Effect of duct geometry on shock wave discharge

This paper describes computational work to understand the unsteady flow-field of a shock wave discharging froman exit of a duct and impinging upon a flat plate.A flat plate is located downstream, and normal to the axis of theduct.The distance between the exit of the duct and fiat plate is changed.In the present study,two different ductgeometries(i.e.,square and cross section)are simulated to investigate the effect of duct geometry on theun-steady flows of a shock wave.In computation,the total variation diminishing(TVD)scheme is employed tosolve three-dimensional,unsteady,compressible,Euler equations.Computations are performed over the range ofshock Mach number from 1.05 to 1.75.Computational results can predict the three-dimensional dynamic behav-iour of the shock wave impinging upon the flat plate.The results obtained show that the pressure increase gener-ated on the plate by the shock impingement depends on the duct geometry and the distance between the duct exitand plate,as well as the shock Mach number.It is also found that for the duct with cross-section,the unsteadyloads acting on the flat plate are less,compared with the square duct.     

Refinement method for structure from stereo motion

A new method for overcoming bas-relief ambiguity, using a calibrated stereo image sequence, is presented. The proposed method uses a direct method for motion estimation as the initial guess, and refines both stereo and motion displacement with sub-pixel accuracy. Experimental results show that the proposed algorithm improves the estimation accuracy under such ambiguity     

Comparison of the Cisterna Maturation-Progression Model with the Kiss-and-Run Model of Intra-Golgi Transport: Role of Cisternal Pores and Cargo Domains

The Golgi complex is the central station of the secretory pathway. Knowledge about the mechanisms of intra-Golgi transport is inconsistent. Here, we compared the explanatory power of the cisterna maturation-progression model and the kiss-and-run model. During intra-Golgi transport, conventional cargoes undergo concentration and form cisternal distensions or distinct membrane domains that contain only one membrane cargo. These domains and distension are separated from the rest of the Golgi cisternae by rows of pores. After the arrival of any membrane cargo or a large cargo aggregate at the Golgi complex, the cis-Golgi SNAREs become enriched within the membrane of cargo-containing domains and then replaced by the trans-Golgi SNAREs. During the passage of these domains, the number of cisternal pores decreases. Restoration of the cisternal pores is COPI-dependent. Our observations are more in line with the kiss-and-run model.     

Modification of cathode structure by introduction of CNT for air-breathing DMFC

Optimization of the structure and texture of the cathode catalyst layer for air-breathing DMFC has been studied. Application of carbon nanotubes (CNT) as an additive to the cathode catalyst layer resulted in the increase of BET surface area and porosity of the catalyst layer due to filamentous morphology of CNT. Best performance was observed at the intermediate CNT/catalyst ratio of 0.05. I–U polarization and impedance analysis indicated that the faster oxygen reduction reaction at the open cathode is responsible for the power density improvement. Excessive cathode porosity was not favorable due to the decrease of the effective ionic conductivity of the catalyst layer.     

Physical characteristics of sweet potato pulp/polycaprolactone blends

Sweet potato pulp (SSP) obtained as a by‐product from starch extraction was blended with polycaprolactone (PCL) to prepare a biodegradable plastic material. In the blends, PCL was used as a reinforcing agent. The SPP/PCL blends were prepared by compression‐molding under high temperature and pressure, at different SPP/PCL ratios, and the mechanical properties of the molded specimens were tested. Matrix structure and thermal properties were measured by using a Fourier transform infrared (FTIR) spectrophotometer, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). Mechanical properties (tensile and flexural properties) were also measured to find the most suitable ratio in a SSP/PCL blend. During compression molding of the SPP/PCL blends under high pressure and temperature, chemical reaction occurred between SPP and PCL, and thus, thermal stability and mechanical strength of the blends increased and water uptake decreased. Also, by increasing the PCL content in the blend, the matrix in the blend became more homogeneous, and consequently, mechanical strength of the molded specimen increased. At 7/3 or 6/4 weight ratio of SSP/PCL, water uptake of the molded specimen became substantially less than that at 8/2. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 861–866, 2004     

Oxygen barrier properties of biaxially oriented polypropylene/polyvinyl alcohol blend films

The biaxially oriented PP/PVA blend film was prepared and had the higher oxygen barrier property by about 130 times than that of a biaxially oriented PP film. When the viscosity ratio (η_d(PVA)/η_m(PP)) decreased, the dispersed PVA phase was developed into platelets during stretching process. Oxygen permeability was dependent on the number and size of PVA platelet. However, the Oxygen permeability was not sensitively changed in above 25 wt% of PVA. To obtain excellent barrier property, the optimum amount of plasticizer and initiator was required. A pasticizer was related to the size and degree of crystallization of PVA platelet. An initiator played the role of a compatibilizer. The oxygen barrier was enhanced with increasing the viscosity of PP and draw ratio. The higher viscosity of PP was advantageous for preventing the delamination of a blend film, and the moisture vapor permeability was not affected with the laminar structure. As a result, the biaxially oriented PP/PVA blend film had the potential of substituting for the PVDC coated BOPP film.     

Evaluation of coagulation and PAC adsorption pretreatments on membrane filtration for a surface water in Korea: A pilot study

Application of membrane filtration has been significantly expanded throughout the world in two decades. A project was launched to facilitate the application of membrane filtration in drinking water plants in Korea in 2004. Five pilot plants each with a capacity of 500 m³/d were installed in a Gueui Drinking Water Plant. The Han River water was a main raw water source for the plants. Key parameters of the raw water were examined. The raw water characteristics are tremendously varied with seasons and rain fall, especially in terms of turbidity and algae numbers. The operation of pretreatment was of substantial importance due to the variation of the raw water. Coagulation and powdered activated carbon adsorption were performed as pretreatment options of microfiltration. The coagulant doses were optimized with increasing turbidity compared to the conventionally used operational manual. PAC adsorption was applied to overcome fouling by high algae numbers. The addition of PAC relieved the aggravation of fouling. However, the PAC addition could not stop the undergoing fouling. A set of laboratory experiments showed that the removal of floc aggregates after coagulation and PAC was critical to maintain high water flux in the membrane system.     

Covalently cross-linked sulfonated poly(ether ether ketone)/tungstophosphoric acid composite membranes for water electrolysis application

Composite polymer electrolyte membranes consisting of covalently cross-linked sulfonated polyether ether ketone (SPEEK) with tungstophosphoric acid (TPA) are prepared and their electrochemical and mechanical properties are investigated with regards to application in water electrolysis. Covalently cross-linked membranes (CL-SPEEK) comprised of sulfochlorinated SPEEK membranes and SPEEK partially lithiated by LiCl, are prepared by reaction with 1,4-diiodobutane, and blended with TPA to avoid excessive water swelling and to reinforce their mechanical properties. These ion-exchange membranes show good electrochemical properties, including proton conductivity, ion exchange capacity (IEC), thermal stability, anti-oxidative stability, and satisfactory mechanical characteristics, such as tensile strength and elongation. In particular, among the TPA-composite membranes, the CL-SPEEK/TPA30 (30 wt.% TPA) membrane displays higher proton conductivity (0.128 S cm⁻¹) and tensile strength (75.01 MPa) than Nafion^® 117 at 80 °C. The ion-exchange membranes are used to construct membrane electrode assemblies (MEAs) of use in polymer electrolyte membrane electrolysis (PEME). The MEA are prepared using a non-equilibrium impregnation–reduction (I–R) method. The electrochemical surface area (ESA) and roughness factor of the MEA prepared with CL-SPEEK/TPA30 electrolyte measured by cyclic voltammetry are 25.11 m² g⁻¹ and 321.4 cm² Pt cm⁻², respectively. The prepared MEAs are used in the water-electrolysis unit cells. The cell voltage is 1.78 V at 1 A cm⁻² and 80 °C, with a platinum loading of 1.28 mg cm⁻². The results of the present study suggest that the good conductivity and mechanical properties of covalently CL-SPEEK/TPA composite membranes make them well suited for use in PEME.     

Preparation and electrostatic properties of antistatic acrylics

Very good antistatic acrylic films or fabrics can be prepared by exposing the acrylic samples containing oxidizing agent to aniline vapor. The conductivity, the maximum static charge, and the half-life time are used for estimation of electrostatic properties. The effects of the content of polyaniline and the temperature and time of exposure to aniline vapor on the electrostatic properties have been investigated. The stability of conductivity to ambient air exposure and the temperature dependence of conductivity for antistatic acrylic films have also been investigated.     

Effects of ZnO on the piezoelectric properties of Pb(Mn1/3Sb2/3)O3-Pb(Zr,Ti)O3 ceramics

Perovskite-type 0.05 Pb(Mn_1/3Sb_2/3)O₃-0.95 Pb(Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0∼0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200°C for 2 hrs. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d₃₁) and piezoelectric voltage output coefficient (g₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant () reached to the maximum of 56% and 1,727, respectively.