Nondestructive determination of crystallinity by diffuse reflectance FT-IR in composites made from polyphenylene sulphide and carbon fibres

Diffuse reflection Fourier transform infrared spectroscopy can be used for nondestructive determination of the degree of crystallinity at the surface of composite materials made from polyphenylene sulphide reinforced with carbon fibres. In particular, the ratio of the heights of the peaks at 1075 and 1093 cm^–1 can be used as a quantitative indicator of the crystallinity. This has been confirmed by annealing highly amorphous prepreg to give samples of varying degrees of crystallinity, in which case a good linear relationship is observed between the peak ratio and the enthalpy of crystallization as determined by differential scanning calorimetry.     

Determination of net atomic charges using a modified partial equalization of orbital electronegativity method. IV. Application to hypervalent sulfur- and phosphorus-containing molecules

The parameters for an empirical point charge calculation method, Mulliken Population Constrained Potential Derived–Modified Partial Equalization of Orbital Electronegativity (MPCPD–MPEOE) method, for hypervalent sulfur, phosphorus, and the atoms bonded to these atoms, were determined. A new empirical method, MPCPD, which has inherent advantages over both the Mulliken population and potential derived methods, is proposed here. The MPCPD net atomic charges are transferable and reproduce the electrostatic potential. The electrical properties were calculated with the MPCPD and MPCPD–MPEOE charges. These properties agreed well with experimental results and with 6-31G** ab initio results. The MPEOE parameters for the sulfur atom in aromatic molecules and trivalent phosphorus in phosphite molecules were also determined. The dipole moments calculated with the MPCPD–MPEOE point charges agreed well with experimental results. All the parameters obtained in this work are consistent with those obtained in our previous work. © 1995 by John Wiley & Sons, Inc.     

Protein changes in post mortem sea bass (Dicentrarchus labrax) muscle monitored by one- and two-dimensional gel electrophoresis

This study was devoted to the identification of specific peptides and proteins which can be used as indicators of freshness in fish. The post mortem evolution of protein patterns in farmed sea bass muscle was monitored by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE) after 0, 2, 4, and 6 days cold storage. SDS-electrophoresis, of total proteins and proteins soluble in low-ionic-strength solutions, revealed the gradual disappearance of a protein band of 16 kDa immediately after fish death. 2-DE allowed the classification of fish samples according to post mortem time. Three spots of interest, which disappeared progressively, were identified on the 2-DE patterns. Further research is required to establish the identity of these polypeptides and to evaluate their expression and post mortem evolution in another fish species.     

On the specific heat of nonstoichiometric ceria

Ceria (CeO₂) can readily be reduced to form a wide range of binary compounds CeO_y, 2 ≥y ≥ 1.5. Specific heat measurements at constanty were carried out for the composition range 2≥y > 1.714 and for the temperature range 300 K <T < 1200 K. In thisy,T region the specific heat exhibits a complex form reflecting various transformations. The results and theoretical evaluations of the specific heat are presented as the temperature is varied from low values (T ≈ 400K) where two phases coexist, through several phase transformations to a high temperature α phase. Special features of the specific heat due apparently to increased internal local pressure appearing for small deviations from stoichiometry are also discussed.     

Syntheses and conformations of tetrahomodioxacalix[4]arene tetraamides and tetrathioamides

A series of tetrahomodioxacalix[4]arene tetraamides and tetrathioamides with four p-phenyl groups on their upper rim were synthesized. From the (1)H and (13)C NMR and crystal structure, N-butylamido homooxacalix[4]arene (4) was found to be in the 1,3-alternate conformation and has intramolecular hydrogen bonding between N-H and facing oxygen atoms of the carbonyl O=C group. This hydrogen bonding decreased the metal ion complex ability. Transformation of the 1,3-alternate N-butylamido (4) into N-butylthioamido homooxacalix[4]arene (5) using Lawesson's reagent gave a conformational change to the C-1,2-alternate.     

Determination of net atomic charges using a modified partial equalization of orbital electronegativity method. III. Application to halogenated and aromatic molecules

The net atomic charge parameters for halogen atoms and the atoms in aromatic molecules have been determined by the modified partial equalization of orbital electronegativity method. The same parameters are used for the halogen atoms both in aromatic and nonaromatic systems. The calculated dipole moments of haloalkanes agree well with experiment, but those of the halogenated aromatic molecules do not reproduce the experimental values as well as those of the haloalkanes; in particular, the computed dipole moments for monohalogenated benzenes are all lower than the experimental values because of the influence of the lonepair electrons on the halogens. Within the limitations of an atom-centered point-charge approximation, our calculated dipole moments, both for haloalkanes and halogented aromatic molecules, agree well with experimental values. © John Wiley & Sons, Inc.     

QMR: a quasi-minimal residual method for non-Hermitian linear systems

Summary The biconjugate gradient (BCG) method is the natural generalization of the classical conjugate gradient algorithm for Hermitian positive definite matrices to general non-Hermitian linear systems. Unfortunately, the original BCG algorithm is susceptible to possible breakdowns and numerical instabilities. In this paper, we present a novel BCG-like approach, the quasi-minimal residual (QMR) method, which overcomes the problems of BCG. An implementation of QMR based on a look-ahead version of the nonsymmetric Lanczos algorithm is proposed. It is shown how BCG iterates can be recovered stably from the QMR process. Some further properties of the QMR approach are given and an error bound is presented. Finally, numerical experiments are reported.This work was supported in part by DARPA via Cooperative Agreement NCC 2-387 between NASA and the Universities Space Research Association (USRA).     

Improved Cd determination in glasses by laser ablation inductively coupled plasma mass spectrometry using nitrogen as a matrix modifier

The addition of 5-10 mL min-1 nitrogen to the central channel of plasma in Laser ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) increases the sensitivities of Cd by a factor of 3 and decreases oxide interferences by one order of magnitude, which allows the direct analysis of trace levels of Cd in glass samples. This simple method shows a great potential for the direct determination of Cd in various kinds of samples.     

Development and calibration of a WDXRF routine applied to provenance studies on archaeological ceramics

Elemental analysis of ancient ceramics is primarily used in provenance research, where defined compositional groups are attributed to particular raw materials sources or production locations. Requirements in data quality and analytical performance are high, as is the need for clear and reproducible methodologies and the availability of information on the above to ensure interlaboratory comparability and long‐term data validity. This paper outlines the measurement parameters of a dedicated calibration set‐up for the analysis of ancient ceramics using wavelength‐dispersive X‐ray fluorescence spectrometry. The specimens are prepared as concentrated glass beads, allowing the measurement of 26 elements from a single sample, thus minimising sample size requirements. Certified and non‐commercial standards are used to evaluate the performance of the method in terms of detection limits, precision, repeatability and accuracy. The materials used cover a range of compositions in line with the matrix variability encountered in archaeological ceramics. The data confirm the high standard of the method and highlight specific limitations. An initial assessment of comparability with other set‐ups used in ceramic analyses, primarily neutron activation analysis, is given through a discussion of performance on commonly analysed materials. The advantages of the proposed method include excellent analytical performance, analysis of a large suite of elements including all major, minor and a good range of traces, relatively small sample sizes and preparation of samples that can be stored and reanalysed. Copyright © 2017 John Wiley & Sons, Ltd.