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

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

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

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

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

Media effects and Russian elections, 1999-2000

The Russian parliamentary and presidential elections of December 1999 and March 2000 appeared to have been won in large part through the partisan use of (particularly state) television. According to the evidence of a spring 2001 national survey, television was the main source of political information for the supporters of all parties and candidates. However, state television (which had been most supportive of the Kremlin) was much more likely to be favoured by the supporters of the pro-regime Unity party; while commercial television (which had provided a more even-handed coverage of the elections) was more popular and respected among the supporters of anti-Kremlin parties and candidates and less popular among supporters of Vladimir Putin. Regression analysis that takes account of reciprocal causation between media source and vote choice indicates that these were not spurious associations. The findings suggest that the state itself may exercise a disproportionate influence upon the electoral process in newly established systems in which social structures and political allegiances remain fluid

How do galactic winds affect the Lyalpha forest?

We investigate the effect of galactic winds on the Lyalpha forest in cosmological simulations of structure and galaxy formation. We combine high resolution N-body simulations of the evolution of the dark matter with a semi-analytic model for the formation and evolution of galaxies which includes detailed prescriptions for the long-term evolution of galactic winds. This model is the first to describe the evolution of outflows as a two-phase process (an adiabatic bubble followed by a momentum--driven shell) and to include metal--dependent cooling of the outflowing material. We find that the main statistical properties of the Lyalpha forest, namely the flux power spectrum P(k) and the flux probability distribution function (PDF), are not significantly affected by winds and so do not significantly constrain wind models. Winds around galaxies do, however, produce detectable signatures in the forest, in particular, increased flux transmissivity inside hot bubbles, and narrow, saturated absorption lines caused by dense cooled shells. We find that the Lyalpha flux transmissivity is highly enhanced near strongly wind-blowing galaxies, almost half of all high-redshift galaxies in our sample, in agreement with the results of Adelberger et al. (2005). Finally, we propose a new method to identify absorption lines potentially due to wind shells in the Lyalpha forest: we calculate the abundance of saturated regions in spectra as a function of region width and we find that the number with widths smaller than about 1 Angstrom at z=3 and 0.6 Angstrom at z=2 may be more than doubled. This should be detectable in real spectra.Comment: 14 pages, 11 figures. Minor changes in the text. Accepted for publication in MNRA