7,275 research outputs found
Apparatus and process for microbial detection and enumeration
An apparatus and process for detecting and enumerating specific microorganisms from large volume samples containing small numbers of the microorganisms is presented. The large volume samples are filtered through a membrane filter to concentrate the microorganisms. The filter is positioned between two absorbent pads and previously moistened with a growth medium for the microorganisms. A pair of electrodes are disposed against the filter and the pad electrode filter assembly is retained within a petri dish by retainer ring. The cover is positioned on base of petri dish and sealed at the edges by a parafilm seal prior to being electrically connected via connectors to a strip chart recorder for detecting and enumerating the microorganisms collected on filter
Multimegawatt thermionic reactor systems for space applications
Design features and performance characteristics of thermionic reactor systems for space application
Driving extreme variability: The evolving corona and evidence for jet launching in Markarian 335
Variations in the X-ray emission from the narrow line Seyfert 1 galaxy,
Markarian 335 (Mrk 335), are studied on both long and short timescales through
observations made between 2006 and 2013 with XMM-Newton, Suzaku and NuSTAR.
Changes in the geometry and energetics of the corona that give rise to this
variability are inferred through measurements of the relativistically blurred
reflection seen from the accretion disc. On long timescales, we find that
during the high flux epochs the corona has expanded, covering the inner regions
of the accretion disc out to a radius of 26(-7,+10)rg. The corona contracts to
within 12rg and 5rg in the intermediate and low flux epochs, respectively.
While the earlier high flux observation made in 2006 is consistent with a
corona extending over the inner part of the accretion disc, a later high flux
observation that year revealed that the X-ray source had become collimated into
a vertically-extended jet-like corona and suggested relativistic motion of
material upward. On short timescales, we find that an X-ray flare during a low
flux epoch in 2013 corresponded to a reconfiguration from a slightly extended
corona to one much more compact, within just 2~3rg of the black hole. There is
evidence that during the flare itself, the spectrum softened and the corona
became collimated and slightly extended vertically as if a jet-launching event
was aborted. Understanding the evolution of the X-ray emitting corona may
reveal the underlying mechanism by which the luminous X-ray sources in AGN are
powered.Comment: 21 pages, 9 figures. Accepted for publication in MNRA
Description and field test of an in situ coliform monitoring system
A prototype in situ system for monitoring the levels of fecal coliforms in shallow water bodies was developed and evaluated. This system was based on the known relationship between the concentration of the coliform bacteria and the amount of hydrogen they produce during growth in a complex organic media. The prototype system consists of a sampler platform, which sits on the bottom; a surface buoy, which transmits sampler-generated data; and a shore station, which receives, displays the data, and controls the sampler. The concept of remote monitoring of fecal coliform concentrations by utilizing a system based on the electrochemical method was verified during the evaluation of the prototype
Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles
To gain a better understanding of the inner disc region that comprises active
galactic nuclei it is necessary to understand the pattern in which the disc is
illuminated (the emissivity profile) by X-rays emitted from the continuum
source above the black hole (corona). The differences in the emissivity
profiles produced by various corona geometries are explored via general
relativistic ray tracing simulations. Through the analysis of various
parameters of the geometries simulated it is found that emissivity profiles
produced by point source and extended geometries such as cylindrical slabs and
spheroidal coronae placed on the accretion disc are distinguishable. Profiles
produced by point source and conical geometries are not significantly
different, requiring an analysis of reflection fraction to differentiate the
two geometries. Beamed point and beamed conical sources are also simulated in
an effort to model jet-like coronae, though the differences here are most
evident in the reflection fraction. For a point source we determine an
approximation for the measured reflection fraction with the source height and
velocity. Simulating spectra from the emissivity profiles produced by the
various geometries produce distinguishable differences. Overall spectral
differences between the geometries do not exceed 15 per cent in the most
extreme cases. It is found that emissivity profiles can be useful in
distinguishing point source and extended geometries given high quality spectral
data of extreme, bright sources over long exposure times. In combination with
reflection fraction, timing, and spectral analysis we may use emissivity
profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA
Wavelet spectral timing: X-ray reverberation from a dynamic black hole corona hidden beneath ultrafast outflows
Spectral timing analyses based upon wavelet transforms provide a new means to
study the variability of the X-ray emission from accreting systems, including
AGN, stellar mass black holes and neutron stars, and can be used to trace the
time variability of X-ray reverberation from the inner accretion disc. The
previously-missing iron K reverberation time lags in the AGN IRAS 13224-3809
and MCG-6-30-15 are detected and found to be transitory in nature.
Reverberation can be hidden during periods in which variability in the iron K
band becomes dominated by ultrafast outflows (UFO). Following the time
evolution of the reverberation lag between the corona and inner accretion disc,
we may observe the short-timescale increase in scale height of the corona as it
is accelerated away from the accretion disc during bright X-ray flares in the
AGN I Zw 1. Measuring the variation of the reverberation lag that corresponds
to the continuous, stochastic variations of the X-ray luminosity sheds new
light on the disc-corona connection around accreting black holes. Hysteresis is
observed between the X-ray count rate and the scale height of the corona, and a
time lag of 10~40ks is observed between the rise in luminosity and the increase
in reverberation lag. This correlation and lag are consistent with viscous
propagation through the inner accretion disc, leading first to an increase in
the flux of seed photons that are Comptonised by the corona, before mass
accretion rate fluctuations reach the inner disc and are able to modulate the
structure of the corona.Comment: 20 pages, 13 figures. Accepted for publication in MNRA
Black hole magnetosphere with small scale flux tubes--II. Stability and dynamics
In some Seyfert Galaxies, the hard X-rays that produce fluorescent emission
lines are thought to be generated in a hot corona that is compact and located
at only a few gravitational radii above the supermassive black hole. We
consider the possibility that this X-ray source may be powered by small scale
magnetic flux tubes attached to the accretion disk near the black hole. We use
three dimensional, time dependent force-free simulations in a simplified
setting to study the dynamics of such flux tubes as they get continuously
twisted by the central compact star/black hole. We find that, the dynamical
evolution of the flux tubes connecting the central compact object and the
accretion disk is strongly influenced by the confinement of the surrounding
field. Although differential rotation between the central object and the disk
tends to inflate the flux tubes, strong confinement from surrounding field
quenches the formation of a jet-like outflow, as the inflated flux tube becomes
kink unstable and dissipates most of the extracted rotational energy relatively
close to the central object. Such a process may be able to heat up the plasma
and produce strong X-ray emission. We estimate the energy dissipation rate and
discuss its astrophysical implications.Comment: 16 pages, 17 figures. Accepted for publication in MNRA
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