12,217 research outputs found
Symmetric mode resonance of bubbles near a rigid boundary - the nonlinear case with time delay effects
A fundamental understanding of the effect of a surface on the resonance frequency of bubbles will be useful in the future development of diagnostic medical ultrasound equipment, and specifically in the area of targeted contrast agents for the screening and possible treatment of colon cancer. In this work we turn to the wall effects on the nonlinear resonance frequency response of air bubbles in water, following on from an earlier work which considered linear interactions (E. M. B. Payne, S. Illesinghe, A. Ooi, R. Manasseh, J. Acoust Soc. Am. 118, 2841-2849 (2005)). Numerical results for micron-sized bubbles near a rigid boundary are presented, showing the shift in frequency caused by the presence of the boundary and the presence of other bubbles. Time delay effects are also included, showing a damping of the frequency response. Simulations are limited to the special case where all bubbles are in phase (i.e., the symmetric mode), which refers to the case where all bubbles have the same initial conditions and are subjected to the same excitation pressure field. As a result they have identical time histories. An experimental method for measuring the frequency response of a single bubble attached to a surface is also briefly mentioned
An Empirically Derived Three-Dimensional Laplace Resonance in the Gliese 876 Planetary System
We report constraints on the three-dimensional orbital architecture for all
four planets known to orbit the nearby M dwarf Gliese 876 based solely on
Doppler measurements and demanding long-term orbital stability. Our dataset
incorporates publicly available radial velocities taken with the ELODIE and
CORALIE spectrographs, HARPS, and Keck HIRES as well as previously unpublished
HIRES velocities. We first quantitatively assess the validity of the planets
thought to orbit GJ 876 by computing the Bayes factors for a variety of
different coplanar models using an importance sampling algorithm. We find that
a four-planet model is preferred over a three-planet model. Next, we apply a
Newtonian MCMC algorithm to perform a Bayesian analysis of the planet masses
and orbits using an n-body model in three-dimensional space. Based on the
radial velocities alone, we find that a 99% credible interval provides upper
limits on the mutual inclinations for the three resonant planets
( for the "c" and "b" pair and for
the "b" and "e" pair). Subsequent dynamical integrations of our posterior
sample find that the GJ 876 planets must be roughly coplanar
( and ), suggesting the amount of
planet-planet scattering in the system has been low. We investigate the
distribution of the respective resonant arguments of each planet pair and find
that at least one argument for each planet pair and the Laplace argument
librate. The libration amplitudes in our three-dimensional orbital model
supports the idea of the outer-three planets having undergone significant past
disk migration.Comment: 19 pages, 11 figures, 8 tables. Accepted to MNRAS. Posterior samples
available at https://github.com/benelson/GJ87
Experimental study of beam distortion due to fiducial markers during salvage HIFU in the prostate
BACKGROUND: Prostate cancer is frequently treated using external beam radiation therapy (EBRT). Prior to therapy, the prostate is commonly implanted with a small number of permanent fiducial markers used to monitor the position of the prostate during therapy. In the case of local cancer recurrence, high-intensity focused ultrasound (HIFU) provides a non-invasive salvage treatment option. However, the impact of the fiducial markers on HIFU treatment has not been thoroughly studied to date. The objective of this study was to experimentally investigate the effect of a single EBRT fiducial marker on the efficacy of HIFU treatment delivery using a tissue-mimicking material (TMM).
METHODS: A TMM with the acoustic properties of the prostate was developed based on a polyacrylamide hydrogel containing bovine serum albumin. Each phantom was implanted with a cylindrical fiducial marker and then sonicated using a 3.3 MHz focused bowl HIFU transducer. Two sets of experiments were performed. In the first, a single lesion was created at different positions along either the anteroposterior or left-right axes relative to the marker. In the second, a larger ablation volume was created by raster scanning. The size and position of the ablated volume were assessed using a millimetre grid overlaid on the phantom.
RESULTS: The impact of the marker on the position and size of the HIFU lesion was significant when the transducer focus was positioned within 7 mm anteriorly, 18 mm posteriorly or within 3 mm laterally of the marker. Beyond this, the generated lesion was not affected. When the focus was anterior to the marker, the lesion increased in size due to reflections. When the focus was posterior, the lesion decreased in size or was not present due to shadowing.
CONCLUSIONS: The presence of an EBRT fiducial marker may result in an undertreated region beyond the marker due to reduced energy arriving at the focus, and an overtreated region in front of the marker due to reflections. Depending on the position of the targeted regions and the distribution of the markers, both effects may be undesirable and reduce treatment efficacy. Further work is necessary to investigate whether these results indicate the necessity to reconsider patient selection and treatment planning for prostate salvage HIFU after failed EBRT
Multifrequency Radio Observations of a SNR in the LMC. The Case of SNR J0527-6549 (DEM l204)
We present a detailed study and results of new Australia Telescope Compact
Array (ATCA) observations of supernova remnant, SNR J0527-6549. This Large
Magellanic Cloud (LMC) ob ject follows a typical supernova remnant (SNR)
horseshoe morphology with a diameter of D=(66x58)+-1 pc which is among the
largest SNRs in the LMC. Its relatively large size indicates older age while a
steeper than expected radio spectral index of aplha=-0.92+-0.11 is more typical
for younger and energetic SNRs. Also, we report detections of regions with a
high order of polarization at a peak value of ~54+-17% at 6 cm.Comment: 9 Pages, 6 figures, accepted for publication in SA
Tunnel mounted auto destruct module Scout vehicle
Tunnel mounted, automatic, electronic destruction module for Scout launch vehicle first and second stage
Projective Ring Line Encompassing Two-Qubits
The projective line over the (non-commutative) ring of two-by-two matrices
with coefficients in GF(2) is found to fully accommodate the algebra of 15
operators - generalized Pauli matrices - characterizing two-qubit systems. The
relevant sub-configuration consists of 15 points each of which is either
simultaneously distant or simultaneously neighbor to (any) two given distant
points of the line. The operators can be identified with the points in such a
one-to-one manner that their commutation relations are exactly reproduced by
the underlying geometry of the points, with the ring geometrical notions of
neighbor/distant answering, respectively, to the operational ones of
commuting/non-commuting. This remarkable configuration can be viewed in two
principally different ways accounting, respectively, for the basic 9+6 and 10+5
factorizations of the algebra of the observables. First, as a disjoint union of
the projective line over GF(2) x GF(2) (the "Mermin" part) and two lines over
GF(4) passing through the two selected points, the latter omitted. Second, as
the generalized quadrangle of order two, with its ovoids and/or spreads
standing for (maximum) sets of five mutually non-commuting operators and/or
groups of five maximally commuting subsets of three operators each. These
findings open up rather unexpected vistas for an algebraic geometrical
modelling of finite-dimensional quantum systems and give their numerous
applications a wholly new perspective.Comment: 8 pages, three tables; Version 2 - a few typos and one discrepancy
corrected; Version 3: substantial extension of the paper - two-qubits are
generalized quadrangles of order two; Version 4: self-dual picture completed;
Version 5: intriguing triality found -- three kinds of geometric hyperplanes
within GQ and three distinguished subsets of Pauli operator
The Balian-Br\'ezin Method in Relativistic Quantum Mechanics
The method suggested by Balian and Br\'ezin for treating angular momentum
reduction in the Faddeev equations is shown to be applicable to the
relativistic three-body problem.Comment: 14 pages in LaTe
Supplemental lysine sulfate does not negatively affect the performance of broiler chicks fed dietary sulfur from multiple dietary and water sources
Commercial broiler producers and nutritionists have questioned the performance consequences of sulfur (S) from various dietary and water sources combined in current commercial production. The combination of high-S feed ingredients, including dried distillers grains with solubles, and dietary additives that contain S, such as lysine sulfate or copper sulfate, has the potential to create high S exposure, especially when combined with high-S drinking water. The tolerance of growing broiler chicks to S was determined by supplementation of a corn-soybean-5% dried distillers grains with solubles diet with up to 1% lysine sulfate or an equal amount of S from sodium sulfide. An additional diet containing copper and zinc sulfate served as a positive control for the source of S and high-S inclusion. These diets were fed to chicks provided with normal (0.008% or 80 ppm) or high water S (0.113% or 1130 ppm). We hypothesized that the addition of S sources to a commercial diet would not reduce the performance of growing chicks given access to normal or high-S water. Data showed dietary S requirements were met and excess S was easily excreted, hence, under the experimental feeding conditions, supplementation with up to 1% additional lysine sulfate (or a similar product) did not reduce performance in comparison with chicks fed a lower S diet with access to normal or high-S water. The high-S diet from copper and zinc sulfate resulted in reduced water and feed consumption, although there were no effects on chick weight gain
Charge-Symmetry-Breaking Three-Nucleon Forces
Leading-order three-nucleon forces that violate isospin symmetry are
calculated in Chiral Perturbation Theory. The effect of the
charge-symmetry-breaking three-nucleon force is investigated in the trinucleon
systems using Faddeev calculations. We find that the contribution of this force
to the 3He - 3H binding-energy difference is approximately 5 keV.Comment: 14 pages, 3 figure
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