149 research outputs found
Point contact spectroscopy of the electron-doped cuprate superconductor Pr{2-x}Ce{x}CuO4: The dependence of conductance-voltage spectra on cerium doping, barrier strength and magnetic field
We present conductance-voltage (G-V) data for point contact junctions between
a normal metal and the electron doped cuprate superconductor Pr{2-x}Ce{x}CuO4
(PCCO). We observe a zero bias conductance peak (ZBCP) for the under-doped
composition of this cuprate (x=0.13) which is consistent with d-wave pairing
symmetry. For optimally-doped (x=0.15) and over-doped (x=0.17) PCCO, we find
that the G-V characteristics indicate the presence of an order parameter
without nodes. We investigate this further by obtaining point contact
spectroscopy data for different barrier strengths and as a function of magnetic
field.Comment: 13 pages, 9 figure
Germanium on Silicon Avalanche Photodiode for High-Speed fiber Communication
Silicon photonics is one of the promising technologies for high-speed optical fiber communications. Among various silicon photonic devices, germanium on silicon avalanche photodiode (Ge/Si APDs) received tremendous attentions because of its superior performance and integration compatibility. In 2016, normal incidence Ge/Si APD demonstrated a NRZ 10−12 sensitivity of −23.5 dBm at 25 Gb/s; more recently, a waveguide-integrated Ge/Si APD receiver presents a 106Gb/s PAM4 sensitivity of −18.9 dBm. These results are best reported performance among all APD-based devices, and these breakthroughs are mainly benefited from Ge/Si APD’s structure and material characteristics. Ge/Si APD adopts a separated charge-absorption-multiplication (SCAM) structure with a pure Ge absorber and an intrinsic Si avalanche layer. Since, Si is one of well-known best avalanche materials with large gain-bandwidth products and low ionization noise ratio, which make Ge/Si APDs demonstrating superior performance at high data rates. Moreover, this Si-based device is manufactured by standard CMOS foundries and is process-compatible with other silicon photonic devices including silicon-based waveguides, demux, hybrid, etc. This advantage simplifies the assembly of photonic systems and makes a large-scale integrated silicon photonic chip possible, which provides compact solutions for high-density communication systems. In this chapter, we review recent progresses on Ge/Si APD structure design, material, and performance
Cooperativity and flexibility in enzyme evolution
Enzymes are flexible catalysts, and there has been substantial
discussion about the extent to which this flexibility contributes
to their catalytic efficiency. What has been significantly less
discussed is the extent to which this flexibility contributes to
their evolvability. Despite this, recent years have seen an
increasing number of both experimental and computational
studies that demonstrate that cooperativity and flexibility play
significant roles in enzyme innovation. This review covers key
developments in the field that emphasize the importance of
enzyme dynamics not just to the evolution of new enzyme
function(s), but also as a property that can be harnessed in the
design of new artificial enzymes.The European Research Council has provided financial support under the
European Community’s Seventh Framework Program (FP7/2007-2013)/ERC
Grant Agreement No. 306474. This work was also funded by the Feder
Funds, Grants from the Spanish Ministry of Economy and Competitiveness
(BIO2015-66426-R and CSD2009-00088) and the Human Frontier Science
Program (RGP0041/2017). A.P. is a Wenner-Gren Foundations Postdoctoral
Fellow and S. C. L. K. is a Wallenberg Academy Fellow
A glacial cryptic refuge in south-east Australia: human occupation and mobility from 36 000 years ago in the Sydney Basin, New South Wales
Excavations across a source-bordering dune overlooking the Hawkesbury River in north-west Sydney, Australia, suggest initial occupation of the region by at least 36 ka, with variable but uninterrupted use until the early Holocene; following abandonment, the site was then re-occupied by ∼3 ka. Along with a handful of other sites, the results provide the earliest reliable evidence of permanent regional populations within south-eastern Australia, and support a model in which early colonizers followed the coastal fringe with forays along the main river systems. The evidence is consistent with the demographic model of Williams, 2013 (Proceedings of the Royal Society Series B 280: 20130486), which suggested low, but established regional populations before the Last Glacial Maximum (LGM), a population nadir following the LGM and increasing use of the region from ∼12 to 8 ka. The site exhibits increased use at the onset and peak of the LGM, and provides an example of a cryptic refuge as defined by Smith, 2013 (The Archaeology of Australia's Deserts. Cambridge University Press: New York). Specifically, changing artefact densities and attributes show the site was used repeatedly, but for shorter periods through this time, and suggest it formed one of a series of key localities in a point-to-point (rather than home-base) subsistence strategy. This strategy was maintained until the site's abandonment in the early Holocene, despite changing population and climatic conditions through the Terminal Pleistocene
Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases
The production of peroxide and superoxide is an inevitable consequence of
aerobic metabolism, and while these particular "reactive oxygen species" (ROSs)
can exhibit a number of biological effects, they are not of themselves
excessively reactive and thus they are not especially damaging at physiological
concentrations. However, their reactions with poorly liganded iron species can
lead to the catalytic production of the very reactive and dangerous hydroxyl
radical, which is exceptionally damaging, and a major cause of chronic
inflammation. We review the considerable and wide-ranging evidence for the
involvement of this combination of (su)peroxide and poorly liganded iron in a
large number of physiological and indeed pathological processes and
inflammatory disorders, especially those involving the progressive degradation
of cellular and organismal performance. These diseases share a great many
similarities and thus might be considered to have a common cause (i.e.
iron-catalysed free radical and especially hydroxyl radical generation). The
studies reviewed include those focused on a series of cardiovascular, metabolic
and neurological diseases, where iron can be found at the sites of plaques and
lesions, as well as studies showing the significance of iron to aging and
longevity. The effective chelation of iron by natural or synthetic ligands is
thus of major physiological (and potentially therapeutic) importance. As
systems properties, we need to recognise that physiological observables have
multiple molecular causes, and studying them in isolation leads to inconsistent
patterns of apparent causality when it is the simultaneous combination of
multiple factors that is responsible. This explains, for instance, the
decidedly mixed effects of antioxidants that have been observed, etc...Comment: 159 pages, including 9 Figs and 2184 reference
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