Late Paleozoic and Mesozoic deformations in the southwestern Primorye region

Two types of tectonic deformations indicating different geodynamic settings are defined in the southwestern Primorye region. Near-latitudinal compression forces were responsible for the oldest, Late Paleozoic deformations. The Permian stratified complexes host a near-meridional system of folds and zones of dynamothermal metamorphism, cleavage, and foliation oriented orthogonally relative to the compression. Late Proterozoic (?) mafic-ultramafic rocks are characterized by similar deformations. In the Late Permian, the deformations were accompanied by granitoid magmatism controlled by fold and cleavage structures. The younger, Mesozoic deformations produced by near-meridional compression are represented by NE-trending sinistral strike-slip faults and their structural parageneses: an ENE-trending system of folds and downdip-thrusts both superimposed on Paleozoic protostructures and manifested in Mesozoic and Cenozoic sequences. It is inferred that, at the Paleozoic-Mesozoic boundary, near-latitudinal compression was replaced by near-meridional compression, probably, in response to the corresponding change in direction of the lateral displacement of the interacting Asian continent and (or) Pacific Plate.     

Atmospheric circulation over western Siberia in 1976–2004

Cyclonic and anticyclonic activity over western Siberia for 1976–2004 is considered. Trajectories of motion of baric formations of various genesis and their frequency are analyzed.     

The Contribution of Magnetic Flux Tubes to Brightness Fluctuations on the Extreme Limb of the Sun

Magnetic flux tubes are considered to be a possible source of observed brightness variations on the extreme limb of the Sun. A computer code to simulate the brightness fluctuations is developed. It follows from numerical modeling that a filling factor of f=4% is required to explain the observed fine structure. Such a value is typical for the boundaries of supergranules. Tubes produce a local maximum of intensity just inside the limb.     

The orbit and exposure history of the Piplia Kalan eucrite

Abstract— Cosmogenic radionuclides, particle tracks and rare gases have been measured in two fragments of the Piplia Kalan eucrite that fell in Rajasthan, India on 1996 June 20. The cosmic-ray exposure age of the meteorite is calculated to be 23 Ma, which is similar to ages of some other eucrites. The track density in feldspars and pyroxenes varies between 0.2 × 10⁶ to ～4.5 × 10⁶ cm^?2. The mass ablation of the meteorite, based on the distribution of track density in near-surface samples of the two fragments, is calculated to be ～75%, which corresponds to an entry velocity of ～17 km/s. The orbital parameters of the eucrite have been computed from the radiant of the meteor trail and the geocentric velocity. The best estimates are a = 2.47 AU, e = 0.62 and i = 7.54°, which is similar to the orbital elements of other meteorites, most of which have been inferred to originate within 2.6 AU of the Sun. The activity of the radionuclide ²⁶Al agrees with the expected production rate; whereas the shortlived radionuclides ²²Na, ⁵⁴Mn, ⁴⁶Sc etc. have levels that are consistent with the galactic cosmic-ray fluxes that are expected during the solar minimum period before the time of fall. All the cosmogenic effects (i.e., radio- and stable- nuclides and particle tracks) are consistent with the meteoroid having had a simple, one-stage exposure history in interplanetary space. Lower radio genic ages of U, Th-He (0.7 Ga) and K-Ar (3.6 Ga) indicate severe losses of ⁴He and ⁴⁰Ar, as observed in most eucrites. A Pu-Xe age, concordant with Angra dos Reis, shows that Piplia belongs to the “old” eucrite group.     

Velocity Oscillations in Active Sunspot Groups

Time series of two-dimensional spectra were taken with the Göttingen 2D spectrometer at the VTT on Tenerife in 1996. They were investigated for Doppler velocities and velocity oscillations in small spots and pores of rapidly evolving sunspot groups. For the present measurements the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm were selected. Spots with penumbrae exhibit the Evershed effect. Some pores seem to be connected with downflows, but the centres of the downflows are somewhat displaced from their associated pores. The surroundings of the pores show red shifts relative to the whole field of view. The power in the 5-min range is reduced inside the spots and pores as well as in their immediate vicinity. This reduction inside the spots is in agreement with former results. Outside the area of the spot group the 5-min power has a patchy structure with a typical size of 5 arc sec. For periods below 3.3 min, the behaviour of individual spots and pores is different. Some spots show clearly enhanced power for these periods, and it remains high down to the Nyquist period at 1.5 min. The small pores do not show enhanced three-minute oscillations compared with their vicinity. Inside one spot we find a ring of enhanced power in the period range between 8 and 20 min corresponding to the time scales of granular variations. This result could be an indication of a relation between spots and convection, but magneto-accoustic waves are also possible. The same ring exhibits also enhanced power for short periods.     

Analyzing the Solar Proton Event of 22 October 1989, Using the Method of Spectrographic Global Survey

Using ground-level observations of cosmic-ray (CR) intensities from a worldwide network of stations during the ground-level enhancement (GLE) of 22–23 October 1989, variations of the particle distribution function in all phases of the event were investigated.It is shown that time intensity profiles of 2–4 GV rigidity particles differ greatly from those of higher-energy particles. After the high-energy particle intensity attains a maximum, there is an abrupt decrease in intensity below the background level, followed by the phase of slow recovery to background values. The angular distribution of high-energy particles across the celestial sphere shows, along with an increased intensity, also regions with decreased relative background intensity.To explain the detected phenomenon, it is concluded that it is necessary to consider the solar CR propagation process in the heliosphere not in terms of the movement of particles in the external electromagnetic field but with proper account of the self-consistency of fields with the particle distribution function.     

Status and Results from the HEGRA Air Shower Experiment

The HEGRA experiment investigates the relativistic (non thermal) universe by measuring air showers initiated in the atmosphere by photons and charged particles from the cosmos, using the imaging atmospheric Cherenkov light technique (> 500 GeV) and the showerfront sampling technique (> 20 TeV). New results concerning the search and study of gamma ray sources above 500 GeV, the measurement of the energy spectrum and chemical composition of cosmic rays above 1 PeV and the search of TeV counterparts of Gamma Ray Bursts are briefly described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stellar dynamics in a galactic centre surrounded by a massive accretion disc — I. Newtonian description

The long-term evolution of stellar orbits bound to a massive centre is studied in order to understand the cores of star clusters in central regions of galaxies. Stellar trajectories undergo tiny perturbations, the origins of which are twofold: (i) the gravitational field of a thin gaseous disc surrounding the galactic centre, and (ii) cumulative drag arising from successive interactions of the stars with the material of the disc. Both effects are closely related because they depend on the total mass of the disc, assumed to be a small fraction of the central mass. It is shown that, in contrast to previous works, most of the retrograde (with respect to the disc) orbits are captured by the central object, presumably a massive black hole. Initially prograde orbits are also affected, so that statistical properties of the central star cluster in quasi-equilibrium may differ significantly from those deduced in previous analyses.