Novel,Organically Doped,Sol–Gel-Derived Materials for Photonics: Multiphasic Nanostructured Composite Monoliths and Optical Fibers

Sol–gel-processed organic–inorganic hybrid materials combine the merits of inorganic glass and organic molecules, and are therefore a class of materials with good potential for photonics. In this review, two approaches which have shown promising results for producing useful materials for photonics are described: (i) a novel way to fabricate organically doped, multiphasic nanostructured composite monoliths and (ii) a method of fabrication of organically doped, sol–gel-derived optical fibers. For each approach, the preparation process is presented, together with selected applications such as multidye solid-state tunable laser, multiphasic optical power limiter, a micron-scale chemical-sensing and biosensing fibers and solid-state dye-doped fiber lasers. © 1997 by John Wiley & Sons Ltd.     

Polymer support oligonucleotide synthesis-XV: Synthesis of oligodeoxynucleotides on controlled pore glass (CPG) using phosphate and a new phosphite triester approach

Controlled pore glass (CPG) has been functionalized with suitably protected deoxynucleosides and used to synthesize d(TTTATT) and d(CATCAGGAAGT) following the phosphate triester approach with 1-(mesitylene-2-sulfonyl)-3-nitro-1,2,4-triazole (MSNT) as condensing agent and ZnBr₂; as detritylating agent. The efficiency of monomer and dimer additions is discussed. The nonamer d(AACCAGCAC) has been synthesized by a modified phosphite triester approach using suitably protected methyl deoxynucleoside-N-morpholino-phosphoamidites as new active phosphitylating nucleotides. The sequence has been built up by monomer additions after activation of the phosphoamidites with tetrazole, capping with acetic anhydride/DMAP and detritylation with either ZnBr₂; (purine nucleotides) or trichloroacetic acid (pyrimidine nucleotides). Deprotection are performed by treatment with thiophenol, aqueous concentrated ammonia and tert. butylamine and the nonamer characterized by reversed phase hplc, polyacrylamide gel electrophoresis and sequence determination. The favourable properties of CPG as carrier for oligonucleotide syntheses are discussed.     

Copper(II) acetate and picrate complexes of sulfa drugs

Summary Copper(II) acetate and picrate complexes of sulfa drugsviz., sulfanilamide, sulfaguanidine, sulfathiazole, sulfadiazine, sulfamerazine and sulfamethazine were prepared and characterized with the help of analytical, electronic, i.r. and magnetic moment data. The complexes are paramagnetic, planar or mixed planar and octahedral, insoluble and melt (with decomposition) in the 185°–225° range. The sulfa drugs coordinate through their amino groups and the acetate or picrate ions are bonded to the metal through the -C(O)O group.     

Near-GeV-energy laser-wakefield acceleration of self-injected electrons in a centimeter-scale plasma channel

The first three-dimensional, particle-in-cell (PIC) simulations of laser-wakefield acceleration of self-injected electrons in a 0.84 cm long plasma channel are reported. The frequency evolution of the initially 50 fs (FWHM) long laser pulse by photon interaction with the wake followed by plasma dispersion enhances the wake which eventually leads to self-injection of electrons from the channel wall. This first bunch of electrons remains spatially highly localized. Its phase space rotation due to slippage with respect to the wake leads to a monoenergetic bunch of electrons with a central energy of 0.26 GeV after 0.55 cm propagation. At later times, spatial bunching of the laser enhances the acceleration of a second bunch of electrons to energies up to 0.84 GeV before the laser pulse intensity is significantly reduced.     

Exact solution for entrance region flow between parallel plates

A method of obtaining an exact solution of the complete Navier-Stokes equations for incompressible flow has been developed to study the development of fluid flow between parallel plates. An analytical solution has been developed in the form of a convergent infinite series and a numerical solution obtained for Reynolds numbers of 10 and 500. These results have been compared with data available elsewhere. The method developed here is expected to have general application     

Synthesis,Electronic and IR Spectral Studies of Some Polymeric Cobalt(II), Nickel(II), Zinc(II) and Cadmium(II) Azido Complexes with Hydrazine

A series of polymeric cobalt(II), nickel(II), zinc(II) and cadmium(II) azido complexes with hydrazine of the type [M(N₂H₄)(H₂O)(N₃)Cl]_n, [M(N₂H₄)(N₃)₂]_n and [M(N₂H₄)₂(N₃)₂]_n have been prepared. These were characterized by elemental analyses, magnetic susceptibility measurements, electronic and IR spectra. The complexes are highly insoluble in polar and non polar solvents. All the complexes decompose with explosion at different temperatures between 100°C to 200°C. The magnetic moment and electronic spectral data for Co(II) and Ni(II) complexes suggest that the complexes have octahedral structure. The ligand-field parameters (10 Dq, B, β, β° and LFSE) have also been calculated for all Co(II) and Ni(II) complexes which indicate a significant covalent character of M-L bonds. The IR spectra of the complexes show that the azide group and hydrazine molecule both act as bidentate bridging ligands in [M(N₂H₄)(H₂O)(N₃)Cl]_n and [M(N₂H₄)(N₃)₂]_n type complexes but the azide group is terminally bonded to metal in all [M(N₂H₄)₂(N₃)₂]_n type complexes.     

A pulsed NMR study of hydrogen diffusion in hydrides of group IVa transition metals

Activation energies E_A for hydrogen diffusion in hydrides of Group IVa transition metals have been determined by ¹H nuclear magnetic resonance measurements of spin lattice relaxation in both the laboratory (T₁) and rotating (T_1p) frames. For the HfHx system both activation energies obtained from T₁ data, and the value of T₁ at the minimum appear to be insensitive to hydrogen content x in the range 1.58 ? x ? 1.98. For hydrides of titanium and zirconium of approximately stoichiometric composition MH₂ (where M = metal), there is excellent agreement between activation energies obtained from T₁ and T_1p data. Mean activation energies obtained were 0.51 eV for TiH_1.98 and 0.83 eV for ZrH_1.96, consistent with a single diffusion mechanism in each case over the temperature range 260–600K and 400–800K respectively. In the case of HfH_1.98 the agreement was less good, values of 0.64 and 0.55 eV being obtained from T₁ and T_1p respectively.