Correction approach of detector backlighting in radiography.

In various kinds of radiography, deficient transmission imaging may occur due to backlighting inside the detector itself arising from light or radiation scattering. The related intensity mismatches barely disturb the high resolution contrast, but its long range nature results in reduced attenuation levels which are often disregarded. Based on X-ray observations and an empirical formalism, a procedure is developed for a first order correction of detector backlighting. A backlighting factor is modeled as a function of the relative detector coverage by the sample projection. Different cases of sample transmission are regarded at different backlight factors and detector coverage. The additional intensity of backlighting may strongly affect the values of materials' attenuation up to a few 10%. The presented scenario provides a comfortable procedure for corrections of X-ray or neutron transmission imaging data.

A threshold model for polydactyly.

We present a cellular automaton-based model for threshold behaviors in vertebrate digit patterning and polydactyly formation. The rules of the model follow classical reactor-diffusion algorithms. Yet it is not physical diffusion that is taken as the required natural agent but the propagation of cellular states, which can be represented by the same differential equations. The bistable cellular states in the model correspond to mesenchymal limb bud cells that can be either "on" or "off" for the cartilage differentiation pathway. Simulation runs demonstrate that reaction rate and cell number have the most decisive influence on the number of digit-like cell activation patterns. Threshold-based effects can generate supernumerary activation stripes via de novo condensation, stabilized bifurcation, and free floaters. All three behaviors are consistent with processes in natural polydactyly formation. It is argued that these effects are rooted in cell-based behaviors, not in gene regulation or globally diffusing morphogens. Our model suggests that the origin of discrete character states, such as individual digits, is a consequence of an additive cell state variable with a normal distribution that is transformed by a growth function with Turing behaviors into discontinuous phenotypic units. We discuss the application of this type of autopod patterning to the mutational, developmental, experimental, and evolutionary occurrences of polydactyly. The model provides a refinement of the previous Hemingway model for digit novelty and supports Turing type pattern formation in the vertebrate limb.

Polydactyly in Development, Inheritance, and Evolution.

The occurrence of supernumerary digits or toes in humans and other tetrapods has attracted general interest since antiquity and later influenced scientific theories of development, inheritance, and evolution. Seventeenth-century genealogical studies of polydactyly were at the beginning of an understanding of the rules of inheritance. Features of polydactyly were also part of the classical disputes on the nature of development, including the preformation-versus-epigenesis and the atavism-versus-malformation debates. In the evolutionary domain, polydactyly was used in the criticism of the gradualist account of variation underlying Darwin's theory. Today, extra digit formation plays a role in the conceptualization of gene regulation and pattern formation in vertebrate limb evolution. Recent genetic, experimental, and modeling accounts of extra digit formation highlight the existence of nongradual transitions in phenotypic states, suggesting a distinction between continuous and discontinuous variation in evolution. Unless otherwise noted, all translations are our own.

Missing wedge computed tomography by iterative algorithm DIRECTT.

A strategy to mitigate typical reconstruction artefacts in missing wedge computed tomography is presented. These artefacts appear as elongations of reconstructed details along the mean direction (i.e. the symmetry centre of the projections). Although absent in standard computed tomography applications, they are most prominent in advanced electron tomography and also in special topics of X-ray and neutron tomography under restricted geometric boundary conditions. We investigate the performance of the DIRECTT (Direct Iterative Reconstruction of Computed Tomography Trajectories) algorithm to reduce the directional artefacts in standard procedures. In order to be sensitive to the anisotropic nature of missing wedge artefacts, we investigate isotropic substructures of metal foam as well as circular disc models. Comparison is drawn to filtered backprojection and algebraic techniques. Reference is made to reconstructions of complete data sets. For the purpose of assessing the reconstruction quality, Fourier transforms are employed to visualize the missing wedge directly. Deficient reconstructions of disc models are evaluated by a length-weighted kernel density estimation, which yields the probabilities of boundary orientations. The DIRECTT results are assessed at different signal-to-noise ratios by means of local and integral evaluation parameters.

Quantitative structural assessment of heterogeneous catalysts by electron tomography.

We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells.

A horizontal V-Y advancement lower eyelid flap.

BACKGROUND: The authors were surprised to realize that the horizontal V-Y advancement flap of the lower eyelid is not even mentioned in the textbooks about eyelid repair, and they wanted to report their very positive experience with this subcutaneous pedicled flap. METHODS: Between 2000 and 2006, 21 patients were operated on, 13 women and eight men, aged 37 to 98 years, with a mean age of 67.5 years. The diagnosis was basal cell carcinoma in 20 cases and melanoma in one case. The size of the defect ranged from 10 to 30 mm, with a mean of 20 mm. RESULTS: All flaps survived and the aesthetic quality of the repair was excellent in 17 of 21 cases. Postoperative recovery was usually very fast. CONCLUSIONS: The lower eyelid is covered with remarkably thin skin, and for the repair of defects, especially after removal of basal cell carcinomas, it is preferable to avoid using tissues coming from another facial area (e.g., forehead, nose, or cheek), which has a different thickness and texture, or a full-thickness skin graft, which can leave a patch-like appearance. The ideal is to use the adjacent eyelid skin. For many years, the authors have used a horizontal large V-Y advancement flap on a muscular pedicle for the repair of lower eyelid defects, mostly after basocellular carcinoma excision, with very satisfactory results and often nearly invisible repairs.

Congenital erosive and vesicular dermatosis with reticulated scarring in a newborn: an innovative treatment using a silicone dressing.

Congenital erosive and vesicular dermatosis healing with reticulated supple scarring is a rare entity presenting in the newborn with crusted erosions and vesicles that heal relatively rapidly, forming unique reticulated scars. We report the case of a premature baby 31 weeks old. Diagnosis was confirmed by skin biopsies, and the clinical improvement was excellent, with complete healing observed within 7 weeks. This report highlights clinical and histopathologic features, and a new successful treatment approach using a silicone dressing.

Analyser-based tomography images of cartilage.

Analyser-based imaging expands the performance of X-ray imaging by utilizing not only the absorption properties of X-rays but also the refraction and scatter rejection (extinction) properties. In this study, analyser-based computed tomography has been implemented on imaging an articular cartilage sample, depicting substructural variations, without overlay, at a pixel resolution of 3.6 microm.