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排序方式: 共有348条查询结果,搜索用时 15 毫秒
241.
Dominicus Danardono Dwi Prija Tjahjana Zainal Arifin Suyitno Suyitno Wibawa Endra Juwana Aditya Rio Prabowo Catur Harsito 《力学快报》2021,11(3):100249
This study investigates the effect of Reynolds number on the performance of Savonius wind turbine with slotted blades. The turbine performance investigation was based on the torque coefficient( Ct), power coefficient( Cp), and tip speed ratio( TSR). The experiment used two number of blade configuration, blade overlap ratio of 10%, 12.5% and 20%, slotted position of 15%, 20%, 25% and 35%, and also slotted gap width of 3 mm, 5 mm, 7 mm, and 9 mm. The wind speed carried out in this experiment are 5.94 m/s, 6.46 m/s, 6.99 m/s, and 7.27 m/s, which are generated from the fan blowers as a wind source. The Savonius turbine with 10% overlap ratio shows the best performance. The highest Cp obtained is 0.138 by the variation of a 3 mm gap with Re of 1.44 × 10~4 and 0.526 TSR. 相似文献
242.
Gillespie D Khair AS Bardhan JP Pennathur S 《Journal of colloid and interface science》2011,359(2):520-529
The electrokinetic behavior of nanofluidic devices is dominated by the electrical double layers at the device walls. Therefore, accurate, predictive models of double layers are essential for device design and optimization. In this paper, we demonstrate that density functional theory (DFT) of electrolytes is an accurate and computationally efficient method for computing finite ion size effects and the resulting ion-ion correlations that are neglected in classical double layer theories such as Poisson-Boltzmann. Because DFT is derived from liquid-theory thermodynamic principles, it is ideal for nanofluidic systems with small spatial dimensions, high surface charge densities, high ion concentrations, and/or large ions. Ion-ion correlations are expected to be important in these regimes, leading to nonlinear phenomena such as charge inversion, wherein more counterions adsorb at the wall than is necessary to neutralize its surface charge, leading to a second layer of co-ions. We show that DFT, unlike other theories that do not include ion-ion correlations, can predict charge inversion and other nonlinear phenomena that lead to qualitatively different current densities and ion velocities for both pressure-driven and electro-osmotic flows. We therefore propose that DFT can be a valuable modeling and design tool for nanofluidic devices as they become smaller and more highly charged. 相似文献
243.
Gottumukkala AL Teichert JF Heijnen D Eisink N van Dijk S Ferrer C van den Hoogenband A Minnaard AJ 《The Journal of organic chemistry》2011,76(9):3498-3501
Pd(OAc)(2)/3 is an efficient catalyst system for the base-free oxidative Heck reaction that outperforms the currently available catalysts for the more challenging substrates studied. The catalyst system is highly selective, and works at room temperature with dioxygen as the oxidant. 相似文献
244.
Khair AS 《Journal of colloid and interface science》2012,381(1):183-188
We quantify the phoretic migration of a spherical cation-permselective colloidal particle immersed in a binary electrolyte under a time-dependent electric field. We invoke the thin-Debye-layer approximation, where the size of ionic Debye layer enveloping the particle is much smaller than the particle radius. The imposed electric field generates ion concentration gradients, or concentration polarization, in the bulk (electroneutral) electrolyte outside the Debye layer. The bulk ion concentration polarization--and consequently the particle's phoretic velocity--evolves on the time scale for ion diffusion around the particle, which can be on the order of milliseconds for typical colloidal dimensions. Notably, concentration polarization arises here solely due to the permselectivity of the particle; it does not require non-uniform ionic transport in the Debye layer (i.e., surface conduction). Thus, the phoretic transport of a permselective particle is significantly different to that of a inert, dielectric particle, since surface conduction is necessary to achieve bulk concentration polarization in the (more commonly studied) latter case. Calculations are presented for a permselective particle under oscillatory (ac) and suddenly applied electric fields. In the former case, the particle velocity possesses frequency-dependent components in phase and out of phase with the driving field; in the latter case, the particle approaches its terminal velocity with a long-time (algebraic) tail. 相似文献
245.
Lewis acid catalyzed quaternary ammonium salt mediated highly regioselective ring-opening of chiral activated aziridines and azetidines with alcohols to nonracemic β- and γ-amino ethers has been developed. The reaction mainly proceeds via an S(N)2 pathway, and the partial racemization of the starting substrate was effectively controlled by using quaternary ammonium salts. β- and γ-amino ethers are obtained with high enantio- and diastereospecificity (ee up to >99%, de up to 99%). The methodology was further extended to synthesize morpholines and their homologues with high enantiospecificity (ee up to 90%) when halo alcohols were employed as the nucleophiles. 相似文献
246.
Rhodium-catalyzed asymmetric arylation of N-(tert-butanesulfinyl)imines with sodium tetraarylborates
A diastereoselective rhodium-catalyzed arylation of N-(tert-butanesulfinyl)imines with sodium tetraarylborates is described. This method is general for constructing various chiral α-branched amines and 2-substituted pyrrolidines with high diastereoselectivity. A practical asymmetric approach to access chiral amines has been developed involving the use of air-stable Rh catalysts and reagents and in the absence of an external ligand. 相似文献
247.
Jayashree A. Dharmadhikari Rucha A. Deshpande Arpita Nath Krithika Dota Deepak Mathur Aditya K. Dharmadhikari 《Applied physics. B, Lasers and optics》2014,117(1):471-479
We experimentally investigate the spectral extent and spectral profile of the supercontinuum (SC) generated in transparent solids: barium fluoride, calcium fluoride, and fused silica upon irradiation by intense femtosecond-long pulses of 800, 1,380, and 2,200 nm light. These wavelengths correspond to the normal and anomalous group velocity dispersion (GVD) regimes in fused silica calcium fluoride and barium fluoride. We observe an isolated (anti-Stokes) wing on the blue side most prominently in fused silica but also in CaF2. The SC conversion efficiency is measured for the long wavelengths used in our experiments. We also present results on filamentation in BaF2 in the anomalous GVD regime, including visualization of focusing–refocusing events within the crystal; the size of a single filament is also determined. The 15-photon absorption cross section in BaF2 is deduced to be 6.5 × 10?190 cm30 W?15 s?1. 相似文献
248.
Here we proposed a novel architecture of wavelength division multiplexed-passive optical network (WDM-PON) in which the downlink unicast data, broadcast data and uplink unicast data transmission is possible with the symmetric data rate of 10 Gbps. At remote node (RN) cyclic wavelength routing property of array waveguide grating (AWG) and power splitting capacity of power splitter is used in the architecture so that broadcast channel can be overlaid on downlink unicast channels. At ONU carriers sent from central office (CO) is reused for upstream data transmission with the help of integration of a reflective semiconductor amplifier (RSOA) and an electro-absorption modulator (EAM) so there is no need of extra laser sources at ONUs which makes them colorless. EAM can be operated at very high speed; a modulation bandwidth of tens of GHz can be achieved. Broadcast channel causes a limited interference with downlink and uplink unicast channels so it does not affect the system performance. Since each channel has different wavelength so NRZ data is used which eliminates expensive DPSK receivers and detection becomes very easy. Simulation is performed with all channels having data rate of 10 Gbps having acceptable performance. 相似文献
249.
Ryter F Leuterer F Pereverzev G Fahrbach HU Stober J Suttrop W;ASDEX Upgrade Team 《Physical review letters》2001,86(11):2325-2328
Energy transport by the electrons in a tokamak is examined in steady-state and power modulation experiments using electron cyclotron heating. The results are consistent with the assumption that temperature profiles are limited by a critical gradient length, leading to "stiff" profiles. The modulation experiments show that the stiffness factor increases with temperature. They strongly suggest that turbulence driven by the electron temperature gradient may be a dominant mechanism of electron transport. Although possibly not universal, these results are valid under various plasma conditions. 相似文献
250.
Greenfield CM Burrell KH DeBoo JC Doyle EJ Stallard BW Synakowski EJ Fenzi C Gohil P Groebner RJ Lao LL Makowski MA McKee GR Moyer RA Rettig CL Rhodes TL Pinsker RI Staebler GM West WP;DIII-D Team 《Physical review letters》2001,86(20):4544-4547
A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate. 相似文献