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

Political communications in the USSR: letters to party, state and press

The letters sent by Soviet citizens to party and state bodies and to the press have been relatively little studied in the West, although the Soviet authorities themselves have been devoting increasing attention to this ‘link with the masses’ since at least the late 1960s. An examination of the extent and nature of such communications shows that their total number has increased significantly since the 1950s, and that more constructive and general proposals have been increasing at the expense of particular individual grievances, although this change is less apparent at the local level. Critics are sometimes victimized and frequently ignored, but the evidence suggests that a considerable groundswell of opinion as reflected in letters can have some influence upon public policy and that particular cases of maladministration or abuse of position can be relatively readily corrected in this way

A Two-dimensional Infinte System Density Matrix Renormalization Group Algorithm

It has proved difficult to extend the density matrix renormalization group technique to large two-dimensional systems. In this Communication I present a novel approach where the calculation is done directly in two dimensions. This makes it possible to use an infinite system method, and for the first time the fixed point in two dimensions is studied. By analyzing several related blocking schemes I find that there exists an algorithm for which the local energy decreases monotonically as the system size increases, thereby showing the potential feasibility of this method.Comment: 5 pages, 6 figure

The Effects of a Rapidly-Fluctuating Random Environment on Systems of Interacting Species

Some models of interacting species in a random environment are analyzed. Approximate solutions of the stochastic differential or delay-differential equations describing the systems are obtained, on the assumption that the random environment is fluctuating rapidly

Looking Back at Five Eras: The Mott Foundation's First 75 Years

Summarizes five distinct eras in the foundation's first 75 years, and takes a look forward to continuing the practice of building long-term relationships and partnering with community groups in order to enable philanthropy at the local level

Spin Gaps in a Frustrated Heisenberg model for CaV4_4O9_9

I report results of a density matrix renormalization group (DMRG) study of a model for the two dimensional spin-gapped system CaV$_4$O$_9$. This study represents the first time that DMRG has been used to study a two dimensional system on large lattices, in this case as large as $24\times 11$, allowing extrapolation to the thermodynamic limit. I present a substantial improvement to the DMRG algorithms which makes these calculations feasible.Comment: 10 pages, with 4 Postscript figure

A Renormalization Group Method for Quasi One-dimensional Quantum Hamiltonians

A density-matrix renormalization group (DMRG) method for highly anisotropic two-dimensional systems is presented. The method consists in applying the usual DMRG in two steps. In the first step, a pure one dimensional calculation along the longitudinal direction is made in order to generate a low energy Hamiltonian. In the second step, the anisotropic 2D lattice is obtained by coupling in the transverse direction the 1D Hamiltonians. The method is applied to the anisotropic quantum spin half Heisenberg model on a square lattice.Comment: 4 pages, 4 figure

The Putin phenomenon

The Putin presidency in Russia became increasingly popular as it progressed and a leadership cult developed around the president himself. Not only was there general satisfaction with the leadership as a whole, there was also evidence that it was regarded as increasingly successful in all fields of policy, particularly in international affairs; and focus group discussions as well as surveys suggested the newly elected president, Dmitri Medvedev, would be expected to continue those policies. A closer examination of the survey evidence suggests that the Putin leadership in fact had relatively weak roots in the wider society, and drew widely but superficially on public support. More than anything else it was the strong economic performance of these years that generated support for the Putin presidency, and this suggested that any future leader would depend for his position on maintaining that economic performance in what were now more difficult circumstances