No abstract available

No abstract available

[en] A new close-coupling scheme for the numerical calculation of quantum-mechanical probabilities for collision-induced dissociation of a diatomic molecule by an atom is presented. Fully converged preliminary results for a collinear model are given for the first time. (Auth.)

[en] Under short pulse laser excitation, we have observed an extra high-energy photoluminescence (PL) emission from GaNAs/GaAs single quantum wells (QWs). It dominates the PL spectra under high excitation and/or at high temperature. By measuring the PL dependence on both temperature and excitation power and by analyzing the time-resolved PL results, we have attributed the PL peak to the recombination of delocalized excitons in QWs. Furthermore, a competition process between localized and delocalized excitons is observed in the temperature-dependent PL spectra under the short pulse excitation. This competition is believed to be responsible for the temperature-induced S-shaped PL shift often observed in the disordered alloy semiconductor system under continuous-wave excitation. copyright 2001 American Institute of Physics

[en] The system of a trapped ion translationally excited by a blue-detuned near-resonant laser, sometimes described as an instance of a phonon laser, has recently received attention as interesting in its own right and for its application to non-destructive readout of internal states of non-fluorescing ions. Previous theoretical work has been limited to cases of two-level ions. Here, we perform simulations to study the dynamics of a phonon laser involving the Λ-type ${}^{138}\mathrm{B}{\mathrm{a}}^{+}$ ion, in which coherent population trapping (CPT) effects lead to different behavior than in the previously studied cases. We explore optimization of the laser parameters to maximize amplification gain for initially seeded motion and consider the related signal-to-noise ratios for internal state readout. We find that good Doppler amplification and state readout performance can be obtained even when operating quite near the CPT dip. (paper)

[en] We study the creation of stationary light pulses (SLPs), i.e., light pulses without motion, based on the effect of electromagnetically induced transparency with two counterpropagating coupling fields in cold atoms. We show that the Raman excitations created by counterpropagating probe and coupling fields prohibit the formation of SLPs in media of cold and stationary atoms such as laser-cooled atom clouds, Bose condensates or color-center crystals. A method is experimentally demonstrated to suppress these Raman excitations and SLPs are realized in laser-cooled atoms. Furthermore, we report the first experimental observation of a bichromatic SLP at wavelengths for which no Bragg grating can be established. Our work advances the understanding of SLPs and opens a new avenue to SLP studies for few-photon nonlinear interactions.

[en] In this paper the results of DFT/TDDFT-based theoretical calculations of an electroluminescent zinc(II) chelate complex with 5-amino-2-(1H-benzoimidazol-2-yl)-phenol (HL), namely [ZnL²] (1), are presented. The molecular geometry, the orbital interaction between the L^– ligand and the Zn(II) center, and the effect of the substituted NH² group on its absorption/emission property and colors are analyzed in detail. Moreover, the important Zn-ligand bonding property is analyzed by means of PDOS, OPDOS spectra, and the Mulliken population analysis scheme. It is the main ionic interaction between Zn(II) and the L^– ligand. Owing to the effect of the substituted NH² group on its absorption/emission property and colors, it is quite probable that by introducing different substituted groups, a series of new OLED-relevant metal chelate complexes can be designed with their absorption/emission property and colors being tuned.

[en] In this paper, we describe an easy procedure for the preparation of differently shaped and sized Au-Ag nanocomposites from gold nanorod (AuNR) seeds in various amino acid solutions-arginine (Arg), cysteine (Cys), glycine (Gly), glutamate (Glu), glutamine (Gln), histidine (His), lysine (Lys), and methionine (Met), respectively-at values of pH ranging from 8.0 to 11.5. Our results suggest that the pH, the nature of the amino acid, and its concentration all have significant impact on the preparation of Au-Ag nanocomposites; these factors exhibit their effects mainly through control over the reducing ability of ascorbate and/or its recognition capability, as well as through control over the surface charges of the amino acids on the AuNRs. Depending on the value of pH, we were able to prepare I-shaped, dumbbell-shaped, and/or sphere-shaped Au-Ag nanocomposites in 0.1 M solutions of Arg, Gly, Glu, Gln, Lys, and Met. In His solutions at pH 8.0 and 9.0, we obtained peanut-shaped Au-Ag nanocomposites. Corn-shaped Au-Ag nanocomposites were prepared in 0.1 M Met solutions (pH 9.0 and 10.0). By controlling the Lys concentration at pH 10.0, we synthesized pearl-necklace-shaped Au-Ag nanoparticles and Au-Ag wires. Based on the TEM images, we conclude that this simple and reproducible synthetic approach allows preparation of high-quality (>87%, beside>77% in His solutions) Au-Ag nanocomposites with various shapes and sizes under different conditions

[en] Protein kinase C (PKC) family of serine/threonine protein kinases is sensitive signaling transducers in response to lead acetate (Pb) that could transmit phosphorylation cascade for proliferation and de-differentiation of neural cells. However, little is known as to the impact of PKC on Pb genotoxicity. Here we investigate whether Pb activates the conventional/classical subfamily of PKC (cPKC) signaling to affect cytotoxicity and mutagenicity in CL3 human non-small-cell lung adenocarcinoma cells. Pb specifically promoted membrane localization of the α isoform of PKC in CL3 cells. Pb also elicited Raf-1 activation as measured by the induction of phospho-Raf-1^S338 and the dissociation from the Raf-1 kinase inhibitor protein. Inhibition of cPKC activity using Goe6976 or depletion of PKCα by introducing specific small interfering RNA blocked the induction of phospho-Raf-1^S338, phospho-MKK1/2 and phospho-ERK1/2 in cells exposed to Pb. Intriguingly, declining PKCα enhanced the Pb cytotoxicity and revealed the Pb mutagenicity at the hprt gene. The results suggest that PKCα is obligatory for activation of the Raf-1-MKK1/2-ERK1/2 signaling module and plays a defensive role against cytotoxicity and mutagenicity following Pb exposure. Results obtained in this study also support our previous report showing that ERK1/2 activity is involved in preventing Pb genotoxicity

[en] Optical thin films designed for multispectral band-pass filters and a primary Ag mirror were deposited on radiation-resistant glass by ion-beam-assisted deposition. The filters and mirror are for use in the optical payload of a remote sensing instrument. The optical parameters of the films and mirror were optimized by using admittance loci analysis. The simulation shows that the band-pass filters can achieve average transmittances of 95% in the blue (B1), green (B2), red (B3), near-infrared (B4), and panchromatic (400-900 nm) spectral ranges and an average reflectance of 99% for the primary Ag mirror in the visible spectrum. The corresponding properties of the films were investigated by in situ optical monitoring, spectrometry, and high-resolution transmission electron microscopy. It was found that the average transmittances are above 85% for all five band-pass filters, with a rejection transmittance below 1% in the spectral range of 350-1100 nm. The average reflectance of the primary Ag mirror (with a protective coating) is above 98%. Interference coatings were added to the basic protected silver design to enhance the reflectance in the visible spectral range. Furthermore, to investigate the optical stability of optical thin films for aerospace applications, a space environment was simulated by using a Co⁶⁰ gamma (γ) radiation source (total doses of 35 krad and 1 Mrad). The experimental results indicate that both the dielectric thin film stacks and radiation-protected glass are resistant to γ radiation in the simulated space environment.