7,841 research outputs found
open-UST: An Open-Source Ultrasound Tomography Transducer Array System
Fast imaging methods are needed to promote widespread clinical adoption of Ultrasound Tomography (UST), and more widely available UST hardware could support the experimental validation of new measurement configurations. In this work, an open-source 256-element transducer ring array was developed (morganjroberts.github.io/open-UST) and manufactured using rapid prototyping, for only £2k. Novel manufacturing techniques were used, resulting in a 1.17° mean beam axis skew angle, a 104 μm mean element position error, and a ±13.6 μm deviation in matching layer thickness. The nominal acoustic performance was measured using hydrophone scans and watershot data, and the 61.2 dB SNR, 55.4° opening angle, 10.2 mm beamwidth and 54% transmit-receive bandwidth (-12 dB), were found to be similar to existing systems, and compatible with state of the art full-waveform-inversion image reconstruction methods. The inter-element variation in acoustic performance was typically <10% without using normalisation, meaning that the elements can be modelled identically during image reconstruction, removing the need for individual source definitions based on hydrophone measurements. Finally, data from a phantom experiment was successfully reconstructed. These results demonstrate that the open-UST system is accessible for users, and suitable for UST imaging research
Linear angular momentum multiplexing-conceptualization and experimental evaluation with antenna arrays
Linear Angular Momentum Multiplexing is a new method for providing highly spectrally efficient short range communication between a transmitter and receiver, where one may move at speed transverse to the propagation. Such applications include rail, vehicle and hyperloop transport systems communicating with fixed infrastructure on the ground. This paper describes how the scientific concept of linear angular momentum multiplexing evolves from orbital angular momentum multiplexing. The essential parameters for implementing this concept are: a long array at least at one of the ends of the link; antenna element radiation characteristics; and the array element spacing relative to the propagation distance. These parameters are also backed by short range measurements carried out at 2.4GHz used to model the Rice fading channel and determine resilience to multipath fading
Flexible Lipid Bilayers in Implicit Solvent
A minimalist simulation model for lipid bilayers is presented. Each lipid is
represented by a flexible chain of beads in implicit solvent. The hydrophobic
effect is mimicked through an intermolecular pair potential localized at the
``water''/hydrocarbon tail interface. This potential guarantees realistic
interfacial tensions for lipids in a bilayer geometry. Lipids self assemble
into bilayer structures that display fluidity and elastic properties consistent
with experimental model membrane systems. Varying molecular flexibility allows
for tuning of elastic moduli and area/molecule over a range of values seen in
experimental systems.Comment: 5 pages, 5 figure
Risky Driving by Recently Licensed Teens: Self-Reports and Simulated Performance
U.S. teens are overrepresented in motor vehicle crashes, with the majority due to driver error; however, causal pathways remain to be elucidated. This research aimed to identify driving performance factors that might underlie newly-licensed male teens’ risk. Surveys were conducted with 21 16-year-olds at the time of intermediate licensure. During the second month of licensure they completed drives in a high-fidelity simulator. Simulator scenarios allowed assessment of responses to yellow traffic lights changing to red and to a visual search task, for which previous data on older age groups of drivers were available. All teens had an A or B grade point average, previously found to be associated with lower crash and citation risk. Nonetheless, 71% reported risky driving in terms of prior unlicensed, unsupervised driving. In the simulator, 46% went through an intersection as the light turned red, compared to 33% of adults. In the visual search task, teens had shorter mean perception-reaction times and identified more targets than adults and older drivers, but similar to young drivers. Therefore, even teens with good grades, perceived to be less risky, were willing to take driving risks. Their driving performance suggests there may be subtle differences in the way recently-licensed teens drive that might predispose them to crashes. Further research of this nature can increase understanding of such differences and inform the development of more targeted intervention
Interaction potential in compact three-dimensional QED with mixed action
We use a variational wave function to calculate the energy of the interaction
between external charges in the compact Abelian gauge theory in 2+1 dimensions
with mixed action. Our variational wave functions preserve the compact gauge
invariance of the theory both in the vacuum and in the charged sectors. We find
that a good estimate of the interaction energy is obtained only when we allow
more variational parameters in the charged sector than in the vacuum sector.
These extra parameters are the profile of an induced electric field. We find
that the theory has a two-phase structure: When the charge-2 coupling is large
and negative there is no mass gap in the theory and no confinement, while
otherwise a mass gap is generated dynamically and the theory confines charges.
The pure Wilson theory is in the confining phase.Comment: 22 pages, Latex -- final version, minor changes from first versio
Stringent constraints on neutron-star radii from multimessenger observations and nuclear theory
The properties of neutron stars are determined by the nature of the matter
that they contain. These properties can be constrained by measurements of the
star's size. We obtain stringent constraints on neutron-star radii by combining
multimessenger observations of the binary neutron-star merger GW170817 with
nuclear theory that best accounts for density-dependent uncertainties in the
equation of state. We construct equations of state constrained by chiral
effective field theory and marginalize over these using the gravitational-wave
observations. Combining this with the electromagnetic observations of the
merger remnant that imply the presence of a short-lived hyper-massive neutron
star, we find that the radius of a neutron star is
(90% credible
interval). Using this constraint, we show that neutron stars are unlikely to be
disrupted in neutron-star black-hole mergers; subsequently, such events will
not produce observable electromagnetic emission.Comment: 39 pages, 4 figure
Self-Gravitating Strings In 2+1 Dimensions
We present a family of classical spacetimes in 2+1 dimensions. Such a
spacetime is produced by a Nambu-Goto self-gravitating string. Due to the
special properties of three-dimensional gravity, the metric is completely
described as a Minkowski space with two identified worldsheets. In the flat
limit, the standard string is recovered. The formalism is developed for an open
string with massive endpoints, but applies to other boundary conditions as
well. We consider another limit, where the string tension vanishes in
geometrical units but the end-masses produce finite deficit angles. In this
limit, our open string reduces to the free-masses solution of Gott, which
possesses closed timelike curves when the relative motion of the two masses is
sufficiently rapid. We discuss the possible causal structures of our spacetimes
in other regimes. It is shown that the induced worldsheet Liouville mode obeys
({\it classically}) a differential equation, similar to the Liouville equation
and reducing to it in the flat limit. A quadratic action formulation of this
system is presented. The possibility and significance of quantizing the
self-gravitating string, is discussed.Comment: 55 page
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