Electron drag in intermediate magnetic fields with low electron density

Electron drag between two two-dimensional electron systems has been measured in intermediate magnetic fields (/τ<ω_ck_BT) with a relatively low electron density. We explore, in this sample, the unusual increase of drag in intermediate magnetic fields which was well characterized by a nearly temperature independent B³ dependence. The anomalous behavior of electron drag observed in higher density samples is found to persist for low sample density.     

Stoichiometrically Different Inclusion Complexes of 2-Aminofluorene and 2-Amino-9-Hydroxyfluorene in β-Cyclodextrin: A Spectrofluorimetric Study

β-cyclodextrin (β-CDx) forms inclusion complexes with 2-aminofluorene (2AF) and 2-amino-9-hydroxyfluorene (2AHF) in different stoichiometries (Guest-host ratio 1:1 and 1:2 respectively) which is discussed on the basis of study by absorption and fluorescence spectroscopy. The ground and the excited state acidity constants for the neutral‒monocation equilibrium of the two fluorophores in aqueous β-CDx medium are determined by spectrophotometric and fluorimetric titration methods respectively. The dual fluorescence observed for 2AHF monocation in aqueous solution is due to the formation of monocation-water exciplex. This monocation-water exciplex formation is hindered in β-CDx solution by the inclusion complexation. Based on the results obtained, the structures of the inclusion complexes are proposed.     

Dielectric properties of some MM′O4 and MTiM′O6 (M=Cr, Fe, Ga; M′=Nb, Ta, Sb) rutile-type oxides

We describe an investigation of the structure and dielectric properties of MM′O₄ and MTiM′O₆ rutile-type oxides for M=Cr, Fe, Ga and M′=Nb, Ta and Sb. All the oxides adopt a disordered rutile structure (P4₂/mnm) at ambient temperature. A partial ordered trirutile-type structure is confirmed for FeTaO₄ from the low temperature (17 K) neutron diffraction studies. While both the MM′O₄ oxides (CrTaO₄ and FeTaO₄) investigated show a normal dielectric property MTiM′O₆ oxides for M=Fe, Cr and M′=Nb/Ta/Sb display a distinct relaxor/relaxor-like response. Significantly the corresponding gallium analogs, GaTiNbO₆ and GaTiTaO₆, do not show a relaxor response at T<500 K.     

Environmentally safe one-pot solvent-free synthesis of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) catalyzed by NaHSO4-SiO2

One-pot condensation of thiourea (urea), diverse aromatic aldehydes, and ammonium acetate in the presence of repeatedly usable heterogeneous catalyst NaHSO₄-SiO₂ in the absence of solvent under the microwave irradiation proceeds faster and with better yields of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) that under common heating. Compounds synthesized exist as a rule as two isomers distinguished by the position of the phenyl ring: It is located in the major isomer nearly in the equatorial position, in the minor one, close to axial position.     

Ultrafast nonlinear optical response of carbon nanotubes functionalized with water soluble porphyrin

A new nanocomposite is obtained by functionalizing carbon nanotubes (CNTs) with a water soluble metalloprophyrin using a simple chemical technique and characterized by optical absorption, IR, and Raman spectroscopy. Results from spectroscopic studies indicate the noncovalent nature of interaction between CNTs and porphyrin. The ultrafast nonlinear response is characterized by measuring the nonlinear absorption coefficient and refractive index by z-scan technique in the femtosecond pulse regime. The nanocomposite is found to exhibit two-photon absorption (TPA) with a reasonably large nonlinear optical coefficient, whereas pure CNTs is known to exhibit saturable absorption. Design of such water soluble nanocomposites offers scope for obtaining materials with enhanced ultrafast optical nonlinearity.     

Investigations on the Nucleation Kinetics of L-Arginine Phosphate single crystals

The nucleation parameters, such as radius of the critical nucleus and critical free energy change have been evaluated for LAP single crystals. The interfacial tension determined by conducting the induction period measurements has been used for the evaluation of nucleation parameters. The determined interfacial tension is found to be comparable with theoretical literature values.