Simulation of the percolation of water into rigid polyurethane foams at applied hydraulic pressures

The hydraulic resistance of polyurethane foams is studied by means of simulations of water penetration into model foams. The model foams of cubical shape are constructed by generating the centers of the cells randomly. The strength of the window separating two cells is assumed to be a function of the distance between the centers of the cells in one set of computations. In another set of computations the strengths of the windows are assigned randomly from a specified distribution. The foam is exposed to an elevated pressure at its boundaries and water penetrates into the foam by rupturing the windows with strengths lesser than the applied pressure. The variation of equilibrium volume fraction of the foam filled with water for increasing hydraulic pressures shows typical percolation behavior: there is a sharp increase in the volume filled beyond a threshold pressure. Simulations show that beyond a certain sample size there is no change in the percolation curve with sample size, and indicate that it is mainly the weaker windows that control the hydraulic resistance of the foam. The simulation results are compared with experimental data. POLYM. ENG. SCI. 46:970–983, 2006. © 2006 Society of Plastics Engineers     

Molecular interactions in intercalated organically modified clay and clay-polycaprolactam nanocomposites: Experiments and modeling

In this work we have evaluated molecular interactions in organically modified clay and polymer clay nanocomposite using a combination of experimental (photoacoustic FTIR, XRD) and computational (molecular dynamics (MD)) techniques. The FTIR data reveals hydrogen bond and ionic bond interaction between functional end groups of organic modifier and surface oxygen of interlayer clay sheet lying in the organically modified clay; and, the hydrogen bond formation between intercalated polymer and organic modifier and surface oxygen of clay sheet lying in the interlayer clay gallery in the polymer clay nanocomposite. In this work we report the nature of interactions between clay and polymer, clay and organic modifier in polymer-clay nanocomposites through experiments and molecular dynamics simulations.     

A comparative study of walking‐induced dust resuspension using a consistent test mechanism

Human walking influences indoor air quality mainly by resuspending dust particles settled on the floor. This study characterized walking‐induced particle resuspension as a function of flooring type, relative humidity (RH), surface dust loading, and particle size using a consistent resuspension mechanism. Five types of flooring, including hardwood, vinyl, high‐density cut pile carpet, low‐density cut pile carpet, and high‐density loop carpet, were tested with two levels of RH (40% and 70%) and surface dust loading (2 and 8 g/m²), respectively. Resuspension fraction r_a (fraction of surface dust resuspended per step) for house dust was found to be varied from 10^?7 to 10^?4 (particle size: 0.4–10 µm). Results showed that for particles at 0.4–3.0 µm, the difference in resuspension fraction between carpets and hard floorings was not significant. For particles at 3.0–10.0 µm, carpets exhibited higher resuspension fractions compared with hard floorings. Increased RH level enhanced resuspension on high‐density cut pile carpet, whereas the opposite effect was observed on hard floorings. Higher surface dust loading was associated with lower resuspension fractions on carpets, while on hard floorings the effect of surface dust loading varied with different RH levels.     

Hydrogeochemistry,Elemental Flux,and Quality Assessment of Mine Water in the Pootkee-Balihari Mining Area,Jharia Coalfield,India

Ninety nine mine water discharge samples were collected and analyzed for pH, electrical conductivity (EC), major cations, anions, and trace metals in the Pootkee-Balihari coal mining area of the Jharia coalfield. The mines of the area annually discharge 34.80 × 10⁶ m³ of mine water and 39,099 t of solute loads. The pH of the analyzed mine waters ranged from 6.97 to 8.62. EC values ranged from 711 μS cm⁻¹ to 1862 μS cm⁻¹, and reflect variations in lithology, geochemical processes, and hydrological regimes in the mines. The cation and anion chemistry indicate the general ionic abundance as: Mg²⁺ > Ca²⁺ > Na⁺ > K⁺ and HCO₃ ⁻ > SO₄ ²⁻ > Cl⁻ > NO₃ ⁻ > F⁻, respectively. Elevated SO₄ ²⁻ concentrations in the Gopalichuck, Kendwadih, and Kachhi-Balihari mine waters are attributed to pyrite weathering. The water quality assessment indicated that TDS, hardness, Mg²⁺, and SO₄ ²⁻ are the major parameters of concern in the study area. Except for Fe, all of the measured metals in the mine water were well within the levels recommended for drinking water. With only a few exceptions, the mine water is of good to permissible quality and suitable for irrigation.     

Experimental and FE analysis of submerged arc weld induced residual stress and angular deformation of single and double sided fillet welded joint

Submerged arc welding is well-known for its very high deposition rate and thus the capability to join very high thickness metal pieces in large structural applications. Fillet joints are mostly used in structural applications which can be extensively seen in shipbuilding, bridge construction, house buildings, automobile or any other large structures. Thermal stresses generates in a fusion welded joint due to high temperature gradient, which is the cause of the residual stresses upon cooling followed by the angular deformation and failure of the welded structure. As an effect of the thermal gradient, the induced longitudinal, transverse residual stress & angular distortion can vary in single sided and double sided submerged arc welded fillet joints, during designing & manufacturing welded structures which should be taken into account. The main objective of this paper is to quantify the amount of residual stresses and angular deformation in a fillet welding joint. An elasto-plastic thermomechanical model has been developed for predicting residual stresses. A comparison of the residual stress and angular deformation between single and double sided fillet weld joint has been made. The simulation results reveal that the amount of residual stress present in the single sided fillet weld is more and unbalanced in both side of the center of weld line compared to the double sided fillet weld and the predicted results have been matched with the experiments as well as published literatures.     

Microstructure and growth of ZnTe films

The microstructure and growth of ZnTe films deposited onto glass and freshly cleaved NaCl substrates are carefully studied by a TEM. Effect of different stimulator on the grain growth is also described.     

Galvanic deposition of nanocrystalline ZnO thin films from a ZnO-Zn(OH)(2) mixed phase precursor on p-Si substrate

A galvanic technique for the deposition of ZnO thin films is reported. The depositions were carried out on p-type single-crystal silicon substrates at room temperature, from a solution of ZnSO(4), where the Zn rod acted as a sacrificing anode and p-Si was the cathode. The deposition of ZnO by this method is pH sensitive, and a pH between 4 and 5 is found to be optimum for film deposition. This deposition technique is simple, inexpensive and can be carried out at room temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies revealed the nanocrystalline structure of the films. The resistivity of the annealed ZnO films was determined by the Van der Pauw measurement technique.     

FEM Modeling of the Interface Strength and Its Effect on the Deformation Behaviour of Aluminum Cenosphere Syntactic Foam

The interface in aluminum cenosphere syntactic foam (ACSF) is modeled using FEM to study its deformation behaviour as a function of interface characteristics such as interface stiffness and thickness. The interface is modeled as a thin layer of object. The effective modulus and stress of ACSF examined when it contain 50% cenosphere by volume. In this study, the shell wall thickness of cenosphere is fixed at 1µm. The width of the interface varies from 0.2% to 0.6% of cenosphere volume fraction. The interface strength and modulus varies in the range of 10 to 50% of the matrix alloy. The values of the normalized yield stress and the modulus decrease with increase in the interface width and decrease in the interface strength. The FEM predicted values are also validated with experimental value. The proposed study shows that unit representative shell techniques are reasonably ideal and fast method for predicting compressive deformation behaviour of ACSF.     

One-dimensional ZnO nanostructures: fabrication, optoelectronic properties, and device applications

One-dimensional (1D) zinc oxide (ZnO) nanostructures have been extensively and intensively studied for several decades not only for their extraordinary chemical and physical properties, but also for their current and future different electronic and optoelectronic device applications. This review provides a brief overview of the progress of different synthesis methods and applications of 1D-ZnO nanostructures. Morphology of ZnO nanostructures grown by various methods and progress in the optical properties are briefly described. Using low-temperature photoluminescence (LTPL) study, detailed informations about the defect states and impurity of such nanostructures are reported. Improvement of field emission properties by modifying the edge of 1D-ZnO nanostructures is briefly discussed. Applications such as different sensors, field effect transistor, light-emitting diodes (LEDs), and photodetector are briefly reviewed. ZnO has large exciton binding energy (60 meV) and wide band gap (3.37 eV), which could lead to lasing action based on exciton recombination. As semiconductor devices are being aggressively scaled down, ZnO 1D nanostructures based resistive switching (RS) memory (resistance random access memory) is very attractive for nonvolatile memory applications. Switching properties and mechanisms of Ga-doped and undoped ZnO nanorods/NWs are briefly discussed. The present paper reviews the recent activities of the growth and applications of various 1D-ZnO nanostructures for sensor, LED, photodetector, laser, and RS memory devices.     

Load Forecasting Technique for System Expansion in Isolated Area Using Time Invariant Socio-Economic Factors of Identical Agglomerations

Load forecasting is a critical issue for operational planning as well as grid expansion to ensure an uninterruptable electric power system. Being a small but densely populated country in South Asia, Bangladesh has many isolated places which are not connected to national grid yet. If concern authority opts to expand grid to those areas, they need reliable demand data for designing and dimensioning of different power system entities, e.g., capacity, overhead line capacity, tie line capacity, spinning reserve, load-shedding scheduling, etc., for reliable operation and to prevent possible obligatory redesigning. This paper represents an analysis to forecast the electricity demand of an isolated island in Bangladesh where past history of electrical load demand is not available. The analysis is based on the identification of factors, e.g., population, literacy rate, per capita income, occupation, communication, etc., on which electrical load growth of an area depends. Data has been collected from the targeted isolated area and form a grid connected area which is similar to target area from social and geographical perspective. Weights of those factors on load have been calculated by matrix inversion. Demand of the new area is forecasted using these weights factors by matrix multiplication.