8,165 research outputs found
Extrasolar planets in stellar multiple systems
Analyzing exoplanets detected by radial velocity or transit observations, we
determine the multiplicity of exoplanet host stars in order to study the
influence of a stellar companion on the properties of planet candidates.
Matching the host stars of exoplanet candidates detected by radial velocity or
transit observations with online multiplicity catalogs in addition to a
literature search, 57 exoplanet host stars are identified having a stellar
companion. The resulting multiplicity rate of at least 12 percent for exoplanet
host stars is about four times smaller than the multiplicity of solar like
stars in general. The mass and the number of planets in stellar multiple
systems depend on the separation between their host star and its nearest
stellar companion, e.g. the planetary mass decreases with an increasing stellar
separation. We present an updated overview of exoplanet candidates in stellar
multiple systems, including 15 new systems (compared to the latest summary from
2009).Comment: 11 pages, 4 figures, appendix with 6 tables, accepted for publication
in A&
Fingerprinting white marbles of archaeometric interest by means of combined SANS and USANS
We have performed a series of USANS and SANS measurements on
a selected group of marble samples characterized by similar chemical composition but wide range of known metamorphic conditions. With these samples we start the building up of a data base in an attempt to correlate metamorphism and mesoscopic structure of white marbles. Experimental data have been analysed in terms of a hierarchical model. The present data highlight the importance of the structure at
meso scale in identifying the provenance of the marble samples. A remarkable simple relation between the model parameters and the metamorphic degree has been found. This curve might represent a master curve to allow fingerprinting of white marbles. Also, two coloured marbles from Villa Adriana (Tivoli, Italy) have been investigated
by means of the same techniques. Results obtained follow the general trend found for the white marbles
Nematic phases and the breaking of double symmetries
In this paper we present a phase classification of (effectively)
two-dimensional non-Abelian nematics, obtained using the Hopf symmetry breaking
formalism. In this formalism one exploits the underlying double symmetry which
treats both ordinary and topological modes on equal footing, i.e. as
representations of a single (non-Abelian) Hopf symmetry. The method that exists
in the literature (and is developed in a paper published in parallel) allows
for a full classification of defect mediated as well as ordinary symmetry
breaking patterns and a description of the resulting confinement and/or
liberation phenomena. After a summary of the formalism, we determine the double
symmetries for tetrahedral, octahedral and icosahedral nematics and their
representations. Subsequently the breaking patterns which follow from the
formation of admissible defect condensates are analyzed systematically. This
leads to a host of new (quantum and classical) nematic phases. Our result
consists of a listing of condensates, with the corresponding intermediate
residual symmetry algebra and the symmetry algebra characterizing the effective
``low energy'' theory of surviving unconfined and liberated degrees of freedom
in the broken phase. The results suggest that the formalism is applicable to a
wide variety of two dimensional quantum fluids, crystals and liquid crystals.Comment: 17 pages, 2 figures, correction to table VII, updated reference
Coupling biochemistry and mechanics in cell adhesion: a model for inhomogeneous stress fiber contraction
Biochemistry and mechanics are closely coupled in cell adhesion. At sites of
cell-matrix adhesion, mechanical force triggers signaling through the
Rho-pathway, which leads to structural reinforcement and increased
contractility in the actin cytoskeleton. The resulting force acts back to the
sites of adhesion, resulting in a positive feedback loop for mature adhesion.
Here we model this biochemical-mechanical feedback loop for the special case
when the actin cytoskeleton is organized in stress fibers, which are
contractile bundles of actin filaments. Activation of myosin II molecular
motors through the Rho-pathway is described by a system of reaction-diffusion
equations, which are coupled into a viscoelastic model for a contractile actin
bundle. We find strong spatial gradients in the activation of contractility and
in the corresponding deformation pattern of the stress fiber, in good agreement
with experimental findings.Comment: Revtex, 35 pages, 13 Postscript figures included, in press with New
Journal of Physics, Special Issue on The Physics of the Cytoskeleto
The Solar Twin Planet Search. V. Close-in, low-mass planet candidates and evidence of planet accretion in the solar twin HIP 68468
[Methods]. We obtained high-precision radial velocities with HARPS on the ESO
3.6 m telescope and determined precise stellar elemental abundances (~0.01 dex)
using MIKE spectra on the Magellan 6.5m telescope. [Results]. Our data indicate
the presence of a planet with a minimum mass of 26 Earth masses around the
solar twin HIP 68468. The planet is a super-Neptune, but unlike the distant
Neptune in our solar system (30 AU), HIP 68468c is close-in, with a semi-major
axis of 0.66 AU, similar to that of Venus. The data also suggest the presence
of a super-Earth with a minimum mass of 2.9 Earth masses at 0.03 AU; if the
planet is confirmed, it will be the fifth least massive radial velocity planet
discovery to date and the first super-Earth around a solar twin. Both
isochrones (5.9 Gyr) and the abundance ratio [Y/Mg] (6.4 Gyr) indicate an age
of about 6 billion years. The star is enhanced in refractory elements when
compared to the Sun, and the refractory enrichment is even stronger after
corrections for Galactic chemical evolution. We determined a NLTE Li abundance
of 1.52 dex, which is four times higher than what would be expected for the age
of HIP 68468. The older age is also supported by the low log(R'HK) (-5.05) and
low jitter. Engulfment of a rocky planet of 6 Earth masses can explain the
enhancement in both lithium and the refractory elements. [Conclusions]. The
super-Neptune planet candidate is too massive for in situ formation, and
therefore its current location is most likely the result of planet migration
that could also have driven other planets towards its host star, enhancing thus
the abundance of lithium and refractory elements in HIP 68468. The intriguing
evidence of planet accretion warrants further observations to verify the
existence of the planets that are indicated by our data and to better constrain
the nature of the planetary system around this unique star.Comment: A&A, in pres
Elastic interactions of active cells with soft materials
Anchorage-dependent cells collect information on the mechanical properties of
the environment through their contractile machineries and use this information
to position and orient themselves. Since the probing process is anisotropic,
cellular force patterns during active mechanosensing can be modelled as
anisotropic force contraction dipoles. Their build-up depends on the mechanical
properties of the environment, including elastic rigidity and prestrain. In a
finite sized sample, it also depends on sample geometry and boundary conditions
through image strain fields. We discuss the interactions of active cells with
an elastic environment and compare it to the case of physical force dipoles.
Despite marked differences, both cases can be described in the same theoretical
framework. We exactly solve the elastic equations for anisotropic force
contraction dipoles in different geometries (full space, halfspace and sphere)
and with different boundary conditions. These results are then used to predict
optimal position and orientation of mechanosensing cells in soft material.Comment: Revtex, 38 pages, 8 Postscript files included; revised version,
accepted for publication in Phys. Rev.
Controlling spin relaxation with a cavity
Spontaneous emission of radiation is one of the fundamental mechanisms by
which an excited quantum system returns to equilibrium. For spins, however,
spontaneous emission is generally negligible compared to other non-radiative
relaxation processes because of the weak coupling between the magnetic dipole
and the electromagnetic field. In 1946, Purcell realized that the spontaneous
emission rate can be strongly enhanced by placing the quantum system in a
resonant cavity -an effect which has since been used extensively to control the
lifetime of atoms and semiconducting heterostructures coupled to microwave or
optical cavities, underpinning single-photon sources. Here we report the first
application of these ideas to spins in solids. By coupling donor spins in
silicon to a superconducting microwave cavity of high quality factor and small
mode volume, we reach for the first time the regime where spontaneous emission
constitutes the dominant spin relaxation mechanism. The relaxation rate is
increased by three orders of magnitude when the spins are tuned to the cavity
resonance, showing that energy relaxation can be engineered and controlled
on-demand. Our results provide a novel and general way to initialise spin
systems into their ground state, with applications in magnetic resonance and
quantum information processing. They also demonstrate that, contrary to popular
belief, the coupling between the magnetic dipole of a spin and the
electromagnetic field can be enhanced up to the point where quantum
fluctuations have a dramatic effect on the spin dynamics; as such our work
represents an important step towards the coherent magnetic coupling of
individual spins to microwave photons.Comment: 8 pages, 6 figures, 1 tabl
Timing of eplerenone initiation and outcomes in patients with heart failure after acute myocardial infarction complicated by left ventricular systolic dysfunction: insights from the EPHESUS trial â€
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102721/1/ejhfhfp136.pd
Outcomes following stereotactic radiosurgery or whole brain radiation therapy by molecular subtype of metastatic breast cancer
BACKGROUND: This study quantified clinical outcomes by molecular subtype of metastatic breast cancer (BC) following whole brain radiation therapy (WBRT) or stereotactic radiosurgery (SRS). Doing so is important for patient counseling and to assess the potential benefit of combining targeted therapy and brain radiotherapy for certain molecular subtypes in ongoing trials.
MATERIALS AND METHODS: The National Cancer Database was queried for BC (invasive ductal carcinoma) cases receiving brain radiotherapy (divided into WBRT and SRS). Statistics included multivariable logistic regression to determine factors associated with SRS delivery, Kaplan-Meier analysis to evaluate overall survival (OS), and Cox proportional hazards modeling.
RESULTS: Of 1,112 patients, 186 (16.7%) received SRS and 926 (83.3%) underwent WBRT. Altogether, 410 (36.9%), 195 (17.5%), 162 (14.6%), and 345 (31.0%) were ER+/HER2-, ER+/HER2+, ER–/HER2+, and ER–/HER2–, respectively. In the respective molecular subtypes, the proportion of subjects who underwent SRS was 13.4%, 19.4%, 24.1%, and 15.7%. Respective OS for WBRT patients were 12.9, 22.8, 10.6, and 5.8 months; corresponding figures for the SRS cohort were 28.3, 40.7, 15.0, and 12.9 months (p < 0.05 for both). When comparing OS between treatment different histologic subtypes, patients with ER-/HER2+ and ER–/HER2– disease had worse OS than patients with ER+/HER2– disease, for both patients treated with SRS and for patients treated with WBRT.
CONCLUSIONS: Molecular subtype may be a useful prognostic marker to quantify survival following SRS/WBRT for metastatic BC. Patients with HER2-enriched and triple-negative disease had the poorest survival following brain irradiation, lending credence to ongoing studies testing the addition of targeted therapies for these subtypes
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