THEORY AND DESIGN OF A TUNABLE QUASI-LUMPED QUADRATURE COUPLER

In this article, we present the theory and a design methodology for a unable Quasi-Lumped Quadrature Coupler (QLQC). Because of its topology, the coupler is simply reconfigured by switching the bias of two varactor diodes via a very simple DC bias circuitry. No additional capacitors or inductors are required. A prototype at 3.5 GHz is etched on a 0.130-mm-thick layer substrate with a dielectric material of relative permittivity of 2.22. The simulated and measured scattering parameters are, presented. (c) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2219-2222 2009: Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24526

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 1: wetting and compression behaviour

Over the last 40 years considerable progress has been made in understanding the complex behaviour of unsaturated soils. Research using constitutive modelling has extended the critical state framework and the concept of yielding in saturated soils to encompass unsaturated soils experiencing suction. However, validation testing of the framework for unsaturated soils has shown disagreement with the basic propositions. The main reason for this disparity is the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. The paper describes the detailed testing carried out to justify this statement. As part of the work presented, samples of unsaturated kaolin were prepared using isotropic compression. The suctions in these samples were reduced to predefined values by wetting under low isotropic loading. The pore size distributions, the pressure–volume relationships and yielding under subsequent isotropic loading are compared with tests on samples prepared by statically compressing kaolin into a one-dimensional compaction mould. The anisotropically compressed samples had initial water contents and specific volumes similar to those of the isotropically prepared samples and were also tested under reducing suctions; they exhibited distinctly different behaviour when tested under similar conditions. The results obtained from the isotropically prepared and tested samples have shown, probably for the first time, the existence of a unique normal compression surface that is not dependent on the initial conditions of the samples. The shape of the loading–collapse (LC) yield locus is shown to be different from the generally accepted form.

Developing critical social work in theory and in practice: child protection and communicative reason

This paper argues that a critical analysis of the ideologies that inform contemporary child care has been missing from the ‘re-focusing debate’. Such an analysis points up the necessity of reasserting a critical social work position in order to provide a basis for reconstructing practice and engaging with other social actors and their ideologies in an open and creative fashion compatible with Habermas’ aspiration of ‘communicative reason’.