5,316 research outputs found
Evaluating multisite rCBV consistency from DSC-MRI imaging protocols and postprocessing software across the NCI Quantitative Imaging Network sites using a digital reference object (DRO)
Experimental Violation of Bell Inequality beyond Cirel'son's Bound
The correlations between two qubits belonging to a three-qubit system can
violate the Clauser-Horne-Shimony-Holt-Bell inequality beyond Cirel'son's bound
[A. Cabello, Phys. Rev. Lett. 88, 060403 (2002)]. We experimentally demonstrate
such a violation by 7 standard deviations by using a three-photon
polarization-entangled Greenberger-Horne-Zeilinger state produced by Type-II
spontaneous parametric down-conversion. In addition, using part of our results,
we obtain a violation of the Mermin inequality by 39 standard deviations.Comment: 4 pages, 3 figure
GHZ-type and W-type entangled coherent states: generation and Bell-type inequality tests without photon counting
We study GHZ-type and W-type three-mode entangled coherent states. Both the
types of entangled coherent states violate Mermin's version of the Bell
inequality with threshold photon detection (i.e., without photon counting).
Such an experiment can be performed using linear optics elements and threshold
detectors with significant Bell violations for GHZ-type entangled coherent
states. However, to demonstrate Bell-type inequality violations for W-type
entangled coherent states, additional nonlinear interactions are needed. We
also propose an optical scheme to generate W-type entangled coherent states in
free-traveling optical fields. The required resources for the generation are a
single-photon source, a coherent state source, beam splitters, phase shifters,
photodetectors, and Kerr nonlinearities. Our scheme does not necessarily
require strong Kerr nonlinear interactions, i.e., weak nonlinearities can be
used for the generation of the W-type entangled coherent states. Furthermore,
it is also robust against inefficiencies of the single-photon source and the
photon detectors.Comment: 8 pages, 5 figures, to be published in Phys. Rev.
An attractor for dark matter structures
Cosmological simulations of dark matter structures have identified a set of
universal profiles, and similar characteristics have been seen in
non-cosmological simulations. It has therefore been speculated whether these
profiles of collisionless systems relate to accretion and merger history, or if
there is an attractor for the dark matter systems. Here we identify such a
1-dimensional attractor in the 3-dimensional space spanned by the 2 radial
slopes of the density and velocity dispersion, and the velocity anisotropy.
This attractor effectively removes one degree of freedom from the Jeans
equation. It also allows us to speculate on a new fluid interpretation for the
Jeans equation, with an effective polytropic index for the dark matter
particles between 1/2 and 3/4. If this attractor solution holds for other
collisionless structures, then it may hold the key to break the mass-anisotropy
degeneracy, which presently prevents us from measuring the mass profiles in
dwarf galaxies uniquely.Comment: 7 pages, 2 figures, comments welcom
Evaluating the use of rCBV as a tumor grade and treatment response classifier across NCI Quantitative Imaging Network sites: Part II of the DSC-MRI digital reference object (DRO) challenge
We have previously characterized the reproducibility of brain tumor relative cerebral blood volume (rCBV) using a dynamic susceptibility contrast magnetic resonance imaging digital reference object across 12 sites using a range of imaging protocols and software platforms. As expected, reproducibility was highest when imaging protocols and software were consistent, but decreased when they were variable. Our goal in this study was to determine the impact of rCBV reproducibility for tumor grade and treatment response classification. We found that varying imaging protocols and software platforms produced a range of optimal thresholds for both tumor grading and treatment response, but the performance of these thresholds was similar. These findings further underscore the importance of standardizing acquisition and analysis protocols across sites and software benchmarking
The Case for the Dual Halo of the Milky Way
Carollo et al. have recently resolved the stellar population of the Milky Way
halo into at least two distinct components, an inner halo and an outer halo.
This result has been criticized by Schoenrich et al., who claim that the
retrograde signature associated with the outer halo is due to the adoption of
faulty distances. We refute this claim, and demonstrate that the Schoenrich et
al. photometric distances are themselves flawed because they adopted an
incorrect main-sequence absolute magnitude relationship from the work of
Ivezi\'c et al. When compared to the recommended relation from Ivezi\'c et al.,
which is tied to a Milky Way globular cluster distance scale and accounts for
age and metallicity effects, the relation adopted by Schoenrich et al. yields
up to 18% shorter distances for stars near the main-sequence turnoff (TO). Use
of the correct relationship yields agreement between the distances assigned by
Carollo et al. and Ivezi\'{c} et al. for low-metallicity dwarfs to within
6-10%. Schoenrich et al. also point out that intermediate-gravity stars (3.5 <=
log g <= 4.0) with colors redder than the TO region are likely misclassified,
with which we concur. We implement a new procedure to reassign luminosity
classifications for the TO stars that require it. New derivations of the
rotational behavior demonstrate that the retrograde signature and high velocity
dispersion of the outer-halo population remains. We summarize additional lines
of evidence for a dual halo, including a test of the retrograde signature based
on proper motions alone, and conclude that the preponderance of evidence
strongly rejects the single-halo interpretation.Comment: 46 pages, 2 tables, 15 figures, Accepted for publication in the
Astrophysical Journa
A statistical-mechanical explanation of dark matter halo properties
Cosmological N-body simulations have revealed many empirical relationships of
dark matter halos, yet the physical origin of these halo properties still
remains unclear. On the other hand, the attempts to establish the statistical
mechanics for self-gravitating systems have encountered many formal
difficulties, and little progress has been made for about fifty years. The aim
of this work is to strengthen the validity of the statistical-mechanical
approach we have proposed previously to explain the dark matter halo
properties. By introducing an effective pressure instead of the radial pressure
to construct the specific entropy, we use the entropy principle and proceed in
a similar way as previously to obtain an entropy stationary equation. An
equation of state for equilibrated dark halos is derived from this entropy
stationary equation, by which the dark halo density profiles with finite mass
can be obtained. We also derive the anisotropy parameter and pseudo-phase-space
density profile. All these predictions agree well with numerical simulations in
the outer regions of dark halos. Our work provides further support to the idea
that statistical mechanics for self-gravitating systems is a viable tool for
investigation.Comment: 5 pages, 4 figures, Accepted by A&
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