ESTG - Comunicações em conferências e congressos internacionais
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Browsing ESTG - Comunicações em conferências e congressos internacionais by Field of Science and Technology (FOS) "Ciências Naturais::Ciências Físicas"
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- Alternative heavy tailed models in seismologyPublication . Felgueiras, Miguel; Martins, João; Santos, RuiGreat earthquakes are commonly considered as the ones with moment magnitude (Mw ) above or equal to 8.0. Since these earthquakes can destroy entire communities located near the epicentre, the search of physical laws that explain the energy released by them is an important issue. There is a connection between the radiated energy of an earthquake, its magnitude and its seismic moment (M 0). Thence, when fitting a heavy or an extremely heavy tailed distribution to a seismic moment dataset, we are in fact adjusting a mathematical model which explains the amount of energy released by these great seisms. Therefore, the main goal of this work is to study the more appropriated Pareto based models (the most used family in this field) when explaining the seismic moment of the great earthquakes. With this purpose in mind, we selected two different catalogs that accommodate recent events and are considered more accurate than other catalogs used in previous works. We conclude that the traditional Pareto distribution remains a good choice to deal with this kind of data, but Log-Pareto lead to higher p-values and Location-scale Pareto is better fitted to the biggest events.
- DMLS technology for automotive toolingPublication . Leal, R.; Barreiros, Fatima; Alves, M.L.; Romeiro, F.; Vasco, J.; Santos, M.; Marto, C.The automotive industry is challenged every day, with companies competing and developing new models and facelifts in short term, requiring new tools or tool reshaping. Concerning the current world economic scenario, decreasing time-for-tooling becomes as important as decreasing time-to-market. Such scenario opens up the horizons for new manufacturing approaches like additive manufacturing. In this case-study, additive manufacturing is applied for tooling up a stamping process for the production of body panels for the automotive industry. This approach enables the manufacturing of stamping tool inserts with similar high performance alloy steel as in conventional tooling, although, without any loss of tool properties and saving a significant part of the tool manufacturing time. The evaluation of the tool performance and tool life estimation was carried out based on three point bending fatigue tests using specimens manufactured by the same additive process and using the same powder material. From these data, it was possible to establish realistic scenarios for the use of additive tooling and to evaluate its feasibility on the automotive industry.
- Estimation of prevalence in rare disease using pooled samplesPublication . Martins, J. P.; Santos, R.; Felgueiras, M.The use of pooled samples for screening infected individuals is a known procedure to reduce costs. In an estimation problem, the aim is only to determine how many individuals are infected instead of determining who is infected (classification problem). In that setting, our goal was to compare the performance of using one or two-dimensional arrays. The best performance was established according to one of the following criteria: minimizing the number of individuals or the number of tests required to attain a certain estimate accuracy. It is observed that when we want to minimize the number of individuals used, the two-dimensional procedures have a little advantage over the one-dimensional procedures. However, when the major concern is the cost, the one-dimensional procedures clearly outperform the two-dimensional procedures.
- The Higher Moments Dynamic on SIS ModelPublication . Pinto, Alberto; Gouveia Martins, José Maria; Stollenwerk, NicoThe basic contact process or the SIS model is a well known epidemic process and have been studied for a wide class of people. In an epidemiological context, many authors worked on the SIS model considering only the dynamic of the first moments of infecteds, i.e., the mean value and the variance of the infected individuals. In this work, we study not only the dynamic of the first moments of infecteds but also on the dynamic of the higher moments. Recursively, we consider the dynamic equations for all the moments of infecteds and, applying the moment closure approximation, we obtain the stationary states of the state variables. We observe that the stationary states of the SIS model, in the moment closure approximation, can be used to obtain good approximations of the quasi-stationary states of the SIS model.
- The impact of long-term memory effects on diode power probesPublication . Gomes, Hugo; Testera, Alejandro R.; Carvalho, Nuno Borges; Barciela, Mónica F.; Remley, Kate A.This paper presents an analysis of long term-memory effects on power measurements with diode power probes. We show that a power probe calibrated with a single-tone sinusoidal excitation can provide erroneous values when used with modulated signals. This fact is ascribed to the low-frequency response imposed by the power probe baseband circuit. This hypothesis is first theoretically demonstrated by use of a Volterra series, and then validated by simulations and measurements using a diode power probe.
- On the formability, geometrical accuracy, and surface quality of sheet metal parts produced by SPIFPublication . Alves, Maria; Silva, M. B.; Alves, L. M.; Martins, P. A. F.; Xiaoyuan He; Huimin Xie; YiLan KangConventional sheet metal forming processes are not suitable for flexible small-batch production and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles, development and production lead times. In fact, the present need for flexible sheet metal forming techniques requires the development of innovative technological solutions that are capable of reducing the fixed and capital costs of sheet metal forming to a level where small-batch production becomes economically feasible. Single point incremental forming (SPIF) is a new sheet metal forming process with a high potential economic payoff for rapid prototyping applications and for small quantity production. In general terms a typical SPIF set-up makes use of a small number of low cost active tools components; (i) a blankholder, (ii) a backing plate and (iii) a single point forming tool. The tool path is generated in a CNC machining center and during the process there is no backup die supporting the back surface of the sheet. Despite the contributions of many researchers on the development of industrial applications and better characterization of the forming limits of the process, several key topics related to the mechanics of deformation, likely mode of failure, geometric accuracy and surface quality of the formed parts remain little understood and scarcely systematized. This paper attempts to provide new contributions about the abovementioned issues by means of a comprehensive experimental investigation performed under laboratory controlled conditions.
- Phase Diagram and Critical Properties within an Effective Model of QCD: The Nambu–Jona-Lasinio Model Coupled to the Polyakov LoopPublication . Costa, Pedro; Ruivo, Maria C.; Sousa, Célia A. de; Hansen, HubertWe investigate the phase diagram of the so-called Polyakov-Nambu-Jona-Lasinio model at finite temperature and non-zero chemical potential with three quark flavors. Chiral and deconfinement phase transitions are discussed and the relevant order-like parameters are analyzed. The results are compared with simple thermodynamic expectations and lattice data. We present the phase diagram in the (T, μB) plane, paying special attention to the critical end point: as the strength of the flavor-mixing interaction becomes weaker, the critical end point moves to low temperatures and can even disappear.