On the Origin of Near-Infrared Extragalactic Background Light Anisotropy

Extragalactic background light (EBL) anisotropy traces variations in the total production of photons over cosmic history, and may contain faint, extended components missed in galaxy point source surveys. Infrared EBL fluctuations have been attributed to primordial galaxies and black holes at the epoch of reionization (EOR), or alternately, intra-halo light (IHL) from stars tidally stripped from their parent galaxies at low redshift. We report new EBL anisotropy measurements from a specialized sounding rocket experiment at 1.1 and 1.6 micrometers. The observed fluctuations exceed the amplitude from known galaxy populations, are inconsistent with EOR galaxies and black holes, and are largely explained by IHL emission. The measured fluctuations are associated with an EBL intensity that is comparable to the background from known galaxies measured through number counts, and therefore a substantial contribution to the energy contained in photons in the cosmos.Comment: 65 pages, 29 figures, Published in Science Nov 7 2014 (includes supplementary material

Intrinsic electrochemical activity of single walled carbon nanotube–Nafion assemblies

The intrinsic electrochemical properties and activity of single walled carbon nanotube (SWNT) network electrodes modified by a drop-cast Nafion film have been determined using the one electron oxidation of ferrocene trimethyl ammonium (FcTMA+) as a model redox probe in the Nafion film. Facilitated by the very low transport coefficient of FcTMA+ in Nafion (apparent diffusion coefficient of 1.8 × 10−10 cm2 s−1), SWNTs in the 2-D network behave as individual elements, at short (practical) times, each with their own characteristic diffusion, independent of neighbouring sites, and the response is diagnostic of the proportion of SWNTs active in the composite. Data are analysed using candidate models for cases where: (i) electron transfer events only occur at discrete sites along the sidewall (with a defect density typical of chemical vapour deposition SWNTs); (ii) all of the SWNTs in a network are active. The first case predicts currents that are much smaller than seen experimentally, indicating that significant portions of SWNTs are active in the SWNT–Nafion composite. However, the predictions for a fully active SWNT result in higher currents than seen experimentally, indicating that a fraction of SWNTs are not connected and/or that not all SWNTs are wetted completely by the Nafion film to provide full access of the redox mediator to the SWNT surface

Single Crystal Investigations Unravel the Magnetic Anisotropy of the “Square-In Square” Cr4Dy4 SMM Coordination Cluster

In the search for new single molecule magnets (SMM), i.e., molecular systems that can retain their magnetization without the need to apply an external magnetic field, a successful strategy is to associate 3d and 4f ions to form molecular coordination clusters. In order to efficiently design such systems, it is necessary to chemically project both the magnetic building blocks and the resultant interaction before the synthesis. Lanthanide ions can provide the required easy axis magnetic anisotropy that hampers magnetization reversal. In the rare examples of 3d/4f SMMs containing CrIII ions, the latter turn out to act as quasi-isotropic anchors which can also interact via 3d-4f coupling to neighbouring Ln centres. This has been demonstrated in cases where the intramolecular exchange interactions mediated by CrIII ions effectively reduce the efficiency of tunnelling without applied magnetic field. However, describing such high nuclearity systems remains challenging, from both experimental and theoretical perspectives, because the overall behaviour of the molecular cluster is heavily affected by the orientation of the individual anisotropy axes. These are in general non-collinear to each other. In this article, we combine single crystal SQUID and torque magnetometry studies of the octanuclear [Cr4Dy4(μ3-OH)4(μ-N3)4(mdea)4(piv)8]·3CH2Cl2 single molecule magnet (piv=pivalate and mdea=N-methyldiethanol amine). These experiments allowed us to probe the magnetic anisotropy of this complex which displays slow magnetization dynamics due to the peculiar arrangement of the easy-axis anisotropy on the Dy sites. New ab initio calculations considering the entire cluster are in agreement with our experimental results

A communal catalogue reveals Earth’s multiscale microbial diversity

Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity

A communal catalogue reveals Earth's multiscale microbial diversity

Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.Peer reviewe

Single Crystal Investigations Unravel the Magnetic Anisotropy of the "Square-In Square" Cr4Dy4 SMM Coordination Cluster

In the search for new single molecule magnets (SMM), i.e., molecular systems that can retain their magnetization without the need to apply an external magnetic field, a successful strategy is to associate 3d and 4f ions to form molecular coordination clusters. In order to efficiently design such systems, it is necessary to chemically project both the magnetic building blocks and the resultant interaction before the synthesis. Lanthanide ions can provide the required easy axis magnetic anisotropy that hampers magnetization reversal. In the rare examples of 3d/4f SMMs containing CrIII ions, the latter turn out to act as quasi-isotropic anchors which can also interact via 3d-4f coupling to neighbouring Ln centres. This has been demonstrated in cases where the intramolecular exchange interactions mediated by CrIII ions effectively reduce the efficiency of tunnelling without applied magnetic field. However, describing such high nuclearity systems remains challenging, from both experimental and theoretical perspectives, because the overall behaviour of the molecular cluster is heavily affected by the orientation of the individual anisotropy axes. These are in general non-collinear to each other. In this article, we combine single crystal SQUID and torque magnetometry studies of the octanuclear [Cr4Dy4(μ3-OH)4(μ-N3)4(mdea)4(piv)8]·3CH2Cl2 single molecule magnet (piv=pivalate and mdea=N-methyldiethanol amine). These experiments allowed us to probe the magnetic anisotropy of this complex which displays slow magnetization dynamics due to the peculiar arrangement of the easy-axis anisotropy on the Dy sites. New ab initio calculations considering the entire cluster are in agreement with our experimental results.status: publishe