Production of unusual mesons in photon-photon collisions

The cross-section for the production of unusual mesons, such as (bc?) or (b?c), in photon-photon collisions is obtained in a high energy approximation. For a 100 + 100 GeV e⁺e^? collider, the cross section is estimated to be about one unit of R for (bc?) and (b?c).     

Defence response of Sitka spruce before and after inoculation with Heterobasidion annosum: 1H NMR fingerprinting of bark and sapwood metabolites

Metabolite fingerprinting of Sitka spruce (Picea sitchensis) bark and sapwood was carried out by ¹H nuclear magnetic resonance after wounding and artificial inoculation with the white rot fungus Heterobasidion annosum sensu stricto. The aim was to determine whether metabolites would differ in clones showing differing levels of susceptibility to H. annosum, in the fungal as compared with the control treatment (wounding, no fungus) and the reference (healthy sample collected at 0 days), at two different locations on the host, and at different sampling times (3 and 43 days after treatment). The results suggested that different metabolic processes occur in bark and sapwood after wounding and fungal inoculation, compared with healthy samples collected before treatment: In bark, greater peaks were elicited in the aromatic region whereas, in sapwood, lower amounts of all metabolites were observed in inoculated samples, compared with healthy samples. Multivariate statistical analysis carried out with analysis of variance–principal component analysis showed highly significant effects of reference, location, and time (PC1), and significant effects of clone and fungus. Differences between clones were apparent in sapwood but not in bark and were due to peaks in the aliphatic and carbohydrate regions. Over time, in bark, there was a decrease in carbohydrate peaks, followed by an increase in aliphatic and aromatic peaks. Sapwood, by contrast, showed a decrease in all peaks, followed by an increase in carbohydrate and aliphatic peaks. Changes in carbohydrate levels were observed within the lesion compared with the more distal location in both bark and sapwood.     

Epistemological Skepticism, Semantic Blindness, and Competence-Based Performance Errors

The semantic blindness objection to contextualism challenges the view that there is no incompatibility between (i) denials of external-world knowledge in contexts where radical-deception scenarios are salient, and (ii) affirmations of external-world knowledge in contexts where such scenarios are not salient. Contextualism allegedly attributes a gross and implausible form of semantic incompetence in the use of the concept of knowledge to people who are otherwise quite competent in its use; this blindness supposedly consists in wrongly judging that there is genuine conflict between claims of type (i) and type (ii). We distinguish two broad versions of contextualism: relativistic-content contextualism and categorical-content contextualism. We argue that although the semantic blindness objection evidently is applicable to the former, it does not apply to the latter. We describe a subtle form of conflict between claims of types (i) and (ii), which we call différance-based affirmatory conflict. We argue that people confronted with radical-deception scenarios are prone to experience a form of semantic myopia (as we call it): a failure to distinguish between différance-based affirmatory conflict and outright inconsistency. Attributing such semantic myopia to people who are otherwise competent with the concept of knowledge explains the bafflement about knowledge-claims that so often arises when radical-deception scenarios are made salient. Such myopia is not some crude form of semantic blindness at all; rather, it is an understandable mistake grounded in semantic competence itself: what we call a competence-based performance error.     

Exclusive production of heavy mesons in photon-photon collisions: The double scattering mechanism

We present two mechanisms which can compete with constituent interchange in the exclusive production at wide angle of heavy mesons in photon-photon collisions. We show that they have the same energy behaviour as constituent interchange, and that their amplitudes are free from large logarithms. We exploit this to calculate the double-scattering diagrams numerically. We find that while constituent interchange dominates at 90°, double scattering becomes dominant for angles less than about 45°.     

Spatial decay estimates for the heat equation via the maximum principle

Spatial decay estimates for the solution of the heat equation, similar to those obtained by other authors using energy inequalities, are established through use of the maximum principle.

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Résumé A l'aide du principe du maximum, on obtient des évaluations pour la décroissance spatiale des solutions de l'équation de la chaleur. Ces résultats ressemblent à ceux d'autres auteurs, qui utilisaient des inégalités pour l'énergie.

     

Automatic recognition of maize cell types using context information

When classifying objects in images of biological specimens, it is usual for there to be some dependence among neighbouring objects. This can in theory be used to augment the information available for classifying each object. However, much of the methodology developed for this type of contextual classification assumes a fixed number of neighbours, such as is found on a regular grid. In this paper, we show how Markov random fields can be used in the case where the number of neighbours varies, and we illustrate this with an application in the classification of cells types in microscope images of plant stems.     

On the Fiber Stretch in Shearing Deformations of Fibrous Soft Materials

The behavior of the fiber stretch in simple shear of soft materials fiber-reinforced with a single family of oriented parallel fibers is examined. The analysis is purely kinematical and the results are valid for both compressible and incompressible materials. It is shown that for a given amount of shear, for all fiber orientation angles in the range \(0 < \theta < \pi /4\), the fiber stretch increases with increasing \(\theta\) whereas in the range \(\pi /4 < \theta < \pi /2\), this is no longer the case and there is a particular fiber orientation for which the fiber stretch is a maximum. For a particular amount of shear corresponding to a special angle of shear (a “magic” angle of \(35.26^{\circ}\)), the fiber-orientation angle at which the fiber stretch is a maximum is its geometric complement namely a magic angle of \(54.74^{\circ}\). The results are also valid for torsion of a circular cylinder reinforced with a single family of helically wound fibers.     

Simple Shearing of Incompressible and Slightly Compressible Isotropic Nonlinearly Elastic Materials

The classical problem of simple shear in nonlinear elasticity has played an important role as a basic pilot problem involving a homogeneous deformation that is rich enough to illustrate several key features of the nonlinear theory, most notably the presence of normal stress effects. Here our focus is on certain ambiguities in the formulation of simple shear arising from the determination of the arbitrary hydrostatic pressure term in the normal stresses for the case of an incompressible isotropic hyperelastic material. A new formulation in terms of the principal stretches is given. An alternative approach to the determination of the hydrostatic pressure is proposed here: it will be required that the stress distribution for a perfectly incompressible material be the same as that for a slightly compressible counterpart. The form of slight compressibility adopted here is that usually assumed in the finite element simulation of rubbers. For the particular case of a neo-Hookean material, the different stress distributions are compared and contrasted.     

Inhomogeneous shearing of strain-stiffening rubber-like hollow circular cylinders

The purpose of this paper is to investigate the effects of strain-stiffening for the classical problems of axial and azimuthal shearing of a hollow circular cylinder composed of an incompressible isotropic non-linearly elastic material. For some specific strain-energy densities that give rise to strain-stiffening in the stress–stretch response, the stresses and resultant axial forces are obtained in explicit closed form. While such results are well known for classical constitutive models such as the Mooney–Rivlin and neo-Hookean models, our main focus is on materials that undergo severe strain-stiffening in the stress–stretch response. In particular, we consider in detail two phenomenological constitutive models that reflect limiting chain extensibility at the molecular level and involve constraints on the deformation. The amount of shearing that tubes composed of such materials can sustain is limited by the constraint. Numerical results are also obtained for an exponential strain-energy that exhibits a less abrupt strain-stiffening effect. Potential applications of the results to the biomechanics of soft tissues are indicated.