559 research outputs found
Low Temperature Scanning Electron Microscopy of Fungi
The object of the work was to assess the advantages of examining fungal material in the scanning electron microscope whilst in a fully hydrated state (cryofixed). The results indicated that conidia of the ascomycete fungi Xylaria hypoxylon and Nectria cinnabarina were well preserved with no indication of artifacts of contraction and wrinkling, features noted when the material was critical point-dried. Similarly cryofixed basidia of the mycorrhizal basidiomycete, Laccaria laccata, were well preserved as was the mucilaginous film enveloping them. The basidiospores of critical point-dried material were also reasonably well preserved, presumably due to their thick walls, but basidia in such material had a wrinkled appearance, as did the mucilage film which survived the effects of the chemical fixatives and dehydrating solvents.
The conclusion is that cryofixing is a desirable, rapid technique for microbiological specimens and excludes the potentially adverse effects of chemical fixatives and dehydrating agents
Discovery of multiple Lorentzian components in the X-ray timing properties of the Narrow Line Seyfert 1 Ark 564
We present a power spectral analysis of a 100 ksec XMM-Newton observation of
the narrow line Seyfert 1 galaxy Ark~564. When combined with earlier RXTE and
ASCA observations, these data produce a power spectrum covering seven decades
of frequency which is well described by a power law with two very clear breaks.
This shape is unlike the power spectra of almost all other AGN observed so far,
which have only one detected break, and resemble Galactic binary systems in a
soft state. The power spectrum can also be well described by the sum of two
Lorentzian-shaped components, the one at higher frequencies having a hard
spectrum, similar to those seen in Galactic binary systems. Previously we have
demonstrated that the lag of the hard band variations relative to the soft band
in Ark 564 is dependent on variability time-scale, as seen in Galactic binary
sources. Here we show that the time-scale dependence of the lags can be
described well using the same two-Lorentzian model which describes the power
spectrum, assuming that each Lorentzian component has a distinct time lag. Thus
all X-ray timing evidence points strongly to two discrete, localised, regions
as the origin of most of the variability. Similar behaviour is seen in Galactic
X-ray binary systems in most states other than the soft state, i.e. in the
low-hard and intermediate/very high states. Given the very high accretion rate
of Ark 564 the closest analogy is with the very high (intermediate) state
rather than the low-hard state. We therefore strengthen the comparison between
AGN and Galactic binary sources beyond previous studies by extending it to the
previously poorly studied very high accretion rate regime.Comment: 11 pages, 11 figures, accepted for publication in MNRA
The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
We report on a large HST imaging survey of BL Lac objects, at spatial
resolution ~10 times better than previous ground-based surveys. We focus on
data reduction and analysis, describing the procedures used to model the host
galaxy surface brightness radial profiles. A total of 69 host galaxies were
resolved out of 110 objects observed, including almost all sources at z < 0.5.
We classify them morphologically by fitting with either an exponential disk or
a de~Vaucouleurs profile; when one fit is preferred over the other, in 58 of 69
cases, it is invariably the elliptical morphology. This is a very strong result
given the large number of BL Lac objects, the unprecedented spatial resolution,
and the homogeneity of the data set. With the present reclassification of the
host galaxy of 1418+546 as an elliptical, there remain no undisputed examples
of a disk galaxy hosting a BL Lac nucleus. This implies that, at 99%
confidence, fewer than 7% of BL Lacs can be in disk galaxies. The apparent
magnitude of the host galaxies varies with distance as expected if the absolute
magnitudes are approximately the same, with a spread of +-1 mag, out to
redshift z < 0.5. At larger redshifts, only 6 of 23 BL Lacs are resolved so the
present data do not constrain possible luminosity evolution of the host
galaxies. The collective Hubble diagram for BL Lac host galaxies and radio
galaxies strongly supports their unification.Comment: Accepted for publication on ApJS. 43 pages. 10 figures. Figure 1 can
also be downloaded from http://icarus.stsci.edu/~scarpa/tmp/hst_figure1.ta
Geodetic VLBI Observations of EGRET Blazars
We present VLBI observations of the EGRET quasars 0202+149, CTA 26, and
1606+106, as well as additional analysis of VLBI observations of 1156+295
presented in Piner & Kingham (1997b). We have produced 8 and 2 GHz VLBI images
at 11 epochs, 8 epochs, and 12 epochs, spanning the years 1989 to 1996, of
0202+149, CTA 26, and 1606+106 respectively. The VLBI data have been taken from
the Washington VLBI correlator's geodetic database. We have measured the
apparent velocities of the jet components and find that CTA 26 and 1606+106 are
superluminal sources, with average apparent speeds of 8.9 and 2.9 h^{-1}c
respectively (H_{0}=100h km s^{-1} Mpc^{-1}, q_{0}=0.5). The components in
0202+149 are stationary, and we identify this source as a compact F double.
These sources all have apparently bent jets, and we detected non-radial motion
of components in CTA 26 and 1156+295. We have not yet detected any components
emerging subsequent to the gamma-ray flares in CTA 26, 1156+295, and 1606+106,
and we derive lower limits on the ejection times of any such components. The
misalignment angle distribution of the EGRET sources is compared to the
distribution for blazars as a whole, and we find that EGRET sources belong
preferentially to neither the aligned nor the misaligned population. We also
compare the average values for the apparent velocities and Doppler beaming
factors for the EGRET and non-EGRET blazars, and find no significant
differences. We thus find no indication, within the measurement errors, that
EGRET blazars are any more strongly beamed than their counterparts which have
not been detected in gamma-rays.Comment: 47 pages, including 13 figures; accepted for publication in the
Astrophysical Journa
Self-Organized Criticality in Compact Plasmas
Compact plasmas, that exist near black-hole candidates and in gamma ray burst
sources, commonly exhibit self-organized non-linear behavior. A model that
simulates the non-linear behavior of compact radiative plasmas is constructed
directly from the observed luminosity and variability. The simulation shows
that such plasmas self organize, and that the degree of non-linearity as well
as the slope of the power density spectrum increase with compactness. The
simulation is based on a cellular automaton table that includes the properties
of the hot (relativistic) plasmas, and the magnitude of the energy
perturbations. The plasmas cool or heat up, depending on whether they release
more or less than the energy of a single perturbation. The energy release
depends on the plasmas densities and temperatures, and the perturbations
energy. Strong perturbations may cool the previously heated plasma through
shocks and/or pair creation.
New observations of some active galactic nuclei and gamma ray bursters are
consistent with the simulationComment: 9 pages, 5 figures, AASTeX, Submitted to ApJ
Toward a holistic understanding of conduct disorder across the lifespan
Conduct Disorder is a developmental disorder characterized by clinically significant and culturally unexpected aggressive and antisocial behaviors. While much work has focused on the numerous predisposing genetic, neurobiological, psychological, and environmental risk factors for Conduct Disorder, its causal mechanisms, several developmental trajectories, and interacting risks have still yet to be properly elucidated within the context of these factors. With the aim of integrating the literature’s current understanding of Conduct Disorder, we searched APA PsycNet and Google Scholar using a scoping review to select peer-reviewed articles relating to age of onset, presentation, trajectory, persistence, and outcomes of Conduct Disorder. Of the 29 papers found, abstract screening and full text review identified 21 relevant peer-reviewed articles. When taken together and critically examined from a developmentally informed perspective, this holistic review of the literature highlights age of onset and persistence as important influences of disorder trajectory and outcome. The vast heterogeneity of Conduct Disorder should be given greater weight in future research, diagnosis, and early intervention efforts
Fourier-resolved energy spectra of the Narrow Line Seyfert 1 Mkn 766
We compute Fourier-resolved X-ray spectra of the Seyfert 1 Markarian 766 to
study the shape of the variable components contributing to the 0.3-10 keV
energy spectrum and their time-scale dependence. The fractional variability
spectra peak at 1-3 keV, as in other Seyfert 1 galaxies, consistent with either
a constant contribution from a soft excess component below 1 keV and Compton
reflection component above 2 keV, or variable warm absorption enhancing the
variability in the 1-3 keV range. The rms spectra, which shows the shape of the
variable components only, is well described by a single power law with an
absorption feature around 0.7 keV, which gives it an apparent soft excess. This
spectral shape can be produced by a power law varying in normalisation,
affected by an approximately constant (within each orbit) warm absorber, with
parameters similar to those found by Turner et al. for the warm-absorber layer
covering all spectral components in their scattering scenario. The total soft
excess in the average spectrum can therefore be produced by a combination of
constant warm absorption on the power law plus an additional less variable
component. On shorter time-scales, the rms spectrum hardens and this evolution
is well described by a change in power law slope, while the absorption
parameters remain the same. The frequency dependence of the rms spectra can be
interpreted as variability arising from propagating fluctuations through an
extended emitting region, whose emitted spectrum is a power law that hardens
towards the centre. This scenario reduces the short time-scale variability of
lower energy bands making the variable spectrum harder on shorter time-scales
and at the same time explains the hard lags found in these data by Markowitz et
al.Comment: accepted for publication in MNRA
X-ray variability time scales in Active Galactic Nuclei
X-ray variability in Active Galactic Nuclei (AGN) is commonly analysed in
terms of the Power Spectral Density (PSD). The break observed in the power
spectrum can be interpreted as a characteristic X-ray variability time scale.
Here we study variability properties within the framework of clumpy accretion
flows, in which shocks between accreting elements account for the UV and X-ray
emissions. We derive a characteristic X-ray time scale, , and compare
it with the measured PSD break time scale, . A quite good agreement is
found in both magnitude and trend. In particular, the model dependence on black
hole mass and accretion rate precisely reproduces the empirical relation
obtained by McHardy et al. (2006). We suggest a possible physical
interpretation of the break time scale and briefly discuss the related aspects
of optical/UV variability and correlations between different wavelengths.Comment: 6 pages, 1 figure, accepted for publication in Astronomy and
Astrophysic
Chandra Observations of Galaxy Cluster Abell 2218
We present results from two observations (combined exposure of ~17 ks) of
galaxy cluster A2218 using the Advanced CCD Imaging Spectrometer on board the
Chandra X-ray Observatory that were taken on October 19, 1999. Using a
Raymond-Smith single temperature plasma model corrected for galactic absorption
we find a mean cluster temperature of kT = 6.9+/-0.5 keV, metallicity of
0.20+/-0.13 (errors are 90 % CL) and rest-frame luminosity in the 2-10 keV
energy band of 6.2x10^{44} erg/s in a LambdaCDM cosmology with H_0=65 km/s/Mpc.
The brightness distribution within 4'.2 of the cluster center is well fit by a
simple spherical beta model with core radius 66".4 and beta = 0.705 . High
resolution Chandra data of the inner 2' of the cluster show the x-ray
brightness centroid displaced ~22" from the dominant cD galaxy and the presence
of azimuthally asymmetric temperature variations along the direction of the
cluster mass elongation. X-ray and weak lensing mass estimates are in good
agreement for the outer parts (r > 200h^{-1}) of the cluster; however, in the
core the observed temperature distribution cannot reconcile the x-ray and
strong lensing mass estimates in any model in which the intracluster gas is in
thermal hydrostatic equilibrium. Our x-ray data are consistent with a scenario
in which recent merger activity in A2218 has produced both significant
non-thermal pressure in the core and substructure along the line of sight; each
of these phenomena probably contributes to the difference between lensing and
x-ray core mass estimates.Comment: 33 pages, 6 figures, uses AASTeX 5.02, ApJ submitte
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