Advanced memory effects in the aging of a polymer glass

A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant ε. A temporary stop of cooling produces a downward relaxation of ε. Two main features are observed (i) when cooling is resumed ε goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating ε keeps the memory of all the cooling stops (Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs. Received 24 September 2001 and Received in final form 20 November 2001     

Diels-Alder adducts from flavonoid

A quinoflavonoid was synthesized from commercially available products over three steps. The quinoflavonoid turned out to be an excellent dienophile in Diels-Alder reaction. Reactions were easily performed in dichloromethane, and after evaporation of the solvent, expected products were obtained in good yields.     

Efficient white light emission by upconversion in Yb(3+)-, Er(3+)- and Tm(3+)-doped Y2BaZnO5

We report efficient white upconversion luminescence in Yb(3+)-, Er(3+)- and Tm(3+)-doped monophasic and biphasic Y(2)BaZnO(5) phosphors under 977 nm near-infrared excitation and at low excitation power densities (down to ～25 mW mm(-2)).     

Dynamical amplification of phase conjugation using a modulated optical feedback in a Nd:YVO4 laser

We demonstrate an efficient dynamical amplification of phase conjugation in the gain medium of a diode-pumped Nd(3+)YVO4 solid-state laser via excitation of its relaxation oscillations. Consequently, enhancement in the modulated amplitude of the phase conjugate wave is observed with up to +30?dB compared to the classical homodyne approach.     

Variable desorbent strength: influence on SMB operating conditions and performance

The aim of this work was to evaluate the role of desorbent selectivity variation on the tuning and the performance of a SMB process. For this purpose a separation regions study in the case of a four-zones non-linear transfer limited SMB was carried out. The SMB unit was modelled considering the equivalent True Moving Bed (TMB). A set of 11 desorbents with different strength was considered: 3 desorbents with constant strength and 8 desorbents with variable strength. For each system, the optimal operating conditions are determined using the separation regions approach, with plots in both (Q₂, Q_F) and (Q₄, Q_D) planes. Depending on the separation considered, a variable selectivity desorbent can lead to an improvement or can be detrimental to process performances. A careful choice of desorbent selectivity (either constant or variable) is then crucial to achieve maximal process performance.     

ToF‐SIMS multivariate characterization of surface modification of polymers by N2?H2 atmospheric pressure dielectric barrier discharge

Time of flight secondary ion mass spectrometry (ToF‐SIMS) is a powerful tool for the surface characterization of plasma‐modified surface. However, the SIMS fragmentation patterns of the resulting surface are quite complex and a full interpretation may be prohibitive. As a result, many studies are turning to multivariate statistical methods to simplify the interpretation. In this study, a principal component analysis (PCA) was used to obtain a more detailed interpretation of the surface modification of polymers by an atmospheric pressure plasma. The dataset was obtained from three polymers with different chemical compositions [namely, polyethylene, polyvinylidene fluoride, and poly(tetrafluoroethylene)], where each material was treated with an atmospheric pressure dielectric barrier discharge (DBD) in an atmosphere composed of different N₂/H₂ ratios. The results are discussed in terms of the suitability of ToF‐SIMS analysis combined with PCA for the discrimination between the three polymers and the possibility to create a predictive model that would describe the plasma surface modification, independent of the polymer substrate chemical composition. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparison of gold and silver dispersion laws suitable for FDTD simulations

We report optical planar waveguide formation and modal characterization in β-BaB₂O₄ crystals by Cu²⁺-ion implantation at an energy of 3.0 MeV and doses of ∼ 10¹⁴ ions/cm². The prism-coupling method was used to investigate the dark-mode property at wavelengths of 633 nm and 1539 nm. The refractive-index profile of the waveguide was reconstructed by an effective refractive index method. The modal analysis indicates that the fields of TM modes can be well restricted in the guiding region, which means the formation of a non-leaky waveguide in the crystal. The results show that the β-BaB₂O₄ waveguides may be used in the application of high efficiency frequency conversion. PACS 61.80.Jh; 42.70.Mp; 42.65.Wi     

Observation of a maximum roton velocity in superfluid 4He

Using heat pulses, we detect atoms “evaporated” by ballistic rotons at the free liquid surface. A maximum roton velocity of 160 ± 10ms^?1 is observed.     

Beat-note jitter suppression in a dual-frequency laser using optical feedback

An efficient locking technique based on optical feedback is demonstrated to suppress jitter on the rf beat note between the two modes of a dual-frequency Yb:Er glass laser. The method consists of a self-injection process in which one selected mode serves as a master oscillator to lock and stabilize the second mode via a frequency-shifted optical feedback. The beat note adjusted near 170 MHz was stabilized with an accuracy of 250 mHz using an optical feedback loop with a double pass through an acousto-optic modulator. The beating note can be tuned over 300 kHz by controlling the reference oscillator. The extensions and limitations of the technique are discussed.     

Theory of molecular excitation and relaxation near a plasmonic device

The new optical concepts currently developed in the research field of plasmonics can have significant practical applications for integrated optical device miniaturization as well as for molecular sensing applications. Particularly, these new devices can offer interesting opportunities for optical addressing of quantum systems. In this article, we develop a realistic model able to explore the various functionalities of a plasmon device connected to a single fluorescing molecule. We show that this theoretical method provides a useful framework to understand how quantum and plasmonic entities interact in a small area. Thus, the fluorescence signal evolution from excitation control to relaxation control depending on the incident light power is clearly observed.