Birefringent Bragg Gratings in Highly-Nonlinear Photonic Crystal Fiber

Efficient writing of Bragg gratings in 12-ring highly-nonlinear photonie crystal fibers is described. Experimental and numerical investigations are performed to reveal the optimum angle for coupling UV writing light to the core. Furthermore, we show that the formation of a strongly briefringent grating is at a particular angle of orientation.     

Cone-beam reprojection using projection-matrices

This paper addresses reprojection of three-dimensional (3-D) reconstructions obtained from cone-beam scans using a C-arm imaging equipment assisted by a pose-determining system. The emphasis is on reprojecting without decomposing the estimated projection matrix (P-matrix) associated with a pose. Both voxel- and ray-driven methods are considered. The voxel-driven reprojector follows the algorithm for backprojection using a P-matrix. The ray-driven reprojector is derived by extracting from the P-matrix the equation of the line joining a detector-pixel and the X-ray source position. This reprojector can be modified to a ray-driven backprojector. When the geometry is specified explicitly in terms of the physical parameters of the imaging system, the projection matrices can be constructed. The resulting "projection-matrix method" is advantageous, especially when the scanning trajectory is irregular. The algorithms presented are useful in iterative methods of image reconstruction and enhancement procedures, apart from their well-known role in visualization and volume rendering. Reprojections of 3-D patient data compare favorably with the original X-ray projections obtained from a prototype C-arm system. The algorithms for reprojection can be modified to compute perspective maximum intensity projection.     

Virtual angiography for visualization and validation of computational models of aneurysm hemodynamics

It has recently become possible to simulate aneurysmal blood flow dynamics in a patient-specific manner via the coupling of three-dimensional (3-D) X-ray angiography and cmputational fluid dynamics (CFD). Before such image-based CFD models can be used in a predictive capacity, however, it must be shown that they indeed reproduce the in vivo hemodynamic environment. Motivated by the fact that there are currently no techniques for adequately measuring complex blood velocity fields in vivo, in this paper we describe how cine X-ray angiograms may be simulated for the purpose of indirectly validating patient-sperific CFD models. Mimicking the radiological procedure, a virtual angiogram is constructed by first simulating the time-varying injection of contrast agent into a precomputed, patient-specific CFD model. A time-series of images is then constructed by simulating the attenuation of X-rays through the computed 3-D contrast-agent flow dynamics. Virtual angiographic images and residence time maps, here derived from an image-based CFD model of a giant aneurysm, are shown to be in excellent agreement wiith the corresponding clinical images and residence time maps, but only when the interaction between the quasisteady contrast agent injection and the pulsatile flow are properly accounted for. These virtual angiographic techniques pave the way for validating image-based CFD models against routinely available clinical data, and provide a means of visualizing complex, 3-D blood flow dynamics in a clinically relevant manner. They also clearly show how the contrast agent injection perturbs the noraml blood flow patterns, further highlighting the potential utility of image-based CFD as a window into the true aneurysmal hemodynamics.     

What women want: single older women and their housing preferences

It is increasingly recognized in Australia that single, older women are particularly vulnerable to housing-related stress and homelessness. This paper reports on a qualitative study that explored the housing experiences of single, older, non-homeowning women in regional New South Wales, Australia. Interviews were conducted with 47 participants living independently in precarious housing. This paper focuses upon the housing preferences expressed by the participants. A feminist standpoint perspective was adopted and thematic analysis was employed to interrogate the data. Findings showed the women’s primary preference is security of tenure in housing that is affordable and suited to their needs. Further, they want to feel they have autonomy in the private sphere. Over the participants’ life course, twin discourses of patriarchy and neoliberalism were identified as influential in shaping social arrangements, both in Australia and other developed countries. These findings may assist policy-makers in planning future housing for this ageing cohort.     

An agenda for integrated system-wide interdisciplinary agri-food research

This paper outlines the development of an integrated interdisciplinary approach to agri-food research, designed to address the ‘grand challenge’ of global food security. Rather than meeting this challenge by working in separate domains or via single-disciplinary perspectives, we chart the development of a system-wide approach to the food supply chain. In this approach, social and environmental questions are simultaneously addressed. Firstly, we provide a holistic model of the agri-food system, which depicts the processes involved, the principal inputs and outputs, the actors and the external influences, emphasising the system’s interactions, feedbacks and complexities. Secondly, we show how this model necessitates a research programme that includes the study of land-use, crop production and protection, food processing, storage and distribution, retailing and consumption, nutrition and public health. Acknowledging the methodological and epistemological challenges involved in developing this approach, we propose two specific ways forward. Firstly, we propose a method for analysing and modelling agri-food systems in their totality, which enables the complexity to be reduced to essential components of the whole system to allow tractable quantitative analysis using LCA and related methods. This initial analysis allows for more detailed quantification of total system resource efficiency, environmental impact and waste. Secondly, we propose a method to analyse the ethical, legal and political tensions that characterise such systems via the use of deliberative fora. We conclude by proposing an agenda for agri-food research which combines these two approaches into a rational programme for identifying, testing and implementing the new agri-technologies and agri-food policies, advocating the critical application of nexus thinking to meet the global food security challenge.     

Cool thinking: Unlocking earth's energy

The ground is as universal as air and solar radiation. Over the past twenty years, as the hunt for natural low-carbon energy sources has intensified, there has been an increased endeavour to investigate and develop both earth and ground water thermal energy storage and usage. Bill Holdsworth reports on some recent pioneering developments in the Netherlands and UK.     

Characterization of Catheter Dynamics During Percutaneous Transluminal Catheter Procedures

Remote catheter navigation systems are being developed to reduce the occupational risk of the intervening physician. Despite the success of such systems, development has occurred with little fundamental knowledge of the catheter dynamics applied by the interventionalist. This paper characterizes the kinematics of a catheter during manipulation, the minimum applied force/torque during interventional procedures, and the maximum force/torque applied by an operator to overcome vasculature friction. Ten operators manipulated a 6F catheter inside a specialized catheter movement sensor to determine the velocities and accelerations of catheter motion. A mass-spring apparatus was constructed to measure the forces and torques required to overcome introducer sheath and vasculature friction. Results showed the catheter was manipulated at peak velocities and accelerations of (muplusmnsigma) : 360 plusmn 180 mmldrs^-1 and 22200 plusmn 14000 mmldrs^-2, and 19 plusmn 7 radldrs^-1 and 900 plusmn 510 radldrs^-2, for axial and radial directions of motion, respectively. A minimum force of 0.29 plusmn 0.06 N and a torque of 1.15 plusmn0.3 mNldrm was required to move the catheter through the introducer sheath; while the observed maximum applied torque was 15 mNldrm to overcome vasculature friction. The implications of these results for future design optimization of an intuitive remote catheter navigation system are considered.