946 research outputs found
Range-only underwater target localization : error characterization
Locating a target from range measurements
using only one mobile transducer has been increased
over the last years. This method allows us to reduce the
high costs of deployment and maintenance of
traditional fixed systems on the seafloor such as Long
Baseline. The range-only single-beacon is one of the
new architectures developed using the new capabilities
of modern acoustic underwater modems, which can be
time synchronization, time stamp, and range
measurements.
This document presents a method to estimate the
sources of error in this type of architecture so as to
obtain a mathematical model which allows us to
develop simulations and study the best localization
algorithms. Different simulations and real field tests
have been carried out in order to verify a good
performance of the model proposed.Postprint (published version
Secondary flows in a laterally heated horizontal cylinder
In this paper we study the problem of thermal convection in a laterally heated, finite, horizontal cylinder. We consider cylinders of moderate aspect ratio (height/diameter approximate to 2) containing a small Prandtl number fluid (sigma < 0.026) typical of molten metals and molten semiconductors. We use the Navier-Stokes and energy equations in the Boussinesq approximation to calculate numerically the basic steady states, analyze their linear stability, and compute some nonlinear secondary flows originated from the instabilities. All the calculated flows and the stability analysis are characterized by their symmetry properties. Due to the confined cylindrical geometry, -presence of lateral walls and lids-, all the flows are completely three dimensional even for the basic steady states. In the range of Prandtl numbers studied, we have identified four different types of instabilities, either oscillatory or stationary. The physical mechanisms, shear or buoyancy, of the corresponding flow transitions have been analyzed. As the value of the Prandtl number approaches sigma = 0.026 the scenario of bifurcations becomes more complicated due to the existence of two different stable basic states originated in a saddle-node bifurcation; a fact that had been overlooked in previous works. (C) 2014 AIP Publishing LLC.Postprint (published version
Dynamics of domain walls intersecting black holes
Previous studies concerning the interaction of branes and black holes
suggested that a small black hole intersecting a brane may escape via a
mechanism of reconnection. Here we consider this problem by studying the
interaction of a small black hole and a domain wall composed of a scalar field
and simulate the evolution of this system when the black hole acquires an
initial recoil velocity. We test and confirm previous results, however, unlike
the cases previously studied, in the more general set-up considered here, we
are able to follow the evolution of the system also during the separation, and
completely illustrate how the escape of the black hole takes place.Comment: 4 pages, 6 figure
Possibilitats de desenvolupament de la formació professional en la negociació col·lectiva a Catalunya
La necessitat d'invertir en formació professional es justifica per dues raons. D'una banda, hi ha una àmplia bibliografia, teòrica i empírica, relativa a la importància de l'educació i la formació per impulsar el creixement econòmic i la millora de la carrera professional dels individus. D'altra banda, el nostre país té uns compromisos adquirits amb la Unió Europea, respecte a la formació permanent, que obliguen a fer polítiques que fomentin la formació de la població activa
Probability distributions of Linear Statistics in Chaotic Cavities and associated phase transitions
We establish large deviation formulas for linear statistics on the
transmission eigenvalues of a chaotic cavity, in the framework of
Random Matrix Theory. Given any linear statistics of interest , the probability distribution of generically
satisfies the large deviation formula
, where
is a rate function that we compute explicitly in many cases
(conductance, shot noise, moments) and corresponds to different
symmetry classes. Using these large deviation expressions, it is possible to
recover easily known results and to produce new formulas, such as a closed form
expression for (where
) for arbitrary integer . The universal limit
is also computed exactly. The
distributions display a central Gaussian region flanked on both sides by
non-Gaussian tails. At the junction of the two regimes, weakly non-analytical
points appear, a direct consequence of phase transitions in an associated
Coulomb gas problem. Numerical checks are also provided, which are in full
agreement with our asymptotic results in both real and Laplace space even for
moderately small . Part of the results have been announced in [P. Vivo, S.N.
Majumdar and O. Bohigas, {\it Phys. Rev. Lett.} {\bf 101}, 216809 (2008)].Comment: 31 pages, 16 figures. To appear in Phys. Rev. B. Added section IVD
about comparison with other theories and numerical simulation
What a Difference a Case Makes: Teaching Economic Evaluation of Public Policies to Non-Economists
The adaptation process to the European Higher Education Area (EHEA) provides an opportunity for incorporating new methodologies and making students play the main role in the learning process. In this context, a group of teachers from the University of Barcelona began in the 2012-13 academic year a new pedagogical experience, which consisted in the introduction of case-study methodology in the subject Economic Evaluation of Public Policies, taught at the Political and Administration Sciences undergraduate programme. The aims of the experience were the following: Firstly, making more attractive the subject to non-economists; secondly, developing skills such as collaborative work and critical analysis; finally, increasing academic performance. Results from the experience show enhanced levels of student satisfaction and motivation. Additionally, 2012 students outperform their 2011 colleagues
Hell to touch the sky? Private tutoring and academic achievement in Korea
Although not exclusive to the Republic of Korea’s educational system, the pervasiveness of private tutoring, and its consequences, serve to distinguish it from Systems operated in other countries. However, the identification of inefficiencies linked to this phenomenon have seen the educational authorities struggling against private tutoring since the 1980s. Yet, public policies have systematically failed because of the widely held belief that private tutoring services increase students’ academic performance. This paper quantifies the impact of time spent in private tutoring on the performance of students in the three competence fields assessed in the PISA-2006 (Programme for International Student Assessment). Instrumental variables are applied in a multilevel model framework in an attempt at addressing the endogeneity of the effects of private tutoring on acadèmic performance. Our results indicate that the impact of time dedicated to private tutoring on academic performance depends on the particular competence: positive for mathematics,positive but decreasing for reading, and non-significant for science
Yaws.
INTRODUCTION: Yaws, caused by Treponema pallidum ssp. pertenue, is endemic in parts of West Africa, Southeast Asia and the Pacific. The WHO has launched a campaign based on mass treatment with azithromycin, to eradicate yaws by 2020. SOURCES OF DATA: We reviewed published data, surveillance data and data presented at yaws eradication meetings. AREAS OF AGREEMENT: Azithromycin is now the preferred agent for treating yaws. Point-of-care tests have demonstrated their value in yaws. AREAS OF CONTROVERSY: There is limited data from 76 countries, which previously reported yaws. Different doses of azithromycin are used in community mass treatment for yaws and trachoma. GROWING POINTS: Yaws eradication appears an achievable goal. The programme will require considerable support from partners across health and development sectors. AREAS TIMELY FOR DEVELOPING RESEARCH: Studies to complete baseline mapping, integrate diagnostic tests into surveillance and assess the impact of community mass treatment with azithromycin are ongoing
Predator-driven natural selection on risk-taking behavior in anole lizards
Biologists have long debated the role of behavior in evolution, yet understanding of its role as a driver of adaptation is hampered by the scarcity of experimental studies of natural selection on behavior in nature. After showing that individual Anolis sagrei lizards vary consistently in risk-taking behaviors, we experimentally established populations on eight small islands either with or without Leiocephalus carinatus, a major ground predator. We found that selection predictably favors different risk-taking behaviors under different treatments: Exploratory behavior is favored in the absence of predators, whereas avoidance of the ground is favored in their presence. On predator islands, selection on behavior is stronger than selection on morphology, whereas the opposite holds on islands without predators. Our field experiment demonstrates that selection can shape behavioral traits, paving the way toward adaptation to varying environmental contexts
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