10,657 research outputs found
Failure of separation by quasi-homomorphisms in mapping class groups
We show that mapping class groups of surfaces of genus at least two contain
elements of infinite order that are not conjugate to their inverses, but whose
powers have bounded torsion lengths. In particular every homogeneous
quasi-homomorphism vanishes on such an element, showing that elements of
infinite order not conjugate to their inverses cannot be separated by
quasi-homomorphisms.Comment: 4 page
Bounded cohomology and non-uniform perfection of mapping class groups
Using the existence of certain symplectic submanifolds in symplectic
4-manifolds, we prove an estimate from above for the number of singular fibers
with separating vanishing cycles in minimal Lefschetz fibrations over surfaces
of positive genus. This estimate is then used to deduce that mapping class
groups are not uniformly perfect, and that the map from their second bounded
cohomology to ordinary cohomology is not injective.Comment: to appear in Invent. Mat
Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis
We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands that catalyze highly Z-selective olefin metathesis. A very simple and convenient procedure for the synthesis of such catalysts has been developed. Intramolecular C–H bond activation of the NHC ligand, promoted by anion ligand substitution, forms the appropriate chelate for stereocontrolled olefin metathesis
Photodarkening of amorphous selenium under high pressure
The photodarkening phenomena of amorphous Se have been studied by the optical absorption coefficient, sound velocity and attenuation measurements. The light illumination at low temperatures induces the photodarkening, and the photodarkened state is completely recovered by annealing near 306 K corresponding to the glass transition temperature. The photodarkening is enhanced by application of pressure. The sound velocity decreases and the sound attenuation increases by the illumination at low temperature. These suggest that a structural disorder increases in the photodarkened state. Three stages are observed for the recovery process of the photodarkened specimen. The photodarkening and the recovery process are discussed on the basis of VAP (valence alternative pair) model.<br /
General Solution of the Quantum Damped Harmonic Oscillator
In this paper the general solution of the quantum damped harmonic oscillator
is given.Comment: Latex ; 10 pages ; no figure ; typos corrected. The quantum damped
harmonic oscillator is solved completel
Z-Selective Homodimerization of Terminal Olefins with a Ruthenium Metathesis Catalyst
The cross-metathesis of terminal olefins using a novel ruthenium catalyst results in excellent selectivity for the Z-olefin homodimer. The reaction was found to tolerate a large number of functional groups, solvents, and temperatures while maintaining excellent Z-selectivity, even at high reaction conversions
Configurational factors in the perception of unfamiliar faces
Young et al (1987) have demonstrated that the juxtaposition of top and bottom halves of different faces produces a powerful impression of a novel face. It is difficult to isolate perceptually either half of the 'new' face. Inversion of the stimulus, however, makes this task easier. Upright chimeric faces appear to evoke strong and automatic configurational processing mechanisms which interfere with selective piecemeal processing. In this paper three experiments are described in which a matching paradigm was used to show that Young et al's findings apply to unfamiliar as well as to familiar faces. The results highlight the way in which minor procedural differences may alter the way in which subjects perform face-recognition tasks
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