Observation of nonconventional spin waves in composite-fermion ferromagnets

We find unexpected low energy excitations of fully spin-polarized composite-fermion ferromagnets in the fractional quantum Hall liquid, resulting from a complex interplay between a topological order manifesting through new energy levels and a magnetic order due to spin polarization. The lowest energy modes, which involve spin reversal, are remarkable in displaying unconventional negative dispersion at small momenta followed by a deep roton minimum at larger momenta. This behavior results from a nontrivial mixing of spin-wave and spin-flip modes creating a spin-flip excitonic state of composite-fermion particle-hole pairs. The striking properties of spin-flip excitons imply highly tunable mode couplings that enable fine control of topological states of itinerant two-dimensional ferromagnets.     

A class of new LRS Bianchi type-I perfect fluid universes with decaying vacuum energy density Λ

A class of new LRS Bianchi type-I cosmological models with a variable cosmological term is investigated in presence of perfect fluid. A procedure to generate new exact solutions to Einstein’s field equations is applied to LRS Bianchi type-I space-time. Starting from some known solutions a class of new perfect fluid solutions of LRS Bianchi type-I are obtained. The cosmological constant Λ is found to be positive and a decreasing function of time which is supported by results from recent supernovae Ia observations. The physical and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed.     

The model for self-dual chiral bosons as a Hodge theory

We consider (1+1) dimensional theory for a single self-dual chiral boson as a classical model for gauge theory. Using the Batalin–Fradkin–Vilkovisky (BFV) technique, the nilpotent BRST and anti-BRST symmetry transformations for this theory have been studied. In this model other forms of nilpotent symmetry transformations like co-BRST and anti-co-BRST, which leave the gauge-fixing part of the action invariant, are also explored. We show that the nilpotent charges for these symmetry transformations satisfy the algebra of the de Rham cohomological operators in differential geometry. The Hodge decomposition theorem on compact manifold is also studied in the context of conserved charges.     

Free‐radical trapping in the precipitation polymerization of acrylamide

Electron spin resonance spectroscopy revealed that some free radicals were trapped in the precipitated polymer during the precipitation polymerization of acrylamide conducted in nonsolvents of the polymer [t‐butyl alcohol (TBA), acetone and methanol]. The trapped radical concentration decreased with an increase in the chain‐transfer activity of the aforementioned liquids. A 100% polymerized acrylamide in TBA prepared with a 10% monomer concentration and a 3 × 10^?3 mol/dm³ azobisisobutyronitrile concentration at 50 °C contained approximately 2 radicals per 100 polymer molecules. The trapped radicals on exposure to air decayed with time according to second‐order kinetics. The rate constant was evaluated and found to be in reasonably good agreement with the rate constant evaluated from data published long ago for the decay of trapped polyacrylonitrile radicals following their exposure to air. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1192–1197, 2003     

Transition-Metal-Free Synthesis of Heterobiaryls through 1,2-Migration of Boronate Complex

The synthesis of a diverse range of heterobiaryls has been achieved by a transition-metal-free sp²–sp² cross-coupling strategy using lithiated heterocycle, aryl or heteroaryl boronic ester and an electrophilic halogen source. The construction of heterobiaryls was carried out through electrophilic activation of the aryl–heteroaryl boronate complex, which triggered 1,2-migration from boron to the carbon atom. Subsequent oxidation of the intermediate boronic ester afforded heterobiaryls in good yield. A comprehensive ¹¹B NMR study has been conducted to support the mechanism. The cross coupling between two nucleophilic cross coupling partners without transition metals reveals a reliable manifold to procure heterobiaryls in good yields. Various heterocycles like furan, thiophene, benzofuran, benzothiophene, and indole are well tolerated. Finally, we have successfully demonstrated the gram scale synthesis of the intermediates for an anticancer drug and OLED material using our methodology.     

Green synthesis of nano-titania (TiO2 NPs) utilizing aqueous Eucalyptus globulus leaf extract: applications in the synthesis of 4H-pyran derivatives

Research on Chemical Intermediates - We have presented the green synthesis and characterization of nano-titania (TiO2 NPs) by using Eucalyptus globulus leaf aqueous extract in a greener approach...     

PMA-SiO2 catalyzed synthesis of β-keto enol ethers

An efficient conversion of β-diketones into corresponding β-keto enol ethers with catalytic amount of PMA-SiO2 has been achieved.     

X-ray diffraction and optical birefringence studies on four nematogenic difluorobenzene derivatives

The results of optical microscopy, DSC, X-ray diffraction and optical birefringence studies on four nematogenic difluorobenzene derivatives are presented. The thermal stability of the compounds increases substantially as greater flexibility is introduced into the core structure. Average intermolecular distances, obtained from X-ray data, are found to increase when a comparatively rigid planar phenyl ring is substituted by a flexible non-planar cyclohexyl ring in the core structure. From the values of apparent molecular lengths in the nematic phase, a short range antiferroelectric type of association is found to exist between neighbouring molecules. Density values suggest that the molecular packing is less efficient with increasing flexibility either in chain- or in core-structure. All the refractive indices exhibit normal dispersive behaviour, and a positive optical anisotropy is observed in all the compounds which decreases quickly with temperature. Temperature dependences of orientational order parameters, determined from both X-ray and optical birefringence studies, are presented. Variations of different physical properties with order parameters are discussed.     

Projection method for 4d non-orthogonal hyperlattices

The Wigner-Seitz cell of a lattice inn-dimensional space displays the complete point group of such a lattice. The vertices of the cell when projected onto pseudo space can serve as the outer shape of acceptance domain or motif. This general procedure leads to acceptance domain or motif identical to those discussed in literature for primitive orthogonal hyperlattices. Example of 4d non-orthogonal hyperlattices corresponding to 12-fold symmetry will be considered. It will be shown that the first Wigner-Seitz cell degenerates into more than one shape in 2d pseudo space and can serve as a natural partition of the motif. Following a parallel procedure, the consequence of projection of first 4d Brillouin zone will also be discussed.