New skyrmions in the attractive Hubbard model with broken SO(4) symmetry

The coexistence of superconducting and charge-density-wave order in the half-filled attractive Hubbard model is interpreted as a consequence of the pseudospin SU(2) symmetry spontaneously broken to a `hidden' subgroup U(1). By topological arguments we show that there must exist new skyrmion textures associated with this symmetry breakdown. This fact is illustrated via a non-linear $\sigma$-model. Unlike the spin textures previously known in an antiferromagnetic background, doping the model away from half-filling leads the new skyrmions to unwrap.Comment: 10 pages, 1 table, final version to be published in Phys. Lett.

LensMEM: A Gravitational Lens Inversion Algorithm Using the Maximum Entropy Method

We present a new algorithm for inverting poorly resolved gravitational lens systems using the maximum entropy method (MEM). We test the method with simulations and then apply it to an 8 GHz VLA map of the radio ring lens MG1654+134. We model the lens as a singular isothermal sphere embedded in an external shear field and find the critical radius of the lens is b=0\parcs9820, the dimensionless shear is $\gamma=0.0771$, and the position angle of the shear is \theta=100\pdeg8. These results are consistent with the results obtained by Kochanek (1995) using a complementary inversion algorithm based on Clean.Comment: 27 pages, uuencoded, gzip compressed postscrip

Employee share options and the equity-liability distinction: a way forward?

This paper explores the distinction between ‘equity’ and ‘liabilities’ in financial reporting in order to assess the merits of the current system of accounting for share-based payment transactions. It applies an interpretive methodology. Data were collected from a series of interviews with purposefully selected experts. Criticisms of and support for the current accounting regime are interpretively analysed and used to identify key themes or principles for evaluating the merits of three models proposed in the academic literature: the strict liability, narrow equity and ownership-settlement models. The study finds that the strict liability approach remains supported on the grounds that it provides decisionuseful information with which users are familiar. The other models are rejected as they are perceived as diminishing the usefulness of financial reporting. The study also identifies support for an obligation-centric approach, not fully developed in the literature, which may require detailed consideration by standard-setters. Overall, these findings will be useful for both practitioners and academics grappling with the difficulty of defining ‘equity’ and ‘liabilities’. In addition, the research makes a valuable contribution by addressing the need for interpretive-inspired financial reporting research. To the best of the author’s knowledge, this thesis is also the first South African study to investigate the appropriate classification criteria for instruments such as share-based payments and provide normative recommendations for the International Accounting Standards Board

Spin-orbit transitions in α\alpha and γ\gamma-CoV2_{2}O6_{6}

$\gamma$-triclinic and $\alpha$-monoclinic polymorphs of CoV$_{2}$O$_{6}$ are two of the few known transition metal ion based materials that display stepped $1/3$ magnetization plateaus at low temperatures. Neutron diffraction [M. Markkula et al. Phys. Rev. B 86, 134401 (2012)], x-ray dichroism [N. Hollmann et al. Phys. Rev. B 89, 201101(R) (2014)], and dielectric measurements [K. Singh et al. J. Mater. Chem. 22, 6436 (2012)] have shown a coupling between orbital, magnetic and structural orders in CoV$_{2}$O$_{6}$. We apply neutron inelastic scattering to investigate this coupling by measuring the spin-orbit transitions in both $\alpha$ and $\gamma$ polymorphs. We find the spin-exchange and anisotropy in monoclinic $\alpha$-CoV$_{2}$O$_{6}$ to be weak in comparison with the spin-orbit coupling $\lambda$ and estimate an upper limit of $|J/\lambda| \sim$ 0.05. However, the spin exchange is larger in the triclinic polymorph and we suggest the excitations are predominately two dimensional. The local compression of the octahedra surrounding the Co$^{2+}$ ion results in a direct coupling between higher energy orbital levels, the magnetic ground state, and elastic strain. CoV$_{2}$O$_{6}$ is therefore an example where the local distortion along with the spin-orbit coupling provides a means of intertwining structural and magnetic properties. We finish the paper by investigating the low-energy magnetic fluctuations within the ground state doublet and report a magnetic excitation that is independent of the local crystalline electric field. We characterize the temperature and momentum dependence of these excitations and discuss possible connections to the magnetization plateaus.Comment: (15 pages, 10 figures

Perturbative reconstruction of a gravitational lens: when mass does not follow light

The structure and potential of a complex gravitational lens is reconstructed using the perturbative method presented in Alard 2007, MNRAS, 382L, 58; Alard 2008, MNRAS, 388, 375. This lens is composed of 6 galaxies belonging to a small group. The lens inversion is reduced to the problem of reconstructing non-degenerate quantities: the 2 fields of the perturbative theory of strong gravitational lenses. Since in the perturbative theory the circular source solution is analytical, the general properties of the perturbative solution can be inferred directly from the data. As a consequence, the reconstruction of the perturbative fields is not affected by degeneracy, and finding the best solution is only a matter of numerical refinement. The local shape of the potential and density of the lens are inferred from the perturbative solution, revealing the existence of an independent dark component that does not follow light. The most likely explanation is that the particular shape of the dark halo is due to the merging of cold dark matter halos. This is a new result illustrating the structure of dark halos at the scale of galaxies.Comment: Final version (Astronomy and Astrophysics in press

Corpus-Based Approaches to Figurative Language: Metaphor and Austerity

Austerity is a by-product of the ongoing financial crisis. As Kitson et al (2001) explain, what was a \u201cNICE\u201d (\u2018non-inflationary consistent expansion\u2019) economy has turned \u201cVILE\u201d (\u2018volatile inflation, little expansion\u2019), and the economic and social fall-out is now becoming visible. Unemployment, redundancy, inflation, recession, insecurity, and poverty all loom, causing governments, businesses and individuals to reevaluate their priorities. A changing world changes attitudes, and the earliest manifestations of such change can often be found in figurative language. Political rhetoric attempts to sweeten the bitter pill that nations have no choice but to swallow; all are invited to share the pain, make sacrifices for the common good, and weather the storm. But more sinister undertones can also be perceived. In times of social and financial dire straits, scapegoats are sought and mercilessly pursued in the press. The elderly, unemployed, and disabled are under fire for \u201csponging off the state\u201d; and as jobs become scarcer and the tax bill rises, migrant populations and asylum seekers are viewed with increasing suspicion and resentment. Calls for a \u201cbig society\u201d fall on deaf ears. Society, it seems, is shrinking as self-preservation takes hold. Austerity is a timely area of study: although austerity measures have been implemented in the past, most of the contributions here address the current political and economic situation, which means that some of the studies reported are work in progress while others look at particular \u201cwindows\u201d of language output from the recent past. Whichever their focus, the papers presented here feature up-to-the-minute research into the metaphors being used to comment upon our current socioeconomic situation. The picture of austerity that emerges from these snapshots is a complex one, and one which is likely to be developed further and more widely in the coming future

Evidence for substructure in lens galaxies?

We discuss whether one should expect that multiply imaged QSOs can be understood with `simple' lens models which contain a handful of parameters. Whereas for many lens systems such simple mass models yield a remarkably good description of the observed properties, there are some systems which are notoriously difficult to understand quantitatively. We argue that at least in one case (B 1422+231) these difficulties are not due to a `wrong' parametrization of the lens model, but that the discrepancy between observed and model-predicted flux ratios are due to substructure in the lens. Similar to microlensing for optical fluxes, such substructure can distort also the radio flux ratios predicted by `simple' mass models, in particular for highly magnified images, without appreciably changing image positions. Substructure also does not change the time delay significantly and therefore has little effect on the determination of the Hubble constant using time delays. We quantify these statements with several simple scenarios for substructure, and propose a strategy to model lens systems in which substructure is suspected.Comment: plain tex, 13 pages with four figure