Charge Stripe in an Antiferromagnet: 1d Band of Composite Excitations

With the help of analytical and numerical studies of the $t$-$J_z$ model we argue that the charge stripe in an antiferromagnetic insulator should be understood as a system of holon-spin-polaron excitations condensed at the self-induced antiphase domain wall. The structure of such a charge excitation is studied in detail with numerical and analytical results for various quantities being in a very close agreement. An analytical picture of these excitations occupying an effective 1D stripe band is also in a very good accord with numerical data. The emerging concept advocates the primary role of the kinetic energy in favoring the stripe as a ground state. A comparative analysis suggests the effect of pairing and collective meandering on the energetics of the stripe formation to be secondary.Comment: 5 pages, 3 figures, proceedings of SCES'01 conference, Ann Arbor, 2001, to be published in Physica

Embedding realistic surveys in simulations through volume remapping

Connecting cosmological simulations to real-world observational programs is often complicated by a mismatch in geometry: while surveys often cover highly irregular cosmological volumes, simulations are customarily performed in a periodic cube. We describe a technique to remap this cube into elongated box-like shapes that are more useful for many applications. The remappings are one-to-one, volume-preserving, keep local structures intact, and involve minimal computational overhead.Comment: 4 pages, 4 figures. Companion material at http://mwhite.berkeley.edu/BoxRemap

Minding our ps and qs: Issues of property, provenance, quantity and quality in institutional repositories

The development of institutional repositories has opened the path to the mass availability of peer-reviewed scholarly information and the extension of information democracy to the academic domain. A secondary space of free-to-all documents has begun to parallel the hitherto-closed world of journal publishing and many publishers have consented to the inclusion of copyrighted documents in digital repositories, although frequently specifying that a version other than the formally-published one be used. This paper will conceptually examine the complex interplay of rights, permissions and versions between publishers and repositories, focussing on the New Zealand situation and the challenges faced by university repositories in recruiting high-quality peer-reviewed documents for the open access domain. A brief statistical snapshot of the appearance of material from significant publishers in repositories will be used to gauge the progress that has been made towards broadening information availability. The paper will also look at the importance of harvesting and dissemination, in particular the role of Google Scholar in bringing research information within reach of ordinary internet users. The importance of accuracy, authority, provenance and transparency in the presentation of research-based information and the important role that librarians can and should play in optimising the open research discovery experience will be emphasised

The parliamentary election and referendum in Belarus, October 2004

Belarus became an independent state in December 1991 on the dissolution of the USSR; and it became a presidential state under its constitution of March 1994. At the first election under that constitution, in July 1994, Alexander Lukashenko won a convincing mandate with 80% of the vote in a second-round runoff against the then prime minister, Vyacheslav Kebich. Once elected, Lukashenko moved quickly to extend the powers of his office, which soon brought him into conflict with the Belarusian parliament (then known as the Supreme Soviet) and the Constitutional Court. He sought to resolve this by calling a referendum, in May 1995, when a positive vote allowed him to expand his presidential powers. In November 1996, a further and more controversial referendum approved an extension of the presidential term and replaced the parliament with a smaller and wholly subordinate National Assembly (Natsional'noe Sobranie). This was effectively a constitutional coup, which paved the way for the establishment of an increasingly authoritarian regime

Comment on ``Stripes and the t-J Model''

This is a comment being submitted to Physical Review Letters on a recent letter by Hellberg and Manousakis on stripes in the t-J model.Comment: One reference correcte

Topological Change in Mean Convex Mean Curvature Flow

Consider the mean curvature flow of an (n+1)-dimensional, compact, mean convex region in Euclidean space (or, if n<7, in a Riemannian manifold). We prove that elements of the m-th homotopy group of the complementary region can die only if there is a shrinking S^k x R^(n-k) singularity for some k less than or equal to m. We also prove that for each m from 1 to n, there is a nonempty open set of compact, mean convex regions K in R^(n+1) with smooth boundary for which the resulting mean curvature flow has a shrinking S^m x R^(n-m) singularity.Comment: 19 pages. This version includes a new section proving that certain kinds of mean curvature flow singularities persist under arbitrary small perturbations of the initial surface. Newest update (Oct 2013) fixes some bibliographic reference