Development of Electrochemical Micro Machining

The machining of materials on micrometer and sub-micrometer scale is considered the technology of the future. The current techniques for micro manufacturing mostly are silicon based. These manufacturing techniques are not suitable for use in demanding applications like aerospace and biomedical industries. Micro electrochemical machining (μECM) removes material while holding micron tolerances and μECM can machine hard metals and alloys. This study aims at developing a novel μECM utilizing high frequency voltage pulses and closed loop control. Stainless steel SS-316L and copper alloy CA-173 were chosen as the workpiece materials. A model was developed for material removal rate. The research studied the effect of various parameters such as voltage, frequency, pulse ON/OFF time, and delay between pulses of the stepper motor on the machined profiles. Experimental data on small drilled holes agreed with theoretical models within 10%. Micro burrs can be effectively removed by optimal μECM. A sacrificial layer helped to improve the hole profile since it reduced 43% of corner rounding

Electrochemical Micro Machining: A Case Study for Synergistic International Industry - Academia Collaboration

Micro fabrication is generally confined to silicon-based processes for microelectronic applications. The advent of micro electromechanical systems (MEMS) using silicon and silicon based processes has opened up a new basis for micro fabrication technology, but the applications have been limited due to the brittle nature of silicon. Novel technologies have been sought for non-silicon micro components and systems. The electrochemical micro machining (µECM) is standing out among other solutions. An international group comprised of industry and academic institutes in Mexico and USA was formed to provide synergistic effort in developing this new technology. The funding came from the involved companies, National Science Foundation, National Consortium of Science and Technology (CONACyT, Mexico), and Texas A&M University. Both graduate and undergraduate students are involved in this research and educational project. Some research objectives have been achieved by dividing an objective into manageable laboratory projects that can be completed by undergraduate students in a few weeks. The anodic dissolution µECM process effectively forms and shapes micro components from any conductive material. Unlike classical ECM technology, the novel µECM utilizes very high frequency pulses and proprietary electrode shapes/motions to remove materials at the micro or nano scales, and can mass-produce micro components with exceptional quality and surface integrity. A theoretical model is developed which agrees with experimental data for 316L stainless steel and copper beryllium alloy. The environmentally friendly technology shows promise as a high-resolution production manufacturing process with excellent throughput and repeatability

Chapter 13 - Knock, knock-let the bacteria in: enzymatic potential of plant associated bacteria

Beneficial bacteria associated with plants have evolved for thousands of years together with their hosts to an intricate communication system that allow the recognition and penetration into plant tissues without harming them. Within the molecules involved in this communication system, the enzymes produced by the bacteria have an important role and some of them have been shown essential at first steps of plant colonization. In this chapter, we analyze the implication of some of the most well-known enzymes related to plant probiotic bacteria and their hosts, the steps at which these enzymes participate to allow the recognition by the plants and the bacterial penetration into their inner tissues. Between these enzymes we will examine the importance of (i) cellulases, produced by important plant growth promoters to penetrate plant tissues; (ii) chitinases, implicated in the defense of the plant against fungi and recognition by the plants; (iii) lectins, implicated in the attachment and first recognition steps; (iv) pectinases, which are usually expressed early during infection, in the penetration steps; and (v) xylanases, implicated in the recycling at senescence, amongst others. The upregulated expression of some of these enzymes in plant growth promoting bacteria was surprising at first, as they would be expected in pathogens, not in mutualistic microorganisms. However, as more data are available, the implication of hydrolytic enzymes in beneficial plant colonization is become clear

Path and Ridge Regression Analysis of Seed Yield and Seed Yield Components of Russian Wildrye (Psathyrostachys juncea Nevski) under Field Conditions

The correlations among seed yield components, and their direct and indirect effects on the seed yield (Z) of Russina wildrye (Psathyrostachys juncea Nevski) were investigated. The seed yield components: fertile tillers m-2 (Y1), spikelets per fertile tillers (Y2), florets per spikelet- (Y3), seed numbers per spikelet (Y4) and seed weight (Y5) were counted and the Z were determined in field experiments from 2003 to 2006 via big sample size. Y1 was the most important seed yield component describing the Z and Y2 was the least. The total direct effects of the Y1, Y3 and Y5 to the Z were positive while Y4 and Y2 were weakly negative. The total effects (directs plus indirects) of the components were positively contributed to the Z by path analyses. The seed yield components Y1, Y2, Y4 and Y5 were significantly (P<0.001) correlated with the Z for 4 years totally, while in the individual years, Y2 were not significant correlated with Y3, Y4 and Y5 by Peason correlation analyses in the five components in the plant seed production. Therefore, selection for high seed yield through direct selection for large Y1, Y2 and Y3 would be effective for breeding programs in grasses. Furthermore, it is the most important that, via ridge regression, a steady algorithm model between Z and the five yield components was founded, which can be closely estimated the seed yield via the components

A review of phase change heat transfer in shape-stabilized phase change materials (ss-PCMs) based on porous supports for thermal energy storage

Latent heat thermal energy storage (LHTES) uses phase change materials (PCMs) to store and release heat, and can effectively address the mismatch between energy supply and demand. However, it suffers from low thermal conductivity and the leakage problem. One of the solutions is integrating porous supports and PCMs to fabricate shape-stabilized phase change materials (ss-PCMs). The phase change heat transfer in porous ss-PCMs is of fundamental importance for determining thermal-fluidic behaviours and evaluating LHTES system performance. This paper reviews the recent experimental and numerical investigations on phase change heat transfer in porous ss-PCMs. Materials, methods, apparatuses and significant outcomes are included in the section of experimental studies and it is found that paraffin and metal foam are the most used PCM and porous support respectively in the current researches. Numerical advances are reviewed from the aspect of different simulation methods. Compared to representative elementary volume (REV)-scale simulation, the pore-scale simulation can provide extra flow and heat transfer characteristics in pores, exhibiting great potential for the simulation of mesoporous, microporous and hierarchical porous materials. Moreover, there exists a research gap between phase change heat transfer and material preparation. Finally, this review outlooks the future research topics of phase change heat transfer in porous ss-PCMs

Purification of an alpha amylase from Aspergillus flavus NSH9 and molecular characterization of its nucleotide gene sequence

In this study, an alpha-amylase enzyme from a locally isolated Aspergillus flavus NSH9 was purified and characterized. The extracellular α-amylase was purified by ammonium sulfate precipitation and anion-exchange chromatography at a final yield of 2.55-fold and recovery of 11.73%. The molecular mass of the purified α-amylase was estimated to be 54 kDa using SDS-PAGE and the enzyme exhibited optimal catalytic activity at pH 5.0 and temperature of 50 °C. The enzyme was also thermally stable at 50 °C, with 87% residual activity after 60 min. As a metalloenzymes containing calcium, the purified α-amylase showed significantly increased enzyme activity in the presence of Ca2+ ions. Further gene isolation and characterization shows that the α-amylase gene of A. flavus NSH9 contained eight introns and an open reading frame that encodes for 499 amino acids with the first 21 amino acids presumed to be a signal peptide. Analysis of the deduced peptide sequence showed the presence of three conserved catalytic residues of α-amylase, two Ca2+-binding sites, seven conserved peptide sequences, and several other properties that indicates the protein belongs to glycosyl hydrolase family 13 capable of acting on α-1,4-bonds only. Based on sequence similarity, the deduced peptide sequence of A. flavus NSH9 α-amylase was also found to carry two potential surface/secondary-binding site (SBS) residues (Trp 237 and Tyr 409) that might be playing crucial roles in both the enzyme activity and also the binding of starch granules. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature

Efficacy of Commercial Phage Based Treatment as a Control Strategy against Listeria Spp. and Effect of Host Characteristics on Lytic Capacity

Listeria monocytogenes can persist on food contact (FCS) and non-food contact surfaces (NFCS) and enter the food continuum by cross-contamination. Meat processing facilities are a known source of Listeria spp. contamination. Specificity and safety of use render bacteriophages suitable to control Listeria spp. in foods and food environments. Previous research has shown that host characteristics can affect lytic efficacy of bacteriophages. This study focuses on evaluating how phenotypic and genotypic characteristics of Listeria hosts influence lytic capacity of a commercial listeriophage cocktail in vitro. We also investigated the efficacy of listeriophage as a biocontrol strategy for Listeria spp. on non-food contact surfaces (NFCS) in a meat processing facility. In vitro lytic capacity was tested quantitatively using spot assay for 475 Listeria spp. isolates with varied phenotypic (attachment capacity, sanitizer tolerance) and genotypic (PFGE) characteristics. Lytic capacity was measured quantitatively for 55 isolates by monitoring growth of L. monocytogenes cultures with and without listeriophage over time and enumerating bacterial counts after 4h. Fifty-nine NFCS were tested in a meat processing facility for Listeria spp. weekly for three weeks. Each Listeria spp. positive site was treated with commercial phage then assessed for reduction in Listeria spp. Although enhanced attachment capacity and sanitizer tolerance of Listeria spp. isolates did not significantly (p\u3e0.05) influence phage susceptibility in vitro; history of persistence, incubation temperature, and concentration of listeriophage treatment were critical. Quantitatively, listeriophage treatment significantly (p\u3c0.001) affected growth and reduced bacterial counts of Listeria spp. compared to control samples. A total of 15, 21, and 14 sites were positive for Listeria spp. at weeks one, two, and three, respectively. Post-treatment Listeria spp. were detected in 12/23 sites, and numerically reduced in 4/12 sites by an average of 2.1 log CFU/sponge. Among the isolates subjected to spot assay, 60% strains showed low susceptibility to listeriophage, 36% showed moderate lysis, and 4% isolates showed confluent lysis by listeriophage. This study illustrates influence of bacterial host characteristics on lytic efficacy of listeriophage treatment. Further, we have preliminary evidence for listeriophage as a potential control strategy in food environments

Volatility, flexibility, and the multinational enterprise

Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, 1992.Includes bibliographical references.by Arun Sundarram Muralidhar.Ph.D

On thermal conductivity of micro‐and nanocellular polymer foams

Many theoretical and empirical models exist to predict the effective thermal conductivity of polymer foams. However, most of the models only consider the effect of porosity, while the pore size effect is ignored. The objective of this study is to understand the effect of pore size on the thermal conductivity of polymer foams, especially when it reduces to the micro and nanometer scales. A wide range of pore sizes from 1 nm to 1 mm were studied in conjunction with the porosity effect using finite element analysis and molecular dynamics simulation methods. Experimental data was used to validate the modeling result. It is shown that the pore size has significant effect on thermal conductivity, even for microcellular and conventional foams. The contribution of heat conduction through air is negligible when pore size is reduced to the micrometer scale. The extremely low thermal conductivity of nanofoams is attributed to extensive diffusive scattering of heat carriers in the solid phase of polymer matrix, instead of air. This study provides quantitative understanding of the pore size effect on thermal conductivity of polymer foams. It is also shown that polyetherimide (PEI) nanofoams could have a thermal conductivity as low as 0.015 W/m-K. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineer

Fabrication and characterization of open celled micro and nano foams

textOpen celled micro and nano foams fabricated from polymers and metals have attracted tremendous attention in the recent past because of their applications in numerous areas such as catalyst carriers, filtration media, ion exchange membranes and tissue engineering scaffolds. In this study open celled polymer micro- and nano foams with controllable pore size and porosity were fabricated via solid state foaming of immiscible blends. The polymer foams were used as templates for fabricating nickel foams using an ethanol based electroless plating process. Thermal conductivity of micro- and nano foams was studied as a function of pore size and porosity using finite element and molecular dynamics based models. The effect of pore size and porosity on performance of phase change material infiltrated metal foams for thermal management was investigated via numerical models. Open celled micro foams were fabricated via solid state foaming of ethylene acrylic acid (EAA) and polystyrene (PS) co-continuous blends. Blending temperature was the main parameters affecting the formation of co-continuous structure. Gas saturation and foaming studies were performed to determine ideal processing conditions for the blend. The results indicated that saturation pressure and foaming temperature were major process parameters determining the porosity of the foamed samples. Open celled polymer templates were obtained by selective extraction of PS phase using dichloromethane (DCM). Foaming resulted in faster extraction of PS and also in a higher porosity. Open celled nano foams were fabricated via solid state foaming of polyetherimide (PEI) and polyethersulfone (PES). The effect of process parameters namely saturation pressure and temperature, desorption time, and foaming temperature and time on porosity and pore size was studied. A high gas concentration and foaming temperature were required to obtain nano pore-sized foams. Throughout the cross section there existed regions with varying pore size and porosity and solid skins at the surface regions of the foam. A solvent surface dissolution process using dimethylformamide (DMF) was employed to access the internal porous structure. Micro- and nano cellular nickel foams were fabricated from EAA and PES templates via electroless plating. The structure of the nickel foams was an inverse of the polymer templates. Ethanol based electroless plating solutions were used to ensure infiltration into the porous structure because of the small pore sizes. Finite element and molecular dynamics based models were developed to predict thermal conductivity of polymer foams as a function of pore size and porosity. Pore sizes ranging from 1 nm to 1 mm were studied. Models were partially validated using experimental data. The results showed that pore size has significant effect on thermal conductivity even for microcellular and conventional foams. When the pore size is reduced to the nanometer scale, the thermal conductivity of the nano foam dramatically reduces and the value could be lower than that of air for certain porosity levels. The extremely low thermal conductivity of polymer nanofoams is possibly due to increased phonon-phonon scattering in the solid phases of the polymer matrix in addition to low thermal conductivity of gas trapped in nano sized pores. Finite element based models were also developed to study the effect of pore size and porosity on performance of phase change material infiltrated metal foams for thermal management applications. The results showed that foams with smaller pore sizes can delay the temperature rise of the heat source for an extended period of time by rapidly dissipating heat in the phase change material. The lower temperatures resulting from the use of a smaller pore size metal foam could significantly increase the lifetime of IC chips.Mechanical Engineerin