Ferromagnetic Mn-doped Si0.3Ge0.7 nanodots self-assembled on Si(100)

Densely packed epitaxial Mn-doped Si(0.3)Ge(0.7) nanodots self-assembled on Si(100) have been obtained. Their structural properties were studied using reflection high-energy electron diffraction, energy dispersive x-ray diffraction, atomic force microscopy, extended x-ray absorption fine structure measurements and high-resolution transmission electron microscopy. Mn(5)Ge(1)Si(2) crystallites embedded in Si(0.3)Ge(0.7) were found. They exhibit a ferromagnetic behaviour with a Curie temperature of about 225?K.     

High order harmonic generation by non-linear reflection of a pedestal-free intense laser pulse on a plasma

We demonstrate the influence of the prepulses and ASE of ultrashort pulses interacting with a solid target by addressing the direct comparison of the harmonic spectra generated by reflection onto a solid target with and without the introduction of a plasma mirror system. Harmonics up to the 20th of the fundamental of the Ti-Sa laser are clearly visible in a situation free from any plasma expansion. PACS 42.65. Ky; 52.38.-r; 52.38.Ph; 52.50.Jm     

Experimental investigation of high-quality synchronization of coupled oscillators

We describe two experiments in which we investigate the synchronization of coupled periodic oscillators. Each experimental system consists of two identical coupled electronic periodic oscillators that display bursts of desynchronization events similar to those observed previously in coupled chaotic systems. We measure the degree of synchronization as a function of coupling strength. In the first experiment, high-quality synchronization is achieved for all coupling strengths above a critical value. In the second experiment, no high-quality synchronization is observed. We compare our results to the predictions of the several proposed criteria for synchronization. We find that none of the criteria accurately predict the range of coupling strengths over which high-quality synchronization is observed. (c) 2000 American Institute of Physics.     

On the definition of the resonance with examples two-channel models

In an exactly solvable model of separable potentials a two channel scattering problem is solved in l = 0 state. The location and the width of a resonance are then defined in three different ways and the resonance parameters so extracted are then compared. This problem is of interest vis-a-vis the Δ(3, 3) resonance parameters.     

Tests of resonance recognition criteria in coupled channel problems with separable potentials

Exactly soluble two-body two-channel problems are set up with separable potentials. Resonance is defined theoretically then the empirical resonance recognition criteria used in two-body data analyses are tested. Results are summarized in the last section of the paper.     

Monophotonically UV excited delayed luminescence in rigid solutions of aromatic amines

During a study of neutralization luminescence following photoionization of aromatic solutes in rigid organic glasses, a new type of long-lived luminescence has been observed simultaneously with the well-known neutralization luminescence following biphotonic ionization. It has been extensively studied for tetramethyl-p-phenylenediamine in methylcyclohexane or ethanol: it is one-photon excited but differs from the ordinary luminescence by the emission spectrum (λ_max 430 nm compared to λ_{max f.} 395 nm and λ_{max ph.} 490 nm in ethanol) and by the excitation spectrum, the present luminescence being observed only for short wavelength excitation. Finally the lifetime (of the order of seconds) depends on experimental conditions. Other solid and liquid phase studies suggest that the precursor of this new luminescence is a solute-solvent charge transfer state.     

Development of ion-conducting polymer electrolytes for use in high-energy lithium rechargeable batteries

Polymers based on poly(thylene oxide) (PEO) are a very promising new type of stable electrolytes for lithium rechargeable batteries. Their relatively low ionic conductivities can be more than compensated by the very small electrolyte thicknesses that can be used. Specific energies of 100 Wh/kg at sustained specific powers of 70 W/kg, have been obtained at Hydro-Québec with 100 μm of PEO electrolyte at 100°C. In an electric vehicle, this would give a driving range of over 300 km at 80 km/h, more than three times as much as lead-acid batteries. PEO-related polymers have been developed for lower temperature applications such as computers or portable appliances. Advantages over competitive Ni-Cd batteries are higher energy densities and absence of self-discharge, with expected shell lifes of 10 years. Laboratory prototypes (3600 cm², 10 Wh) demonstrate the absence of scale-up effects and excellent cycling capability (over 300 charge-discharge cycles).     

Compensation of phase-to-amplitude modulation conversion in a complete frequency conversion system with an all-fiber system

We report on an experimental demonstration of linear precompensation of nonlinear phase and amplitude transfer functions. We show the effective compensation with a linear all-fiber system of phase-to-amplitude modulation conversion due to a complete frequency conversion system including plane gratings and a nonlinear crystal.     

Approximation by harmonic functions on closed subsets of Riemann surfaces

Given continuous functionsu and ∈ on a closed subsetF of a Riemann surface, we seek a harmonic functionv on the surface (possibly with logarithmic singularities) such that |u−v|<∈ onF. Research supported in part by NSERC—Canada and FCAR—Quebec.     

Contextual effects on vowel duration, closure duration, and the consonant/vowel ratio in speech production

Acoustic measurements were conducted to determine the degree to which vowel duration, closure duration, and their ratio distinguish voicing of word-final stop consonants across variations in sentential and phonetic environments. Subjects read CVC test words containing three different vowels and ending in stops of three different places of articulation. The test words were produced either in nonphrase-final or phrase-final position and in several local phonetic environments within each of these sentence positions. Our measurements revealed that vowel duration most consistently distinguished voicing categories for the test words. Closure duration failed to consistently distinguish voicing categories across the contextual variables manipulated, as did the ratio of closure and vowel duration. Our results suggest that vowel duration is the most reliable correlate of voicing for word-final stops in connected speech.