Electroproduction of single charged pions from deuterons at Q2 ∼0.5 (GeV/c)2

The ratio of π^? to π⁺ electroproduction cross sections from deuterons has been measured in the resonance region at an average four-momentum transfer squared of 0.5 (GeV/c)². Results are presented over a wide range of pion production angles and comparisons are made with theoretical predictions based on SU(6)_w symmetry and the Melosh transformation.     

Crack velocity dependence of electron emission during fracture of filled elastomers

In this article we examine the electron emission accompanying the fracture of filled elastomers, where in previous work we have shown the emission to be intense and due predominately to interfacial failure. In this study we show that there is a strong velocity dependence on the rate of electron emission during the propagation of a crack in filled silicone rubber and polybutadiene filled with glass beads. This dependence cannot be explained by a simple proportionality between emission rate and rate of surface area production. We propose that the concentration of free radicals produced by crack propagation increases rapidly with crack velocity which in turn produces more intense electron emission by a chemiemission mechanism.     

Quantitative use of the angular variation technique in studies of tin by X-ray photoelectron spectroscopy

The relative photoionisation cross-sections of the tin 3d and 4d electrons are determined and combined with angular variation studies to establ     

Uplift of microorganisms by electric fields above thunderstorms

Collections of microorganisms have been reported at altitudes above the tropopause where it is difficult to explain their presence. In fact, modern science can still not answer the question “How high can a microorganism be found?” This paper will describe our analysis of the ability of electric fields, related to the presence/formation of thunderstorms, to uplift either charged ice particles (which may contain microorganisms) or microorganisms, which inherently contain an electric charge, into the stratosphere. Here we show, via simulation, that strong electric fields found during thunderstorms could accelerate charged micron-scale particles rapidly up against the forces of drag and gravity. This uplift mechanism may therefore help explain the presence of microorganisms in the stratosphere at altitudes of 40 km and above.     

Scaling relationship between the copositive cone and Parrilo’s first level approximation

We investigate the relation between the cone ${\mathcal{C}^{n}}$ of n × n copositive matrices and the approximating cone ${\mathcal{K}_{n}^{1}}$ introduced by Parrilo. While these cones are known to be equal for n ≤ 4, we show that for n ≥ 5 they are not equal. This result is based on the fact that ${\mathcal{K}_{n}^{1}}$ is not invariant under diagonal scaling. We show that for any copositive matrix which is not the sum of a nonnegative and a positive semidefinite matrix we can find a scaling which is not in ${\mathcal{K}_{n}^{1}}$ . In fact, we show that if all scaled versions of a matrix are contained in ${\mathcal{K}_{n}^{r}}$ for some fixed r, then the matrix must be in ${\mathcal{K}_{n}^{0}}$ . For the 5 × 5 case, we show the more surprising result that we can scale any copositive matrix X into ${\mathcal{K}_{5}^{1}}$ and in fact that any scaling D such that ${(DXD)_{ii} \in \{0,1\}}$ for all i yields ${DXD \in \mathcal{K}_{5}^{1}}$ . From this we are able to use the cone ${\mathcal{K}_{5}^{1}}$ to check if any order 5 matrix is copositive. Another consequence of this is a complete characterisation of ${\mathcal{C}^{5}}$ in terms of ${\mathcal{K}_{5}^{1}}$ . We end the paper by formulating several conjectures.     

Scattering by small defects in the neighbourhood of a fluid-solid interface

The scattering of incident plane elastic waves by a varietyof different defects that lie upon a fluid-solid interface isconsidered here using matched asymptotic expansions. The expansionscheme is developed in terms of a parameter , the ratio of typicaldefect length scale to a typical wavelength of the incidentfield, taken to be small. Three different canonical situations occur and these are illustratedvia three specific examples treated here: a rigid strut, anedge crack, and a rigid strip. In each case the leading-ordermatching is performed to identify the leading-order contributionof the defect to the acoustic field in the far field. In particular,each defect is identified with a source of dipole response ininterfacial stress of displacement. It is shown in the limit as s<<s1 that in the inner problemsthe fluid and solid pieces uncouple in a particularly convenientmanner allowing analytical solutions to be deduced. These arethen matched with appropriate outer solutions.