Experimental Investigation and optimization of Process Parameters for Shear Strength of Compound Cast Bimetallic Joints

Joining of A356 alloy and magnesium was carried out by vacuum assisted sand mold compound casting process. Microstructure at the joint interface was studied by using optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffractometer. Characterization indicated that a relatively uniform joint interface was obtained. The joint interface was composed of three distinct layers containing Mg₂Al₃ on aluminum side, Mg₁₇Al₁₂?+?δ eutectic structure on magnesium side and Mg₁₇Al₁₂ as middle layer. As a result of interaction between silicon, present in A356 with magnesium, Mg₂Si compound was formed. Push out test was conducted on electronics universal testing machine to measure the shear strength across the joint interface. The important process parameters (grit size of sand paper, insert temperature, pouring temperature and vacuum pressure) were optimized to maximize the shear strength. Optimization was carried out by using response surface methodology, desirability analysis and genetic algorithm (GA) techniques. It was observed that the shear strength increased by 14.21, 8.60 and 4.80% with genetic algorithm, desirability analysis and regression model respectively. GA reported the optimal value of shear strength.     

Reduction of Escherichia coli O157:H7 population on baby spinach leaves by liquid sanitizers

The effectiveness of various liquid sanitizers and methods of application against Escherichia coli on baby spinach was investigated. Inoculated spinach was treated with (i) Pro‐San L (commercially prepared solution containing 0.66% citric acid, 0.036% sodium dodecyl sulfate (SDS); (ii) chlorine solution (200 ppm), alone or with addition of 0.036% SDS; and (iii) aqueous solution of 0.66% levulinic acid with 0.036% SDS. Population reduction in response to these treatments ranged between 2.1 and 2.8 log CFU/g. No significant difference (p > .05) was found among tested sanitizers in microbial count reduction. Spraying, dipping, and “dry” vacuum impregnation methods of Pro‐San L application were compared. Dipping was the most effective in reducing E. coli O157:H7 population (4.4 log CFU/g reduction). Dry vacuum impregnation was less effective (3.3 log CFU/g reduction) and caused damage to the produce. The effectiveness of spray Pro‐San L application and holding for prolonged time (up to 3 days) was also evaluated. However, increasing time of exposure to organic acid sanitizer did not increase sanitizing effectiveness and led to progressive damage of spinach leaves.     

Effect of moderate electric fields on salt diffusion into vegetable tissue

Although salt infusion, through blanching or marinating, has been known to successfully increase the electrical conductivity of solid food components, pretreatment times are long, and in most cases, equilibration between the solid and the liquid is still incomplete. A faster pretreatment method is needed.     

Study of oxygen permeability and flame retardancy properties of biodegradable polymethylmethacrylate/starch composites

Polymethylmethacrylate/starch (PMMA/starch) composites were prepared by emulsion polymerization method using potassium persulphate (KPS) as the radical initiator. The interaction of starch with polymethylmethacrylate was evidenced by ultraviolet–visible (UV–visible) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The structure of PMMA/starch composite was studied by X‐ray diffraction (XRD) study and Scanning Electron Microscopy (SEM). The thermal properties of starch, PMMA/starch composites were compared with the virgin PMMA sample. The PMMA/starch composites were found to be flame retardant material from the measurement of limiting oxygen index (LOI) of samples. The biodegradability of the PMMA/starch composites were studied by active sludge water and it was found that degradability of composites increases with increasing time interval. The oxygen permeability of PMMA/starch composites was substantially decreased as compared to virgin PMMA. The reduction of oxygen permeability of the PMMA/starch composites may enable the materials applicable in packaging industries. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Microstructures using RF sputtered PSG film as a sacrificial layer in surface micromachining

In this paper, we explore RF magnetron sputtered Phosphor-silicate-glass (PSG) film as a sacrificial layer in surface micromachining technology. For this purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P₂O₅ and SiO₂ powders. The PSG films were prepared in a RF (13·56 MHz) magnetron sputtering system at 300 watt RF power, 20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. Microstructures of sputtered silicon dioxide film were fabricated using sputtered PSG film as sacrificial layer in surface micromachining process.     

DNA extraction and Escherichia coli quantification of anaerobically digested biosolids using the competitive touchdown PCR method

Accurate enumeration of indicator organisms such as Escherichia coli is important for assessing the safety of water and wastewater samples. Recent research has shown that E. coli can enter a viable but non-culturable state; therefore, traditional cultivation methods could potentially underestimate the quantities of the organisms. The goals of the research were to develop and verify a DNA extraction protocol and a quantitative polymerase chained reaction (PCR) method for E. coli enumeration in digested biosolids. A solvent-based DNA extraction protocol with extensive cell lysis recovered approximately 78-84% of spiked DNA. In comparison, a commercial kit only recovered 28-42% of DNA, likely from inefficient cell lysis. The developed competitive touchdown PCR (cPCR) method for E. coli enumeration was comparable to both real-time PCR (rt-PCR) and cultivation methods with sensitivity of approximately 50,000-500,000 E. coli per gram dry solids (DS), which is suitable for Class B biosolids monitoring in the US and "conventional" biosolids in the European Union. The cPCR protocol provides a less expensive alternative than the rt-PCR as a culturing independent method for enumerating E. coli.     

Fabrication and characterization of 7075 Al alloy reinforced with SiC particulates

7075 aluminum (Al) alloy as matrix and silicon carbide (SiC) as reinforcement has been identified since it has potential applications in aircraft and space industries because of lower weight to strength ratio, high wear resistance and creep resistance. Thorough investigations about the microstructure and characterization of Al alloy/SiC composite are needed so that metal matrix composites (MMCs) fabricated for aircraft and space industries are defect free and have sound microstructure. Objective of this research work are the fabrication and microstructural investigations of AA7075–SiCp MMCs. 7075 Al alloy is reinforced with 10 and 15 wt.% SiCp of size 20–40 μm by stir casting process. The resulting as-cast composite structures are analyzed using scanning electron microscopy, X-ray diffraction (XRD), differential thermal analysis, and electron probe microscopic analysis (EPMA). SiCp distribution and interaction with 7075 Al alloy matrix is studied. The 7075 Al alloy–SiCp composite microstructure showed excellent SiCp distribution into 7075 Al alloy matrix. In addition to this, no evidence of secondary chemical reactions is observed in XRD and EPMA analysis. Decomposition step in derivative thermogravimetric curve is seen at temperature of 1,257, 1,210, and 1,256 °C for 7075 Al alloy, AA7075/10 wt.%/SiCp (20–40 μm) and AA7075/15 wt.%/SiCp (20–40 μm) composites, respectively. So, these composites can be successfully used for applications where temperature does not exceed beyond 1,250 °C.     

Reactivation and growth of non-culturable indicator bacteria in anaerobically digested biosolids after centrifuge dewatering

Recent literature has reported that high concentrations of indicator bacteria such as fecal coliforms (FCs) were measured in anaerobically digested sludges immediately after dewatering even though low concentrations were measured prior to dewatering. This research hypothesized that the indicator bacteria can enter a non-culturable state during digestion, and are reactivated during centrifuge dewatering. Reactivation is defined as restoration of culturability. To examine this hypothesis, a quantitative polymerase chain reaction (qPCR) method was developed to enumerate Escherichia coli, a member of the FC group, during different phases of digestion and dewatering. For thermophilic digestion, the density of E. coli measured by qPCR could be five orders of magnitude greater than the density measured by standard culturing methods (SCMs), which is indicative of non-culturable bacteria. For mesophilic digestion, qPCR enumerated up to about one order of magnitude more E. coli than the SCMs. After centrifuge dewatering, the non-culturable organisms could be reactivated such that they are enumerated by SCMs, and the conditions in the cake allowed rapid growth of FCs and E. coli during cake storage.     

Role of Nano-YbF3-Treated Carbon Fabric on Improving Abrasive Wear Performance of Polyetherimide Composites

A method for surface treatment of carbon fabric with nano-particles of rare earth salt (ytterbium fluoride–YbF₃) was tried first time in the authors’ laboratory to enhance the fiber–matrix interface, and has been reported here. In this article authors have reported on the performance evaluation of composites developed from the four fabrics treated with various doses viz. 0, 0.1, 0.3, and 0.5 wt% of YbF₃. The abrasive wear performance of these composites was evaluated by abrading the composites against silicon carbide abrasive paper under varying loads. The treated fabric composites exhibited lower coefficient of friction and higher wear resistance as compared with untreated fabric composite. A linear correlation between ILSS (interlaminar shear strength) and wear resistance was observed. Both were the highest for 0.3% dosing of fabric. Since it was also desirable to compare the efficiency of this novel method of treatment of carbon fibers with conventional one, a few results of composites with plasma-treated carbon fabric were compared with the nano-particle-treated fabric composites. It was concluded that the latest method improved the abrasive wear resistance of composites almost two times more than the plasma-treated composites. Fiber–matrix interface was strengthened because of the treatment as observed from SEM studies, ILSS, and matrix pick-up studies. Increased roughness of fiber surface was observed in topographical analysis by SEM. Effect of treatment on fiber was also observed by adhesion test and fiber tow tension test. SEM studies of worn surfaces were performed to understand wear mechanisms.     

Influence of adjuncts as a debittering aids in encountering the bitterness developed in cheese slurry during accelerated ripening

An attempt was made to accelerate the flavour development in cheese base with the help of exogenous proteolytic and lipolytic enzymes (1:1 proportion, each at the rate of 0.025% by weight of cheese‐base) and ripening at elevated temperatures (i.e. 20 ± 1 °C) for up to 12 days. To counter the bitterness developed, adjunct cultures were used: viable or attenuated (freeze‐shocked or heat shocked). Study of biochemical characteristics, electrophoretic pattern and sensory evaluation of the product were carried out. An acceptable enzyme‐modified, lightly salted cheese base was obtained using 0.025% each of proteolytic and lipolytic enzymes, along with 5% starter culture and adjuncts followed by ripening up to 12 days. Freeze‐shocked adjunct Lactobacillus helveticus produced enzyme‐modified cheese base with no detectable bitterness. The usage of exogenous enzymes, temperature of ripening, ripening period and interactions amongst these parameters had significant (P < 0.01) influence on all of the biochemical characteristics monitored.