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991.
Gehrhus B Hitchcock PB Pongtavornpinyo R Zhang L 《Dalton transactions (Cambridge, England : 2003)》2006,(15):1847-1857
Reduction of Cl2Si[(NR)2C6H4-1,2] (R = CH2Bu(t)) with potassium is known to lead to the stable silylene Si[(NR)2C6H4-1,2] (1). However, silylene is now shown to react further with an alkali metal (Na or K) to yield the (1)(2)2-, c-(1)(3)-*, c-(1)(3)2- or c-(1)(4)2- derivatives. Reduction of Cl2Si[(NR)2C6H4-1,2] (R = CH2CH3 or CH2CHMe2) with potassium does not lead to an isolable silylene, but such a silylene is proposed to be an intermediate and, as for 1, reacts further to afford the potassium salts of c-[Si{(NR)2C6H4-1,2}]4-* and c-[Si{(NR)2C6H4-1,2}](4)2-. The pathways leading to the anionic cyclotri- and cyclotetrasilanes are discussed and supported experimentally; including by X-ray structures of relevant intermediates. 相似文献
992.
Efficient quenching of photoluminescence from functionalized single-walled carbon nanotubes by nitroaromatic molecules 总被引:2,自引:0,他引:2
Kose ME Harruff BA Lin Y Veca LM Lu F Sun YP 《The journal of physical chemistry. B》2006,110(29):14032-14034
The photoluminescence from functionalized single-walled carbon nanotubes was found to be highly sensitive to the presence of nitroaromatic compounds such as nitrobenzene, 4-nitrotoluene, and 2,4-dinitrotoluene. The strong luminescence quenching in solution was at the upper limit of diffusion-control and also showed significant static quenching contributions. Mechanistic implication of the results and potential applications are discussed. 相似文献
993.
Fred Espen Benth Barbara Rüdiger Andre Süss 《Stochastic Processes and their Applications》2018,128(2):461-486
We propose a non-Gaussian operator-valued extension of the Barndorff-Nielsen and Shephard stochastic volatility dynamics, defined as the square-root of an operator-valued Ornstein–Uhlenbeck process with Lévy noise and bounded drift. We derive conditions for the positive definiteness of the Ornstein–Uhlenbeck process, where in particular we must restrict to operator-valued Lévy processes with “non-decreasing paths”. It turns out that the volatility model allows for an explicit calculation of its characteristic function, showing an affine structure. We introduce another Hilbert space-valued Ornstein–Uhlenbeck process with Wiener noise perturbed by this class of stochastic volatility dynamics. Under a strong commutativity condition between the covariance operator of the Wiener process and the stochastic volatility, we can derive an analytical expression for the characteristic functional of the Ornstein–Uhlenbeck process perturbed by stochastic volatility if the noises are independent. The case of operator-valued compound Poisson processes as driving noise in the volatility is discussed as a particular example of interest. We apply our results to futures prices in commodity markets, where we discuss our proposed stochastic volatility model in light of ambit fields. 相似文献
994.
We first give an example of a rigid structure of computable dimension 2 such that the unique isomorphism between two non-computably isomorphic computable copies has Turing degree strictly below , and not above . This gives a first example of a computable structure with a degree of categoricity that does not belong to an interval of the form for any computable ordinal α. We then extend the technique to produce a rigid structure of computable dimension 3 such that if , , and are the degrees of isomorphisms between distinct representatives of the three computable equivalence classes, then each . The resulting structure is an example of a structure that has a degree of categoricity, but not strongly. 相似文献
995.
This study investigates the optical properties of selected metal oxides due to their high dielectric constants. The local-spin-density approximation plus Hubbard U (commonly called LDA+U) is used in a study of the structural, mechanical and optical properties of UO2. The inclusion of a Hubbard U correction to 5f electrons of uranium changes UO2 from a metal to an insulator and, therefore, has a dramatic effect on the localisation of the electron spin and charge density of uranium. However although the band gap can be reproduced using the effective U parameter, which is equal to 3.5 eV and optical properties were calculated in our previous work, it is difficult to calculate ionic contribution to the static dielectric constant within LDA+U formalism for this compound. It is shown in the present work that the electronic structures of both ceria and thoria exhibit similarities to urania within LDA or PBE functional implementations. Within this functional and linear response theory one can easily calculate static dielectric permittivity and it is shown that in agreement with experiment the predicted values are an order of magnitude larger than the dielectric constant of SiO2. In this work, high accuracy, first-principles calculations are also used to compare properties of urania versus ceria and thoria and how these similarities can help in understanding these compounds. It is also shown that the B3LYP functional predicts slightly overestimated band gaps for ceria and thoria as well as smaller than experimentally observed electronic contribution to the static dielectric constant, while the index of refraction is well reproduced for thoria. 相似文献
996.
Structural Modifications of cis‐Glycofused Benzopyran Compounds and Their Influence on the Binding to Amyloid‐β Peptide 下载免费PDF全文
Dr. Cristina Airoldi Dr. Giuseppe D'Orazio Dr. Barbara Richichi Dr. Cinzia Guzzi Dr. Veronica Baldoneschi Dr. Laura Colombo Dr. Mario Salmona Prof. Cristina Nativi Prof. Francesco Nicotra Prof. Barbara La Ferla 《化学:亚洲杂志》2016,11(2):299-309
A small library of glycofused tricyclic compounds with a central pyran ring chemically modified in the position para to the ring oxygen has been synthesised. The influence of the chemical modification on the structural conformation of the compounds and on their ability to bind Aβ peptide has been evaluated respectively using molecular mechanics (MM) and molecular dynamics (MD) simulations, and STD NMR spectroscopy. The introduction of particularly polar/charged groups leads to the loss of binding ability, without a significant change in the conformation, whilst other substitutions does not significantly affect either the structural conformation or the binding. 相似文献
997.
The partition model of retention is developed for reversed phase liquid chromatography with multicomponent mobile phases. Simple equations for the retention and selectivity in ternary mobile phases are derived. For the systems in which the ratio of volume fractions of organic modifiers remains fixed, new linear dependences for retention factor and selectivity are proposed. These equations are successfully used to describe experimental data found in the literature. An influence of the nature of organic solvents and proportion in which they are mixed on retention and selectivity is discussed. 相似文献
998.
Barbara Schüpp‐Niewa Larysa Shlyk Yurii Prots Rainer Niewa Gernot Krabbes 《无机化学与普通化学杂志》2006,632(4):572-576
Single crystals of the new 6H‐perovskite Ba3ZrRu2O9 have been grown from BaCO3 and RuO2 in presence of BaCl2 on ZrO2 bars. Ba3ZrRu2O9 crystallizes in the space group P63/mmc (No. 194) with a = 5.7827(2) Å and c = 14.2509(5) Å (Z = 2, R1 = 0.037, wR2 = 0.078). The structure consists of pairs of face‐shared RuO6 octahedra forming [Ru2O9] units, which are interconnected by corner‐sharing ZrO6 octahedra. The structural relationships of the title compound and of the already known barium‐zirconium‐ruthenate Ba4ZrRu3O12, 4H‐ and 9R‐BaRuO3 and BaZrO3 are discussed. 相似文献
999.
Calum Kinnear Sandor Balog Barbara Rothen‐Rutishauser Alke Petri‐Fink 《Macromolecular rapid communications》2014,35(23):2012-2017
The directed self‐assembly of gold nanoparticles through the crystallization of surface‐grafted polyethylene oxide (PEO) in ethanol–water mixtures is described. This process is fully reversible and tunable through either the size of the core or the polymeric coating. Characterization by X‐ray scattering and electron microscopy of the self‐assembled structures reveals order at the nanoscale, typically not the case for thermoresponsive gold nanoparticles coated with lower or upper critical solution temperature polymers. A further novelty is the result of selective binding of calcium ions to the PEO in the fluid state: a reversible thermoresponsive transition become irreversible.
1000.
Paci P Zvinevich Y Tanimura S Wyslouzil BE Zahniser M Shorter J Nelson D McManus B 《The Journal of chemical physics》2004,121(20):9964-9970
We used a tunable diode laser absorption spectrometer to follow the condensation of D(2)O in a supersonic Laval nozzle. We measured both the concentration of the condensible vapor and the spectroscopic temperature as a function of position and compared the results to those inferred from static pressure measurements. Upstream and in the early stages of condensation, the quantitative agreement between the different experimental techniques is good. Far downstream, the spectroscopic results predict a lower gas phase concentration, a higher condensate mass fraction, and a higher temperature than the pressure measurements. The difference between the two measurement techniques is consistent with a slight compression of the boundary layers along the nozzle walls during condensation. 相似文献