Grafting Vinyl Monomers onto Tussah Silk Fiber. I. Graft Copolymerization of Methyl Methacrylate onto Nonmulberry Tussah Silk by Tetravalent Cerium Ion

The graft copolymerization of methyl methacrylate onto nonmulberry natural tussah silk fibers was investigated in aqueous solution using tetravalent cerium as initiator. The rate of grafting was determined by varying the monomer concentration, the cerium (IV) concentration, the temperature, and the nature of the silk. With increasing monomer concentration the graft yield increased (up to 0.657 M) and thereafter decreased. The graft yield also increased with increasing cerium (IV) concentration. The graft-on was influenced by chemical modification of the tussah silk prior to grafting. The effect of certain inorganic salts on the rate of grafting was investigated.     

Effect of FCNC mediated <Emphasis Type="Italic">Z</Emphasis> boson on lepton flavor violating decays

We study the three body lepton flavor violating (LFV) decays μ ^?→e ^? e ⁺ e ^?, \(\tau^{-} \to l_{i}^{-} l_{j}^{+} l_{j}^{-}\) and the semileptonic decay τ→μφ in the flavor changing neutral current (FCNC) mediated Z boson model. We also calculate the branching ratios for LFV leptonic B decays, B _d,s →μe, B _d,s →τe, B _d,s →τμ and the conversion of muon to electron in Ti nucleus. The new physics parameter space is constrained by using the experimental limits on μ ^?→e ^? e ⁺ e ^? and τ ^?→μ ^? μ ⁺ μ ^?. We find that the branching ratios for τ→eee and τ→μφ processes could be as large as \({\sim}{\mathcal{O}}(10^{-8})\) and \(\mathrm{Br}(B_{d,s} \to \tau \mu,~ \tau e) \sim {\mathcal{O}}(10^{-10})\). For other LFV B decays the branching ratios are found to be too small to be observed in the near future.     

Diverse synthetic approach for sulfur and nitrogen-containing spiroheterocycles from dimedone and their pharmacological evaluation

Novel spiro(3-hydroxy-5,5-dimethyl)-1,5’-(2’-substituated[1,3,4]-oxadiazole/thiadiazolo[3,2-c] thiazolines and 3-hydroxy-5,5-dimethyl-spiro[cyclohex-2-ene-thiazolo/thiazino[3,2-b]-s-tetrazine were prepared from previously reported hydrazone, semicarbazone, carbazone, and spiro-s-tetrazine intermediates derived from dimedone precursor. All the newly synthesized heterocycles have been characterized by analytical and spectral (¹H NMR and ^hC NMR) data and screened their in vitro antibacterial activity against gram negative bacteria Escherichia coli and gram positive bacteria Staphylococcus aureus. Some of the compounds showed moderate to good activities towards the bacteria chosen.     

Radiative decays of heavy baryons with heavy quark symmetry

The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model. Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results are quite different from that of the heavy quark bag model calculations.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

Synthesis,molecular and supramolecular structure,spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound

The synthesis, molecular and supramolecular structure, spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound [(UO₂)₂(L)₂(dimethylformamide)₂] (1) derived from the Schiff base ligand H₂L, obtained on condensation of 3-methoxysalicylaldehyde with 2-aminoethanol, have been described. The compound has been characterized by IR, UV–Vis, NMR and mass spectra, as well as by single crystal X-ray structure determination. The title compound crystallizes in the monoclinic P2₁/n space group with the following unit cell parameters a = 10.5713(2) Å, b = 11.9895(2) Å, c = 12.9372(2) Å, β = 102.773(3)° and Z = 2. The structure of 1 reveals that it is a dialkoxo-bridged dinuclear compound of uranium(VI) containing two deprotonated ligands, [L]²⁻, two dimethylformamide (dmf) molecules and two UO₂²⁺ centers. The coordination geometry around the uranium(VI) center is distorted pentagonal bipyramidal; two uranyl oxygens occupy the axial positions, while the basal pentagonal plane is defined by a phenoxo oxygen, two bridging alkoxo oxygens, one imine nitrogen, and one dmf oxygen. Three C–H?O type hydrogen bonds involving one uranyl oxygen, two dmf hydrogens and the imine hydrogen link the dinuclear units into a two-dimensional network. The ESI-MS spectrum of 1 in dimethylsulfoxide exhibits two peaks at m/z = 464.17 and 927.26, which are assignable to [(UO₂)₂L₂H]⁺ (60%) and [(UO₂)₂LH]⁺ (100%) cations, respectively. Cyclic voltammetric measurements of 1 reveal that the uranium(VI) center is reduced quasireversibly at E_1/2 = −1112 mV with ΔE_P = 97 mV.     

Porous Silica‐Coated Gold Nanorods: A Highly Active Catalyst for the Reduction of 4‐Nitrophenol

The successful coating of thin porous silica layers of various thicknesses [(10±1), (12±1), and (14±1) nm] on cetyl trimethylammonium bromide (CTAB) capped gold nanorods was achieved through a modified Stöber procedure. The resulting material was applied as a novel catalyst for the reduction of 4‐nitrophenol. The catalytic activities of the gold nanorods increased up to eight times after coating with a layer of porous silica and the reaction followed a zero‐order kinetics, having a rate constant as high as 2.92×10^?1 mol L^?1 min^?1. The spectral changes during the reduction reaction of 4‐nitrophenol were observed within a very short span of time and a complete conversion to 4‐aminophenol occured within 5–6 mins, including the induction period of ≈2 mins. The reusability of the catalyst was studied by running the catalytic reaction during five consecutive cycles with good efficiency without destroying the nanostructure. The methodology can be effectively applied to the development of composite catalysts with highly enhanced catalytic activity.     

Significant Fowler–Nordheim tunneling across ZnO – Nanorod based nanojunctions for nanoelectronic device applications

We demonstrate significant Fowler–Nordheim (FN) tunneling across Al/Al₂O₃/ZnO metal–insulator–semiconductor (MIS) and Ag/ZnO metal–semiconductor (MS) nanojunctions. The transport properties of ZnO nanostructures in the form of urchins and randomly distributed nanorods were investigated in terms of various conduction mechanism. The minimum voltage necessary for triggering Fowler–Nordheim (FN) tunneling, under forward biasing, was ～1.2 V and ～3.4 V; respectively, below which only direct tunneling and thermionic emission events were evident. Mediated through Al₂O₃ layer, the FN tunneling was more prominent across MIS junction than MS one. The weak FN tunneling across MS junction was owing to interfacial charge transfer process through the atomic scale gapping between adjacent nanostructures. The extent of such type of tunneling is found to be nanostructure morphology dependent and largely rely on the free electrons donated by the native donor defects in the crystal structure of ZnO. The significant FN tunneling across the MIS and MS junctions has a direct relevance in designing nanoscale field emission devices/components working at low voltage with high throughputs.     

Strong Kerr-signals from optically isotropic ZnSe nanocrystals: a study using Mach-Zehnder principles

In the present work, we show that Mach-Zehnder interferometry (MZI) can be an asset to explore the birefringence properties of semiconductor nanocrystallites (NCs). A 0.352 μm thick polymer containing ZnSe–NCs (size dispersion: 2.5×10¹⁰/cm²) was kept on either of the arms of the MZI (λ=632.8 nm) and the phase angles were measured at the output, corresponding to three selected spots of the specimen. Owing to the non-resonant excitation led transient polarization in the NCs, strong optical Kerr-signals were detected with Kerr coefficient values ~1.87 × 10^-9 m/V². The approach may be extended to other optically isotropic nanoscaled materials having a center of inversion including liquid crystals.