Coulomb effects in granular materials at not very low temperatures

We consider effects of Coulomb interaction in a granular normal metal at not very low temperatures suppressing weak localization effects. In this limit calculations with the initial electron Hamiltonian are reduced to integrations over a phase variable with an effective action, which can be considered as a bosonization for the granular metal. Conditions of the applicability of the effective action are considered in detail and importance of winding numbers for the phase variables is emphasized. Explicit calculations are carried out for the conductivity and the tunneling density of states in the limits of large $g\gg 1$ and small $g\ll 1$ tunnelling conductances. It is demonstrated for any dimension of the array of the grains that at small $g$ the conductivity and the tunnelling density of states decay with temperature exponentially. At large $g$ the conductivity also decays with decreasing the temparature and its temperature dependence is logarithmic independent of dimensionality and presence of a magnetic field. The tunnelling density of states for $g\gg 1$ is anomalous in any dimension but the anomaly is stronger than logarithmic in low dimensions and is similar to that for disordered systems. The formulae derived are compared with existing experiments. The logarithmic behavior of the conductivity at large $g$ obtained in our model can explain numerous experiments on systems with a granular structure including some high $T_{c}$ materials.Comment: 30 page

A locus involved in the regulation of replication in plasmid pSC 101

The origin of replication of plasmid pSC101 contains three directly repeated sequences RS1, RS2, and RS3 separated by 22 bp from two palindromic sequences, IR1 and IR2, which are partially homologous to the direct repeats. These inverted repeat (IR) sequences overlap the promoter of the repA gene which encodes a protein essential for plasmid replication. We have shown that RepA binds to the RS sites as a monomer and to the IR sites as a dimer. The influence of the IR1 site, and of the DNA segment that separates it from RS3, on plasmid copy number control has been studied in detail. We show that the integrity of IR1 is essential for efficient replication and plasmid stability, the critical site extending to the left of IR1 proper. We also show that the presence of IR1 modifies profoundly the binding properties of purified RepA protein to a segment of DNA containing the RS sequences. IR1 is separated from its homologous site on RS3 by approximately four turns of the DNA helix. Replication is abolished if this distance is increased by half a turn of the helix but it is restored if the distance is increased by a whole turn. These results suggest a DNA looping interaction, in the initiation of replication, between the RepA dimer that binds iR1 and the RepA monomers that bind the RS sequences