Tensile,flexural and morphological properties of electron beam-crosslinked LDPE–EPDM blends

The effect of electron beam (EB) irradiation on the tensile, flexural and morphological properties of low-density polyethylene (LDPE)/ethylene-propylene diene elastomer (EPDM) blends had been studied in the absence and presence of crosslink promoters, such as trimethylolpropane triacrylate (TMPTA) and triallyl cyanurate (TAC). Blends were prepared by melt mixing of LDPE and EPDM followed by EB irradiation at various doses. The gel fraction (%) of irradiated blends was increased with an increase in EPDM content as well as EB irradiation dose and consequently the tensile and flexural properties of the blends increased. The incorporation of crosslinking promoters accelerated the gel formation and improved the properties upon irradiation more efficiently. The phase morphology of fractured surface displayed immiscibility with a rough appearance before irradiation. But after irradiation, the surface became fine, smooth and uniform, which went on increasing upon irradiation, supporting the steady increase in mechanical properties. Surface appeared even smoother in the presence of TMPTA and TAC.     

Synthesis of Polyelectrolyte and Studies of its Conductivity Changes with Respect to Molecular Weight

Aqueous solutions of acrylamide monomer were irradiated by γ-rays using a Co-60 source to synthesize polyacrylamide of different molecular weight (M_w). Solubility tests together with ultraviolet and infrared spectroscopic studies were performed for examining the irradiated samples to ensure that the prepared products were gradually converted from monomer to polymer (polyacrylamide), depending on the radiation dose. Various physico-chemical properties like polymer conversion, gel content, viscosity, and molecular weight of the products were determined. The conversion of polymer from monomer is initiated at a dose of 0.06 kGy and completed at about 0.14 kGy. The gel point, which indicates a dose for the onset of a network polymer structure, is identified to be 0.15 kGy providing valuable information about γ-ray synthesis of polyacrylamides. Viscosity and molecular weight are found to increase with radiation dose. Since polyacrylamides exhibit polyelectrolytic behavior in aqueous solutions, studies on conductivity changes of polyelectrolytes with respect to M_w, which is the main issue of this investigation, also were performed. The equivalent conductance of polyelectrolyte solutions was found to decrease with the molecular weight of the synthesized polymer. This change of conducting property of the prepared samples is explained based on the theory of polyelectrolyte solutions.     

Elevated temperature fatigue behaviour of structural materials for advanced ultra supercritical application

Nickel-based alloy 617 with controlled composition (designated as alloy 617M) and ferritic/martensitic 10% Cr steel are candidate materials for the steam rotor forgings in the high and low pressure regions respectively, in the Indian advanced ultra supercritical (AUSC) programme. Present investigation deals with the high cycle fatigue (HCF) behaviour of alloy 617M, 10% Cr steel and the dissimilar metal weld (DMW) joints of alloy 617M and 10% Cr steel over a wide temperature range (300–973 K). Constant life Haigh diagrams corresponding to different cyclic lives were constructed through tests performed using different R-ratios at 973 K.Influence of mean stress was established through Goodman diagrams at 853 K, using different R-ratios. Weld-strength reduction factor was determined based on HCF tests conducted on the DMW joints.     

A heuristic approach for balancing mixed-model assembly line of type I using genetic algorithm

The mixed model assembly line is becoming more important than the traditional single model due to the increased demand for higher productivity. In this paper, a set of procedures for mixed-model assembly line balancing problems (MALBP) is proposed to make it efficiently balance. The proposed procedure based on the meta heuristics genetic algorithm can perform improved and efficient allocation of tasks to workstations for a pre-specified production rate and address some particular features, which are very common in a real world mixed model assembly lines (e.g. use of parallel workstations, zoning constraints, resource limitation). The main focus of this study is to study and modify the existing genetic algorithm framework. Here a heuristic is proposed to reassign the tasks after crossover that violates the constraints. The new method minimises the total number of workstation with higher efficiency and is suitable for both small and large scale problems. The method is then applied to solve a case of a plastic bag manufacturing company where the minimum number of workstations is found performing more efficiently.     

Optimum number of stages and intermediate pressure level for highest exergy efficiency in large helium liquefiers

In this paper, an attempt has been made to study the influence of different design and operating parameters on the performance of large scale helium liquefiers through the concept of pre-cooling stages. Through exergy analysis and simulation with Aspen HYSYS^® 7.0, it has been demonstrated that four refrigeration stages is the best option for large helium liquefiers when all expanders operate between the entire available pressure differences. However, when some of the expanders are operated at intermediate pressure, a more number of stages gives a higher thermodynamic efficiency. Relationship between the number of stages, effective heat exchanger area and operating pressure levels of expanders, which could optimally be employed for least specific power consumption has been established through exergy analysis. Optimum number of stages, intermediate pressure and corresponding plant efficiency are, however to a large extent, dictated by the prevailing compressor efficiency. The intermediate pressure that gives the maximum exergy efficiency for the plant increases from 0.2 MPa with constant compressor efficiency to 0.35 MPa when considering two-staged compressor where pressure ratio influences compressor efficiency. Results presented may be useful in designing energy-efficient helium liquefiers of large capacity.     

Defect annealing processes for polycrystalline silicon thin-film solar cells

A variety of defect healing methods was analyzed for optimization of polycrystalline silicon (poly-Si) thin-film solar cells on glass. The films were fabricated by solid phase crystallization of amorphous silicon deposited either by plasma enhanced chemical vapor deposition (PECVD) or by electron-beam evaporation (EBE). Three different rapid thermal processing (RTP) set-ups were compared: A conventional rapid thermal annealing oven, a dual wavelength laser annealing system and a movable two sided halogen lamp oven. The two latter processes utilize focused energy input for reducing the thermal load introduced into the glass substrates and thus lead to less deformation and impurity diffusion. Analysis of the structural and electrical properties of the poly-Si thin films was performed by Suns-V_OC measurements and Raman spectroscopy. 1 cm² cells were prepared for a selection of samples and characterized by I–V-measurements. The poly-Si material quality could be extremely enhanced, resulting in increase of the open circuit voltages from about 100 mV (EBE) and 170 mV (PECVD) in the untreated case up to 480 mV after processing.     

Investigations on the thermal and flexural properties of plain weave carbon/epoxy-nanoclay composites by hand-layup technique

The matrix of carbon fiber/SC-15 epoxy composites was modified with Nanomer^® I-28E nanoclay, a surface modified montmorillonite mineral, to determine the effects of particle reinforcement on the response of these materials to flexural and thermomechanical loading. Different weight percentages of nanoclay were dispersed in SC-15 epoxy using sonication route. The nanophased epoxy was then used to manufacture plain weave carbon/epoxy nanocomposites using hand-layup process followed by vacuum bagging. Control samples of woven carbon fiber/epoxy were fabricated for comparison purposes. Effect of post curing on these samples was also investigated. 3-point bend flexure and Dynamic Mechanical Analysis (DMA) studies were carried out on 8- and 3-layered samples respectively. Results of flexural tests indicate significant improvements in flexural strength and modulus for nanoclay reinforced composites as compared to the control samples. DMA studies also showed enhancement in thermomechanical properties especially in storage modulus though no appreciable change was noticed in glass transition temperature, T _g. Scanning electron microscopy (SEM) studies were carried out to comprehend the effect of nanoclay on the microstructure and the failure modes.     

A simple time domain algorithm for the detection of ventricular fibrillation in electrocardiogram

Ventricular fibrillation (VF) is the most serious variety of arrhythmia which requires quick and accurate detection to save lives. In this paper, we propose a new time domain algorithm, called threshold crossing sample count (TCSC), which is an improved version of the threshold crossing interval (TCI) algorithm for VF detection. The algorithm is based on an important feature of the VF signal which relies on the random behavior of the electrical heart vector. By two simple operations: comparison and count, the technique calculates an effective measure which is used to separate life-threatening VF from other heart rhythms. For assessment of the performance of the algorithm, the method is applied on the complete MIT-BIH arrhythmia and CU databases, and a promising good performance is observed. Seven other classical and new VF detection algorithms, including TCI, have been simulated and comparative performance results in terms of different quality parameters are presented. The TCSC algorithm yields the highest value of the area under the receiver operating characteristic curve (AUC). The new algorithm shows strong potential to be applied in clinical applications for faster and accurate detection of VF.     

Microstructure and Mechanical Properties of Fiber-Laser-Welded and Diode-Laser-Welded AZ31 Magnesium Alloy

The microstructures, tensile properties, strain hardening, and fatigue strength of fiber-laser-welded (FLW) and diode-laser-welded (DLW) AZ31B-H24 magnesium alloys were studied. Columnar dendrites near the fusion zone (FZ) boundary and equiaxed dendrites at the center of FZ, with divorced eutectic β-Mg₁₇Al₁₂ particles, were observed. The FLW joints had smaller dendrite cell sizes with a narrower FZ than the DLW joints. The heat-affected zone consisted of recrystallized grains. Although the DLW joints fractured at the center of FZ and exhibited lower yield strength (YS), ultimate tensile strength (UTS), and fatigue strength, the FLW joints failed at the fusion boundary and displayed only moderate reduction in the YS, UTS, and fatigue strength with a joint efficiency of ~91 pct. After welding, the strain rate sensitivity basically vanished, and the DLW joints exhibited higher strain-hardening capacity. Stage III hardening occurred after yielding in both base metal (BM) and welded samples. Dimple-like ductile fracture characteristics appeared in the BM, whereas some cleavage-like flat facets together with dimples and river marking were observed in the welded samples. Fatigue crack initiated from the specimen surface or near-surface defects, and crack propagation was characterized by the formation of fatigue striations along with secondary cracks.     

Value-based system facility planning - a rational response to conflicting customer and regulatory demands

In a competitive energy market in which power supply reliability influence customer's purchasing decisions, utilities throughout the world are rapidly recognizing that they cannot ignore customer preferences. Reliability of electric service should be based on balancing the costs to a utility and the value of the benefits received by its customers. The customer survey approach is based on the assumption that customers are in the best position to understand how interruptions impact their activities that depend on electricity supply. A challenge to electric utilities is to increase the market value of the services they provide with the right amount of reliability and to lower its costs of operation, maintenance, and construction to provide lower rates for customers. Lastly, the value-based reliability cost-benefit assessment helps electric utilities to achieve the goal of providing reliable energy service at the lowest possible cost, which their customer values.