Fabrication of various micropatterns by maskless micro-electrochemical texturing

In this paper, an innovative and alternative concept of maskless micro-electrochemical texturing is exploited for the fabrication of simple and complex micropatterns. In this process, the tool is masked incorporated with the textured patterns and the workpiece has no mask. This research study concentrates on generation of simple micropattern, i.e. linear micropattern, and complex micropattern, i.e. cascade micropattern using maskless micro-electrochemical texturing method without repeated use of photolithography process. A single masked patterned tool with SU-8 2150 mask can produce many high-quality simple and complex micropatterns economically using this method. A well-planned experimental set-up consisting of electrochemical micromachining (EMM) cell, electrode fixtures, electrical connections and constricted vertical cross-flow electrolyte system has been designed and developed indigenously for carrying out the experiments. Influences of major influencing parameters, i.e. machining voltage, interelectrode gap, flow rate and machining time, are investigated on width overcut and machining depth of micropatterns. For higher machining accuracy, controlled depth and lower standard deviations, machining with lower machining time, lower voltage, lower interelectrode gap and higher flow rate is recommended. From the detailed experimental investigation, the best parametric combination are voltage of 8 V, duty ratio of 30%, pulse frequency of 15 kHz, electrolyte of NaCl (0.34 M) + NaNO3 (0.23 M), flow rate of 5.35 m3/h, interelectrode gap of 50 µm and machining time of 40 s

Molecular biology of tubulin: its interaction with drugs and genomic organization

Microtubules are ubiquitous cellular structures found in eukaryotic organisms and responsible for a variety of functions. These functions include mitosis, motility, cytoskeletal architecture, intracellular transport and secretion. The major structural component of microtubules is tubulin, a dimeric protein molecule consisting of two similar but nonidentical subunits (α and β) each of about molecular weight 55,000. With the introduction of radioactive colchicine for the first time it has been reported that colchicine binds specifically to tubulin. At this point microtubule research stepped up to a new era linking microtubules with other spindle poisons which are structurally diverse as well as binding at different sites on to the tubulin heterodimer. These antimicrotubular agents have already provided valuable information regarding microtubule-mediated cellular functions and its association and dissociation phenomena. Tubulins appear to be conserved proteins based onin vitro copolymerization and comigration on polyacrylamide gel electrophoretic properties. Further, amino acid sequences of both α and β subunits from a variety of sources also appear to be mostly conserved. The evolutionary conservation of tubulin genes is highly reflected at the nucleic acid level as well. The estimation of the number of genes for tubulin and their organization in a variety of organisms have opened up a new dimension to microtubule and tubulin research. The multigene family for tubulins comprising also pseudogenes is suggestive that more than one gene for each α and β tubulin is functional in the cell. Therefore, it has been speculated that different tubulin gene products contribute to functionally different microtubules at specific stages in cell cycle and cell growth. Heterogeneity in both α and β tubulins has already been established during different stages of development of the cell. Obviously, it reflects that tubulin genes are highly regulated and this regulation might be at the transcriptional and/or translational level. Whatever is the actual control mechanism it appears that cells can detect an enhanced pool of depolymerized subunits and a rapid and specific control in tubulin gene expression at the transcriptional and/or post transcriptional level does occur

Applications of optimization techniques for parametric analysis of non-traditional machining processes: A Review

The constrained applications of conventional machining processes in generating complex shape ge-ometries with the desired degree of tolerance and surface finish in various advanced engineering materials are being gradually compensated by the non-traditional machining (NTM) processes. These NTM processes usually have higher procurement, maintenance, operating and tooling cost. Hence, in order to attain their maximum machining performance, they are usually operated at their optimal or near optimal parametric settings which can easily be determined by the application of dif-ferent optimization techniques. In this paper, 133 international research papers published during 2012-16 on parametric optimization of NTM processes are extensively reviewed to have an idea on the selected process parameters, observed responses, work materials machined and optimization techniques employed in those processes while generating varying part geometries for their industrial use. It is observed that electro discharge machining is the mostly employed NTM process, applied voltage is the identified process parameter with maximum importance, surface roughness and material removal rate are the two maximally preferred responses, different steel grades are the mostly machined work materials and grey relational analysis is the most popular tool utilized for para-metric optimization of NTM processes. These observations would help the process engineers to attain the machining performance of the NTM processes at their fullest extents for different work material and shape feature combinations

Integrative analysis of large scale expression profiles reveals core transcriptional response and coordination between multiple cellular processes in a cyanobacterium

<p>Abstract</p> <p>Background</p> <p>Cyanobacteria are the only known prokaryotes capable of oxygenic photosynthesis. They play significant roles in global biogeochemical cycles and carbon sequestration, and have recently been recognized as potential vehicles for production of renewable biofuels. <it>Synechocystis </it>sp. PCC 6803 has been extensively used as a model organism for cyanobacterial studies. DNA microarray studies in <it>Synechocystis </it>have shown varying degrees of transcriptome reprogramming under altered environmental conditions. However, it is not clear from published work how transcriptome reprogramming affects pre-existing networks of fine-tuned cellular processes.</p> <p>Results</p> <p>We have integrated 163 transcriptome data sets generated in response to numerous environmental and genetic perturbations in <it>Synechocystis</it>. Our analyses show that a large number of genes, defined as the core transcriptional response (CTR), are commonly regulated under most perturbations. The CTR contains nearly 12% of <it>Synechocystis </it>genes found on its chromosome. The majority of genes in the CTR are involved in photosynthesis, translation, energy metabolism and stress protection. Our results indicate that a large number of differentially regulated genes identified in most reported studies in <it>Synechocystis </it>under different perturbations are associated with the general stress response. We also find that a majority of genes in the CTR are coregulated with 25 regulatory genes. Some of these regulatory genes have been implicated in cellular responses to oxidative stress, suggesting that reactive oxygen species are involved in the regulation of the CTR. A Bayesian network, based on the regulation of various KEGG pathways determined from the expression patterns of their associated genes, has revealed new insights into the coordination between different cellular processes.</p> <p>Conclusion</p> <p>We provide here the first integrative analysis of transcriptome data sets generated in a cyanobacterium. This compilation of data sets is a valuable resource to researchers for all cyanobacterial gene expression related queries. Importantly, our analysis provides a global description of transcriptional reprogramming under different perturbations and a basic framework to understand the strategies of cellular adaptations in <it>Synechocystis</it>.</p

Modelling and optimization of Nd:YAG laser micro-turning process during machining of aluminum oxide (Al

Pulsed Nd:YAG laser has high intensity and high quality beam characteristics, which can be used to produce micro-grooves and micro-turning surface on advanced engineering ceramics. The present research attempts to develop mathematical models by using response surface methodology approach for correlating the machining process parameters and the process responses during laser micro-turning of aluminum oxide (Al2O3) ceramics. The process parameters such as laser average power, pulse frequency, workpiece rotating speed, assist air pressure and Y feed rate were varied during experimentation. The rotatable central composite design experimental planning has been used to design the experimentation. The performance measures considered are surface roughness (Ra) and micro-turning depth deviation. Multi-objective optimization has been carried out for achieving the desired surface roughness as well as minimum depth deviation during laser micro-turning operation. Further, an artificial neural network (ANN) model has been developed to predict the process criteria. Levenberg-Marquadt training algorithm is used for multilayer feed forward backpropagation neural network. The developed ANN model has 5-10-2 feed forward network. There are 5 neurons in the input layer, 10 neurons in the hidden layer and 2 neurons in the output layers corresponding to two output responses, respectively. The developed ANN model has been validated using data obtained by conducting additional set of experiments. It was found that the developed ANN model can predict the process criteria more accurately than response surface methodology (RSM) based developed models

Kinetic and thermodynamic analysis of taxol-induced polymerization of purified tubulin

The kinetic and thermodynamic behavior of in vitro taxol-induced polymerization of purified tubulin has been studied. The assembly of tubulin initiated by taxol has a critical concentration of 0.1 mg/mL at 37 &#176;C and consists of two consecutive pseudo first-order processes, a fast phase followed by a slow phase. The rate constants of the fast and slow phase polymerizations increase linearly with increasing tubulin concentration. This implies that the polymerization is a true pseudo first-order process. The In (1/t<SUB>0.5</SUB>) of polymerization for both fast and slow phases follows a linear function with ln [tubulin] fulfilling one of the criteria of condensation polymerization mechanism. From the Arrhenius plot, the temperature dependence of the rate of tubulin polymerization in the presence of taxol is biphasic. The apparent activation enthalpies for the overall polymerization reaction are 13.0 and 50.8 kcal/mol (1 cal = 4.1868 J), respectively, above and below 26 &#176;C. The apparent activation enthalpies for the elongation reaction have also been determined. The values are 11.6 and 28.4 kcal/mol above and below 28 &#176;C. The temperature dependence of the equilibrium constants as revealed by the van't Hoff plot is also biphasic. The standard enthalpy and entropy values are &#916;H&#176; = 7.4 and 22.5 kcal/mol above and below 30 &#176;C, and &#916;S&#176; = 50.3 and 101.0 cal/(deg&#183;mol), at high and low temperatures, respectively. This suggests that the taxol-induced assembly of purified tubulin is a process driven by the effect of entropy

A Systems-Level Analysis of the Effects of Light Quality on the Metabolism of a Cyanobacterium1[W][OA]

Photosynthetic organisms experience changes in light quantity and light quality in their natural habitat. In response to changes in light quality, these organisms redistribute excitation energy and adjust photosystem stoichiometry to maximize the utilization of available light energy. However, the response of other cellular processes to changes in light quality is mostly unknown. Here, we report a systematic investigation into the adaptation of cellular processes in Synechocystis species PCC 6803 to light that preferentially excites either photosystem II or photosystem I. We find that preferential excitation of photosystem II and photosystem I induces massive reprogramming of the Synechocystis transcriptome. The rewiring of cellular processes begins as soon as Synechocystis senses the imbalance in the excitation of reaction centers. We find that Synechocystis utilizes the cyclic photosynthetic electron transport chain for ATP generation and a major part of the respiratory pathway to generate reducing equivalents and carbon skeletons during preferential excitation of photosystem I. In contrast, cytochrome c oxidase and photosystem I act as terminal components of the photosynthetic electron transport chain to produce sufficient ATP and limited amounts of NADPH and reduced ferredoxin during preferential excitation of photosystem II. To overcome the shortage of NADPH and reduced ferredoxin, Synechocystis preferentially activates transporters and acquisition pathways to assimilate ammonia, urea, and arginine over nitrate as a nitrogen source. This study provides a systematic analysis of cellular processes in cyanobacteria in response to preferential excitation and shows that the cyanobacterial cell undergoes significant adjustment of cellular processes, many of which were previously unknown

Integration of Carbon and Nitrogen Metabolism with Energy Production Is Crucial to Light Acclimation in the Cyanobacterium Synechocystis1[W][OA]

Light drives the production of chemical energy and reducing equivalents in photosynthetic organisms required for the assimilation of essential nutrients. This process also generates strong oxidants and reductants that can be damaging to the cellular processes, especially during absorption of excess excitation energy. Cyanobacteria, like other oxygenic photosynthetic organisms, respond to increases in the excitation energy, such as during exposure of cells to high light (HL) by the reduction of antenna size and photosystem content. However, the mechanism of how Synechocystis sp. PCC 6803, a cyanobacterium, maintains redox homeostasis and coordinates various metabolic processes under HL stress remains poorly understood. In this study, we have utilized time series transcriptome data to elucidate the global responses of Synechocystis to HL. Identification of differentially regulated genes involved in the regulation, protection, and maintenance of redox homeostasis has offered important insights into the optimized response of Synechocystis to HL. Our results indicate a comprehensive integrated homeostatic interaction between energy production (photosynthesis) and energy consumption (assimilation of carbon and nitrogen). In addition, measurements of physiological parameters under different growth conditions showed that integration between the two processes is not a consequence of limitations in the external carbon and nitrogen levels available to the cells. We have also discovered the existence of a novel glycosylation pathway, to date known as an important nutrient sensor only in eukaryotes. Up-regulation of a gene encoding the rate-limiting enzyme in the hexosamine pathway suggests a regulatory role for protein glycosylation in Synechocystis under HL