4,305 research outputs found
A Trade-Off between Somatosensory and Auditory Related Brain Activity during Object Naming But Not Reading.
The parietal operculum, particularly the cytoarchitectonic area OP1 of the secondary somatosensory area (SII), is involved in somatosensory feedback. Using fMRI with 58 human subjects, we investigated task-dependent differences in SII/OP1 activity during three familiar speech production tasks: object naming, reading and repeatedly saying "1-2-3." Bilateral SII/OP1 was significantly suppressed (relative to rest) during object naming, to a lesser extent when repeatedly saying "1-2-3" and not at all during reading. These results cannot be explained by task difficulty but the contrasting difference between naming and reading illustrates how the demands on somatosensory activity change with task, even when motor output (i.e., production of object names) is matched. To investigate what determined SII/OP1 deactivation during object naming, we searched the whole brain for areas where activity increased as that in SII/OP1 decreased. This across subject covariance analysis revealed a region in the right superior temporal sulcus (STS) that lies within the auditory cortex, and is activated by auditory feedback during speech production. The tradeoff between activity in SII/OP1 and STS was not observed during reading, which showed significantly more activation than naming in both SII/OP1 and STS bilaterally. These findings suggest that, although object naming is more error prone than reading, subjects can afford to rely more or less on somatosensory or auditory feedback during naming. In contrast, fast and efficient error-free reading places more consistent demands on both types of feedback, perhaps because of the potential for increased competition between lexical and sublexical codes at the articulatory level
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X-ray reflection from the inner disc of the AGN Ton S180
We analyse a long archival XMM-Newton observation of the narrow-line Seyfert
1 galaxy Ton S180, using the latest reflection models to explore the high
quality X-ray spectrum. We find that the iron line is relatively narrow and
sharp, and the soft excess is extremely smooth. We cannot find an acceptable
reflection model that describes both components, and conclude that the soft
excess cannot be produced by relativistic reflection. Fitting the 3-10 keV band
with relativistic reflection to model the iron line strongly prefers low spin
values (< 0.4), with the exact value depending on the model and not well
constrained. We then model the broad- band spectrum with a two-component
Comptonization continuum plus relativistic reflection. This gives a much better
fit than a pure reflection model, which again prefers a low spin value. The
photon index of the reflection component is intermediate between the two
Comptoniza- tion components, suggesting that both illuminate the disk a similar
amount and therefore both contribute to the reflection
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Pigment-specific relationships between feather corticosterone concentrations and sexual coloration
The adrenocortical stress response may divert energy away from sexual ornamentation, such that ornaments signal exposure or resistance to physiological stress. Alternatively, steroid glucocorticoids released via the stress response may support ornament development by stimulating foraging and metabolism. The relationship between glucocorticoids and ornamentation may vary with ornament type and across age and sex classes that experience different resource allocation tradeoffs. In yellow warblers (Setophaga petechia), we conducted the first study to simultaneously assess whether relationships between corticosterone (the primary avian glucocorticoid) and ornamentation depend on sexual pigment type, age, and sex. We quantified carotenoid- and phaeomelanin-based pigmentation using spectrometry, and assayed corticosterone in feathers (CORTf) to derive an integrative metric of corticosterone levels during molt. Yellow warblers with lower carotenoid hue (lambda R50) had higher CORTf, suggesting that carotenoid hue may signal stress during molt across age and sex classes. Carotenoid chroma also negatively correlated with CORTf. However, this correlation was absent in older males, seemingly because these males display more saturated carotenoid pigmentation, and thus less variance in carotenoid chroma. Young males with higher CORTf also tended to have poorer quality tertial feathers, indicating poor condition at molt. Phaeomelanin-based pigmentation was largely unrelated to CORTf, suggesting that pleiotropic effects do not link phaeomelanogenesis and CORT release. Finally, CORTf was repeatable across years within individuals. Thus, carotenoid- and phaeomelanin-based pigmentation communicate nonequivalent information about physiological stress, with carotenoid pigmentation having the potential to signal stable differences in stress levels that could affect fitness
Using principal component analysis to understand the variability of PDS 456
We present a spectral-variability analysis of the low-redshift quasar PDS 456
using principal component analysis. In the XMM-Newton data, we find a strong
peak in the first principal component at the energy of the Fe absorption line
from the highly blueshifted outflow. This indicates that the absorption feature
is more variable than the continuum, and that it is responding to the
continuum. We find qualitatively different behaviour in the Suzaku data, which
is dominated by changes in the column density of neutral absorption. In this
case, we find no evidence of the absorption produced by the highly ionized gas
being correlated with this variability. Additionally, we perform simulations of
the source variability, and demonstrate that PCA can trivially distinguish
between outflow variability correlated, anti-correlated, and un-correlated with
the continuum flux. Here, the observed anti-correlation between the absorption
line equivalent width and the continuum flux may be due to the ionization of
the wind responding to the continuum. Finally, we compare our results with
those found in the narrow-line Seyfert 1 IRAS 13224-3809. We find that the Fe K
UFO feature is sharper and more prominent in PDS 456, but that it lacks the
lower energy features from lighter elements found in IRAS 13224-3809,
presumably due to differences in ionization
Discovery of an ~2-h high-frequency X-ray QPO and iron KĪ± reverberation in the active galaxy MS 2254.9-3712
We report the discovery of a Hz ( hr) X-ray
quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a
ks XMM-Newton observation. The QPO is significantly detected () in the keV band only, connecting its origin with the
primary X-ray power-law continuum. We detect a highly coherent soft lag between
the keV and keV energy bands at the QPO frequency and
at a frequency band in a 3:2 ratio, strongly suggesting the presence of a QPO
harmonic. An iron K reverberation lag is found at the harmonic
frequency, indicating the reflecting material subtends some angle to the
primary continuum, which is modulated by the QPO mechanism. Frequency resolved
spectroscopy reveals the QPO and harmonic to have a hard energy dependence.
These properties of the QPO variability, together with the current black hole
mass estimate, , are consistent
with the QPO originating from the same process as the high frequency QPO
phenomenon observed in black hole X-ray binaries. Principle component analysis
reveals the spectral variability in MS 2254.9-3712 is similar to that of the
active galaxy RE J1034+396, a source which also displays an X-ray QPO. This
suggests a distinct spectral variability pattern for accreting black holes when
in a state where QPOs are present
Sensory-to-motor integration during auditory repetition: a combined fMRI and lesion study.
The aim of this paper was to investigate the neurological underpinnings of auditory-to-motor translation during auditory repetition of unfamiliar pseudowords. We tested two different hypotheses. First we used functional magnetic resonance imaging in 25 healthy subjects to determine whether a functionally defined area in the left temporo-parietal junction (TPJ), referred to as Sylvian-parietal-temporal region (Spt), reflected the demands on auditory-to-motor integration during the repetition of pseudowords relative to a semantically mediated nonverbal sound-naming task. The experiment also allowed us to test alternative accounts of Spt function, namely that Spt is involved in subvocal articulation or auditory processing that can be driven either bottom-up or top-down. The results did not provide convincing evidence that activation increased in either Spt or any other cortical area when non-semantic auditory inputs were being translated into motor outputs. Instead, the results were most consistent with Spt responding to bottom up or top down auditory processing, independent of the demands on auditory-to-motor integration. Second, we investigated the lesion sites in eight patients who had selective difficulties repeating heard words but with preserved word comprehension, picture naming and verbal fluency (i.e., conduction aphasia). All eight patients had white-matter tract damage in the vicinity of the arcuate fasciculus and only one of the eight patients had additional damage to the Spt region, defined functionally in our fMRI data. Our results are therefore most consistent with the neurological tradition that emphasizes the importance of the arcuate fasciculus in the non-semantic integration of auditory and motor speech processing
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X-ray lags in PDS 456 revealed by Suzaku observations
X-ray reverberation lags from the vicinity of supermassive black holes have been detected in almost 30 active galactic nuclei (AGNs). The soft lag, which is the time delay between the hard and soft X-ray light curves, is usually interpreted as the time difference between the direct and reflected emission, but is alternatively suggested to arise from the direct and scattering emission from distant clouds. By analysing the archival Suzaku observations totalling an exposure time of ā¼770 ks, we discover a soft lag of 10 Ā± 3.4 ks at 9.58 Ć 10ā6āHz in the luminous quasar PDS 456, which is the longest soft lag and lowest Fourier frequency reported to date. In this study, we use the maximum likelihood method to deal with non-continuous nature of the Suzaku light curves. The result follows the massāscaling relation for soft lags, which further supports that soft lags originate from the innermost areas of AGNs and hence are best interpreted by the reflection scenario. Spectral analysis has been performed in this work and we find no evidence of clumpy partial-covering absorbers. The spectrum can be explained by a self-consistent relativistic reflection model with warm absorbers, and spectral variations over epochs can be accounted for by the change of the continuum, and of column density and ionization states of the warm absorbers.EMC gratefully acknowledges support from the NSF through CAREER award number AST-1351222. CSR thanks NASA for support under grant NNX15AU54G. ACF acknowledges ERC Advanced Grant 340442
Revealing the ultrafast outflow in IRAS 13224-3809 through spectral variability
We present an analysis of the long-term X-ray variability of the extreme
narrow-line Seyfert 1 (NLS1) galaxy IRAS 13224-3809 using principal component
analysis (PCA) and fractional excess variability (Fvar) spectra to identify
model-independent spectral components. We identify a series of variability
peaks in both the first PCA component and Fvar spectrum which correspond to the
strongest predicted absorption lines from the ultra-fast outflow (UFO)
discovered by Parker et al. (2017). We also find higher order PCA components,
which correspond to variability of the soft excess and reflection features. The
subtle differences between RMS and PCA results argue that the observed
flux-dependence of the absorption is due to increased ionization of the gas,
rather than changes in column density or covering fraction. This result
demonstrates that we can detect outflows from variability alone, and that
variability studies of UFOs are an extremely promising avenue for future
research
Marine bioinvasion management: structural framework
Significant global change has occurred through the accidental and intentional
human mediated introductions of species in regions outside of their evolutionary
origins can no longer be disputed (e.g., Lubchenco et al. 1991; Carlton 2001;
Pimentel 2002). This change is well documented in a variety of terrestrial and
freshwater ecosystems (e.g., Drake and Mooney 1989) and is becoming increasingly
apparent in marine and estuarine habitats in all of the worldās oceans (e.g.,
Carlton 2001; Chap. 2, Carlton). Documenting the scale and rates of marine introductions
and the subsequent changes to invaded systems has captured much of the
marine invasion ecology effort during the last 25 years (e.g., Grosholz et al. 2000;
Carlton and Ruiz 2004).
While the lessons that can be learned about evolution, ecosystem function,
community dynamics, and species biology and ecology from the study of biological
introductions are fascinating (e.g., Harper 1965; Carlton and Ruiz 2004), the challenge
āwhat should we and/or what can we do?ā remains. The options appear to be
simple, however the details of implementation are difficult: we can choose to do
nothing or we can choose to act
Broadband Observations of High Redshift Blazars
We present a multi-wavelength study of four high redshift blazars, S5 0014+81 (z = 3.37), CGRaBS J0225+1846 (z = 2.69), BZQ J1430+4205 (z = 4.72), and 3FGL J1656.2ā3303 (z = 2.40) using quasi-simultaneous data from the Swift, Nuclear Spectroscopic Telescope Array (NuSTAR) and the Fermi-Large Area Telescope (LAT) and also archival XMM-Newton observations. Other than 3FGL J1656.2ā3303, none of the sources were known as Ī³-ray emitters, and our analysis of ~7.5 yr of LAT data reveals the first time detection of statistically significant Ī³-ray emission from CGRaBS J0225+1846. We generate the broadband spectral energy distributions (SED) of all the objects, centering at the epoch of NuSTAR observations and reproduce them using a one-zone leptonic emission model. The opticalāUV emission in all the objects can be explained by radiation from the accretion disk, whereas the X-ray to Ī³-ray windows of the SEDs are found to be dominated by inverse Compton scattering off the broad line region photons. All of them host black holes that are billions of solar masses. Comparing the accretion disk luminosity and the jet power of these sources with a large sample of blazars, we find them to occupy a high disk luminosityājet power regime. We also investigate the X-ray spectral properties of the sources in detail with a major focus on studying the causes of soft X-ray deficit, a feature generally seen in high redshift radio-loud quasars. We summarize that this feature could be explained based on the intrinsic curvature in the jet emission rather than being due to the external effects predicted in earlier studies, such as host galaxy and/or warm absorption.A.C.F. thanks Greg Madejski for discussions on the curvature of blazar X-ray spectra and acknowledges support from ERC Advanced Grant 340442. This research has made use of data, software, and/or web tools obtained from NASAs High Energy Astrophysics Science Archive Research Center (HEASARC), a service of Goddard Space Flight Center and the Smithsonian Astrophysical Observatory. Part of this work is based on archival data, software, or online services provided by the ASI Science Data Center (ASDC). This research has made use of the XRT Data Analysis Software (XRTDAS) developed under the responsibility of the ASDC, Italy. This research has also made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (Caltech, USA). This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/
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