225 research outputs found
Exploration of the effects of classroom humidity levels on teachers’ respiratory symptoms
Previous studies indicate that teachers have higher asthma prevalence than other non-industrial worker groups. Schools frequently have trouble maintaining indoor relative humidity (RH) within the optimum range (30-50%) for reducing allergens and irritants. However, the potential relationship between classroom humidity and teachers’ health has not been explored. Thus, we examined the relationship between classroom humidity levels and respiratory symptoms among North Carolina teachers
Transient alpha and beta synchrony underlies preparatory recruitment of directional motor networks
Modulations in motor cortical beta and alpha activity have been implicated in the preparation, execution, and termination of voluntary movements. The functional role of motor cortex beta activity is yet to be defined, though two opposing theories prevail. The idling cortex theory suggests that large-scale motor networks, in the absence of input, revert to an intrinsic oscillatory state. The alternative theory proposes that beta activity promotes postural tone at the expense of voluntary movement. These theories are primarily based on observations of event-related desynchronization associated with movement onset. Here, we explore the changes in alpha and beta oscillatory activity associated with the specific behavioral patterns during an established directional uncertainty paradigm. We demonstrate that, consistent with current proposals, alpha and beta desynchronization reflects a process of disengagement from existing networks to enable the creation of functional assemblies. We demonstrate that, following desynchronization, a novel signature of transient alpha synchrony underlies the recruitment of functional assemblies required for directional control. Although alpha and beta desynchronization are dependent upon the number of cues presented, they are not predictive of movement preparation. However, the transient alpha synchrony occurs only when participants have sufficient information to prepare for movement and shows a direct relationship with behavioral performance measures. </jats:p
M 33 X-7: ChASeM33 reveals the first eclipsing black hole X-ray binary
The first observations conducted as part of the Chandra ACIS survey of M 33
(ChASeM33) sampled the eclipsing X-ray binary M 33 X-7 over a large part of the
3.45 d orbital period and have resolved eclipse ingress and egress for the
first time. The occurrence of the X-ray eclipse allows us to determine an
improved ephemeris of mid-eclipse and binary period as HJD (2453639.119+-0.005)
+- N x (3.453014+-0.000020) and constrain the eclipse half angle to (26.5+-1.1)
degree. There are indications for a shortening of the orbital period. The X-ray
spectrum is best described by a disk blackbody spectrum typical for black hole
X-ray binaries in the Galaxy. We find a flat power density spectrum and no
significant regular pulsations were found in the frequency range of 10^{-4} to
0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be
identified as an O6III star with the help of extinction and colour corrections
derived from the X-ray absorption. Based on the optical light curve, the mass
of the compact object in the system most likely exceeds 9 M_sun. This mass, the
shape of the X-ray spectrum and the short term X-ray time variability identify
M 33 X-7 as the first eclipsing black hole high mass X-ray binary.Comment: 14 pages, 5 figures, ApJ accepte
High-resolution x-ray telescopes
High-energy astrophysics is a relatively young scientific field, made
possible by space-borne telescopes. During the half-century history of x-ray
astronomy, the sensitivity of focusing x-ray telescopes-through finer angular
resolution and increased effective area-has improved by a factor of a 100
million. This technological advance has enabled numerous exciting discoveries
and increasingly detailed study of the high-energy universe-including accreting
(stellar-mass and super-massive) black holes, accreting and isolated neutron
stars, pulsar-wind nebulae, shocked plasma in supernova remnants, and hot
thermal plasma in clusters of galaxies. As the largest structures in the
universe, galaxy clusters constitute a unique laboratory for measuring the
gravitational effects of dark matter and of dark energy. Here, we review the
history of high-resolution x-ray telescopes and highlight some of the
scientific results enabled by these telescopes. Next, we describe the planned
next-generation x-ray-astronomy facility-the International X-ray Observatory
(IXO). We conclude with an overview of a concept for the next next-generation
facility-Generation X. The scientific objectives of such a mission will require
very large areas (about 10000 m2) of highly-nested lightweight
grazing-incidence mirrors with exceptional (about 0.1-arcsecond) angular
resolution. Achieving this angular resolution with lightweight mirrors will
likely require on-orbit adjustment of alignment and figure.Comment: 19 pages, 11 figures, SPIE Conference 7803 "Adaptive X-ray Optics",
part of SPIE Optics+Photonics 2010, San Diego CA, 2010 August 2-
The Chandra ACIS Survey of M33 (ChASeM33): The final source catalog
This study presents the final source catalog of the Chandra ACIS Survey of
M33 (ChASeM33). With a total exposure time of 1.4 Ms, ChASeM33 covers ~70% of
the D25 isophote (R\approx4kpc) of M33 and provides the deepest, most complete,
and detailed look at a spiral galaxy in X-rays. The source catalog includes 662
sources, reaches a limiting unabsorbed luminosity of ~2.4x10^(34) erg/s in the
0.35-8.0keV energy band, and contains source positions, source net counts,
fluxes and significances in several energy bands, and information on source
variability. The analysis challenges posed by ChASeM33 and the techniques
adopted to address these challenges are discussed. To constrain the nature of
the detected X-ray source, hardness ratios were constructed and spectra were
fit for 254 sources, followup MMT spectra of 116 sources were acquired, and
cross-correlations with previous X-ray catalogs and other multi-wavelength data
were generated. Based on this effort, 183 of the 662 ChASeM33 sources could be
identified. Finally, the luminosity function for the detected point sources as
well as the one for the X-ray binaries in M33 is presented. The luminosity
functions in the soft band (0.5-2.0 keV) and the hard band (2.0-8.0 keV) have a
limiting luminosity at the 90% completeness limit of 4.0x10^(34) erg/s and
1.6x10^(35) erg/s (for D=817kpc), respectively, which is significantly lower
than what was reported by previous X-ray binary population studies in galaxies
more distant than M33. The resulting distribution is consistent with a dominant
population of high mass X-ray binaries as would be expected for M33.Comment: 186 pages, 11 figures, 10 tables. Accepted for publication in the
ApJS. For a high resolution version of the paper, see
http://hea-www.harvard.edu/vlp_m33_public
An X-ray upper limit on the presence of a Neutron Star for the Small Magellanic Cloud and Supernova Remnant 1E0102.2-7219
We present Chandra X-ray Observatory archival observations of the supernova
remnant 1E0102.2-7219, a young Oxygen-rich remnant in the Small Magellanic
Cloud. Combining 28 ObsIDs for 324 ks of total exposure time, we present an
ACIS image with an unprecedented signal-to-noise ratio (mean S/N ~ sqrt(S) ~6;
maximum S/N > 35) . We search within the remnant, using the source detection
software {\sc wavdetect}, for point sources which may indicate a compact
object. Despite finding numerous detections of high significance in both broad
and narrow band images of the remnant, we are unable to satisfactorily
distinguish whether these detections correspond to emission from a compact
object. We also present upper limits to the luminosity of an obscured compact
stellar object which were derived from an analysis of spectra extracted from
the high signal-to-noise image. We are able to further constrain the
characteristics of a potential neutron star for this remnant with the results
of the analysis presented here, though we cannot confirm the existence of such
an object for this remnant.Comment: Accepted to the Astrophysical Journa
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