39 research outputs found
Error Distribution for One-Dimensional Stochastic Differential Equation Driven By Fractional Brownian Motion
We can define the error distribution as the limiting distribution of the
error between the solution of a given stochastic differential equation
(SDE) and its numerical approximation , weighted by the
convergence rate between the two. A goal when studying the error distribution
is to provide a way of determination for error distributions for any SDE and
numerical scheme that converge to the exact solution. By dividing the error
into a main term and a remainder term in a particular way, the author shows
that the remainder term can be negligible compared to the main term under
certain suitable conditions. Under these conditions, deriving the error
distribution reduces to deriving the limiting distribution of the main term.
Even if the dimension is one, there are unsolved problems about the asymptotic
behavior of the error when the SDE has a drift term and , but our
result in the one-dimensional case can be adapted to any Hurst exponent. The
main idea of the proof is to define a stochastic process with the
parameter interpolating between and and to estimate
the asymptotic expansion for it. Using this estimate, we determine the error
distribution of the ()-Milstein scheme and of the Crank-Nicholson scheme in
unsolved cases.Comment: 55 page
New physics searches at the ILC positron and electron beam dumps
We study capability of the ILC beam dump experiment to search for new
physics, comparing the performance of the electron and positron beam dumps. The
dark photon, axion-like particles, and light scalar bosons are considered as
new physics scenarios, where all the important production mechanisms are
included: electron-positron pair-annihilation, Primakoff process, and
bremsstrahlung productions. We find that the ILC beam dump experiment has
higher sensitivity than past beam dump experiments, with the positron beam dump
having slightly better performance for new physics particles which are produced
by the electron-positron pair-annihilation.Comment: 26 pages, 7 figure
Half-Integer Shapiro Steps in a Short Ballistic InAs Nanowire Josephson Junction
We report on half-integer Shapiro steps observed in an InAs nanowire
Josephson junction. We observed the Shapiro steps of the short ballistic InAs
nanowire Josephson junction and found anomalous half-integer steps in addition
to the conventional integer steps. The half-integer steps disappear as the
temperature increases or transmission of the junction decreases. These
experimental results agree closely with numerical calculation of the Shapiro
response for the skewed current phase relation in a short ballistic Josephson
junction
Sub-GeV dark matter search at ILC beam dumps
Light dark matter particles may be produced in electron and positron beam
dumps of the International Linear Collider (ILC). We propose an experimental
setup to search for such events, the Beam-Dump eXperiment at the ILC (ILC-BDX).
The setup consists of a muon shield placed behind the beam dump, followed by a
multi-layer tracker and an electromagnetic calorimeter. The calorimeter can
detect electron recoils due to elastic scattering of dark matter particles
produced in the dump, while the tracker is sensitive to decays of excited
dark-sector states into the dark matter particle. We study the production,
decay and scattering of sub-GeV dark matter particles in this setup in several
models with a dark photon mediator. Taking into account beam-related
backgrounds due to neutrinos produced in the beam dump as well as the
cosmic-ray background, we evaluate the sensitivity reach of the ILC-BDX
experiment. We find that the ILC-BDX will be able to probe interesting regions
of the model parameter space and, in many cases, reach well below the relic
target.Comment: 39 pages, 12 figure
Equal-Spin Andreev Reflection in Junctions of Spin-Resolved Quantum Hall Bulk State and Spin-Singlet Superconductor
The recent development of superconducting spintronics has revealed the
spin-triplet superconducting proximity effect from a spin-singlet
superconductor into a spin-polarized normal metal. In addition recently
superconducting junctions using semiconductors are in demand for highly
controlled experiments to engineer topological superconductivity. Here we
report experimental observation of Andreev reflection in junctions of
spin-resolved quantum Hall (QH) states in an InAs quantum well and the
spin-singlet superconductor NbTi. The measured conductance indicates a sub-gap
feature and two peaks on the outer side of the sub-gap feature in the QH
plateau-transition regime increases. The observed structures can be explained
by considering transport with Andreev reflection from two channels, one
originating from equal-spin Andreev reflection intermediated by spin-flip
processes and second arising from normal Andreev reflection. This result
indicates the possibility to induce the superconducting proximity gap in the
the QH bulk state, and the possibility for the development of superconducting
spintronics in semiconductor devices
Dominant non-local superconducting proximity effect due to electron-electron interaction in a ballistic double nanowire
Cooper pair splitting (CPS) can induce non-local correlation between two
normal conductors coupling to a superconductor. CPS into a double
one-dimensional electron gas is an appropriate platform for extracting large
amount of entangled electron pairs and one of the key ingredients for
engineering Majorana Fermions with no magnetic field. Here we study CPS using a
Josephson junction of a gate-tunable ballistic InAs double nanowire. The
measured switching current into the two nanowires significantly larger than sum
of that into the respective nanowires, indicating the inter-wire
superconductivity dominant compared to the intra-wire superconductivity. From
dependence on the number of propagating channels in the nanowires, the observed
CPS is assigned to one-dimensional electron-electron interaction. Our results
will pave the way for utilizing one-dimensional electron-electron interaction
to reveal physics of high-efficient CPS and engineer Majorana Fermions in
double nanowire systems via CPS
Volumetric measurement of paranasal sinuses and its clinical significance in pituitary neuroendocrine tumors operated using an endoscopic endonasal approach
ObjectiveEndoscopic endonasal surgery (EES) for deep intracranial lesions has gained popularity following recent developments in endoscopic technology. The operability of invasive pituitary neuroendocrine tumors (PitNETs) depends on the anatomy of the nasal cavity and paranasal sinus. This study aimed to establish a simple volume reconstruction algorithm of the nasal cavity and paranasal sinus. Additionally, this is the first study to demonstrate the relationship between the segmentation method and the clinical significance in patients with PitNET.MethodsPre-and postoperative tumor volumes were analyzed in 106 patients with primary (new-onset) PitNETs (80 nonfunctioning and 26 functioning) who underwent EES. The efficiency and accuracy of the semiautomatic segmentation with manual adjustments (SSMA) method was compared with other established segmentation methods for volumetric analysis in the nasal cavity and paranasal sinuses. Correlations between the measured nasal cavity and paranasal sinus volumes and the extent of tumor removal were evaluated.ResultsThe SSMA method yielded accurate and time-saving results following the volumetric analyses of nasal cavity and paranasal sinuses with complex structures. Alternatively, the manual and semiautomatic segmentation methods proved time-consuming and inaccurate, respectively. The sphenoid sinus volume measured by SSMA was significantly correlated with the extent of tumor removal in patients with nonfunctioning Knosp grade 3 and 4 PitNET (r = 0.318; p = 0.015).ConclusionThe volume of sphenoid sinus potentially could predict the extent of resection due to better visualization of the tumor for PitNETs with CS invasion
Surface Oxide Film and its Influence on the Oxygen Reduction on Pd-Co and Pt-Co PEFC Cathodes
PtCo and PdCo alloy electrodes were investigated in a 0.5 M sulfuric acid solution by electrochemistry, ellipsometry, laser Raman scattering spectroscopy, XPS, and GD-OES. The corrosion resistibility of Pt-Co and Pd-Co alloys decreased with increase of Co addition. The increase of Co addition, however, enhanced the catalytic efficiency on the ORR. The alloy surfaces may be covered by CoOOH and Pt or Pd oxide 2-3nm thick. At the potential of 1.2V vs. Ag/ AgCl/ sat. KCl, the thickness of oxide film increased with the Co addition. The presence of the oxide film on the alloy electrodes increases the overvoltage for the ORR. The effect of the oxide thickness on the ORR was discussed