Radical and radiation-induced grafting of some synthetic high polymers within the temperature range of their glass transition

The temperature dependence of radiation-induced grafting onto poly(ethylene terephthalate), polyamides, polyacrylonitrile, and polypropylene has been investigated for several monomers. In all cases a maximum grafting yield is obtained when the reaction is performed in the temperature range of the glass transition T_g of the polymer used. This maximum yield does not only appear with radiation-induced simultaneous grafting. It also appears when the graft polymerization is induced by pre-irradiation or even by thermal decomposition of organic peroxides. It is assumed that the pronounced maximum of the reactivity at T_g is obtained because in the glassy state below T_g the radicals formed cannot react due to a reduced diffusion of the monomer, whereas above T_g the number of radicals available for polymerization will be reduced with increasing temperature.     

Knot wormholes in geometrodynamics?

The familiar wormhole model of geometrodynamics is extended to allow for knotted embeddings of the initial hypersurface. It is shown that topology change is not only a means to modify the connectivity of the space, but also the knot invariants of its embedding. In a probabilistic framework the process of wormhole scattering can be expressed by creation and annihilation operators acting on the wave function of quantum geometrodynamics. Implications concerning Wheeler's exciton model of elementary particles, thef-gravity approach to hadronic matter, and interrelations with Jehle's flux quantization program are discussed.Work supported by a grant of the Studienstiftung des deutschen Volkes and in part by National Science Foundation grant No. GP 30799 X to Princeton University.     

An Improved Method for Preparation of Carboxylic Esters Using CsF-Celite/Alkyl Halide/Ch3Cn Combination

Preparations of compound 4 and of truxene derivatives 5, 6a,b, 7, 8, 10a, b, 11, 12a,b, and 13a,b are described. These substances are potential starting materials for the synthesis of bowl shaped polyaromatic compounds containing structural elements of fullerenes.     

Giant improvement of time-delayed feedback control by spatio-temporal filtering

Control of spatio-temporal chaos by the time-delay autosynchronization method is improved by several orders of magnitude. Unstable time periodic patterns are efficiently stabilized if one employs filters and couplings which originate from the Floquet eigenvalue problem of the unstable orbit. We illustrate our scheme by an application to a globally coupled reaction-diffusion model which describes charge transport in semiconductor devices.     

Boson Stars: Rotation, Formation, and Evolution

Boson stars are descendants of the so-calledgeons of Wheeler, except that they are built from scalarparticles instead of electromagnetic fields. If scalarfields exist in nature, such localized configurations kept together by their self-generatedgravitational field can form within Einstein's generalrelativity. In the case of complex scalar fields, anabsolutely stable branch of such non-topologicalsolitons with conserved particle number exists. Thepresent surge of interest stems from the speculativepossibility that these compact objects could provide aconsiderable fraction of the non-baryonic part of dark matter. In any case, they may serve as aconvenient laboratory for studyingnumerically rapidly rotating bodies in generalrelativity and the generation of gravitational waves.Furthermore, we mention how to detect boson stars by gravitationallensing or gravitational redshift. Finally, we explorethe evolution of boson stars within scalar-tensortheories.     

Are Axidilaton Stars Massive Compact Halo Objects?

Boson stars built from a very light Kalb–Ramond axion, the dilaton or other moduli fields of effective string models could provide a considerable fraction of the non-baryonic part of dark matter. Gravitational microlensing of 0.5 M MACHOs within the halo of galaxies may indirectly "weighing" the mass of the constituent scalar particle, resulting in 10^–10 eV/c².     

On the chiral anomaly in non-Riemannian spacetimes

Thetranslation Chern-Simons type three-formcoframe∧torsion on a Riemann-Cartan spacetime is related (by differentiation) to the Nieh-Yan fourform. Following Chandia and Zanelli, two spaces with nontrivial translational Chern-Simons forms are discussed. We then demonstrate, first within the classical Einstein-Cartan-Dirac theory and second in the quantum heat kernel approach to the Dirac operator, how the Nieh-Yan form surfaces in both contexts, in contrast to what has been assumed previously.