Spin-polarized proximity effect in superconducting junctions

We study spin dependent phonomena in superconducting junctions in both ballistic and diffusive regimes. For ballistic junctions we study both ferromagnet / $s$- and d-wave superconductor junctions and two dimensional electron gas / s-wave superconductor junctions with Rashba spin-orbit coupling. It is shown that the exchange field alway suppresses the conductance while the Rashba spin-orbit coupling can enhance it. In the latter part of the article we study the diffusive ferromagnet / insulator / $s$- and d-wave superconductor junctions, where the proximity effect can be enhanced by the exchange field in contrast to common belief. It is shown that the resonant proximity effect originating from the exchange field strongly influences the tunneling conductance and density of states.Comment: 14 pages, 7 figures, submitted to Comptes Rendus de l'Acadeacute;mie des Sciences (Comptes Rendus Physique) Special Issue " Magnetism and Superconductivity Coexistence". Figures 4-7 are modified in v

The Towuti Drilling Project:paleoenvironments, biological evolution, and geomicrobiology of a tropical Pacific lake

The Towuti Drilling Project (TDP) is an international research program, whose goal is to understand long-term environmental and climatic change in the tropical western Pacific, the impacts of geological and environmental changes on the biological evolution of aquatic taxa, and the geomicrobiology and biogeochemistry of metal-rich, ultramafic-hosted lake sediments through the scientific drilling of Lake Towuti, southern Sulawesi, Indonesia. Lake Towuti is a large tectonic lake at the downstream end of the Malili lake system, a chain of five highly biodiverse lakes that are among the oldest lakes in Southeast Asia. In 2015 we carried out a scientific drilling program on Lake Towuti using the International Continental Scientific Drilling Program (ICDP) Deep Lakes Drilling System (DLDS). We recovered a total of  ∼ 1018 m of core from 11 drilling sites with water depths ranging from 156 to 200 m. Recovery averaged 91.7 %, and the maximum drilling depth was 175 m below the lake floor, penetrating the entire sedimentary infill of the basin. Initial data from core and borehole logging indicate that these cores record the evolution of a highly dynamic tectonic and limnological system, with clear indications of orbital-scale climate variability during the mid- to late Pleistocene

Metabolic Capability and Phylogenetic Diversity of Mono Lake during a Bloom of the Eukaryotic Phototroph Picocystis sp. Strain ML

Algal blooms in lakes are often associated with anthropogenic eutrophication; however, they can occur without the human introduction of nutrients to a lake. A rare bloom of the alga Picocystis sp. strain ML occurred in the spring of 2016 at Mono Lake, a hyperalkaline lake in California, which was also at the apex of a multiyear-long drought. These conditions presented a unique sampling opportunity to investigate microbiological dynamics and potential metabolic function during an intense natural algal bloom. We conducted a comprehensive molecular analysis along a depth transect near the center of the lake from the surface to a depth of 25 m in June 2016. Across sampled depths, rRNA gene sequencing revealed that Picocystis-associated chloroplasts were found at 40 to 50% relative abundance, greater than values recorded previously. Despite high relative abundances of the photosynthetic oxygenic algal genus Picocystis, oxygen declined below detectable limits below a depth of 15 m, corresponding with an increase in microorganisms known to be anaerobic. In contrast to previously sampled years, both metagenomic and metatranscriptomic data suggested a depletion of anaerobic sulfate-reducing microorganisms throughout the lake's water column. Transcripts associated with photosystem I and II were expressed at both 2 m and 25 m, suggesting that limited oxygen production could occur at extremely low light levels at depth within the lake. Blooms of Picocystis appear to correspond with a loss of microbial activity such as sulfate reduction within Mono Lake, yet microorganisms may survive within the sediment to repopulate the lake water column as the bloom subsides

Metabolic Capability and Phylogenetic Diversity of Mono Lake during a Bloom of the Eukaryotic Phototroph Picocystis sp. Strain ML

Algal blooms in lakes are often associated with anthropogenic eutrophication; however, they can occur without the human introduction of nutrients to a lake. A rare bloom of the alga Picocystis sp. strain ML occurred in the spring of 2016 at Mono Lake, a hyperalkaline lake in California, which was also at the apex of a multiyear-long drought. These conditions presented a unique sampling opportunity to investigate microbiological dynamics and potential metabolic function during an intense natural algal bloom. We conducted a comprehensive molecular analysis along a depth transect near the center of the lake from the surface to a depth of 25 m in June 2016. Across sampled depths, rRNA gene sequencing revealed that Picocystis-associated chloroplasts were found at 40 to 50% relative abundance, greater than values recorded previously. Despite high relative abundances of the photosynthetic oxygenic algal genus Picocystis, oxygen declined below detectable limits below a depth of 15 m, corresponding with an increase in microorganisms known to be anaerobic. In contrast to previously sampled years, both metagenomic and metatranscriptomic data suggested a depletion of anaerobic sulfate-reducing microorganisms throughout the lake's water column. Transcripts associated with photosystem I and II were expressed at both 2 m and 25 m, suggesting that limited oxygen production could occur at extremely low light levels at depth within the lake. Blooms of Picocystis appear to correspond with a loss of microbial activity such as sulfate reduction within Mono Lake, yet microorganisms may survive within the sediment to repopulate the lake water column as the bloom subsides

Carnosine:can understanding its actions on energy metabolism and protein homeostasis inform its therapeutic potential?

The dipeptide carnosine (β-alanyl-L-histidine) has contrasting but beneficial effects on cellular activity. It delays cellular senescence and rejuvenates cultured senescent mammalian cells. However, it also inhibits the growth of cultured tumour cells. Based on studies in several organisms, we speculate that carnosine exerts these apparently opposing actions by affecting energy metabolism and/or protein homeostasis (proteostasis). Specific effects on energy metabolism include the dipeptide's influence on cellular ATP concentrations. Carnosine's ability to reduce the formation of altered proteins (typically adducts of methylglyoxal) and enhance proteolysis of aberrant polypeptides is indicative of its influence on proteostasis. Furthermore these dual actions might provide a rationale for the use of carnosine in the treatment or prevention of diverse age-related conditions where energy metabolism or proteostasis are compromised. These include cancer, Alzheimer's disease, Parkinson's disease and the complications of type-2 diabetes (nephropathy, cataracts, stroke and pain), which might all benefit from knowledge of carnosine's mode of action on human cells. © 2013 Hipkiss et al.; licensee Chemistry Central Ltd

Chromium isotopes, iron speciation, and the evolution of Earth's surface chemistry through time

The oxygen concentration of the ocean atmosphere system regulates the nature, activity and diversity of life on Earth. Atmospheric and ocean oxygenation is tightly coupled to the global biogeochemical cycles of C, N, P, S and Fe, as well as climate. Reconstructing the history of oxygen on planet Earth, therefore, is a key component to understanding the evolution of life. Our emergent picture of the evolution of Earth’s surface redox state with its links to the evolution of life and climate relies heavily on interpretations of geochemical information preserved in the rock record. The Cr isotope and Fe-speciation proxies are two widely applied tools used to diagnose redox conditions in both modern and ancient depositional environments. Many aspects of the precise mechanisms that lend the use of these two transition metals as paleoredox proxies, however, remain unclear, confounding accurate reconstructions of paleo-oxygen concentrations that rely on Cr isotope and Fe-speciation data. In this work I studied Cr isotope and Fe speciation proxy systematics to develop more nuanced frameworks for how these two paleoredox proxies may be employed to reconstruct depositional redox states in both modern and past environments. I determined the Cr isotope and Fe mineral composition of modern marine hydrothermal sediments, revealing Cr isotope fractionations that imply deposition from an oxygenated deep ocean. I determined Cr isotope fractionations associated with the reduction of Cr(VI) in modern ferruginous sediments, revealing that the magnitude of Cr isotope fractionation in such environments is linked to the speciation of Fe and the oxygen penetration depth of the sediments. I determined Fe-speciation and trace metal abundances of sediments deposited during oceanic anoxic event 1a (OAE1a), revealing that during this interval the oceans were anoxic and Fe-rich (ferruginous) for more than 1 million years. Lastly, I determined the Fe-speciation of suspended and sedimented material from two modern ferruginous lakes, revealing that the mineral magnetite forms authigenically in the ferruginous water columns. This new knowledge of Cr and Fe proxy systematics will allow for more refined interpretations of paleo oxygen concentrations based on Cr isotope and Fe-speciation signals captured in the rock record through time.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat