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941.
J. Oscar C. JimÉnez‐halla Eduard Matito LluÍs Blancafort Juvencio Robles Miquel Solà 《Journal of computational chemistry》2009,30(16):2764-2776
In this work, we analyze the geometry and electronic structure of the [XnM3]n?2 species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo‐[M3]2? unit. The cyclo‐[M3]2? ring is held together through a three‐center two‐electron bond of σ‐character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo‐[M3]2? ring and leads to a change from σ‐aromaticity in the bound state of the cyclo‐[M3]2? to π‐aromaticity in the XM3? and X2M3 metallic clusters. Our results also show that the aromaticity of the cyclo‐[M3]2? unit in the X2M3 metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M3 ring. The Na2Mg3, Li2Mg3, and X2Ca3 clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M3 ring, whereas X2Be3 and K2Mg3 keep its aromaticity relatively constant along this process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
942.
Miroslav Bulíček Eduard Feireisl Josef Málek 《Nonlinear Analysis: Real World Applications》2009,10(2):992-1015
We consider a complete thermodynamic model for unsteady flows of incompressible homogeneous Newtonian fluids in a fixed bounded three-dimensional domain. The model comprises evolutionary equations for the velocity, pressure and temperature fields that satisfy the balance of linear momentum and the balance of energy on any (measurable) subset of the domain, and is completed by the incompressibility constraint. Finding a solution in such a framework is tantamount to looking for a weak solution to the relevant equations of continuum physics. If in addition the entropy inequality is required to hold on any subset of the domain, the solution that fulfills all these requirements is called the suitable weak solution. In our setting, both the viscosity and the coefficient of the thermal conductivity are functions of the temperature. We deal with Navier’s slip boundary conditions for the velocity that yield a globally integrable pressure, and we consider zero heat flux across the boundary. For such a problem, we establish the large-data and long-time existence of weak as well as suitable weak solutions, extending thus Leray [J. Leray, Sur le mouvement d’un liquide visquex emplissant l’espace, Acta Math. 63 (1934) 193–248] and Caffarelli, Kohn and Nirenberg [L. Caffarelli, R. Kohn, L. Nirenberg, Partial regularity of suitable weak solutions of the Navier–Stokes equations, Comm. Pure Appl. Math. 35 (6) (1982) 771–831] results, that deal with the problem in a purely mechanical context, to the problem formulated in a fully thermodynamic setting. 相似文献
943.
Eduard Matito Juan Manuel Barroso Emili Besalú Ove Christiansen Josep M. Luis 《Theoretical chemistry accounts》2009,123(1-2):41-49
In this work a new method to calculate anharmonic vibrational ground and excited state energies is proposed. The method relies on the auto-adjusting perturbation theory (APT) which has been successfully used to diagonalize square matrices. We use as zeroth order correction the self-consistent vibrational energies, and with the APT approach we calculate the vibrational anharmonic correlation correction to any desired order. In this paper we present the methodology and apply it to a model system and formaldehyde. Vibrational APT approach shows a robust convergent behavior even for the states where the standard (Rayleigh-Schrödinger) vibrational Møller-Plesset perturbation theory is clearly divergent. 相似文献
944.
The two-directional desymmetrization of prochiral precursors with α,β-unsaturated branches by catalyst-controlled 1,4-addition of silicon and likewise boron nucleophiles allows for a general enantioselective access to syn,anti-triols with 1,n + 1,2n + 1 (n = 2 and 3) substitution patterns. The utility is demonstrated in the synthesis of the C17-C25 fragment of dermostatin A. 相似文献
945.
Michael Gerken Prof. Dr. Gottfried Pawelke Dr. Eduard Bernhardt Dr. Helge Willner Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(25):7527-7536
The new tris(perfluoroalkyl)borane carbonyls, (C2F5)3BCO and (C3F7)3BCO, were prepared by means of a novel synthetic route using commercially available precursors by reacting K[(C2F5)3BCOOH] and K[(C3F7)3BCOOH] with concentrated sulfuric acid in the last step. The carboxylic acids, K[(C2F5)3BCOOH] and K[(C3F7)3BCOOH], were prepared by oxidative cleavage of the C?C triple bonds in Cs[(C2F5)3BC?CPh] and Cs[(C3F7)3BC?CPh] in a two‐step process to yield K[(C2F5)3BCO? COPh] and K[(C3F7)3BCO? COPh] as isolable intermediates. Crystal structures were obtained of K[(C2F5)3BCO? COPh], K[(C2F5)3BCOOH] ? H2O, (C2F5)3BCO, K[(C3F7)3BCOOH] ? 2 H2O, and (C3F7)3BCO. In the crystal structures of (C2F5)3BCO and (C3F7)3BCO the C?O bond lengths are 1.109(2) and 1.103(5) Å, respectively, which are among the shortest observed to date. Tris(pentafluoroethyl)borane carbonyl and (C3F7)3BCO slowly decompose at room temperature to yield CO, difluoroperfluoroalkylboranes and perfluoroalkenes. The decomposition of (C2F5)3BCO was found to follow a first‐order rate law with Ea=107 kJ mol?1. 相似文献
946.
Sergey S. Skiba Eduard G. Larionov Andrey Yu. Manakov Sergey I. Kozhemjachenko 《Journal of inclusion phenomena and macrocyclic chemistry》2010,67(3-4):353-359
Decomposition curves of gas hydrates formed in the ethane–hydrogen–water system were studied in the pressure interval 2–250 MPa. Gas hydrates synthesized at low (up to 5 MPa) pressures were also studied with use of X-ray powder diffraction and Raman spectroscopy. It was shown that ethane–hydrogen mixtures with hydrogen contents 0–30 mol.% form cubic structure I gas hydrates. Higher hydrogen concentration most probably results in appearance of another hydrate phase. We speculate that the gas mixtures with the hydrogen content above 60 mol.% form cubic structure II double hydrate of hydrogen and ethane at temperatures below ≈280 K and pressures above 25 MPa. 相似文献
947.
Eduard Cremades Jorge Echeverría Prof. Santiago Alvarez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(34):10380-10396
Herein we analyze the accessibility of the trigonal‐prismatic geometry to metal complexes with different electron configurations, as well as the ability of several hexadentate ligands to favor that coordination polyhedron. Our study combines i) a structural database analysis of the occurrence of the prismatic geometry throughout the transition‐metal series, ii) a qualitative molecular orbital analysis of the distortions expected for a trigonal‐prismatic geometry, and iii) a computational study of complexes of several transition‐metal ions with different hexadentate ligands. Also the tendency of specific electron configurations to present a cis bond‐stretch Jahn–Teller distortion is analyzed. 相似文献
948.
Eduard Marušić-Paloka 《Applicable analysis》2013,92(4):939-950
In this article we study purely viscous nonstationary flow of quasi-Newtonian fluids with share dependent viscosity obeying the power-law and the Carreau's law. We prove the existence and regularity of the solution using the Galerkin's procedure. 相似文献
949.
Eduard Feireisl 《偏微分方程通讯》2013,38(10):1778-1796
We discuss several aspects of the problem of propagation and dispersion of acoustic waves arising in the low Mach number asymptotic limits of compressible fluid systems. A general approach is proposed based on analysis of the spectral measures associated to the corresponding wave propagator. In particular, the local decay estimates based on a result of Tosio Kato and on RAGE theorem are obtained as limit cases. The approach is applied to problems on domains their shape may vary with the Mach number. 相似文献
950.
Van Wijk R Kobayashi M Van Wijk EP 《Journal of photochemistry and photobiology. B, Biology》2006,83(1):69-76
Ultra-weak photon emission of a living system has received scientific attention because of its potential for monitoring oxidative metabolism and oxidative damage to tissues. Heretofore, most studies have focused only on the emission from hands. The data regarding emission from other anatomic locations are limited. A previous multi-anatomic site recording of four subjects quantitatively demonstrated that the emission from several corresponding anatomic locations could differ by as much as a factor of 4. The data also suggested a "common" anatomic emission percentage distribution pattern. This information raised the question whether such a typical anatomic percentage emission exists. The objective of the present paper is to systematically replicate the emission from identical anatomic locations to document whether the anatomic percentage distribution pattern is generic. Part 1 includes the recording of ultra-weak photon emission from one sample subject over the torso, head and upper extremities with a highly sensitive charge-coupled device (CCD). Part 2 includes the analysis of that data to select a series of anatomic locations that were subsequently studied with a group of 20 subjects utilizing a highly sensitive, cooled and moveable (in three directions) photomultiplier system. Total sum emission of all recorded anatomic locations per subject fluctuates in this study almost 5-fold between subjects. However, the contribution of each anatomic location to the total emission from each subject was approximately the same percentage for each subject and similar to the sample CCD subject. The deviation of the anatomic percentage contribution for each subject was also established. The study presents evidence that there is a "common" anatomic percentage distribution pattern of ultra-weak photon emission for corresponding locations from each subject. 相似文献