Studies on the conversions of diols and cyclic ethers—49: Stereochemistry of cyclodehydration of 1,4-diols on the action of brönsted and lewis acids: a comprehensive study

The stereochemistry of the cyclodehydration of (±)- and meso-2,5-hexanediol on the action of various dehydrating agents was investigated. The earlier assumed and confirmed intramolecular S_N2 mechanism for acid-catalysed ring-closure was found to hold in most cases. Various extents of racemisation can be observed on the action of certain Lewis acids, and the solvents concentrated H₂SO₄ and HMPT (hexamethyl phosporic acid triamide) under previously unexamined reaction conditions.     

Evaluation of a dual electrospray ionization/atmospheric pressure chemical ionization source at low flow rates (∼50 µL/min) for the analysis of both highly and weakly polar compounds

The atmospheric pressure ionization (API) source for a commercial mass spectrometer was modified to operate as a dual source in both the electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) techniques by simultaneously utilizing the electrospray probe and the corona discharge needle. A switching box was designed to operate in either manual or programmable modes to permit rapid switching between ionization techniques without changing sources, probes, or breaking vacuum. The source can be operated using the following ionization techniques: ESI only, APCI only, ESI/APCI simultaneously, and ESI/APCI alternatingly. The optimum operating conditions for these ionization techniques were similar to the manufacturer’s original specifications except that the APCI flow rate was lower (～50 µL/min versus 1000 µL/min) and externally heated nebulizing gas was found to be desirable. A four-component mixture, introduced by flow injection, was used to demonstrate the versatility of the dual ESI/APCI source.     

Dynamic Global Constraints in Backtracking Based Environments

Global constraints provide strong filtering algorithms to reduce the search space when solving large combinatorial problems. In this paper we propose to make the global constraints dynamic, i.e., to allow extending the set of constrained variables during search. We describe a generic dynamisation technique for an arbitrary monotonic global constraint and we compare it with the semantic-based dynamisation for the alldifferent constraint. At the end we sketch a dynamisation technique for non-monotonic global constraints. A comparison with existing methods to model dynamic problems is given as well.     

Szegö-Kolmogorov-Krein theorems on weighted trigonometrical approximation and Cárleman-type relations

We consider the well-known Szegö — Kolmogorov — Krein theorems on weighted approximations by functions with semibounded spectra defined on a circle or on a line and suggest an efficient construction that realizes these approximations. This construction is based on relations similar to the Cárleman formula for reconstructing analytic functions in terms of their traces on the boundary of their domains of definition.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 46, Nos. 1–2, pp. 100–127, January–February. 1994.     

Genetics of Vocal Quality Characteristics in Monozygotic Twins: A Multiparameter Approach

The main purpose of this study was to determine the vocal quality characteristics among the 45 monozygotic cotwins (MT). As the performance of the voice is related to several genetically determined anatomical and physiological factors, the authors hypothesized that the vocal characteristics and the overall vocal quality by means of the Dysphonia Severity Index (DSI) will be identical in MT. An additional objective of this study was to determine whether sex and age influence vocal similarities in MT and to compare the voice characteristics of MT with the normative data of unrelated peers. As more environmental factors influence the aging of the voice, age-related differences were expected. No sex-related differences were expected. Subjective and objective assessment techniques determined the vocal quality. No significant differences were obtained, and most comparisons resulted in significant correlation coefficients. For the acoustic parameters jitter and shimmer only, no significant correlation coefficients could be obtained. It is clear that the perceptual voice characteristics, the laryngeal aerodynamic measurements of maximum phonation time (MPT), the vocal performances, and the overall vocal quality by means of the DSI are similar in MT. These vocal characteristics are not influenced either by the subjects' age or sex and are situated within the normative range of unrelated peers. To what extent other aspects (environment, anxiety, tension, etc) might play a role in the acoustical dimensions regarding frequency and amplitude perturbation, which were in the normal range, is a subject of further research.     

Mueller matrices in fluorescence scattering

A reappraisal of the 1929 analysis of luminescence by Soleillet reveals the form of the Mueller matrix for fluorescence scattering whose parameters are directly defined in terms of the now-familiar fluorescence anisotropy parameter. If the scattering analyte is optically active, it is further shown how fluorescence detected circular dichroism and circularly polarized luminescence can be recovered, simultaneously and free of artifacts.