6,301 research outputs found
Transonic small disturbances equation applied to the solution of two-dimensional nonsteady flows
Transonic nonsteady flows are of large practical interest. Aeroelastic instability prediction, control figured vehicle techniques or rotary wings in forward flight are some examples justifying the effort undertaken to improve knowledge of these problems is described. The numerical solution of these problems under the potential flow hypothesis is described. The use of an alternating direction implicit scheme allows the efficient resolution of the two dimensional transonic small perturbations equation
Computing NodeTrix Representations of Clustered Graphs
NodeTrix representations are a popular way to visualize clustered graphs;
they represent clusters as adjacency matrices and inter-cluster edges as curves
connecting the matrix boundaries. We study the complexity of constructing
NodeTrix representations focusing on planarity testing problems, and we show
several NP-completeness results and some polynomial-time algorithms. Building
on such algorithms we develop a JavaScript library for NodeTrix representations
aimed at reducing the crossings between edges incident to the same matrix.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Pole Dancing: 3D Morphs for Tree Drawings
We study the question whether a crossing-free 3D morph between two
straight-line drawings of an -vertex tree can be constructed consisting of a
small number of linear morphing steps. We look both at the case in which the
two given drawings are two-dimensional and at the one in which they are
three-dimensional. In the former setting we prove that a crossing-free 3D morph
always exists with steps, while for the latter steps
are always sufficient and sometimes necessary.Comment: Appears in the Proceedings of the 26th International Symposium on
Graph Drawing and Network Visualization (GD 2018
Which diagnostic tests are most useful in a chest pain unit protocol?
Background
The chest pain unit (CPU) provides rapid diagnostic assessment for patients with acute, undifferentiated chest pain, using a combination of electrocardiographic (ECG) recording, biochemical markers and provocative cardiac testing. We aimed to identify which elements of a CPU protocol were most diagnostically and prognostically useful.
Methods
The Northern General Hospital CPU uses 2–6 hours of serial ECG / ST segment monitoring, CK-MB(mass) on arrival and at least two hours later, troponin T at least six hours after worst pain and exercise treadmill testing. Data were prospectively collected over an eighteen-month period from patients managed on the CPU. Patients discharged after CPU assessment were invited to attend a follow-up appointment 72 hours later for ECG and troponin T measurement. Hospital records of all patients were reviewed to identify adverse cardiac events over the subsequent six months. Diagnostic accuracy of each test was estimated by calculating sensitivity and specificity for: 1) acute coronary syndrome (ACS) with clinical myocardial infarction and 2) ACS with myocyte necrosis. Prognostic value was estimated by calculating the relative risk of an adverse cardiac event following a positive result.
Results
Of the 706 patients, 30 (4.2%) were diagnosed as ACS with myocardial infarction, 30 (4.2%) as ACS with myocyte necrosis, and 32 (4.5%) suffered an adverse cardiac event. Sensitivities for ACS with myocardial infarction and myocyte necrosis respectively were: serial ECG / ST segment monitoring 33% and 23%; CK-MB(mass) 96% and 63%; troponin T (using 0.03 ng/ml threshold) 96% and 90%. The only test that added useful prognostic information was exercise treadmill testing (relative risk 6 for cardiac death, non-fatal myocardial infarction or arrhythmia over six months).
Conclusion
Serial ECG / ST monitoring, as used in our protocol, adds little diagnostic or prognostic value in patients with a normal or non-diagnostic initial ECG. CK-MB(mass) can rule out ACS with clinical myocardial infarction but not myocyte necrosis(defined as a troponin elevation without myocardial infarction). Using a low threshold for positivity for troponin T improves sensitivity of this test for myocardial infarction and myocardial necrosis. Exercise treadmill testing predicts subsequent adverse cardiac events
Hierarchical Partial Planarity
In this paper we consider graphs whose edges are associated with a degree of
{\em importance}, which may depend on the type of connections they represent or
on how recently they appeared in the scene, in a streaming setting. The goal is
to construct layouts of these graphs in which the readability of an edge is
proportional to its importance, that is, more important edges have fewer
crossings. We formalize this problem and study the case in which there exist
three different degrees of importance. We give a polynomial-time testing
algorithm when the graph induced by the two most important sets of edges is
biconnected. We also discuss interesting relationships with other
constrained-planarity problems.Comment: Conference version appeared in WG201
Wide-Field Hubble Space Telescope Observations of the Globular Cluster System in NGC1399
We present a comprehensive high spatial-resolution imaging study of globular
clusters (GCs) in NGC1399, the central giant elliptical cD galaxy in the Fornax
galaxy cluster, conducted with HST/ACS. Using a novel technique to construct
drizzled PSF libraries for HST/ACS data, we accurately determine the fidelity
of GC structural parameter measurements from detailed artificial star cluster
experiments. The measurement of rh for the major fraction of the NGC1399 GC
system reveals a trend of increasing rh versus galactocentric distance, Rgal,
out to about 10 kpc and a flat relation beyond. This trend is very similar for
blue and red GCs which are found to have a mean size ratio of
rh(red)/rh(blue)=0.82+/-0.11 at all galactocentric radii from the core regions
of the galaxy out to ~40 kpc. This suggests that the size difference between
blue and red GCs is due to internal mechanisms related to the evolution of
their constituent stellar populations. Modeling the mass density profile of
NGC1399 shows that additional external dynamical mechanisms are required to
limit the GC size in the galaxy halo regions to rh~2 pc. We suggest that this
may be realized by an exotic GC orbit distribution function, an extended dark
matter halo, and/or tidal stress induced by the increased stochasticity in the
dwarf halo substructure at larger Rgal. We match our GC rh measurements with
radial velocity data from the literature and find that compact GCs show a
significantly smaller line-of-sight velocity dispersion, =225+/-25
km/s, than their extended counterparts, =317+/-21 km/s. Considering
the weaker statistical correlation in the GC rh-color and the GC rh-Rgal
relations, the more significant GC size-dynamics relation appears to be
astrophysically more relevant and hints at the dominant influence of the GC
orbit distribution function on the evolution of GC structural parameters.Comment: 22 pages, 17 figures, accepted for publication in The Astrophysical
Journal, a high-quality PDF version is available at
http://www.astro.puc.cl/~tpuzia/PUC/Home.htm
High Frequency dynamics in metallic glasses
Using Inelastic X-ray Scattering we studied the collective dynamics of the
glassy alloy NiZr in the first pseudo Brillouin zone, an
energy-momentum region still unexplored in metallic glasses. We determine key
properties such as the momentum transfer dependence of the sound velocity and
of the acoustic damping, discussing the results in the general context of
recently proposed pictures for acoustic dynamics in glasses. Specifically, we
demonstrate the existence in this strong glass of well defined (in the Ioffe
Regel sense) acoustic-like excitations well above the Boson Peak energy.Comment: 4 pages, 4 .eps figures, accepted in Phys. Rev. Let
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