5,366 research outputs found
Ion sputter textured graphite electrode plates
A specially textured surface of pyrolytic graphite exhibits extremely low yields of secondary electrons and reduced numbers of reflected primary electrons after impingement of high energy primary electrons. Electrode plates of this material are used in multistage depressed collectors. An ion flux having an energy between 500 iV and 1000 iV and a current density between 1.0 mA/sq cm and 6.0 mA/sq cm produces surface roughening or texturing which is in the form of needles or spires. Such textured surfaces are especially useful as anode collector plates in high tube devices
Ion sputter textured graphite
A specially textured surface of pyrolytic graphite exhibits extremely low yields of secondary electrons and reduced numbers of reflected primary electrons after impingement of high energy primary electrons. An ion flux having an energy between 500 eV and 1000 eV and a current density between 1.0 mA/sq cm and 6.0 mA/sq cm produces surface roughening or texturing which is in the form of needles or spines. Such textured surfaces are especially useful as anode collector plates in high efficiency electron tube devices
XMM-Newton observations of the Perseus Cluster I: The temperature and surface brightness structure
We present preliminary results of the XMM-Newton 50 ksec observation of the
Perseus cluster. The global east/west asymmetry of the gas temperature and
surface brightness distributions, approximately aligned with the chain of
bright galaxies, suggests an ongoing merger, although the modest degree of the
observed asymmetry certainly excludes a major merger interpretation. The chain
of galaxies probably traces the filament along which accretion has started some
time ago and is continuing at the present time. A cold and dense (low entropy)
cluster core like Perseus is probably well "protected" against the penetration
of the gas of infalling groups and poor clusters whereas in non-cooling core
clusters like Coma and A1367, infalling subclusters can penetrate deeply into
the core region. In Perseus, gas associated with infalling groups may be
stripped completely at the outskirts of the main cluster and only compression
waves (shocks) may reach the central regions. We argue that the passage of such
a wave(s) can qualitatively explain the overall horseshoe shaped appearance of
the gas temperature map (the hot horseshoe surrounds the colder, low entropy
core) as well as other features of the Perseus cluster core. As compression
waves traverse the cluster core, they can induce oscillatory motion of the
cluster gas which can generate multiple sharp "edges", on opposite sides or the
central galaxy. Gas motions induced by mergers may be a natural way to explain
the high frequency of "edges" seen in clusters with cooling cores.Comment: 16 pages, 14 figures, submitted to Ap
The infall of the Virgo elliptical galaxy M60 toward M87 and the gaseous structures produced by Kelvin-Helmholtz instabilities
We present Chandra observations of hot gas structures, characteristic of gas stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. 0.5−2 keV Chandra X-ray images show a sharp leading edge in the surface brightness 12.4±0.1 kpc north and west of the galaxy center in the direction of M87 characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00±0.02 keV for abundance 0.5Z⊙ inside the edge and 1.37+0.35−0.19 keV for abundance 0.1Z⊙ in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio of 6.44+1.04−0.67 between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of 4.7+1.7−1.4 and Mach number 1.7±0.3. For 1.37 keV Virgo gas we find a total infall velocity for M60 of 1030±180 kms−1. We calculate the motion in the plane of the sky to be 1012+183−192 km−1 implying an inclination angle ξ=11±3 degrees. Surface brightness profiles show the presence of a faint diffuse gaseous tail. We identify filamentary, gaseous wing structures caused by the galaxy's motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin-Helmholtz instabilities as expected if the gas stripping is close to inviscid
The acceleration and propagation of solar flare energetic particles
Observations and theories of particle acceleration in solar flares are reviewed. The most direct signatures of particle acceleration in flares are gamma rays, X-rays and radio emissions produced by the energetic particles in the solar atmosphere and energetic particles detected in interplanetary space and in the Earth's atmosphere. The implication of these observations are discussed. Stochastic and shock acceleration as well as acceleration in direct electric fields are considered. Interplanetary particle propagation is discussed and an overview of the highlights of both current and promising future research is presented
The Semiclassical Limit for and Gauge Theory on the Torus
We prove that for and quantum gauge theory on a torus,
holonomy expectation values with respect to the Yang-Mills measure d\mu_T(\o)
=N_T^{-1}e^{-S_{YM}(\o)/T}[{\cal D}\o] converge, as , to
integrals with respect to a symplectic volume measure on the moduli
space of flat connections on the bundle. These moduli spaces and the symplectic
structures are described explicitly.Comment: 18 page
Shear thickening in densely packed suspensions of spheres and rods confined to few layers
We investigate confined shear thickening suspensions for which the sample
thickness is comparable to the particle dimensions. Rheometry measurements are
presented for densely packed suspensions of spheres and rods with aspect ratios
6 and 9. By varying the suspension thickness in the direction of the shear
gradient at constant shear rate, we find pronounced oscillations in the stress.
These oscillations become stronger as the gap size is decreased, and the stress
is minimized when the sample thickness becomes commensurate with an integer
number of particle layers. Despite this confinement-induced effect, viscosity
curves show shear thickening that retains bulk behavior down to samples as thin
as two particle diameters for spheres, below which the suspension is jammed.
Rods exhibit similar behavior commensurate with the particle width, but they
show additional effects when the thickness is reduced below about a particle
length as they are forced to align; the stress increases for decreasing gap
size at fixed shear rate while the shear thickening regime gradually
transitions to a Newtonian scaling regime. This weakening of shear thickening
as an ordered configuration is approached contrasts with the strengthening of
shear thickening when the packing fraction is increased in the disordered bulk
limit, despite the fact that both types of confinement eventually lead to
jamming.Comment: 21 pages, 14 figures. submitted to the Journal of Rheolog
X-ray Over-Luminous Elliptical Galaxies: A New Class of Mass Concentrations in the Universe?
We detect four isolated, X-ray over-luminous (Lx>2e43 [h/0.5]**-2 erg/s)
elliptical galaxies (OLEGs) in our 160 square degree ROSAT PSPC survey. The
extent of their X-ray emission, total X-ray luminosity, total mass, and mass of
the hot gas in these systems correspond to poor clusters, and the optical
luminosity of the central galaxies (M_R<-22.5 + 5 lg h) is comparable to that
of cluster cDs. However, there are no detectable fainter galaxy concentrations
around the central elliptical. The mass-to-light ratio within the radius of
detectable X-ray emission is in the range 250-450 Msun/Lsun, which is 2-3 times
higher than typically found in clusters or groups. These objects can be the
result of galaxy merging within a group. However, their high M/L values are
difficult to explain in this scenario. OLEGs must have been undisturbed for a
very long time, which makes them the ultimate examples of systmes in
hydrostatic equilibrium. The number density of OLEGs is n=2.4(+3.1-1.2}x10**-7
(h/0.5)**-3 Mpc**-3 at the 90% confidence. They comprise 20% of all clusters
and groups of comparable X-ray luminosity, and nearly all galaxies brighter
than M_R=-22.5. The estimated contirubution of OLEGs to the total mass density
in the Universe is close to that of T>7 keV clusters.Comment: 4 pages, 2 figures, uses emulateapj.sty, submitted to ApJ Letter
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