Diode pumped active-mirror Yb:YAG ceramic lasers

Lasers from Yb:YAG ceramic at different temperature were reported in this paper. The Yb:YAG ceramic laser with active-mirror structure was end-pumped by a laser diode whose central wavelength was 940 nm. At 80 K, with doping concentration of 5 at % Yb:YAG ceramic slab, output energy of 0.68 J at 10 Hz repetition rate was obtained under the pump energy of 2.49 J, corresponding to a slope efficiency of 40% and a conversion efficiency of 27.3%, respectively.     

On the nature of the active centres in the anionic polymerization of methacrylonitrile—II. Initiation with organomagnesium compounds

It is shown by i.r. spectroscopy that the anionic polymerization of methacrylonitrile using organomagnesium compounds as initiators leads to two types of “living” ends i.e.

and

The active centres form complexes with the monomer, as well as with the nitrile groups of the monomer units in the polymer chain, in a hydrocarbon medium. The complexes are characterized by bands in the 2250–2280 cm^?1 region. Addition of donors destroys the complexes and in some cases (hexamethylphosphorous triamide) converts the complex of organomagnesium compound with monomer into a “living” end. In ethers as solvent, the dominant side-reaction is addition of the initiator to the nitrile group of the monomer.     

Etude par effusiometrie de torsion des proprietes thermodynamiques en phase solide des laitons binaries (Cu,Zn)

The Gibbs thermodynamic variables which we have determined for thirteen brass alloys (Cu, Zn) are in good accord with the literature. The experimental conditions were as close as possible to those of sublimation in static vacuum. The application of the test of the third law in β-brass shows that our free enthalphy measurements are in agreement with the measurements of specific heat by Moser. The primary solid solution α copper of the binary brasses shows quasi-regular behaviour over the whole composition range. Our measurements seem to indicate the existence of a β′/(α + γ) eutectoïd at a temperature less than 100°C. The high degree of order of the γ phase is seen in the large negative values of excess entropy.     

A Level-1 Limit Order Book with Time Dependent Arrival Rates

We propose a simple stochastic model for the dynamics of a limit order book, extending the recent work of Cont and de Larrard (SIAM J Financial Math 4(1), 1–25 2013), where the price dynamics are endogenous, resulting from market transactions. We also show that the conditional diffusion limit of the price process is the so-called Brownian meander.

     

High-performance Mössbauer spectroscopy: Criteria,possibilities, limitations

Increasing attention is being paid to non-conventional Mössbauer methods in view of the extension of Mössbauer Spectroscopy (MS) to a broadening field of applications. With such long-lasting experiments the shortening of the measuring time required for a given statistical significance is of major practical importance. It is shown that the statistical utility rateu allows one to determine which experimental parameters have a primary role, and it also enables sucessive optimization. It is pointed out for various MS measurements that the strategy for improving the experimental performance is strongly dependent on the given problem. As examples, time-differential Mössbauer measurements and conversion electron Mössbauer spectroscopy are discussed.     

Low-energy transitions in the 197Pb and 198Pb isotopes

The ¹⁹⁸Pb and ¹⁹⁷Pb isotopes are produced through the ¹⁸⁶W(¹⁶O, 4n, 5n) reactions. Conversion-electron, γ- and X-ray spectra are measured using the compound-nucleus recoil method. Conversion coefficients and multipolarities are deduced for a large number of transitions. Together with angular distribution measurements and the results of γγt multidimensional coincidences they lead to decay schemes for the two isotopes. Microscopic calculations, performed in the two- or three-quasiparticle approximation with a surface delta interaction, fail to reproduce completely the observed properties, showing similar defects for the odd and even isotope.     

Radiation detected resonance ionization spectroscopy on208Tl and242fAm

An ultra-sensitive laser spectroscopic method has been developed for the hyperfine spectroscopy of short-lived isotopes far off stability produced by heavy ion induced nuclear reactions at very weak intensity (> 1/s). It is based on resonance ionization spectroscopy in a buffer gas cell with radiation detection of the ionization process (RADRIS). As a first on-line application of RADRIS optical spectroscopy at^242fAm fission isomers is in progress at the low target production rate of 10/s. The resonance ionization has been performed in two steps utilizing an excimer dye laser combination with a repetition rate of 300 Hz. The first resonant step proceeds through terms which correspond to wavelengths of 466.28, 468.17 or 426.56 nm; the second non-resonant step is achieved with the 351 nm radiation of the excimer laser itself, running with XeF. The frequency scans of the tuneable dye laser at 466.28 and 468.17 nm exhibit broad resonance ionization signals, the latter with a large isotope shift between^242fAm and²⁴³Am which is in accordance with the large quadrupole moment of the^242fAm fission isomer.Work supported by the Bundesministerium für Forschung und Technologie under contract 06 MZ 188 I.     

Trees, Renormalization and Differential Equations

The Butcher group and its underlying Hopf algebra of rooted trees were originally formulated to describe Runge–Kutta methods in numerical analysis. In the past few years, these concepts turned out to have far-reaching applications in several areas of mathematics and physics: they were rediscovered in noncommutative geometry, they describe the combinatorics of renormalization in quantum field theory. The concept of Hopf algebra is introduced using a familiar example and the Hopf algebra of rooted trees is defined. Its role in Runge–Kutta methods, renormalization theory and noncommutative geometry is described.