904 research outputs found
Parity lifetime of bound states in a proximitized semiconductor nanowire
Quasiparticle excitations can compromise the performance of superconducting
devices, causing high frequency dissipation, decoherence in Josephson qubits,
and braiding errors in proposed Majorana-based topological quantum computers.
Quasiparticle dynamics have been studied in detail in metallic superconductors
but remain relatively unexplored in semiconductor-superconductor structures,
which are now being intensely pursued in the context of topological
superconductivity. To this end, we introduce a new physical system comprised of
a gate-confined semiconductor nanowire with an epitaxially grown superconductor
layer, yielding an isolated, proximitized nanowire segment. We identify
Andreev-like bound states in the semiconductor via bias spectroscopy, determine
the characteristic temperatures and magnetic fields for quasiparticle
excitations, and extract a parity lifetime (poisoning time) of the bound state
in the semiconductor exceeding 10 ms.Comment: text and supplementary information combine
Hard gap in epitaxial semiconductor-superconductor nanowires
Many present and future applications of superconductivity would benefit from
electrostatic control of carrier density and tunneling rates, the hallmark of
semiconductor devices. One particularly exciting application is the realization
of topological superconductivity as a basis for quantum information processing.
Proposals in this direction based on proximity effect in semiconductor
nanowires are appealing because the key ingredients are currently in hand.
However, previous instances of proximitized semiconductors show significant
tunneling conductance below the superconducting gap, suggesting a continuum of
subgap states---a situation that nullifies topological protection. Here, we
report a hard superconducting gap induced by proximity effect in a
semiconductor, using epitaxial Al-InAs superconductor-semiconductor nanowires.
The hard gap, along with favorable material properties and gate-tunability,
makes this new hybrid system attractive for a number of applications, as well
as fundamental studies of mesoscopic superconductivity.Comment: Combined text and supplementary information, Nature Nanotechnology
(2015
Genome-Wide Massively Parallel Sequencing of Formaldehyde Fixed-Paraffin Embedded (FFPE) Tumor Tissues for Copy-Number- and Mutation-Analysis
Cancer re-sequencing programs rely on DNA isolated from fresh snap frozen tissues, the preparation of which is combined with additional preservation efforts. Tissue samples at pathology departments are routinely stored as formalin-fixed and paraffin-embedded (FFPE) samples and their use would open up access to a variety of clinical trials. However, FFPE preparation is incompatible with many down-stream molecular biology techniques such as PCR based amplification methods and gene expression studies.
Methodology/Principal Findings
Here we investigated the sample quality requirements of FFPE tissues for massively parallel short-read sequencing approaches. We evaluated key variables of pre-fixation, fixation related and post-fixation processes that occur in routine medical service (e.g. degree of autolysis, duration of fixation and of storage). We also investigated the influence of tissue storage time on sequencing quality by using material that was up to 18 years old. Finally, we analyzed normal and tumor breast tissues using the Sequencing by Synthesis technique (Illumina Genome Analyzer, Solexa) to simultaneously localize genome-wide copy number alterations and to detect genomic variations such as substitutions and point-deletions and/or insertions in FFPE tissue samples.
Conclusions/Significance
The application of second generation sequencing techniques on small amounts of FFPE material opens up the possibility to analyze tissue samples which have been collected during routine clinical work as well as in the context of clinical trials. This is in particular important since FFPE samples are amply available from surgical tumor resections and histopathological diagnosis, and comprise tissue from precursor lesions, primary tumors, lymphogenic and/or hematogenic metastases. Large-scale studies using this tissue material will result in a better prediction of the prognosis of cancer patients and the early identification of patients which will respond to therapy
Epitaxy of Semiconductor-Superconductor nanowires
Controlling the properties of semiconductor/metal interfaces is a powerful
method for designing functionality and improving the performance of electrical
devices. Recently semiconductor/superconductor hybrids have appeared as an
important example where the atomic scale uniformity of the interface plays a
key role for the quality of the induced superconducting gap. Here we present
epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam
epitaxy, a method that provides a conceptually new route to controlled
electrical contacting of nanostructures and for designing devices for
specialized applications such as topological and gate-controlled
superconducting electronics. Our materials of choice, InAs/Al, are grown with
epitaxially matched single plane interfaces, and alternative
semiconductor/metal combinations allowing epitaxial interface matching in
nanowires are discussed. We formulate the grain growth kinetics of the metal
phase in general terms of continuum parameters and bicrystal symmetries. The
method realizes the ultimate limit of uniform interfaces and appears to solve
the soft-gap problem in superconducting hybrid structures.Comment: Combined text and Supplementary Informatio
Impact of an in-hospital endocarditis team and a state-wide endocarditis network on perioperative outcomes
Background: Infective endocarditis (IE) requires multidisciplinary management. We established an endocarditis team within our hospital in 2011 and a state-wide endocarditis network with referring hospitals in 2015. We aimed to investigate their impact on perioperative outcomes. Methods: We retrospectively analyzed data from patients operated on for IE in our center between 01/2007 and 03/2018. To investigate the impact of the endocarditis network on referral latency and pre-operative complications we divided patients into two eras: before ( n = 409) and after ( n = 221) 01/2015. To investigate the impact of the endocarditis team on post-operative outcomes we conducted multivariate binary logistic regression analyses for the whole population. Kaplan–Meier estimates of 5-year survival were reported. Results: In the second era, after establishing the endocarditis network, the median time from symptoms to referral was halved (7 days (interquartile range: 2–19) vs. 15 days (interquartile range: 6–35)), and pre-operative endocarditis-related complications were reduced, i.e., stroke (14% vs. 27%, p < 0.001), heart failure (45% vs. 69%, p < 0.001), cardiac abscesses (24% vs. 34%, p = 0.018), and acute requirement of hemodialysis (8% vs. 14%, p = 0.026). In both eras, a lack of recommendations from the endocarditis team was an independent predictor for in-hospital mortality (adjusted odds ratio: 2.12, 95% CI: 1.27–3.53, p = 0.004) and post-operative stroke (adjusted odds ratio: 2.23, 95% CI: 1.12–4.39, p = 0.02), and was associated with worse 5-year survival (59% vs. 40%, log-rank < 0.001). Conclusion: The establishment of an endocarditis network led to the earlier referral of patients with fewer pre-operative endocarditis-related complications. Adhering to endocarditis team recommendations was an independent predictor for lower post-operative stroke and in-hospital mortality, and was associated with better 5-year survival
AGN accretion disks as spatially resolved by polarimetry
A crucial difficulty in understanding the nature of the putative accretion
disk in AGNs is that some of its key intrinsic spectral signatures cannot be
observed directly. The strong emissions from the broad-line region (BLR) and
the obscuring torus, which are generally yet to be spatially resolved,
essentially 'bury' such signatures. Here we argue that we can actually isolate
the disk emission spectrum by using optical and near-infrared polarization of
quasars and uncover the important spectral signatures. In these quasars, the
polarization is considered to originate from electron scattering interior to
the BLR, so that the polarized flux shows the disk spectrum with all the
emissions from the BLR and torus eliminated. The polarized flux observations
have now revealed a Balmer edge feature in absorption and a blue near-infrared
spectral shape consistent with a specific and robust theoretical prediction.
These results critically verify the long-standing picture of an optically thick
and locally heated disk in AGNs.Comment: Proceedings for "The Universe under the Microscope" (AHAR 2008), held
in Bad Honnef (Germany) in April 2008, to be published in Journal of Physics:
Conference Series by Institute of Physics Publishing, R. Schoedel, A. Eckart,
S. Pfalzner, and E. Ros (eds.
The characteristic blue spectra of accretion disks in quasars as uncovered in the infrared
Quasars are thought to be powered by supermassive black holes accreting
surrounding gas. Central to this picture is a putative accretion disk which is
believed to be the source of the majority of the radiative output. It is well
known, however, that the most extensively studied disk model -- an optically
thick disk which is heated locally by the dissipation of gravitational binding
energy -- is apparently contradicted by observations in a few major respects.
In particular, the model predicts a specific blue spectral shape asymptotically
from the visible to the near-infrared, but this is not generally seen in the
visible wavelength region where the disk spectrum is observable. A crucial
difficulty was that, toward the infrared, the disk spectrum starts to be hidden
under strong hot dust emission from much larger but hitherto unresolved scales,
and thus has essentially been impossible to observe. Here we report
observations of polarized light interior to the dust-emiting region that enable
us to uncover this near-infrared disk spectrum in several quasars. The revealed
spectra show that the near-infrared disk spectrum is indeed as blue as
predicted. This indicates that, at least for the outer near-infrared-emitting
radii, the standard picture of the locally heated disk is approximately
correct. The model problems at shorter wavelengths should then be directed
toward a better understanding of the inner parts of the revealed disk. The
newly uncovered disk emission at large radii, with more future measurements,
will also shed totally new light on the unanswered critical question of how and
where the disk ends.Comment: published in Nature, 24 July 2008 issue. Supplementary Information
can be found at
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/suppl_info.pdf Published
version can be accessed from
http://www.nature.com/nature/journal/v454/n7203/pdf/nature07114.pd
Nanometer Scale Dielectric Fluctuations at the Glass Transition
Using non-contact scanning probe microscopy (SPM) techniques, dielectric
properties were studied on 50 nanometer length scales in poly-vinyl-acetate
(PVAc) films in the vicinity of the glass transition. Low frequency (1/f) noise
observed in the measurements, was shown to arise from thermal fluctuations of
the electric polarization. Anomalous variations observed in the noise spectrum
provide direct evidence for cooperative nano-regions with heterogeneous
kinetics. The cooperative length scale was determined. Heterogeneity was
long-lived only well below the glass transition for faster than average
processes.Comment: 4 pages, 4 embedded PS figures, RevTeX - To appear in Phys. Rev. Let
The low density, hot Jupiter TOI-640 b is on a polar orbit
TOI-640 b is a hot, puffy Jupiter with a mass of M
and radius of R, orbiting a slightly evolved F-type
star with a separation of R. Through
spectroscopic in-transit observations made with the HARPS spectrograph, we
measured the Rossiter-McLaughlin effect, analysing both in-transit radial
velocities and the distortion of the stellar spectral lines. From these
observations, we find the host star to have a projected obliquity of
. From the TESS light curve, we measured the stellar
rotation period, allowing us to determine the stellar inclination,
, meaning we are viewing the star pole-on. Combining
this with the orbital inclination allowed us to calculate the host star
obliquity, . TOI-640 b joins a group of planets orbiting
over stellar poles within the range . The origin of this
orbital configuration is not well understood.Comment: 15 pages, 12 figures, accepted for publication in A&A, in pres
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