919 research outputs found

    The size, composition and fissioning in baboon troops (Papio ursinus Kerr, 1792)

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    Several baboon troops were studied during a two year study period. Sub-troop formation in troops was regularly observed and such sub-troops are defined as temporary or semi-permanent. Sub-troops are either normally or abnormally composed as far as age and sex classes are concerned. A temporary sub-troop sleeps apart from the main sub-troop, and these sub-troops reunite the following morning. A semi-permanent sub-troop separates from the main sub-troop for several days. During this period the semi-permanent sub-troop only joins the main sub-troop at sleeping places. The behaviour of certain males is prominent when sub-troops are formed. This study revealed that the baboon troop is wrongly referred to as a stable unit

    A reduced model for shock and detonation waves. I. The inert case

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    We present a model of mesoparticles, very much in the Dissipative Particle Dynamics spirit, in which a molecule is replaced by a particle with an internal thermodynamic degree of freedom (temperature or energy). The model is shown to give quantitavely accurate results for the simulation of shock waves in a crystalline polymer, and opens the way to a reduced model of detonation waves

    An efficient sampling algorithm for Variational Monte Carlo

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    We propose a new algorithm for sampling the NN-body density Ψ(R)2/R3NΨ2|\Psi({\bf R})|^2/\int_{\mathbb{R}^{3N}} |\Psi|^2 in the Variational Monte Carlo (VMC) framework. This algorithm is based upon a modified Ricci-Ciccotti discretization of the Langevin dynamics in the phase space (R,P)({\bf R},{\bf P}) improved by a Metropolis acceptation/rejection step. We show through some representative numerical examples (Lithium, Fluorine and Copper atoms, and phenol molecule), that this algorithm is superior to the standard sampling algorithm based on the biased random walk (importance sampling).Comment: 23 page

    Enantioselective palladium-catalyzed allylic alkylation reactions in the synthesis of Aspidosperma and structurally related monoterpene indole alkaloids

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    Enantioselective Pd-catalyzed allylic alkylations of prochiral enolates represent a powerful tool for the construction of all-carbon quaternary stereocenters. This review describes the emergence of such reactions as strategic linchpins that enable efficient, stereocontrolled syntheses of Aspidosperma and related monoterpene indole alkaloids

    Enantioselective palladium-catalyzed allylic alkylation reactions in the synthesis of Aspidosperma and structurally related monoterpene indole alkaloids

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    Enantioselective Pd-catalyzed allylic alkylations of prochiral enolates represent a powerful tool for the construction of all-carbon quaternary stereocenters. This review describes the emergence of such reactions as strategic linchpins that enable efficient, stereocontrolled syntheses of Aspidosperma and related monoterpene indole alkaloids

    Ultra Fast Nonlinear Optical Tuning of Photonic Crystal Cavities

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    We demonstrate fast (up to 20 GHz), low power (5 μW\mu W) modulation of photonic crystal (PC) cavities in GaAs containing InAs quantum dots. Rapid modulation through blue-shifting of the cavity resonance is achieved via free carrier injection by an above-band picosecond laser pulse. Slow tuning by several linewidths due to laser-induced heating is also demonstrated

    A reduced model for shock and detonation waves. II. The reactive case

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    We present a mesoscopic model for reactive shock waves, which extends a previous model proposed in [G. Stoltz, Europhys. Lett. 76 (2006), 849]. A complex molecule (or a group of molecules) is replaced by a single mesoparticle, evolving according to some Dissipative Particle Dynamics. Chemical reactions can be handled in a mean way by considering an additional variable per particle describing a rate of reaction. The evolution of this rate is governed by the kinetics of a reversible exothermic reaction. Numerical results give profiles in qualitative agreement with all-atom studies

    The Total Synthesis of (–)-Scabrolide A

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    The first total synthesis of the norcembranoid diterpenoid scabrolide A is disclosed. The route begins with the synthesis of two chiral pool-derived fragments, which undergo a convergent coupling to expediently introduce all 19 carbon atoms of the natural product. An intramolecular Diels–Alder reaction and an enone–olefin cycloaddition/fragmentation sequence are then employed to construct the fused [5–6–7] linear carbocyclic core of the molecule and complete the total synthesis

    Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation of 1,4-Diazepan-5-ones

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    We report the palladium-catalyzed asymmetric allylic alkylation of 1,4-diazepan-5-ones. This reaction proceeds smoothly to give gem-disubstituted diazepanone heterocycles bearing various functional groups in up to >99% yield and up to 95% ee. An electron-rich p-anisoyl lactam protecting group and the use of a nonpolar solvent proved crucial to obtaining high enantioselectivity in most cases. Additionally, we demonstrate the use of our methodology in the synthesis of a gem-disubstituted analogue of the FDA-approved anti-insomnia drug suvorexant
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