space. It is then systematically converted to a first class constraint model. Performing the momentum integrations, the corresponding fully gauge symmetry Lagrangian as well as its partition function in phase space are obtained. 相似文献
213.
Hamid Meghdadi Vahid Meghdadi Jean-Pierre Cances 《Wireless Personal Communications》2013,71(1):83-108
This paper addresses the problem of transmitting data to multiple mobile stations using a decode-and-forward strategy. Precoding vectors are used in relays to cancel out multiple access interference at the mobile stations. The diversity gain of the system has been analytically calculated for the case of two mobile stations. The system performance for arbitrary number of mobile stations is calculated using a semi analytic approach. In this approach the distribution of signal to noise ratio is approximated by a mixture of Nakagami laws using an Expectation-Maximization algorithm. Then the symbol error probability of this mixture is analytically calculated. Simulations confirm the theoretical results showing that the full diversity advantage can be obtained, which is the product of the number of antennas at each relay by the number of relays minus the total number of system constraints. 相似文献
214.
Glen P. Jackson Cris L. Lewis Stephen K. Doorn Vahid Majidi Fred L. King 《Spectrochimica Acta Part B: Atomic Spectroscopy》2001,56(12):816-2464
Time resolved atomic emission, atomic absorbance, and laser-induced atomic fluorescence measurements of a millisecond pulsed glow discharge, made perpendicular to the insertion probe, provide temporal profiles of 1s5 (3P2) and 1s3 (3P0) metastable argon atom populations. Acquisition of these profiles at different spatial positions in the plasma provides data from which two-dimensional spatial plots of relative populations are constructed. Each map, the result of 368 individual pulse profiles, provides insight into the production of metastable argon atoms as a function of time and position within the plasma. During power application, intensities plateau after 3 ms as the plasma reaches a steady state condition. Metastable argon atoms are most abundant 1–2 mm above the cathode surface during this time. Excitation mechanisms such as electron excitation and fast atom/ion impact appear to dominate in this temporal regime. In contrast, argon ion–electron recombination dominates metastable formation after pulse termination. The relative population maximum for metastable argon atoms in the afterpeak shifts to 5–9 mm above the cathode surface. This shift should impact signals for analyte species generated by Penning processes in the plasma. Absorption and fluorescence measurements of the 3P2 (11.55 eV) and the 3P0 (11.72 eV) metastable argon atom states indicate possible differences in the populations of these two states between the plateau and afterpeak time regimes. 相似文献
215.
216.
Vahid F. Motlaq Leva Momtazi Kaizheng Zhu Kenneth D. Knudsen Bo Nystrm 《Journal of Polymer Science.Polymer Physics》2019,57(9):524-534
The self‐assembly process in aqueous solutions of the methoxyl‐poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic sodium)‐block‐poly(N‐isopropyl acrylamide) (PNIPAAM) triblock copolymer, synthesized via two different atomic transfer radical polymerization methods, namely “one‐pot” (P3‐sample) and “two‐pot” (P2‐sample), was studied by various experimental techniques. The “one‐pot” procedure leads to a copolymer (P3) where the PNIPAAM block is contaminated with a minor quantity of 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (AMPS) residuals and this sample does not form micelles over the considered temperature region, but unimers and temperature‐induced aggregates coexist in the presence of a small amount of salt. The P2 polymer forms micelles and intermicellar structures, but the former moieties disappear at high temperatures, whereas the latter species contract with increasing temperature. Small‐angle neutron scattering results revealed correlation peaks, both for P3 and P2, and no micelle formation for P3, but a pronounced upturn of the scattered intensity at low wavevector values at elevated temperatures for the P2 copolymer. The findings from this study clearly show that the spurious AMPS residuals have a drastic influence on the self‐assembly and micelle formation of the triblock copolymer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 524–534 相似文献
217.
218.
Farhad Shirini Meysam Alipour Khoshdel Masoumeh Abedini Seyyed Vahid Atghia 《中国化学快报》2011,22(10):1211-1214
Nanocrystalline TiO2 was used as an efficient and recyclable catalyst for the chemoselective trimethylsilylation of primary and less hindered secondary alcohols and phenols with hexamethyldisilazane(HMDS).All reactions were performed under mild and completely heterogeneous conditions in good to excellent yields. 相似文献
219.
Hossein Roghani-Mamaqani Vahid Haddadi-Asl Mohammad Najafi Mehdi Salami-Kalajahi 《Polymer Science Series B》2012,54(3-4):153-160
Polystyrene nanocomposites, being a combination of nanoclay-attached and free polystyrene chains were prepared using in situ atom transfer radical polymerization. Subsequently, they were electrospun to form fibers with diameter varying from 450?C700 nm according to scanning electron microscopy data; in addition, the transmission electron microscopy and x-ray diffraction analysis revealed that nanoclay layers were oriented along the nanofiber axis during the electrospinning process. Molecular weight of the extracted free polymer chains from the nanocomposites is higher than the attached chains. However, Anchored chains are characterized by higher polydispersity index in comparison with the free ones. Polydispersity index of polymer chains increases by the addition of nanoclay. Thermogravimetric analysis results shows that increasing clay content leads to a decrease in the quantity of polymer chains attached to the clay surface. 相似文献
220.
In this paper, secure channel coding schemes based on turbo codes are suggested for time reversal ultra wideband (TR-UWB)
systems. Turbo code has the capability of error correction near Shannon’s limit. Adding security to turbo code is an attractive
idea since it could reduce the overall processing cost of providing secure coded data and enjoys the advantages of high-speed
encryption and decryption with high security, smaller encoder and decoder size and greater efficiency. The proposed turbo
code schemes are labeled as follows: secure puncturing rate, secure frame length, and secure interleaving. Using these scenarios,
secure turbo code is defined in a way that the redundant information used for error correction is not pre-determined by the
nature of the error correction part of the algorithm but it can be chosen arbitrarily out of the whole set of possible strings.
The lower bound of bit error probability for secure turbo code schemes in AWGN and TR-UWB systems are evaluated. Analytical
and simulation results show secure turbo code performance is very satisfying. Various crypto-analytical attacks are investigated
against these schemes. Based on this analysis, secure turbo code structures changed during the encryption procedure to increase
the complexity of linear and differential cryptanalysis. It is seen that the performance of conventional turbo code and random
frame length with Poisson distribution are the same. Comparing these schemes shows, secure interleaving approach has the best
performance and secure puncturing rate the worst, but the latter provides the most security. The enhanced security of UWB,
due to rich multipath nature of UWB channel, could be exploited. Due to space-time focusing property of time reversal UWB,
there is an environmental confidentiality (or spatial security), which is additional security for secure turbo code in this
system. Using secure turbo code, it is possible to increase the transmission range of UWB systems. 相似文献