The reconstruction of maximal planar graphs. I. Recognition

The object of this paper is to show that every maximal planar graph is recognizable from its family of vertex-deleted subgraphs.     

Stable operation of a cw optical parametric oscillator near the signal-idler degeneracy

The frequency stability of a cw optical parametric oscillator (cw OPO) near the signal-idler degeneracy has been studied. The strong tendency of a near-degenerate OPO to mode hop has been suppressed by using a bulk Bragg grating as a spectral filter in the OPO cavity. An experimental demonstration of stable parametric oscillation in a single longitudinal mode of the OPO cavity is reported, together with the capability of tuning the signal-idler difference frequency from 1 to 4 THz. The OPO has potential use in cw terahertz generation.     

Optimal correlation function for Fermi HNC equations

We show how to find variational equations for the Jastrow pair-correlation function which minimizes the energy of a normal Fermi liquid in the hypernetted chain approximation. By a straightforward extension of the method of Lagrange multipliers, a set of coupled, non-linear integrodifferential equations is obtained. The solutions give both the trial function and the corresponding radial distribution function. For bosons, our equations coincide with the results of paired-phonon analysis.     

Edge-reconstruction of 4-connected planar graphs

The object of this paper is to show that 4-connected planar graphs are uniquely determined from their collection of edge-deleted subgraphs.     

Time-dependent density-functional theory in the projector augmented-wave method

We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties. We demonstrate different applications of the methods by calculating excitation energies and excited state Born-Oppenheimer potential surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear emission spectra using the time-propagation method.     

ISO 17025 quality system in a university environment

The experience of working under an ISO 17025 compliant quality system in a university environment is described in the example of the Testing Centre of University of Tartu. University-specific features of the quality system include that the Testing Centre acts as the “quality system server” for other units of the university and graduate students participate in the work carried out under the quality system. The benefits for the university and the graduate students are discussed. It is concluded that implementation of an ISO 17025 compatible quality system in a university is fully accomplishable and gives significant added value to the university by helping to destroy the ivory tower perception about universities and by introducing real-world flavour into the studies and broaden the minds (quality awareness) of the students.     

Effects of prolonged oral reading on F0, SPL, subglottal pressure and amplitude characteristics of glottal flow waveforms

The effects of prolonged (5x45 minute) reading (vocal loading) on fundamental frequency (F0), sound pressure level (SPL), subglottal (intraroral) pressure (p), and two glottal flow waveform parameters (AC amplitude of glottal flow, f, and negative peak amplitude of differentiated flow (d) of normal female and male subjects (N = 80) were studied. Two rest (morning and noon) and three loading (two in the morning and one in the afternoon) samples were recorded and analyzed. The glottal waveforms were obtained by inverse filtering of the acoustic pressure waveforms of speaking voice samples. The analyses were based on measurement and inverse filtering of the first stressed syllable of "paappa" words repeated 3x5 times for normal, as soft as possible, and as loud as possible phonation. In normal phonation the parameter values changed statistically significantly due to loading. In many cases the values obtained in the morning samples changed after the first loading session. This is interpreted as a vocal "warming-up effect." Especially in soft phonation p, d, and f were sensitive indicators of vocal loading. In both normal and soft phonation, the SPL, p, d, and f values tended to rise due to prolonged reading in the morning and afternoon samples, indicating increased effort (normal phonation) and a rise in the phonatory threshold (soft phonation). The lunch break vocal rest ("rest effect") considerably affected the parameter values in many cases.     

Quantum mechanical models correlating structure with selectivity: predicting the enantioselectivity of beta-amino alcohol catalysts in aldehyde alkylation

Quantitative structure selectivity relationship (QSSR) models are described that provide consistently reliable predictions for the asymmetric addition of Et2Zn to PhCHO catalyzed by beta-amino alcohols. Statistically valid two-variable linear regression models that correlate the structures of the chiral catalysts with their enantioselectivities are obtained from three-dimensional physical property grids. The strength of the present method is that statistical models obtained from a small set of experimentally determined selectivities and relatively simple theoretical calculations yield selectivity predictions that are as accurate as those derived from higher-level calculations of transition-structure energies. Only minutes of computing time are required. Simple models are obtained which permit straightforward physical interpretation and generate realistic predictions.     

Overcharging of polyelectrolyte complexes by the guest polyelectrolyte studied by fluorescence spectroscopy

Polyion complexes (PICs) of anionic block copolymer poly(ethylene oxide)-block-poly(sodium methacrylate), PEO-block-(PMA)Na, and a cationic homopolymer, poly((methacryloyloxyethyl)trimethylammonium chloride), PMOTAC, have been studied by fluorescence spectroscopy. Pyrene and naphthalene singly labeled block copolymers were used with two different sodium methacrylate block lengths. The chain exchange between the stoichiometric PICs at the equilibrium state and the formation of the negatively charged PICs on addition of excess PEO-block-(PMA)Na to stoichiometric PIC solution were of interest. The chain exchange between the stoichiometric complexes was observed to occur via two mechanisms. The faster chain exchange occurs via insertion and expulsion of single chains, while merging and splitting of the PIC particles is behind the slower chain exchange event. Incorporation of an excess amount of the guest polyion into a stoichiometric PIC took place on further addition of the PEO-block-(PMA)Na. The same mechanisms were recognized in the overcharging process of the PICs as in the chain exchange between the stoichiometric PICs.     

A versatile stereocontrolled approach to chiral tetrahydrofuran and tetrahydropyran derivatives by use of sequential asymmetric Horner-Wadsworth-Emmons and ring-closure reactions

An approach to chiral tetrahydrofuran and tetrahydropyran derivatives based on the sequential use of an asymmetric Horner-Wadsworth-Emmons reaction and a cyclization step is presented. The approach is both stereochemically and structurally versatile since three different cyclization methods can be employed starting from the same HWE product: (i) palladium-catalyzed substitution, (ii) hetero-Michael addition, or (iii) epoxide opening. The asymmetric HWE reaction controls the absolute configuration of the ultimate product, whereas the relative configuration is controlled by the combined influence of the geometric selectivity in the HWE reaction and the stereochemistry of the respective cyclization method.