7,390 research outputs found
Increased lymph node yield in colorectal cancer is not necessarily associated with a greater number of lymph node positive cancers
Peer reviewedPublisher PD
The Spitzer View of Low-Metallicity Star Formation: II. Mrk 996, a Blue Compact Dwarf Galaxy with an Extremely Dense Nucleus
(abridged) We present new Spitzer, UKIRT and MMT observations of the blue
compact dwarf galaxy (BCD) Mrk 996, with an oxygen abundance of
12+log(O/H)=8.0. This galaxy has the peculiarity of possessing an
extraordinarily dense nuclear star-forming region, with a central density of
~10^6 cm^{-3}. The nuclear region of Mrk 996 is characterized by several
unusual properties: a very red color J-K = 1.8, broad and narrow emission-line
components, and ionizing radiation as hard as 54.9 eV, as implied by the
presence of the OIV 25.89 micron line. The nucleus is located within an
exponential disk with colors consistent with a single stellar population of age
>1 Gyr. The infrared morphology of Mrk 996 changes with wavelength. The IRS
spectrum shows strong narrow Polycyclic Aromatic Hydrocarbon (PAH) emission,
with narrow line widths and equivalent widths that are high for the metallicity
of Mrk 996. Gaseous nebular fine-structure lines are also seen. A CLOUDY model
requires that they originate in two distinct HII regions: a very dense HII
region of radius ~580 pc with densities declining from ~10^6 at the center to a
few hundreds cm^{-3} at the outer radius, where most of the optical lines
arise; and a HII region with a density of ~300 cm^{-3} that is hidden in the
optical but seen in the MIR. We suggest that the infrared lines arise mainly in
the optically obscured HII region while they are strongly suppressed by
collisional deexcitation in the optically visible one. The hard ionizing
radiation needed to account for the OIV 25.89 micron line is most likely due to
fast radiative shocks propagating in an interstellar medium. A hidden
population of Wolf-Rayet stars of type WNE-w or a hidden AGN as sources of hard
ionizing radiation are less likely possibilities.Comment: 48 pages, 13 figures, accepted for publication in the Astrophysical
Journa
Spin squeezing of high-spin, spatially extended quantum fields
Investigations of spin squeezing in ensembles of quantum particles have been
limited primarily to a subspace of spin fluctuations and a single spatial mode
in high-spin and spatially extended ensembles. Here, we show that a wider range
of spin-squeezing is attainable in ensembles of high-spin atoms, characterized
by sub-quantum-limited fluctuations in several independent planes of
spin-fluctuation observables. Further, considering the quantum dynamics of an
ferromagnetic spinor Bose-Einstein condensate, we demonstrate
theoretically that a high degree of spin squeezing is attained in multiple
spatial modes of a spatially extended quantum field, and that such squeezing
can be extracted from spatially resolved measurements of magnetization and
nematicity, i.e.\ the vector and quadrupole magnetic moments, of the quantum
gas. Taking into account several experimental limitations, we predict that the
variance of the atomic magnetization and nematicity may be reduced as far as 20
dB below the standard quantum limits.Comment: 18 pages, 5 figure
Recommended from our members
Gain Modulation by Corticostriatal and Thalamostriatal Input Signals during Reward-Conditioned Behavior.
The cortex and thalamus send excitatory projections to the striatum, but little is known about how these inputs, either individually or collectively, regulate striatal dynamics during behavior. The lateral striatum receives overlapping input from the secondary motor cortex (M2), an area involved in licking, and the parafascicular thalamic nucleus (PF). Using neural recordings, together with optogenetic terminal inhibition, we examine the contribution of M2 and PF projections on medium spiny projection neuron (MSN) activity as mice performed an anticipatory licking task. Each input has a similar contribution to striatal activity. By comparing how suppressing single or multiple projections altered striatal activity, we find that cortical and thalamic input signals modulate MSN gain and that this effect is more pronounced in a temporally specific period of the task following the cue presentation. These results demonstrate that cortical and thalamic inputs synergistically regulate striatal output during reward-conditioned behavior
A Coverage Criterion for Spaced Seeds and its Applications to Support Vector Machine String Kernels and k-Mer Distances
Spaced seeds have been recently shown to not only detect more alignments, but
also to give a more accurate measure of phylogenetic distances (Boden et al.,
2013, Horwege et al., 2014, Leimeister et al., 2014), and to provide a lower
misclassification rate when used with Support Vector Machines (SVMs) (On-odera
and Shibuya, 2013), We confirm by independent experiments these two results,
and propose in this article to use a coverage criterion (Benson and Mak, 2008,
Martin, 2013, Martin and No{\'e}, 2014), to measure the seed efficiency in both
cases in order to design better seed patterns. We show first how this coverage
criterion can be directly measured by a full automaton-based approach. We then
illustrate how this criterion performs when compared with two other criteria
frequently used, namely the single-hit and multiple-hit criteria, through
correlation coefficients with the correct classification/the true distance. At
the end, for alignment-free distances, we propose an extension by adopting the
coverage criterion, show how it performs, and indicate how it can be
efficiently computed.Comment: http://online.liebertpub.com/doi/abs/10.1089/cmb.2014.017
Muon-Spin Rotation Measurements of an Unusual Vortex-Glass Phase in the Layered Superconductor Bi2.15Sr1.85CaCu2O8+δ
Muon-spin rotation measurements, performed on the mixed state of the classic anisotropic superconductor Bi2.15Sr1.85CaCu2O8+δ, obtain quantities directly related to two- and three-body correlations of vortices in space. A novel phase diagram emerges from such local probe measurements of the bulk, revealing an unusual glassy state at intermediate fields which appears to freeze continuously from the equilibrium vortex liquid but differs both from the lattice and the conventional high-field vortex glass state in its structure.Publisher PDFPeer reviewe
The Trans-Pacific Partnership Agreement: Looking Ahead to the Next Steps
Pressure has been building for the conclusion of the 12-country Trans-Pacific Partnership (TPP) negotiations. Getting the deal done is important, but the TPP is not just another free trade agreement (FTA). It represents the chance to set a trade agenda for the future across a wide range of topics for countries throughout the Asia-Pacific region. This means that the agreement should not be settled in haste. More importantly, it also means that key decisions need to be reached about broader issues related to the institutional structure of the TPP. These decisions must be made now, before the deal is closed, on issues such as how to create the TPP as a living agreement, the formation of a TPP Secretariat, and the clarification of entry conditions for future members such as the People’s Republic of China (PRC). These choices must be made deliberately and carefully even while officials are struggling with reaching closure on the most highly sensitive issues still remaining in the agreement. It will not be easy, but wise decisions are necessary now to ensure the long-term success of the TPP
The SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei
We have observed two kinematically offset active galactic nuclei (AGN), whose
ionised gas is at a different line-of-sight velocity to their host galaxies,
with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas
kinematics very different to the stellar kinematics, indicating a recent merger
or accretion event. We demonstrate that the star formation associated with this
event was triggered within the last 100 Myr. The other galaxy shows simple disc
rotation in both gas and stellar kinematics, aligned with each other, but in
the central region has signatures of an outflow driven by the AGN. Other than
the outflow, neither galaxy shows any discontinuity in the ionised gas
kinematics at the galaxy's centre. We conclude that in these two cases there is
no direct evidence of the AGN being in a supermassive black hole binary system.
Our study demonstrates that selecting kinematically offset AGN from
single-fibre spectroscopy provides, by definition, samples of kinematically
peculiar objects, but IFS or other data are required to determine their true
nature.Comment: MNRAS accepted. 14 pages, 11 figure
How Low Can You Go? The Photoeccentric Effect for Planets of Various Sizes
It is well-known that the light curve of a transiting planet contains
information about the planet's orbital period and size relative to the host
star. More recently, it has been demonstrated that a tight constraint on an
individual planet's eccentricity can sometimes be derived from the light curve
via the "photoeccentric effect," the effect of a planet's eccentricity on the
shape and duration of its light curve. This has only been studied for large
planets and high signal-to-noise scenarios, raising the question of how well it
can be measured for smaller planets or low signal-to-noise cases. We explore
the limits of the photoeccentric effect over a wide range of planet parameters.
The method hinges upon measuring directly from the light curve, where
is the ratio of the planet's speed (projected on the plane of the sky) during
transit to the speed expected for a circular orbit. We find that when the
signal-to-noise in the measurement of is , the ability to measure
eccentricity with the photoeccentric effect decreases. We develop a "rule of
thumb" that for per-point relative photometric uncertainties , the critical values of planet-star radius ratio
are for Kepler-like 30-minute
integration times. We demonstrate how to predict the best-case uncertainty in
eccentricity that can be found with the photoeccentric effect for any light
curve. This clears the path to study eccentricities of individual planets of
various sizes in the Kepler sample and future transit surveys
Computation of Kolmogorov's Constant in Magnetohydrodynamic Turbulence
In this paper we calculate Kolmogorov's constant for magnetohydrodynamic
turbulence to one loop order in perturbation theory using the direct
interaction approximation technique of Kraichnan. We have computed the
constants for various , i.e., fluid to magnetic energy ratios
when the normalized cross helicity is zero. We find that increases from
1.47 to 4.12 as we go from fully fluid case to a situation when , then it decreases to 3.55 in a fully magnetic limit .
When , we find that .Comment: Latex, 10 pages, no figures, To appear in Euro. Phys. Lett., 199
- …