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Mechanistic studies on the biosorption of Pb(II) by Pseudomonas aeruginosa
No full textThe biosorption of Pb(II) ions from aqueous solution has been studied using both the intact and thermolyzed cells of Pseudomonas aeruginosa. Further, the role of the major cell wall components, namely DNA, protein, polysaccharide, and lipid, in Pb(II) binding has been assessed using an enzymatic treatment method. The Pb(II) bioremediation capability of P. aeruginosa cells has been investigated by varying the parameters of pH, time of interaction, amount of biomass, and concentration of Pb(II). The complete bioremoval of Pb(II) using intact cells has been achieved for an initial Pb(II) concentration of 12.4 mg L at pH 6.2 and temperature 29 +/- 1 degrees C. The biosorption isotherm follows Langmuirian behavior with a Gibbs free energy of -30.71d mol(-1), indicative of chemisorption. The biosorption kinetics is consistent with a pseudo-second-order model. The possible Pb(II) binding mechanisms of P. aeruginosa cells are discussed based on characterization using zeta potential measurements, Fourier transform infra-red spectroscopy, and energy dispersive X-ray spectroscopy. The results confirm that among the major cell wall components studied, polysaccharide shows the highest contribution towards Pb(II) binding, followed by DNA, lipid, and protein. Similar studies using thermolyzed cells show higher Pb(II) uptake compared to the intact cells both before and after enzymatic treatment
Effect of reverse austenitic transformation on mechanical property and associated texture evolution in AISI 316 austenitic stainless steel processed by low temperature rolling and annealing
No full textThe tensile behaviour of austenitic stainless steel after cryorolling and subsequent annealing has been reported. The defect structures generated during cryorolling, lead to the formation of alpha' and epsilon-martensite. Subsequent annealing leads to the formation of refined austenitic grains surrounded by martensitic islands. These martensitic islands consist of alpha' phase only. The dislocation-martensite interaction leads to discontinuous yielding for high Ultimate Tensile Strength (UTS)/Yield Strength (YS) ratio. In case of annealing at 923 K (650 degrees C) for 10 min after 30% cryorolling leads to nearly 30% untransformed martensite whereas only 7% martensite remains after annealing for 1 h. The effect of remnant martensite on tensile behaviour leading to yield plateau has been discussed in this work. It can be noticed that sample with 20% cryo rolling and annealed at 650 degrees C for 1 h shows higher YS (721 MPa) with YS/UTS ratio of 0.79 and similar to 18% uniform elongation. Sample with 30% cryo rolling and annealed at 650 degrees C for 1 h shows YS of 305 MPa with YS/UTS ratio of 0.27 and uniform elongation of similar to 24%. Therefore, 20% cryo rolled and annealed at 650 degrees C for 1 h has the best combination of mechanical properties
Enhancement of breakdown voltage in AlGaN/GaN HEMT using passivation technique for microwave application
No full textThe AlGaN/GaN High Electron Mobility Transistor (HEMT) on Silicon Carbide (SiC) substrate with SiO2 passivation is proposed in this paper. The maximum drain current of 0.8 A/mm is observed at V-gs = 0 V for gate width (W-G) = 600 mu m. The breakdown voltage of device with SiO2 passivation is compared with breakdown voltage of device with SiN passivation and it is found that the breakdown voltage improved in the device with SiO2 passivation. The breakdown voltage of the device with SiO2 and SiN passivation are 312 V and 287 V, respectively. Furthermore, the improvement in the breakdown voltage is observed with increase of buffer thickness. The obtained breakdown voltages are 312 V, 390 V and 412 V for buffer thickness of 2 mu m, 3 mu m and 5 mu m, respectively. In addition to breakdown analysis, the impact of passivation on intrinsic capacitance is investigated and found that the device with SiO2 passivation exhibits a reduction in gate-source capacitance (C-SG) and gate - to - drain capacitance (C-GD)
Effective Activation Energy for the Solid-State Sintering of Silicon Carbide Ceramics
No full textEffective activation energy for densification of SiC in the presence of C and B4C additives is determined by constant heating rate experiments through analysis of shrinkage in hot pressing. The activation energy (AE) for sintering increased linearly with the relative density (RD) in two different regimes. The effective AE increased from 407 +/- 50 kJ/mole at 75 pct RD to 1132 +/- 75 kJ/mole at 95 pct RD. Lattice diffusion is proposed as the predominant mechanism for SiC densification at higher density. This is also validated by the uniform distribution of sintering additive through electron probe microanalysis. The low AE in the regime of lower density could be attributed to the pressure-assisted particle rearrangement during hot pressing. The relative contribution of both the mechanisms between two density limits resulted in the change in AE for sintering. The mechanisms of defect generation resulting in densification are also discussed. (C) The Minerals, Metals & Materials Society and ASM International 2018
High temperature negative magnetization, spin reorientation and their suppression with magnetic field in ErFe0.55Mn0.45O3 single crystal
No full textErFe0.55Mn0.45O3 single crystal shows canted antiferromagnetic ordering below 365 K with weak ferro-magnetic moment along c axis. On cooling, the magnetic moment is completely suppressed at a certain temperature due to Er and Fe/Mn sublattice compensation, below which negative magnetization is observed. The compensation and negative magnetization temperatures are much higher than those in other orthoferrite systems. There is a spin reorientation transition from Gamma(4)(G(x), A(y), F-z) to Gamma(1)(A(x), G(y), C-z) structure at 255 K along c axis which is not seen along a and b axes. The spin reorientation is tunable with applied magnetic field and is completely suppressed at sufficiently high magnetic field. The behavior is explained by spin configuration and net magnetization orientation of individual Er and Fe/Mn sublattices. The proposed model is further validated by measurements using `training' protocol. (C) 2018 Elsevier B.V. All rights reserved
Catalytic Enantioselective C-C Bond-Forming Reactions of Deconjugated Butyrolactams: Michael Addition to alpha,beta-Unsaturated Aldehydes and Ketones
No full textNucleophilic reactivity of deconjugated butyrolactams has been demonstrated for enantioselective Michael additions to alpha,beta-unsaturated aldehydes and ketones. These reactions are catalyzed by diphenylprolinol silyl ether and trans-1,2-diaminocyclohexane-derived bifunctional primary aminothiourea, respectively, producing the Michael adducts with moderate diastereoselectivities and good to excellent enantioselectivities (up to 99:1 er). Unlike in the case of structurally related deconjugated butenolides where vinylogous addition is prevalent, an exclusive alpha-addition is observed for deconjugated butyrolactams
Structural and biochemical studies on the role of active site Thr166 and Asp236 in the catalytic function of D-Serine deaminase from Salmonella typhimurium
No full textD-Serine deaminase (DSD) degrades D-Ser to pyruvate and ammonia. Uropathogenic bacteria survive in the toxic D-Ser containing mammalian urine because of DSD activity. The crystal structure of the apo form of Salmonella typhimurium DSD (StDSD) has been reported earlier. In the present work, we have investigated the role of two active site residues, Thr166 and Asp236 by site directed mutagenesis (T166A and D236L). The enzyme activity is lost upon mutation of these residues. The 2.7 angstrom resolution crystal structure of T166A DSD with bound PLP reported here represents the first structure of the holo form of StDSD. PLP binding induces small changes in the relative dispositions of the minor and major domains of the protein and this inter-domain movement becomes substantial upon interaction with the substrate. The conformational changes bring Thr166 to a position at the active site favorable for the degradation of D-Ser. Examination of the different forms of the enzyme and comparison with structures of homologous enzymes suggests that Thr166 is the most probable base abstracting proton from the C alpha atom of the substrate and Asp236 is crucial for binding of the cofactor. (C) 2018 Elsevier Inc. All rights reserved
Fiber Bragg Grating Goniometer for Joint Angle Measurement
No full textGoniometers are extensively used in the medical field, in order to assess the range of angular motion of a joint, especially for therapeutic assessment during physiotherapy. This paper reports a novel device for the dynamic measurement of angular motion of joints using a fiber Bragg grating (FBG) senor. The fiber Bragg grating goniometer (FBGG) is proposed, essentially converts the rotational motion of a joint into strain variation on a cantilever, which is acquired by the FBG sensor bonded over it. The FBGG developed has the capability of measuring joint angles in the range of 0 degrees-200 degrees with a resolution of 0.06 degrees. The FBGG developed has been put to use in the measurement of angular motion of elbow joint along with ankle joint. The angular measurements obtained from the FBGG are validated against the angular measurements from the Polhemus liberty sensor. It is observed that the angular motions acquired from both the methodologies are in good agreement with each other, which proves the usefulness of the FBGG developed. Also, with the inherent advantages of the FBG sensor, the FBGG developed provides an efficient means of evaluation of angular motion of joint, which may be utilized as a platform sensor methodology for angular measurement of various other joints in the human body
Supramolecular architecture of organotin(IV) N-methyl ferrocenyl N-ethanol dithiocarbamates: Crystallographic and computational studies
No full textFour new organotin(IV) ferrocenyl dithiocarbamate complexes viz. (FcCH(2)EtOHdtc)(2)SnR2] (R = Me (1), n-Bu (2) and Ph (3)) and (FcCH(2)EtOHdtc) SnPh3] (4) have been synthesized and characterized by electronic absorption, IR, H-1, C-13 and Sn-119 NMR spectroscopy. The molecular structures of 1 and 2 have been confirmed by single crystal X-ray diffraction technique. The X-ray analyses for 1 and 2 reveal a skew trapezoidal bipyramid geometry around Sn(IV) which is being satisfied by the two sulfur atoms of the two dithiocarbamate ligands in anisobidentate fashion. In the crystal structure of 1, an interesting one dimensional chain held by O-H center dot center dot center dot O intermolecular interactions and also display weak C-H center dot center dot center dot pi and C-H center dot center dot center dot S interactions. The crystal structure of 2 exhibit the formation of one dimensional chain held by weak O-H center dot center dot center dot S, (Cp) C-H center dot center dot center dot O and pi center dot center dot center dot pi interactions. Additionally 2 also display the formation of one dimensional chain because of the (Cp) C-H center dot center dot center dot S and (Cp) C-H center dot center dot center dot pi interactions. These interactions have been addressed by ab initio and atoms-in-molecules analyses. (C) 2017 Elsevier B.V. All rights reserved
Visual detection of a nerve agent simulant using chemically modified paper strips and dye-assembled inorganic nanocomposite
No full textChromogenic probe with oxidized bis-indolyl scaffold has been synthesized for the detection of a nerve gas mimicking agent, DCNP (diethyl cyanophosphonate) at pH 8.0 in water. The mechanism of interaction was proposed as the release of cyanide ion through the indole group mediating the hydrolysis of phosphorous-hetero atom bond and, thereafter, the Michael addition of the liberated CN-ion to the electron deficient C=C bond of the bis-indolyl moiety. The reaction featured a remarkable change in color from red to colorless at ambient condition. Then, low-cost and portable paper strips were designed for a rapid and on-site vapor phase detection of DCNP without involving any sophisticated instrument or skilled personnel. Finally, a dye assembled inorganic nanocomposite material was devised to achieve a more sensitive `turn-on' detection of DCNP in water