An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distribution...An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.展开更多
Particle inertia effect plays a significant role in sediment dispersion which has not been fully elucidated.In this paper,the profound effect of particle inertia on the sediment dispersion was analyzed.The theoretical...Particle inertia effect plays a significant role in sediment dispersion which has not been fully elucidated.In this paper,the profound effect of particle inertia on the sediment dispersion was analyzed.The theoretical expression for the drift velocity based on the two-phase mixture theory in turbulent open channels is firstly introduced.The influence of particle inertia on sediment dispersion was investigated through three different aspects including vertical dispersion,motion,and flux properties based on the drift velocity.Results show that the dispersion of suspended sediment in turbulent open-channel flows is affected by three major processes including turbulence of water sediment mixtures,particle random motion,and collisions among particles,of which the contributions of particle turbulence and collisions to the sediment dispersion are remarkable for particles of high inertia.With respect to the vertical mean velocity and sediment flux,it shows that the predictive results agree well with the measurements when the term of particle inertia is considered.As a result,particle inertia considerably affects the behavior of suspended sediment.In particular,the influence of inertia must be accounted for in circumstances of flows laden with high-inertia particles.展开更多
We investigate the dispersion properties ofnanometer-scaled silicon nitride suspended membrane wave- guides around the communication wavelength and systematically study their relationship with the key structural param...We investigate the dispersion properties ofnanometer-scaled silicon nitride suspended membrane wave- guides around the communication wavelength and systematically study their relationship with the key structural parameters of the waveguide. The simulation results show that a suspended membrane waveguide can realize anomalous dispersion with a relatively thinner silicon nitride thickness in the range of 400 to 600 nm, whereas, for the same membrane thickness, a conventional rib or strip silicon nitride waveguide cannot support anomalous dispersion. In particular, a waveguide with 400 nm silicon nitride thickness and deep etch depth （r = 0.05） exhibits anomalous dispersion around the communication wavelength when the waveguide width ranges from 990 to 1255 nm, and the maximum dispersion is 22.56 ps/（nm.km）. This specially designed anomalous dispersion silicon nitride waveguide is highly desirable for micro-resonator based optical frequency combs due to its potential to meet the phase-matching condition required for cascaded four-wave-mixing.展开更多
Liquid-phase exfoliation （LPE） is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too sm...Liquid-phase exfoliation （LPE） is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS2 nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersion in the absence of silk fibroin powder, sonicated MoS2 dispersions with silk fibroin powder （MoSJSilk dispersion） show noticeably higher exfoliated MoS2 nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg.mL-1, respectively. The MoS2 concentration in the MoS2/Silk dispersion after centrifugation above 10,000 rpm is more than four times that without the silk fibroin. The size of the dispersed silk fibroin is controlled by the change of centrifugation rate, showing the removal of silk fibroin above tens of micrometers in size after centrifugation at 2,000 rpm. Size-controlled silk fibroin biomolecules combined with MoS2 nanosheets are expected to increase the practical use of such materials in fields related to tissue engineering, biosensors and electrochemical electrodes. Atomic force microscopy and Raman spectroscopy provide the height of the MoS2 nanosheets spin-cast from MoS2/Silk dispersions, showing thicknesses of 3--6 nm. X-ray photoelectron spectroscopy and X-ray diffraction indicate that the outermost surface layer of the hydrophobic MoS2 crystals interact with oxygen-containing functional groups that exist in the hydrophobic part of silk fibroins. The amphiphilic properties of silk fibroin combined with the MoS2 nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS2 nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS2 nanosheets contents.展开更多
A novel compact electromagnetic bandgap （EBG） structure constructed by etching two reverse split rings （RSRs） and inserting interleaving edge （IE） on the patch of conventional mushroom-like EBG （CML-EBG） is in...A novel compact electromagnetic bandgap （EBG） structure constructed by etching two reverse split rings （RSRs） and inserting interleaving edge （IE） on the patch of conventional mushroom-like EBG （CML-EBG） is investigated. Simulated dispersion diagrams show that the proposed EBG structure presents a 13.6% size reduction in the center frequency of the bandgap. Two comparisons have been carried out for the analysis of the effect of the RSRs and IE configuration. Then, a sample of this novel EBG is fabricated and tested, further experimental data agree well with the simulated results. Thus, this EBG structure makes a good candidate to decrease mutual coupling in compact microstrip patch array.展开更多
基金Project support by the National Natural Science Foundation of China (Grant No: 50479034), the Natural Science Foundation of Tianjin (Grant No: 05YFSZSF02100).
文摘An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.
基金supported by the Natural National Science Foundation of China(Grant Nos.51379102,51039004)the National Key Technologies Research and Development Program of China during the 12th Five-Year Plan Period(Grant No.2012BAB05B01)
文摘Particle inertia effect plays a significant role in sediment dispersion which has not been fully elucidated.In this paper,the profound effect of particle inertia on the sediment dispersion was analyzed.The theoretical expression for the drift velocity based on the two-phase mixture theory in turbulent open channels is firstly introduced.The influence of particle inertia on sediment dispersion was investigated through three different aspects including vertical dispersion,motion,and flux properties based on the drift velocity.Results show that the dispersion of suspended sediment in turbulent open-channel flows is affected by three major processes including turbulence of water sediment mixtures,particle random motion,and collisions among particles,of which the contributions of particle turbulence and collisions to the sediment dispersion are remarkable for particles of high inertia.With respect to the vertical mean velocity and sediment flux,it shows that the predictive results agree well with the measurements when the term of particle inertia is considered.As a result,particle inertia considerably affects the behavior of suspended sediment.In particular,the influence of inertia must be accounted for in circumstances of flows laden with high-inertia particles.
基金Project supported by the National Natural Science Foundation of China(Nos.61435002,61527823 61321063)
文摘We investigate the dispersion properties ofnanometer-scaled silicon nitride suspended membrane wave- guides around the communication wavelength and systematically study their relationship with the key structural parameters of the waveguide. The simulation results show that a suspended membrane waveguide can realize anomalous dispersion with a relatively thinner silicon nitride thickness in the range of 400 to 600 nm, whereas, for the same membrane thickness, a conventional rib or strip silicon nitride waveguide cannot support anomalous dispersion. In particular, a waveguide with 400 nm silicon nitride thickness and deep etch depth （r = 0.05） exhibits anomalous dispersion around the communication wavelength when the waveguide width ranges from 990 to 1255 nm, and the maximum dispersion is 22.56 ps/（nm.km）. This specially designed anomalous dispersion silicon nitride waveguide is highly desirable for micro-resonator based optical frequency combs due to its potential to meet the phase-matching condition required for cascaded four-wave-mixing.
文摘Liquid-phase exfoliation （LPE） is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS2 nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersion in the absence of silk fibroin powder, sonicated MoS2 dispersions with silk fibroin powder （MoSJSilk dispersion） show noticeably higher exfoliated MoS2 nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg.mL-1, respectively. The MoS2 concentration in the MoS2/Silk dispersion after centrifugation above 10,000 rpm is more than four times that without the silk fibroin. The size of the dispersed silk fibroin is controlled by the change of centrifugation rate, showing the removal of silk fibroin above tens of micrometers in size after centrifugation at 2,000 rpm. Size-controlled silk fibroin biomolecules combined with MoS2 nanosheets are expected to increase the practical use of such materials in fields related to tissue engineering, biosensors and electrochemical electrodes. Atomic force microscopy and Raman spectroscopy provide the height of the MoS2 nanosheets spin-cast from MoS2/Silk dispersions, showing thicknesses of 3--6 nm. X-ray photoelectron spectroscopy and X-ray diffraction indicate that the outermost surface layer of the hydrophobic MoS2 crystals interact with oxygen-containing functional groups that exist in the hydrophobic part of silk fibroins. The amphiphilic properties of silk fibroin combined with the MoS2 nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS2 nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS2 nanosheets contents.
文摘A novel compact electromagnetic bandgap （EBG） structure constructed by etching two reverse split rings （RSRs） and inserting interleaving edge （IE） on the patch of conventional mushroom-like EBG （CML-EBG） is investigated. Simulated dispersion diagrams show that the proposed EBG structure presents a 13.6% size reduction in the center frequency of the bandgap. Two comparisons have been carried out for the analysis of the effect of the RSRs and IE configuration. Then, a sample of this novel EBG is fabricated and tested, further experimental data agree well with the simulated results. Thus, this EBG structure makes a good candidate to decrease mutual coupling in compact microstrip patch array.
