The role of moisture fluctuations in unsaturated transport

Within the framework of stochastic theory and the spectral perturbation techniques, three-dimensional dispersion in partially saturated soils with a finite correlation scale of log-hydraulic conductivity is analyzed. The effects of spatial variability of the moisture distribution parameter on the asymptotic spreading behavior of a unsaturated solute plume are assessed. This is accomplished by comparing two asymptotic macrodispersivities and two variance of solute concentration, obtained for a constant moisture content and spatially varied moisture, respectively.     

Attenuation of P and pP waves in Vrancea area – Romania

The seismic attenuation in the Vrancea region (Romania) is investigated from teleseismic recordings of P and pP waves during the four major, intermediate-depth Romanian events that occurred since the onset of digital instrumentation. Most stations are located in Canada and in the United States, being equipped with a variety of sensors, especially short-period ones. The amplitude spectral ratio method is used, assuming no frequency dependence of the Q _P factor in the range 0.2–2 Hz. No apparent correlation between the derived attenuation value and the type of recording sensor is observed. Lateral variations of the attenuation are obtained, with a very low Q _P area (values down to 33) located in the northwestern part of the Vrancea seismogenic volume. For the stations with different azimuth angles in relation to the epicentral area, Q _P values routinely exceed 200. Most likely, the low attenuation values are related to an upwelling mantle material located immediately beneath the crust, but limited in depth to at least 100 km.     

Locations of Footpoints of Transequatorial Interconnecting Loops

We discuss footpoints of loops seen by Yohkoh in soft X-rays that connect active regions across the equator (transequatorial interconnecting loops – TILs). While most TILs are rooted in moderately strong fields at peripheries of active regions, there are also cases when these loops are anchored in very weak or very strong fields, ranging from < 30 G to several hundred gauss. Some have their footpoints near sunspot penumbrae, creating `X-ray fountains' in a combination with active region loops. But TILs are never rooted in sunspots. The most likely explanation is that magnetic field lines leave spots almost vertically so that TILs rooted in them extend high into the corona and density in them is below the limit of visibility in X-rays. The fact that in force-free modeling some TILs are rooted in sunspots is most probably due to the difference between field-line connections in `vacuum' and in the highly conductive plasma on the Sun. Some TILs end before they reach active regions which sometimes may indicate the real situation, but mostly this `gap' is probably due to a temperature decrease near the loop footpoints which makes them invisible in X-rays. In that case the fact that these cool lowest parts of TILs are never found in TRACE or SOHO EIT images indicates that plasma density in TILs must be very low. Still, the total absence of any counterparts of X-ray TILs in TRACE and EIT images is puzzling and, therefore, other possible interpretations of the `gap' origin are also briefly mentioned.     

Ring Current Formed During the Bombardment of a Rotating Gas Torus by Neutral Beams

A new mechanism for the generation of the electric ring current is presented. During the radial bombardment of a rotating gas torus by a neutral beam, electrons and protons are dragged by rotating gas. Due to collisions electrons obtain the torus velocity faster than protons, therefore in some layer there is a difference in electron and proton beam toroidal velocities; the electric current is thus generated. This current is discussed as the seed magnetic field in early stages of evolving galaxies, which is then amplified by the dynamo process to present values of the magnetic field. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Growth rate of upper-hybrid waves and dynamics of microwave zebra structures

The growth rate of the upper-hybrid waves with different velocities of superthermal electrons is computed considering a finite temperature of the background plasma and relativistic corrections. Based on these computations two examples of high-frequency zebra structures are interpreted. The sequence of the continuum, zebra structure, and continuum observed in the 29 October 2000, event is explained as an increase and following decrease of the velocity of superthermal electrons in the range of v=0.1–0.3 c. On the other hand, the zebra structure observed during the 18 March 2003 event represents an example with fast electron acceleration.     

Melt segregation from silicic crystal mushes: a critical appraisal of possible mechanisms and their microstructural record

One of the outstanding problems in understanding the behavior of intermediate-to-silicic magmatic systems is the mechanism(s) by which large volumes of crystal-poor rhyolite can be extracted from crystal-rich mushy storage zones in the mid-deep crust. The mechanisms commonly invoked are hindered settling, micro-settling, and compaction. The concept of micro-settling involves extraction of grains from a crystal framework during Ostwald ripening and has been shown to be non-viable in the metallic systems for which it was originally proposed. Micro-settling is also likely to be insignificant in silicic mushes, because ripening rates are slow for quartz and plagioclase, contact areas between grains in a crystal mush are likely to be large, and abundant low-angle grain boundaries promote grain coalescence rather than ripening. Published calculations of melt segregation rates by hindered settling (Stokes settling in a crystal-rich system) neglect all but fluid dynamical interactions between particles. Because tabular silicate minerals are likely to form open, mechanically coherent, frameworks at porosities as high as ~?75%, settling of single crystals is only likely in very melt-rich systems. Gravitationally-driven viscous compaction requires deformation of crystals by either dissolution–reprecipitation or dislocation creep. There is, as yet, no reported microstructural evidence of extensive, syn-magmatic, internally-generated, viscous deformation in fully solidified silicic plutonic rocks. If subsequent directed searches do not reveal clear evidence for internally-generated buoyancy-driven melt segregation processes, it is likely that other factors, such as rejuvenation by magma replenishment, gas filter-pressing, or externally-imposed stress during regional deformation, are required to segregate large volumes of crystal-poor rhyolitic liquids from crustal mushy zones.     

Relevance of building site categories implementation into the land use plan in underground mining area in the region of Petrvald (Czech Republic)

Deep mining of mineral resources causes extensive changes in rock environment and ground morphology and must be considered in the land use planning. Subsidence as a result of underground mining activities in terrains is one of the serious geological hazards because they can effect slopes and damage engineering structures, settlement areas, natural lakes and allow infiltration of contaminant into the groundwater. The main aim of this article was implementation of the building site categories of underground mining regions into the land use plans. This case study area was selected from the region of Orlova town within the Ostrava-Karvina Coal district, and this region is one of the most affected areas by underground mining of black coal in the Czech Republic. Certain risk categories of land, where the individual categories express generalized influence of deep mining of coal in current and planned constructions were also represented in this article. Extensive variations caused by underground mining were identified within a wide variability of risk categories. An important finding was also the extensive variability over time, manifested by spatial variations in the stated categories in the studied time periods. Moreover, technical documentation of environmental impacts related to underground mining activities was provided; importance of existing and proposed underground mining projects that may significantly impact the land use was discussed and pointed out in this article, especially.