Non-Line-of-Sight(NLOS)Ultraviolet(UV)communication uses the atmosphere as a propagation medium.As the communication range increases,turbulence becomes a significant atmospheric process that affects the propagation of...Non-Line-of-Sight(NLOS)Ultraviolet(UV)communication uses the atmosphere as a propagation medium.As the communication range increases,turbulence becomes a significant atmospheric process that affects the propagation of optical waves.This paper presents a more accurate NLOS channel model by considering turbulence-induced Scintillation Attenuation(SA).Then,the Bit Error Rate(BER)during turbulence of the NLOS UV communication system with On-Off Keying(OOK)modulation and Maximum Likelihood(ML)detection is analysed and compared with that in free space without turbulence.The BER dependence is also analysed for different factors,including the refractive index structure parameter,transceiver range,pointing angles,transmitted power,and data rate.展开更多
The effects of interchannel scattering of conduction electrons by the impu rity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper.It ...The effects of interchannel scattering of conduction electrons by the impu rity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper.It is shown that these two perturbations will substantially modify the usual local non-Fermi liquid behavior of the two-channel Kondo model.With bosonization and unitary transformations we find that the system can be transformed into a single channel Kondo model with anisotropy between longitudinal and transverse exchange couplings.Whatever for originally antiferromagnetic or ferromagnetic isotropic coupling,the system always flows to strong-coupling limit,which exhibits local Fermi liquid behavior at low temperatures.展开更多
A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynol...A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.展开更多
The u Mhlatuzana, u Mbilo and a Manzimnyama river catchments located on the eastern seaboard of the Kwa Zulu-Natal province, South Africa, form the core of urbanization and industrialization, contributing the only nat...The u Mhlatuzana, u Mbilo and a Manzimnyama river catchments located on the eastern seaboard of the Kwa Zulu-Natal province, South Africa, form the core of urbanization and industrialization, contributing the only natural freshwater inflows to the Bayhead Canal portion of the Durban Harbour. In this study, seasonal discharges and physico–chemical water properties were used to quantitatively determine the material mass transport capacity of the river systems on the basis of hydrographic inputs and chemical loading from the surrounding land use sectors.The mass transport of the total dissolved solids(TDS),ammonia(NH_4), phosphorous(P), aluminum(Al), calcium(Ca), copper(Cu), chromium(Cr), mercury(Hg), potassium(K), magnesium(Mg), sodium(Na), nickel(Ni), lead(Pb), sulphur(S) and vanadium(V) was determined for each river. Results indicated that land use, seasonality and river flow were significant determinants for the material loading in the rivers and the receiving port waters. The spatio-temporal distribution patterns of chemical fluxes indicated that industrial activity associated with the a Manzimnyama canal contributed the most, with regards to TDS, NH_4, Ca, K, Mg, Na, S and V, loading in both wet and dry seasons, as well as Al, Cu, Hg and Pb during the dry season. Similarly, industrial activity associated with the u Mbilo/u Mhlatuzana Canal at the lower reaches accounted for the highest P, Al, Cu and Pb fluxes in the wet season alone. Fluxes of these parameters are used to explain theobserved elemental concentrations and patterns of the receiving port waters of the Bayhead Canal.展开更多
In this work, experiment efforts were devoted to study the effect of the longitudinal slope of channel on the discharge coefficient for ogee spillway and broad crested weir. A comprehensive laboratory study including ...In this work, experiment efforts were devoted to study the effect of the longitudinal slope of channel on the discharge coefficient for ogee spillway and broad crested weir. A comprehensive laboratory study including 17 tests was conducted to estimate the variation of the discharge coefficient due to variation of the longitudinal slope. It was shown that the discharge coefficient is significantly increasing with the increase of the slope by more than 90% or 75% and 80% or 70% for weir and spillway in case of excluding or including the approach velocity head, respectively. Also, CFD （computational fluid dynamics） with a help of Comsol-multyphsics program was used to simulate the problem. The program explained that the linear distribution of the hydraulic pressure changes to a non-linear distribution as the longitudinal slope is considered. Consequently, the values of the discharge coefficient are also affected.展开更多
To improve the simulation accuracy of SIMULINK, a novel inclusive behavior model of an integrator is proposed that introduces the effects of different circuit nonidealities of a switched-capacitor sigma-delta modulato...To improve the simulation accuracy of SIMULINK, a novel inclusive behavior model of an integrator is proposed that introduces the effects of different circuit nonidealities of a switched-capacitor sigma-delta modulator into SIMULIK simulation. The nonlinear DC gain and nonlinear settling process are introduced into the op-amp module. The signaldependent charge injection and nonlinear resistance are introduced into the switch module. In addition, the noise source including flicker and thermal noise is introduced into system as an independent module. The novel model is verified by SIMULINK behavioral simulations. The results are compared with results from circuit level simulation in Cadence SPICE using TSMC 0.35μm mixed signal technology. It shows that the novel model succeeds in introducing the influences of the nonidealities into behavior simulation to more realistically describe the circuit performances and increase the accuracy of SIMULINK simulation.展开更多
Peristaltic flow of a conducting Jeffrey fluid in an inclined asymmetric channel is investigated. The channel asymmetry is produced by considering a peristaltic wave train on the flexible walls of the channel with dif...Peristaltic flow of a conducting Jeffrey fluid in an inclined asymmetric channel is investigated. The channel asymmetry is produced by considering a peristaltic wave train on the flexible walls of the channel with different amplitudes and phases. The nonlinear governing equations are solved analytically by a perturbation technique. The expressions for the stream function, axial velocity and the pressure rise per wavelength are determined in terms of the Jeffrey number λ1, the Froude number Fr, the perturbation parameter 5, the angle of inclination θ and the phase difference Ф. Effects of the physical parameters on the velocity field and the pumping characteristics are discussed. It is observed that the size of the trapping bolus increase with an increase in the magnetic parameter and the volume flow rate. That is, the magnetic parameter and the volume flow rate have strong influence on the trapping bolus phenomenon.展开更多
基金supported by the Open Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications),China
文摘Non-Line-of-Sight(NLOS)Ultraviolet(UV)communication uses the atmosphere as a propagation medium.As the communication range increases,turbulence becomes a significant atmospheric process that affects the propagation of optical waves.This paper presents a more accurate NLOS channel model by considering turbulence-induced Scintillation Attenuation(SA).Then,the Bit Error Rate(BER)during turbulence of the NLOS UV communication system with On-Off Keying(OOK)modulation and Maximum Likelihood(ML)detection is analysed and compared with that in free space without turbulence.The BER dependence is also analysed for different factors,including the refractive index structure parameter,transceiver range,pointing angles,transmitted power,and data rate.
文摘The effects of interchannel scattering of conduction electrons by the impu rity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper.It is shown that these two perturbations will substantially modify the usual local non-Fermi liquid behavior of the two-channel Kondo model.With bosonization and unitary transformations we find that the system can be transformed into a single channel Kondo model with anisotropy between longitudinal and transverse exchange couplings.Whatever for originally antiferromagnetic or ferromagnetic isotropic coupling,the system always flows to strong-coupling limit,which exhibits local Fermi liquid behavior at low temperatures.
基金Supported by the National Natural Science Foundation of China(Nos.51579036,51579030)the Fundamental Research Funds for the Central Universities of China(No.DUT14YQ108)
文摘A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.
基金the National Research Foundation(NRF)for financial support during this study
文摘The u Mhlatuzana, u Mbilo and a Manzimnyama river catchments located on the eastern seaboard of the Kwa Zulu-Natal province, South Africa, form the core of urbanization and industrialization, contributing the only natural freshwater inflows to the Bayhead Canal portion of the Durban Harbour. In this study, seasonal discharges and physico–chemical water properties were used to quantitatively determine the material mass transport capacity of the river systems on the basis of hydrographic inputs and chemical loading from the surrounding land use sectors.The mass transport of the total dissolved solids(TDS),ammonia(NH_4), phosphorous(P), aluminum(Al), calcium(Ca), copper(Cu), chromium(Cr), mercury(Hg), potassium(K), magnesium(Mg), sodium(Na), nickel(Ni), lead(Pb), sulphur(S) and vanadium(V) was determined for each river. Results indicated that land use, seasonality and river flow were significant determinants for the material loading in the rivers and the receiving port waters. The spatio-temporal distribution patterns of chemical fluxes indicated that industrial activity associated with the a Manzimnyama canal contributed the most, with regards to TDS, NH_4, Ca, K, Mg, Na, S and V, loading in both wet and dry seasons, as well as Al, Cu, Hg and Pb during the dry season. Similarly, industrial activity associated with the u Mbilo/u Mhlatuzana Canal at the lower reaches accounted for the highest P, Al, Cu and Pb fluxes in the wet season alone. Fluxes of these parameters are used to explain theobserved elemental concentrations and patterns of the receiving port waters of the Bayhead Canal.
文摘In this work, experiment efforts were devoted to study the effect of the longitudinal slope of channel on the discharge coefficient for ogee spillway and broad crested weir. A comprehensive laboratory study including 17 tests was conducted to estimate the variation of the discharge coefficient due to variation of the longitudinal slope. It was shown that the discharge coefficient is significantly increasing with the increase of the slope by more than 90% or 75% and 80% or 70% for weir and spillway in case of excluding or including the approach velocity head, respectively. Also, CFD （computational fluid dynamics） with a help of Comsol-multyphsics program was used to simulate the problem. The program explained that the linear distribution of the hydraulic pressure changes to a non-linear distribution as the longitudinal slope is considered. Consequently, the values of the discharge coefficient are also affected.
基金the National Natural Science Foundation of China(No.90707002)~~
文摘To improve the simulation accuracy of SIMULINK, a novel inclusive behavior model of an integrator is proposed that introduces the effects of different circuit nonidealities of a switched-capacitor sigma-delta modulator into SIMULIK simulation. The nonlinear DC gain and nonlinear settling process are introduced into the op-amp module. The signaldependent charge injection and nonlinear resistance are introduced into the switch module. In addition, the noise source including flicker and thermal noise is introduced into system as an independent module. The novel model is verified by SIMULINK behavioral simulations. The results are compared with results from circuit level simulation in Cadence SPICE using TSMC 0.35μm mixed signal technology. It shows that the novel model succeeds in introducing the influences of the nonidealities into behavior simulation to more realistically describe the circuit performances and increase the accuracy of SIMULINK simulation.
文摘Peristaltic flow of a conducting Jeffrey fluid in an inclined asymmetric channel is investigated. The channel asymmetry is produced by considering a peristaltic wave train on the flexible walls of the channel with different amplitudes and phases. The nonlinear governing equations are solved analytically by a perturbation technique. The expressions for the stream function, axial velocity and the pressure rise per wavelength are determined in terms of the Jeffrey number λ1, the Froude number Fr, the perturbation parameter 5, the angle of inclination θ and the phase difference Ф. Effects of the physical parameters on the velocity field and the pumping characteristics are discussed. It is observed that the size of the trapping bolus increase with an increase in the magnetic parameter and the volume flow rate. That is, the magnetic parameter and the volume flow rate have strong influence on the trapping bolus phenomenon.
