28 research outputs found
Accessibility for Line-Cutting in Freeform Surfaces
Manufacturing techniques such as hot-wire cutting, wire-EDM, wire-saw cutting, and flank CNC machining all belong to a class of processes called line-cutting where the cutting tool moves tangentially along the reference geometry. From a geometric point of view, line-cutting brings a unique set of challenges in guaranteeing that the process is collision-free. In this work, given a set of cut-paths on a freeform geometry as the input, we propose a conservative algorithm for finding collision-free tangential cutting directions. These directions, if they exist, are guaranteed to be globally accessible for fabricating the geometry by line-cutting. We then demonstrate how this information can be used to generate globally collision-free cut-paths. We apply our algorithm to freeform models of varying complexity.RYC-2017-2264
The Construction of Conforming-to-shape Truss Lattice Structures via 3D Sphere Packing
Truss lattices are common in a wide variety of engineering applications, due to their high ratio of strength versus relative density. They are used both as the interior support for other structures, and as structures on their own. Using 3D sphere packing, we propose a set of methods for generating truss lattices that fill the interior of B-rep models, polygonal or (trimmed) NURBS based, of arbitrary shape. Once the packing of the spheres has been established, beams between the centers of adjacent spheres are constructed, as spline based B-rep geometry. We also demonstrate additional capabilities of our methods, including connecting the truss lattice to (a shell of) the B-rep model, as well as constructing a tensor-product trivariate volumetric representation of the truss lattice - an important step towards direct compatibility for analysis.RYC-2017-2264
Mass segregation in rich clusters in the Large Magellanic Cloud - III. Implications for the initial mass function
The distribution of core radii of rich clusters in the Large Magellanic Cloud
(LMC) systematically increases in both upper limit and spread with increasing
cluster age. Cluster-to-cluster variations in the stellar initial mass function
(IMF) have been suggested as an explanation. We discuss the implications of the
observed degree of mass segregation in our sample clusters for the shape of the
initial mass function.
Our results are based on Hubble Space Telescope/WFPC2 observations of six
rich star clusters in the LMC, selected to include three pairs of clusters of
similar age, metallicity, and distance from the LMC centre, and exhibiting a
large spread in core radii between the clusters in each pair.
All clusters show clear evidence of mass segregation: (i) their luminosity
function slopes steepen with increasing cluster radius, and (ii) the brighter
stars are characterized by smaller core radii. For all sample clusters, both
the slope of the luminosity function in the cluster centres and the degree of
mass segregation are similar to each other, within observational errors of a
few tenths of power-law slope fits to the data. This implies that their INITIAL
mass functions must have been very similar, down to ~0.8 - 1.0 M(sun).
We therefore rule out variations in the IMF of the individual sample clusters
as the main driver of the increasing spread of cluster core radii with cluster
age.Comment: 14 pages LaTeX (incl. 9 postscript figures), accepted for publication
in MNRA
Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
Recent progress in studies of globular clusters has shown that they are not
simple stellar populations, being rather made of multiple generations. Evidence
stems both from photometry and spectroscopy. A new paradigm is then arising for
the formation of massive star clusters, which includes several episodes of star
formation. While this provides an explanation for several features of globular
clusters, including the second parameter problem, it also opens new
perspectives about the relation between globular clusters and the halo of our
Galaxy, and by extension of all populations with a high specific frequency of
globular clusters, such as, e.g., giant elliptical galaxies. We review progress
in this area, focusing on the most recent studies. Several points remain to be
properly understood, in particular those concerning the nature of the polluters
producing the abundance pattern in the clusters and the typical timescale, the
range of cluster masses where this phenomenon is active, and the relation
between globular clusters and other satellites of our Galaxy.Comment: In press (The Astronomy and Astrophysics Review
The X-ray source population of the globular cluster M15: Chandra high resolution imaging
The globular cluster M15 was observed on three occasions with the High
Resolution Camera on board Chandra in 2001 in order to investigate the X-ray
source population in the cluster centre. After subtraction of the two bright
central sources, four faint sources were identified within 50 arcsec of the
core. One of these sources is probably the planetary nebula, K648, making this
the first positive detection of X-rays from a planetary nebula inside a
globular cluster. Another two are identified with UV variables (one previously
known), which we suggest are cataclysmic variables (CVs). The nature of the
fourth source is more difficult to ascertain, and we discuss whether it is
possibly a quiescent soft X-ray transient (qSXT) or also a CV.Comment: 9 pages, 6 figures, accepted for publication in MNRAS. Original
figures can be obtained from http://www.astro.helsinki.fi/~diana/M15.htm
The Compact Linear Collider (CLIC) - 2018 Summary Report
The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years