4,399 research outputs found
Morse matchings on polytopes
We show how to construct homology bases for certain CW complexes in terms of
discrete Morse theory and cellular homology. We apply this technique to study
certain subcomplexes of the half cube polytope studied in previous works. This
involves constructing explicit complete acyclic Morse matchings on the face
lattice of the half cube; this procedure may be of independent interest for
other highly symmetric polytopes
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Development of Optical Fibre Humidity Sensors for Assessing the Quality of Housing Insulation Materials
A fibre optic-based relative humidity (RH) sensing system has been developed for assessing the qualities of housing insulation materials, based on a Polyimide (PI)-coated Fibre Bragg Grating (FBG) device. This forms the key moisture sensitive element, allowing a carefully-designed and packaged sensor system to be fabricated, evaluated and calibrated, creating the robustness and reusability needed. Following calibration, the system performance evaluated on a range of commercial housing insulation materials shows excellent performance in establishing the key moisture-transport parameters of the materials routinely used by structural engineers. Cross-sensitivity issues are addressed allowing the RH sensor system to operate over a wide range of RH level experienced normally in this application. A sensitivity of 1.1 pm/%RH, with low hysteresis from a ruggedized sensor, is observed
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
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
Dynamics of Triangulations
We study a few problems related to Markov processes of flipping
triangulations of the sphere. We show that these processes are ergodic and
mixing, but find a natural example which does not satisfy detailed balance. In
this example, the expected distribution of the degrees of the nodes seems to
follow the power law
Complex diffuse radio emission in the merging PLANCK ESZ cluster Abell 3411
We present VLA radio and Chandra X-ray observations of the merging galaxy
cluster Abell 3411. For the cluster, we find an overall temperature of 6.4 keV
and an X-ray luminosity of 2.8 x 10^{44} erg s^{-1} between 0.5 and 2.0 keV.
The Chandra observation reveals the cluster to be undergoing a merger event.
The VLA observations show the presence of large-scale diffuse emission in the
central region of the cluster, which we classify as a 0.9 Mpc size radio halo.
In addition, a complex region of diffuse, polarized emission is found in the
southeastern outskirts of the cluster, along the projected merger axis of the
system. We classify this region of diffuse emission as a radio relic. The total
extent of this radio relic is 1.9 Mpc. For the combined emission in the cluster
region, we find a radio spectral index of -1.0 \pm 0.1 between 74 MHz and 1.4
GHz. The morphology of the radio relic is peculiar, as the relic is broken up
into five fragments. This suggests that the shock responsible for the relic has
been broken up due to interaction with a large-scale galaxy filament connected
to the cluster or other substructures in the ICM. Alternatively, the complex
morphology reflects the presence of electrons in fossil radio bubbles that are
re-accelerated by a shock.Comment: Accepted for publication in ApJ, 8 pages, 5 figure
VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics
Cluster mergers leave distinct signatures in the ICM in the form of shocks
and diffuse cluster radio sources that provide evidence for the acceleration of
relativistic particles. However, the physics of particle acceleration in the
ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very
Large Array (VLA) and archival Chandra observations of the HST Frontier Fields
Cluster Abell 2744. In our new VLA images, we detect the previously known
Mpc radio halo and Mpc radio relic. We carry out a radio
spectral analysis from which we determine the relic's injection spectral index
to be . This corresponds to a shock Mach
number of = 2.05 under the assumption of
diffusive shock acceleration. We also find evidence for spectral steepening in
the post-shock region. We do not find evidence for a significant correlation
between the radio halo's spectral index and ICM temperature. In addition, we
observe three new polarized diffuse sources and determine two of these to be
newly discovered giant radio relics. These two relics are located in the
southeastern and northwestern outskirts of the cluster. The corresponding
integrated spectral indices measure and for
the SE and NW relics, respectively. From an X-ray surface brightness profile we
also detect a possible density jump of co-located with
the newly discovered SE relic. This density jump would correspond to a shock
front Mach number of .Comment: accepted for publication in Ap
Hot Gas Structure in the Elliptical Galaxy NGC 4472
We present X-ray spectroscopic and morphological analyses using Chandra ACIS
and ROSAT observations of the giant elliptical galaxy NGC 4472 in the Virgo
cluster. We discuss previously unobserved X-ray structures within the extended
galactic corona. In the inner 2' of the galaxy, we find X-ray holes or cavities
with radii of ~2 kpc, corresponding to the position of radio lobes. These holes
were produced during a period of nuclear activity that began 1.2 x 10^7 years
ago and may be ongoing. We also find an asymmetrical edge in the galaxy X-ray
emission 3' (14 kpc) northeast of the core and an ~8' tail (36 kpc) extending
southwest of the galaxy. These two features probably result from the
interaction of NGC 4472 gas with the Virgo gas, which produces compression in
the direction of NGC 4472's infall and an extended tail from ram pressure
stripping. Assuming the tail is in pressure equilibrium with the surrounding
gas, we compute its angle to our line of sight and estimate that its true
extent exceeds 100 kpc. Finally, in addition to emission from the nucleus
(first detected by Soldatenkov, Vikhlinin & Pavlinsky), we detect two small
extended sources within 10'' of the nucleus of the galaxy, both of which have
luminosities of ~7 x 10^38 erg/s.Comment: 25 pages, 11 figures, accepted by Ap
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
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