Complexity of the XY antiferromagnet at fixed magnetization

We prove that approximating the ground energy of the antiferromagnetic XY model on a simple graph at fixed magnetization (given as part of the instance specification) is QMA-complete. To show this, we strengthen a previous result by establishing QMA-completeness for approximating the ground energy of the Bose-Hubbard model on simple graphs. Using a connection between the XY and Bose-Hubbard models that we exploited in previous work, this establishes QMA-completeness of the XY model

Internet Directory… 2002: International Year of ECOTOURISM

The following outlines internet resources useful to the practicing surveyor. It includes overview and internet linkages to International Year of Ecotourism (IYE); Eco-tourism in Australia and furthers the discussion with a brief overview of the Australian Year of the Outback

Mass-loading and parallel magnetized shocks

Recent observations at comets Giacobini-Zinner and Halley suggest that simple non-reacting gas dynamics or MHD is an inappropriate description for the bow shock. The thickness of the observed (sub)shock implies that mass-loading is an important dynamical process within the shock itself, thereby requiring that the Rankine-Hugoniot conditions possess source terms. This leads to shocks with properties similar to those of combustion shocks. We consider parallel magnetized shocks subjected to mass-loading, describe some properties which distinguish them from classical MHD parallel shocks, and establish the existence of a new kind of MHD compound shock. These results will be of importance both to observations and numerical simulations of the comet-solar wind interaction

Dopant site selectivity in BaCe0.85M0.15O3-δ by extended x-ray absorption fine structure

Rare earth doped BaCeO3 has been widely investigated as a proton conducting material. Trivalent dopants are generally assumed to fully occupy the Ce4+-site, and thereby introduce oxygen vacancies into the perovskite structure. Recent studies indicate the possibility of partial dopant incorporation onto the Ba2+-site concomitant with BaO evaporation, reducing the oxygen vacancy content. Because proton incorporation requires, as a first step, the generation of oxygen vacancies such dopant partitioning is detrimental to protonic conductivity. A quantitative Extended X-ray Absorption Fine Structure (EXAFS) study of BaCe0.85M0.15O3-δ (M=Yb,Gd) is presented here along with complementary x-ray powder diffraction and electron probe chemical analyses. The EXAFS results demonstrate that as much as 4.6% of the ytterbium and 7.2% of the gadolinium intended for incorporation onto the Ce site, in fact, resides on the Ba site. The results are in qualitative agreement with the diffraction and chemical analyses, which additionally show an even greater extent of Nd incorporation on the Ba site

Political participation: the vocational motivations of Labour party employees

Party employees are an under-researched group in political science. This article begins to address this oversight by examining Labour Party employees using new quantitative and qualitative data. It argues that party employment should be regarded as a form of political participation and as a consequence, existing models of political participation can be utilised to help explain why people work for political parties. After testing these propositions, the article concludes that existing models are indeed helpful in explaining the motivations for party employment