Synthesis of uracil derivatives by oxidation of Fischer tungsten-carbene uracil complexes

A study on the oxidation of Fischer tungsten-carbene uracil complexes has been carried out. Several commonly used oxidants gave results strongly influenced by the presence of substituent on nitrogen atoms. In particular, usual oxidants failed in the oxidation of 3-alkyl uracil carbene complexes. Finally, we showed that t-butyl hydroperoxide is able to oxidize successfully also 3-alkyl uracil carbene complexes and can be used as a good alternative to the other methods.     

Using the pointwise dimension to filter time series

This paper provides an insight into dimension analysis from time series. In particular, we propose a procedure based on the pointwise dimension in order to extract, for each embedding dimension, the subset of points in the phase space (and the corresponding ones in the time series) which give rise to the scaling behaviour. We may consider the output time series as the result of a filtering process, based on correlations of points in the phase-space domain. Furthermore, the procedure gives the statistics of points which determine the scaling behaviour.     

Efficient low-voltage operation of a reverse-biased autoprepulse XeCl laser

An improved version of the auto-prepulse excitation scheme for long-pulse operation of the XeCl excimer laser is reported. A pulsed reverse bias on the small peaking capacitance allows efficient (1.7%) operation at 100 mJ output level with a charge voltage limited to 5–7 kV. Analogies and differences with other long-pulse operation schemes are also discussed.     

Coulomb interaction symmetries and the Mayer series in the two-dimensional dipole gas

We study the Mayer series of the two-dimensional dipole gas in the high-temperature, low-density regime. Without performing any multiscale analysis, we obtain bounds showing that the Mayer coefficients are finite in the thermodynamic limit. These bounds are obtained by exploiting a particular partial symmetry of the interaction (which we nameO-symmetry), already used in some problems related to the two-dimensional Coulomb gas. By direct bounds on some Mayer graphs we also conjecture that any technique based uniquely on theO-symmetry will not be sufficient to prove analyticity of the series.     

A note on ω-permutable semigroups

Communicated by Dominique Perrin     

Numerical analysis of a shock-wave solution of the Enskog equation obtained via a Monte Carlo method

In this paper a planar stationary shock-wave-like solution of the Enskog equation obtained via a Monte Carlo technique is studied; both the algorithm used to obtain the solution and the qualitative behavior of the macroscopic quantities are discussed in comparison with the corresponding solution of the Boltzmann equation.     

High-quality drilling with copper vapour lasers

High-quality materials processing on transparent substrates of BK7 glass, fused silica, corundum and ruby using a copper vapour laser (CVL) is described and discussed. The driling process using the radiation emitted by a small diffraction-limited CVL is described and investigated by optical diagnostic methods allowed by the transparency of the materials. In particular the hole making was entirely monitored in real time through a video camera. Images achieved in this way are reported to illustrate the morphology of the hole and of the ejected materials via the time-resolved fluorescence. This investigation provides the evaluation of the plume expansion speed, while the imaging supplies the quantitative evaluations of the drilling speed and threshold. The high quality of the hole in terms of wall smoothness and elevated aspect ratio is described in detail. We report according to our findings an interpretation of the peculiar combination of physical processes involved.     

A mixed algorithm for the calculation of rapidly varying fluid flows: The impulsively started circular cylinder

A mixed discrete Fourier transform-Finite difference algorithm is developed and used for the calculation of rapidly changing viscous fluid flows past a circular cylinder. The numerical approach has been designed to overcome certain difficulties arising for high Reynolds number simulations. The foremost advantage of the technique lies in its fast calculations of the convolution sums portraying the convective terms of the governing equations. Third-order spatial discretizations and fourth-order time marching are implemented. New schemes are proposed for the boundary conditions at the solid wall and at large distances. The techniques are tested on a case study with other schemes (summarized by Roache¹) in order to obtain an optimal choice. Definite indications on the stability and accuracy of boundary condition schemes are achieved. Support for the statement of dominant importance of boundary conditions is also given. A comparison of computational results with experimental data is presented for the case study of the flow past an impulsively started cylinder at Reynolds number 20. The time development of the symmetrical zone of recirculation, which is formed at an early stage of the flow, has been studied for 300 ≤ Re ≤ 9500 by means of the proposed algorithm. Computational results, comparisons with experimental data² and discussion of upper limits of validity of the procedure will be presented in a companion paper.