2,504 research outputs found
The dependence of intrinsic alignment of galaxies on wavelength using KiDS and GAMA
The outer regions of galaxies are more susceptible to the tidal interactions
that lead to intrinsic alignments of galaxies. The resulting alignment signal
may therefore depend on the passband if the colours of galaxies vary spatially.
To quantify this, we measured the shapes of galaxies with spectroscopic
redshifts from the GAMA survey using deep gri imaging data from the KiloDegree
Survey. The performance of the moment-based shape measurement algorithm DEIMOS
was assessed using dedicated image simulations, which showed that the
ellipticities could be determined with an accuracy better than 1% in all bands.
Additional tests for potential systematic errors did not reveal any issues. We
measure a significant difference of the alignment signal between the g,r and
i-band observations. This difference exceeds the amplitude of the linear
alignment model on scales below 2 Mpc/h. Separating the sample into
central/satellite and red/blue galaxies, we find that that the difference is
dominated by red satellite galaxies.Comment: 16 pages, 13 figures, accepted, to appear in A&
Comments on Supersymmetry Algebra and Contact Term in Matrix String Theory
Following hep-th/0309238 relating the matrix string theory to the light-cone
superstring field theory, we write down two supercharges in the matrix string
theory explicitly. After checking the supersymmetry algebra at the leading
order, we proceed to discuss higher-order contact terms.Comment: 17 pages, no figures, v2: eq. (5.1) and related appendices corrected,
v3: final version to appear in JHE
An Optically-Programmable Absorbing Metasurface
A tunable metasurface absorber is presented in this work using an optically-programmable capacitor as the tuning element. The tuning element does not employ conventional semiconductor technologies to operate but rather a bases its tuning by changing the optomechanical properties of its dielectric, poly disperse red 1 acrylate (PDR1A). Doing so there are no conventional semiconductor devices in the RF signal path. The metasurface operates at a design frequency of 5.5 GHz and it achieves an optically-tuned bandwidth of 150 MHz, from 5.50 GHz to 5.65 GHz
Wang-Landau study of the random bond square Ising model with nearest- and next-nearest-neighbor interactions
We report results of a Wang-Landau study of the random bond square Ising
model with nearest- () and next-nearest-neighbor ()
antiferromagnetic interactions. We consider the case for
which the competitive nature of interactions produces a sublattice ordering
known as superantiferromagnetism and the pure system undergoes a second-order
transition with a positive specific heat exponent . For a particular
disorder strength we study the effects of bond randomness and we find that,
while the critical exponents of the correlation length , magnetization
, and magnetic susceptibility increase when compared to the
pure model, the ratios and remain unchanged. Thus, the
disordered system obeys weak universality and hyperscaling similarly to other
two-dimensional disordered systems. However, the specific heat exhibits an
unusually strong saturating behavior which distinguishes the present case of
competing interactions from other two-dimensional random bond systems studied
previously.Comment: 9 pages, 3 figures, version as accepted for publicatio
Spectral statistics of random geometric graphs
We use random matrix theory to study the spectrum of random geometric graphs,
a fundamental model of spatial networks. Considering ensembles of random
geometric graphs we look at short range correlations in the level spacings of
the spectrum via the nearest neighbour and next nearest neighbour spacing
distribution and long range correlations via the spectral rigidity Delta_3
statistic. These correlations in the level spacings give information about
localisation of eigenvectors, level of community structure and the level of
randomness within the networks. We find a parameter dependent transition
between Poisson and Gaussian orthogonal ensemble statistics. That is the
spectral statistics of spatial random geometric graphs fits the universality of
random matrix theory found in other models such as Erdos-Renyi, Barabasi-Albert
and Watts-Strogatz random graph.Comment: 19 pages, 6 figures. Substantially updated from previous versio
800-5 Improving Accuracy of Ultrafast Computed Tomography in the Detection of Angiographically Significant Coronary Artery Disease
In differentiating coronary calcium from artifact by ultrafast computed tomography (UFCT), many different thresholds have been proposed. UFCT has demonstrated a high sensitivity and only modest specificity to detect coronary calcifications when compared to angiography. The Agatston method is most widely used today, utilizing a minimum CT number of 130 Hounsfield units (HU). In an attempt to improve specificity without markedly reducing sensitivity, we evaluated 272 coronary vessels from 68 patients with angiography and UFCT coronary scanning. All patients underwent coronary angiography for clinical indications, and had UFCT scanning done within three months of the angiogram. A blinded reader evaluated all the UFCT scans. We then varied the minimum CT number to assess whether 130 HU was truly the best threshold. Sensitivity, specificity and accuracy for different thresholds are listed.Threshold130 HU150 HU170 HU200 HUSensitivity95%92%89%87%Specificity65%72%75%78%Accuracy72%77%78%79%The results above indicate that 130 HU is too low a threshold to maximize accuracy of this test when compared with angiography. Sensitivity is reduced as the threshold is improved, however this result is not significant (p=0.61). The improved specificity from 130 to 150 represents a significant improvement (p<0.0001), although a larger study must be performed before widespread use of this new threshold is employed
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
Gluon Scattering Amplitudes in Finite Temperature Gauge/Gravity Dualities
We examine the gluon scattering amplitude in N=4 super Yang-Mills at finite
temperature with nonzero R-charge densities, and in Non-Commutative gauge
theory at finite temperature. The gluon scattering amplitude is defined as a
light-like Wilson loop which lives at the horizon of the T-dual black holes of
the backgrounds we consider. We study in detail a special amplitude, which
corresponds to forward scattering of a low energy gluon off a high energy one.
For this kinematic configuration in the considered backgrounds, we find the
corresponding minimal surface which is directly related to the gluon scattering
amplitude. We find that for increasing the chemical potential or the
non-commutative parameter, the on-shell action corresponding to our Wilson loop
in the T-dual space decreases. For all of our solutions the length of the short
side of the Wilson loop is constrained by an upper bound which depends on the
temperature, the R-charge density and the non-commutative parameter. Due to
this constraint, in the limit of zeroth temperature our approach breaks down
since the upper bound goes to zero, while by keeping the temperature finite and
letting the chemical potential or the non-commutative parameter to approach to
zero the limit is smooth.Comment: 30 pages, 16 figures, minor corrections (plus improved numerical
computation for the non-commutative case
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