Antisymmetric tensor fields in a generalized Randall–Sundrum scenario

Bulk antisymmetric tensor fields of different ranks have been studied in the context of a generalized Randall–Sundrum model with a non-vanishing induced cosmological constant on the visible brane. It is shown that instead of the usual exponential suppression of the couplings of the zero modes of these bulk fields with the brane fermions in the original Randall–Sundrum model, here the couplings are proportional to the brane cosmological constant. Thus in an era of large cosmological constant these fields have significant role in physical phenomena because of their enhanced couplings with the visible brane fermions.     

Does a Kalb–Ramond field make spacetime optically active?

A spacetime with torsion produced by a Kalb–Ramond field coupled gravitationally to the Maxwell field, in accordance with a recent proposal by two of us (PM and SS), is argued to lead to optical activity in synchrotron radiation from cosmologically distant radio sources. We show that this indicates a very small, but possibly observable rotation of the plane of polarization of the radiation, above and beyond the Faraday rotation due to magnetized galactic plasma. Implications for heterotic string theory are outlined. Received: 27 October 2001 / Published online: 25 January 2002     

Dendron-based model systems for flavoenzyme activity: towards a new class of synthetic flavoenzyme

Three generations of water-soluble flavin dendrons have been synthesized and the role dendrimer generation has on the physical and catalytic properties of these assemblies has been investigated.     

Iron(III) metallomesogen of [N2O2] donor Schiff base ligand containing 4-substituted alkoxy chains

Two new square pyramidal iron(III)-complexes of ‘salen’-type Schiff base ligands containing 4-substituted long alkoxy arms on the aromatic rings, [Fe(4-C₁₆H₃₃O)₂salcn)]Cl and [Fe(4-C₁₆H₃₃O)₂salophen)]Cl {salcn = N,N?-cyclohexanebis(salicylideneiminato) and salophen = N,N?-phenylenebis(salicylideneiminato)}, have been successfully synthesised, and their mesomorphic property investigated. The ligands and complexes were characterised by elemental analyses, UV–Vis, FT-IR, ESI–MS, ¹H and ¹³C NMR (for ligands only). The phase behaviour of the iron(III) complexes were ascertained by differential scanning calorimetry, polarising optical microscopy and variable temperature PXRD study. Ligands are non-mesomorphic, however, mesomorphism got induced upon complexation with the iron(III) centre. X-ray diffraction study revealed a layer-like arrangement of the five coordinated mesomorphic iron(III) complexes. The mesophase is stable over a wide range of temperature. The density functional theory calculations were carried out using Gaussian 09 program at B3LYP level using unrestricted 6–31G (d, p) basis set to obtain the optimised geometry of the iron(III) complexes.     

Growth mechanism of tantalum silicides by interdiffusion

Interdiffusion studies were conducted to understand the atomic mechanism of the diffusing species and the growth mechanism of the phases. Integrated diffusion coefficients and the ratio of tracer diffusion coefficients were estimated for these analyses. The activation energies for the integrated diffusion coefficients were calculated as 550?±?70 and 410?±?39?kJ/mol in the TaSi₂ and Ta₅Si₃ phases, respectively. In the TaSi₂ phase, Ta has a slightly lower but comparable diffusion rate with respect to Si, although no Ta–Ta bonds are present in the crystal. In the Ta₅Si₃ phase, Si has a higher diffusion rate, which is rather unusual, if we consider the atoms in the nearest-neighbour positions for both the elements. The ratio of Si to Ta tracer diffusion coefficients is found to be lower in the Si-rich phase, TaSi₂, compared to the Si-lean phase, Ta₅Si₃, which is also unusual. This indicates the type of structural defects present. An analysis on the growth mechanism of the phases indicates that duplex morphology and the Kirkendall marker plane should only be present in the TaSi₂ phase. This is not present in the Ta₅Si₃ phase due to the very high growth rate of the TaSi₂ phase, which consumes most of the Ta₅Si₃ phase layer. The problems in the calculation method used previously by others in this system are also explained.     

A visible-light-mediated oxidative cn bond formation/aromatization cascade: photocatalytic preparation of N-arylindoles

Just add light and air: Structurally diverse N-arylindoles can be prepared from readily prepared o-styryl anilines through visible-light photocatalysis. The reaction, which is conducted open to air, is mediated by [Ru(bpz)(3) ](PF(6) )(2) (bpz=2,2'-bipyrazine) and involves both C?N bond formation and aromatization. Using suitably substituted substrates, a 1,2-carbon shift can be also incorporated into this cascade reaction.     

ipso-Nitration of arylboronic acids with bismuth nitrate and perdisulfate

An efficient and one pot synthetic method of ipso-nitration of arylboronic acids has been developed. The high efficiency, general applicability, and broader substrate scope including heterocycles and functional groups make this method advantageous. Due to its simplicity, we expect to find application of this method in synthesis.     

Radion tunneling in modified theories of gravity

We consider a five dimensional warped spacetime where the bulk geometry is governed by higher curvature F(R) gravity. In this model, we determine the modulus potential originating from the scalar degree of freedom of higher curvature gravity. In the presence of this potential, we investigate the possibility of modulus (radion) tunneling leading to an instability in the brane configuration. Our results reveal that the parametric regions where the tunneling probability is highly suppressed, corresponds to the parametric values required to resolve the gauge hierarchy problem.     

TBAI/TBHP‐Promoted Generation of Malonyl Radicals: Oxidative Coupling with Styrenes Leads to γ‐Keto Diesters

A metal‐free protocol for oxidative coupling of malonic esters with styrenes to form γ‐keto diesters has been developed. Key to the success of this process is the generation of malonyl radicals from unfunctionalized malonic esters under organo‐catalysis conditions with TBAI and TBHP. This process tolerates both terminal and internal olefins with diverse malonic esters. It provides a new green metal‐free alternative to traditional metal mediated process for generation of malonyl radicals and there by γ‐keto diesters.