Scattering from coated targets using a frequency-dependent, surfaceimpedance boundary condition in FDTD

One method for reducing the radar cross section of objects such as aircraft and missiles is the application of a lossy coating. Computing scattering from targets coated with dielectric/magnetic materials is challenging due to the reduced wavelengths of an incident field inside the coating. These smaller wavelengths require finer sampling of the fields. A technique for implementing this calculation without greatly increased memory requirements or computation times has previously been developed using a finite-difference time-domain (FDTD) code which has been tested in one, two, and three dimensions. The method requires knowledge of the frequency behaviour of the complex permittivity and permeability, and the thickness of the dielectric coating and is applicable to thin coatings when one or more reflections from the conducting surface are significant. The impedance at the surface of the coating is computed based on the given information and then approximated using a summation of causal functions. The approximated impedance is Z-transformed and added to the FDTD code in special update equations for the fields at the surface of the coating. No computations are required inside the coatings so the FDTD grid can be sized based on the free-space wavelength. The result obtained is valid over the entire frequency range of interest, assuming that the approximated surface impedance is a good match over the entire range. Comparisons with measurements of a scale model coated missile show good agreement and almost no increase in resource requirements over a standard FDTD calculation for an uncoated metal target     

Interactional Order and Constructed Ways of Seeing with Touchless Imaging Systems in Surgery

While surgical practices are increasingly reliant on a range of digital imaging technologies, the ability for clinicians to interact and manipulate these digital representations in the operating theatre using traditional touch based interaction devices is constrained by the need to maintain sterility. To overcome these concerns with sterility, a number of researchers are have been developing ways of enabling interaction in the operating theatre using touchless interaction techniques such as gesture and voice to allow clinicians control of the systems. While there have been important technical strides in the area, there has been little in the way of understanding the use of these touchless systems in practice. With this in mind we present a touchless system developed for use during vascular surgery. We deployed the system in the endovascular suite of a large hospital for use in the context of real procedures. We present findings from a study of the system in use focusing on how, with touchless interaction, the visual resources were embedded and made meaningful in the collaborative practices of surgery. In particular we discuss the importance of direct and dynamic control of the images by the clinicians in the context of talk and in the context of other artefact use as well as the work performed by members of the clinical team to make themselves sensable by the system. We discuss the broader implications of these findings for how we think about the design, evaluation and use of these systems.     

Noniterative compensation for the distance-dependent detector response and photon attenuation in SPECT imaging

A filtering approach is described, which accurately compensates for the 2D distance-dependent detector response, as well as for photon attenuation in a uniform attenuating medium. The filtering method is based on the frequency distance principle (FDP) which states that points in the object at a specific source-to-detector distance provide the most significant contribution to specified frequency regions in the discrete Fourier transform (DFT) of the sinogram. By modeling the detector point spread function as a 2D Gaussian function whose width is dependent on the source-to-detector distance, a spatially variant inverse filter can be computed and applied to the 3D DFT of the set of all sinogram slices. To minimize noise amplification the inverse filter is rolled off at high frequencies by using a previously published Wiener filter strategy. Attenuation compensation is performed with Bellini's method. It was observed that the tomographic point response, after distance-dependent filtering with the FDP, was approximately isotropic and varied substantially less with position than that obtained with other correction methods. Furthermore, it was shown that processing with this filtering technique provides reconstructions with minimal degradation in image fidelity.     

The effect of the initial gas volume to meat weight ratio on the storage life of chilled beef packaged under carbon dioxide

Normal pH (5·5-5·7) and high pH (>6·0) beef cuts of 400 g were vacuum packaged in polyvinylidine chloride (PVDC) laminate, in aluminium foil laminate or in foil laminate with a CO(2) scavenger (Ba(OH)(2)); or were packaged under CO(2) in foil laminate with CO(2) added at 200, 400, 700, 1000 or 2000 ml per kg of meat. The process used to prepare meat before packaging resulted in an initial flora containing a high fraction of eneterobacteria but with undetectable numbers of lactobacilli. During storage at +1°C, all vacuum packaged meat developed floras containing substantial fractions of enterobacteria. The enterobacteria fractions were larger on high pH than on normal pH meat, and on normal pH meat in PVDC or in foil laminate plus CO(2) scavenger packs than on normal pH meat in foil laminate without the CO(2) scavenger. All vacuum packaged meat was spoiled by putrid flavours, high pH meat at 7 weeks and normal pH meat at 12 weeks. Increasing amounts of added CO(2) progressively retarded the development of putrid spoilage, as growth of the spoilage floras was slowed while the relative numbers of lactobacilli in the floras were enhanced. With the two largest amounts of added CO(2), spoilage was delayed until 15 weeks and 21 weeks for high pH meat and normal pH meat, respectively, and enterobacteria were detected in the spoilage floras only at later sampling times. With lesser amounts of added CO(2), enterobacteria persisted or re-emerged at earlier times, in the floras.     

The Software Architecture for a Large Telephone Switch

This paper describes the software and the software structure used in a family of high-capacity digital telephone switches. The call processing task is complex, and has great diversity. It must support existing and future features, including some not yet envisioned. The software must also provide man-machine interfaces, maintain the office database, and offer automatic recovery from hardware and software errors. It must also meet critical real-time performance specifications. The techniques adopted to meet these requirements include the use of a strongly typed high-level language, independent design and compilation of software modules, and the provision of an automated program library system and problem reporting system. Considerable experience in the development and support of large software systems has been accumulated, and is described in the paper.     

Parallel and Turbulent Flow Precipitator Efficiencies for Distributions of Particle Mobilities

Regimes of parallel and turbulent flow in a parallel plate precipitator are discussed as theoretical idealizations. Particle trajectories and resultant efficiency of an ideal parallel flow device are described and compared with the Deutsch equation analysis, based upon complete mixing in turbulent flow, for a single mobility species. A relationship is developed between particle size and mobility which incorporates field and diffusion charging and the Cunningham correction to Stoke's drag. Log normal distributions of particle size are transformed into mobility distribution functions. Efficiencies based upon parallel flow and turbulent mixing are expressed for the particle mobility distributions by finding incremental efficiencies for each segment of a given distribution and weighting each segment by its relative proportion of the whole. These efficiencies are compared with each other and with the result obtained by inserting the mean mobility into the Deutsch equation. It is shown that, for relatively high standard deviation, use of an average mobility value in the Deutsch equation can result in device efficiency characteristics quite similar to those resulting from collection of the various mobility species in parallel flow. A much lower efficiency results from incremental analysis of the same distribution under the assumption of turbulent mixing.     

Modification of in-pack conditions to extend the storage life of vacuum packaged lamb

High pH (>5·9) lamb loins from a research abattoir were subjected to differing packaging treatments to determine whether package modification could reliably extend the storage life of chilled lamb cuts beyond that attained by cuts vacuum-packaged in film of low gas permeability, as in current commercial practice. Treatments applied were carbon dioxide flushing or addition of a citrate buffer (pH 4·8), a 5% lactic acid solution or a Lactobacillus inoculum (plastic packs only) and packaging in a plastic film of moderately low oxygen permeability (140 cc/m(2)/24 h at 25°C and 90% relative humidity) or in a foil laminate of immeasurably low oxygen permeability. After 12 weeks' storage at -0.5°C, the cuts packaged in the plastic film were spoiled by off-odours produced by enterobacteria, except for inoculated cuts, which, instead, had developed unacceptable dairy flavours. In contrast, cuts packaged in foil laminate developed floras of lactobacilli that had not caused spoilage after 12 weeks, and meat colour was much improved by the exclusion of oxygen. Loin cuts from a commercial packaging operation were packaged in a shrinkable plastic film of low oxygen permeability (30 to 40 cc/m(2)/24 h at 25°C and 90% relative humidity), in foil laminate, or in foil laminate after the addition of 5% lactic acid solution. For the first 6 weeks, cuts were stored in a commercial chiller nominally operating at 0°C; subsequently, they were held in a laboratory chiller at -0.5°C. Some cuts packaged in the shrinkable plastic were spoiled after 9 weeks' storage and all were spoiled at 12 weeks, because of off-flavours produced by enterobacteria. All cuts packaged in the foil laminate were very acceptable at 9 weeks but most were spoiled by off-flavours at 12 weeks. Most cuts treated with lactic acid and packaged in foil laminate were unspoiled after 12 weeks. The packaging requirements indicated to be necessary for reliable extension of the storage life of vacuum packaged lamb are discussed.     

An unusual case of primary leptomeningeal marginal zone B-cell lymphoma

Primary leptomeningeal lymphomas are rare, and usually follow a rapid clinical course with early systemic involvement. A 60-year-old woman presented with a 3-year history of worsening seizures and memory loss. Neuroimaging showed widespread meningeal calcification. After extensive investigations a meningeal biopsy revealed a low-grade B-cell lymphoma categorized as an extranodal marginal zone B-cell lymphoma, attributed to the same histological group as the MALT (mucosa-associated lymphoid tissue) lymphomas described in the stomach, thyroid, salivary glands and orbit. There was no evidence of systemic involvement. The extensive meningeal calcification would appear to be a novel finding in primary leptomeningeal lymphoma whereas the unusually long clinical history in this case is possibly related to the particular histological type of low-grade B-cell lymphoma.