Laboratory simulation of energy release in solar flares

A laboratory simulation method is proposed for energy release processes occurring in a fragment of the flare current sheet on the Sun. The method relies on the assumption that the spatial scale of such processes is represented by the current sheet's thickness whose values can be close for both the solar and laboratory conditions. It is shown that in an extended current sheet, current dissipation on anomalous resistivity that ensures the specific power of energy release close to that observed in a flare, is the main energy release mechanism. A rapid compression of the sheet by external magnetic fields can provide the condition for switching on a powerful energy release. The tearing instability developing in a homogeneous neutral sheet, leads to the formation of magnetic islands in which the energy release is localized.     

Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator

The aim of this work is to model the jets produced by conical wire arrays on the MAGPIE generator, and to design and test new setups to strengthen the link between laboratory and astrophysical jets. We performed the modelling with direct three-dimensional magneto-hydro-dynamic numerical simulations using the code GORGON. We applied our code to the typical MAGPIE setup and we successfully reproduced the experiments. We found that a minimum resolution of ∼100 μm is required to retrieve the unstable character of the jet. We investigated the effect of changing the number of wires and found that arrays with less wires produce more unstable jets, and that this effect has magnetic origin. Finally, we studied the behaviour of the conical array together with a conical shield on top of it to reduce the presence of unwanted low density plasma flows. The resulting jet is shorter and less dense.     

Composition,sources, and geodynamic nature of giant batholiths in Central Asia: Evidence from the geochemistry and Nd isotopic characteristics of granitoids in the Khangai zonal magmatic area

Data on the composition, inner structure, and magma sources of giant batholith in the Central Asian Orogenic Belt are analyzed with reference to the Khangai batholith. The Khangai batholith was emplaced in the Late Permian–Early Triassic (270–240 Ma) and is the largest accumulations (>150000 km²) of granite plutons in central Mongolia. The plutons are dominated by granites of normal alkalinity and contain subalkaline granites and more rare alkaline granites. The batholith is hosted in the Khangai zonal magmatic area, which consists of the batholith itself and surrounding rift zones. The zones are made up of bimodal basalt–trachyte–comendite (pantellerite) or basalt-dominated (alkaline basalt) volcanic associations, whose intrusive rocks are dominated by syenite and granite, granosyenite, and leucogranite. Both the batholith and the rift zones were produced within the time span of 270–240 Ma. Although the rocks composing the batholith and its rift surroundings are different, they are related through a broad spectrum of transitional varieties, which suggests that that the mantle and crustal melts could interact at various scale when the magmatic area was produced. A model is suggested to explain how the geological structure of the magmatic area and the composition of the magmatic associations that make up its various zones were controlled by the interaction between a mantle plume and the lithospheric folded area. The mantle melts emplaced into the lower crust are thought to not only have been heat sources and thus induced melting but also have predetermined the variable geochemical and isotopic characteristics of the granitoids. In the marginal portions of the zonal area, the activity of the mantle plume triggered rifting associated with bimodal and alkaline granite magmatism. The formation of giant batholiths was typical of the evolution of the active continental margin of the Siberian paleocontinent in the Late Paleozoic and Early Mesozoic: the Khangai, Angara–Vitim, and Khentei batholiths were formed in this area within a relatively brief time span between 300 and 190Ma. The batholiths share certain features: they consist of granitoids of a broad compositional range, from tonalite and plagiogranite to granosyenite and rare-metal granites; and the batholiths were produced in relation to rifting processes that also formed rift magmatic zones in the surroundings of the batholiths. The large-scale and unusual batholith-forming processes are thought to have occurred when the active continental margin of the Late Paleozoic Siberian continent overlapped a number of hotspots in the Paleo- Asian Ocean. This resulted in the origin of a giant anorogenic magmatic province, which included batholiths, flood-basalt areas in Tarim and Junggar, and the Central Asian Rift System. The batholiths are structural elements of the latter and components of the zonal magmatic areas.     

3D MHD Simulations of Laboratory Plasma Jets

Jets and outflows are thought to be an integral part of accretion phenomena and are associated with a large variety of objects. In these systems, the interaction of magnetic fields with an accretion disk and/or a magnetized central object is thought to be responsible for the acceleration and collimation of plasma into jets and wider angle flows. In this paper we present three-dimensional MHD simulations of magnetically driven, radiatively cooled laboratory jets that are produced on the MAGPIE experimental facility. The general outflow structure comprises an expanding magnetic cavity which is collimated by the pressure of an extended plasma background medium, and a magnetically confined jet which develops within the magnetic cavity. Although this structure is intrinsically transient and instabilities in the jet and disruption of the magnetic cavity ultimately lead to its break-up, a well collimated, “knotty” jet still emerges from the system; such clumpy morphology is reminiscent of that observed in many astrophysical jets. The possible introduction in the experiments of angular momentum and axial magnetic field will also be discussed.     

Formation stages and ore matter sources of the Devdoraki copper deposit,Kazbek volcanic center,the Greater Caucasus

Comprehensive petrological–mineralogical, geochronological, and isotope-geochemical studies have been carried out at the Devdoraki copper deposit situated in the Kazbek neovolcanic center, the frontier territory between Georgia and Russia. The formation history of this deposit has been deciphered on the basis of K–Ar isotopic geochronological data, and the multistage evolution of ore–magmatic system has been established. The subeconomic disseminated and less abundant stringer pyrite mineralization formed at the first stage in the Early Cretaceous back to 130–120 Ma at the retrograde stage of regional metamorphism. The second productive stage was related to intense Quaternary volcanism of the Kazbek center. The late stringer base-metal mineralization formed about 400 ka ago in connection with the activity of minor volcanoes in the eastern part of deposit. In its western part adjoining the Kazbek volcanic cone, ore formation apparently continued over the entire period of recent magmatic activity from 400 to 100 ka ago. It is quite probable that this process is currently proceeding at deep levels of the Devdoraki deposit. Pb–Pb isotope-geochemical data show that Jurassic metasedimentary rocks that host sulfide mineralization could have been a main source of matter for early pyrite. At the second stage of base-metal mineralization formation, the source of ore matter was earlier metamorphic pyrite combined with hydrothermal solutions related to Quaternary endogenic activity within the Kazbek volcanic center. Gangue mineral matter (quartz, carbonates) was supplied simultaneously from the postmagmatic hydrothermal solution and host shale.     

M 101 group galaxies

Based on archival Hubble Space Telescope images, we have performed stellar photometry for the galaxy M 101 and other neighboring galaxies located at a small angular distance from M 101 and having radial velocities similar to that of M 101: M 51, M 63, NGC 5474, NGC 5477, UGC 9405, Ho IV, KUG1413+573, and others. Based on the TRGB method, we have determined the distances to these galaxies. We have found that the M 101 group lies at a distance of 6.8 Mpc and is a small compact galaxy group consisting of four galaxies: NGC 5474, NGC 5477, UGC 9405, and Ho IV. The bright massive galaxies M 51 and M 63 are considerably farther (D = 9.0 and 9.3 Mpc, respectively) than the M 101 group and do not belong to it. Applying the virial theorem to 27 objects (H II regions and galaxies),M 101 satellites located at different distances from the galaxy, has revealed an increase in the dynamical mass of M 101 with increasing sizes of the system of satellites used in calculating the mass. The maximum calculated mass of M 101 is 7.5 × 10¹¹ M _⊙. The dynamical mass of M 101 calculated on the basis of the four galaxies constituting the group is 6.2 × 10¹¹ M _⊙. The mass-to-light ratio for this mass is M/L = 18 (at the adopted luminosity of M 101, M _B = ?20.8).