The UV,blue and green up-conversion luminescence of PbF2+GeO2:Er2O3 pumped with 650 nm

A detailed study of the spectroscopic properties of the PbF₂+GeO₂:Er₂O₃ vitroceramic sample upon 650 nm excitation was investigated. The absorption, emission, excitation spectra, and time-resolved spectra have been measured. The up-conversion of red radiation (650 nm) into UV (368 nm and 379 nm), blue (406.8 nm) and green (522 nm and 540 nm) emissions is observed for Er³⁺ ions in the sample. The up-conversion process involves a two-photon absorption for the violet, blue, and green emission bands. A three-photon process happens for another violet (379 nm) band.     

Attenuation of Cross-Flow Instability in a Three-Dimensional Boundary Layer by Means of a Multidischarge Actuator System

Doklady Physics - The results of experiments in a low-turbulence subsonic wind tunnel confirming the possibility of a significant attenuation of the cross-flow velocity and the intensity of...     

On the equation of state of classical one-component systems with long-range forces

Several definitions of the pressure are introduced for one-component systems and shown to be nonequivalent in the presence of a rigid neutralizing background. Relations between these pressures are derived for finite and infinite systems; these relations depend on the asymptotic behavior of the force at infinity, with the Coulomb force at the borderline between different properties. It is argued that only one of those definitions is physically acceptable and its properties are discussed in relation to the asymptotic behavior of the force. It is seen in particular that a knowledge of the state of the infinite system is not sufficient to determine its thermodynamic properties. The results are illustrated by some typical examples.For example, for two-dimensional systems with three-dimensional Coulomb interaction see refs. 2–4.     

Computation of high order derivatives in optimal shape design

Summary. In shape optimization problems, each computation of the cost function by the finite element method leads to an expensive analysis. The use of the second order derivative can help to reduce the number of analyses. Fujii ([4], [10]) was the first to study this problem. J. Simon [19] gave the second order derivative for the Navier-Stokes problem, and the authors describe in [8], [11], a method which gives an intrinsic expression of the first and second order derivatives on the boundary of the involved domain. In this paper we study higher order derivatives. But one can ask the following questions: -- are they expensive to calculate? -- are they complicated to use? -- are they imprecise? -- are they useless? \medskip\noindent At first sight, the answer seems to be positive, but classical results of V. Strassen [20] and J. Morgenstern [13] tell us that the higher order derivatives are not expensive to calculate, and can be computed automatically. The purpose of this paper is to give an answer to the third question by proving that the higher order derivatives of a function can be computed with the same precision as the function itself. We prove also that the derivatives so computed are equal to the derivatives of the discrete problem (see Diagram 1). We call the discrete problem the finite dimensional problem processed by the computer. This result allows the use of automatic differentiation ([5], [6]), which works only on discrete problems. Furthermore, the computations of Taylor's expansions which are proposed at the end of this paper, could be a partial answer to the last question. Received January 27, 1993/Revised version received July 20, 1993     

Damping of Vibrations in a SystemWith Two Beams by Structural Friction

This paper presents the results of tests on free and forced harmonic vibrations in a system with two beams with structural friction taken into account. The beams are clamped together with uniform unitary pressure. The hysteresis loop describing the frictional-elastic properties of the system has a form of a parallelogram. The autor created a mathematical model of the vibrating system with two beams. During free vibrations of the system, its damping characteristics were tested by a digital simulation method. The vibration damping decrement as a function of amplitude displacement was determined. When vibrations were harmonically forced, the amplitude - frequency characteristics of the system were determined numerically. The system was used as a nonlinear vibration damper in a linear system with a harmonic force. The equations of motion of the nonlinear two-degree of freedom system were solved by means of a digital simulation method. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical Evidence for Temperature-induced Proton Mobility in Isolated Lysine-rich Polyalanines

A multistate molecular mechanics method is introduced to model the possible competition between various protonation sites in gas-phase biomolecules with excess protons. The method relies on the Amber force field for each site and is calibrated against density-functional theory benchmark calculations at the 6-31+G(d,p) level. In its adiabatic version, where it has similarities with constant-pH algorithms, the model predicts that the small protonated Ala(4)-Lys peptide, unprotected at the N-terminus, changes protonation site above 400 K. In the larger [Ala(9)-Lys+H ](+) peptide, the proton remains at the lysine amine group in a favored charge/electric dipole conformation. In the three-state Ala(4)-Lys-Ala(4)-Lys peptide, the excess proton is found to be partially delocalized on the amine group of the first lysine and on the N-terminus. The statistical properties of the protonated peptides are found to significantly depend on the localized character of the proton. Finally, the model is extended by considering possible couplings between the protonation sites, in an empirical valence-bond version. Strong couplings can stabilize the peptides into unexpected proton-bound conformations over broad ranges of temperature.     

Chemistry of naphthazarin derivatives. 11. Trisubstituted hydroquinone derivatives in the preparative synthesis of naphthazarins

The Friedel—Crafts acylation of trimethylhydroquinone, 3,5-diethyl-2-hydroxyhydroquinone, and 3,5-diethyl-1,2,4-trimethoxybenzene with dichloromaleic or citraconic anhydride in an AlCl₃—NaCl melt is accompanied by o-C-dealkylation to afford functionally substituted naphthazarins.     

Recherches en série diazépine-1,4 et triazépine-1,2,4. XI—etude en spectrométrie de masse des fragmentations de triazépines-1,2,4

The mass spectra of eleven 1,2,4-triazepines with oxo, thioxo, methoxy and methylmercapto groups in the 3 and 5 positions are reported and analysed. Each of the five structures of the triazepine ring present is characterized by a particular group of fragmentations.