Simulation and experimental analyses of electromagnetic transients behaviors of lightning surge on vertical conductors

Simulation of very fast surge phenomena in a three-dimensional (3-D) structure requires a method based on Maxwell's equations, such as the finite-difference time-domain (FDTD) method or the method of moments, because circuit-equation-based methods cannot handle the phenomena. This paper uses a method of thin-wire representation of the vertical conductor system for the FDTD method which is suitable for the 3-D surge simulation. The thin-wire representation is indispensable to simulate electromagnetic surges on wires or steel frames in which the radius is smaller than a discretized space step used in the FDTD simulation. In this paper, a general surge analysis program named the virtual surge test lab based on the Maxwell's equations formulated by the FDTD method, is used to simulate the surge phenomena of a vertical conductor, including the effects of horizontal wave incidence and vertical wave incidence. Experimental results on the reduced scale model have been presented in order to compare among the simulation results by the FDTD method and the results using numerical electromagnetic code based on the MoM.     

Providing application-level QoS in 3G/4G wireless systems: a comprehensive framework based on multirate CDMA

The emerging applications for 3G and 4G wireless systems typically require highly heterogeneous and time-varying quality of service from the underlying protocol layers. The wireless links, however, provide only an unreliable communication channel that suffers from temporal outages. As a consequence, protocol mechanisms are needed that, based on the unreliable wireless links, provide the different service qualities required by the emerging applications. We identify the emerging IP-based applications for 3G and 4G wireless systems and categorize their QoS requirements. We discuss the wireless access mechanisms that show promise as the basis for supporting these applications. We then propose a set of protocol mechanisms that, based on the discussed wireless access mechanisms, provide the required QoS for the different application categories.     

Novel bipolar differential input/output current-controlled current source

A new bipolar differential input/output current-controlled current source (CCCS) is described. The basic cell consists of a translinear array of six transistors with two bipolar inputs, and is suited for the input stage of a differential current-mode operational amplifier.     

On the use of elliptical side branches to thick-walled cylinders

The boundary integral equation (boundary element) method of numerical stress analysis is used to compute stress concentration factors at the intersections between side branches and thick-walled tubes or pressure vessels. Cases of both circular and elliptical side branch cross sections are considered, the effect of the latter being to significantly reduce the maximum stresses generated under internal pressure. For the typical geometries considered, reductions of more than 20% are obtained at optimum ellipse aspect ratios of about 0·8.     

Tg/Tm for unsubstituted polymers

Polymers under discussion can be represented by [CH₂)_nR]_p where R is CH₂, CF₂, O, S or CH = CH; and where n can vary from 0 to ∞. The copolymer, P(ethylene-alt-TFE) is also included. These polymers tend to be highly crystalline with resultant confusion about their Tg and hence their Tg/Tm values and a clarification scheme is proposed in which it is considered that each such polymer has a double glass transition, Tg(L)/f(χ_c), Tg(U) = F(χc); and a sub-glass T<Tg(L) at 0.75 Tg(L), where F(χc) signifies a function of fractional crystallinity, χ_c. T<Tg(L) and Tg(L) increase linearly with Tm. The ratio, Tg(L)/Tm, is therefore, not a constant but is close to 0.5. T<Tg(L)/Tg(L) is also not a constant but is close to 0.75. Tg(U) lies within a wedge whose top and bottom sides increase with Tm. The premelting, intracrystalline transition temperature, Tα_c, is also a linear function of Tm. It is suggested that the scheme outlined above should help to resolve uncertainties in assigning transition temperatures for unsubstituted polymers. The low Tg/Tm values for these polymers is discussed in terms of their small da/dc ratios and small crosssectional areas per chain.     

Colloidal silica removal in coagulation processes for wastewater reuse in a high-tech industrial park.

Four experiments of coagulation and flocculation were conducted to investigate the characteristics of colloidal silica removal in a high-tech industrial wastewater treatment plant for reclamation and reuse of the effluent. Experimental results illustrated that poly-aluminium chloride (PACl) showed higher performances on colloidal silica removal than alum. Interestingly, the two coagulants demonstrated the same capacity on silica removal. The specific silica removal capacity was approximately 0.135 mg SiO2/mg Al2O3 when the dosage of coagulants was in the range 30-150 mg/L Al2O3. In addition, the silica was reduced significantly at the condition of pH above 8. Experimental data implied that precipitation of aluminium flocs was the major mechanism for colloid silica removal in PACl and alum coagulation, besides, charge adsorption was also important for improving removal efficiency. Moreover, the addition of polyacrylic acid (PAA) as a flocculant could slightly advance silica removal in the PACl coagulation. The combined PACl/PAA/flocs coagulation was effective for the removal of colloidal silica, soluble COD, and turbidity and also suitable as a pretreatment unit in wastewater reclamation and reuse processes.