Analytic Properties of the Transition Admittance of an Infinite Plate in a medium and the Regularization of Boundary-Contact Integrals in Acoustics

A condition for regularization of boundary-contact integrals in two-dimensional problems of acoustics is considered. With an example of the simplest boundary-contact problem of acoustics, it is shown that a known sufficient condition for regularization is also a necessary one. The study of analytic properties of the transition admittance of an infinite plate that is in contact with a medium is conducted in order to obtain this statement. The considerations are carried out in general terms. The results obtained may be used in arbitrary models of plate theory, and they also may be adapted to boundary-contact problems of another physical nature. Bibliography: 9 titles.     

Relativistic Notion of Mass and a Resolution of a Conflict Between Schopenhauer and Hegel

We discuss a mass change that has its origin in the action of forces on an object. This phenomenon, well-known in the context of quantum field theory (mass renormalization), can be discussed systematically in both classical and quantum mechanics in a framework given by Stückelberg. We employ this framework to resolve an interesting conflict of opinions between Schopenhauer and Hegel in the mid-19th century. We show that Hegel, Kant, and Schopenhauer demonstrated remarkable prescience in their views as seen from a modern perspective.     

Nonequilibrium Ionization by Vibrationally Excited Molecules in Supersonic Flows

The results of experimental investigations on thermal nonequilibrium ionization in CO₂: N₂: He mixtures are presented. Measurements of electron density, n_e, in vibrationally excited nitrogen were made in a supersonic flow with different CO₂ contents as well as in a CO₂: N₂: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N₂ and CO₂ + He was used in some experiments. The measured values of n_e in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed.     

A solvent-free synthesis of coumarins using a Wells-Dawson heteropolyacid as catalyst

Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H₆P₂W₁₈O₆₂·24H₂O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples).     

Cochran's statistical theorem for outer inverses of matrices and matrix quadratic forms

We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures.     

Determination of melengestrol acetate in bovine tissues by automated coupled-column normal-phase high-performance liquid chromatography

A method has been developed for the determination of melengestrol acetate in bovine tissues at lower levels than previously reported. Liquid-liquid extraction of tissue homogenates provided crude clean-up while final isolation, screening, and quantification was done on-line with an automated, normal-phase, coupled-column high-performance liquid chromatographic system. The chromatographic system included phenyl and silica analytical columns for the purposes of isolation and final separation, respectively. These columns provided a large difference in selectivity when operated under normal-phase conditions which allowed for the efficient isolation of melengestrol acetate from the complex tissue extracts. Mobile phases were composed of hexane and dichloromethane modified with methanol and water. Transfer and enrichment of the analyte from the primary phenyl column to the silica column was via a short (12 mm x 4 mm I.D.) silica column. Regeneration and equilibration of the phenyl column was performed after the injection of each tissue extract and was accomplished simultaneously while analytical separation occurred on the final silica column. Routing of the mobile phases and regeneration solvent was performed with automated switching valves. The total time required for each analysis was 12 min. Quantification is demonstrated using external standards with UV detection at 287 nm. The overall recovery of the method was 86% with a coefficient of variation of 9.84% at the 10 ppb [the American billion (10(9] is used in this article] level in bovine liver extracts.     

Derivation of fluorine-containing pyridine dicarboxylates. II. Elaboration at the 4-position

In response to the bio-activity found in fluorine-containing 4-alkyl-3, 5-pyridinedicarboxylates, a series of novel 4-substituted derivatives, not directly available by Hantzsch sequences, were prepared. Starting 4-alkylpyridines, 1 , were converted via enamine 2 to materials 3–8 . Derivatives 9–16 in turn were derived from aldehyde 3 , while acid derivatives 28–36 were prepared from 14 . Addition of oxygen, sulfur, and carbenoids effected conversion of 4-allylpyridine 16 to epoxy and cyclopropyl derivative 16–22 . A number of neighboring group effects were noted, including those forming the fused-ring systems 23-27 .