Influence of activation of Si29+ ion-implantation in GaAs on ohmic contact resistance and electrical performances of MESFETs

The active layers of Metal Semiconductor Field Effect Transistors (MESFETs) are obtained by Si²⁹⁺ ion implantation in GaAs. Implantation was done at 35 keV with a higher dose near the wafer surface for facilitating easier formation of ohmic contacts, and at 180 keV with a lower dose for obtaining the device channel. Post-implantation annealing was carried out in a rapid thermal processor for activating the implants. Very high activation levels of about 60% for the n⁺ GaAs layer, and 85% for the n-GaAs channel layer were achieved by annealing at 955 °C for 25 s. Activation was characterized using C–V profiling, secondary ion mass spectrometry and by electrical device data of fabricated MESFETs. We attempt an experimental correlation between the ohmic contact resistance (R _c) and activation of both the n⁺ and the channel layer. It was found that very high and simultaneous activation of the n⁺ and channel layers results in very low contact resistances. The conduction of source-drain current into the channel is easily facilitated due to reduction in the resistance of the transition region at the interface of n⁺-contact and n-channel layers.     

Breather-like director reorientations in a nematic liquid crystal with nonlocal nonlinearity

The nature of nonlinear molecular deformations in a homeotropically aligned nematic liquid crystal (NLC) is presented. We start from the basic dynamical equation for the director axis of a NLC with elastic deformations and adopt space curve mapping procedure to analyze the dynamics. The NLC is governed by an integro-differential perturbed nonlocal nonlinear Schrödinger equation and we solve the same using Jacobi elliptic function method aided with symbolic computation and construct an exact solitary wave solution. In order to better understand the effect of nonlocality on the director reorientations of nematic liquid crystal, we have constructed the component forms of director axis using Darboux vector transformation. This intriguing property as a result of the relation between the coherence of the breather-like solitary deformation and the nonlocality reveals a strong need for a deeper understanding in the theory of self-localization in NLC systems.     

Reply to the Letter-to-the-Editor of Dr. Noble Jacob regarding article “Radon isotope assessment of Submarine Groundwater Discharge (SGD) in Coleroon River Estuary,Tamil Nadu,India”, DOI: https://doi.org/10.1007/s10967-018-5877-2

Journal of Radioanalytical and Nuclear Chemistry -     

Shock tunnel study of spiked aerodynamic bodies flying at hypersonic Mach numbers

A three-component accelerometer balance system is used to study the drag reduction effect of an aerodisc on large angle blunt cones flying at hypersonic Mach numbers. Measurements in a hypersonic shock tunnel at a freestream Mach number of 5.75 indicate more than 50% reduction in the drag coefficient for a 120° apex angle blunt cone with a forward facing aerospike having a flat faced aerodisc at moderate angles of attack. Enhancement of drag has been observed for higher angles of attack due to the impingement of the flow separation shock on the windward side of the cone. The flowfields around the large angle blunt cone with aerospike assembly flying at hypersonic Mach numbers are also simulated numerically using a commercial CFD code. The pressure and density levels on the model surface, which is under the aerodynamic shadow of the flat disc tipped spike, are found very low and a drag reduction of 64.34% has been deduced numerically.     

Interprotein Electron Transfer between FeS-Protein Nanowires and Oxygen-Tolerant NiFe Hydrogenase

Self-assembled redox protein nanowires have been exploited as efficient electron shuttles for an oxygen-tolerant hydrogenase. An intra/inter-protein electron transfer chain has been achieved between the iron-sulfur centers of rubredoxin and the FeS cluster of [NiFe] hydrogenases. [NiFe] Hydrogenases entrapped in the intricated matrix of metalloprotein nanowires achieve a stable, mediated bioelectrocatalytic oxidation of H₂ at low-overpotential.     

Purification,crystallization, and X-ray diffraction analysis of succinyl-diaminopimelate desuccinylase from Wolbachia endosymbiont of Brugia malayi

Lymphatic filariasis (LF) is a debilitating mosquito-borne parasitic disease caused by Brugia malayi in humans in the lymphatic system. Although limited drugs are available to treat this disease, these drugs are only effective against the larvae of Brugia malayi. As resistance has been reported to the available drugs, a new antifilarial drug is needed with better prognostic features, a short period of time of use, and efficiency at preventing adult worm survival. In this study, we have targeted succinyl-diaminopimelate desuccinylase (DapE) from the Wolbachia endosymbiont of Brugia malayi (WBm), which is involved in the production of lysine and meso-diaminopimelic acid, an essential component for the formation of bacterial cell walls, and plays a vital role in pathogen survival. Deletion of DapE gene is lethal to WBm since the organism has no alternative pathway for lysine biosynthesis. Here, the expression, purification, and crystallization of DapE are reported. The crystals of DapE, with an estimated solvent content of 50.76%, diffract synchrotron X-rays to a resolution of 2.3 Å and belong to the space group C222₁, with unit-cell parameters of a = 51.78, b = 78.83, and c = 216.20 Å. The X-ray absorption spectroscopy further confirms that zinc atoms are incorporated in DapE.     

Coordination chemistry and biological activity of nickel(II) and copper(II) ion complexes with nitrogen–sulphur donor ligands derived from S-benzyldithiocarbazate (SBDTC)

A bidentate and a quadridentate Schiff base having NS and NNSS donor sequences were prepared by condensing S-benzyldithiocarbazate (NH₂NHCSSCH₂Ph) with 2,3-butanedione (1:1 and 1:2 mole ratio). Ni^II and Cu^II complexes of these ligands were studied and characterised by elemental analyses and various physico-chemical techniques. The nickel complexes, [Ni(NS)₂] and [Ni(SNNS)], were diamagnetic with square-planar and five-coordinate structures, respectively. The copper complex was, however, pentacoordinated. The ligands and the complexes were screened for anticancer activity against T-lymphoblastic leukemic cells (CEM-SS) and colon cancer cells (HT-29). The NS Schiff base was strongly active against leukemic cells with a CD₅₀ value of 2.05 g cm^–3. The nickel and copper complexes were found to be stronger antioxidants than Vitamin E.     

Development of an HPLC Assay Method for Lenalidomide

Chromatographic separation of lenalidomide and its impurities was achieved on an Inertsil ODS-3 V column using a mobile phase consisting of a mixture of buffer, acetonitrile and methanol in the ratio 80:8:12 v/v. Degradation studies were performed on bulk samples of lenalidomide subjected to 0.5 N hydrochloric acid, 0.5 N sodium hydroxide, 10% v/v hydrogen peroxide, heating to 60 °C and UV light at 254 nm. Degradation was observed only under base hydrolysis conditions. The developed LC method gave a mass balance close to 99.5%, proving it to be suitable for stability studies and was validated with respect to linearity, accuracy, precision and robustness.     

Open-mouthed metallic microcapsules: exploring performance improvements at agglomeration-free interiors

Although artificial capsule structures have been thoroughly investigated, functionality at the surfaces of their interiors has been surprisingly overlooked. In order to exploit this aspect of capsular structure, we here report the breakthrough fabrication of metallic (platinum) microcapsules with sufficient accessibility and electroactivity at both interior and exterior surfaces (open-mouthed platinum microcapsules), and also we demonstrate improvements in electrochemical and catalytic functions to emphasize the practical importance of our concept. The open-mouthed platinum microcapsules were prepared by template synthesis using polystyrene spheres, where surface-fused crystalline nanoparticles formed a capsule shell. Subsequent removal of the polystyrene spheres induced formation of mouth-like openings. The open-mouthed platinum microcapsules exhibit a substantial increase of their electrode capability for methanol oxidation and catalytic activities for carbon monoxide (CO) oxidation. Notably, activity loss during CO oxidation due to undesirable particle agglomeration can be drastically suppressed using the open-mouthed microcapsules.     

Estimation of Olefin Dimerisation Products by GC/GC–MS and IR Techniques

A GC and IR based protocol was developed for monitoring the isobutene dimerisation process wherein the complete characterisation of the products was carried out by GC coupled with mass spectrometry. In the dimerisation process, LPG from FCC process comprising a mixture of saturated and unsaturated C4 hydrocarbons is subjected to a dimerisation process using a catalyst to produce C8 hydrocarbons. The reaction is carried out keeping in view the demand for high-octane blending components in gasoline. The isooctene generated in the process (mainly from the dimerisation of isobutene) is converted into isooctane having the RON and MON value 100. The monitoring process requires the use of two different column chemistries, viz., a 100 m CPSIL PONA CB non-polar column for C8 and its isomers and an Alumina PLOT column for C4 hydrocarbons. A 100 m non-polar column does not separate the C4 mixture since the column is meant for gasoline range products containing C5 and above hydrocarbons. Therefore, a need was felt for an improvised method which can handle both the analyses simultaneously. A cryogenic oven program starting from 0 °C was developed for separating the isomers of C4 hydrocarbons and C8 hydrocarbons on a single column during the single run by Detailed Hydrocarbon Analyzer. The data obtained using the cryo programme was validated with data obtained using Alumina PLOT column on C4 mixture since the Alumina PLOT column is the widely accepted column chemistry for separating the C4 hydrocarbons. An IR method for the estimation of the total olefin content was developed using 2,2,4-trimethyl pentene-1 as the reference standard. The total olefins generated during the process were identified by GC–MS, quantified by DHA-FID and validated by infrared spectroscopy. A good correlation was found between GC and IR spectral results (correlation coefficient R ²  = 0.99).