Aging functions and multivariate notions of NBU and IFR

For d≥2, let X=(X1, …, Xd) be a vector of exchangeable continuous lifetimes with joint survival function $\overline{F}$. For such models, we study some properties of multivariate aging of $\overline{F}$ that are described by means of the multivariate aging function $B_{\overline{F}}$, which is a useful tool for describing the level curves of $\overline{F}$. Specifically, the attention is devoted to notions that generalize the univariate concepts of New Better than Used and Increasing Failure Rate. These multivariate notions are satisfied by random vectors whose components are conditionally independent and identically distributed having univariate conditional survival function that is New Better than Used (respectively, Increasing Failure Rate). Furthermore, they also have an interpretation in terms of comparisons among conditional survival functions of residual lifetimes, given a same history of observed survivals

Optimization of industrial processes for forging of carbon and stainless steels

The possibility to produce stainless steel components at limited cost and characterized by elevated mechanical properties, has gained more importance in the last years. Nowadays, the cold and warm forging processes of carbon steels are widely used to form industrial parts due to their economic advantages, but there is still lack of extensive research on industrial process design and evaluation of the microstructural properties of cold-warm forged stainless steel parts. In the last few decades, the environment concerning the recent forging industry has been rapidly changed. Now, near-net-shape or net-shape manufacturing processes are becoming a useful practice in metal forming, resulting in saving material and energy. Many parts produced with machining can be manufactured at lower cost by cold and warm forging. Traditionally, forging design is carried out using mainly empirical guidelines, experience, and trial-and-error, which results in a long process development time and high production costs. In order to avoid this, in recent years, computer-aided simulation approaches have proved to be powerful tools to predict and analyze material deformation during a metal forming operation. There are now many commercial finite-element (FE) packages to simulate forging and bulk metalworking processes. To date, most have focussed on predicting the shape of the final product after simple or complex single- or multi-stage forming operations. On the other hand, other aspects are being included in these numerical models, such as an improved understanding of the constitutive material behaviour, friction and lubrication conditions, and the properties of the final product, in order to predict more complicated phenomena such as tool life prediction, ductile fracture and microstructure evaluation. The focus of this PhD thesis is the development of an innovative approach based on the design of integrated experimental procedures and modelling tools, in order to accurately re-design a range of industrial single-stage cold-warm forming processes to form stainless steel components and investigate the microstructural evolution of forged parts obtained at different forging temperatures. In addition, the design of a multi-stage cold forging process of a low-carbon steel and the prediction of surface defects that occur in each stage of the forming-sequence have been carried out. To this aim, a series of tensile tests were conducted to evaluate the influence of temperature and strain rate on the materials elasto-plastic properties. Futhermore, an innovative experimental setup was used to reproduce the realistic friction conditions at the tool-workpiece interface, in order to accurately predict metal flow during forging cycles. Experimental data were subsequently validated and implemented in a commercial 3D-FE software and accurately calibrated to perform fully coupled numerical simulations for the reference processes. Finally, the forged parts obtained were characterized by macro- and microstructural inspections in order to evaluate the presence of underfilling problems and surface defects, which were consistent with the numerical FE results coming from both simulated processes (i.e. single- and multi-stage forging), and to analyze the microstructural evolution of α- and γ-phase during single-stage tests both at room temperature and from 400 to 700 °C. The materials investigated in this work are low-carbon AISI 1005 ferritic-pearlitic steel (Wr. N. 1.0303), AISI 304L austenitic (Wr. N. 1.4307) and commercially named Duplex 2205 ferritic-austenitic stainless steel (Wr. N. 1.4462). The developed experimental tests are suitable to proper evaluation of steels behaviour in terms of mechanical properties, and to precisely calibrate coupled numerical models when they are applied to conventional and re-design forging processes. The techniques used in this work include: tensile tests, T-shape compression tests, visual inspections (i.e. supported by vernier calliper and micrometer measurements), hardness and micro-hardness tests, LOM (Light Optical Microscopy), FEG-ESEM (Field-Emission Gun Environmental Scanning Electron Microscope), EDS (Energy Dispersive X-ray Spectroscopy), EBSD (Electron Back Scattering Diffraction) and numerical models carried out with FORGE2011®-3D

Aspectos críticos do direito das telecomunicações da Comissão Europeia: a próxima reforma

Palestra Seminário Internacional de Regulação de Serviços Públicos: Direito Comparado da Energia Elétrica e das Telecomunicações Realizado em 26 a 28 de junho de 2007 Local: Faculdade de Direito da Universidade de Brasília, Brasília/DF Realização: UnB-RomaTre-Unisc Palestra ministrada em 26 de junho de 200

Distributed Temperature Sensing System Using A Commercial Otdr And A Standard Edfa With Controlled Gain

The distributed temperature sensor system based in the spontaneous Raman backscattering is demonstrated for the first time to our knowledge, using a commercial OTDR (Optical Time Domain Reflectometer) and a standard erbium doped fiber amplifier (EDFA) with controlled gain. We evaluated this approach in a 30 km of single mode fiber using an OTDR pulse width of 100 ns and an EDFA with 17 dBm of output power.9852Conference on Fiber Optic Sensors and Applications XIIIAPR 18-21, 2016Baltimore, M

Threshold copulas and positive dependence

Starting with a notion of positive dependence View the MathML source and with the family of the lower threshold copulas Ct associated with a bivariate distribution having copula C, we define different notions of positive dependence for C, reflecting the dependence properties of the copulas Ct for some t. Then, we analyze some structural aspects of lower threshold copulas and of the given definitions. Furthermore we consider several specific cases arising from relevant special choices of View the MathML source (e.g., PQD, LTD, TP2 and PLR). Our analysis, in particular, allows us to present a number of relevant examples and counter-examples, which can be useful in the study of the tail dependence for a bivariate distribution

Liquid actuated gravity experiments

We describe a new actuation technique for gravity experiments based on a liquid field mass. The Characterizing idea is to modulate the gravity force acting on a test mass by controlling the level of a liquid in a suitable container. This allows to obtain a periodical gravity force without moving parts (except the liquid level) close to the TM. We describe in detail the most relevant aspects of the liquid actuator and discuss how it can be used in gravity experiments. In particular we analyse an application to test the inverse square law in the mm to cm distance region

A quasi-complete mechanical model for a double torsion pendulum

We present a dynamical model for the double torsion pendulum nicknamed PETER, where one torsion pendulum hangs in cascade, but off-axis, from the other. The dynamics of interest in these devices lies around the torsional resonance, that is at very low frequencies (mHz). However, we find that, in order to properly describe the forced motion of the pendulums, also other modes must be considered, namely swinging and bouncing oscillations of the two suspended masses, that resonate at higher frequencies (Hz). Although the system has obviously 6+6 Degrees of Freedom, we find that 8 are sufficient for an accurate description of the observed motion. This model produces reliable estimates of the response to generic external disturbances and actuating forces or torques. In particular, we compute the effect of seismic floor motion (tilt noise) on the low frequency part of the signal spectra and show that it properly accounts for most of the measured low frequency noise.Comment: 15 pages, 6 figure

Atributos morfológicos configuracionais e copresença em loteamentos residenciais dispersos de cidades médias brasileiras

O objetivo do trabalho é identificar quais os atributos morfológicos configuracionais de maior correlação com a copresença no contexto sócio-espacial de dois loteamentos residenciais dispersos em Santa Maria (RS), Brasil. Por copresença, entende-se o conjunto de pessoas que estão juntas em determinado espaço. A metodologia é composta por: i) modelagem sintática axial e segmentada da área de estudo com diferentes raios; (ii) coleta da variável copresença categorizada em ‘pedestres em movimento’ e ‘pedestres estacionários’; e iii) cálculo dos coeficientes de correlação de Pearson entre copresença e variáveis sintáticas. Parte-se do seguinte questionamento: como a forma urbana explica a apropriação social dos espaços livres nos loteamentos dispersos? Os resultados mostraram que, embora os dois loteamentos tenham padrões diferenciados de copresença, as variáveis ‘integração’ e ‘escolha’ têm as correlações positivas mais fortes com o número de pedestres. Os tipos de modelagem e de raio influenciaram na força das correlações: a análise angular segmentada com raio métrico mostrou-se mais eficiente para o maior número de categorias de copresença quando estas não são compostas essencialmente por movimento natural. Em geral, raios maiores aplicados às medidas locais geraram as correlações mais fortes: R1000m para a análise angular, e R5 para a análise axial.This paper aims at identifying which configurational morphological attributes have stronger correlation with co-presence in the socio-spatial context of two dispersed residential allotments in Santa Maria (RS), Brazil. Co-presence is the group of people who are together in a given space. The methodology consists of: i) axial and segment analysis of the study area with different radii; ii) measurement of co-presence levels categorized as ‘moving pedestrians’ and ‘stationary pedestrians; and iii) calculation of the Pearson correlation coefficients between co-presence and syntactic measures. It is based on the following question: how does the urban form explain the social appropriation of open spaces in dispersed settlements? The results showed that, although the two neighborhoods have different co-presence patterns, the measures of ‘integration’ and ‘choice’ have the strongest positive correlations with the number of pedestrians. The types of analysis and radius influenced the strength of the correlations: segment angular analysis with metric radius was more efficient for the largest number of categories of co-presence when these were not composed essentially by natural movement. In general, larger radii applied to local measurements generated the strongest correlations: R1000m for angular analysis, and R5 for axial analysis

Measurement of gravitational and thermal effects in a liquid-actuated torsion pendulum

We describe a proof-of-principle experiment aiming to investigate the inverse-square law of gravitation at the centimeter scale. The sensor is a two-stage torsion pendulum, while actuation is accomplished by a variable liquid mass. The time-varying gravitational force is related to the level of the circulating fluid in one or two containers at a short distance from the test mass, with all moving mechanical parts positioned at a large distance. We provide a description of the apparatus and present the first results. We identified a systematic effect of thermal origin, producing offsets of few fNm in torque and of about 10 pN in force. When this effect is neutralized, the measurements agree well with the predictions of simulations. We also discuss the upcoming instrument upgradations and the expected sensitivity improvement that will allow us to perform measurements with adequate accuracy to investigate the unexplored regions of the α−λ parameter space of a Yukawa-like deviation from the Newtonian potential