Visualization of space charge field effect on excitons in a GaAs quantum dot by near-field optical wavefunction mapping

Near-field photoluminescence (PL) imaging spectroscopy was used to investigate multi-exciton and charged-exciton states confined in a single GaAs interface fluctuation quantum dot. We determined the origin of peaks in the PL spectra by employing a wavefunction mapping technique. We observed distortion of the exciton wavefunction due to the electric field produced by an excess electron at a nearby confined state. Near-field wavefunction mapping was demonstrated to be a powerful tool for visualizing the local environment, which affects the emission properties of quantum dots.     

On global stability of an HIV pathogenesis model with cure rate

In this paper, applying both Lyapunov function techniques and monotone iterative techniques, we establish new sufficient conditions under which the infected equilibrium of an HIV pathogenesis model with cure rate is globally asymptotically stable. By giving an explicit expression for eventual lower bound of the concentration of susceptible CD4⁺ T cells, we establish an affirmative partial answer to the numerical simulations investigated in the recent paper [Liu, Wang, Hu and Ma, Global stability of an HIV pathogenesis model with cure rate, Nonlinear Analysis RWA (2011) 12 : 2947–2961]. Our monotone iterative techniques are applicable for the small and large growth rate in logistic functions for the proliferation rate of healthy and infected CD4⁺ T cells. Copyright © 2014 John Wiley & Sons, Ltd.     

High-intensity near-field generation for silicon nanoparticle arrays with oblique irradiation for large-area high-throughput nanopatterning

We present near-field distributions around an isolated 800-nm silica or silicon nanoparticle, and nanoparticle arrays of 800-nm silica or silicon nanoparticles, on a silicon substrate by the finite-difference time-domain method when 800-nm light is irradiated obliquely to the substrate. Nanopatterning mediated with the nanoparticle system is promising for large-area, high-throughput patterning by using an enhanced localized near-field ablation by the nanoscattered light lens effect. The irradiation area cannot be extended for silica nanoparticles, because the optical field enhancement factor is low. Gold nanoparticles can generate highly enhanced near fields, although at present there are no useful ways to arrange the gold nanoparticles on the substrate at a high throughput. Silicon nanoparticles with high dielectric permittivity have optical characteristics of both silica and gold nanoparticles. The particle arrangement on the Si substrate is technically easy using a wet pulling process. From the calculation, high optical field intensity is acquired with oblique s-polarized irradiation to the substrate under silicon nanoparticle arrays, and the intensity is almost the same as that under gold nanoparticle arrays under the same condition. With this method, high-throughput nanopatterning for a large area would be achievable.     

Theoretical study on the phenyl torsional potentials of trans-diphenyldiphosphene

The phenyl torsional potentials of trans-diphenyldiphosphene ( trans-phosphobenzene; t-DPP), which is an analogue of trans-azobenzene ( t-AZB), have been examined by means of ab initio complete active space self-consistent field (CASSCF) calculations. Though the electronic structures of t-DPP are similar to those of t-AZB, the phenyl torsional potentials are different from each other. In S 0, the potential energy curve of t-DPP has double minima at nonplanar conformations with C 2 and C i symmetries, while that of t-AZB has only minimum at a planar conformation with C 2 h . In S 1, the phenyl torsion of t-AZB is impeded from a planar geometry more than that in S 0. On the other hand, the phenyl torsion of t-DPP is promoted so that the phenyl groups are perpendicularly twisted against the PP double bond around the Franck-Condon region. Comments on the experimental findings of realistic diphosphenes protected by bulky substituents are also made.     

Two new monodesmosidic triterpene saponins from Gypsophila oldhamiana

Two new monodesmosidic triterpene saponins were isolated from the roots of Gypsophila oldhamiana (Caryophyllaceae). Their structures were elucidated on the basis of spectral data to be quillaic acid, alpha-L-arabinopyranosyl-(1-->4)-alpha-L-arabinopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl ester (1), and vaccaric acid, beta-D-glucopyranosyl-(1-->3)-[beta-D-xylopyranosyl-(1-->4)]-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl ester (2). Compound 1 showed a significant enhancement of granulocyte phagocytosis in vitro.     

Acid catalyzed ring contractions in endo-2,8-trimethylene-cis-bicyclo[3.3.0]octyl cations to methylperhydrotriquinacenes. One of the methyl ext

Sulfuric acid catalyzed ring contractions with extrusion of a methyl group were examined for alcohol and olefin derivatives (28–31) of endo-2,8-trimethylene-cis-bicyclo[3.3.0]octane (11), which was one of the two possible progenitors, among altogether 69 isomers, for methylperhydrotriquinacenes (6, 7 and 12), the only methyltricyclodecane intermediates found so far, in the tricycloundecane rearrangement. Only minor amounts (1.6–2.0%) of methylperhydrotriquinacenes were formed from these reactants 28–31, and the results support the earlier theoretical conclusion that the methyl extrusions were in general energetically quite unfavorable processes owing to the formation of primary carbinyl cations at the expense of more stable secondary bridge or tertiary bridgehead ones. Reaction pathways for these precursors 28–31 were discussed with reference to those of perhydrotriquinacene 2-carbinyl cations (33a's), which corresponded to some of the ring contraction product cations from 28–31.     

Redox-switching of intramolecular magnetic interaction through π-conjugation mode change of 1,2-bis(4-dianisylamino)-1,2-bis(3-N-oxylamino)-substituted tetraarylethylene

To develop the redox-switching system of intramolecular magnetic interaction, 1,2-bis[3-(N-tert-butyl-N-oxylamino)phenyl]-1,2-bis[4-{N,N-bis(4-methoxyphenyl)amino}phenyl]ethylene, tetraarylethylene with two nitroxide radical groups at the meta-position, was synthesized, and characterized by the electrochemical method and ESR spectroscopy. Cyclic voltammetry showed the tetraarylethylene core has the lower oxidation potential than the substituted nitroxide radical moiety. ESR spectroscopy in frozen solution revealed that the neutral form shows the fine-structured spectrum characteristic of the spin triplet species, while the dicationic form shows the anisotropic hyperfine-structured spectrum characteristic of the randomly-oriented nitroxide radical, indicating the drastic change of intramolecular magnetic interaction.     

Linear free energy relationships for carbon-13 NMR chemical shifts of substituted benzoic acids1

In order to examine ¹³C-SCS of substituted benzoic acids, chemical shifts of the acid form (I) and the dissociated form (II) have been obtained separately. Single substituent parameters, σ⁰ or σ⁺ are correlated with the shifts for the carboxyl (δ_co) or ipso carbons (δ_ipso), respectively. Among the available five equations which are developed for the analysis with dual (or divided) substituent parameters (DSP), the Swain-Lupton equation (eqn 3) and the Taft-Swain-Lupton equation (eqn 4) give much better correlations, not only for δ_co and δ_ipso but also for the results for ring carbons (C(2), C(5), C(6)), except for those attached to or neighboured by substituents. It is concluded that the SCS of aromatic compounds are best analyzed with substituent parameters derived from reactions or equilibria on the basis of linear free energy relationships.     

Sorption of ethanesulfonic acid by nylon-6 containing various numbers of end groups

From the analysis of the permeation of ³⁵S labeled ethanesulfonic acid, through nylon-6 films sorption isotherms were obtained. The films are characterized by their largely different content of carboxyl and amino end groups. It was found that the shape of the isotherm depends on the molar ratio of the two end groups: an S-shape curve for the film containing the carboxyl end group larger than the amino end group and a Langmuir-type curve for the film containing comparable numbers of end groups. These results were explained by the McGregor-Harris theory in which the acid dissociation constants of the two end groups in nylon were estimated experimentally.