Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Novel nonperipheral octa-3-hydroxypropylthio substituted metallo-phthalocyanines: synthesis,characterization, and investigation of their electrochemical,photochemical and computational properties

The current study describes the synthesis, electrochemical, computational, and photochemical properties of octa (3-hydroxypropylthio) substituted cobalt (II) ( 4 ), copper (II) ( 5 ), nickel (II) ( 6 ) and zinc(II) ( 7 ) phthalocyanine derivatives. These novel compounds were characterized by elemental analysis,¹H,¹³C NMR, FT-IR, UV-Vis, and MS. The redox behaviors of these metallo-phthalocyanines were investigated by the cyclic voltammetric method. The optimized molecular structure and gauge-including atomic orbital (GIAO)¹H and¹³C NMR chemical shift values of these phthalocyanines in the ground state had been calculated by using B3LYP/6–31G(d,p) basis set. The outcomes of the optimized molecular structure were given and compared with the experimental NMR values. The photochemical properties including photodegradation and singlet oxygen generation of zinc(II) phthalocyanine were studied in DMSO solution for the determination of its photosensitizer behaviors.     

Supramolecular assembly on surfaces: manipulating conductance in noncovalently modified mesoscale structures

Molecules capable of complementary hydrogen bonding were used to control the noncovalent self-assembly and electronic properties of a chemically well-defined surface mesostructure. In this work, we patterned a footprint region for molecular assembly on a surface and used moieties featuring complementary recognition to tune the current-voltage properties of the patterned region. With the appropriate functionalities on the complementary moieties, we were able to increase and decrease the observed conductance in surface-bound mesoscale structures imaged by scanning tunneling microscopy (STM).     

Asymptotic properties of some triangulations of the sphere

In this paper we analyse a method for triangulating the sphere originally proposed by Baumgardner and Frederickson in 1985. The method is essentially a refinement procedure for arbitrary spherical triangles that fit into a hemisphere. Refinement is carried out by dividing each triangle into four by introducing the midpoints of the edges as new vertices and connecting them in the usual ‘red’ way. We show that this process can be described by a sequence of piecewise smooth mappings from a reference triangle onto the spherical triangle. We then prove that the whole sequence of mappings is uniformly bi-Lipschitz and converges uniformly to a non-smooth parameterization of the spherical triangle, recovering the Baumgardner and Frederickson spherical barycentric coordinates. We also prove that the sequence of triangulations is quasi-uniform, that is, areas of triangles and lengths of the edges are roughly the same at each refinement level. Some numerical experiments confirm the theoretical results.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Large-angle proton emission in the 9Be(p, 2p) reaction at 300 MeV

A ⁹Be(p, 2p) coincidence experiment performed to further elucidate the reaction mechanism for the production of energetic wide-angle protons in intermediate-energy proton-induced reac- tions is reported. Detectors in a coplanar geometry were used to measure coincidences between trigger protons at 90° to the beam and forward-angle protons on the opposite side of the beam. The incident proton energy was 300 MeV. We report both the inclusive spectra for the trigger protons and the differential mean multiplicities for the coincidence events.The outgoing proton energies were measured using NaI detectors. Trigger protons were grouped into 10 MeV bins covering the kinetic energy range from 55 to 155 MeV. The forward protons were measured over a kinetic energy range of 65–280 MeV and an angular range of 14–60° with respect to the beam.The present results are compared with two previous experiments which covered a more restrictive kinematical range. Calculations are performed with both phase-space and direct knockout models, and compared with experiment. Observation of angle and energy correlation effects suggested by knockout models indicate that such direct mechanisms provide a significant contribution to energetic wide-angle inclusive proton spectra.