199 research outputs found
Delocalised oxygen as the origin of two-level defects in Josephson junctions
One of the key problems facing superconducting qubits and other Josephson
junction devices is the decohering effects of bi-stable material defects.
Although a variety of phenomenological models exist, the true microscopic
origin of these defects remains elusive. For the first time we show that these
defects may arise from delocalisation of the atomic position of the oxygen in
the oxide forming the Josephson junction barrier. Using a microscopic model, we
compute experimentally observable parameters for phase qubits. Such defects are
charge neutral but have non-zero response to both applied electric field and
strain. This may explain the observed long coherence time of two-level defects
in the presence of charge noise, while still coupling to the junction electric
field and substrate phonons.Comment: 5 pages, 4 figures. This version streamlines presentation and focuses
on the 2D model. Also fixed embarrassing typo (pF -> fF
Origins of plateau formation in ion energy spectra under target normal sheath acceleration
Target normal sheath acceleration (TNSA) is a method employed in
laser--matter interaction experiments to accelerate light ions (usually
protons). Laser setups with durations of a few 10 fs and relatively low
intensity contrasts observe plateau regions in their ion energy spectra when
shooting on thin foil targets with thicknesses of order 10 m. In
this paper we identify a mechanism which explains this phenomenon using one
dimensional particle-in-cell simulations. Fast electrons generated from the
laser interaction recirculate back and forth through the target, giving rise to
time-oscillating charge and current densities at the target backside. Periodic
decreases in the electron density lead to transient disruptions of the TNSA
sheath field: peaks in the ion spectra form as a result, which are then spread
in energy from a modified potential driven by further electron recirculation.
The ratio between the laser pulse duration and the recirculation period
(dependent on the target thickness, including the portion of the pre-plasma
which is denser than the critical density) determines if a plateau forms in the
energy spectra.Comment: 11 pages, 12 figure
Agents.jl: A performant and feature-full agent based modelling software of minimal code complexity
Agent based modelling is a simulation method in which autonomous agents
interact with their environment and one another, given a predefined set of
rules. It is an integral method for modelling and simulating complex systems,
such as socio-economic problems. Since agent based models are not described by
simple and concise mathematical equations, code that generates them is
typically complicated, large, and slow. Here we present Agents.jl, a
Julia-based software that provides an ABM analysis platform with minimal code
complexity. We compare our software with some of the most popular ABM software
in other programming languages. We find that Agents.jl is not only the most
performant, but also the least complicated software, providing the same (and
sometimes more) features as the competitors with less input required from the
user. Agents.jl also integrates excellently with the entire Julia ecosystem,
including interactive applications, differential equations, parameter
optimization, and more. This removes any ``extensions library'' requirement
from Agents.jl, which is paramount in many other tools
Vestibular ontogeny: Measuring the influence of the dynamic environment
In comparison to other special senses, we are only meagerly informed about the development of vestibular function and the mechanisms that may operate to control or influence the course of vestibular ontogeny. Perhaps one contributing factor to this disparity is the difficulty of evaluating vestibular sense organs directly and noninvasively. The present report describes a recently developed direct noninvasive vestibular function test that can be used to address many basic questions about the developing vestibular system. More particularly, the test can be used to examine the effects of the dynamic environment (e.g. gravitational field and vibration) on vestibular ontogeny
Experimental Validation of ARFI Surveillance of Subcutaneous Hemorrhage (ASSH) Using Calibrated Infusions in a Tissue-Mimicking Model and Dogs
Acoustic radiation force impulse (ARFI) Surveillance of Subcutaneous Hemorrhage (ASSH) has been previously demonstrated to differentiate bleeding phenotype and responses to therapy in dogs and humans, but to date, the method has lacked experimental validation. This work explores experimental validation of ASSH in a poroelastic tissue-mimic and in vivo in dogs. The experimental design exploits calibrated flow rates and infusion durations of evaporated milk in tofu or heparinized autologous blood in dogs. The validation approach enables controlled comparisons of ASSH-derived bleeding rate (BR) and time to hemostasis (TTH) metrics. In tissue-mimicking experiments, halving the calibrated flow rate yielded ASSH-derived BRs that decreased by 44% to 48%. Furthermore, for calibrated flow durations of 5.0 minutes and 7.0 minutes, average ASSH-derived TTH was 5.2 minutes and 7.0 minutes, respectively, with ASSH predicting the correct TTH in 78% of trials. In dogs undergoing calibrated autologous blood infusion, ASSH measured a 3-minute increase in TTH, corresponding to the same increase in the calibrated flow duration. For a measured 5% decrease in autologous infusion flow rate, ASSH detected a 7% decrease in BR. These tissue-mimicking and in vivo preclinical experimental validation studies suggest the ASSH BR and TTH measures reflect bleeding dynamics
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