The role played by hydrogen in the ionic thermocurrents of beryl

Abstract

Ionic thermocurrents (ITC) were measured in pink (morganite) and colourless (goshenite) samples of natural beryl from 77K up to 250K at a constant rate b = 0.1 Ks^?1. The spectra present three distinct bands, at 170K, 200K and 220K. The band at 200K predominates in the untreated crystals. After thermal treatments between 700K and 1300K, the ITC bands at 170K and 220K become prominent, masking the 200K band. The reduction of Fe³⁺ into Fe²⁺ in two distinct positions in the beryl lattice justify this observation. Infrared (IR) spectra show that treatments above 1000K remove water from the channels of the beryls. Ultraviolet (UV) irradiation of these thermally treated samples enhance the two bands at 170K and 220K.     

Fluxes of cosmic rays: a delicately balanced stationary state

The analysis of cosmic rays fluxes as a function of energy reveals a knee slightly below 10¹⁶ eV and an ankle close to 10¹⁹ eV. Their physical origins remain up to now quite enigmatic; in particular, no elementary process is known which occurs at energies close to 10¹⁶ eV. We propose a phenomenological approach along the lines of nonextensive statistical mechanics, a formalism which contains Boltzmann–Gibbs statistical mechanics as a particular case. The knee then appears as a crossover between two fractal-like thermal regimes, the crossover being caused by process occurring at energies ten million times lower than that of the knee, in the region of the quark hadron transition (10⁹ eV). This opens the door to an unexpected standpoint for further clarifying the phenomenon.     

Catalytic effect of dimethyl sulfoxide in the Cu(0)/tris(2‐dimethylaminoethyl)amine‐catalyzed living radical polymerization of methyl methacrylate at 0–90 °C initiated with CH3CHClI as a model compound for α,ω‐di(iodo)poly(vinyl chloride) chain ends

A variety of conditions, including catalysts [CuCl, CuI, Cu₂O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me₆‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH₃CHClI, CH₂I₂, CHI₃, and F(CF₂)₈I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH₃CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me₆‐TREN at 90 °C, whereas the second involved Cu(0)/Me₆‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me₆‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me₆‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005     

Catalytic effect of CO2 on peroxynitrite decomposition in the presence of cyanide complexes

The catalytic effect of CO2 on the kinetics and yields of peroxynitrite decomposition in the presence of cyanide complexes was investigated as a function of pH, substrate, bicarbonate and nitrite concentration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Menverins A–D,New Highly Oxygenated Guaiane Lactones from Hainan Gorgonian Menella verrucosa (Brundin)

Four new highly oxygenated guaiane lactones, menverins A–D ( 1 – 4 ), were isolated from the gorgonian Menella verrucosa (Brundin ) from the South China Sea. Their structures and relative configurations were elucidated on the basis of spectroscopic data. All compounds contain a conjugated α‐methyl‐substituted α, β‐unsaturated γ‐lactone moiety, a C(8)?C(9) conjugated with the γ‐lactone moiety, and an exocyclic methylene group at C(4) (trivial numbering).     

Effective Estimates for the Distribution of Values of Euler Products

We prove effective upper bounds for the almost periodicity of polynomial Euler products L(s){\cal L}(s) in the half-plane of absolute convergence. From this we deduce estimates for the roots of the equation L(s) = c{\cal L}(s) = c , where c is any non-zero complex number which is attained by L(s){\cal L}(s) . The method relies mainly on effective diophantine approximation.