Synthesis of two new thioesters bearing ferrocene: Vibrational characterization and ab initio calculations. X-ray crystal structure of S-(2-methoxyphenyl)ferrocenecarbothioate

Structural and conformational properties of S-benzyl ferrocenecarbothioate (I) and S-(2-methoxyphenyl) ferrocenecarbothioate (II) are analyzed using data obtained from X-ray diffraction, vibrational data and theoretical calculations. According to chemical quantum calculations, the synperiplanar and antiperiplanar forms are found as the first and second more stable conformations, respectively, for the title compounds. The geometric parameters and normal modes of vibration were calculated using a density functional theory method (B3LYP) and the 6-31+G∗∗ basis set for all atoms except for iron. For this atom the calculations were carried out with the Lanl2dz basis set. The calculated parameters are in good agreement with the corresponding X-ray diffraction values. The combined experimental and theoretical approach allows a consistent assignment for most of the fundamental modes.     

Laboratory measurement of sound absorption of occupied pews and standing audiences

Places of worship, as well as other performing spaces or large arenas are characterized by lightweight pews or seats, with moderate or negligible upholstery, leading to very low absorption coefficients. Consequently, the audience becomes the most important sound absorbing element, capable of playing a fundamental role in determining the acoustic characteristics of the space. Consequently accurate knowledge of its acoustic properties is required for any design purpose. Several studies have been carried out with reference to audiences seated on upholstered theatre seats but there is a considerable lack of information about occupied pews. The well known difficulty of taking into account edge effects during such measurements poses further questions as well as the effect of the density of occupation, and the seasonal variations due to clothing. This paper presents the results of a series of laboratory measurements aimed at clarifying such aspects. The measurements showed that the edge effects are negligible and that total absorption is better related to the number of persons present than to the area they cover. Nonetheless, as the density grows, or when the audience is seated, there is a reduction in absorption which may be explained by the reduction in exposed body surface. Lightweight clothes show a considerable reduction in sound absorption over all the frequency bands, suggesting that significant seasonal fluctuations in reverberation time should be expected in places where the audience is the only sound absorbing surface.     

Tunneling control of strongly correlated particles on a lattice: a photonic realization

We propose a photonic realization of tunneling control for two strongly correlated particles moving on a one-dimensional lattice, based on light transport in a square waveguide lattice with a periodically curved axis. We show the photonic analogue of dynamic localization of correlated particles and suggest the possibility to coherently suppress particle interaction.     

Kinetics and mechanism of the thermal gas‐phase oxidation of perfluorobutene‐2 in presence of trifluoromethyl hypofluorite

The oxidation of perfluorobutene‐2 (C₄F₈) initiated by trifluoromethyl hypofluorite (CF₃OF) in presence of O₂ has been studied at 323.1, 332.6, 342.5, and 352.0 K, using a conventional static system. The initial pressure of CF₃OF was varied between 4.8 and 23.6 Torr, that of C₄F₈ between 48.7 and 302.4 Torr, and that of O₂ between 51.5 and 270.4 Torr. Several runs were made in presence of 325.5–451.2 Torr of N₂. The main products were COF₂, CF₃C(O)F, and CF₃OC(O)F. Small amounts of compound containing ? CF(CF₃)? O? C(O)CF₃ group were also formed, as detected by ¹³C NMR spectroscopy. The oxidation is a homogeneous short‐chain reaction, attaining, at the pressure of O₂ used, the pseudo‐zero‐order condition with respect to O₂ as reactant. The reaction is independent of the total pressure. Its basic steps are as follows: the thermal generation of CF₃O^? radicals by the abstraction of fluorine atom of CF₃OF by C₄F₈, the addition of CF₃O^? to the alkene, the formation of perfluoroalkoxy radicals RO^? in presence of O₂, and the decomposition of these radicals via the C? C bond scission, giving products containing ? C(O)F end group and reforming RO^? and CF₃O^? radicals. The mechanism consistent with experimental results is postulated. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 532–541, 2003     

Ott—Liebler numbers

We define an analogue of the Ott—Liebler number for an arbitrary C _n-geometry. We study properties of C _n-geometries related with that invariant and we give some applications to quotients of C _n-geometries.     

Two new formulas for the numerical evaluation of the Hilbert Transform

We develop two algorithms for the numerical evaluation of the semi-infinite Hilbert Transform of functions with a given algebraic behaviour at the origin and at infinity. The first algorithm is connected with a Gauss-Jacobi type quadrature formula for unbounded intervals; the second is based on a rational Bernstein-type operator. Error estimates for different classes of functions are shown. Finally numerical examples are given, comparing the rules among themselves.     

Analytical and Experimental Investigation of Squeeze-Film Dampers Executing Circular Orbits

We have referred here the first results obtained in the course of an experimental research intended to examine oil film pressure of a squeeze film damper (with inertialess lubricant) executing circular orbits. An analytical expression for pressure arising into the gap was obtained before, for the short bearing SFD, in the general case of offset circular orbits. The expression obtained has permitted, in a simple way, the examination of the influence of the offset on pressure. Two approximated expressions for pressure (the one for pressure as a function of time at a fixed measuring section, the other for pressure along the circumference of the bearing at a given time), corresponding to centered orbits, were compared with the exact ones. We observed that the limits within which the nondimensional offset can be considered negligible, change according to comparisons between circumferential pressure diagrams or between pressure diagrams as functions of time. In the second case they are much wider. The experimental results concerned offset orbits with nominal radius r=0.5C and offset <0.1. Good accordance between theoretical and experimental pressure trends has been found, as concerns the positive part of dynamic pressure. As concerns the negative part of dynamic pressure, tests have shown that cavitation takes place for a more or less wide length, depending on feeding groove pressure, other conditions being equal. Complete effective pressure diagram coinciding with the theoretical one has been found for particular feeding conditions. Oil film tensile stresses have been frequently detected with both complete and incomplete diagrams owing to cavitation. Maximum measured tensile stress was about 220kN/m². It was finally found that theoretical and experimental trends are coincident only if the SFD is not starved. Analytical expression for pressure in the long bearing SFD executing offset circular orbits is referred in the appendix.     

Hydrogen–hydrogen bonding: The current density perspective

Current density plots of closed‐shell intermolecular H? H interactions characterized by a bond critical point (BCP) show two vortices separated by a saddle, a pattern which allows for a clear definition of a pair current strength. This H? H current strength turns out to be roughly related to the potential energy density at the BCP and then to the dissociation energy. The same pattern is also recognizable, at least for an azimuthal orientation of a field perpendicular to the H? H line, for the intramolecular interactions previously investigated to propose the H? H bonding. In the case of the H atoms of the bay region of polycyclic aromatic hydrocarbons, the current of the H? H delocalized diatropic vortex gives a quantitative indication of stabilization; however, on rotation of the field and the subsequent onset of a bay‐delocalized paratropic vortex (a typical signature of antiaromaticity), the diatropic vortex can be reshaped or it can even disappear, consistently with its smallness, and thus showing the effect of other more relevant interactions. © 2015 Wiley Periodicals, Inc.