2,372 research outputs found
Fitting isochrones to open cluster photometric data III. Estimating metallicities from UBV photometry
The metallicity is a critical parameter that affects the correct
determination fundamental characteristics stellar cluster and has important
implications in Galactic and Stellar evolution research. Fewer than 10 % of the
2174 currently catalog open clusters have their metallicity determined in the
literature. In this work we present a method for estimating the metallicity of
open clusters via non-subjective isochrone fitting using the cross-entropy
global optimization algorithm applied to UBV photometric data. The free
parameters distance, reddening, age, and metallicity simultaneously determined
by the fitting method. The fitting procedure uses weights for the observational
data based on the estimation of membership likelihood for each star, which
considers the observational magnitude limit, the density profile of stars as a
function of radius from the center of the cluster, and the density of stars in
multi-dimensional magnitude space. We present results of [Fe/H] for nine
well-studied open clusters based on 15 distinct UBV data sets. The [Fe/H]
values obtained in the ten cases for which spectroscopic determinations were
available in the literature agree, indicating that our method provides a good
alternative to determining [Fe/H] by using an objective isochrone fitting. Our
results show that the typical precision is about 0.1 dex
On a family of topological invariants similar to homotopy groups
The intimacy relation between smooth loops, which is a strong homotopy relation, is generalized to smooth maps defined on the n-cube, leading to a family of groups similar to the classical homotopy groups. The formal resemblance between the two families of groups is explored. Special attention is devoted to the role of these groups as topological invariants for manifolds and as tools for describing geometrical structures defined on manifolds such as bundles and connections
Image transfer through a chaotic channel by intensity correlations
The three-wave mixing processes in a second-order nonlinear medium can be
used for imaging protocols, in which an object field is injected into the
nonlinear medium together with a reference field and an image field is
generated. When the reference field is chaotic, the image field is also chaotic
and does not carry any information about the object. We show that a clear image
of the object be extracted from the chaotic image field by measuring the
spatial intensity correlations between this field and one Fourier component of
the reference. We experimentally verify this imaging protocol in the case of
frequency downconversion.Comment: 17 pages, 7 figure
Large Graph Analysis in the GMine System
Current applications have produced graphs on the order of hundreds of
thousands of nodes and millions of edges. To take advantage of such graphs, one
must be able to find patterns, outliers and communities. These tasks are better
performed in an interactive environment, where human expertise can guide the
process. For large graphs, though, there are some challenges: the excessive
processing requirements are prohibitive, and drawing hundred-thousand nodes
results in cluttered images hard to comprehend. To cope with these problems, we
propose an innovative framework suited for any kind of tree-like graph visual
design. GMine integrates (a) a representation for graphs organized as
hierarchies of partitions - the concepts of SuperGraph and Graph-Tree; and (b)
a graph summarization methodology - CEPS. Our graph representation deals with
the problem of tracing the connection aspects of a graph hierarchy with sub
linear complexity, allowing one to grasp the neighborhood of a single node or
of a group of nodes in a single click. As a proof of concept, the visual
environment of GMine is instantiated as a system in which large graphs can be
investigated globally and locally
The Viana footbridge: construction and dynamic monitoring
A new moveable footbridge was recently built at the entrance of Marina Atlantico in the city of Viana do Castelo, Portugal. This paper presents a brief description of the global solution, with a special focus on the characterisation of the construction methods adopted. Particular consideration is given to the construction of the pivot pylon and the steel structure, showing how all the bridge components work together to ensure a safe working relationship with the marina, the river and users of the continuous bicycling and pedestrian pathway running across the closed bridge. The mechanical, hydraulic, electrical and navigational light systems play fundamental roles, especially during bridge opening and closing operations. Moreover, as this light footbridge is susceptible to vibrations due to human traffic, the paper also describes the dynamic tests performed during and after construction, including two ambient vibration tests, the measurement of cable-stay forces, and tests with groups of pedestrians used to evaluate induced vibration levels along with the monitoring of bridge accelerations over 4 months of use
Entrepreneurship as a career option: do temporary workers have the competencies, intention and willingness to become entrepreneurs?
This study analyses the entrepreneurial intentions and the willingness of temporary workers to consider entrepreneurship as a career option. Specifically, we analyse the self-perception of entrepreneurial competencies of a group of temporary workers. A total of 184 temporary workers participated in the study. We performed a multiple correspondence analysis (MCA) to identify profiles of entrepreneurial competencies according to temporary workers' entrepreneurial intention and willingness to consider entrepreneurship as a career option. We conclude that temporary workers do not always perceive themselves as having the necessary competencies to choose for entrepreneurship in their occupational paths. The self-perception of different levels of entrepreneurial competencies is also associated with different intentions and willingness to consider entrepreneurship as a career option. Finally, we provide insights for practice, which can be considered as a starting point for activities aiming to develop entrepreneurial competencies at the individual or organisational levels.info:eu-repo/semantics/submittedVersio
Continuous dynamic monitoring of bridges: different perspectives of application
This paper makes a brief characterisation of some aspects related with the extensive research activity of the Laboratory of Vibrations and Structural Monitoring (ViBest) of the Faculty of Engineering of the University of Porto (FEUP) in the field of Continuous Dynamic Monitoring of Bridges and Special Structures, selecting four examples where large high quality databases have been created since 2007, namely Infante D. Henrique bridge, Pedro e Ines footbride, FEUP Campus stress-ribbon footbridge and Trezoi railway bridge
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