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  • Author: K. Sujatha x
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Abstract

This paper deals with design, simulation, fabrication, analysis of mixing efficiency and thin film bonding stability of the micromixer devices with different flow rates used for lab on chip applications. The objective of the present study is to achieve complete mixing with low flow rate and less pressure drop in low cost polymer microfluidic devices. This paper emphasis the design, simulation and fabrication of straight channel micromixer, serpentine channel micromixer with and without quadrant shaped grooves to study the mixing behavior by the effect of structural dimensions of the microfluidic channel at different flow rates. The designed micromixers were tested with varying rates of flow such as 1, 10, 25, 50, 75 and 100 µL/min.

Abstract

We have studied the variation of diffuse ultraviolet (UV) radiation in the northern part of the Orion constellation using a set of eight areas of the GALEX All-Sky Imaging Survey in the far and near UV. Different components of diffuse UV radiation, like dust scattered emission and H2 fluorescence, were quantified and separated after removing the point sources and the foreground emission in each of the fields. Then the dependence of the individual UV components on the infrared 100 μm dust emission was studied. We did not find any positive correlation between the diffuse-UV and IR-100 micron intensities, probably due to the high optical depth of the region or the entire dust column not contributing to the diffuse UV radiation. However, in the far UV we noticed the presence of an excess emission in addition to the dust scattered radiation, which is clearly absent in the near UV. This excess emission, identified as the H2 fluorescence, is produced by the Trapezium stars in the surrounding molecular clouds. We also compare our results with those of previous studies in the region, based on Far Ultraviolet Spectroscopic Explorer (FUSE) observations.

Abstract

This paper deals with the design, analysis and optimization of micro-mixer for fluids having very low diffusivity (in the order of 10−12 m2/s) to be used in Lab on Chip (LOC) for medical diagnosis. As flow is laminar and the cross-sectional area is in microscale, the viscous forces are strong causing the fluids to be transported in streamline with minimum diffusion. The main objective in designing a micro mixer is to achieve complete mixing with minimum channel length and pressure drop. In this work a passive micro mixer with two inlets and one outlet (Y shaped passive micro mixer) with obstacles in various shapes and sizes is modelled, to study the effect of mixing. After a CFD analysis, Analysis of variance (ANOVA) of 3K design with 3 parameters as well as a 2K design with 4 parameters was performed to study the effect of parameters on mixing index (mixing length) and pressure loss. There is a negative correlation between the response obtained for mixing length and pressure loss while varying the parameters. This makes it difficult to predict the optimum configuration. Taguchi method is used to obtain an optimum configuration to overcome this negative correlatiozn.

The extraction of plutonium from tissue paper matrix was carried out using supercritical carbon dioxide (Sc-CO2). The removal of plutonium was also studied from other matrices such as teflon, glass and stainless steel. Initial experiments were carried out under subcritical conditions. Supercritical extraction conditions were also employed in some experiments for the recovery of plutonium from tissue paper matrix. Complete extraction of Pu(III) as well as Pu(IV) in their nitrate form from tissue paper was achieved for the first time using supercritical carbon dioxide modified with n-octyl(phenyl)-N,N-diisobutyl carbamoylmethyl phosphine oxide (φCMPO) in methanol. Pu(IV) was also completely removed from other matrices such as teflon, stainless steel and glass. Studies on the extraction of Am(III) using supercritical carbon dioxide modified with CMPO in methanol resulted in its complete recovery from tissue paper.

Abstract

A novel method has been developed for the controlled delivery of various ligands including solid extractants using supercritical carbon dioxide (Sc-CO2). A ligand delivery vessel with a restricted geometry where its inlet and outlet are located beside each other, accomplished the task of the controlled delivery of ligands. The proposed method eliminates the usage of modifier solvent such as methanol for the delivery of various ligands during the supercritical fluid extraction of metal ions. Using neat Sc-CO2, the delivery profiles for the various ligands such as octyl(phenyl)-N,N-diisobutylcarbamoylmethyl-phosphineoxide (CMPO), tri-n-butyl phosphate (TBP), tri-n-octyl phosphine oxide (TOPO), theonyltrifluroacetone (TTA) and di(2-ethylhexyl)isobutyramide (D2EHIBA) were established. The delivery profiles were optimised by investigating the influence of various extraction parameters such as ligand delivery vessel geometry, temperature, pressure, flow rate of Sc-CO2 and ligand content. Applications of these ligand delivery modes were demonstrated for the supercritical fluid extraction of uranium from tissue paper matrix and preferential extraction of uranium over thorium. These results are compared with the extraction studies involving methanol or hexane modifier under similar experimental conditions. The extraction of neodymium nitrate was also demonstrated using modifier free delivery mode.

SUMMARY

The cultural characteristics and histochemical variations following infection with Alternaria helianthi was studied in six wild Helianthus species of three ploidy levels (diploid, tetraploid and hexaploid) possessing different degrees of resistance to the pathogen and in cultivated sunflower (H. annuus cv. CO-4, susceptible check). Of these, the species H. occidentalis and H. tuberosus were found to be highly resistant while H. hirsutus was moderately resistant. Media supplemented with leaf extracts of wild species, with the exception of H. grosseserratus, supported less growth and sporulation of A. helianthi than media supplemented with leaf extract of cultivated sunflower. Reduced infectivity of the pathogen was recorded when grown on leaf extract media of H. occidentalis, H. hirsutus and H. tuberosus. Furthermore, abnormalities in the shape of conidia were noticed on supplemented media with leaf extracts of H. occidentalis and H. tuberosus. RAPD analysis of the fungal DNA isolated from the pathogen grown on leaf extract media of cultivated and wild Helianthus species revealed no polymorphism. Histochemical studies showed restriction of the pathogen to epidermal cells in resistant wild sunflowers as well as an increased accumulation of phenols.

in Helia

SUMMARY

The biochemical basis of resistance to the leaf spot/blight pathogen A. helianthi was compared in six wild Helianthus species, possessing three ploidy levels (diploid, tetraploid and hexaploid) and different degrees of resistance to A. helianthi, and cultivated sunflower (H. annuus cv. CO-4, susceptible check) in terms of sugar, phenols and isozymes of peroxidase, polyphenol oxidase and chitinase. The resistant species of wild sunflowers (H. tuberosus, H. occidentalis) possessed higher levels of constitutive as well as induced total phenols and total sugars as compare with cultivated sunflower and susceptible wild sunflowers. Polyacrylamide gel electrophoretic (PAGE) isozyme analysis of defence-related enzymes showed a positive correlation of resistance with chitinase and polyphenol oxidase and a negative correlation with peroxidase.

in Helia

Abstract

In recent years, Supercritical Fluid Extraction (SFE) technique has been widely used for the extraction of metal ions. In the present study, extraction of uranium from nitric acid medium was investigated using supercritical carbon dioxide (Sc-CO2) containing various organophosphorous compounds such as trialkyl phosphates e.g. tri-iso-amyl phosphate (TiAP), tri-sec-butyl phosphate (TsBP) and tri-n-butyl phosphate (TBP), dialkylalkyl phosphonates, e.g. diamylamyl phosphonate (DAAP) and dibutyl butyl phosphonate (DBBP), dialkyl hydrogen phosphonates, e.g. dioctyl hydrogen phosphonate (DOHP), dioctylphosphineoxide (DOPO), trioctyl phosphine oxide (TOPO), n-octylphenyl N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO) and di-2-ethyl-hexyl phosphoric acid (HDEHP). Some of these ligands have been investigated for the first time in the supercritical phase for the extraction of uranium. The extraction efficiency of uranium was studied with TiAP, DAAP and DBBP as a function of nitric acid concentration; the kinetics of the equilibration period (static extraction) and transportation of the metal complex (dynamic extraction) was investigated. The influence of pressure and temperature on the extraction behaviour of uranium with DAAP was studied from 4 N HNO3. The extraction efficiency of uranium from 4 N nitric acid medium was found to increase in the order of phosphates < phosphonates < HDEHP < TOPO < CMPO. In the case of phosphates and phosphonates, the maximum extraction of uranium was found to be from 4 N HNO3 medium. The acidic extractants, HDEHP and DOHP showed relatively higher extraction at lower acidities. The relative extraction of uranium and thorium from their mixture was also examined using Sc-CO2 containing phosphates, phosphonates and TOPO. The ligand, TsBP provided better fractionation between uranium and thorium compared to trialkyl phosphates, dialkyl alkyl phosphonates and TOPO.