3,583 research outputs found
Improved asteroseismic inversions for red-giant surface rotation rates
Asteroseismic observations of internal stellar rotation have indicated a
substantial lack of angular momentum transport in theoretical models of
subgiant and red-giant stars. Accurate core and surface rotation rate
measurements are therefore needed to constrain internal transport processes
included in the models. We eliminate substantial systematic errors of
asteroseismic surface rotation rates found in previous studies. We propose a
new objective function for the Optimally Localized Averages method of
rotational inversions for red-giant stars, which results in more accurate
envelope rotation rate estimates obtained from the same data. We use synthetic
observations from stellar models across a range of evolutionary stages and
masses to demonstrate the improvement. We find that our new inversion technique
allows us to obtain estimates of the surface rotation rate that are independent
of the core rotation. For a star at the base of the red-giant branch, we reduce
the systematic error from about 20% to a value close to 0, assuming constant
envelope rotation. We also show the equivalence between this method and the
method of linearised rotational splittings. Our new rotational inversion method
substantially reduces the systematic errors of red-giant surface rotation
rates. In combination with independent measures of the surface rotation rate,
this will allow better constraints to be set on the internal rotation profile.
This will be a very important probe to further constrain the internal angular
momentum transport along the lower part of the red-giant branch.Comment: 17 pages, 22 figures, accepted for publication in Astronomy and
Astrophysic
Asteroseismic sensitivity to internal rotation along the red-giant branch
Transport of angular momentum in stellar interiors is currently not well
understood. Asteroseismology can provide us with estimates of internal rotation
of stars and thereby advances our understanding of angular momentum transport.
We can measure core-rotation rates in red-giant stars and we can place upper
bounds on surface-rotation rates using measurements of dipole () modes.
Here, we aim to determine the theoretical sensitivity of modes of different
spherical degree towards the surface rotation. Additionally, we aim to identify
modes that can potentially add sensitivity at intermediate radii. We used
asteroseismic rotational inversions to probe the internal stellar rotation
profiles in red-giant models from the base of the red-giant branch up to the
luminosity bump. We used the inversion method of multiplicative optimally
localised averages (MOLA) to assess how well internal and surface rotation
rates can be recovered from different mode sets and different synthetic
rotation profiles. We confirm that dipole mixed modes are sufficient to set
constraints on the average core-rotation rates in red giants. However,
surface-rotation rates estimated with only dipole mixed modes are contaminated
by the core rotation. We show that the sensitivity to the surface rotation
decreases from the base of the red-giant branch until it reaches a minimum at
0.6-0.8 due to a glitch in the buoyancy frequency. Thereafter a
narrow range of increased surface sensitivity just below the bump luminosity
exists. Quadrupole and octopole modes have more sensitivity in the outer parts
of the star. If observed, quadrupole and octopole modes enable us to
distinguish between differential and solid body rotation in the convection
zone. To obtain accurate estimates of rotation rates at intermediate radii,
acoustic oscillation modes with a spherical degree of are needed.Comment: accepted for publication in Astronomy and Astrophysics, revised
manuscript after language editin
Inverse analysis of asteroseismic data: a review
Asteroseismology has emerged as the best way to characterize the global and
internal properties of nearby stars. Often, this characterization is achieved
by fitting stellar evolution models to asteroseismic observations. The star
under investigation is then assumed to have the properties of the best-fitting
model, such as its age. However, the models do not fit the observations
perfectly. This is due to incorrect or missing physics in stellar evolution
calculations, resulting in predicted stellar structures that are discrepant
with reality. Through an inverse analysis of the asteroseismic data, it is
possible to go further than fitting stellar models, and instead infer details
about the actual internal structure of the star at some locations in its
interior. Comparing theoretical and observed stellar structures then enables
the determination of the locations where the stellar models have discrepant
structure, and illuminates a path for improvements to our understanding of
stellar evolution. In this invited review, we describe the methods of
asteroseismic inversions, and outline the progress that is being made towards
measuring the interiors of stars.Comment: 12 pages, 1 figure. Invited review, Dynamics of the Sun and Star
Residual cognitive deficits 50 years after lead poisoning during childhood
The long term neurobehavioural consequences of childhood lead poisoning are not known. In this study adult subjects with a documented history of lead poisoning before age 4 and matched controls were examined with an abbreviated battery of neuropsychological tests including measures of attention, reasoning, memory, motor speed, and current mood. The subjects exposed to lead were inferior to controls on almost all of the cognitive tasks. This pattern of widespread deficits resembles that found in children evaluated at the time of acute exposure to lead rather than the more circumscribed pattern typically seen in adults exposed to lead. Despite having completed as many years of schooling as controls, the subjects exposed to lead were lower in lifetime occupational status. Within the exposed group, performance on the neuropsychological battery and occupational status were related, consistent with the presumed impact of limitations in neuropsychological functioning on everyday life. The results suggest that many subjects exposed to lead suffered acute encephalopathy in childhood which resolved into a chronic subclinical encephalopathy with associated cognitive dysfunction still evident in adulthood. These findings lend support to efforts to limit exposure to lead in childhood
Artificial Intelligence Tool for Assessment of Indeterminate Pulmonary Nodules Detected with CT
Background: Limited data are available regarding whether computer-aided diagnosis (CAD) improves assessment of malignancy risk in indeterminate pulmonary nodules (IPNs).
Purpose: To evaluate the effect of an artificial intelligence-based CAD tool on clinician IPN diagnostic performance and agreement for both malignancy risk categories and management recommendations.
Materials and Methods: This was a retrospective multireader multicase study performed in June and July 2020 on chest CT studies of IPNs. Readers used only CT imaging data and provided an estimate of malignancy risk and a management recommendation for each case without and with CAD. The effect of CAD on average reader diagnostic performance was assessed using the Obuchowski-Rockette and Dorfman-Berbaum-Metz method to calculate estimates of area under the receiver operating characteristic curve (AUC), sensitivity, and specificity. Multirater Fleiss κ statistics were used to measure interobserver agreement for malignancy risk and management recommendations.
Results: A total of 300 chest CT scans of IPNs with maximal diameters of 5-30 mm (50.0% malignant) were reviewed by 12 readers (six radiologists, six pulmonologists) (patient median age, 65 years; IQR, 59-71 years; 164 [55%] men). Readers\u27 average AUC improved from 0.82 to 0.89 with CAD (P \u3c .001). At malignancy risk thresholds of 5% and 65%, use of CAD improved average sensitivity from 94.1% to 97.9% (P = .01) and from 52.6% to 63.1% (P \u3c .001), respectively. Average reader specificity improved from 37.4% to 42.3% (P = .03) and from 87.3% to 89.9% (P = .05), respectively. Reader interobserver agreement improved with CAD for both the less than 5% (Fleiss κ, 0.50 vs 0.71; P \u3c .001) and more than 65% (Fleiss κ, 0.54 vs 0.71; P \u3c .001) malignancy risk categories. Overall reader interobserver agreement for management recommendation categories (no action, CT surveillance, diagnostic procedure) also improved with CAD (Fleiss κ, 0.44 vs 0.52; P = .001).
Conclusion: Use of computer-aided diagnosis improved estimation of indeterminate pulmonary nodule malignancy risk on chest CT scans and improved interobserver agreement for both risk stratification and management recommendations
Desynchronizing effect of high-frequency stimulation in a generic cortical network model
Transcranial Electrical Stimulation (TCES) and Deep Brain Stimulation (DBS)
are two different applications of electrical current to the brain used in
different areas of medicine. Both have a similar frequency dependence of their
efficiency, with the most pronounced effects around 100Hz. We apply
superthreshold electrical stimulation, specifically depolarizing DC current,
interrupted at different frequencies, to a simple model of a population of
cortical neurons which uses phenomenological descriptions of neurons by
Izhikevich and synaptic connections on a similar level of sophistication. With
this model, we are able to reproduce the optimal desynchronization around
100Hz, as well as to predict the full frequency dependence of the efficiency of
desynchronization, and thereby to give a possible explanation for the action
mechanism of TCES.Comment: 9 pages, figs included. Accepted for publication in Cognitive
Neurodynamic
Biodiversity of the Collembola Fauna of Wetland Kerkini (N. Greece), with description of the sexual dimorphism of Entomobrya atrocincta Schött 1896 (Collembola: Entomobryomorpha)
A report on the results of a research into some aspects of the collembolan fauna of the
Greek Nature Reserve associated with Lake Kerkini, known as Wetland Kerkini, is presented. The
nature reserve is large and includes a wide variety of habitats, many of which were not included in
this preliminary survey. From the areas sampled we recorded 44 species, of which 39 were previously
described, two (Folsomia potapovi Jordana & Baquero n. sp., Entomobrya naziridisi Jordana & Baquero
n. sp.), are new to science, while three are identifi ed to generic level; a further 21 are new records for
Greece, and an additional 11 species are new records to the Greek Mainland. Sampling with Berlese-
Tullgren funnels and Malaise traps allowed us to capture species typical of soil and species present
over vegetation. This summary is based on the records held in the online database of the Fauna
Europaea Project
Measurement of the p\bar{p}\sqrt{s}$ = 1.8 TeV
We update the measurement of the top production cross section using the CDF
detector at the Fermilab Tevatron. This measurement uses decays to
the final states +jets and +jets. We search for quarks from
decays via secondary-vertex identification or the identification of
semileptonic decays of the and cascade quarks. The background to the
production is determined primarily through a Monte Carlo simulation.
However, we calibrate the simulation and evaluate its uncertainty using several
independent data samples. For a top mass of 175 , we measure
pb and pb using
the secondary vertex and the lepton tagging algorithms, respectively. Finally,
we combine these results with those from other decay channels and
obtain pb.Comment: The manuscript consists of 130 pages, 35 figures and 42 tables in
RevTex. The manuscript is submitted to Physical Review D. Fixed typo in
author lis
Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV
We present results of searches for diphoton resonances produced both
inclusively and also in association with a vector boson (W or Z) using 100
pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on
the product of cross section times branching ratio for both p\bar
p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive
production to the expectations from heavy sgoldstinos we derive limits on the
supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the
sgoldstino mass and the choice of other parameters. Also, using a NLO
prediction for the associated production of a Higgs boson with a W or Z boson,
we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we
set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which
couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82
GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure
Measurement of J/Psi and Psi(2S) Polarization in ppbar Collisions at sqrt(s) = 1.8 TeV
We have measured the polarization of J/Psi and Psi(2S) mesons produced in
p\bar{p} collisions at \sqrt{s} = 1.8 TeV, using data collected at CDF during
1992-95.
The polarization of promptly produced J/Psi [Psi(2S)] mesons is isolated from
those produced in B-hadron decay, and measured over the kinematic range 4[5.5]
< P_T < 20 GeV/c and |y| < 0.6. For P_T \gessim 12 GeV/c we do not observe
significant polarization in the prompt component.Comment: Revised version, accepted for publication in Physical Review Letter
- …