A simplified approach for evaluation of the polarity parameters for polymer using the K coefficient of the Mark-Houwink-Sakurada equation

Since two solvent polarity parameters, e.g., the Et(30) defined by Reichardt and the pi* defined by Kamlet and Taft, respectively, plotted with the K coefficient of the Mark-Houwink-Sakurada equation, presented good linear fits, this paper suggests applying the extrapolating method in the same way as the Zisman plot to obtain similar polarity parameters for polymers. In order to verify those obtained polarity parameter values for various polymers, literature-reported polarity values determined using other techniques are referenced and indicate that this paper introduced a simplified approach that can be applied to evaluate the polarity parameters for polymers. In this paper, since we observe that various polymers are of interest to present absolutely different slope tendencies, e.g., positive and negative, it is also suggested that polarity properties of polymers may be reinterpreted.     

Design of two-dimensional random surfaces with specified scattering properties

A method is proposed for designing a two-dimensional randomly rough Dirichlet surface that, when illuminated at normal incidence, scatters a scalar plane wave with a specified angular distribution of its intensity. The method is validated by computer simulation calculations.     

74% Slope efficiency from a diode-pumped Yb3+:LiNbO3:MgO laser crystal

An optimization of the laser action performance from a diode-pumped Yb³⁺-doped LiNbO₃:MgO crystal has been carried out. In this sense, efficient laser action at 1.06 m when pumping with a fiber-coupled laser diode at 980 nm has been demonstrated, achieving laser slope efficiencies as high as 74%. The influence of output mirror transmittance on both pumping threshold and laser slope efficiency has been investigated, and the parameters of relevance in laser dynamics (emission cross section and optical losses) have been determined. Under the experimental conditions leading to maximum slope efficiency, the pump power at threshold was 300mW, and the pump-to-laser conversion efficiency was 40%. PACS 42.55.Xi; 42.55.Rz; 42.60.Lh     

A prototype calix[4]arene-based receptor for carbohydrate recognition containing peptide and phosphate binding groups

A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed.     

Reexamination of CeCl3 and InCl3 as activators in the diastereoselective Mukaiyama aldol reaction in aqueous media

A search for suitable reaction conditions in Mukaiyama-type aldol condensations activated by CeCl(3) and InCl(3) revealed that the reaction proceeds best in i-PrOH/H(2)O (95:5). Contrary to literature precedent, no reaction was observed in pure water, and the encountered destruction of the starting silyl enol ether can be ascribed to initial hydrolysis of the Lewis acid. As anticipated from the dual parameter (pK(h), WERC value) characteristics of CeCl(3) and InCl(3), the former proved more efficient as Lewis acid-promoter, in terms of reaction speed and yield. Nevertheless, InCl(3) was a superior catalyst during evaluation of the diastereoselectivity of the process. In this regard, determination of diastereoselectivity as a function of time showed that the InCl(3)-catalyzed reaction is irreversible, whereas the CeCl(3)-catalyzed reaction is a reversible process. In both cases, formation of the syn product is kinetically preferred, although DeltaDeltaG(++)273K(InCl(3)) = 1.50 kcal/mol versus DeltaDeltaG(++)273K (CeCl(3)) = 0.38 kcal/mol. Molecular modeling (semiempirical PM3, ab initio HF/3-21G*, hybrid B3LYP/3-21G*, and B3LYP/LANL2DZ) of the diastereoselective aldol reaction promoted by InCl(3) supports a "closed", Zimmermann-Traxler transition state.     

Ferromagnetic Coupling through Spin Polarization in a Dinuclear Copper(II) Metallacyclophane

No Abstract     

Structure and polarity of 8CB films evaporated onto solid substrates

Brewster-angle reflection ellipsometry and surface optical second harmonic generation were used to study the growth of 4'-n-octyl-4-cyanobiphenyl (8CB) films evaporated in air onto polymeric and quartz glass substrates. The layer-by-layer growth of the films terminates after formation of two distinctive interfacial layers. Both of these two layers are polar and tilted. In the first layer the molecules lie nearly flat on the surface, while in the second layer they point on average about 50° toward the surface normal. The dipole moment of the second layer has a lower magnitude and an opposite direction with respect to the dipole moment of the first layer.     

Focal-shift formula in apodized nontelecentric focusing systems

A single analytical formulation for evaluating the focal shift in any apodized nontelecentric focusing setup is reported. The formulation is also useful in the case of imaged paraxial beams. We show explicitly that the magnitude of the focal shift is determined by only one parameter that depends on the effective width of the pupil filter and its axial position. To illustrate our approach we examine different focusing setups.     

Dynamics of carriers photogenerated in a dot-in-a-well nanostructure

We review our recent results on the investigation of carrier dynamics of semiconductor nanostructures, i.e., dot-in-a-well. We introduced a technique based on the measurement of time-resolved differential photoluminescence spectra induced by subpicosecond pump and probe laser pulses. In this technique, the temporal resolution was achieved by adjusting the temporal delay between the pump and probe pulses. Using such a new technique, we measured the exciton decay times and then studied the dependences of integrated photoluminescence intensity and photoluminescence linewidth on temperature in InAs quantum dots embedded in InGaAs/GaAs quantum wells. We gave consistent interpretations to our experimental results.