Photon channelling in foams

Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling only occurs in a finite range of ɛ.     

A Case Study on the Development of the Home Defence Training Game HOT SEAT

Home defence is concerned with enhancing the prospects for survival and recovery of this country in the eventuality of nuclear war. Contingency plans exist for the creation of a system of wartime regional government which includes elements from peacetime local and central governments. Senior officers in local government with designated wartime roles receive training at the Home Defence College. The Home Office decided that a crisis management game should form part of their overall programme of indoctrination. The resulting game, which is known as HOT SEAT, has been successfully implemented and is now in regular use at the College. This paper describes how the need for the game arose, the structure of the resulting game, the problems that arose during its development, and should be of interest to those concerned with the development of management and crisis games.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

CONVERGENCE OF THE NONCONFORMING WILSON''''S BRICK FOR ARBITRARY HEXAHEDRAL MESHES

The nonconforming Wilson's brick classically is restricted to regular hexahedral meshes. Lesaint and Zlamal[6] relaxed this constraint for the two-dimensional analonue of this element In this paper we extend their results to three dimensions and prove that and where u is the exact solution, u_h is the approximate solution and is the usual norm for the Sobolev space H~1(?).     

Accuracy and validity of stereology as a quantitative method for assessment of human temporal lobe volumes acquired by magnetic resonance imaging

The object of this study was to compare the accuracy and validity of stereology as a method for determining whole temporal lobe volume with the more established technique of semi-automated thresholding and tracing. Ten, fixed, post-mortem human brains, were imaged using a three dimensional (3D) acquisition protocol. The volume of the left temporal lobe, dissected from each brain, was determined by fluid displacement. Each volume was compared to measurements obtained from magnetic resonance images (MRI) of the post-mortem brain using each of the two segmentation methods. Post-acquisition processing was performed using MEASURE software. Three investigators performed each measurement three times using each method, yielding a total of 180 measurements. Stereology took, on average, half the time of thresholding/tracing. Using a clinically acceptable variation for 95% of repeat measures; both intra-observer and inter-observer variation were acceptable for each technique. However, validity, as demonstrated by graphs of agreement against water displacement showed that the "limits of agreement" using stereology were within the acceptable range, while those using the thresholding/tracing technique were not. Quantitative estimates of variation and a graphical representation of the limits of agreement show that stereology is at least as precise as the thresholding/tracing method but is superior in terms of speed and validity. This has broad implications for published estimates of brain region volumes in human diseases such as epilepsy, dementia and other neurodegenerative disorders.     

Rapid and robust spin state amplification

Electron and nuclear spins have been employed in many of the early demonstrations of quantum technology. However, applications in real world quantum technology are limited by the difficulty of measuring single spins. Here we show that it is possible to rapidly and robustly amplify a spin state using a lattice of ancillary spins. The model we employ corresponds to an extremely simple experimental system: a homogenous Ising-coupled spin lattice in one, two, or three dimensions, driven by a continuous microwave field. We establish that the process can operate at finite temperature (imperfect initial polarization) and under the effects of various forms of decoherence.     

Quantum information processing with delocalized qubits under global control

Conventional quantum computing schemes are incompatible with nanometer-scale "hardware," where the closely packed spins cannot be individually controlled. We report the first experimental demonstration of a global control paradigm: logical qubits delocalize along a spin chain and are addressed via the two terminal spins. Using NMR studies on a three-spin molecule, we implement a globally clocked quantum mirror that outperforms the equivalent swap network. We then extend the protocol to support dense qubit storage and demonstrate this experimentally via Deutsch and Deutsch-Jozsa algorithms.     

Integrating mathematics,statistics, and technology in vocational and workplace education

In the workplace mathematics and statistics are essential for communication and decision-making. Process workers at lower classifications of skill levels are likely to be confronted with statistical charts and warnings about nonconformity. Mathematics, statistics, and technology education in and for the workplace must take account of the cultural diversity which exists within and between workplaces. The design of generic mathematics, and in some cases statistics, curricula rarely reflect actual workplace practice except at a superficial level. One way of overcoming these problems is for mathematics/statistics educators to work in cooperation with industry, particularly at the local level, in a way that will encourage and support lifelong learning yet remain critical of the uses to which mathematics, statistics, and technology are put. This paper outlines some ways in which to address the challenge of making mathematics, statistics, and technology education take on real meaning within the context of the workplace.