The use of geomagnetic field models in magnetic surveys

The importance of global geomagnetic field models for the reduction of magnetic surveys is discussed. It is demonstrated that a numerical model with adequate secular variation correction, provides a suitable representation of the regional field. The limitations of the presently available models are reported, with emphasis on the International Geomagnetic Reference Field

Tree-level electron-photon interactions in graphene

Graphene's low-energy electronic excitations obey a 2+1 dimensional Dirac Hamiltonian. After extending this Hamiltonian to include interactions with a quantized electromagnetic field, we calculate the amplitude associated with the simplest, tree-level Feynman diagram: the vertex connecting a photon with two electrons. This amplitude leads to analytic expressions for the 3D angular dependence of photon emission, the photon-mediated electron-hole recombination rate, and corrections to graphene's opacity $\pi \alpha$ and dynamic conductivity $\pi e^2/2 h$ for situations away from thermal equilibrium, as would occur in a graphene laser. We find that Ohmic dissipation in perfect graphene can be attributed to spontaneous emission.Comment: 5 pages, 3 figure

The determination of the direction of the optic axis of uniaxial crystalline materials

The birefringence of crystalline substances in general, and of sapphire in particular, is described. A test is described whose purpose is to determine the direction of the optic axis of a cylindrically machined single crystal of sapphire. This test was performed on the NASA Lewis sapphire cylinder and it was found that the optic axis made an angle of 18 deg with the axis of symmetry of the cylinder

A global magnetic anomaly map

A subset of POGO satellite magnetometer data has been formed that is suitable for analysis of crustal magnetic anomalies. Using a thirteenth order field model, fit to these data, magnetic residuals have been calculated over the world to latitude limits of plus 50 deg. These residuals averaged over one degree latitude-longitude blocks represent a detailed global magnetic anomaly map derived solely from satellite data. Preliminary analysis of the map indicates that the anomalies are real and of geological origin

The Vortex Phase Diagram of Rotating Superfluid 3^3He-B

We present the first theoretical calculation of the pressure-temperature-field phase diagram for the vortex phases of rotating superfluid $^3$He-B. Based on a strong-coupling extension of the Ginzburg-Landau theory that accounts for the relative stability of the bulk A and B phases of $^3$He at all pressures, we report calculations for the internal structure and free energies of distinct broken-symmetry vortices in rotating superfluid $^3$He-B. Theoretical results for the equilibrium vortex phase diagram in zero field and an external field of H=284\,\mbox{G} parallel to the rotation axis, $\vec{H}\parallel\vec{\Omega}$, are reported, as well as the supercooling transition line, $T^{*}_ {v} (p,H)$. In zero field the vortex phases of $^3$He-B are separated by a first-order phase transition line $T_ {v} (p)$ that terminates on the bulk critical line $T_{c}(p)$ at a triple point. The low-pressure, low-temperature phase is characterized by an array of singly-quantized vortices that spontaneously breaks axial rotation symmetry, exhibits anisotropic vortex currents and an axial current anomaly (D-core phase). The high-pressure, high-temperature phase is characterized by vortices with both bulk A phase and $\beta$ phase in their cores (A-core phase). We show that this phase is metastable and supercools down to a minimum temperature, $T^{*}_ {v} (p,H)$, below which it is globally unstable to an array of D-core vortices. For H\gtrsim 60\,\mbox{G} external magnetic fields aligned along the axis of rotation increase the region of stability of the A-core phase of rotating $^3$He-B, opening a window of stability down to low pressures. These results are compared with the experimentally reported phase transitions in rotating $^3$He-B.Comment: 14 pages, 11 figure

Rapid and efficient stable gene transfer to mesenchymal stromal cells using a modified foamy virus vector

Mesenchymal stromal cells (MSCs) hold great promise for regenerative medicine. Stable ex vivo gene transfer to MSCs could improve the outcome and scope of MSC therapy, but current vectors require multiple rounds of transduction, involve genotoxic viral promoters and/or the addition of cytotoxic cationic polymers in order to achieve efficient transduction. We describe a self-inactivating foamy virus vector (FVV), incorporating the simian macaque foamy virus envelope and using physiological promoters, which efficiently transduces murine MSCs (mMSCs) in a single-round. High and sustained expression of the transgene, whether GFP or the lysosomal enzyme, arylsulphatase A (ARSA), was achieved. Defining MSC characteristics (surface marker expression and differentiation potential), as well as long-term engraftment and distribution in the murine brain following intracerebroventricular delivery, are unaffected by FVV transduction. Similarly, greater than 95% of human MSCs (hMSCs) were stably transduced using the same vector, facilitating human application. This work describes the best stable gene transfer vector available for mMSCs and hMSCs

Microscopic Surface Structure of Liquid Alkali Metals

We report an x-ray scattering study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure factor of the eutectic K67Na33 alloy is characteristic of an ideal mixture, and so shares the properties of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity shows that the surface roughness of the K-Na alloy follows simple capillary wave behavior with a surface structure factor indicative of surface induced layering. Comparison of thelow-angle tail of the K67Na33 surface structure factor with the one measured for liquid Ga and In previously suggests that layering is less pronounced in alkali metals. Controlled exposure of the liquid to H2 and O2 gas does not affect the surface structure, indicating that oxide and hydride are not stable at the liquid surface under these experimental conditions.Comment: 12 pages, 3 figures, published in Phys. Rev.

Evolutionary quantitative genetics of juvenile body size in a population of feral horses reveals sexually antagonistic selection

This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.Inter-individual variation in juvenile body size can have important consequences for individual fitness, population dynamics, and adaptive evolution. In wild vertebrate populations, larger juvenile size is usually expected to be selected for. However, understanding how such selection may translate into adaptive evolution requires an understanding of the genetic underpinnings of early development and the factors modulating selection. In this study, we characterised the genetic basis of and selection pressures acting upon juvenile body size in a large insular population of feral horses on Sable Island, Canada, to gain insights into the evolution of juvenile body size in wild vertebrate populations. We used pedigree-based quantitative genetic ‘animal models’ to quantify the sources of phenotypic variation in withers-knee length, and assessed the influence of maternal age, sex, and temporal (birth year) and spatial environmental heterogeneity in modulating overwinter survival selection. We found that withers-knee length is moderately heritable and that there was a significant positive genetic correlation between males and females. There was no indication of directional selection in a pooled-sex analysis, but we did find evidence for significant sexually antagonistic selection, with a tendency for smaller body size to be favoured in males and larger body size to be favoured in females. These results suggest that juvenile body size has the potential to evolve in this population, and that selection on juvenile size may play an important role in modulating sex-specific contributions to population dynamics. However, our results also suggest that there is unlikely to be evolutionary change in the mean body size of Sable Island foals.Natural Sciences and Engineering Research Council of CanadaCanada Foundation for InnovationRoyal SocietyUniversity of Exete