Chiral Algebras of (0, 2) Models: Beyond Perturbation Theory

We show that the chiral algebras of ${\mathcal{N} = (0, 2)}$ sigma models with no left-moving fermions are totally trivialized by worldsheet instantons for flag manifold target spaces. Consequently, supersymmetry is spontaneously broken in these models. Our results affirm Stolz’s idea (Stolz in Math Ann 304(4):785–800, 1996) that there are no harmonic spinors on the loop spaces of flag manifolds. Moreover, they also imply that the kernels of certain twisted Dirac operators on these target spaces will be empty under a quantum deformation of their geometries.     

Simple and validated UHPLC method coupled to UV detection for determination of daptomycin in human plasma and urine

Daptomycin, a lipopeptide antibiotic with excellent activity against Gram‐positive bacteria, is excreted primarily by the kidneys. Development of effective chromatographic methodologies for the determination of daptomycin in human specimens is necessary for clinical use. This study developed a simple and validated ultra‐high‐performance liquid chromatography method coupled to ultraviolet detection for determination of daptomycin in human plasma and urine. After the pretreatments involving protein precipitation, the supernatants were separated using a 2.3 µm particle size octadecylsilyl column, and the run time was 1 min. The calibration curves were linear over the concentration ranges of 2–200 mg/L for plasma and 25–300 mg/L for urine. Intra‐ and inter‐assay precision and accuracy values of plasma were within 13.5 and 92–100% and within 10.7 and 100–107%, respectively. Those of urine were within 5.0 and 101–104% and within 3.7 and 100–101%, respectively. The validated method was applied to the determination of plasma and urine samples in patients receiving 4–6 mg/kg of intravenous daptomycin, resulting in sufficient sensitivity for evaluating the plasma exposure and urinary excretion. In conclusion, the present method with acceptable analytical performance can be helpful for evaluating the pharmacokinetic disposition of daptomycin in clinical settings. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and properties of functional dyes with squaraine–naphthalene diimide hybrid structure

Naphthalene diimides (NDIs) are promising candidate for electron acceptors due to their low-lying HOMOs and LUMOs. The functinalization of soluble NDIs at the 2,6-position affects the absorption and electrochemical properties. In this study, NDI-based hybrid dyes NDI-SQ-A, B fused with squaraine chromophore were designed and synthesized in order to elucidate the effects of the substitution on their optical and electrochemical properties. These dyes were successfully synthesized by Stille coupling reactions using 3-stannylcyclobutenediones and brominated NDI derivative, followed by a condensation reaction. DFT calculation predicts that the present dyes adopt distorted structures coming from a steric hindrance between semisquaraine and NDI moieties. The hybrid dyes show low-lying LUMOs due to the introduction of electron-deficient NDI moiety and broad absorption spectra in the far-red region. The absorption spectra of their thin films were bathochromically shifted relative to those in solution, indicating that hybrid dyes formed J aggregates.     

Phloroglucinol derivatives and a chromone glucoside from the leaves of Myrtus communis

Seven new phloroglucinol derivatives, myrtucommunins A–D (1–4), 6-methylisomyrtucommulone B (5), 4-methylmyrtucommulone B (6), and 2-isobutyryl-4-methylphloroglucinol 1-O-β-d-glucopyranoside (7), and one new chromone derivative, undulatoside A 6′-O-gallate (8), were isolated from the leaves of Myrtus communis (Myrtaceae). Myrtucommunins A–D (1–4) were conjugates of polymethylated acylphloroglucinol and flavonol rhamnoside. The absolute configurations of the rhamnosyl moieties for 1–4 were confirmed to be l in each case by HPLC analyses, while those of the aglycones were assigned by comparisons of the experimental and TDDFT calculated ECD spectra. 6-Methylisomyrtucommulone B (5) and 4-methylmyrtucommulone B (6) were assigned as 6/6/6 tricyclic acylphloroglucinol derivatives with a racemic nature. Antimicrobial activities of 1–8 and related known compounds were evaluated.     

Microhardness and fracture toughness of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-and Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>-based nanocrystalline laser ceramics

The microhardness and fracture toughness of laser nanocrystalline ceramics based on the cubic oxides Y₂O₃ and Y₃Al₅O₁₂ are determined experimentally. It is shown by comparative measurements that the fracture toughness and microhardness of Y₂O₃ ceramics exceed the corresponding parameters of Y₂O₃ single crystals by factors of 2.5 and 1.3, respectively. The fine morphology of grains and grain boundaries in fractures is investigated. It is ascertained that changes in the mechanical properties of the nanocrystalline ceramics under study are related to both the sizes and structure of grains and the structure of grain boundaries. It is suggested that twinning processes determine the mechanisms of formation of nanocrystalline ceramics.     

Refractive indices of laser nanocrystalline ceramics based on Y3Al5O12

Refractive indices of the nanocrystalline Y₃Al₅O₁₂ ceramic and a garnet single crystal of the same composition have been measured. In the visible and near IR range (0.4–1.064 μm), the prism method was used; in the medium IR range (2–6.2 μm), the interference method with the use of thin plates was applied. The refractive indices of these crystalline materials are practically the same over the entire spectral range studied and are described by the approximate formula proposed earlier for a single crystal. The parameters of the continuos-wave lasing in the nanocrystalline Y₃Al₅O₁₂ ceramic doped with Nd³⁺ and Yb³⁺ ions measured recently are presented.     

Vibrational quasi-degenerate perturbation theory: applications to fermi resonance in CO2, H2CO, and C6H6

A quasi-degenerate perturbation method with vibrational self-consistent field (VSCF) reference wavefunction is developed. It simultaneously accounts for strong anharmonic mode-mode coupling among a few states (static correlation) by a configuration interaction theory and for weak coupling with a vast number of the other states (dynamic correlation) by a perturbation theory. A general formula is derived based on the van Vleck perturbation theory. An algorithm that selects a compact set of the most important VSCF configurations which contribute to the static correlation is proposed and a scheme to limit the number of configurations considered for dynamic correlation is also implemented. This method reproduces the vibrational frequencies of CO2 and H2CO that are subject to the strongest anharmonic mode-mode coupling within 10 cm(-1) of vibrational configuration interaction results in a computational expense reduced by a factor of one to two orders of magnitude. The method also reproduces the infrared absorption of C6H6 in the CH stretching (nu12) frequency region, in which combination tones nu13nu16 and nu2nu13nu18 appear on account of an intensity borrowing from nu12via the anharmonic coupling.     

Efficient configuration selection scheme for vibrational second-order perturbation theory

A fast algorithm of vibrational second-order Moller-Plesset perturbation theory is proposed, enabling a substantial reduction in the number of vibrational self-consistent-field (VSCF) configurations that need to be summed in the calculations. Important configurations are identified a priori by assuming that a reference VSCF wave function is approximated well by harmonic oscillator wave functions and that fifth- and higher-order anharmonicities are negligible. The proposed scheme has reduced the number of VSCF configurations by more than 100 times for formaldehyde, ethylene, and furazan with an error in computed frequencies being not more than a few cm(-1).     

Optical properties and highly efficient laser oscillation of Nd:YAG ceramics

Optical absorption, emission spectra have been measured for polycrystalline Nd-doped Y₃Al₅O₁₂ ceramics. Fluorescence lifetimes of 257.6 μs, 237.6 μs, 184.2 μs and 95.6 μs have been obtained for 0.6%, 1%, 2% and 4% neodymium-doped YAG ceramics, respectively. For the first time, highly efficient laser oscillation at 1064 nm has been obtained with this kind of ceramics. Slope efficiency of 53% has been achieved on a uncoated 4.8-mm thick 1% Nd:YAG ceramics sample. Optical to optical conversion efficiency is 47.6%. Laser oscillation has also been obtained with a 2% Nd:YAG ceramics. The optical properties and laser output results have been compared with that of Nd:YAG single crystal grown by the Czochralski method. Almost identical results have been achieved including laser experiments results. But fabrication of Nd:YAG ceramics is much easier compared to the single-crystal growth method. And also large size (now of about 400 mm diameter×5 mm is available) and high-concentration (>1%) Nd:YAG ceramics can be fabricated. The results show that this kind of Nd:YAG ceramics is a very good alternative to Nd:YAG single crystal. Received: 20 April 2000 / Published online: 16 August 2000