57 research outputs found
Observation of EDM plasma behavior influenced by parasitic working gap capacitance
Machining large surfaces to good surface qualities is currently difficult, as optimisation of parameters does not always lead to a satisfactory outcome. This appears to be an issue with traditional EDM, and the cause is not understood very well. Observing this effect by looking at current and voltage is very difficult because of the parasitic capacitance. As the capacitance is a function of surface area and gap width, small gaps, as they occur when using small energies, result in a large capacitance. The charge of the capacitance can have the same order of magnitude as the discharge itself. This makes it hard to understand what actually happens in the gap while measuring current and voltage on the outside. In order to understand this phenomenon large, optically transparent SiC electrodes were used to observe the gap with a high speed camera. By doing so it is possible to locate consecutive discharges and to determine if the capacitance has a large effect on the behaviour of the plasma. The goal of this work is to identify the effect that is responsible for the difficulties with the machining of large high-quality surfaces in order to work out possibilities to enable those machining operations
Suzaku observations of the hard X-ray variability of MCG-6-30-15: the effects of strong gravity around a Kerr black hole
Suzaku has, for the first time, enabled the hard X-ray variability of the
Seyfert 1 galaxy MCG-6-30-15 to be measured. The variability in the 14-45 keV
band, which is dominated by a strong reflection hump, is quenched relative to
that at a few keV. This directly demonstrates that the whole reflection
spectrum is much less variable than the power-law continuum. The broadband
spectral variability can be decomposed into two components - a highly variable
power-law and constant reflection - as previously inferred from other
observations in the 2-10 keV band. The strong reflection and high iron
abundance give rise to a strong broad iron line, which requires the inner disc
radius to be at about 2 gravitational radii. Our results are consistent with
the predictions of the light bending model which invokes the very strong
gravitational effects expected very close to a rapidly spinning black hole.Comment: accepted for publication in PASJ Suzaku special issu
The ASTRO-H X-ray Observatory
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly
successful X-ray missions initiated by the Institute of Space and Astronautical
Science (ISAS). ASTRO-H will investigate the physics of the high-energy
universe via a suite of four instruments, covering a very wide energy range,
from 0.3 keV to 600 keV. These instruments include a high-resolution,
high-throughput spectrometer sensitive over 0.3-2 keV with high spectral
resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in
the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers
covering 5-80 keV, located in the focal plane of multilayer-coated, focusing
hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12
keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and
a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the
40-600 keV band. The simultaneous broad bandpass, coupled with high spectral
resolution, will enable the pursuit of a wide variety of important science
themes.Comment: 22 pages, 17 figures, Proceedings of the SPIE Astronomical
Instrumentation "Space Telescopes and Instrumentation 2012: Ultraviolet to
Gamma Ray
The Quiescent Intracluster Medium in the Core of the Perseus Cluster
Clusters of galaxies are the most massive gravitationally-bound objects in
the Universe and are still forming. They are thus important probes of
cosmological parameters and a host of astrophysical processes. Knowledge of the
dynamics of the pervasive hot gas, which dominates in mass over stars in a
cluster, is a crucial missing ingredient. It can enable new insights into
mechanical energy injection by the central supermassive black hole and the use
of hydrostatic equilibrium for the determination of cluster masses. X-rays from
the core of the Perseus cluster are emitted by the 50 million K diffuse hot
plasma filling its gravitational potential well. The Active Galactic Nucleus of
the central galaxy NGC1275 is pumping jetted energy into the surrounding
intracluster medium, creating buoyant bubbles filled with relativistic plasma.
These likely induce motions in the intracluster medium and heat the inner gas
preventing runaway radiative cooling; a process known as Active Galactic
Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus
cluster core, which reveal a remarkably quiescent atmosphere where the gas has
a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from
the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s
is found across the 60 kpc image of the cluster core. Turbulent pressure
support in the gas is 4% or less of the thermodynamic pressure, with large
scale shear at most doubling that estimate. We infer that total cluster masses
determined from hydrostatic equilibrium in the central regions need little
correction for turbulent pressure.Comment: 31 pages, 11 Figs, published in Nature July
Hitomi (ASTRO-H) X-ray Astronomy Satellite
The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month
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