Compositions and taxonomy of 15 unusual carbonaceous chondrites

Abstract– We used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification: Acfer 094 (type 3.0, ungrouped CM‐related); Belgica‐7904 (mildly metamorphosed, anomalous, CM‐like chondrite, possibly a member of a new grouplet that includes Wisconsin Range (WIS) 91600, Dhofar 225, and Yamato‐86720); Dar al Gani (DaG) 055 and its paired specimen DaG 056 (anomalous, reduced CV3‐like); DaG 978 (type 3 ungrouped); Dominion Range 03238 (anomalous, magnetite‐rich CO3.1); Elephant Moraine 90043 (anomalous, magnetite‐bearing CO3); Graves Nunataks 98025 (type 2 or type 3 ungrouped); Grosvenor Mountains (GRO) 95566 (anomalous CM2 with a low degree of aqueous alteration); Hammadah al Hamra (HaH) 073 (type 4 ungrouped, possibly related to the Coolidge‐Loongana [C‐L] 001 grouplet); Lewis Cliff (LEW) 85311 (anomalous CM2 with a low degree of aqueous alteration); Northwest Africa 1152 (anomalous CV3); Pecora Escarpment (PCA) 91008 (anomalous, metamorphosed CM); Queen Alexandra Range 99038 (type 2 ungrouped); Sahara 00182 (type 3 ungrouped, possibly related to HaH 073 and/or to C‐L 001); and WIS 91600 (mildly metamorphosed, anomalous, CM‐like chondrite, possibly a member of a new grouplet that includes Belgica‐7904, Dhofar 225, and Y‐86720). Many of these meteorites show fractionated abundance patterns, especially among the volatile elements. Impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies. The metamorphosed CM chondrites comprise two distinct clusters on the basis of their Δ¹⁷O values: approximately ?4‰ for PCA 91008, GRO 95566, DaG 978, and LEW 85311, and approximately 0‰ for Belgica‐7904 and WIS 91600. These six meteorites must have been derived from different asteroidal regions.     

Anthropogenic influence of trace metals in sediments of the Al-Qilt catchment,West Bank,Palestine: 1. Contamination factor and bonding forms

Al-Qilt catchment, located east of both the Ramallah and Jerusalem districts is strongly influenced by waste waters discharged from Israeli settlements and Palestinian urban centers. In this research, our aim was to verify the chemical status of the surface sediments from the Al-Qilt catchment during 2008/2009. For this purpose, 36 surface sediment samples were collected and analyzed with ICP/MS within the fraction of below 63 μm. The extent of contamination of trace metals from Al-Qilt sediments sites were measured by evaluating the contamination factors (CF) from digestion by aqua regia and additionally by sequential extraction steps using the BCR-method. On the basis of the calculated CF, sediments appear particularly contaminated with Zn, Cu, Ag, Sn, Cd, Hg, Bi, and B. Three regions, Wadi Sweanit, Ras Al-Qilt, and Qalandiah have been identified as critical points of contamination. Trace metal inputs to the Al-Qilt catchment need to be kept under strict control in the future since Ras Al-Qilt is considered as one of the important springs in the area and is used for domestic purposes. Moreover, it will be susceptible to pollution if no action is taken to decrease the pollution at the upstream of Al-Qilt.     

New Methodology to Characterize Shear Behavior of Joints by Combination of Direct Shear Box Testing and Numerical Simulations

A new procedure is presented, which combines big shear box tests on rocks and corresponding numerical simulations with explicit consideration of joint roughness to get deeper insight into the shear behavior of rock joints. The procedure consists of three parts: (1) constant normal load- or CNS-shear box tests with registration of shear- and normal-components of stress and displacements and deduction of basis rock mechanical parameters; (2) high resolution 3D-scanning of joint surface to deduce joint topography; and (3) set-up, run and evaluation of 3-dimensional numerical model with explicit duplication of joint roughness as back-analysis of shear box tests. The numerical back-analysis provides deeper insight into the joint behavior at the micro-scale. Several parameters can be deduced, like micro-slope angle distribution, aperture size distribution, local normal stress distribution and detailed analysis of dilation in relation to shear direction. The potential of the new procedure is illustrated exemplary by shear box tests on slate.     

Why the fundamental plane of black hole activity is not simply a distance driven artifact

The fundamental plane of black hole activity is a non-linear correlation among radio core luminosity, X-ray luminosity and mass of all accreting black holes, both of stellar mass and supermassive, found by Merloni et al. [Merloni, A., Heinz, S., di Matteo, T. 2003. MNRAS 345, 1057 (MHD03)] and, independently, by Falcke et al. [Falcke, H., Körding, E., Markoff, S., 2004. A& A 414, 895]. Here we further examine a number of statistical issues related to this correlation. In particular, we discuss the issue of sample selection and quantify the bias introduced by the effect of distance in two of the correlated quantities. We demonstrate that the fundamental plane relation cannot be a distance artifact, and that its non-linearity must represent an intrinsic characteristic of accreting black holes. We also discuss possible future observational strategies to improve our understanding of this correlation.     

Response of precipitation over Greenland and the adjacent ocean to North Pacific warm spells during Dansgaard–Oeschger stadials

ABSTRACT Palaeoceanographic reconstructions from the North Atlantic indicate massive ice breakouts from East Greenland near the onset of cold Dansgaard–Oeschger (D–O) stadials. In contrast to these coolings in the North Atlantic area, a new sea-surface temperature record reveals concomitant warm spells in the northern North Pacific. A sensitivity experiment with an atmospheric general circulation model is used to test the potential impact of sea-surface warmings by 3.5 °C in the North Pacific, on top of otherwise cold stadial climate conditions, on the precipitation regime over the Northern Hemisphere ice sheets. The model predicts a maximum response over East Greenland and the Greenland Sea, where a 40% increase in net annual snow accumulation occurs. This remote effect of North Pacific warm spells on the East Greenland snow-accumulation rate may play an important role in generating D–O cycles by rebuilding the ice lost during ice breakouts. In addition, the increased precipitation over the Greenland Sea may help to sustain the D–O stadial climate state.     

Spherically symmetric cosmological perturbations in the de Donder gauge

Cosmological perturbations on a F-R-W background are considered in a modified de Donder gauge. To guarantee the energy-momentum conservation for the perturbations in the de Donder gauge a compatibility condition is obtained. Finally we present the basic equations for the propagation of spherically symmetric perturbations. These equations are the basis for investigating the influence of cosmological epoches on the growing of density contrasts.     

The effect of iron availability on the regulation of inorganic carbon acquisition in the coccolithophore Emiliania huxleyi and the significance of cellular compartmentation for stable carbon isotope fractionation

Iron is limiting phytoplankton productivity in large parts of today’s oceans, the so-called HNLC (high nutrient low chlorophyll) areas. It is a key component in photosynthesis during which inorganic carbon fixation in most phytoplankton species is sustained by so-called carbon concentrating mechanisms (CCMs). Here we investigate CCM regulation in the coccolithophore Emiliania huxleyi in response to varying degrees of iron limitation by means of membrane-inlet mass spectrometry. Compared to iron replete conditions rates of both active CO₂ and uptake were markedly reduced under iron limitation leading to significantly diminished growth rates. Moreover, there was a concomitant decrease in CCM efficiency, reflected in an increased CO₂ loss from the cell in relation to carbon fixation. Under such conditions higher values for carbon isotope fractionation (?_p) would be expected. However, direct measurements of ?_p showed that carbon isotope fractionation was insensitive to changes in growth rates and CCM activity. This can be explained by concomitant changes in internal DIC fluxes in and out of the chloroplast as demonstrated with a simple cell model comprising two compartments. Thus, carbon isotope fractionation reflects the ability of phytoplankton to actively control their inorganic carbon acquisition depending on environmental conditions. The insensitivity of carbon isotope fractionation to changes in the availability of iron could be of interest for paleoreconstructions in the HNLC areas of today’s oceans.     

Mechanical and microseismic characteristics of sandstones subject to moderate low-frequency differential cyclic loading (DCL) followed by monotonic loading up to failure

Acta Geotechnica - This work aims to experimentally investigate the behaviour of sandstone drilled from an underground coal mine exposed to low-frequency cyclic loading with distinct...     

Characteristics and generation mechanisms of key infrared radiation signals during damage evolution in sandstone

Acta Geotechnica - Infrared radiation count (IRC) is considered as an indicator for damage evolution of rocks. This new indicator links damage intensity and corresponding infrared radiation...