The first example of the cascade assembly of a spirocyclopropane structure: direct transformation of benzylidenemalononitriles and N,N′-dialkylbarbituric acids into substituted 2-aryl-4,6,8-trioxo-5,7-diazaspiro[2.5]octane-1,1-dicarbonitriles

The direct formation of substituted 2-aryl-4,6,8-trioxo-5,7-diazaspiro[2.5]octane-1,1-dicarbonitriles in 75-95% yields from benzylidenemalononitriles and N,N′-dialkylbarbituric acids is described.     

Convenient synthesis of 2-(het)arylpyrrolidines via stable 1-pyrrolinium salts

The efficient method for the synthesis of 2-(het)aryl-substituted pyrrolidines possessing exocyclic carbon-carbon double bond via the Mannich-type reaction of stable 3-arylidene-1-pyrrolinium salts with different heterocyclic C-nucleophiles is proposed.     

Imaging performance and light emission efficiency of Lu<Subscript>2</Subscript> SiO<Subscript>5</Subscript>:Ce (LSO:Ce) powder scintillator under X-ray mammographic conditions

The aim of the present study was to measure the imaging transfer characteristics and the luminescence efficiency (XLE) of a Lu₂SiO₅:Ce (LSO:Ce) powder scintillator for use in X-ray mammography detectors. An LSO:Ce powder scintillating screen, with a coating thickness of 25 mg/cm², was prepared in our laboratory. The imaging performance of the screen was assessed by experimental determination of the modulation transfer function (MTF) and the detective quantum efficiency (DQE) as well as single index image quality parameters such as noise equivalent pass band (Ne) and informational efficiency (n _I). A theoretical model, describing radiation and light transfer, was fitted to experimental MTF values in order to estimate optical properties of the scintillator. Screen irradiation was performed under exposure conditions employed in mammographic applications (27 kVp, 63 mAs). MTF was determined by the square wave response function (SWRF) method. Results showed that LSO:Ce exhibits high MTF and DQE values, which are comparable to those of the commercially used Gd₂O₂S:Tb. Considering our image quality parameters and luminescence efficiency results as well as the fast response of the LSO:Ce scintillator screen (40 ns), this material can be considered for use in X-ray mammographic detectors.     

Postinstability models in dynamics

This paper is devoted to the concept of instability in dynamical systems with the main emphasis on orbital, Hadamard, and Reynolds instabilities. It demonstrates that the requirement about differentiability in dynamics in some cases is not consistent with the physical nature of motions, and may lead to unrealistic solutions. Special attention is paid to the fact that instability is not an invariant of motion: it depends upon frames of reference, the metric of configuration space, and classes of functions selected for mathematical models of physical phenomena. This leads to the possibility of elimination of certain types of instabilities (in particular, those which lead to chaos and turbulence) by enlarging the class of functions using the Reynolds-type transformation in combination with the stabilization principle: the additional terms (the so-called Reynolds stresses) are found from the conditions that they suppress the original instability. Based upon these ideas, a new approach to chaos and turbulence as well as a new mathematical formalism for nonlinear dynamics are discussed.     

Coherent π Electroproduction on the Deuteron

A general analysis of polarization phenomena for coherent pion electroproduction on deuterons is presented. The spin and isospin structures of the γ*+d→d+P⁰ amplitudes (where γ* is a virtual photon) are established and relationships between meson electroproduction on deuterons and on nucleons are given in the framework of the impulse approximation. The reaction e+d→e+d+π⁰ is investigated in detail, for a relatively large value of momentum transfer, 0.5 GeV²≤−k²≤2 GeV², both at threshold and in the region of Δ-isobar excitation. Special attention is devoted to the sensitivity of different contributions to the exclusive cross section for d(e, eπ⁰)d, as the γ*πω form factor or the NN-potential. The predicted k²-dependence of the cross section agrees well with the available experimental data.     

Simple and semisimple Lie algebras and codimension growth

We study the exponential growth of the codimensions of a finite dimensional Lie algebra over a field of characteristic zero. In the case when is semisimple we show that exists and, when is algebraically closed, is equal to the dimension of the largest simple summand of . As a result we characterize central-simplicity: is central simple if and only if .

     

The effect of market power on risk-sharing

The paper studies an oligopolistic equilibrium model of financial agents who aim to share their random endowments. The risk-sharing securities and their prices are endogenously determined as the outcome of a strategic game played among all the participating agents. In the complete-market setting, each agent’s set of strategic choices consists of the security payoffs and the pricing kernel that are consistent with the optimal-sharing rules; while in the incomplete setting, agents respond via demand functions on a vector of given tradeable securities. It is shown that at the (Nash) risk-sharing equilibrium, the sharing securities are suboptimal, since agents submit for sharing different risk exposures than their true endowments. On the other hand, the Nash equilibrium prices stay unaffected by the game only in the special case of agents with the same risk aversion. In addition, agents with sufficiently lower risk aversion act as predatory traders, since they absorb utility surplus from the high risk averse agents and reduce the efficiency of sharing. The main results of the paper also hold under the generalized models that allow the presence of noise traders and heterogeneity in agents’ beliefs.     

Optimal control for a Timoshenko beamContrôle optimal d'une barre de Timoshenko

We consider a linear model of a rotating Timoshenko beam, which is clamped at one end to a disk the other being free. The motion of the beam is controlled by the angular acceleration of the disk. We study the minimization problem of mean square deviation of the Timoshenko beam from a given position. For the minimization problem of the first mode we prove that optimal control is the chattering control, i.e., it has an infinite number of switches in a finite time interval. We construct a suboptimal control with a finite number of switches. To cite this article: M.I. Zelikin, L.A. Manita, C. R. Mecanique 334 (2006).     

Single-Atom Alloys for the Electrochemical Oxygen Reduction Reaction

Single-atom alloys (SAAs) consisting of isolated transition-metal atoms doped in the surface of coinage metal hosts exhibit unique catalytic properties, harnessing the high activity of the dopant metals with the selectivity of the coinage metal hosts. Here we use density functional theory (DFT) to study SAAs comprised of Ni, Pd, Pt, Co and Rh doped into Ag and Au hosts, as candidate electrocatalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane (PEM) fuel-cells. Our calculations reveal that the PdAu SAA exhibits a slightly lower theoretical overpotential, enhanced selectivity for 4-e⁻ ORR, and tolerance to CO-poisoning compared to Pt(111). While the number of active sites of PdAu SAA is lower than that of Pt(111), the aforementioned desirable properties could bring the overall catalytic performance thereof close to that of Pt/C, indicating that the PdAu SAA could be a viable material for electrocatalytic ORR in PEM fuel-cells.