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961.
Felix Rosas Rosa M. Domínguez José R. Mora Edgar Marquez Tania Córdova Gabriel Chuchani 《Journal of Physical Organic Chemistry》2010,23(12):1127-1136
The products formed in 2‐methoxytetrahydropyran elimination reaction in the gas phase are 3, 4‐dihydro‐2H‐pyran and methanol. The kinetic study was carried out in a static system, with the vessels deactivated with allyl bromide, and the presence of the free radical suppressor toluene. Temperature and pressure ranges were 400–450 °C and 25–83 Torr, respectively. The process is homogeneous, unimolecular, and follows a first‐order rate law. The observed rate coefficient is represented by the following equation: log k (s?1) = (13.95 ± 0.15) ? (223.1 ± 2.1) (kJ mol?1) (2.303RT)?1. The reactant exists mainly in two low energy chair‐like conformations, with the 2‐methoxy group in axial or equatorial position. However, the transition state (TS) for the elimination of the two conformers is the same. Theoretical calculations of this reaction were carried for two possible mechanisms from these conformations by using DFT functionals B3LYP, MPW1PW91, and PBE with the basis set 6‐31G(d,p) and 6‐31G++(d,p). The calculation results demonstrate that 2‐methoxytetrahydropyran exists mainly in two conformations, with the 2‐methoy group in axial or equatorial position, that are thermal in equilibrium. The average thermodynamic and kinetic parameters, taking into account the populations of the conformers in the equilibrium, are in good agreement with experimental values at B3LYP/6‐31++(d,p) level of theory. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
962.
Michael Bradley S. Brian Edgar M. P. Machado Ramos 《General Relativity and Gravitation》2010,42(1):155-182
Metrics obtained by integrating within the generalised invariant formalism are structured around their intrinsic coordinates,
and this considerably simplifies their invariant classification and symmetry analysis. We illustrate this by presenting a
simple and transparent complete invariant classification of the conformally flat pure radiation metrics (except plane waves)
in such intrinsic coordinates; in particular we confirm that the three apparently non-redundant functions of one variable
are genuinely non-redundant, and easily identify the subclasses which admit a Killing and/or a homothetic Killing vector.
Most of our results agree with the earlier classification carried out by Skea in the different Koutras–McIntosh coordinates,
which required much more involved calculations; but there are some subtle differences. Therefore, we also rework the classification
in the Koutras–McIntosh coordinates, and by paying attention to some of the subtleties involving arbitrary functions, we obtain
complete agreement with the results obtained in intrinsic coordinates. We have corrected and completed statements and results
by Edgar and Vickers, and by Skea, about the orders of Cartan invariants at which particular information becomes available. 相似文献
963.
Solitary waves are lumps of energy. We consider the study of dynamical solitary waves, meaning cases where the energy lumps are moving, as opposed to topological solitary waves where the lumps may be static. Solitary waves have been studied in some form or the other for nearly 450 years. Subsequently, there have been many authoritative works on solitary waves. Nevertheless, some of the most recent studies reveal that these peculiar objects are far more complex than what we might have given them credit for. In this review, we introduce the physics of solitary waves in alignments of elastic beads, such as glass beads or stainless steel beads. We show that any impulse propagates as a new kind of highly interactive solitary wave through such an alignment and that the existence of these waves seems to present a need to re-examine the very definition of the concept of equilibrium. We further discuss the possibility of exploiting nonlinear properties of granular alignments to develop exciting technological applications. 相似文献
964.
965.
Huang Y Yoon SH Heron SR Masselon CD Edgar JS Tureček F Goodlett DR 《Journal of the American Society for Mass Spectrometry》2012,23(6):1062-1070
Surface acoustic wave nebulization (SAWN) has recently been reported as a novel method to transfer non-volatile analytes directly
from solution to the gas phase for mass spectrometric analysis. Here we present a comparison of the survival yield of SAWN
versus electrospray ionization (ESI) produced ions. A series of substituted benzylpyridinium (BzPy) compounds were utilized
to measure ion survival yield from which ion energetics were inferred. We also estimated bond dissociation energies using
higher level quantum chemical calculations than previously reported for BzPy ions. Additionally, the effects on BzPy precursor
ion survival of SAWN operational parameters such as inlet capillary temperature and solution flow-rate were investigated.
Under all conditions tested, SAWN-generated BzPy ions displayed a higher tendency for survival and thus have lower internal
energies than those formed by ESI. 相似文献
966.
Delaunay Refinement for Piecewise Smooth Complexes 总被引:5,自引:0,他引:5
We present a Delaunay refinement algorithm for meshing a piecewise smooth complex in three dimensions. The algorithm protects
edges with weighted points to avoid the difficulty posed by small angles between adjacent input elements. These weights are
chosen to mimic the local feature size and to satisfy a Lipschitz-like property. A Delaunay refinement algorithm using the
weighted Voronoi diagram is shown to terminate with the recovery of the topology of the input. Guaranteed bounds on the aspect
ratios, normal variation, and dihedral angles are also provided. To this end, we present new concepts and results including
a new definition of local feature size and a proof for a generalized topological ball property. 相似文献
967.
We investigate the possibility of inducing the cosmological constant from extra dimensions by embedding our four-dimensional
Riemannian space-time into a five-dimensional Weyl integrable space. Following the approach of the space-time-matter theory
we show that when we go down from five to four dimensions, the Weyl field may contribute both to the induced energy-tensor
as well as to the cosmological constant Λ, or more generally, it may generate a time-dependent cosmological parameter Λ(t). As an application, we construct a simple cosmological model in which Λ(t) has some interesting properties. 相似文献
968.
Ramakrishna Bandi Alexandre Fotue Tabue Edgar Martínez-Moro 《Designs, Codes and Cryptography》2018,86(10):2247-2254
Let \(\texttt {R}\) be a finite commutative Frobenius ring and \(\texttt {S}\) a Galois extension of \(\texttt {R}\) of degree m. For positive integers k and \(k'\), we determine the number of free \(\texttt {S}\)-submodules \(\mathcal {B}\) of \(\texttt {S}^\ell \) with the property \(k=\texttt {rank}_\texttt {S}(\mathcal {B})\) and \(k'=\texttt {rank}_\texttt {R}(\mathcal {B}\cap \texttt {R}^\ell )\). This corrects the wrong result (Bill in Linear Algebr Appl 22:223–233, 1978, Theorem 6) which was given in the language of codes over finite fields. 相似文献
969.
Additive cyclic codes over Galois rings were investigated in Cao et al. (2015). In this paper, we investigate the same problem but over a more general ring family, finite commutative chain rings. When we focus on non-Galois finite commutative chain rings, we observe two different kinds of additivity. One of them is a natural generalization of the study in Cao et al. (2015), whereas the other one has some unusual properties especially while constructing dual codes. We interpret the reasons of such properties and illustrate our results giving concrete examples. 相似文献
970.
Edgar Lee Stout 《Proceedings of the American Mathematical Society》2006,134(8):2303-2308
Every continuous function on a compact, holomorphically convex, real-analytic subset of can be approximated uniformly by functions holomorphic on the set.