608 research outputs found
A reduced model for shock and detonation waves. I. The inert case
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
A reduced model for shock and detonation waves. II. The reactive case
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
Synthesis of enantioenriched γ-quaternary cycloheptenones using a combined allylic alkylation/Stork–Danheiser approach: preparation of mono-, bi-, and tricyclic systems
A general method for the synthesis of β-substituted and unsubstituted cycloheptenones bearing enantioenriched all-carbon γ-quaternary stereocenters is reported. Hydride or organometallic addition to a seven-membered ring vinylogous ester followed by finely tuned quenching parameters achieves elimination to the corresponding cycloheptenone. The resulting enones are elaborated to bi- and tricyclic compounds with potential for the preparation of non-natural analogs and whose structures are embedded in a number of cycloheptanoid natural products
A Unified Approach to the Daucane and Sphenolobane Bicyclo[5.3.0]decane Core: Enantioselective Total Syntheses of Daucene, Daucenal, Epoxydaucenal B, and 14-para-Anisoyloxydauc-4,8-diene
Access to the bicyclo[5.3.0]decane core found in the daucane and sphenolobane terpenoids via a key enone intermediate enables the enantioselective total syntheses of daucene, daucenal, epoxydaucenal B, and 14-para-anisoyloxydauc-4,8-diene. Central aspects include a catalytic asymmetric alkylation followed by a ring contraction and ring-closing metathesis to generate the five- and seven-membered rings, respectively
Three-Dimensional Analysis of Wakefields Generated by Flat Electron Beams in Planar Dielectric-Loaded Structures
An electron bunch passing through dielectric-lined waveguide generates
erenkov radiation that can result in high-peak axial electric field
suitable for acceleration of a subsequent bunch. Axial field beyond
Gigavolt-per-meter are attainable in structures with sub-mm sizes depending on
the achievement of suitable electron bunch parameters. A promising
configuration consists of using planar dielectric structure driven by flat
electron bunches. In this paper we present a three-dimensional analysis of
wakefields produced by flat beams in planar dielectric structures thereby
extending the work of Reference [A. Tremaine, J. Rosenzweig, and P. Schoessow,
Phys. Rev. E 56, No. 6, 7204 (1997)] on the topic. We especially provide
closed-form expressions for the normal frequencies and field amplitudes of the
excited modes and benchmark these analytical results with finite-difference
time-domain particle-in-cell numerical simulations. Finally, we implement a
semi-analytical algorithm into a popular particle tracking program thereby
enabling start-to-end high-fidelity modeling of linear accelerators based on
dielectric-lined planar waveguides.Comment: 12 pages, 2 tables, 10 figure
Ring-Contraction Strategy for the Practical, Scalable, Catalytic Asymmetric Synthesis of Versatile γ-Quaternary Acylcyclopentenes
Contraction action! A simple protocol for the catalytic asymmetric synthesis of highly functionalized γ-quaternary acylcyclopentenes (see schematic) in up to 91 % overall yield and 92 % ee has been developed. The reaction sequence employs a palladium-catalyzed enantioselective alkylation reaction and exploits the unusual stability of β-hydroxy cycloheptanones to achieve a general and robust method for performing two-carbon ring contractions
Palladium-Catalyzed Decarbonylative Dehydration of Fatty Acids for the Production of Linear Alpha Olefins
A highly efficient palladium-catalyzed decarbonylative dehydration reaction of carboxylic acids is reported. This method transforms abundant and renewable even-numbered natural fatty acids into valuable and expensive odd-numbered alpha olefins. Additionally, the chemistry displays a high functional group tolerance. The process employs a low loading of palladium catalyst and proceeds under solvent-free and relatively mild conditions
Transient heat generation in a quantum dot under a step-like pulse bias
We study the transient heat generation in a quantum dot system driven by a
step-like or a square-shaped pulse bias. We find that a periodically
oscillating heat generation arises after adding the sudden bias. One
particularly surprising result is that there exists a heat absorption from the
zero-temperature phonon subsystem. Thus the phonon population in
non-equilibrium can be less than that of the equilibrium electron-phonon
system. In addition, we also ascertain the optimal conditions for the operation
of a quantum dot with the minimum heat generation.Comment: 6 pages, 4 figure
Gas Phase Production and Loss of Isoprene Epoxydiols
Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-β- and trans-β-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-β- and trans-β, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10^(–11), (1.52 ± 0.07) × 10^(–11), and (0.98 ± 0.05) × 10^(–11) cm^3 molecule^(–1) s^(–1) for the δ1, cis-β, and trans-β isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions
Palladium-Catalyzed Construction of Quaternary Stereocenters by Enantioselective Arylation of γ-Lactams with Aryl Chlorides and Bromides
Herein, we report the first Pd‐catalyzed enantioselective arylation of α‐substituted γ‐lactams. Two sets of conditions were developed for this transformation, allowing for the use of either aryl chlorides or bromides as electrophiles. Utilizing a highly electron‐rich, dialkylphosphine ligand, we have been able to construct α‐quaternary centers in good yields (up to 91% yield) and high enantioselectivities (up to 97% ee)
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