Iterative Spherical Downward Continuation Applied to Magnetic and Gravitational Data from Satellite

In the last few decades, satellites have acquired various potential data sets hundreds of kilometers above the Earth’s surface. Conventionally, these global magnetic and gravitational data sets are approximated by using spherical harmonics that allow straightforward work with both fields outside the Earth’s mass. In this article, we present an alternative approach for working with potential data in mass-free space given over a regular coordinate grid on a spherical surface. The algorithm is based on an iterative scheme and the Poisson integral equation for the sphere. With help from the Fourier transform, global potential (magnetic or gravitational) data can efficiently be continued from a mean orbital sphere down to a reference surface without using the spherical harmonics. This is illustrated both with simulated magnetic field data and with real data from the satellite gradiometry mission GOCE. In the case of simulated magnetic data and the downward continuation for 450 km, we have achieved a root mean square at the level of 0.05 nT, while it was <1 E (eotvos) for real GOCE data continued for 250 km. The crucial point is to apply the algorithm twice as a large part of noise can be removed from the input data.     

On the spatial structure and dispersion of slow magnetosonic modes coupled with Alfvén modes in planetary magnetospheres due to field line curvature

The structure of the slow mode coupled with Alfvén mode in the axially symmetric magnetosphere is studied in the paper. Due to the coupling, the slow magnetosonic wave gets dispersion across magnetic shells and becomes not strictly guided. The slow mode is found to be captured between the resonant and cutoff surfaces, where the wave vector radial component goes to infinity and to zero, accordingly. The resonant surface is farther from the Earth than the cutoff surface. The slow mode resonance frequency is much lower than the Alfvén resonance frequency due to small value of the sound velocity near the equator. The maximum of the slow mode amplitude expressed in terms of the parallel magnetic field is concentrated near the equator, but expressed in hydromagnetic terms is concentrated near the ionospheres.     

The influence of gas expulsion and initial mass segregation on the stellar mass function of globular star clusters

Recently, De Marchi, Paresce & Pulone studied a sample of 20 globular clusters and found that all clusters with high concentrations have steep stellar mass functions while clusters with low concentration have comparatively shallow mass functions. No globular clusters were found with a flat mass function and high concentration. This seems curious since more concentrated star clusters are believed to be dynamically more evolved and should have lost more low-mass stars via evaporation, which would result in a shallower mass function in the low-mass part.
We show that this effect can be explained by residual-gas expulsion from initially mass segregated star clusters, and is enhanced further through unresolved binaries. If gas expulsion is the correct mechanism to produce the observed trend in the   c –α  -plane, then observation of these parameters would allow to constrain cluster starting conditions such as star formation efficiency and the time-scale of gas expulsion.     

Video Observations of the 2006 Leonid Outburst

We carried out double station observations of the Leonid meteor shower outburst, which occurred in the morning hours of November 19, 2006. Using image-intensified cameras we recorded approximately 100 Leonid meteors. As predicted, the outburst was rich especially in fainter meteors. The activity profile shows that the peak of the outburst occurred at 4:40 ± 0:05 UT. The maximum reached flux was 0.03 meteoroids km⁻² hod⁻¹ for meteors brighter than +6.5 magnitude.     

Improvements of drilling fluid processing for cable-suspended electromechanical drills

Deep ice drilling in Polar Regions plays a key role in paleo-climate, microbiological and glaciological researches. For deep ice and subglacial coring the special purpose-built electromechanical cable-suspended drills with bottom-hole circulation are designed and explored. Used at present drilling fluid circulation systems are specified by very high fluid wastes during processing. Measurements in deep drilling projects in Antarctic and Greenland ice sheets showed that 25%-40% of the drilling fluid, pumped into the hole, is retrieved to the surface with cable and drill, and up to 45% of retrieved fluid goes to waste. This leads not only to increasing of the fluid consumption and cost of the project in general but also to severe contamination of air, surface and near-surface snow-firn layers at the drilling site. In order to reduce wastes and environmental impact, it is proposed to modify drilling fluid processing system by avoiding of evaporation and leakages of fluid as far as practicable. Drilling fluid is prepared and pumped into the hole according to predetermined program on semiautomatic mode, and volume and density of blended and pumped into the hole drilling fluid are measured continuously. Components of the drilling fluid are stored and mixed in the special closed containers equipped by pressure relief valves. Separation of drilling fluid from ice cuttings is carried out by two steps: firstly, fluid is separated with hydro extractor and then with thermal separator. To reduce the amount of removed drilling fluid with cable special squeezing collar is installed on the borehole mouth. All these arrangements are able to decrease drilling fluid wastes in many times.     

Russian researchers reach subglacial Lake Vostok in Antarctica

Opening a new scientific frontier lying under the Antarctic ice, Russian researchers have drilled down and finally reached the surface of the gigantic freshwater lake, Lake Vostok. The mission chief likened the achievement to placing a man on the moon. Drilling in the area of the lake began 22 years ago in 1990, but progressed slowly as a result of funding shortages, equipment breakdowns, difficulties of drilling in the ＂warm＂ ice, and environmental concerns. In 1996, six years after drilling was started, a group of Russian and British scientists discovered the lake believed to be one of the largest fresh water reservoirs on the planet. This lake is among the last unexplored places on Earth. Sealed from the Earth＇s atmosphere for millions of years, it may provide vital information about microbial evolution, the past climate of the Earth, and the formation of the Antarctic ice sheet. Russian experts waited several years for international approval of their drilling technology before proceeding. As anticipated, lake water under pressure rushed up the borehole, pushing the drilling fluid up and away, then froze, forming a protective plug that prevented contamination of the lake. In December of the next Antarctic season, 2012--2013, researchers plan to re-drill the frozen sample of subglacial water for analysis.     

Simultaneous measurements of the two-dimensional distribution of infrared laser intensity and temperature in a single-sided laser-heated diamond anvil cell

In this report, we demonstrate that combining the laser heating system in a diamond anvil cell (LH-DAC) with a tandem acoustic-optical tunable filter (LH-DAC–TAOTF) allows for the simultaneous measurement of (a) the relative infrared (IR, 1070 nm) power distribution on a specimen surface in the DAC; (b) the temperature distribution under laser heating of a specimen under high-pressure in a DAC; it also (c) provides an opportunity to control the shape of the IR laser spot on the surface of the heated specimen. The effect of the π-shaper on the shape and the position of the focus of the IR laser beam on a specimen using a TAOTF is also presented. For a 10× long-working distance objective, the smallest diameter of the IR laser was found to be around 10 μm, when the focal plane coincides with that of the imaging optical system of LH-DAC. The highest diameter of the IR laser was shown to be 20 μm when the rim of the π-shaper was set at 3 μm. It is demonstrated also that the TAOFT not only permits to measure the two-dimensional (2-D) distribution of the IR laser power, but also allows for the alignment of the laser before each heating event at different pressures.     

Magnetic susceptibility of cambisol profiles in the vicinity of the Vír dam,Czech Republic

Magnetic susceptibility of 72 cambisol profiles from the vicinity of the Vír dam, NW Moravia was measured. The enhanced susceptibility of topsoil, particularly of the horizon O, was assessed from the aspect of vegetation setting and magnetic mineralogy. Magnetic susceptibility variations with field and temperature as well as frequency dependent susceptibility were applied to indicate magnetic carriers. It was found that the enhanced magnetic susceptibility is caused very likely by the presence of maghemite and magnetite of various grain sizes. Magnetic minerals are pedogenic in origin in all three horizons, while in the O and A horizons they are mostly anthropogenic in origin. Magnetic susceptibility was correlated with contents of trace elements Mo, Cu, Pb, Zn, Ag, As, Cd, Sb, Bi, Hg, Se, furthermore with TOT/C, TOT/S, and ¹³⁷C. The close association of susceptibility with Pb, Sb and Hg, or also with Mo, As, Se and their similar depth variations suggest a slight anthropogenic input in soils from a long-distant source. The same is valid for ¹³⁷C, its strong correlation with magnetic susceptibility has been found.     

Magnetostratigraphy and fold tests from Račiška pečina and Pečina v Borštu caves (Classical Karst,Slovenia)

Clastic and chemogenic cave sediments were sampled and analyzed from Račiška pečina and Pečina v Borštu caves of southwestern Slovenia. Samples were subjected to both thermal and alternating field demagnetization; specimens belonging to the same sample of the same layer produce identical results. Unblocking temperatures of 540 to 560°C on average suggests magnetite as the principal carrier of magnetization. These directions also pass a reversals test indicating the demagnetization results are free of secondary overprints and have adequately averaged out paleosecular variation. Normally magnetized clays containing fauna belonging to the MN17 mammal biozone at a depth of ∼ 4 m in Račiška pecina cave indicate these clays were deposited at the beginning of the Olduvai subchron (1.95 Ma). Correlation with the Geomagnetic Polarity Time Scale (GPTS) indicates the base of the speleothems in Račiška pečina terminate in the upper part of subchron C2An.3n with numerous breaks in deposition, lasting up to 250 ka and more. Therefore rates of speleothem growth cannot be calculated. Fold tests on dome-like stalagmites of differing sizes and ages (Pleistocene, Pliocene) from the two caves indicate the domelike structures are primary.     

Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U–Pb zircon and Sr–Nd isotopic evidence from the Brunovistulian Domain,eastern Bohemian Massif

International Journal of Earth Sciences - Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and...