155 research outputs found
Future Needs for Tribo-Corrosion Research and Testing
Tribo-corrosion is an emerging interdisciplinary subject that spans from basic research on the behavior of surfaces in mechanical contact in chemically active surroundings to the test methods needed to quantify its effects, and from the selection of materials for bio-implants to the minimization of surface degradation and wastage in advanced energy conversion systems. Such a diverse field brings with it many challenges in understanding, testing, standardization, and application to engineering practice. This paper summarizes a panel discussion and participant survey held at the Third International Symposium on Tribo-Corrosion in Atlanta, Georgia, USA, in April 2012. It reflects a sense of agreement on many of the key scientific challenges in the field and the fact that tribo-corrosion is still in its infancy in terms of broad industry recognition, education, and the ability of those who conduct tribo-corrosion research to connect their laboratory results and theories to applications. Some sub-fields, notably the bio-tribo-corrosion of medical implants, have witnessed active international research efforts, but the engineering community in many other important areas of technology may not yet be aware of the field despite numerous tribo-corrosion problems that may exist within their purview
Quantized conductance doubling and hard gap in a two-dimensional semiconductor-superconductor heterostructure
The prospect of coupling a two-dimensional (2D) semiconductor heterostructure
to a superconductor opens new research and technology opportunities, including
fundamental problems in mesoscopic superconductivity, scalable superconducting
electronics, and new topological states of matter. For instance, one route
toward realizing topological matter is by coupling a 2D electron gas (2DEG)
with strong spin-orbit interaction to an s-wave superconductor. Previous
efforts along these lines have been hindered by interface disorder and unstable
gating. Here, we report measurements on a gateable InGaAs/InAs 2DEG with
patterned epitaxial Al, yielding multilayer devices with atomically pristine
interfaces between semiconductor and superconductor. Using surface gates to
form a quantum point contact (QPC), we find a hard superconducting gap in the
tunneling regime, overcoming the soft-gap problem in 2D
superconductor-semiconductor hybrid systems. With the QPC in the open regime,
we observe a first conductance plateau at 4e^2/h, as expected theoretically for
a normal-QPC-superconductor structure. The realization of a hard-gap
semiconductor-superconductor system that is amenable to top-down processing
provides a means of fabricating scalable multicomponent hybrid systems for
applications in low-dissipation electronics and topological quantum
information.Comment: includes main text, supplementary information and code for
simulations. Published versio
Unmodified multi-wall carbon nanotubes in polylactic acid for electrically conductive injection-moulded composites
Tailoring the properties of natural polymers such as electrical conductivity is vital to widen the range of future applications. In this article, the potential of electrically conducting multi-wall carbon nanotube (MWCNT)/polylactic acid (PLA) composites produced by industrially viable melt mixing is assessed simultaneously to MWCNT influence on the composite’s mechanical strength and polymer crystallinity. Atomic force microscopy observations showed that melt mixing achieved an effective distribution and individualization of unmodified nanotubes within the polymer matrix. However, as a trade-off of the poor tube/matrix adhesion, the tensile strength was lowered. With 10 wt% MWCNT loading, the tensile strength was 26% lower than for neat PLA. Differential scanning calorimetric measurements indicated that polymer crystallization after injection moulding was nearly unaffected by the presence of nanotubes and remained at 15%. The resulting composites became conductive below 5 wt% loading and reached conductivities of 51 S m−1 at 10 wt%, which is comparable with conductivities reported for similar nanocomposites obtained at lab scale. </jats:p
Electric and Magnetic Tuning Between the Trivial and Topological Phases in InAs/GaSb Double Quantum Wells
Among the theoretically predicted two-dimensional topological insulators,
InAs/GaSb double quantum wells (DQWs) have a unique double-layered structure
with electron and hole gases separated in two layers, which enables tuning of
the band alignment via electric and magnetic fields. However, the rich
trivial-topological phase diagram has yet to be experimentally explored. We
present an in situ and continuous tuning between the trivial and topological
insulating phases in InAs/GaSb DQWs through electrical dual-gating.
Furthermore, we show that an in-plane magnetic field shifts the electron and
hole bands relatively to each other in momentum space, functioning as a
powerful tool to discriminate between the topologically distinct states
Engineering Hybrid Epitaxial InAsSb/Al Nanowire Materials for Stronger Topological Protection
The combination of strong spin-orbit coupling, large -factors, and the
coupling to a superconductor can be used to create a topologically protected
state in a semiconductor nanowire. Here we report on growth and
characterization of hybrid epitaxial InAsSb/Al nanowires, with varying
composition and crystal structure. We find the strongest spin-orbit interaction
at intermediate compositions in zincblende InAsSb nanowires,
exceeding that of both InAs and InSb materials, confirming recent theoretical
studies \cite{winkler2016topological}. We show that the epitaxial InAsSb/Al
interfaces allows for a hard induced superconducting gap and 2 transport in
Coulomb charging experiments, similar to experiments on InAs/Al and InSb/Al
materials, and find measurements consistent with topological phase transitions
at low magnetic fields due to large effective -factors. Finally we present a
method to grow pure wurtzite InAsSb nanowires which are predicted to exhibit
even stronger spin-orbit coupling than the zincblende structure.Comment: 10 pages and 5 figure
Giant spin-orbit splitting in inverted InAs/GaSb double quantum wells
Transport measurements in inverted InAs/GaSb quantum wells reveal a giant
spin-orbit splitting of the energy bands close to the hybridization gap. The
splitting results from the interplay of electron-hole mixing and spin-orbit
coupling, and can exceed the hybridization gap. We experimentally investigate
the band splitting as a function of top gate voltage for both electron-like and
hole-like states. Unlike conventional, noninverted two-dimensional electron
gases, the Fermi energy in InAs/GaSb can cross a single spin-resolved band,
resulting in full spin-orbit polarization. In the fully polarized regime we
observe exotic transport phenomena such as quantum Hall plateaus evolving in
steps and a non-trivial Berry phase
Spin-orbit interaction in a dual gated InAs/GaSb quantum well
Spin-orbit interaction is investigated in a dual gated InAs/GaSb quantum
well. Using an electric field the quantum well can be tuned between a single
carrier regime with exclusively electrons as carriers and a two-carriers regime
where electrons and holes coexist. Spin-orbit interaction in both regimes
manifests itself as a beating in the Shubnikov-de Haas oscillations. In the
single carrier regime the linear Dresselhaus strength is characterized by
28.5 meV and the Rashba coefficient is tuned from 75 to
53 meV by changing the electric field. In the two-carriers regime the spin
splitting shows a nonmonotonic behavior with gate voltage, which is consistent
with our band structure calculations
Matrix Models and D-branes in Twistor String Theory
We construct two matrix models from twistor string theory: one by dimensional
reduction onto a rational curve and another one by introducing noncommutative
coordinates on the fibres of the supertwistor space P^(3|4)->CP^1. We comment
on the interpretation of our matrix models in terms of topological D-branes and
relate them to a recently proposed string field theory. By extending one of the
models, we can carry over all the ingredients of the super ADHM construction to
a D-brane configuration in the supertwistor space P^(3|4). Eventually, we
present the analogue picture for the (super) Nahm construction.Comment: 1+37 pages, reference added, JHEP style, published versio
Suitable Electrode Choice for Robotic-Assisted Cochlear Implant Surgery: A Systematic Literature Review of Manual Electrode Insertion Adverse Events
BACKGROUND AND OBJECTIVE: The cochlear implant (CI) electrode insertion process is a key step in CI surgery. One of the aims of advances in robotic-assisted CI surgery (RACIS) is to realize better cochlear structure preservation and to precisely control insertion. The aim of this literature review is to gain insight into electrode selection for RACIS by acquiring a thorough knowledge of electrode insertion and related complications from classic CI surgery involving a manual electrode insertion process. METHODS: A systematic electronic search of the literature was carried out using PubMed, Scopus, Cochrane, and Web of Science to find relevant literature on electrode tip fold over (ETFO), electrode scalar deviation (ESD), and electrode migration (EM) from both pre-shaped and straight electrode types. RESULTS: A total of 82 studies that include 8,603 ears implanted with a CI, i.e., pre-shaped (4,869) and straight electrodes (3,734), were evaluated. The rate of ETFO (25 studies, 2,335 ears), ESD (39 studies, 3,073 ears), and EM (18 studies, 3,195 ears) was determined. An incidence rate (±95% CI) of 5.38% (4.4–6.6%) of ETFO, 28.6% (26.6–30.6%) of ESD, and 0.53% (0.2–1.1%) of EM is associated with pre-shaped electrodes, whereas with straight electrodes it was 0.51% (0.1–1.3%), 11% (9.2–13.0%), and 3.2% (2.5–3.95%), respectively. The differences between the pre-shaped and straight electrode types are highly significant (p < 0.001). Laboratory experiments show evidence that robotic insertions of electrodes are less traumatic than manual insertions. The influence of round window (RW) vs. cochleostomy (Coch) was not assessed. CONCLUSION: Considering the current electrode designs available and the reported incidence of insertion complications, the use of straight electrodes in RACIS and conventional CI surgery (and manual insertion) appears to be less traumatic to intracochlear structures compared with pre-shaped electrodes. However, EM of straight electrodes should be anticipated. RACIS has the potential to reduce these complications
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