Abundance and isotopic composition of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite

Abstract— Abundances and isotopic compositions of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite were measured. The abundance ratios of spallogenic components in metal reveal a ³He deficiency which is due to the diffusive loss of parent isotopes, that is, tritium (Tilles, 1963; Schultz, 1967). The diffusive loss likely has been induced by thermal heating by the Sun during cosmic‐ray exposure (～160 Ma; Lavielle et al, 1999). Thermal process such as impact‐induced partial loss may have affected the isotopic composition of spallogenic Ne. The ¹²⁹Xe/¹³¹Xe ratio of cosmogenic components in the metal indicates an enhanced production of epi‐thermal neutrons. The abundance ratios of spallogenic components in the graphite reveal that it contained small amounts of metal and silicates. The isotopic composition of heavy noble gases in graphite itself was obtained from graphite treated with HF/HCl. The isotopic composition of the etched graphite shows that it contains two types of primordial Xe (i.e., Q‐Xe and El Taco Xe). The isotopic heterogeneity preserved in the Bohumilitz graphite indicates that the Bohumilitz graphite did not experience any high‐temperature event and, consequently, must have been emplaced into the metal at subsolidus temperatures. This situation is incompatible with an igneous model as well as the impact melting models for the IAB‐IIICD iron meteorites as proposed by Choi et al. (1995) and Wasson et al (1980).     

Structure of the South Powell Ridge (NE Antarctic Peninsula): new clues for changing tectonic regimes near the Scotia/Antarctica Plate boundary

The structure of the South Powell Ridge (SPR), separating the Late Cenozoic ocean-floored Powell Basin and the Mesozoic Weddell Sea domain, is revealed by multichannel seismic data. The SPR appears as a basement high, bounded northward by transtensional faults and by normal and major reverse faults to the south. These margin features seem to be linked to the Powell Basin southern strike-slip margin and to the Jane Arc paleotrench, respectively. We suggest the ridge evolved from the Antarctic Peninsula passive margin to become the deformational front of the Scotia/Antarctica Plate boundary, later being welded to the Antarctic Plate. Received: 18 August 1997 / Revision received: 4 May 1998     

First results from the North Iceland experiment

Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system.     

Nest microhabitat selection in larks from a European semi-arid shrub-steppe: the role of sunlight and predation

We analysed nest site selection in two shrub-steppe larks, the lesser short-toed larkCalandrella rufescensand the Thekla larkGalerida theklae. Both species nest on the ground next to a bush preferably facing north or north-east. Nestling growth and fledging weight are greater when the nest faces these directions. Both species prefer to nest next to camephytes with little foliage, and the lesser short-toed lark chooses sites with high visibility. We conclude that sunlight and nest predation are fundamental selective pressures determining nest microhabitat selection in larks in semi-arid areas.     

Periodic orbits in the restricted four-body problem with two equal masses

The restricted (equilateral) four-body problem consists of three bodies of masses m ₁, m ₂ and m ₃ (called primaries) lying in a Lagrangian configuration of the three-body problem i.e., they remain fixed at the apices of an equilateral triangle in a rotating coordinate system. A massless fourth body moves under the Newtonian gravitation law due to the three primaries; as in the restricted three-body problem (R3BP), the fourth mass does not affect the motion of the three primaries. In this paper we explore symmetric periodic orbits of the restricted four-body problem (R4BP) for the case of two equal masses where they satisfy approximately the Routh’s critical value. We will classify them in nine families of periodic orbits. We offer an exhaustive study of each family and the stability of each of them.     

The role of flares, CMEs and CME shocks in the generation of solar energetic proton events

We examined solar energetic proton (SEP) events associated with intense H flares. We located these flares on the solar disk and obtained their distribution in heliographic longitude as well as their angular distance distribution with respect to the neutral lines corresponding to the heliospheric current sheet at 2.5R. We found that the SEP-associated H flares tend to occur in active regions at the feet of those helmet streamers which form the heliomagnetic equator and are related to coronal mass ejections (CMEs) and CME shocks. We discuss the possible role of flares, CMEs and CME shocks in generating SEPs.     

An array of lens-coupled antennas for cosmic microwave background measurements in the 30 Ghz band

An array of bow-tie slot antennas coupled through an extended hemispherical lens is proposed to operate in the 30?GHz frequency band. The design includes a combination of three microstrip Wilkinson power dividers (WPD) and transitions to coplanar wave guides (CPW) to form the feeding antenna network. This configuration is suitable for the integration with heterodyne imaging detectors commonly used in radioastronomy. Measurements and simulation results exhibit a frequency range of operation from 20 to 40?GHz with a bandwidth of 24% achieved for ?10?dB return loss at the central frequency. The measured radiation patterns show a maximum peak gain of around 13?dB with HPBW of 10° for the E-plane, and whose first side lobes are lower than 13?dB below the main lobe in both angular shift sides. The presented results will be considered as preliminary feasibility studies in the 30?GHz QUIJOTE-CMB Instrument, which is designed to study the anisotropies of the Cosmic Microwave Background (CMB).     

The Dar al Gani meteorite field (Libyan Sahara): Geological setting,pairing of meteorites,and recovery density

Abstract— As of July 2001, 1238 Libyan meteorites have been reported. Most were found in two areas called Dar al Gani and Hamadah al Hamra. Dar al Gani is located on a plateau of marine carbonate rocks with marly components. Eight‐hundred and sixty‐nine meteorites between 6 g and 95 kg totalling 687 kg have been found here but the calculated mean recovery density is comparatively low with one meteorite on 6.5 km². Dar al Gani is a perfect site for the recognition and preservation of meteorites. The existence of meteorites is the result of a combination of specific geological and geomorphological conditions: there is a bright‐colored, old limestone plateau (<2 Ma), under arid weather conditions over long periods of time, with rapid elimination of surface water if present and low erosion rates. The preservation of meteorites is guaranteed through the absence of quartz sand on the plateau, strongly reducing wind erosion and a basic environment emerging from the carbonate ground retards rusting of metallic meteorite components. A supposed soil cover during pluvial times has probably protected older meteorites and led to a concentration of meteorites of different periods. An evaluation of Dar al Gani meteorites suggests the existence of at least 26 strewnfields and 26 meteorite pairs reducing the number of falls to, at most, 534. Shock and weathering grades as a tool for the recognition of pairings turned out to be problematic, as several strewnfields showed paired meteorites which had been classified to different shock and weathering grades.     

Multiperiodic semiregular variable stars in the ASAS data base: A pilot study

Based on a search for multi‐periodic variability among the semi‐regular red variable stars in the database of the All Sky Automated Survey (ASAS), a sample of 72 typical examples is presented. Their period analysis was performed using the Discrete Fourier Transform. In 41 stars we identified two significant periods each, simultaneously present, while the remaining 31 cases revealed even three such periods per star. They occur in a range roughly between 50 and 3000 days. Inter‐relationships between these periods were analyzed using the “double period diagram” which compares adjacent periods, and the so‐called “Petersen diagram”, the period ratio vs. the shorter period. In both diagrams we could identify six sequences of accumulation of the period values. For five of these sequences (containing 97 % of all data points) we found an almost perfect coincidence with those of previous studies which were based on very different samples of semiregular red variables. Therefore, existence and locations of these sequences in the diagrams seem to be universal features, which appear in any data set of semi‐regularly variable red giants of the AGB; we conclude that they are caused by different pulsation modes as the typical and consistent properties of similar stellar AGB configurations. Stellar pulsations can be considered as the principal cause of the observed periodic variability of these stars, and not binary, rotation of a spotted surface or other possible reasons suggested in the literature. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)