Image Similarity Metrics in Image Registration

Measures of image similarity that inspect the intensity probability distribution of the images have proved extremely popular in image registration applications. The joint entropy of the intensity distributions and the marginal entropies of the individual images are combined to produce properties such as resistance to loss of information in one image and invariance to changes in image overlap during registration. However information theoretic cost functions are largely used empirically. This work attempts to describe image similarity measures within a formal mathematical metric framework. Redefining mutual information as a metric is shown to lead naturally to the standardised variant, normalised mutual information

GLM permutation - nonparametric inference for arbitrary general linear models

Introduction: Permutation methods are finding growing use in neuroimag- ing data analyses (e.g. randomise in FSL, SnPM in SPM, XBAMM/BAMM/CAMBA, etc). These methods provide ex- act control of false positives, make only weak assumptions, and allow nonstandard types of statistics (e.g. smoothed variance t- test). With fast and inexpensive computing, there would seem few reasons not to use nonparametric methods. A significant limitation of these methods, however, is the lack of flexibility with respect to the experimental design and nuisance variables. Each specific design dictates the type of exchange- ability of null data, and hence how to permute. Nuisance effects (e.g. age) render data non-exchangeable even when the effect of interest is null. Hence, even something as simple as ANCOVA has no exact permutation test. Recently there has been an active literature on approximate– but accurate–permutation tests for 2-variable regression, one effect of interest, one nuisance (see review by Anderson & Robinson [1]). Here we extend and evaluate these methods for use with an arbitrary General Linear Model (GLM)

The design, construction and application of apparatus for telemetering biological data from the human alimentary tract

A considerable period at the beginning of this work was devoted to the design and construction of the miniaturised electronic and mechanical units required for the capsule part of the telemetering system. The initial difficulties with small components and the micro-manipulation techniques had been almost overcome and the prototype 'probes' were nearing a final state when it was discovered that a similar unit was soon to become available commercially. It did not seem worthwhile continuing work on the capsule at that time, but since I was able to anticipate the appearance of the commercial version, by the time that it appeared on the market, in October 1960, I had built an external detecting system so as to be able to estimate the effects of attenuation through the abdominal wall and movement of the capsule within the bowel; factors which at that time were unknown. As a result of these experiments the original receiving unit was modified and in March 1961, a series of clinical trials was started,in conjunction with a medical colleague, to establish the possible uses of the capsule telemetering method.The instrument, which was developed for measuring pressures within the bowel using a mobile, rather than stationary, transducing system proved quite adequate both for assessing the immediate applications of the system and for estimating its potential for more comprehensive studies. Further refinements, such as a non-directional aerial array, which would have made the routine studies more convenient and a more elaborate receiver with better longterm stability which would have increased the accuracy of the system during extended experiments were put aside in favour of the clinical experiments. This uncertainty in the basal levels was not a serious limitation, however, because we did not attempt to make the complicated computations, involving variations in abdominal pressures and the hydrostatic effects of viscera overlying the bowel, which would have been necessary to deduce absolute pressure levels within the bowel.We devised a method for localising the capsule, using contrast techniques and a series of two or three abdominal radiographs to enable us to make estimates of the long-term movements of the capsule. A method of monitoring the changes in signal intensity was also adopted to enable us to form some idea of the short-term movements of the capsule, as well as making a record of the intra-luminal pressure variations. Neither the method for localising the capsule, nor the monitoring of the short-term movements was sufficiently accurate to make really precise studies, but they allowed us to start the clinical experiments without further delay.The capsule technique proved to be extremely successful in that the clinical procedures involved were simple and from the patient's point of view, completely a traumatic. The uncertain length of the gastric phase presented a practical difficulty which we were not able to solve satisfactorily and sometimes an interesting part of the experiment was missed on this account. The length of the transit periods through the intestine appeared reasonable compared to known rates of transport, although the inertia of the capsule prevented a direct comparison with the more realistic estimates using fluid markers. We were, therefore, satisfied that the capsule did not lead to direct stimulation of the bowel as previous intubation methods have been thought to do, although as 1 have explained earlier, the nature of the method is such that we could not prove this by a direct experimental comparison. The periods of complete quiescence which were recorded on many occasions from all levels of the major organs were also inconsistent with local stimulation.We carried out 40 clinical experiments, each of which involved, on average, 2 or 3 days of recording. The investigations included series of normal controls, a number of patients with abnormal functional conditions and a short series of post-operational studies. The large amount of data collected from each of these experiments was found to be something of a problem because the salient features were sometimes obscure and the records required a careful evaluation which we did not succeed in reducing to a concise, quantitative form. Because of this difficulty, the method did not yield as much information on bowel motility as we had anticipated that it would. The most successful application was found to be the 'all or none' type of experiment, such as the post-operational studies, where we were primarily concerned with showing only that pressure activity was present within a certain period of time and certain of the tests on patients with functional disorders where we were able to show that the affected parts of the bowel still had some muscular ability.The mobility of the capsule sometimes led to uncertainty about the exact site at which it was lying, which was particularly troublesome at times when unusual phenomena were recorded. This uncertainty, which made it virtually impossible to extract meaningful information from motility studies in the stomach could only be removed by tracking the capsule as it moved through the alimentary tract. The simple, qualitative method we adopted to study the short-term movements of the capsule suggested very strongly that a much more comprehensive study of motility could be made if we utilised the mobility of a small capsule with low-inertia to make quantitative recordings of transport along the bowel, as well as the complementary study of intra¬ luminal pressure. It does not seem practicable to reduce the present form of the capsule, but a different approach using an externally energised 'probe' may provide the solution. Also the problems of interpreting the data might be t simplified if a different type of measurement could be made which excludes variations from extra-luminal pressure fluctuations. A lighter capsule of about the same length as the present 'probe* with a differential pressure transducing system which transmitted a measure of relative changes between the ends of the capsule might prove to be a more potent instrument for examining motility, particularly in the small bowel. A differential measurement would also exclude the extra-luminal effects.A few difficulties, therefore, remain to be solved before telemetering from within the human body can become a routine clinical procedure, and in conclusion I would like to express the hope that these studies will form a useful basis for the practical advancement of these 'tubeless' techniques

Are All Static Black Hole Solutions Spherically Symmetric?

The static black hole solutions to the Einstein-Maxwell equations are all spherically symmetric, as are many of the recently discovered black hole solutions in theories of gravity coupled to other forms of matter. However, counterexamples demonstrating that static black holes need not be spherically symmetric exist in theories, such as the standard electroweak model, with electrically charged massive vector fields. In such theories, a magnetically charged Reissner-Nordstrom solution with sufficiently small horizon radius is unstable against the development of a nonzero vector field outside the horizon. General arguments show that, for generic values of the magnetic charge, this field cannot be spherically symmetric. Explicit construction of the solution shows that it in fact has no rotational symmetry at all.Comment: 6 pages, plain TeX. Submitted to GRF Essay Competitio

Structural and elastic characterization of Cu-implanted SiO₂ films on Si(100) substrates

Cu-implanted SiO₂ films on Si(100) have been studied and compared to unimplanted SiO₂ on Si(100) using x-ray methods, transmission electron microscopy, Rutherford backscattering, and Brillouin spectroscopy. The x-ray results indicate the preferred orientation of Cu {111} planes parallel to the Si substrate surface without any directional orientation for Cu-implanted SiO₂∕Si(100) and for Cu-implanted and annealedSiO₂∕Si(100). In the latter case, transmission electron microscopy reveals the presence of spherical nanocrystallites with an average size of ∼2.5 nm. Rutherford backscattering shows that these crystallites (and the Cu in the as-implanted film) are largely confined to depths of 0.4−1.2 μm below the film surface. Brillouin spectra contain peaks due to surface, film-guided and bulk acoustic modes. Surface (longitudinal) acoustic wave velocities for the implanted films were ∼7% lower (∼2% higher) than for unimplanted SiO₂∕Si(100). Elastic constants were estimated from the acoustic wave velocities and film densities. C₁₁ (C₄₄) for the implanted films was ∼10% higher (lower) than that for the unimplanted film. The differences in acoustic velocities and elastic moduli are ascribed to implantation-induced compaction and/or the presence of Cu in the SiO₂ film.B.J. and M.C.R. are grateful for financial support from the Australian Synchrotron Research Program, funded by the Commonwealth of Australia. M.C.R. would also like to thank the Australian Research Council for their financial support. The financial support of the Natural Sciences and Engineering Research Council of Canada NSERC is gratefully acknowledged by G.T.A. and J.S

Extended x-ray absorption fine structure study of porous GaSb formed by ion implantation

Porous GaSb has been formed by Ga ion implantation into crystalline GaSb substrates at either room temperature or −180 °C. The morphology has been characterized using scanning electron microscopy and the atomic structure was determined using extended x-ray absorption fine structure spectroscopy. Room-temperature implantation at low fluences leads to the formation of ∼20-nm voids though the material remains crystalline. Higher fluences cause the microstructure to evolve into a network of amorphous GaSb rods ∼15 nm in diameter. In contrast, implantation at −180 °C generates large, elongated voids but no rods. Upon exposure to air, the surface of the porous material is readily oxidized yielding Ga₂O₃ and metallic Sb precipitates, the latter resulting from the reduction of unstable Sb₂O₃. We consider and discuss the atomic-scale mechanisms potentially operative during the concurrent crystalline-to-amorphous and continuous-to-porous transformations

Resolving asymmetries along the pulsation cycle of the Mira star X Hya

The mass-loss process in Mira stars probably occurs in an asymmetric way where dust can form in inhomogeneous circumstellar molecular clumps. Following asymmetries along the pulsation cycle can give us clues about these mass-loss processes. We imaged the Mira star X Hya and its environnement at different epochs to follow the evolution of the morphology in the continuum and in the molecular bands. We observed X Hya with AMBER in J-H-K at low resolution at two epochs. We modelled squared visibilities with geometrical and physical models. We also present imaging reconstruction results obtained with MiRA and based on the physical a priori images. We report on the angular scale change of X Hya between the two epochs. 1D CODEX profiles allowed us to understand and model the spectral variation of squared visibilities and constrain the stellar parameters. Reconstructed model-dependent images enabled us to reproduce closure phase signals and the azimuthal dependence of squared visibilities. They show evidence for material inhomogeneities located in the immediate environment of the star.Comment: Accepted for publication in A&A, 17 pages, 16 figure