Stripe phase: analytical results for weakly coupled repulsive Hubbard model

Motivated by the stripe developments in cuprates, we review some analytical results of our studies of the charge- and spin density modulations (CDW and SDW) in a weakly coupled one dimensional repulsive electron system on a lattice. It is shown that close to half filling, in the high temperature regime above the mean field transition temperature, short range repulsions favor charge density fluctuations with wave vectors bearing special relations with those of the spin density fluctuations. In the low temperature regime, not only the wave vectors, but also the mutual phases of the CDW and SDW become coupled due to a quantum interference phenomenon, leading to the stripe phase instability in a quasi one-dimensional repulsive electron system. It is shown that away from half filling periodic lattice potential causes cooperative condensation of the spin and charge superlattices. "Switching off" this potential causes vanishing of the stripe order. The leading spin-charge coupling term in the effective Landau functional is derived microscopically. Results of the 1D renormalization group (parquet) analysis away from half filling are also presented, which indicate transient-scale correlations resembling the mean-field pattern. Farther, the self-consistent solution for the spin-charge solitonic superstructure in a quasi-one-dimensional electron system is obtained in the framework of the Hubbard model as a function of hole doping and temperature. Possible relationship with the stripe phase correlations observed in high T_c cuprates is discussed.Comment: 29 pages,10 figures, Late

Initial Stage of Star Formation

Abstract In frame of the hydrodynamics wh irlwind mechanis m of b ipolar outflow formation fro m disk system the data of observations of active starburst region a dense molecular cloud of Orion KL in H 2 O maser rad iation is analyzed. It is shown that the theory as a first appro ximation exp lains the basic observant laws of active region, structure accompanying protostar formation: a disk-a b ipolar outflo w, includ ing its mechanis m ejection and self-collimation, excitation maser radiat ion

Subgap tunneling through channels of polarons and bipolarons in chain conductors

We suggest a theory of internal coherent tunneling in the pseudogap region where the applied voltage is below the free electron gap. We consider quasi 1D systems where the gap is originated by a lattice dimerization like in polyacethylene, as well as low symmetry 1D semiconductors. Results may be applied to several types of conjugated polymers, to semiconducting nanotubes and to quantum wires of semiconductors. The approach may be generalized to tunneling in strongly correlated systems showing the pseudogap effect, like the family of High Tc materials in the undoped limit. We demonstrate the evolution of tunneling current-voltage characteristics from smearing the free electron gap down to threshold for tunneling of polarons and further down to the region of bi-electronic tunneling via bipolarons or kink pairs.Comment: 14 pages, 8 postscript figure

Conductivity in Two-Dimensional Disordered Model with Anisotropic Long-Range Hopping

We consider two-dimensional system of particles localized on randomly distributed sites of squared lattice with anisotropic transfer matrix elements between localized sites. By summing of "diffusion ladder" and "cooperon ladder" type vertices we calculated the conductivity for various sites and particles densities.Comment: Latex, 10 page

Megamaser Disks in Active Galactic Nuclei

Recent spectroscopic and VLBI-imaging observations of bright extragalactic water maser sources have revealed that the megamaser emission often originates in thin circumnuclear disks near the centers of active galactic nuclei (AGNs). Using general radiative and kinematic considerations and taking account of the observed flux variability, we argue that the maser emission regions are clumpy, a conclusion that is independent of the detailed mechanism (X-ray heating, shocks, etc.) driving the collisionally pumped masers. We examine scenarios in which the clumps represent discrete gas condensations (i.e., clouds) and do not merely correspond to velocity irregularities in the disk. We show that even two clouds that overlap within the velocity coherence length along the line of sight could account (through self-amplification) for the entire maser flux of a high-velocity ``satellite'' feature in sources like NGC 4258 and NGC 1068, and we suggest that cloud self-amplification likely contributes also to the flux of the background-amplifying ``systemic'' features in these objects. Analogous interpretations have previously been proposed for water maser sources in Galactic star-forming regions. We argue that this picture provides a natural explanation of the time-variability characteristics of extragalactic megamaser sources and of their apparent association with Seyfert 2-like galaxies. We also show that the requisite cloud space densities and internal densities are consistent with the typical values of nuclear (broad emission-line region-type) clouds.Comment: 55 pages, 7 figures, AASTeX4.0, to appear in The Astrophysical Journal (1999 March 1 issue

The level of air pollution in the impact zone of coal-fired power plant (Karaganda City) using the data of geochemical snow survey (Republic of Kazakhstan)

Coal-fired power plants emissions impact the air quality and human health. Of great significance is assessment of solid airborne particles emissions from those plants and distance of their transportation. The article presents the results of air pollution assessment in the zone of coal-fired power plant (Karaganda City) using snow survey. Based on the mass of solid airborne particles deposited in snow, time of their deposition on snow at the distance from 0.5 to 4.5 km a value of dust load has been determined. It is stated that very high level of pollution is observed at the distance from 0.5 to 1 km. there is a trend in decrease of dust burden value with the distance from the stacks of coal-fired power plant that may be conditioned by the particle size and washing out smaller ash particles by ice pellets forming at freezing water vapour in stacks of the coal-fired power plant. Study in composition of solid airborne particles deposited in snow has shown that they mainly contain particulates of underburnt coal, Al-Si- rich spheres, Fe-rich spheres, and coal dust. The content of the particles in samples decreases with the distance from the stacks of the coal-fired power plant

Expansion of the R4 Water Maser Arc Near Cepheus A HW 2

We present new (April 2000) MERLIN observations of the H2O masers located near the protostar Cepheus A HW2. The MERLIN observations detect many of the structures found in earlier (1996) VLBA observations of Torrelles and collaborators, and the changed positions of these structures are compatible with the VLBA proper motions and astrometric uncertainties. The radius of curvature of the R4 structure of maser arcs appears to have grown by a factor of two, and the displacement of the arcs between 1996 and 2000 are compatible with expansion about a common center. In addition, the MERLIN observations detect red-shifted masers not previously found; taken with the newly discovered masers, the R4 structure now resembles patchy emission from an elliptical ring. We demonstrate that a simple bow-shock model cannot simultaneously account for the shape and the velocity gradient of the R4 structure. A model involving a slow, hydromagnetic shock propagating into a rotating, circumstellar disk better describes the maser spot kinematics and luminosities. In this model, the central mass is 3 solar masses, and we demonstrate that the mass of the disk is negligible in comparison. The expansion velocity of the post-shock gas, roughly 5 km / s, is slow compared to the average shock velocity (roughly 13 km / s) suggesting that the post-shock gas is magnetically supported with a characteristic field strength of roughly 30 mG. We speculate that the expanding maser rings R4 and R5 may be generated by periodic, instability-driven winds from young stars that periodically send spherical shocks into the surrounding circumstellar material.Comment: 16 pages, 12 figures. Accepted for publication in the Astrophysical Journal. Uses emulateapj5.sty. Updated: removed previews from postscript figures to make them more arxiv-friendl