The influence of substructure modeling on the structural-acoustic response of a plate system

Changes in the vibro-acoustic response of a fluid-loaded plate due to variations in some of the modeling details associated with an attached substructure are examined. The attached substructure consists of a smaller plate supported by springs along each edge. To examine the important modeling issues, three studies are performed. In the first study, discrete changes in the system response due to discrete changes in the size of the region over which the spring elasticity is distributed are examined. In the second study, substructure modeling issues are examined by varying the number of degrees-of-freedom included in the substructure model. Finally, sensitivity relationships that express changes in the system response to changes in the scale of the spring elements are developed. These relationships are used to examine changes in the system response due to small variations in the scale of the distributed elasticity. Both the combined system response and acoustic radiation are computed using the Acoustic Surface Variational Principle and Hamilton's Principle. For the example cases considered, it is shown that details associated with the scale of the spring are only important for frequencies near or below the resonances of the isolated subsystem. Furthermore, only the dynamics of the substructure including rigid-body type motions are important.     

Analytic evaluation of nonadiabatic coupling terms at the MR-CI level. I. Formalism

An efficient and general method for the analytic computation of the nonandiabatic coupling vector at the multireference configuration interaction (MR-CI) level is presented. This method is based on a previously developed formalism for analytic MR-CI gradients adapted to the use for the computation of nonadiabatic coupling terms. As was the case for the analytic energy gradients, very general, separate choices of invariant orbital subspaces at the multiconfiguration self-consistent field and MR-CI levels are possible, allowing flexible selections of MR-CI wave functions. The computational cost for the calculation of the nonadiabatic coupling vector at the MR-CI level is far below the cost for the energy calculation. In this paper the formalism of the method is presented and in the following paper [Dallos et al., J. Chem. Phys. 120, 7330 (2004)] applications concerning the optimization of minima on the crossing seam are described.     

Metathesis approach to the synthesis of polyheterocyclic structures from oxanorbornenes

[reaction: see text] The synthesis of stereochemically defined tri- and penta-heterocyclic ring systems 9 and 28, respectively, via the metathesis reaction of substituted oxanorbornanes derived from 3 is described.     

Mössbauer study of iron-cobalt-rhodium spinels

Mössbauer source and absorber studies have been carried out on the spinel system CoFe_xRh_2?xO₄ for x = 0.005, 0.3, 0.5, 1.0, 1.2 and 1.5. For 0.005 ? x ? 1.2, the cation distribution is normal with Co²⁺ on Asites. At x = 1.5, the distribution is nearly inverse. In the cases x = 0.005 and 0.3, iron on the B sites does not produce a quadrupole doublet indicating that the B sites are cubic which is contrary to the usual case in spinels.     

Imino-bridged heterocycles. IV . A facile synthesis of sulfenimines derived from diaryl ketones

Efficient, high-yield syntheses of N-diarylmethylene sulfenamides (sulfenimines) have been developed under mild laboratory conditions. Diaryl ketones have been shown to form ketimines readily by condensation with ammonia in the presence of titanium tetrachloride.     

A high resolution spectroscopic study of rhodium monochloride

Rhodium monochloride has been observed and characterized spectroscopically for the first time. The RhCl molecules were produced in a laser vaporization molecular beam source by the reaction of a laser vaporized rhodium plasma with CCl₄ doped in helium, and laser-induced fluorescence and dispersed fluorescence were used to study 15 of the strongest bands spanning the 535-415 nm region. Twelve of these bands were studied at high resolution using a cw ring dye laser. Two low-lying states separated by 140 cm⁻¹ have been observed. The ground state has Ω = 2 and is attributed to a ³Π_i state resulting from a δ⁴π³σ¹ electronic configuration. The other low-lying state has Ω = 3 and is attributed to a ³Δ_i state resulting from a δ³π⁴σ¹ electronic configuration. Excited states with Ω values ranging from 1 to 4 have been observed. Dispersed fluorescence from these excited levels has been used to identify a large number of low-lying electronic states within an energy range of 5200 cm⁻¹ and has also been used to determine a ground state vibrational frequency of ∼348 cm⁻¹. Λ-doublings have been observed in all the transitions studied at high resolution.     

Self-organization and polyolefin nucleation efficacy of 1,3:2,4-di-p-methylbenzylidene sorbitol

Recent studies have demonstrated that addition of a small quantity of dibenzylidene sorbitol (DBS) to a molten polymer may result in a physical gel if conditions permit the DBS molecules to self-organize into a three-dimensional network composed of highly connected nanofibrils. If the polymer crystallizes, DBS may also serve as a nucleating agent, promoting the formation of spherulites, especially in commercially important polyolefins such as polypropylene. We examine the thermal and mechanical properties, as well as the morphological characteristics, of an isotactic polypropylene copolymer with 3 wt % ethylene upon addition of less than 1 wt % of 1,3:2,4-di-p-methylbenzylidene sorbitol (MDBS). From dynamic rheological measurements, pronounced complex viscosity increases, attributed to MDBS nanofibril network formation, are observed at concentration-dependent temperatures above the melting point of the nucleated copolymer. Transmission electron micrographs of RuO₄-stained sections confirm the existence of MDBS nanofibrils measuring on the order of 10 nm in diameter and, at higher concentrations, fibrillar bundles measuring up to about 200 nm across and several microns in length. The addition of MDBS at different concentrations is also found to promote increases in optical clarity, yield strength, tensile strength, and ultimate elongation of modified copolymer formulations. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2617–2628, 1997     

Mechanism-based cofactor derivatization of a copper amine oxidase by a branched primary amine recruits the oxidase activity of the enzyme to turn inactivator into substrate

The copper amine oxidases (CAOs) have evolved to catalyze oxidative deamination of unbranchedprimary amines to aldehydes. We report that a branched primary amine bearing an aromatization-prone moiety, ethyl 4-amino-4,5-dihydrothiophene-2-carboxylate (1), is recognized enantioselectively (S > R) by bovine plasma amine oxidase (BPAO) both as a temporary inactivator and as a substrate. Substrate activity results from an O(2)-dependent turnover of the covalently modified enzyme, with release of 4-aminothiophene-2-carboxylate (2) as ultimate product. Interaction of (S)-1 with BPAO occurs within the enzyme active site with a dissociation constant of 0.76 microM. Evidence from kinetic and spectroscopic studies, and HPLC analysis of stoichiometric reactions of BPAO with (S)-1, combined with a model study using a quinone cofactor mimic, establishes that the enzyme metabolizes 1 according to a transamination mechanism. Following the initial isomerization of substrate Schiff base to product Schiff base, a facile aromatization of the latter results in a metastable N-aryl derivative of the reduced cofactor aminoresorcinol, which is catalytically inactive. The latter derivative is then slowly oxidized by O(2), apparently facilitated partially by the active-site Cu(II), to form a quinonimine of the native cofactor that releases 2 upon hydrolysis or transimination with substrate amine. Preferential metabolism of (S)-1 is consistent with the preferential removal of the pro-Salpha-proton in metabolism of benzylamine by BPAO. This study represents the first report of product identification in metabolism of a branched primary amine by a copper amine oxidase and suggests a novel type of reversible mechanism-based (covalent) inhibition where inhibition lifetime can be fine-tuned independently of inhibition potency.