1,731 research outputs found
Clustering of Local Group distances: publication bias or correlated measurements? I. The Large Magellanic Cloud
The distance to the Large Magellanic Cloud (LMC) represents a key local rung
of the extragalactic distance ladder. Yet, the galaxy's distance modulus has
long been an issue of contention, in particular in view of claims that most
newly determined distance moduli cluster tightly - and with a small spread -
around the "canonical" distance modulus, (m-M)_0 = 18.50 mag. We compiled 233
separate LMC distance determinations published between 1990 and 2013. Our
analysis of the individual distance moduli, as well as of their two-year means
and standard deviations resulting from this largest data set of LMC distance
moduli available to date, focuses specifically on Cepheid and RR Lyrae
variable-star tracer populations, as well as on distance estimates based on
features in the observational Hertzsprung-Russell diagram. We conclude that
strong publication bias is unlikely to have been the main driver of the
majority of published LMC distance moduli. However, for a given distance
tracer, the body of publications leading to the tightly clustered distances is
based on highly non-independent tracer samples and analysis methods, hence
leading to significant correlations among the LMC distances reported in
subsequent articles. Based on a careful, weighted combination, in a statistical
sense, of the main stellar population tracers, we recommend that a slightly
adjusted canonical distance modulus of (m-M)_0 = 18.49 +- 0.09 mag be used for
all practical purposes that require a general distance scale without the need
for accuracies of better than a few percent.Comment: 35 pages (AASTeX preprint format), 5 postscript figures; AJ, in
press. For full database of LMC distance moduli, see
http://astro-expat.info/Data/pubbias.htm
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Nanotailoring Stereolithography Resins for Unique Applications using Carbon Nanotubes
Nanostructured materials and exploiting their properties in stereolithography (SL) may open
new markets for unique rapidly manufactured functional devices. Controlled amounts of multiwalled carbon nanotubes (MWCNTs) were successfully dispersed in SL epoxy-based resins and
complex three-dimensional (3D) parts were successfully fabricated by means of a multi-material
SL setup. The effect of the nanosized filler was evaluated using mechanical testing. Small
dispersions of MWCNTs resulted in significant effects on the physical properties of the
polymerized resin. A MWCNT concentration of .05 wt% (w/v) in DSM Somos® WaterShed™
11120 resin increased the ultimate tensile stress and fracture stress an average of 17% and 37%,
respectively. Electron microscopy was used to examine the morphology of the nanocomposite
and results showed affinity between the MWCNTs and SL resin and identified buckled
nanotubes that illustrated strong interfacial bonding. These improved physical properties may
provide opportunities for using nanocomposite SL resins in end-use applications. Varying types
and concentrations of nanomaterials can be used to tailor existing SL resins for particular
applications.Mechanical Engineerin
Gravitational conundrum? Dynamical mass segregation versus disruption of binary stars in dense stellar systems
Upon their formation, dynamically cool (collapsing) star clusters will,
within only a few million years, achieve stellar mass segregation for stars
down to a few solar masses, simply because of gravitational two-body
encounters. Since binary systems are, on average, more massive than single
stars, one would expect them to also rapidly mass segregate dynamically.
Contrary to these expectations and based on high-resolution Hubble Space
Telescope observations, we show that the compact, 15-30 Myr-old Large
Magellanic Cloud cluster NGC 1818 exhibits tantalizing hints at the >= 2 sigma
level of significance (> 3 sigma if we assume a power-law secondary-to-primary
mass-ratio distribution) of an increasing fraction of F-star binary systems
(with combined masses of 1.3-1.6 Msun) with increasing distance from the
cluster center, specifically between the inner 10 to 20" (approximately
equivalent to the cluster's core and half-mass radii) and the outer 60 to 80".
If confirmed, this will offer support of the theoretically predicted but thus
far unobserved dynamical disruption processes of the significant population of
'soft' binary systems---with relatively low binding energies compared to the
kinetic energy of their stellar members---in star clusters, which we have
access to here by virtue of the cluster's unique combination of youth and high
stellar density.Comment: Accepted for publication in The Astrophysical Journal; 19 pages in
AASTeX format; 3 figure
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Unified Software for Multi-Functional G-Code: A Method for Implementing Multi-Technology Additive Manufacturing
Additive manufacturing (AM) began a manufacturing revolution moving industrial
production into consumer homes. With interest shifting toward multi-functional parts fabricated
through AM technologies, multi-functional fabrication systems are now being developed.
Merging different manufacturing technologies into a single machine is a challenge, but ongoing
research in the development of multi-technology systems has shown promise. The software and
automation aspects of multi-technology systems are being developed in unison. This paper
explores the challenges and approaches to developing software that interfaces with multifunctional
CADs and creates files for direct use in multi-technology AM machines.Mechanical Engineerin
Expanding the Applicability of FDM-type Technologies Through Materials Development
Currently, the most common form of additive manufacturing is material extrusion 3D
printing (ME3DP) based on fused deposition modeling (FDM®) technology which relies upon a
thermoplastic monofilament as a base material for the fabrication of three dimensional objects.
The dependence on thermoplastics as a feedstock by ME3DP platforms limits the applicability of
this additive manufacturing method. A clear-cut path towards greater applicability is the
introduction of novel materials with diverse physical properties which maintain compatibility
with 3D printing platforms based on FDM® technology. The work in this paper presents efforts
in the development of polymer matrix composites (PMC)s and polymer blends based on
acrylonitrile butadiene styrene (ABS) and polycarbonate (PC), two thermoplastic materials
commonly used by FDM®-type platforms. Mechanical testing and fractography via scanning
electron microscopy (SEM) were the two main metrics used to characterize these new material
systems. Overcoming barriers to the manufacturing of these novel 3D-printable materials
systems is also presented.Mechanical Engineerin
The diet of the Malham Tarn otters: understanding the impacts of a native predator
Otter (Lutra lutra) populations have been recovering in the UK and expanding into new and often isolated
habitats. Otters were first sighted at Malham Tarn in 2009, and have since been observed on a regular basis.
This study looks at the diet of the Malham Tarn otters and considers their possible impact on prey
populations, such as fish, wading birds and white-clawed crayfish
Formal Verification of Neural Network Controlled Autonomous Systems
In this paper, we consider the problem of formally verifying the safety of an
autonomous robot equipped with a Neural Network (NN) controller that processes
LiDAR images to produce control actions. Given a workspace that is
characterized by a set of polytopic obstacles, our objective is to compute the
set of safe initial conditions such that a robot trajectory starting from these
initial conditions is guaranteed to avoid the obstacles. Our approach is to
construct a finite state abstraction of the system and use standard
reachability analysis over the finite state abstraction to compute the set of
the safe initial states. The first technical problem in computing the finite
state abstraction is to mathematically model the imaging function that maps the
robot position to the LiDAR image. To that end, we introduce the notion of
imaging-adapted sets as partitions of the workspace in which the imaging
function is guaranteed to be affine. We develop a polynomial-time algorithm to
partition the workspace into imaging-adapted sets along with computing the
corresponding affine imaging functions. Given this workspace partitioning, a
discrete-time linear dynamics of the robot, and a pre-trained NN controller
with Rectified Linear Unit (ReLU) nonlinearity, the second technical challenge
is to analyze the behavior of the neural network. To that end, we utilize a
Satisfiability Modulo Convex (SMC) encoding to enumerate all the possible
segments of different ReLUs. SMC solvers then use a Boolean satisfiability
solver and a convex programming solver and decompose the problem into smaller
subproblems. To accelerate this process, we develop a pre-processing algorithm
that could rapidly prune the space feasible ReLU segments. Finally, we
demonstrate the efficiency of the proposed algorithms using numerical
simulations with increasing complexity of the neural network controller
A highly specific tool for identification of Xanthomonas vasicola pv. musacearum based on five Xvm-specific coding sequences
This is the final version. Available on open access from Elsevier via the DOI in this recordXanthomonas vasicola pv. musacearum (Xvm) is a bacterial pathogen responsible for the economically important Xanthomonas wilt disease on banana and enset crops in Sub-Saharan Africa. Given that the symptoms are similar to those of other diseases, molecular diagnosis is essential to unambiguously identify this pathogen and distinguish it from closely related strains not pathogenic on these hosts. Currently, Xvm identification is based on polymerase chain reaction (PCR) with GspDm primers, targeting the gene encoding general secretory protein D. Experimental results and examination of genomic sequences revealed poor specificity of the GspDm PCR. Here, we present and validate five new Xvm-specific primers amplifying only Xvm strains.Agropolis Fondatio
A VLT/VIMOS view of two multiple-cluster systems: structure and galaxy properties
We analysed spectroscopic data obtained with VLT-VIMOS for two
multiple-cluster systems, PLCKG and PLCKG, discovered
via their thermal Sunyaev-Zel'dovich signal by . Combining the Optical
spectroscopy, for the redshift determination, and photometric data from galaxy
surveys (SDSS, WISE, DESI), we were able to study the structure of the two
multiple-cluster systems, to determine their nature and the properties of their
member galaxies. We found that the two systems are populated mainly with
passive galaxies and that PLCKG consists of a pair of clusters at
redshift and a background isolated cluster at , whereas
the system PLCKG is a chance association of three independent
clusters at redshifts , , and . We also find
evidence for remaining star formation activity in the highest-redshift cluster
of PLCKG, at .Comment: 12 pages, 9 Figures, 5 Tables. Submitted to A&A, comments are welcom
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