A Vibrating-Wire Viscometer for Dilute and Dense Gases

The vibrating-wire technique has been applied to design a viscometer for precise measurements on gases in the temperature range 25 to 250°C at pressures from 0.1 to 40 MPa employing two Chromel wires with different radii. The technique has been improved to avoid the influence of higher harmonic modes and the degeneracy of perpendicular modes, to eliminate electromagnetic noise from the signal, and to minimize the influence of the magnetic damping. The decrement and frequency of the oscillation have to be determined by extrapolation to zero displacement, and wires with a perfectly smooth surface are needed to meet the requirements of the measuring theory. The viscosity measurements are characterized by a precision of ±0.05% at ambient temperature. Considering the uncertainty of the reference data used for calibration, the total uncertainty amounts to ±0.2% within the calibrated range of the boundary-layer thickness.     

Application of capillary electrophoresis in clinical chemistry--developments from preliminary trials to routine analysis

Since instruments performing capillary electrophoresis (CE) became commercially available in the late 1980s, information on this relatively new analytical technique has been increasing almost exponentially. At the beginning of the last decade, fundamental discoveries in the field were made mainly in the laboratories of analytical chemists; but now, this separation science is giving increasing impact to the laboratories of clinical chemists. This paper briefly reviews the history, instrumentation, different modes and theory of CE, and the prominent fields of its applications in clinical chemistry.     

Reactive sputtering of PTFE films in argon-CF4 mixtures

Polytetrafluoroethylene (PTFE) films of good adherence with electrical and mechanical properties close to those of the bulk material were reactively sputtered in mixtures of argon and CF₄. Mass spectrometry of the effluent gases from the discharge indicates that the sputtering of PTFE in argon results in the generation of relatively large amounts of volatile species like CF₄, C₂F₆, C₃F₈ etc. The addition of up to 25% of CF₄ to the sputtering gas results in more stoichiometric films than can be obtained by sputtering in pure argon. At higher CF₄ concentrations the deposition rate drops to zero and plasma etching of the SiO₂ substrates is observed.     

Coupling phenomena in thermoplasticity

Based on classical continuum mechanics and thermodynamics, a general framework is developed for the formulation of a phenomenological theory of large inelastic nonisothermic deformations particularly of elastic-plastic and elastic-viscoplastic bodies. The framework allows also to take into account such phenomena as recrystallization, recovery, aging, and solid phase transformations. The considerations are focused on the interaction of thermic and mechanical processes. This interaction becomes particularly important in those processes which are very sensitive to material behaviour. Processes of this kind are bifurcation problems, e.g. the accumulation of second-order effects in cyclic processes, the generation of residual stresses in single or cyclic deformations, and many others.     

Comparative genomic hybridisation for the analysis of chromosomal imbalances in solid tumours and haematological malignancies

Comparative genomic hybridisation (CGH) is based on a two-colour, competitive fluorescence in situ hybridisation of differentially labelled tumour and reference DNA to normal metaphase chromosomes. This new technology has made a great impact in molecular tumour pathology due to its possible application to archival specimens and the ability to create copy number karyotypes throughout the whole genome from very small amounts of DNA. If chromosomal imbalances can be correlated with a etiological and clinical features of tumours, CGH could be able to provide new prognostic and diagnostic criteria. CGH findings further provide starting points for the molecular genetic characterisation of altered chromosomal regions harbouring yet unidentified genes involved in tumorigenesis and tumour progression. An overview of the results of published CGH studies on solid tumours and haematological malignancies is presented. Methodological limitations of the CGH technology are reported, as well as future developments which will improve its use in routine analysis.     

An evaluation of evolutionary constraints on microsatellite loci using null alleles

A test to evaluate constraints on the evolution of single microsatellite loci is described. The test assumes that microsatellite alleles that share the same flanking sequence constitute a series of alleles with a common descent that is distinct from alleles with a mutation in the flanking sequence. Thus two or more different series of alleles at a given locus represent the outcomes of different evolutionary processes. The higher rate of mutations within the repeat region (10(-3) or 10(-4)) compared with that of insertion/deletion or point mutations in adjacent flanking regions (10(-9)) or with that of recombination between the repeat and the point mutation (10(-6) for sequences 100 bp long) provides the rationale for this assumption. Using a two-phase, stepwise mutation model we simulated the evolution of a number of independent series of alleles and constructed the distributions of two similarity indices between pairs of these allele series. Applying this approach to empirical data from locus AG2H46 of Anopheles gambiae resulted in a significant excess of similarity between the main and the null series, indicating that constraints affect allele distribution in this locus. Practical considerations of the test are discussed.