On the dynamics of plastic circular plates

The paper is concerned with the dynamics of a thin circular plate made of a plastic-rigid material that obeys the yield condition ofTresca and the associated flow rule. The basic equations are established in the case of rotational symmetry, and their complete solution is given for a simply supported plate subjected to a uniformly distributed load which is brought on suddenly and, after a certain time interval, removed suddenly.

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Résumé Cet article étudie la dynamique d'une plaque circulaire infiniment mince fabriquée avec un matériau plastique qui obéit à la condition de plasticité deTresca et à la loi d'écoulement associée. Les équations fondamentales sont établies dans le cas où existe une symétrie de révolution. Leur solution complète est donnée pour une plaque reposant sur des appuis simples, soumise à une charge uniformément répartie qui est appliquée rapidement et demeure constante pendant un certain temps, après lequel elle est rapidement retirée.

     

Dynamic strain-birefringence apparatus for polymer films

A new apparatus for investigating dynamic strain birefringence in polymer films at frequencies up to 10 Hz and at various degrees of internal sample orientation is described. Samples are elongated at constant low rates while simultaneously being strained sinusoidally. Fast changes in sample retardance are recorded while slow changes are automatically compensated with a servo-controlled Soleil-Babinet compensator. The signal-to-noise ratio of the system is greatly enhanced by incorporating a highly monochromatic laser light source, a synchronous amplifier, and a light beam modulator based on a rotating polarizer. Data obtained from this apparatus can be used to elucidate polymer relaxation mechanisms at various frequencies over a wide range of static strains.     

The diffusion of carbon to and from W(100)

The equilibrium segregation in the system W(100) plus two monolayers of total carbon content has been studied in the range 1600 to 2073 K. The energy of segregation is ?56(±2) kcal mole^?1. The kinetics of carbon segregation at 1350 and 1420 K were observed. From a semi-empirical treatment an upper limit to the activation energy for volume diffision is deduced to be 59 (±8) kcal mole^?1.     

Theoretical and Empirical Relationships Between the Redox Potentials and <Superscript>1</Superscript>(<Emphasis Type="Italic">δ</Emphasis>→<Emphasis Type="Italic">δ</Emphasis>*) Transition Energies of Quadruply Bonded Complexes

An analysis of the available electrochemical and electronic-sectroscopic data for quadruply metal–metal bonded complexes reveals that the ¹(*) transition energy is an approximately linear function of the difference between the electrode potentials at which they are reduced and oxidized to the bond-order 3. 5 complexes. A theoretical framework for interpreting this correlation is provided by extending to the redox potentials a simple zero-differential-overlap model previously applied to ¹(*) transition energies. It is suggested on the basis of this model that the simplicity of the empirical relationship between ¹(*) energies and redox potentials is a consequence of the particular one- and two-electron energy terms that characterize these complexes; a linear relationship is not required by theory.     

Generation of azines by the reaction of a nucleophilic carbene with diazoalkanes: a synthetic and crystallographic study

Reactions of the nucleophilic carbene 1,3-dimesityl-imidazol-2-ylidene (1) with diazofluorene, diphenyldiazomethane, and azidotrimethylsilane were examined. Specifically, carbene 1 reacts with diazofluorene and diphenyldiazomethane to give addition products (azines: 3 and 4, respectively). Compounds 3 and 4 were further characterized in the solid-state by single-crystal X-ray crystallographic studies. [3 (a = 9.7936(6) A, b = 10.0529(7) A, c = 16.251(1) A, alpha = 75.765(1) degrees, beta = 79.711(1) degrees, gamma = 64.321(1) degrees, Z = 2, space group P1); 4 (a = 11.681(3) A, b = 11.861(4) A, c = 21.186(3) A, alpha = 90 degrees, beta = 97.05(2) degrees, gamma = 90 degrees, Z = 4, space group P2(1)/n)]. The structural parameters of 3 and 4 are discussed with reference to previously characterized symmetrical and unsymmetrical azines. Structural data suggest that charge separation is possible in 3.     

Auger and electron energy loss spectra of adsorbed species: α and β states of carbon monoxide and nitrogen on W(100)

Auger and electron energy loss spectra have been recorded for both α and β chemisorbed states of carbon monoxide and nitrogen on W(100). The α state spectra have been analysed with reference to results for the gas phase molecules, those for the β states have been analysed following a quasi-atomic final state model. The results illustrate both the potential and the limitations of AES and ELS in surface chemical analysis.