Fluoroalkylation of aromatic compounds

Perfluoroalkylation of benzene, halobenzenes, pyridine, furan and thiophene has been accomplished through thermolysis of perfluoroalkyl iodides (CF₃I, n-C₁₀F₂₁I and R_fOR_fI) in the presence of the appropriate aromatic compound. Yields of alkylated products vary depending on temperature, presence of an HI acceptor and reactants ratio. Isomeric mixtures are obtained with halobenzenes, pyridine and thiophene. Furan however yields only the alpha substituted product.     

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Ohne Zusammenfassung     

Centrality dependence of charged particle multiplicity in Au-Au collisions at square root of (s)NN = 130 GeV

We present results for the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at square root of [s(NN)] = 130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find dN(ch)/d eta(vertical line eta = 0) = 622+/-1(stat)+/-41(syst). The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.     

Repetitive passive Q-switching and bistability in lasers with saturable absorbers

We report detailed experimental data on the passive Q-switching operation in a CO₂ laser with CH₃I saturable absorber, and on the transient behaviour in the near-Q-switching situation. Under suitable operating conditions, we found bistability in the output power. In some cases, we observed the simultaneous presence of bistability and passive Q-switching. The theoretical part of the paper starts from the four-level model of laser with saturable absorber, as formulated by other authors. By adiabatically eliminating the variables of the resonant levels, we reduce the problem to a set of three differential equations, from which we derive explicit analytical conditions for the rise of passive Q-switching. These conditions turn out to be in good qualitative and partially quantitative agreement with our experimental findings as well as with other experimental data previously obtained by other authors. Finally we classify the possible combinations of passive Q-switching and bistability that one can find in this type of experiments.     

Synthesis and reactions of perfluoro-n-octylmagnesium bromide

Perfluoro-n-octylmagnesium bromide has been conveniently synthesized through the metal-halogen exchange reaction between perfluoro-n-octyl iodide and ethyl- or phenyl-magnesium bromide. The thermal stability of the Grignard reagent and the products of the thermal decomposition have been estimated in diethyl ether and tetrahydrofuran. Reactions of the Grignard reagent with various substrates such as water, acetone, hexafluoroacetone, trimethylchlorosilane and carbon dioxide indicate the synthetic utility of n-octylmagnesium bromide.     

Absolutely continuous spectrum for one-dimensional Schrödinger operators with slowly decaying potentials: Some optimal results

The absolutely continuous spectrum of one-dimensional Schrödinger operators is proved to be stable under perturbation by potentials satisfying mild decay conditions. In particular, the absolutely continuous spectra of free and periodic Schrödinger operators are preserved under all perturbations satisfying This result is optimal in the power scale. Slightly more general classes of perturbing potentials are also treated. A general criterion for stability of the absolutely continuous spectrum of one-dimensional Schrödinger operators is established. In all cases analyzed, the main term of the asymptotic behavior of the generalized eigenfunctions is shown to have WKB form for almost all energies. The proofs rely on maximal function and norm estimates, and on almost everywhere convergence results for certain multilinear integral operators.

     

Thermal relaxation of glycerol and propylene glycol studied by photothermal spectroscopy

In this paper we report on experimental data for the frequency and temperature dependence of the thermal properties of supercooled glycerol and propylene glycol. By using a photopyroelectric method the specific heat capacity and thermal conductivity were separately determined in a bandwidth of several decades. We have recently shown that the thermal conductivity has no relaxation behavior, which simplifies the analysis of our results. The relaxation behavior of the specific heat capacity is compared with literature results for other physical quantities and a detailed analysis of the temperature dependence of the relaxation parameters is presented.     

Addition-elimination reactions between phenyllithium and some perfluorovinylether compounds

Reactions between C₆H₅Li and C₃F₇OCFCF₂ (I) yield phenyl substituted perfluorovinylethers. Stoichiometry and reaction temperature dictate the degree of substitution. With each replacement of F^θ by C₆H₅^θ the subsequent substitutions require more forcing conditions. The F^θ is substituted easier than the C₃F₇O^θ during the addition-elimination reactions.     

Numerical Simulation of the Application of NiTi Alloys in Medical Technologies

Shape memory alloys are nowadays already established as a material which is able to solve exceptional tasks in practical applications. Particularly, its utilization in the field of medical technologies increases steadily. For example micro tools (staple, catheters) and implants (coronary stents) are made out of Nickel-Titanium well known as a basic shape memory alloy. Apart from the advantages like the avoidance of auxiliary components and joints in the system and to utilize the high volume specific work of shape memory alloys, NiTi alloys exhibit a good biocompatibility. This property is necessary with regard to either permanent or temporary implants. To optimize the use of NiTi alloys in the scope of medical technologies, the support of the development of applicable tools by numerical simulations is highly recommended. However the complex material behaviour containing a profoundly thermomechanical coupling poses indeed a big challenge to the material modeling and its implementation into a finite element code. Particularly, the material model proposed by Helm [1] proves to be a firm model containing the most common properties of shape memory alloys, as the pseudoelasticity, the shape memory effect and the two-way effect. In the present contribution the FE modelling of a medical staple used in foot surgery is presented by considering the model of Helm which was investigated by the authors to improve its performance in the finite element method [2]. The foot staple, produced by a group of members of the SFB 459 which is funded by the DFG, avails the shape memory effect to excite the desired clamping effect [3]. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Production of highly aligned microfiber bundles from polymethyl methacrylate via stable jet electrospinning for organic solid-state lasers

The fabrication of micron-sized poly(methyl methacrylate) (PMMA) polymer optical fibers doped with rhodamine B as an organic dye is demonstrated. Highly aligned and defect-free fibers are fabricated by using the stable jet electrospinning (SJES) method and systematically varying critical parameters such as solvent type and polymer concentration. At optimal conditions, for example, a polymer concentration of 35 wt% of PMMA in butanone, ribbon-shaped fibers with a smooth surface and diameter of about 20 μm could be spun using SJES mode and deposited on a rotating drum as target in a highly aligned manner. Photoluminescence spectra of the doped fibers excited longitudinally and transversely with a laser show an excitation peak with full-width-at-half-maximum of only 5.05 nm and a low lasing threshold at a pump energy of 0.55 μJ, indicating that SJES could become a new source of amplified optics components or organic solid-state fiber lasers.