Electromagnetic design search and optimisation of photonic bandgap devices on distributed computational resources

Photonic crystals are devices with periodically modulated dielectric constant, designed to exhibit band gaps in a frequency spectrum in which electromagnetic waves cannot propagate. Tuning the properties of these structures to achieve precise band gaps before fabrication is of high interest to photonic crystal manufacturers. In this paper, we present the process of finding and optimising a photonic crystal design using a high-throughput Condor-based compute cluster and transparent database technology for easy storage, retrieval and reuse of the created designs. We also demonstrate how a band gap diagram can easily be obtained on a compute cluster when using the developed user interface technology. The optimisation process can easily be adapted to other problem area

Optimal finite element modelling and efficient reconstruction in non-linear 3D electrical resistance tomography

Electrical Impedance Tomography can provide images with well-defined characteristics using a fully non-linear reconstruction process when appropriate constraints are imposed on the solution to allow the ill-posed inverse problem to be solved. Using appropriate finite element discretizations for forward solution and inverse problem offers additional advantages in the image reconstruction process, such as (a) inclusion of prior knowledge, (b) generic model templating to adapt to, for example, individual head shapes, and (c) obtaining accurate results without unnecessary computational overhead. We have developed an efficient 3D non-linear reconstruction algorithm based on a regularized inverse conjugate gradient solver which incorporates (a) local image smoothness constraints, and (b) a number of optimisations which reduce the computing power required to obtain an accurate solution. We show results from applying this to various problems which arise in medical resistivity reconstruction given only surface potential measurements and demonstrate the importance of the FE discretization. Keywords: 3D non-linear electrical impedance tomography, FE template modelling, optimal finite element meshes, 3D visualization, FE discretization

Efficient non-linear 3D electrical tomography reconstruction

Non-linear electrical tomography imaging can be performed efficiently if certain optimisations are applied to the computational reconstruction process. We present a 3D non-linear reconstruction algorithm based on a regularized conjugate gradient solver and discuss the optimisations which we incorporated to allow for an efficient and accurate reconstruction. In particular, the application of image smoothness constraints or other regularization techniques and auto-adaptive mesh refinement are highly relevant. We demonstrate the results of applying this algorithm to the reconstruction of a simulated material distribution in a cubic volume

Finite element optimizations for efficient non-linear electrical tomography reconstruction

Electrical Tomography can produce accurate results only if the underlying 2D or 3D volume discretization is chosen suitably for the applied numerical algorithm. We give general indications where and how to optimize a finite element discretization of a volume under investigation to enable efficient computation of potential distributions and the reconstruction of materials. For this, we present an error estimator and material-gradient indicator as a driver for adaptive mesh refinement and show how finite element mesh properties affect the efficiency and accuracy of the solutions

Psychological impact of cardiac testing in adolescents.

Background: Anecdotal evidence suggests that at least 8 young people (aged 14-35) die of undiagnosed cardiac conditions every week. Cardiac screening will detect the majority of cardiac conditions that could lead to a sudden cardiac death (e.g. Hypertrophic Cardiomyopathy, long QT syndrome, Wolff-Parkinson-White syndrome). However, screening of apparently healthy young people may have adverse psychological consequences on those who have negative test results. Objectives The objective of the current research was to evaluate the psychological effects on young people of screening for cardiac conditions that are partly genetic. Methods: The current study (N=746) was a prospective investigation of psychological responses to screening, involving assessments at the time of invitation (T1), immediately before testing (T2), and 2-3 weeks later (T3), following receipt of results. It was carried out in the context of an innovative screening programme being developed by the charity Cardiac Risk in the Young (CRY). All participants were healthy individuals who had consented to cardiac screening in two different contexts, community (N=303) and school (N=443). Anxiety and self-rated health were evaluated using standard measures, and illness representations were assessed with the revised Illness Perception Questionnaire (IPQ-R). Between group analyses were performed for each of the key factors, gender, age, and number of symptoms at the time of screening. Two groups of young people---adolescents (14-19) and adults (20-35)---were compared. Comparisons were also made with an adolescent age-matched control group not offered screening. Results: Anxiety levels in the screening participants were significantly lower than those of the control group (not offered screening) and population norms. There were no changes in anxiety between T1 and T2, but at T3 (after receiving a negative result) anxiety levels significantly declined. Participants with symptoms were more anxious. Similar results were reported for self rated health. Patterns of response differed between adolescents and adults. Cognitive representations of the cardiac conditions were not associated with anxiety during the testing programme. Emotional representations and genetic worries were associated with anxiety at T1 and T2 and emotional representations predicted reassurance at the end of the programme. A small number of participants had positive results in response to screening, and their experiences were also tracked. Discussion: This research provides strong evidence that the tests were acceptable to the participants. The levels of anxiety reported in this study, and the impact on self rated health, are not excessive. They were reassured after the testing satisfied with the information they received reported qualitative responses that were positive and showed they had understood the process that they were engaged in. Selection factors were probably responsible for the lower levels of anxiety in participants than controls. These results suggest that screening apparently healthy young people (both adolescents and adults under the age of 35) for potentially serious cardiac conditions does not have adverse psychological effects

Multiple states of finger propagation in partially occluded tubes

International audienc

Efficient non-linear 3D electrical tomography and finite element optimizations for functional source imaging

An essential factor in functional source imaging is the accurate knowledge of the conducitvity dostribution inside the body. Current models for electrophysiological forward and inverse problems use tabulated conductivity values obtained from experiments. This article shows how EIT-derived conductivities can be used in EEG reconstructions of a head slice

Characterisation, modification and mathematical modelling of sudsing

A programme of research is outlined which considers the foaming performance and foam behaviour of surfactant systems commonly encountered in hand-wash laundry detergent applications. An experimental study of the physical chemistry of foam generation indicates that precipitation of a typical anionic surfactant with calcium forms mesophase particles and causes a marked reduction in the rate of transport of surfactant to air–water surfaces and a concomitant reduction in foaming. Oily soil antifoam effects are however insensitive to the presence of calcium, being equally effective regardless of pH and calcium content. They may be reproduced by a simple particle–oil mixture of a saturated and an unsaturated triglyceride (e.g. tristearin and triolein respectively). A detailed foam rheometry study is performed using foam flowing through a constriction. Bubble shapes are used to deduce the normal and shear stresses across the foam flow field. Broad agreement between the experimental stress field and that obtained from quasistatic simulations is demonstrated. As foam flow-rate increases, a different model, which takes explicit account of viscous dissipative forces within the foam flow field is required. The dissipative foam flow model predicts differential shrinkage and stretch rates of foam films. Coupled to a model for surfactant transport, this shows the extent to which surfactant concentration accumulates in shrinking films and is depleted in stretching films. In addition to film stretching, it is also important to know about film bursting or failure rates. Here failure rates are estimated using capillary suction pressures exerted on the films by Plateau border channels around film edges. The failure rates can then be employed to predict the evolution of bubble size at various spatial locations in a foam: reasonable agreement with experimental bubble size distributions is obtained

A geometry optimization framework for photonic crystal design

AbstractThe performance of photonic crystal devices can depend strongly on their geometry. Alas, their fundamental physics offers relatively little by way of pointers in terms of optimum shapes, so numerical design search techniques must be used in an attempt to determine high performance layouts. We discuss strategies for solving this type of optimization problem, the main challenge of which is the conflict between the enormous size of the space of potentially useful designs and the relatively high computational cost of evaluating the performance of putative shapes. The optimization technique proposed here operates over increasing levels of fidelity, both in terms of the resolution of its non-parametric shape definition and in terms of the resolution of the numerical analysis of the performance of putative designs. This is a generic method, potentially applicable to any type of electromagnetic device shape design problem. We also consider a methodology for assessing the robustness of the optima generated through this process, investigating the impact of manufacturing errors on their performance. As an illustration, we apply this technology to the design of a two-dimensional photonic crystal structure; the result features a large complete band gap structure and a topology that is different from previously published designs