1,444 research outputs found
A Robust Constrained Reference Governor Approach using Linear Matrix Inequalities
The purpose of this paper is to examine and provide a solution to the output reference tracking problem for uncertain systems subject to input saturation. As well-known, input saturation and modelling errors are very common problems at industry, where control schemes are implemented without accounting for such problems. In many cases, it is sometimes difficult to modify the existing implemented control schemes being necessary to provide them with external supervisory control approaches in order to tackle problems with constraints and modelling errors. In this way, a cascade structure is proposed, combining an inner loop containing any proper controller with an outer loop where a generalized predictive controller (GPC) provides adequate references for the inner loop considering input saturations and uncertainties. Therefore, the contribution of this paper consists in providing a state space representation for the inner loop and using linear matrix inequalities (LMI) to obtain a predictive state-vector feedback in such a way that the input reference for the inner loop is calculated to satisfy robust tracking specifications considering input saturations. Hence, the final proposed solution consists in solving a regulation problem to a fixed reference value subjected to a set of constraints described by several LMI and bilinear matrix inequalities (BMI). The main contribution of the paper is that the proposed solution is a non-linear setpoint tracking approach, that is, it is allowed that the system goes into saturation facing the problem of setpoint tracking instead of regulating to the origin. An illustrative numerical example is presented.Ministerio de Ciencia y Tecnología DPI2004-07444-C04-01/0
Unplugging the Universe: the neglected electromagnetic consequence of decoupling
This letter concentrates on the non-equilibrium evolution of magnetic field
structures at the onset of recombination, when the charged particle current
densities decay as neutrals are formed.
We consider the effect that a decaying magnetic flux has on the acceleration
of particles via the transient induced electric field. Since the residual
charged-particle number density is small as a result of decoupling, we shall
consider the magnetic and electric fields essentially to be imposed, neglecting
the feedback from any minority accelerated population.
We find that the electromagnetic treatment of this phase transition can
produce energetic electrons scattered throughout the Universe. Such particles
could have a significant effect on cosmic evolution in several ways: (i) their
presence could delay the effective end of the recombination era; (ii) they
could give rise to plasma concentrations that could enhance early gravitational
collapse of matter by opposing cosmic expansion to a greater degree than
neutral matter could; (iii) they could continue to be accelerated, and become
the seed for reionisation at the later epoch .Comment: 4 pages, no figure
A Rich Population of X-ray Emitting Wolf-Rayet Stars in the Galactic Starburst Cluster Westerlund 1
Recent optical and IR studies have revealed that the heavily-reddened
starburst cluster Westerlund 1 (Wd 1) contains at least 22 Wolf-Rayet (WR)
stars, comprising the richest WR population of any galactic cluster. We present
results of a senstive Chandra X-ray observation of Wd 1 which detected 12 of
the 22 known WR stars and the mysterious emission line star W9. The fraction of
detected WN stars is nearly identical to that of WC stars. The WN stars WR-A
and WR-B as well as W9 are exceptionally luminous in X-rays and have similar
hard heavily-absorbed spectra with strong Si XIII and S XV emission lines. The
luminous high-temperature X-ray emission of these three stars is characteristic
of colliding wind binary systems but their binary status remains to be
determined. Spectral fits of the X-ray bright sources WR-A and W9 with
isothermal plane-parallel shock models require high absorption column densities
log N = 22.56 (cm) and yield characteristic shock temperatures
kT_shock ~ 3 keV (T ~ 35 MK).Comment: ApJL, 2006, in press (3 figures, 1 table
Analysis of decomposition parameters of green manure in the Brazilian Northeast with Association Rules Networks.
Modern agricultural processes are increasingly looking at the use of chemicals, so the constant search for organic alternatives to fertilization becomes frequent. The use of data mining using association rule networks (ARN) can aid in the analysis of the parameters involved in choosing which plant to use as green manure. In this work, an analysis of the parameters of green manures used in the Brazilian Northeast is presented, demonstrating the applicability of the computational technique as well as its use to gain in productivity
Precision Determination of the Mass Function of Dark Matter Halos
The predicted mass function of dark matter halos is essential in connecting
observed galaxy cluster counts and models of galaxy clustering to the
properties of the primordial density field. We determine the mass function in
the concordance CDM cosmology, as well as its uncertainty, using
sixteen -particle nested-volume dark-matter simulations, spanning a
mass range of over five orders of magnitude. Using the nested volumes and
single-halo tests, we find and correct for a systematic error in the
friends-of-friends halo-finding algorithm. We find a fitting form and full
error covariance for the mass function that successfully describes the
simulations' mass function and is well-behaved outside the simulations'
resolutions. Estimated forecasts of uncertainty in cosmological parameters from
future cluster count surveys have negligible contribution from remaining
statistical uncertainties in the central cosmology multiplicity function. There
exists a potentially non-negligible cosmological dependence (non-universality)
of the halo multiplicity function.Comment: 4 pages, 3 figures, submitted to ApJ
Problem-based learning and applied mathematics
Problem-based learning (PBL) is a teaching method that appeared in the early 1960s and is widely applied in distinct areas nowadays. In the presented manuscript, we describe a PBL methodology use restricted to applied mathematics for problem solving among a group of engineering students in a Portuguese university. In the pandemic context, it was a huge challenge both for the students and for the teacher. Supported by the available literature, the experiment was defined. As it is well known, teachers are not only knowledge transmitters but also designers of teaching initiatives. Thus, teachers and students both have a large role in PBL methodologies, where collaboration, reflection and concepts discussion are essential. In the presented pedagogical challenge, students were devoted to integrating the previous knowledge acquired and the one acquired during the project. This process improved their new competences—both personal and team work. Despite being a recent pedagogical method, PBL is revealed to be an important teaching tool.info:eu-repo/semantics/publishedVersio
A Study of the Export Financing System in the Philippines
How much support is the Philippine government giving to its export sector by means of its financing schemes? Are the small and indirect exporters given preference or assistance? How supportive is the entire export financing system in the country to the attainment of an export-driven development strategy? These questions are the primary concern of this paper. Based on a survey sample of seven commercial banks, it examines the various components of the Philippine export financing system. A review of the Philippine trade policies and its export profiles is provided.financial market, financial economy, financial sector, export commodities, financial services
Confecção de compostos orgânicos em Parnaíba, PI.
O emprego de fertilizantes orgânicos como base central de sistemas orgânicos de produção é uma tecnologia adotada no mundo inteiro e cresce exponencialmente no Brasil, principalmente nas regiões produtoras de hortaliças.bitstream/item/149638/1/Comunicado-238.pd
Banco de sementes.
Adubos verdes; Banco de sementes; Produção de sementes para o "Banco"; Conservação/independência; Benefícios; Resultados; Técnico Responsável: Mauro Sergio Teodoro
Adubação verde nos Tabuleiros Litorâneos do Piauí.
A adubação verde é uma prática agrícola muito antiga, utilizada há mais de 2000 anos, cujos primeiros usos foram registrados na China, Grécia e Itália, sobretudo para o aumento da produção das lavouras. No Brasil, é conhecida há quase um século, com resultados agrícolas e retorno econômico bastante positivos, sendo adotada nos mais distintos sistemas de produção.bitstream/item/185336/1/Doc-242-Adubacao-verde.pd
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