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排序方式: 共有341条查询结果,搜索用时 15 毫秒
321.
Määttänen A Vehkamäki H Lauri A Napari I Kulmala M 《The Journal of chemical physics》2007,127(13):134710
We develop a two-component heterogeneous nucleation model that includes exact calculation of the Stauffer-type [D. Stauffer, J. Aerosol Sci. 7, 319 (1976)] steady-state kinetic prefactor using the correct heterogeneous Zeldovich factor for a heterogeneous two-component system. The model, and a simplified version of it, is tested by comparing its predictions to experimental data for water-n-propanol nucleating on silver particles. The model is then applied to water-carbon dioxide system in Martian conditions, which has not been modeled before. Using the ideal mixture assumption, the model shows theoretical possibilities for two-component nucleation adjacent to the initial stages of one-component water nucleation, especially with small water vapor amounts. The numbers of carbon dioxide molecules in the critical cluster are small in the case of large water amounts (up to 300 ppm) in the gas phase, but larger when there is very little water vapor (1 ppm). 相似文献
322.
We calibrate the methodology for the calculation of nuclear magnetic resonance (NMR) properties in novel organo-xenon compounds. The available state-of-the-art quantum-chemical approaches are combined and applied to the HXeCCH molecule as the model system. The studied properties are (129)Xe, (1)H, and (13)C chemical shifts and shielding anisotropies, as well as (131)Xe and (2)H nuclear quadrupole coupling constants. The aim is to obtain, as accurately as currently possible, converged results with respect to the basis set, electron correlation, and relativistic effects, including the coupling of relativity and correlation. This is done, on one hand, by nonrelativistic correlated ab initio calculations up to the CCSD(T) level and, on the other hand, for chemical shifts and shielding anisotropies by the leading-order relativistic Breit-Pauli perturbation theory (BPPT) with correlated ab initio and density-functional theory (DFT) reference states. BPPT at the uncorrelated Hartree-Fock level as well as the corresponding fully relativistic Dirac-Hartree-Fock method are found to be inapplicable due to a dramatic overestimation of relativistic effects, implying the influence of triplet instability in this multiply bonded system. In contrast, the fully relativistic second-order Moller-Plesset perturbation theory method can be applied for the quadrupole coupling, which is a ground-state electric property. The performance of DFT with various exchange-correlation functionals is found to be inadequate for the nonrelativistic shifts and shielding anisotropies as compared to the CCSD(T) results. The relativistic BPPT corrections to these quantities can, however, be reasonably predicted by DFT, due to the improved triplet excitation spectrum as compared to the Hartree-Fock method, as well as error cancellation within the five main BPPT contributions. We establish three computationally feasible models with characteristic error margins for future calculations of larger organo-xenon compounds to guide forthcoming experimental NMR efforts. The predicted (129)Xe chemical shift in HXeCCH is in a novel range for this nucleus, between weakly bonded or solvated atomic xenon and xenon in the hitherto characterized molecules. 相似文献
323.
324.
Masud Chaichian Markku Oksanen Anca Tureanu 《The European Physical Journal C - Particles and Fields》2011,71(6):1657
We study the recently proposed Covariant Renormalizable Gravity (CRG), which aims to provide a generally covariant ultraviolet
completion of general relativity. We obtain a spacetime decomposed form—an Arnowitt–Deser–Misner (ADM) representation—of the
CRG action. The action is found to contain time derivatives of the gravitational fields up to fourth order. Some ways to reduce
the order of these time derivatives are considered. The resulting action is analyzed using the Hamiltonian formalism, which
was originally adapted for constrained theories by Dirac. It is shown that the theory has a consistent set of constraints.
It is, however, found that the theory exhibits four propagating physical degrees of freedom. This is one degree of freedom
more than in Hořava–Lifshitz (HL) gravity and two more propagating modes than in general relativity. One extra physical degree
of freedom has its origin in the higher order nature of the CRG action. The other extra propagating mode is a consequence
of a projectability condition similarly as in HL gravity. Some additional gauge symmetry may need to be introduced in order
to get rid of the extra gravitational degrees of freedom. 相似文献
325.
Guillon G Zanchet A Leino M Viel A Zillich RE 《The journal of physical chemistry. A》2011,115(25):6918-6926
An analytical potential energy surface for a rigid Rb? in the 3Σ(u)? state interacting with one helium atom based on accurate ab initio computations is proposed. This 2-dimensional potential is used, together with the pair approximation approach, to investigate Rb? attached to small helium clusters He(N) with N = 1-6, 12, and 20 by means of quantum Monte Carlo studies. The limit of large clusters is approximated by a flat helium surface. The relative orientation of the dialkali axis and the helium surface is found to be parallel. Dynamical investigations of the pendular and of the in-plane rotation of the rigid Rb? molecule on the surface are presented. 相似文献
326.
A simple method for absolute-frequency measurements of molecular transitions in the mid-IR region is reported. The method is based on a cw singly resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45?μm. The mid-IR frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute-frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated. 相似文献
327.
Single-layer one-dimensional nonpolarizing guided-mode resonance filters under normal incidence 总被引:1,自引:0,他引:1
Alasaarela T Zheng D Huang L Priimagi A Bai B Tervonen A Honkanen S Kuittinen M Turunen J 《Optics letters》2011,36(13):2411-2413
We demonstrate that properly designed one-dimensional guided-mode resonance filters (GMRFs) with only one grating layer can exhibit a nonpolarizing resonant filtering effect under normal incidence. A sinusoidal profile nonpolarizing GMRF is realized by photoinduced surface-relief grating formation on thin films of polymer-azobenzene complexes and subsequent atomic layer deposition, showing the feasibility of fabrication of such compact GMRFs. 相似文献
328.
Harri Heiskanen Peter Denifl Markku Hurme Päivi Pitkänen Marita Oksman 《Journal of Dispersion Science and Technology》2013,34(2):234-244
Microspheres were prepared using a hydrocarbon-perfluorocarbon solvent extraction process. The effect of the physical properties and the emulsification conditions on the mean microsphere size was investigated. The viscosity of the dispersed and the continuous phase greatly affected the microsphere size. Smaller microspheres were produced at the same mixing intensity when the viscosity of the dispersed phase decreased. Increased continuous phase viscosity reduced the coalescenceof the droplets and hence smaller microspheres were produced. The mean microsphere size first decreased as the volume ratio of the dispersed phase to the continuous phase increased but upon further increase the mean microsphere size increased. The effect of the volume ratio on the microsphere size was linked to the surfactant concentration. The stability of the studied hydrocarbon-in-fluorocarbon emulsion is poor. One reason for the poor stability is the high density difference between the phases. The emulsion droplets were solidified by siphoning part of the emulsion in the fresh continuous phase, which extracted the solvent from the dispersed phase. The effect of emulsion transfer time between the emulsification and solidification steps on the particle size was studied but no significant effect was observedduring the controlled time interval. 相似文献
329.
Markus Lindqvist Dr. Kirill Axenov Dr. Martin Nieger Dr. Minna Räisänen Prof. Markku Leskelä Prof. Timo Repo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10412-10418
Dimethylamino‐(+)‐camphorenamine reacted with an equimolar amount of Piers’ borane, HB(C6F5)2, to give the corresponding iminium–hydroborate zwitterionic salt. Being in equilibrium with the parent enamine–HB(C6F5)2 N–B pair, this salt was able to split hydrogen heterolytically, hydrogenating the iminium group in the molecule. Detailed studies revealed that the hydrogen splitting in this reaction proceeded through an intermolecular pathway leading to a bornylamine–HB(C6F5)2 adduct. When the starting enamine is present in excess over HB(C6F5)2, the produced bornylamine–HB(C6F5)2 adduct breaks up, eliminating free bornylamine and forming the initial camphorenamine– HB(C6F5)2 pair. This results in hydrogenation of the camphorenamine framework in a catalytic fashion. 相似文献
330.
Raija Oilunkaniemi Risto S. Laitinen Jouni Pursiainen Markku Ahlgren 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):577-582
The preparation of [M(C4H3SECH3)2Cl2] (M = Pd, Pt; E = Se, Te) and [Pd6Te6(C4H3S)2(PPh3)6Cl2] from methyl(2-thienyl)chalcogenides and bis(2-thienyl) ditelluride is reported. The products are identified and characterized by X-ray crystallography and by 77Se and 125Te NMR spectroscopy. 相似文献