156 research outputs found
Nonlocal mixing of supercurrents in Josephson ballistic point contact
We study coherent current states in the mesoscopic superconducting weak link
simultaneously subjected to the order parameter phase difference on the contact
and to the tangential to the junction interface superfluid velocity in the
banks. The Josephson current-phase relation controlled by the external
transport current is obtained. At phase difference close to pi the nonlocal
nature of the Josephson phase-dependent current results in the appearance of
two vortexlike states in the vicinity of the contact.Comment: 4 pages, 6 figures; to be published in Phys. Rev. B; e-mail:
[email protected]
Astro 2020 Science White Paper: Time Domain Studies of Neutron Star and Black Hole Populations: X-ray Identification of Compact Object Types
What are the most important conditions and processes governing the growth of
stellar-origin compact objects? The identification of compact object type as
either black hole (BH) or neutron star (NS) is fundamental to understanding
their formation and evolution. To date, time-domain determination of compact
object type remains a relatively untapped tool. Measurement of orbital periods,
pulsations, and bursts will lead to a revolution in the study of the
demographics of NS and BH populations, linking source phenomena to accretion
and galaxy parameters (e.g., star formation, metallicity). To perform these
measurements over sufficient parameter space, a combination of a wide-field
(>5000 deg^2) transient X-ray monitor over a dynamic energy range (~1-100 keV)
and an X-ray telescope for deep surveys with <5 arcsec PSF half-energy width
(HEW) angular resolution are required. Synergy with multiwavelength data for
characterizing the underlying stellar population will transform our
understanding of the time domain properties of transient sources, helping to
explain details of supernova explosions and gravitational wave event rates.Comment: 9 pages, 2 figures. Submitted to the Astro2020 Decadal Surve
A 78 Day X-Ray Period Detected from NGC 5907 ULX1 by Swift
We report the detection of a 78.1 ± 0.5 day period in the X-ray light curve of the extreme ultraluminous X-ray source NGC 5907 ULX1 ( erg sâ1), discovered during an extensive monitoring program with Swift. These periodic variations are strong, with the observed flux changing by a factor of ~3â4 between the peaks and the troughs of the cycle; our simulations suggest that the observed periodicity is detected comfortably in excess of 3Ï significance. We discuss possible origins for this X-ray period, but conclude that at the current time we cannot robustly distinguish between orbital and super-orbital variations
Reflectionless tunneling in ballistic normal-metal--superconductor junctions
We investigate the phenomenon of reflectionless tunneling in ballistic
normal-metal--superconductor (NS) structures, using a semiclassical formalism.
It is shown that applied magnetic field and superconducting phase difference
both impair the constructive interference leading to this effect, but in a
qualitatively different way. This is manifested both in the conductance and in
the shot noise properties of the system considered. Unlike diffusive systems,
the features of the conductance are sharp, and enable fine spatial control of
the current, as well as single channel manipulations. We discuss the
possibility of conducting experiments in ballistic semiconductor-superconductor
structures with smooth interfaces and some of the phenomena, specific to such
structures, that could be measured. A general criterion for the barrier at NS
interfaces, though large, to be effectively transparent to pair current is
obtained.Comment: published versio
Applications of the PowerGlove
The hand is important in many daily life activities. During aging, quality of fine motor control of hand and fingers is decreasing. Also motor symptoms of the hand are important to define for instance the neurological state of a Parkinsonâs disease patient. Although objective and reliable measurement of hand and finger dynamics is of interest, current measurement systems are limited. This paper describes the application of the PowerGlove, a new measurement system based on miniature inertial and magnetic sensors, to study the finger interdependency in healthy elderly and objectively quantify hand motor symptoms in Parkinsonâs disease. Results of pilot experiments in young healthy subjects are shown to evaluate the feasibility of the applications
PosMed (Positional Medline): prioritizing genes with an artificial neural network comprising medical documents to accelerate positional cloning
PosMed (http://omicspace.riken.jp/) prioritizes candidate genes for positional cloning by employing our original database search engine GRASE, which uses an inferential process similar to an artificial neural network comprising documental neurons (or âdocumentronsâ) that represent each document contained in databases such as MEDLINE and OMIM. Given a user-specified query, PosMed initially performs a full-text search of each documentron in the first-layer artificial neurons and then calculates the statistical significance of the connections between the hit documentrons and the second-layer artificial neurons representing each gene. When a chromosomal interval(s) is specified, PosMed explores the second-layer and third-layer artificial neurons representing genes within the chromosomal interval by evaluating the combined significance of the connections from the hit documentrons to the genes. PosMed is, therefore, a powerful tool that immediately ranks the candidate genes by connecting phenotypic keywords to the genes through connections representing not only geneâgene interactions but also other biological interactions (e.g. metaboliteâgene, mutant mouseâgene, drugâgene, diseaseâgene and proteinâprotein interactions) and ortholog data. By utilizing orthologous connections, PosMed facilitates the ranking of human genes based on evidence found in other model species such as mouse. Currently, PosMed, an artificial superbrain that has learned a vast amount of biological knowledge ranging from genomes to phenomes (or âomic spaceâ), supports the prioritization of positional candidate genes in humans, mouse, rat and Arabidopsis thaliana
Ballistic Josephson junctions in edge-contacted graphene
Hybrid graphene-superconductor devices have attracted much attention since
the early days of graphene research. So far, these studies have been limited to
the case of diffusive transport through graphene with poorly defined and modest
quality graphene-superconductor interfaces, usually combined with small
critical magnetic fields of the superconducting electrodes. Here we report
graphene based Josephson junctions with one-dimensional edge contacts of
Molybdenum Rhenium. The contacts exhibit a well defined, transparent interface
to the graphene, have a critical magnetic field of 8 Tesla at 4 Kelvin and the
graphene has a high quality due to its encapsulation in hexagonal boron
nitride. This allows us to study and exploit graphene Josephson junctions in a
new regime, characterized by ballistic transport. We find that the critical
current oscillates with the carrier density due to phase coherent interference
of the electrons and holes that carry the supercurrent caused by the formation
of a Fabry-P\'{e}rot cavity. Furthermore, relatively large supercurrents are
observed over unprecedented long distances of up to 1.5 m. Finally, in the
quantum Hall regime we observe broken symmetry states while the contacts remain
superconducting. These achievements open up new avenues to exploit the Dirac
nature of graphene in interaction with the superconducting state.Comment: Updated version after peer review. Includes supplementary material
and ancillary file with source code for tight binding simulation
Probing the nature of the low state in the extreme ultraluminous X-ray pulsar NGC 5907 ULX1
NGC 5907 ULX1 is the most luminous ultra-luminous X-ray pulsar (ULXP) known
to date, reaching luminosities in excess of 1e41 erg/s. The pulsar is known for
its fast spin-up during the on-state. Here, we present a long-term monitoring
of the X-ray flux and the pulse period between 2003-2022. We find that the
source was in an off- or low-state between mid-2017 to mid-2020. During this
state, our pulse period monitoring shows that the source had spun down
considerably. We interpret this spin-down as likely being due to the propeller
effect, whereby accretion onto the neutron star surface is inhibited. Using
state-of-the-art accretion and torque models, we use the spin-up and spin-down
episodes to constrain the magnetic field. For the spin-up episode, we find
solutions for magnetic field strengths of either around 1e12G or 1e13G,
however, the strong spin-down during the off-state seems only to be consistent
with a very high magnetic field, namely, >1e13G. This is the first time a
strong spin-down is seen during a low flux state in a ULXP. Based on the
assumption that the source entered the propeller regime, this gives us the best
estimate so far for the magnetic field of NGC 5907 ULX1.Comment: 10 pages, 1 figure, accepted for publication in A&
Interaction-Induced Enhancement of Spin-Orbit Coupling in Two-Dimensional Electronic System
We study theoretically the renormalization of the spin-orbit coupling
constant of two-dimensional electrons by electron-electron interactions. We
demonstrate that, similarly to the factor, the renormalization corresponds
to the enhancement, although the magnitude of the enhancement is weaker than
that for the factor. For high electron concentrations (small interaction
parameter ) the enhancement factor is evaluated analytically within the
static random phase approximation. For large we use an approximate
expression for effective electron-electron interaction, which takes into
account the local field factor, and calculate the enhancement numerically. We
also study the interplay between the interaction-enhanced Zeeman splitting and
interaction-enhanced spin-orbit coupling.Comment: 18 pages, 2 figures, REVTe
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