Charmonium dissociation by mesons in heavy-ion collisions

The charmonium dissociation by mesons in relativistic heavy-ion reactions is analyzed within the Regge approach. It is shown that the inclusion of the initial and final state interactions in the dissociation of J/Psi to bar{D}* D* close to threshold increases the cross section significantly and can not be neglected in comparison to the total dissociation rate. This is due to resonant bar{D}*-D* interactions in sqrt{s} close to the masses of the Psi(4.04) and Psi(4.16) mesons. We also investigate thermal effects of the (c bar{c}) width for such processes in the medium. All these effects change both the magnitude and the shape of the cross section as a function of sqrt{s}. The results obtained should be applied in the analysis of open and hidden charm production in heavy-ion collisions.Comment: 4 pages, 2 figures; Talk given at ICTP 5th International Conference on Perspectives in Hadronic Physics, Trieste, Italy, 22-26 May 200

Axisymmetric open magnetic systems for plasma confinement

At present, three modern types of different mirror machines for plasma confinement and heating exist in Novosibirsk (Gas Dynamic Trap, -GDT, Multi-mirror, - GOL-3, Tandem Mirror, -AMBAL-M). All these systems are attractive from the engineering point of view because of very simple axisymmetric geometry of magnetic configurations. In this paper, the status of different confinement systems is presented. The experiments most crucial for the mirror concept are described such as a demonstration of different principles of suppression of electron heat conductivity (GDT, GOL-3), finding of MHD stable regimes of plasma confinement in axisymmetric geometric of magnetic field (GDT, AMBAL-M), an effective heating of dense plasma by relativistic electron beam (GOL-3), observation of radial diffusion of quiescent plasma with practically classical diffusion coefficient (AMBAL-M), etc. The main plasma parameters achieved in mentioned above systems are presented

The estimation of coherence length for electron-doped superconductor Nd₂₋xCexCuO₄₊δ

Results of low-temperature upper critical field measurements for Nd₂₋xCexCuO₄₊δ single crystals with various x and nonstoichiometric disorder (δ) are presented. The coherence length of pair correlation ξ and the product kFξ , where kF is the Fermi wave vector, are estimated. It is shown that for investigated single crystals parameter kFξ ≅ 100 and thus phenomenologically NdCeCuO-system is in a range of Cooper-pair-based (BCS) superconductivity

The mixed-state Hall conductivity of single-crystal films Nd₂–xCexCuO₄₊δ (x = 0.14)

The magnetic-field dependencies of the longitudinal and Hall resistivity of the electron-doped compounds Nd₂–xCexCuO₄₊δ in underdoped region (x = 0.14) were investigated. It was established experimentally a strong magnetic field dependence of the Hall conductivity, σxy(B) = C – b/B, in the region of magnetic fields corresponding to a transition from superconducting to resistive state. The observed feature can be explained with the sum of contributions of the quasiparticles and moving Abrikosov vortices into Hall effect in a mixed state of type-II superconductor

Doping effect on the evolution of the pairing symmetry in n-type superconductor near antiferromagnetic phase boundary

We present the investigation results of the in-plane ρ(T) resistivity tensor at the temperature range 0.4–40 K in magnetic fields up to 90 kOe (H || c, J || ab) for electron-doped Nd₂₋xCexCuO₄+δ with different degree of disorder near antiferromagnetic–superconducting phase boundary. We have experimentally found that for optimally doped compound both the upper critical field slope and the critical temperature decrease with increasing of the disorder parameter (d-wave pairing) while in the case of the underdoped system the critical temperature remains constant and dHc₂/dT increases with increasing of the disorder (s-wave pairing). These features suggest a possible implementation of the complex mixture state as the s+id pairing

Anomalous behavior of the Hall effect in electron-doped superconductor Nd₂₋xCexCuO₄₊δ with nonstoichiometric disorder

Magnetoresistivity and Hall effect measured in magnetic fields up to B=9T (B║c, J║ab) in electrondoped Nd₂₋xCexCuO₄₊δ single crystal films with x = 0.14; 0.15; 0.18 and different oxygen content (δ) were studied in a temperature range of 0.4–4.2 K. The resistivity and Hall coefficient behaviors in the mixed state are discussed in the framework of flux-flow model with the inclusion of the back-flow of vortices owing to the pinning forces

Doping effect on the anomalous behavior of the Hall effect in electron-doped superconductor Nd2−x_{2-x}Cex_xCuO4+δ_{4+\delta}

Transport properties of Nd$_{2-x}$Ce$_x$CuO$_{4+\delta}$ single crystal films are investigated in magnetic fields $B$ up to 9T at $T$=(0.4-4.2)K. An analysis of normal state (at $B>B_{c2}$) Hall coefficient $R_H$$^n$ dependence on Ce doping takes us to a conclusion about the existence both of electron-like and hole-like contributions to transport in nominally electron-doped system. In accordance with $R_H$$^n$(x) analysis an anomalous sign reversal of Hall effect in mixed state at $B<B_{c2}$ may be ascribed to a flux-flow regime for two types of carriers with opposite charges.Comment: 14 pages, 5 figure

Coexistence of different base periodicities in prokaryotic genomes as related to DNA curvature, supercoiling, and transcription

We analyzed the periodic patterns in E. coli promoters and compared the distributions of the corresponding patterns in promoters and in the complete genome to elucidate their function. Except the three-base periodicity, coincident with that in the coding regions and growing stronger in the region downstream from the transcriptions start (TS), all other salient periodicities are peaked upstream of TS. We found that helical periodicities with the lengths about B-helix pitch ~10.2-10.5 bp and A-helix pitch ~10.8-11.1 bp coexist in the genomic sequences. We mapped the distributions of stretches with A-, B-, and Z- like DNA periodicities onto E.coli genome. All three periodicities tend to concentrate within non-coding regions when their intensity becomes stronger and prevail in the promoter sequences. The comparison with available experimental data indicates that promoters with the most pronounced periodicities may be related to the supercoiling-sensitive genes.Comment: 23 pages, 6 figures, 2 table

Dynamical spin correlations in Heisenberg ladder under magnetic field and correlation functions in SO(5) ladder

The zero-temperature dynamical spin-spin correlation functions are calculated for the spin-1/2 two-leg Heisenberg ladder in a magnetic field above the lower critical field Hc1. The dynamical structure factors are calculated which exhibit both massless and massive excitations. These modes appear in different sectors characterized by the parity in the rung direction and by the momentum in the direction of the chains. The structure factors have power-law singularities at the lower edges of their support. The results are also applicable to spin-1 Heisenberg chain. The implications are briefly discussed for various correlation functions and the pi-resonance in the SO(5) symmetric ladder model.Comment: 15 pages, 6 figures, added references; final version to appear in Phys. Rev.