4,509 research outputs found
Interview with Huda Zoghbi
An oral history interview with Dr. Huda Zoghbi about her career at Baylor College of Medicine in the Texas Medical Center. She worked as a professor in the Departments of Pediatrics, Molecular and Human Genetics, Neurology and Neuroscience at Baylor College of Medicine. She was also an investigator at the Howard Hughes Medical Institute and the director of the Jan and Dan Duncan Neurological Research Institute (NRI) at Texas Children\u27s Hospital.
SOURCE: Baylor College of Medicine website, http://www.bcm.ed
Relativistic iron K X-ray Reverberation in NGC 4151
Recent X-ray observations have enabled the study of reverberation delays in
AGN for the first time. All the detections so far are in sources with a strong
soft excess, and the measured delay is between the hard (1-3 keV) direct
continuum and the soft excess (0.5-1 keV), interpreted as the reflection
continuum smeared by relativistic effects. There is however an inherent
ambiguity in identifying and studying the details of the lines in the soft
excess. Here we report the first detection of reverberation in the iron K band
in any AGN. Using XMM-Newton observations of NGC 4151, we find delays of order
2000 s on time-scales of 10e5 s between the 5-6 keV band and 2-3 and 7-8 keV
bands, with a broad lag profile resembling a relativistically-broadened iron
line. The peak of the lag spectra shifts to lower energies at higher
frequencies, consistent with the red wing of the line being emitted at smaller
radii, as expected from reflection off the inner accretion disk. This is a
first detection of a broad iron line using timing studies.Comment: final version, corrected small typo
1H0707-495 in 2011: An X-ray source within a gravitational radius of the event horizon
The Narrow Line Seyfert 1 Galaxy 1H0707-495 went in to a low state from 2010
December to 2011 February, discovered by a monitoring campaign using the X-Ray
Telescope on the Swift satellite. We triggered a 100 ks XMM-Newton observation
of the source in 2011 January, revealing the source to have dropped by a factor
of ten in the soft band, below 1 keV, and a factor of 2 at 5 keV, compared with
a long observation in 2008. The sharp spectral drop in the source usually seen
around 7 keV now extends to lower energies, below 6 keV in our frame. The 2011
spectrum is well fit by a relativistically-blurred reflection spectrum similar
to that which fits the 2008 data, except that the emission is now concentrated
solely to the central part of the accretion disc. The irradiating source must
lie within 1 gravitational radius of the event horizon of the black hole, which
spins rapidly. Alternative models are briefly considered but none has any
simple physical interpretation.Comment: 9 pages, 19 figures, MNRAS in pres
Discovery of high-frequency iron K lags in Ark 564 and Mrk 335
We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate
the frequency dependent time-lags for these two well-studied sources. We
discover high-frequency Fe K lags in both sources, indicating that the red wing
of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark
564 and Mrk 335, respectively. Including these two new sources, Fe K
reverberation lags have been observed in seven Seyfert galaxies. We examine the
low-frequency lag-energy spectrum, which is smooth, and shows no feature of
reverberation, as would be expected if the low-frequency lags were produced by
distant reflection off circumnuclear material. The clear differences in the low
and high frequency lag-energy spectra indicate that the lags are produced by
two distinct physical processes. Finally, we find that the amplitude of the Fe
K lag scales with black hole mass for these seven sources, consistent with a
relativistic reflection model where the lag is the light travel delay
associated with reflection of continuum photons off the inner disc.Comment: 10 pages, 12 figures, accepted for publication in MNRA
Evidence for High-Frequency QPOs with a 3:2 Frequency Ratio from a 5000 Solar Mass Black Hole
Following the discovery of 3:2 resonance quasi-periodic oscillations (QPOs)
in M82X-1 (Pasham et al. 2014), we have constructed power density spectra (PDS)
of all 15 (sufficiently long) {\it XMM-Newton} observations of the
ultraluminous X-ray source NGC1313X-1 ( 210
erg/sec). We detect a strong QPO at a frequency of 0.290.01 Hz in data
obtained on 2012 December 16. Subsequent searching of all the remaining
observations for a 3:2/2:3 frequency pair revealed a feature at 0.460.02
Hz on 2003 Dec 13 (frequency ratio of 1.590.09). The global significance
of the 0.29 Hz feature considering all frequencies between 0.1 and 4 Hz is
3.5 . The significance of the 0.460.02 Hz QPO is 3.5
for a search at 2/3 and 3/2 of 0.29 Hz. We also detect lower frequency QPOs
(32.92.6 and 79.71.2 mHz). All the QPOs are super-imposed on a
continuum consisting of flat-topped, band-limited noise, breaking into a
power-law at a frequency of 163 mHz and white noise at 0.1 Hz.
NGC1313X-1's PDS is analogous to stellar-mass black holes' (StMBHs) PDS in the
so-called steep power-law state, but with the respective frequencies (both QPOs
and break frequencies) scaled down by a factor of 1000. Using the
inverse mass-to-high-frequency QPO scaling of StMBHs, we estimate NGC1313X-1's
black hole mass to be 50001300 , consistent with an inference
from the scaling of the break frequency. However, the implied Eddington ratio,
L 0.030.01, is significantly lower compared to StMBHs in the
steep power-law state (L 0.2).Comment: Published in ApJ Letter
Synaptic Dysfunction in Neurodevelopmental Disorders Associated with Autism and Intellectual Disabilities
The discovery of the genetic causes of syndromic autism spectrum disorders and intellectual disabilities has greatly informed our understanding of the molecular pathways critical for normal synaptic function. The top-down approaches using human phenotypes and genetics helped identify causative genes and uncovered the broad spectrum of neuropsychiatric features that can result from various mutations in the same gene. Importantly, the human studies unveiled the exquisite sensitivity of cognitive function to precise levels of many diverse proteins. Bottom-up approaches applying molecular, biochemical, and neurophysiological studies to genetic models of these disorders revealed unsuspected pathogenic mechanisms and identified potential therapeutic targets. Moreover, studies in model organisms showed that symptoms of these devastating disorders can be reversed, which brings hope that affected individuals might benefit from interventions even after symptoms set in. Scientists predict that insights gained from studying these rare syndromic disorders will have an impact on the more common nonsyndromic autism and mild cognitive deficits
¿Es eficaz la disciplina contra la conducta fraudulenta en el trabajo? Una aproximación desde los paradigmas básicos que explican “la mala conducta” en las organizaciones
El presente trabajo discute la eficacia de la estrategia coercitiva en prevenir, disuadir y corregir el “mal comportamiento” en el trabajo. Se discuten los pa-radigmas que sustentan los mecanismos que explican la aparición de la “mala conducta” en las organizaciones, los cuales son usados como pauta de trabajo para calibrar la eficacia de la disciplina. Las conclusiones del presente estudio sugieren una limitada, aunque existente, teórica utilidad de la disciplina para controlar “la mala conducta” en las organizaciones.This paper discusses the effectiveness of coercive strategy to prevent, deter and amend the “bad behavior” at work. Paradigms underlying mechanisms that explain the emergence of misbehavior in working organizations are discussed as a guideline to gauge the effectiveness of the discipline at work. The findings of this study support a limited, although existing, utility of the discipline to control misconduct in organizations.peerReviewe
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