Filtering wireless (Wi-Fi) internet access in public places

This paper discusses selected results from the AHRC-funded ‘Managing Access to the Internet in Public Librarie s' (MAIPLE) project and explores Wi-Fi Internet access in UK public libraries. It investigates how this compares to commercial provision of public Wi-Fi. It discusses security issues, filtering of Wi-Fi access and acceptable use policies. A mixed methods approach was used involving a review of the literature, a questionnaire survey of UK public library authorities and five case studies of selected authorities. A majority of UK public library authorities offer Wi-Fi access to the public at one or more of their libraries and they generally have an authentication system in place for their users. The majority of survey respondents that provide Wi-Fi use filtering software. There are similarities and differences in the ways that public libraries and commercial outlets provide and manage access to their wireless networks. Differences mainly relate to security and privacy: these differences reflect to an extent the underlying purposes of providing public Wi-Fi access as well as legal obligations. In some ways, public library Wi-Fi access is better managed than commercially provided public services. Evidence from the case studies suggests reluctant acceptance of filtering on the part of public library authorities, based on a perceived need to balance providing access to information with providing a safe and trusted public space for all

Rhenium in seawater: Confirmation of generally conservative behavior

A depth profile of the concentration of Re was measured in the Pacific Ocean using a technique we have developed for the clean chemical separation and the precise measurement of Re by isotope dilution and negative thermal ionization mass spectrometry (ID-NTIMS). This technique permits Re concentrations to be determined from 200 mL of seawater with a typical precision of ±5‰. This is an improvement of at least a factor of 100 over the techniques used in previously published determinations of Re in seawater. We obtain a narrow range for Re from 7.20 ± 0.03 to 7.38 ± 0.03 ng/kg for depths between 45 m and 4700 m. This demonstrates that Re is relatively well mixed throughout the water column and confirms the theoretical prediction that the behavior of Re in the oceans is conservative. When examined in detail, both salinity and the concentration of Re increase by approximately 1.5% between 400 and 4700 m, a correlation consistent with conservative behavior. However, Re appears to be depleted relative to salinity by 1.0–1.5% at 100 m, and enriched by approximately 4% at the surface. These observations suggest a minor level of Re scavenging in near surface waters, and an input of Re to the ocean surface. This work demonstrates the utility of ID-NTIMS for geochemical investigations of certain trace elements that have not previously been amenable to detailed study

The World's Highest-Grade Cobalt Mineralization at Bou Azzer Associated With Gondwana Supercontinent Breakup, Serpentinite and Kellwasser Hydrocarbon Source Rocks

Cobalt arsenide deposits associated with Neoproterozoic serpentinite in Morocco represent the highest-grade cobalt resource worldwide. Yet, genetic models for their origin remain controversial. We report here mineralogical and geochemical evidence for arsenide-calcite mineralization at Bou Azzer to constrain the temporal framework and identify the geodynamic trigger for mineralization mechanisms. To this end, radiometric ages for ore minerals are paramount for understanding the origin of the Bou Azzer cobalt arsenide deposit. New safflorite (CoAs2) rhenium-osmium (Re-Os) ages are Late Devonian in age: 380.4 ± 2.9 and 373.4 ± 1.2 to 368.1 ± 5.0 million years ago (Ma) for coarse-grained and fine-grained safflorite, respectively. These dates overlap with the timing of break-up of the supercontinent Gondwana, and the building of an arch-and-basin geometry from northern Africa to Arabia. Our findings temporally and spatially contextualize previous knowledge of fluid chemistry and mineralization mechanisms involving a two-fluid mixing. Arsenide mineralization resulted from mixing of a methane-dominated fluid with highly saline basinal brines that leached Os (187Os/188Osinitial = 0.120 ± 0.001), and by corollary cobalt, from Neoproterozoic serpentinite. Carbon and sulfur stable isotope data of ore-stage calcite and arsenides, respectively, show that hydrocarbons acted as the main reductant for mineralization. We speculate that the seawater-derived brines sank into the sedimentary basins adjacent to a carbonate platform with the Bou Azzer serpentinite in its basement in the Late Devonian. In the context of an enhanced geothermal gradient, such brines would have been involved in warm hydrothermal alteration of hydrocarbon source rocks of the local expression of the Kellwasser event in the geological record of present-day Morocco. This warm hydrothermal alteration of hydrocarbon source rocks may have taken place for coarse-grained safflorite mineralization (380.4 ± 2.9 Ma) shortly after ca. 382–381 Ma Lower Kellwasser horizons were deposited, or, for fine-grained safflorite mineralization (373.4 ± 1.2 to 368.1 ± 5.0 Ma) while the Upper Kellwasser horizons of present-day Morocco were being deposited

Embracing ligands. A synthetic strategy towards new nitrogen-thioether multidentate ligands and characterization of the cobalt(III) complexes

The synthesis of the hexadentate ligand 2,2,9,9-tetra(methyleneamine)-4,7-dithiadecane (EtN(4)S(2)amp) is reported. The ligand is of a type in which bifurcations of the chain occur at atoms other than donor atoms. The cobalt(III) complex [Co(EtN(4)S(2)amp)](3+) (1) was isolated and characterized. The synthetic methodology also results in a number of by-products, notably 2,9,9-tris(methyleneamine)-9-methylenehydroxy-4,7-dithiadecane (Et(HO)N(3)S(2)amp) and an eleven-membered pendant arm macrocyclic ligand 6,10-dimethyl-6,10-bis(methyleneamine)-1,4-dithia-8-azaacycloundec-7- ene (dmatue). The complexes [Co(Et(HO)N(3)S(2)amp)](3+) (2), in which the alcohol is coordinated to the metal ion, and [Co(dmatue)Cl](2+) (4) were isolated and characterized. Et(HO)N(3)S(2)amp also undergoes complexation with cobalt(III) to produce two isomers endo-[Co(Et(HO) N(3)S(2)amp)Cl](2+) (endo-3) and exo-[Co(Et(HO) N(3)S(2)amp)Cl](2+) (exo-3), both with an uncoordinated alcohol group. endo- 3 has the alcohol positioned cis, and exo-3 trans, to the sixth metal coordination site. Reaction of 1 with isobutyraldehyde, paraformaldehyde and base in dimethylformamide results in the encapsulated complex [Co(1,5,5,9,13,13-hexamethyl-18,21-dithia-3,7,11,15-tetraazabicyclo[7.7.6]docosa- 3,14-diene)](ClO4)(3) . 2H(2)O ([Co(Me(6)docosadieneN(4)S(2))](3+) ( 5). All complexes have been characterized by single crystal X-ray study. The low-temperature (11 K) absorption spectrum of 1 has been measured in Nafion films with spin-allowed (1)A(1g) --> T-1(1g) and (1)A(1g) --> T-1(2g) and spin forbidden (1)A(1g) --> T-3(1g) and (1)A(1g) --> T-3(2g) bands observed. The octahedral ligand-field parameters were determined (10Dq = 22570 cm(-1), B = 551 cm(-1); C = 3500 cm(-1)). For 5 10Dq and B were determined (20580 cm(-1); 516 cm(-1), respectively) and compared with those for similar expanded cavity complexes [Co(Me(8)tricosatrieneN(6))](3+) and [Co(Me(5)tricosatrieneN(6))](3+)

Embracing ligands. Synthesis, characterisation and the correlation between 59Co NMR and ligand field parameters of Co(III) complexes with a new class of nitrogen-thioether multidentate ligand

The syntheses of the hexadentate ligands 2,2,10,10-tetra(methyleneamine)-4,8-dithiaundecane (PrN(4)S(2)amp), 2,2,11,11-tetra(methyleneamine)-4,9-dithiadodecane (BuN(4)S(2)amp), and 1,2-bis(4,4-methyleneamine)-2-thiapentyl)benzene (XyN(4)S(2)amp) are reported and the complexes [Co(RN(4)S(2)amp)](3+) (R = Pr, Bu, Xy) characterised by single crystal X-ray study. The low-temperature (11 K) absorption spectra have been measured in Nafion films. From the observed positions of both spin-allowed (1)A(1g) --> T-1(1g) and (1)A(1g) --> T-1(2g) and spin forbidden (1)A(1g) --> T-3(1g) and (1)A(1g) --> T-3(2g) bands, octahedral ligand-field parameters (10D(q), B and C) have been determined. DFT calculations suggest that significant interaction between the d-d and CT excitations occurs for the complexes. The calculations offer an explanation for the observed deviations from linearity of the relationship between Co-59 magnetogyric ratio and beta(DeltaE)(-1) (beta = the nephelauxetic ratio; DeltaE the energy of the (1)A(1g) --> T-1(1g) transition) for a series of amine and mixed amine/thioether donor complexes

Nucleosynthetic osmium isotope anomalies in acid leachates of the Murchison meteorite

We present osmium isotopic results obtained by sequential leaching of the Murchison meteorite, which reveal the existence of very large internal anomalies of nucleosynthetic origin. The Os isotopic anomalies are correlated, and can be explained by the variable contributions of components derived from the s, r and p-processes of nucleosynthesis. Much of the s-process rich osmium is released by relatively mild leaching, suggesting the existence of an easily leachable s-process rich presolar phase, or alternatively, of a chemically resistant r-process rich phase. The s-process composition of Os released by mild leaching diverges slightly from that released by aggressive digestion techniques, perhaps suggesting that the presolar phases attacked by these differing procedures condensed in different stellar environments. The correlation between 190Os and 188Os can be used to constrain the s-process 190Os/188Os ratio to be 1.275 pm 0.043. Such a ratio can be reproduced in a nuclear reaction network for a MACS value for 190Os of ~200 pm 22 mbarn at 30 keV. We also present evidence for extensive internal variation of 184Os abundances in the Murchison meteorite. This suggests that p process rich presolar grains (e.g., supernova condensates) may be present in meteorites in sufficient quantities to influence the Os isotopic compositions of the leachates.Comment: 40 pages, 9 figures, 2 tables. Accepted for publication in Earth and Planetary Science Letter