8 research outputs found
Repeated, protein-encoding heterochromatic genes cause inactivation of a juxtaposed euchromatic gene
AbstractEuchromatic genes are often silenced by rearrangements that place them within or near heterochromatin, a phenomenon known as position effect variegation (PEV). However, little is known about molecular structure of cis-acting heterochromatic fragments responsible for PEV. Here we report that heterochromatic cluster containing Stellate repeats, that encode putative regulatory subunit of protein kinase CK2 cause PEV of a reporter white `mini-gene'. It is the first example of an euchromatic gene being silenced because of the proximity to the natural, well-defined heterochromatic repeat cluster
Weak dissipation does not result in disappearance of persistent current
Experimental results obtained last years corroborate a prediction made by I.O. Kulik forty years ago that the energy dissipation does not result in disappearance of equilibrium circular current observable in the normal state of superconductor rings and normal metal rings. Contrary interpretations of the persistent current as a Brownian motion or a dissipationless current are compared in the point of view of the observations of this phenomenon at presence of an electric potential difference. Distinctions between the quantum phenomena at atomic and mesoscopic levels are accentuated. In connection of the quantum oscillations in magnetic field of potential difference observed on asymmetric rings with the persistent current, it is pointed out that an experimental check of such phenomenon at thermodynamic equilibrium is possible
A possibility of persistent voltage observation in a system of asymmetric superconducting rings
A possibility to observe the persistent voltage in a superconducting ring of
different widths of the arms is experimentally investigated. It was earlier
found that switching of the arms between superconducting and normal states by
ac current induces the dc voltage oscillation in magnetic field with a period
corresponding to the flux quantum inside the ring. We use systems with a large
number of asymmetric rings connected in series in order to investigate the
possibility to observe this quantum phenomenon near the superconducting
transition where thermal fluctuations switch ring segments without external
influence and the persistent current is much smaller than in the
superconducting state.Comment: 7 pages, 4 figure
AC conductivity of a niobium thin film in a swept magnetic field
We report the results of the measurement the ac conductivity of a Nb
superconducting thin film in a swept dc magnetic field. In the mixed state the
swept dc field creates vortices at the film surface which pass through the film
and form the observed ac conductivity. Vortex rate generation does not depend
on the value of the dc field and there is a large plateau-like region of dc
magnetic fields where the dissipation is approximately constant. A proposed
phenomenological model describes quite well the main features of the ac
response in these fields including its dependency on the sweep rate, ac
amplitude, frequency, and value of the second and third harmonics.Comment: 7 pages and 10 figures; Journal of Physics: Condensed Matter, 201