Interaction between a fast rotating sunspot and ephemeral regions as the origin of the major solar event on 2006 December 13

The major solar event on 2006 December 13 is characterized by the approximately simultaneous occurrence of a heap of hot ejecta, a great two-ribbon flare and an extended Earth-directed coronal mass ejection. We examine the magnetic field and sunspot evolution in active region NOAA AR 10930, the source region of the event, while it transited the solar disk centre from Dec. 10 to Dec. 13. We find that the obvious changes in the active region associated with the event are the development of magnetic shear, the appearance of ephemeral regions and fast rotation of a smaller sunspot. Around the area of the magnetic neutral line of the active region, interaction between the fast rotating sunspot and the ephemeral regions triggers continual brightening and finally the major flare. It is indicative that only after the sunspot rotates up to 200$^{\circ}$ does the major event take place. The sunspot rotates at least 240$^{\circ}$ about its centre, the largest sunspot rotation angle which has been reported.Comment: 4 pages, 6 figures, ApJ Letters inpres

Controlling the spin orientation of photoexcited electrons by symmetry breaking

We study reflection of optically spin-oriented hot electrons as a means to probe the semiconductor crystal symmetry and its intimate relation with the spin-orbit coupling. The symmetry breaking by reflection manifests itself by tipping the net-spin vector of the photoexcited electrons out of the light propagation direction. The tipping angle and the pointing direction of the net-spin vector are set by the crystal-induced spin precession, momentum alignment and spin-momentum correlation of the initial photoexcited electron population. We examine non-magnetic semiconductor heterostructures and semiconductor/ferromagnet systems and show the unique signatures of these effects.Comment: 4 pages, 3 figures, resubmitte

Lithium Depletion Boundary in a Pre-Main Sequence Binary System

A lithium depletion boundary is detected in HIP 112312 (GJ 871.1 A and B), a \~12 Myr old pre-main sequence binary system. A strong (EW 300 mA) Li 6708 A absorption feature is seen at the secondary (~M4.5) while no Li 6708 A feature is detected from the primary (~M4). The physical companionship of the two stars is confirmed from common proper motions. Current theoretical pre-main sequence evolutionary models cannot simultaneously match the observed colors, brightnesses, and Li depletion patterns of this binary system. At the age upper limit of 20 Myr, contemporary theoretical evolutionary models predict too slow Li depletion. If true Li depletion is a faster process than predicted by theoretical models, ages of open clusters (Pleiades, alpha Persei, and IC 2391) estimated from the Li depletion boundary method are all overestimated. Because of the importance of the open cluster age scale, development of self-consistent theoretical models to match the HIP 112312 data is desirable.Comment: Accepted in ApJL. 5 pages total (3 tables, 3 figures

Influence of Primary Cosmic Radiation Mass Composition on the Estimation of Eas Energy

At the Yakutsk EAS array E_em is determined by using measurements of EAS Cherenkov light flux and charged particle flux. It is known from calculations that these characteristics depend on a sort of primary particle and, therefore, the estimation of E_em depends on a primary particle mass. In the work the dependence of the E_em/E_0 ratio on the energy is given and experimental data are compared with calculations by the QGSJET model. The calculations have been carried out for the primary proton and iron nucleus. The average calculated meaning of the value of E_em/E_0 ratio (between the proton and iron nucleus) within experimental errors is in agreement with experimental data that doesnt contradict to the mixed mass composition of primary cosmic radiation.Comment: 19th European Cosmic Ray Symposium. Aug 30 - Sep 3 2004, Florence, Italy. 3 pages, 1 figure. Subbmitted for publication in International Journal of Modern Physics

Picovoltmeter for probing vortex dynamics in a single weak-pinning Corbino channel

We have developed a picovoltmeter using a Nb dc Superconducting QUantum Interference Device (SQUID) for measuring the flux-flow voltage from a small number of vortices moving through a submicron weak-pinning superconducting channel. We have applied this picovoltmeter to measure the vortex response in a single channel arranged in a circle on a Corbino disk geometry. The circular channel allows the vortices to follow closed orbits without encountering any sample edges, thus eliminating the influence of entry barriers.Comment: 4 pages, 3 figures, submitted to Review of Scientific Instrument