The effect of molecular biaxiality on the bulk properties of some nematic liquid crystals

The nematic substance 5CB is known from N.M.R. studies to be slightly biaxial, not in the sense that any bulk property measured in a direction at right angles to the director is liable to vary with rotation about the director, but in the sense that there are biaxial terms in the ordering matrix that describes the alignment of individual molecules; (S_xx - S_yy) is non-zero as well as S_zz. We show that the biaxial terms should make a significant contribution to the magnetic anisotropy Δχ^(m) of 5CB, and that the magnitude and temperature dependence of this bulk property, which we have measured, can be understood if, and only if, they are taken into account. The contribution which they make to the optical birefringence term ∑ should, however, be relatively trivial. Although ∑ may in principle be affected by local field corrections of a complicated nature, which do not affect Δχ^(m), a new theory presented in an Appendix to the paper suggests that these too are likely to be relatively trivial. Hence we believe that ∑ is more nearly proportional than is Δχ^(m) to the principal order parameter S_zz.

The paper includes unpublished data for the magnetic anisotropy and/or the principal refractive indices, n_e and n_o, in a number of other nematics (6CB, 7CB, 8CB, 9CB, 5OCB, 6OCB, 7OCB, 8OCB, 7CCH, MBBA and PAA). Comparison between the temperature dependence of Δχ^(m) and of ∑ suggests that biaxiality is present in all cyanobiphenyls, on much the same scale as in 5CB, and is not affected by the presence of an oxygen atom between the phenyl core of the molecule and its alkyl tail.     

Synthesis of 2,5-disubstituted oxazoles from aldehydes and N-(tosylmethyl)imino synthons. Application to the synthesis of pimprinine analogues

A series of N-(tosylmethyl)imino compounds [TosCH₂N?C(L)A] has been applied to a new base-induced, one-operational synthesis of 2,5-disubstituted oxazoles from aromatic aldehydes. For substituent A of the imino compounds, which becomes the 2-substituent in the oxazoles, has been chosen methoxy, methyl and phenyl. The new method has been used also to synthesize seven pimprinine analogues, i.e., 5-(-3)indolyl)oxazoles.     

Generalized quadrangles with an ovoid that is translation with respect to opposite flags

The article [6] contains the result that if a finite generalized quadrangle of order s has an ovoid that is translation with respect to two opposite flags, but not with respect to any two non-opposite flags, then is self-polar and is the set of absolute points of a polarity. In particular, if is the classical generalized quadrangle Q(4, q) then is a Suzuki-Tits ovoid. In this article, we remove the need to assume that is Q(4, q) in order to conclude that is a Suzuki-Tits ovoid by showing that the initial assumptions in fact imply that is Q(4, q). At the same time, we also relax the requirement that have order s.Received: 14 May 2004     

The Higher Spin Laplace Operator

This paper deals with a certain class of second-order conformally invariant operators acting on functions taking values in particular (finite-dimensional) irreducible representations of the orthogonal group. These operators can be seen as a generalisation of the Laplace operator to higher spin as well as a second-order analogue of the Rarita-Schwinger operator. To construct these operators, we will use the framework of Clifford analysis, a multivariate function theory in which arbitrary irreducible representations for the orthogonal group can be realised in terms of polynomials satisfying a system of differential equations. As a consequence, the functions on which this particular class of operators act are functions taking values in the space of harmonics homogeneous of degree k. We prove the ellipticity of these operators and use this to investigate their kernel, focusing on polynomial solutions. Finally, we will also construct the fundamental solution using the theory of Riesz potentials.     

Evidence of neutral radical induced analyte ion transformations in APPI and Near-VUV APLI

We report on the reactions of neutral radical species [OH, Cl, O(³P), H], generated in a typical atmospheric pressure ionization (API) source upon irradiation of the sample gases with either 193 nm laser radiation or 124 nm VUV light, the latter commonly used in atmospheric pressure photoionization (APPI). The present investigations focus on the polycyclic aromatic hydrocarbon pyrene as representative of the aromatic compound class. Experimental results are supported by computational methods: simple kinetic models are used to estimate the temporal evolution of the concentrations of reactants, intermediates, and final products, whereas density functional theory (DFT) energy calculations are carried out to further elucidate the proposed reaction pathways. The neutral radicals are generated upon photolysis of background water and oxygen always present in appreciable mixing ratios in typical API sources. Substantial amounts of oxygenated analyte product ions are observed using both techniques. In contrast, upon atmospheric pressure laser ionization (APLI) with 248 nm radiation, oxygenated products are virtually absent. In addition, kinetic data evaluation yielded a bimolecular rate constant of k=(1.9±0.9)×10⁻⁹ cm³ molecule⁻¹ s⁻¹ for the reaction of the pyrene radical cation with OH radicals.     

SOAS: A free program to analyze electrochemical data and other one-dimensional signals

This paper describes an open source program called SOAS, which we developed with the aim of analysing one-dimensional signals. It offers a large set of commands for handling voltammetric and chronoamperometric data, including smoothing signals, differentiation, subtracting baselines, fitting current responses, measuring limiting currents, and searching for peak positions. Although emphasis is on the analysis of electrochemical signals, particularly protein film voltammetry data, SOAS may also prove useful for processing spectra. This free program is available by download from the Internet, and can be installed on computers running any flavor of Unix or Linux, most easily on MacOS X.     

Regulations in the field of residue and doping analysis should ensure the risk of false positive declaration is well-defined

The purpose of this contribution is twofold, namely, to discuss the fundamental weaknesses of some decision criteria in the field of residue and doping analysis and to draw attention to a statistics-based solution that was proposed and thoroughly validated a decade ago, but nevertheless continues to be overlooked by practitioners. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board, and the Publisher.