191 research outputs found
Specialised Image Capture Systems for a DIET Breast Cancer Screening System
Digital Image-based Elasto-Tomography (DIET) is an
emerging technology for non-invasive breast cancer screening.
This technology actuates breast tissue and measures the surface
motion using digital imaging technology. The internal
distribution of stiffness is then reconstructed using Boundary
Element or Finite Element Methods (FEM or BEM). However,
obtaining accurate imaging at high frequency and high
resolution in terms of numbers of pixels is challenging if
enough accuracy is to be obtained in the motion sensing to
deliver a useful result. The overall focus of such mechatronic
and digitally centred systems is on providing a low-cost,
radiation dose-free and portable screening system capable of
screening numerous patients per day â in direct contrast to
current low throughput, non-portable and high cost x-ray and
MRI based approaches.
Thus, DIET technology relies on obtaining high resolution
images of a breasts surface under high frequency actuation,
typically in the range of 50-100Hz. Off-the-shelf digital
cameras and imaging elements are unable to capture images
directly at these speeds. A method is presented for obtaining the
required high speed image capture at a resolution of 1280x1024
pixels and actuation frequency of 100Hz. The prototype
apparatus presented uses two imaging sensors in combination with frame grabbers and a dSpaceâą control system, to produce
an automated image capture system. The system integrates a
precision controlled strobe lighting system to selectively
capture sinusoids at different points in the sinusoidal cycle of
response.
The final working system produced images that enabled
effective 3D motion tracking of the surface of a silicon phantom
actuated at 100Hz. The surface of the phantom was strobed at
pre-selected phases from 0 to 360 degrees, and an image was
captured for each phase. The times at which image capture
occurred were calculated for a phase lag increment of 10
degrees resulting in an image effectively every 0.00028s for the
actuator cycle of 0.01s. The comparison of the actual trigger
times and pre-selected ideal trigger times gave a mean absolute
error of 1.4%, thus demonstrating the accuracy of the final
system.
Final validation is performed using this system to track
motion in a silicon gel phantom. The motion is tracked
accurately using a novel Euclidean Invariant signature method.
Both cameras delivered similar results with over 90% of points
tracked to within 1-2%. This level of accuracy confirms the
ability to effectively accurately reconstruct the stiffness as
validated in other related studies
Expanding and Collapsing Scalar Field Thin Shell
This paper deals with the dynamics of scalar field thin shell in the
Reissner-Nordstrm geometry. The Israel junction conditions between
Reissner-Nordstrm spacetimes are derived, which lead to the equation
of motion of scalar field shell and Klien-Gordon equation. These equations are
solved numerically by taking scalar field model with the quadratic scalar
potential. It is found that solution represents the expanding and collapsing
scalar field shell. For the better understanding of this problem, we
investigate the case of massless scalar field (by taking the scalar field
potential zero). Also, we evaluate the scalar field potential when is an
explicit function of . We conclude that both massless as well as massive
scalar field shell can expand to infinity at constant rate or collapse to zero
size forming a curvature singularity or bounce under suitable conditions.Comment: 15 pages, 11 figure
The Theory of Brown Dwarfs and Extrasolar Giant Planets
Straddling the traditional realms of the planets and the stars, objects below
the edge of the main sequence have such unique properties, and are being
discovered in such quantities, that one can rightly claim that a new field at
the interface of planetary science and and astronomy is being born. In this
review, we explore the essential elements of the theory of brown dwarfs and
giant planets, as well as of the new spectroscopic classes L and T. To this
end, we describe their evolution, spectra, atmospheric compositions, chemistry,
physics, and nuclear phases and explain the basic systematics of
substellar-mass objects across three orders of magnitude in both mass and age
and a factor of 30 in effective temperature. Moreover, we discuss the
distinctive features of those extrasolar giant planets that are irradiated by a
central primary, in particular their reflection spectra, albedos, and transits.
Aspects of the latest theory of Jupiter and Saturn are also presented.
Throughout, we highlight the effects of condensates, clouds, molecular
abundances, and molecular/atomic opacities in brown dwarf and giant planet
atmospheres and summarize the resulting spectral diagnostics. Where possible,
the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for
publication in the Reviews of Modern Physics. 30 figures are color. Most of
the figures are in GIF format to reduce the overall size. The full version
with figures can also be found at:
http://jupiter.as.arizona.edu/~burrows/papers/rm
Advanced Semi-Active Resetable Devices and Device Modeling Including Non-Linearities
Resetable devices are a novel semi-active approach to managing structural response
energy. Recently developed devices allow independent control of each chamber
enabling unique approaches to sculpting the structural hysteresis loops and
behaviour. This paper creates a non-linear model of experimental prototypes that is
fully generalisable, and does so in a step-by-step fashion adding each non-linear
affect individually. Non-linearities that can significantly affect performance,
including valve size, mass flow rate and friction are characterised experimentally
and modeled. The results are validated against experimental data for cases of all
forms of device control, as well as for several experimental cases utilizing external
pressurized sources to enhance the force capacity. Force capacity, using a
pressurised reservoir and/or accumulator increased force capacity of these devices
from 100-600%, increasing the potential of these designs and approach to seismic
energy dissipation. Final model results have less than 5% error compared to
nonlinear experimental data. There is a strong correlation between the fundamental
nonlinear dynamics modelled and the experimental results, validating the overall
model and approach. The overall results and approach are fully general for
application to the design or analysis of similar device systems
Application of Sensing & Actuation for Online Hybrid Testing of Structural Control Devices
On-line hybrid tests couple virtual structures under dynamic loading with physical sub-structures or devices in a
dynamic test rig. The use of sensors and actuators in a closed-loop feedback system maintains the dynamic
equilibrium of the overall system comprising the physical test article and virtual modelled structure. This
research presents simple, cost-effective and robust hybrid test system by cleverly melding the sensors and
actuators with virtual model. It outlines solutions to the major issues faced in developing any hybrid system. The
overall approach is centred on the dSpaceTM real-time control system development tool
Strobe Imaging System for Digital Image-based Elasto-Tomography Breast Cancer Screening
Digital Image-based Elasto-Tomography (DIET) technology relies on obtaining high resolution images of a breasts surface under high frequency actuation, typically in the range of 50-100Hz. Off-the-shelf digital cameras and imaging elements are unable to capture images directly at these speeds. A method based on strobe imaging is presented for obtaining the required high speed image capture at a resolution of 1280x1024 pixels and actuation frequency of 100 Hz. The final working system produced images that enabled effective 3D motion tracking of the surface of a silicon phantom. The motion is tracked accurately using a novel Euclidean Invariant signature method
Digital image-based elasto-tomography: first experiments in surface based mechanical property estimation of gelatine phantoms
Invited special edition on Bio-EngineeringDigital Image-based Elasto-Tomography (DIET) is a novel surface-based
elasticity reconstruction method for determining the elastic property distribution
within the breast. Following on from proof of concept simulation studies,
this research considers the motion evaluation and stiffness reconstruction
of a soft tissue approximating gelatine phantom. This initial phantom work
provides an intermediate stage between prior simulation studies more detailed
phantom studies to follow. Reference points on the surface of a cylindrical
phantom were successfully tracked and converted into a steady-state
motion description. Motion error based mechanical property reconstruction
allowed an estimation of the stiffness of the gelatine when actuated at 50 Hz.
The reconstructed stiffness compared favorably with independently measured
stiffness properties of the gelatine material when experimental assumptions
were considered. An experimental noise estimate of 50% was confirmed accurate
by comparing experimental motions to simulated motion data with added noise
Re-Shaping Hysteresis: Seismic Semi-Active Control Experiments for a 1/5th Scale Structure
Semi-active resetable devices can improve seismic response. Novel 2-4 devices
independently control each device chamber to customise structural hysteresis loops to
reduce both displacement and base shear demands. Here, 2-4 devices are experimentally
validated on a one-fifth scale test structure weighing 35kN with a natural period of 0.6
seconds. Four seismic inputs over a wide range of intensity levels are use in 27 tests.
Results for resetable semi-active devices that modify hysteretic behaviour using different
control laws are compared to spectral response analyses that predict ~30-50% peak
displacement reductions. Fully uncontrolled tests were also done for lower intensity
ground motions, along with fail-safe valves-open tests. Results show 25-50% peak
displacement reductions compared to the valves open case, depending on the semi-active
control law used and matching spectral analysis results. Additionally, a semi-active
control law designed to simultaneously reduce base shear reduces it 10-20%. In contrast,
10-20% increases are seen for other approaches, as predicted. Overall, these are the first
large-scale tests of this type of novel resetable devices. The results validate prior
simulation and spectral analyses, and clearly show the potential. Finally, semi-active
methods that re-shape hysteresis to control response and simultaneously limit base shear
demand, are experimentally demonstrated for the first time
Experimental Validation of Semi-active Resetable Actuators in a 1/5th Scale Test Structure
The seismic performance of a test structure fitted with semi-active resetable devices is experimentally
investigated. Shaking table tests are conducted on a 15
th scale four-storey building using 27 earthquake
records at different intensity scalings. Different resetable device control laws result in unique hysteretic
responses from the devices and thus the structure. This device adaptability enables manipulation or
sculpting of the overall hysteresis response of the structure to address specific structural cases and types.
The response metrics are presented as maximum 3rd floor acceleration and displacement, and the total
base shear. The devices reduce all the response metrics compared with the uncontrolled case and a
fail-safe surrogate. Cumulative probability functions allow comparison between different control laws and
additionally allow tradeoffs in design to be rapidly assessed. Ease of changing the control law in real-time
during an earthquake record further improves the adaptability of the system to obtain the optimum device
response for the input motion and structural type. The findings are an important step to realizing full-scale
structural control with customized semi-active hysteretic behaviour using these novel resetable device
designs
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