13,444 research outputs found
Tunable coaxial resonators based on silicon optical fibers
Thermal tuning of a coaxial fiber resonator with a silica cladding surrounding an inner silicon core is investigated. By pumping the silicon with below bandgap light, it is possible to redshift the WGM resonances
Intraoperative Organ Motion Models with an Ensemble of Conditional Generative Adversarial Networks
In this paper, we describe how a patient-specific, ultrasound-probe-induced
prostate motion model can be directly generated from a single preoperative MR
image. Our motion model allows for sampling from the conditional distribution
of dense displacement fields, is encoded by a generative neural network
conditioned on a medical image, and accepts random noise as additional input.
The generative network is trained by a minimax optimisation with a second
discriminative neural network, tasked to distinguish generated samples from
training motion data. In this work, we propose that 1) jointly optimising a
third conditioning neural network that pre-processes the input image, can
effectively extract patient-specific features for conditioning; and 2)
combining multiple generative models trained separately with heuristically
pre-disjointed training data sets can adequately mitigate the problem of mode
collapse. Trained with diagnostic T2-weighted MR images from 143 real patients
and 73,216 3D dense displacement fields from finite element simulations of
intraoperative prostate motion due to transrectal ultrasound probe pressure,
the proposed models produced physically-plausible patient-specific motion of
prostate glands. The ability to capture biomechanically simulated motion was
evaluated using two errors representing generalisability and specificity of the
model. The median values, calculated from a 10-fold cross-validation, were
2.8+/-0.3 mm and 1.7+/-0.1 mm, respectively. We conclude that the introduced
approach demonstrates the feasibility of applying state-of-the-art machine
learning algorithms to generate organ motion models from patient images, and
shows significant promise for future research.Comment: Accepted to MICCAI 201
Magnetoelastic and structural properties of azurite Cu3(CO3)2(OH)2 from neutron scattering and muon spin rotation
Azurite, Cu3(CO3)2(OH)2, has been considered an ideal example of a
one-dimensional (1D) diamond chain antiferromagnet. Early studies of this
material imply the presence of an ordered antiferromagnetic phase below K while magnetization measurements have revealed a 1/3 magnetization
plateau. Until now, no corroborating neutron scattering results have been
published to confirm the ordered magnetic moment structure. We present recent
neutron diffraction results which reveal the presence of commensurate magnetic
order in azurite which coexists with significant magnetoelastic strain. The
latter of these effects may indicate the presence of spin frustration in zero
applied magnetic field. Muon spin rotation, SR, reveals an onset of
short-range order below 3K and confirms long-range order below .Comment: 5 pages, 4 figures, PHYSICAL REVIEW B 81, 140406(R) (2010
Educating renal nurses - inferior vena caval ultrasound for intravascular volume assessment
Aim: Volume status of haemodialysis patients can be evaluated by trained doctors using ultrasound (US) of the inferior vena cava (IVC). To date, renal nurses have not been taught this skill. As part of a larger study exploring the use of US by renal nurses we developed an educational program to ensure that renal nurses received adequate US training to attain competence in IVC ultrasound (IVC-US). Methods: The educational program was divided into four parts. Initially a clinical US expert delivered the necessary theoretical and then practical components of the program. After this the nurse undertook a period of self-directed US practice (100 scans). During this period three formative reviews of the recorded scan clips with feedback occurred. Specific feedback covered US technique, image optimisation and acquisition and image interpretation. Finally, as a summative assessment the nurse performed and interpreted 60 scans on 10 dialysis patients. These scans were independently assessed for quality and the nurse interpretations reviewed for accuracy, prior to deeming the candidate competent to independently perform IVC-US. Findings: Ultrasound education involves knowledge and skill acquisition. Initial theoretical and practical education must be translated into competence through task repetition and targeted feedback. A staged educational program that involves these components is likely to be successful. The rate for US skill acquisition varies and a summative assessment ensuring competence prior to independent scanning is important. Conclusions: This four-step program demonstrated that it is feasible to educate a renal nurse in IVC-US for intravascular volume assessment
Characterization of 1D photonic crystal nanobeam cavities using curved microfiber
We investigate high-Q, small mode volume photonic crystal nanobeam cavities using a curved, tapered optical microfiber loop. The strength of the coupling between the cavity and the microfiber loop is shown to depend on the contact position on the nanobeam, angle between the nanobeam and the microfiber, and polarization of the light in the fiber. The results are compared to a resonant scattering measurement
Fusion splicing of silicon optical fibres
The first splicing experiments between silicon optical fibres (SOFs) and conventional fibres are investigated. An optimized fusion splicing approach for a polycrystalline SOF is demonstrated and the material properties after splicing are characterized
Polarimetric Properties of Flux-Ropes and Sheared Arcades in Coronal Prominence Cavities
The coronal magnetic field is the primary driver of solar dynamic events.
Linear and circular polarization signals of certain infrared coronal emission
lines contain information about the magnetic field, and to access this
information, either a forward or an inversion method must be used. We study
three coronal magnetic configurations that are applicable to polar-crown
filament cavities by doing forward calculations to produce synthetic
polarization data. We analyze these forward data to determine the
distinguishing characteristics of each model. We conclude that it is possible
to distinguish between cylindrical flux ropes, spheromak flux ropes, and
sheared arcades using coronal polarization measurements. If one of these models
is found to be consistent with observational measurements, it will mean
positive identification of the magnetic morphology that surrounds certain
quiescent filaments, which will lead to a greater understanding of how they
form and why they erupt.Comment: 22 pages, 8 figures, Solar Physics topical issue: Coronal Magnetis
A Catalogue of Field Horizontal Branch Stars Aligned with High Velocity Clouds
We present a catalogue of 430 Field Horizontal Branch (FHB) stars, selected
from the Hamburg/ESO Survey (HES), which fortuitously align with high column
density neutral hydrogen (HI) High-Velocity Cloud (HVC) gas. These stars are
ideal candidates for absorption-line studies of HVCs, attempts at which have
been made for almost 40 years with little success. A parent sample of 8321 HES
FHB stars was used to extract HI spectra along each line-of-sight, using the HI
Parkes All-Sky Survey. All lines-of-sight aligned with high velocity HI
emission with peak brightness temperatures greater than 120mK were examined.
The HI spectra of these 430 probes were visually screened and cross-referenced
with several HVC catalogues. In a forthcoming paper, we report on the results
of high-resolution spectroscopic observations of a sample of stars drawn from
this catalogue.Comment: 7 pages, 4 figures. ApJS accepted. Full catalogue and all online-only
images available at
http://astronomy.swin.edu.au/staff/cthom/catalogue/index.htm
Thin disk kinematics from RAVE and the solar motion
Aims. We study the Milky Way thin disk with the Radial Velocity Experiment
(RAVE) survey. We consider the thin and thick disks as different Galactic
components and present a technique to statistically disentangle the two
populations. Then we focus our attention on the thin disk component. Methods.
We disentangle the thin disk component from amixture of the thin and thick
disks using a data set providing radial velocities, proper motions, and
photometrically determined distances. Results. We present the trend of the
velocity dispersions in the thin disk component of the Milky Way (MW) in the
radial direction above and below the Galactic plane using data from the RAdial
Velocity Experiment (RAVE). The selected sample is a limited subsample from the
entire RAVE catalogue, roughly mapping up to 500 pc above and below the
Galactic plane, a few degrees in azimuthal direction and covering a radial
extension of 2.0 kpc around the solar position. The solar motion relative to
the local standard of rest is also re-determined with the isolated thin disk
component. Major results are the trend of the velocity mean and dispersion in
the radial and vertical direction. In addition the azimuthal components of the
solar motion relative to the local standard of rest and the velocity dispersion
are discussed.Comment: accepted on A&A, please see companion paper "THICK disk kinem...
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