Imaging of the Shell Galaxies NGC 474 and NGC 7600, and Implications for their Formation

We present photometric observations of two shell galaxies, NGC 474 and NGC 7600. We examine the photometric colours and surface brightnesses of the shells and their host galaxies, and the isophotal parameters of each galaxy. In the case of NGC 474, we find that the shell formation is consistent with a merger origin although it is possible that the close companion NGC 470 is contributing to the shell system via mass transfer. NGC 7600 exhibits shell geometry and colours which also favour a merger origin.Comment: Accepted by MNRA

Fatty acid composition of sulfate-reducing bacteria isolated from deep-sea hydrothermal vent (13° N, East Pacific Rise)

Five strains of vibrio-shaped, mesophilic sulfate-reducing bacteria were isolated from the deep-sea hydrothermal vent site at 13° N on the East Pacific Rise. Phospholipid analyses demonstrated a high percentage of branched-chain fatty acids, including the known biomarker for Desulfovibrio, in all five strains. The cell-wall lipids showed a fatty acid composition markedly different from the phospholipids. While straight-chain fatty acids were predominant the biomarker fatty acid was absent. Based on the morphological characteristics and the fatty acid composition, we tentatively have assigned the isolates to the genus Desulfovibrio

Adaptive density estimation for stationary processes

We propose an algorithm to estimate the common density $s$ of a stationary process $X_1,...,X_n$. We suppose that the process is either $\beta$ or $\tau$-mixing. We provide a model selection procedure based on a generalization of Mallows' $C_p$ and we prove oracle inequalities for the selected estimator under a few prior assumptions on the collection of models and on the mixing coefficients. We prove that our estimator is adaptive over a class of Besov spaces, namely, we prove that it achieves the same rates of convergence as in the i.i.d framework

Detecting modules in dense weighted networks with the Potts method

We address the problem of multiresolution module detection in dense weighted networks, where the modular structure is encoded in the weights rather than topology. We discuss a weighted version of the q-state Potts method, which was originally introduced by Reichardt and Bornholdt. This weighted method can be directly applied to dense networks. We discuss the dependence of the resolution of the method on its tuning parameter and network properties, using sparse and dense weighted networks with built-in modules as example cases. Finally, we apply the method to data on stock price correlations, and show that the resulting modules correspond well to known structural properties of this correlation network.Comment: 14 pages, 6 figures. v2: 1 figure added, 1 reference added, minor changes. v3: 3 references added, minor change

Uptake of Pu(IV) by hardened cement paste in the presence of gluconate at high and low ionic strengths

The uptake of Pu(IV) by hardened cement paste (HCP) at degradation state I was investigated in the absence and presence of gluconate (GLU). Furthermore, the influence of the ionic strength was examined in different background electrolytes. Artificial cement pore water (ACW, pH = 13) was used for low ionic strength (I = 0.3 M), and cement pore water based on the diluted caprock solution (ACW-VGL, pH = 12.5) was used for high ionic strength (I = 2.5 M). Sorption experiments were performed under an Ar atmosphere using HCP in the HCP/GLU binary system ([GLU]0 = 1 × 10−1–1 × 10−8 M) and the HCP/Pu(IV)/GLU ternary system ([239Pu(IV)]0 = 1 × 10−8 M, [GLU]0 = 1 × 10−2 M) with solid-to-liquid (S/L) ratios of 0.5–50 g L–1 within a contact time of 72 h. GLU sorbs strongly on HCP; a saturation of the sorption sites of HCP with GLU was observed at [GLU] ≥ 1 × 10−4 M at S/L = 5 g L–1. The effects of the order of addition of the components Pu(IV) and GLU on the sorption of Pu(IV) on HCP were investigated. In the absence of GLU, a quantitative uptake (S% ≥ 99%) of Pu(IV) by HCP was observed, independent of the ionic strength of the background electrolytes. In the presence of 1 × 10−2 M GLU, the sorption of Pu(IV) on HCP was significantly lower. For X-ray absorption fine structure (XAFS) measurements, powder samples with Pu ([239Pu(III)]0 = 5 × 10−6 M) sorbed on HCP (S/L = 2.5 g L–1) were prepared at pH ≈ 13 in ACW and ACW-VGL, respectively. One additional sample was prepared in the presence of GLU ([GLU]0 = 1 × 10−2 M) with ACW-VGL as the electrolyte for comparison. Pu LIII-edge X-ray absorption near-edge structure (XANES) spectra show that Pu is in the tetravalent oxidation state after being taken up by the HCP. The structural parameters obtained from extended X-ray absorption fine structure (EXAFS) analysis and comparison with literature indicate incorporation of Pu(IV) into the calcium-silicate-hydrate (C-S-H) phases of HCP. The different ionic strengths and the presence of GLU had no influence on the near-neighbor environment of Pu in HCP