16,137 research outputs found
I-BEAT: New ultrasonic method for single bunch measurement of ion energy distribution
The shape of a wave carries all information about the spatial and temporal
structure of its source, given that the medium and its properties are known.
Most modern imaging methods seek to utilize this nature of waves originating
from Huygens' principle. We discuss the retrieval of the complete kinetic
energy distribution from the acoustic trace that is recorded when a short ion
bunch deposits its energy in water. This novel method, which we refer to as
Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a generalization of the
ionoacoustic approach. Featuring compactness, simple operation,
indestructibility and high dynamic ranges in energy and intensity, I-BEAT is a
promising approach to meet the needs of petawatt-class laser-based ion
accelerators. With its capability of completely monitoring a single, focused
proton bunch with prompt readout it, is expected to have particular impact for
experiments and applications using ultrashort ion bunches in high flux regimes.
We demonstrate its functionality using it with two laser-driven ion sources for
quantitative determination of the kinetic energy distribution of single,
focused proton bunches.Comment: Paper: 17 Pages, 3 figures Supplementary Material 16 pages, 7 figure
EchoFusion: Tracking and Reconstruction of Objects in 4D Freehand Ultrasound Imaging without External Trackers
Ultrasound (US) is the most widely used fetal imaging technique. However, US
images have limited capture range, and suffer from view dependent artefacts
such as acoustic shadows. Compounding of overlapping 3D US acquisitions into a
high-resolution volume can extend the field of view and remove image artefacts,
which is useful for retrospective analysis including population based studies.
However, such volume reconstructions require information about relative
transformations between probe positions from which the individual volumes were
acquired. In prenatal US scans, the fetus can move independently from the
mother, making external trackers such as electromagnetic or optical tracking
unable to track the motion between probe position and the moving fetus. We
provide a novel methodology for image-based tracking and volume reconstruction
by combining recent advances in deep learning and simultaneous localisation and
mapping (SLAM). Tracking semantics are established through the use of a
Residual 3D U-Net and the output is fed to the SLAM algorithm. As a proof of
concept, experiments are conducted on US volumes taken from a whole body fetal
phantom, and from the heads of real fetuses. For the fetal head segmentation,
we also introduce a novel weak annotation approach to minimise the required
manual effort for ground truth annotation. We evaluate our method
qualitatively, and quantitatively with respect to tissue discrimination
accuracy and tracking robustness.Comment: MICCAI Workshop on Perinatal, Preterm and Paediatric Image analysis
(PIPPI), 201
Needle Tip Force Estimation using an OCT Fiber and a Fused convGRU-CNN Architecture
Needle insertion is common during minimally invasive interventions such as
biopsy or brachytherapy. During soft tissue needle insertion, forces acting at
the needle tip cause tissue deformation and needle deflection. Accurate needle
tip force measurement provides information on needle-tissue interaction and
helps detecting and compensating potential misplacement. For this purpose we
introduce an image-based needle tip force estimation method using an optical
fiber imaging the deformation of an epoxy layer below the needle tip over time.
For calibration and force estimation, we introduce a novel deep learning-based
fused convolutional GRU-CNN model which effectively exploits the
spatio-temporal data structure. The needle is easy to manufacture and our model
achieves a mean absolute error of 1.76 +- 1.5 mN with a cross-correlation
coefficient of 0.9996, clearly outperforming other methods. We test needles
with different materials to demonstrate that the approach can be adapted for
different sensitivities and force ranges. Furthermore, we validate our approach
in an ex-vivo prostate needle insertion scenario.Comment: Accepted for Publication at MICCAI 201
High-frequency ultrasonic speckle velocimetry in sheared complex fluids
High-frequency ultrasonic pulses at 36 MHz are used to measure velocity
profiles in a complex fluid sheared in the Couette geometry. Our technique is
based on time-domain cross-correlation of ultrasonic speckle signals
backscattered by the moving medium. Post-processing of acoustic data allows us
to record a velocity profile in 0.02--2 s with a spatial resolution of 40
m over 1 mm. After a careful calibration using a Newtonian suspension, the
technique is applied to a sheared lyotropic lamellar phase seeded with
polystyrene spheres of diameter 3--10 m. Time-averaged velocity profiles
reveal the existence of inhomogeneous flows, with both wall slip and shear
bands, in the vicinity of a shear-induced ``layering'' transition. Slow
transient regimes and/or temporal fluctuations can also be resolved and exhibit
complex spatio-temporal flow behaviors with sometimes more than two shear
bands.Comment: 15 pages, 18 figures, submitted to Eur. Phys. J. A
Solitonic State in Microscopic Dynamic Failures
Onset of permanent deformation in crystalline materials under a sharp
indenter tip is accompanied by nucleation and propagation of defects. By
measuring the spatio-temporal strain field nearthe indenter tip during
indentation tests, we demonstrate that the dynamic strain history at the moment
of a displacement burst carries characteristics of formation and interaction of
local excitations, or solitons. We show that dynamic propagation of multiple
solitons is followed by a short time interval where the propagating fronts can
accelerate suddenly. As a result of such abrupt local accelerations, duration
of the fast-slip phase of a failure event is shortened. Our results show that
formation and annihilation of solitons mediate the microscopic fast weakening
phase, during which extreme acceleration and collision of solitons lead to
non-Newtonian behavior and Lorentz contraction, i.e., shortening of solitons
characteristic length. The results open new horizons for understanding dynamic
material response during failure and, more generally, complexity of earthquake
sources
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