7,624 research outputs found
Relativistic ionization-rescattering with tailored laser pulses
The interaction of relativistically strong tailored laser pulses with an
atomic system is considered. Due to a special tailoring of the laser pulse, the
suppression of the relativistic drift of the ionized electron and a dramatic
enhancement of the rescattering probability is shown to be achievable. The high
harmonic generation rate in the relativistic regime is calculated and shown to
be increased by several orders of magnitude compared to the case of
conventional laser pulses. The energies of the revisiting electron at the
atomic core can approach the MeV domain, thus rendering hard x-ray harmonics
and nuclear reactions with single atoms feasible
Volumetric Ultrasound: A Novel Methodology for 3D Evaluation of Cardiovascular Structure and Function
Three-dimensional reconstructions (3DR) of the heart and great vessels are conventionally formed by scanning a single two-dimensional (2-D) plane, and then combining the data in this scan with data obtained from other scan planes taken at different levels. Missing data between planes are filled in by interpolation. Applications of such 3DR’s from ultrasonic, radionuclide and magnetic resonance images have yielded promising results (1). 3DR’s of the left ventricle have been obtained from cardiac ultrasonic and ultrafast computed tomographic images in our laboratory (2,3). We have also utilized the reconstructed geometries for analysis of mechanical deformation of the ventricular chamber and quantitative assessment of wall motion abnormalities in diseased states (4)
Spillway Rock Scour Analysis - Composite of Physical & Numerical Modelling, Paradise Dam, Australia
A number of problems and solutions of rock scour downstream of spillways have been evaluated using a composite approach, based on the gathering of detailed data from a physical model and utilising those data in a sequence of calibration and application of numerical modelling of the scour. Our paper will describe the application of the Computational Scour Model (CSM - Bollaert, 2002 and subsequent) as the numerical procedure that makes the composite approach a proven methodology for such problems. The paper will focus on a case study application of the procedure based on the experiences of flooding and scour at the Paradise Dam, Queensland, Australia.
Flooding in 2013 caused substantial scour downstream of the primary spillway. The occurrence led to a series of studies for the evaluation of the geology, and the evident hydraulics behaviour using a well-instrumented physical model to capture pressure and velocity transients, all as part of a process to determine the scour mechanism, and to determine the response of the spillway and areas downstream to future floods of larger magnitude. Utilising the transient data from approximately 60 pressure transducers, ADV measurements for transient velocities, together with the detailed geologic assessment, the comprehensive scour modelling procedures developed by Bollaert were applied for calibration of the numerical model and its application for possible discharge scenarios.
The paper will discuss the design and construction of the physical model and instrumentation as a key part of securing adequate data for the composite procedure, and go on to illustrate the outcomes of the CSM procedures
How Polarized Have We Become? A Multimodal Classification of Trump Followers and Clinton Followers
Polarization in American politics has been extensively documented and
analyzed for decades, and the phenomenon became all the more apparent during
the 2016 presidential election, where Trump and Clinton depicted two radically
different pictures of America. Inspired by this gaping polarization and the
extensive utilization of Twitter during the 2016 presidential campaign, in this
paper we take the first step in measuring polarization in social media and we
attempt to predict individuals' Twitter following behavior through analyzing
ones' everyday tweets, profile images and posted pictures. As such, we treat
polarization as a classification problem and study to what extent Trump
followers and Clinton followers on Twitter can be distinguished, which in turn
serves as a metric of polarization in general. We apply LSTM to processing
tweet features and we extract visual features using the VGG neural network.
Integrating these two sets of features boosts the overall performance. We are
able to achieve an accuracy of 69%, suggesting that the high degree of
polarization recorded in the literature has started to manifest itself in
social media as well.Comment: 16 pages, SocInfo 2017, 9th International Conference on Social
Informatic
Octupole strength in the neutron-rich calcium isotopes
Low-lying excited states of the neutron-rich calcium isotopes Ca
have been studied via -ray spectroscopy following inverse-kinematics
proton scattering on a liquid hydrogen target using the GRETINA -ray
tracking array. The energies and strengths of the octupole states in these
isotopes are remarkably constant, indicating that these states are dominated by
proton excitations.Comment: 15 pages, 3 figure
Columnar and lamellar phases in attractive colloidal systems
In colloidal suspensions, the competition between attractive and repulsive
interactions gives rise to a rich and complex phenomenology. Here, we study the
equilibrium phase diagram of a model system using a DLVO interaction potential
by means of molecular dynamics simulations and a thermodynamical approach. As a
result, we find tubular and lamellar phases at low volume fraction. Such
phases, extremely relevant for designing new materials, may be not easily
observed in the experiments because of the long relaxation times and the
presence of defects.Comment: 5 pages, 5 figure
Light scattering and phase behavior of Lysozyme-PEG mixtures
Measurements of liquid-liquid phase transition temperatures (cloud points) of
mixtures of a protein (lysozyme) and a polymer, poly(ethylene glycol) (PEG)
show that the addition of low molecular weight PEG stabilizes the mixture
whereas high molecular weight PEG was destabilizing. We demonstrate that this
behavior is inconsistent with an entropic depletion interaction between
lysozyme and PEG and suggest that an energetic attraction between lysozyme and
PEG is responsible. In order to independently characterize the lysozyme/PEG
interactions, light scattering experiments on the same mixtures were performed
to measure second and third virial coefficients. These measurements indicate
that PEG induces repulsion between lysozyme molecules, contrary to the
depletion prediction. Furthermore, it is shown that third virial terms must be
included in the mixture's free energy in order to qualitatively capture our
cloud point and light scattering data. The light scattering results were
consistent with the cloud point measurements and indicate that attractions do
exist between lysozyme and PEG.Comment: 5 pages, 2 figures, 1 tabl
1004-59 Vascular Acoustic Emissions During Angioplasty: Potential Role in Identification of Induced Dissection
A fundamental mechanism of balloon angioplasty (BA) is plaque rupture. Rupture leading to dissection, however, has been implicated as an underlyIng factor responsible for both acute and chronic adverse outcomes. Acoustic emissions (AE) — transient sound waves generated by microstructural alterations of a material subjected to mechanical stress — may provide a novel means of characterizing BA-induced tissue trauma. Using a novel acoustic sensor system, we examined the relationship between cumulative AE energy released by human arterial tissue during BA and the observed pathologic injury. Post-mortem human arterial specimens (19) were subjected to identical SA with simultaneous monitoring of intraluminal pressure and AE. Sound energy was integrated throughout the pressurization period to obtain an estimate of the cumulative AE energy released during dilatation. Postangioplasty inspection revealed a marked difference in AE energy released by specimens that experienced traumatic dissection vs. non-dissection dilatation:Sound energy released by vascular tissue undergoing balloon angioplasty discriminates dissection from non-dissection tissue trauma. Given the deleterious role that dissection can play in SA, this novel system may provide a means of improving procedural outcome
- …