15,945 research outputs found
Connectivity Compression for Irregular Quadrilateral Meshes
Applications that require Internet access to remote 3D datasets are often
limited by the storage costs of 3D models. Several compression methods are
available to address these limits for objects represented by triangle meshes.
Many CAD and VRML models, however, are represented as quadrilateral meshes or
mixed triangle/quadrilateral meshes, and these models may also require
compression. We present an algorithm for encoding the connectivity of such
quadrilateral meshes, and we demonstrate that by preserving and exploiting the
original quad structure, our approach achieves encodings 30 - 80% smaller than
an approach based on randomly splitting quads into triangles. We present both a
code with a proven worst-case cost of 3 bits per vertex (or 2.75 bits per
vertex for meshes without valence-two vertices) and entropy-coding results for
typical meshes ranging from 0.3 to 0.9 bits per vertex, depending on the
regularity of the mesh. Our method may be implemented by a rule for a
particular splitting of quads into triangles and by using the compression and
decompression algorithms introduced in [Rossignac99] and
[Rossignac&Szymczak99]. We also present extensions to the algorithm to compress
meshes with holes and handles and meshes containing triangles and other
polygons as well as quads
Keep All the Wells Full: A Metaphor for Understanding Community Partnerships
Clean water from the community well gives and sustains life, growth, and commerce. Its absence through waste, monopoly, drought, or scarcity leads to sickness, fear, and death. What then is the cost to the community of scarcity or a drought in leadership, healthy children, opportunity, stable families, safety, homes, literacy, timely justice, quality education, income, health care, jobs, hope, motivation, or wealth. It is the wise and caring community that keeps all of its wells full. King Davis, 200
High Redshift Standard Candles: Predicted Cosmological Constraints
We investigate whether future measurements of high redshift standard candles
(HzSCs) will be a powerful probe of dark energy, when compared to other types
of planned dark energy measurements. Active galactic nuclei and gamma ray
bursts have both been proposed as potential HzSC candidates. Due to their high
luminosity, they can be used to probe unexplored regions in the expansion
history of the universe. Information from these regions can help constrain the
properties of dark energy, and in particular, whether it varies over time.
We consider both linear and piecewise parameterizations of the dark energy
equation of state, , and assess the optimal redshift distribution a
high-redshift standard-candle survey could take to constrain these models.
The more general the form of the dark energy equation of state being
tested, the more useful high-redshift standard candles become. For a linear
parameterization of , HzSCs give only small improvements over planned
supernova and baryon acoustic oscillation measurements; a wide redshift range
with many low redshift points is optimal to constrain this linear model.
However to constrain a general, and thus potentially more informative, form of
, having many HzSCs can significantly improve limits on the nature of
dark energy.Comment: Accepted MNRAS, 27 Pages, 15 figures, matches published versio
Pet owner and vet interactions: exploring the drivers of AMR
Background:
Antimicrobial resistance (AMR) is a growing public health problem across the world. As the negative consequences of AMR become apparent at local, national and international levels, more attention is being focussed on the variety of mechanisms by which AMR is potentiated. We explore how interactions between pet owners and veterinarians represent a key arena in which AMR-related behaviours can be shaped.
Methods:
In depth semi-structured interviews were carried out with pet owners (n = 23) and vets (n = 16) across the UK in 2017. A thematic analysis approach was taken, with inductively gathered data analysed deductively using a behavioural framework to identified key behaviours emerging from participant accounts which were amenable to change.
Results:
Interactions between vets and pet owners were characterised by misunderstandings and misconceptions around antibiotics by pet owners, and a lack of clarity about the positions and intentions of the other party. Vets and pet owners had differing perceptions of where pressure to prescribe antibiotics inappropriately originated. Vets perceived it was mostly pet owners who pushed for inappropriate antibiotics, whereas pet owners reported they felt it was vets that overprescribed. Low levels of understanding of AMR in general were apparent amongst pet owners and understandings with regard to AMR in pets specifically were almost non-existent in the sample.
Conclusions:
Improved use of antibiotics could be assisted by educating the pet owning public and by guideline development for companion animal vets, concurrent development of mandatory legislation, increased consultation time to facilitate better communication, development of vet training on antimicrobial therapy and stewardship led interactions with pet owners, and increased levels of knowledge of pet-related AMR amongst pet owners
Mechanical Properties of Hexagonal Lattice Structures Fabricated Using Continuous Liquid Interface Production Additive Manufacturing
The Cool Accretion Disk in ESO 243-49 HLX-1: Further Evidence of an Intermediate Mass Black Hole
With an inferred bolometric luminosity exceeding 10^42 erg/s, HLX-1 in ESO
243-49 is the most luminous of ultraluminous X-ray sources and provides one of
the strongest cases for the existence of intermediate mass black holes. We
obtain good fits to disk-dominated observations of the source with BHSPEC, a
fully relativistic black hole accretion disk spectral model. Due to
degeneracies in the model arising from the lack of independent constraints on
inclination and black hole spin, there is a factor of 100 uncertainty in the
best-fit black hole mass M. Nevertheless, spectral fitting of XMM-Newton
observations provides robust lower and upper limits with 3000 Msun < M < 3 x
10^5 Msun, at 90% confidence, placing HLX-1 firmly in the intermediate-mass
regime. The lower bound on M is entirely determined by matching the shape and
peak energy of the thermal component in the spectrum. This bound is consistent
with (but independent of) arguments based solely on the Eddington limit. Joint
spectral modelling of the XMM-Newton data with more luminous Swift and Chandra
observations increases the lower bound to 6000 Msun, but this tighter
constraint is not independent of the Eddington limit. The upper bound on M is
sensitive to the maximum allowed inclination i, and is reduced to M < 10^5 Msun
if we limit i < 75 deg.Comment: 10 pages, 7 figures, accepted for publication in Ap
Black hole mass estimates from soft X-ray spectra
In the absence of direct kinematic measurements, the mass of an accreting
black hole is sometimes inferred from the X-ray spectral parameters of its
accretion disk; specifically, from the temperature and normalization of a
disk-blackbody model fit. Suitable corrections have to be introduced when the
accretion rate approaches or exceeds the Eddington limit. We summarize
phenomenological models that can explain the very high state, with apparently
higher disk temperatures and lower inner-disk radii. Conversely, ultraluminous
X-ray sources often contain cooler disks with large characteristic radii. We
introduce another phenomenological model for this accretion state. We argue
that a standard disk dominates the radiative output for radii larger than a
characteristic transition radius R_c ~ mdot x R_{ISCO}, where mdot is the
accretion rate in Eddington units and R_{ISCO} is the innermost stable orbit.
For R_{ISCO} < R < R_c, most of the accretion power is released via non-thermal
processes. We predict the location of such sources in a luminosity-temperature
plot. We conclude that black holes with masses ~ 50-100 Msun accreting at mdot
~ 10-20 may explain the X-ray properties of many ULXs.Comment: 14 pages, accepted for publication on Advances in Space Research.
Based on work presented at the 2006 Cospar Scientific Assembl
Redshift and Shear Calibration: Impact on Cosmic Shear Studies and Survey Design
The cosmological interpretation of weak lensing by large-scale structures
requires knowledge of the redshift distribution of the source galaxies. Current
lensing surveys are often calibrated using external redshift samples which span
a significantly smaller sky area in comparison to the lensing survey, and are
thus subject to sample variance. Some future lensing surveys are expected to be
calibrated in the same way, in particular the fainter galaxy populations where
the entire color coverage, and hence photometric redshift estimate, could be
challenging to obtain. Using N-body simulations, we study the impact of this
sample variance on cosmic shear analysis and show that, to first approximation,
it behaves like a shear calibration error 1+/-epsilon. Using the Hubble Deep
Field as a redshift calibration survey could therefore be a problem for current
lensing surveys. We discuss the impact of the redshift distribution sampling
error and a shear calibration error on the design of future lensing surveys,
and find that a lensing survey of area Theta square degrees and limiting
magnitude m_lim}, has a minimum shear and redshift calibration accuracy
requirements given by epsilon = epsilon_0 10^{beta(m_lim-24.5)} / sqrt(Theta/
200). Above that limit, lensing surveys would not reach their full potential.
Using the galaxy number counts from the Hubble Ultra-Deep Field, we find
(epsilon_0,beta)=(0.015,-0.18) and (epsilon_0,beta)=(0.011,-0.23) for ground
and space based surveys respectively. Lensing surveys with no or limited
redshift information and/or poor shear calibration accuracy will loose their
potential to analyse the cosmic shear signal in the sub-degree angular scales,
and therefore complete photometric redshift coverage should be a top priority
for future lensing surveys.Comment: Accepted version to Astroparticle Physic
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