Economic design of two-stage (X)over-bar charts: the Markov chain approach

When the (X) over bar chart is in use, samples are regularly taken from the process, and their means are plotted on the chart. In some cases, it is too expensive to obtain the X values, but not the values of a correlated variable Y. This paper presents a model for the economic design of a two-stage control chart, that is. a control chart based on both performance (X) and surrogate (Y) variables. The process is monitored by the surrogate variable until it signals an out-of-control behavior, and then a switch is made to the (X) over bar chart. The (X) over bar chart is built with central, warning. and action regions. If an X sample mean falls in the central region, the process surveillance returns to the (Y) over bar chart. Otherwise. The process remains under the (X) over bar chart's surveillance until an (X) over bar sample mean falls outside the control limits. The search for an assignable cause is undertaken when the performance variable signals an out-of-control behavior. In this way, the two variables, are used in an alternating fashion. The assumption of an exponential distribution to describe the length of time the process remains in control allows the application of the Markov chain approach for developing the cost function. A study is performed to examine the economic advantages of using performance and surrogate variables. (C) 2003 Elsevier B.V. All rights reserved.

Lesões apendiculares em equinos Puro Sangue Ingleses no Jóquei Clube Brasileiro(Gávea/RJ): descrição e prevalência

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Exports and Firm Productivity: The effect of US steel safeguards. Bruges European Economic Research (BEER) Papers 19/January 2011

This paper investigates possible negative effects of the 2002 US steel safeguards on productivity of Eurozone steel companies. The analysis is based on an extensive literature which predicts that exporting firms not only are bigger and more productive, but also that exporting itself has positive effects, improving efficiency and leading to better utilization of firm resources. The paper investigates a large sample of EU-13 steel producing firms, in the 1998 - 2005 period. Using three methods of Total Factor Productivity (TFP) estimation among which the Olley-Pakes semiparametric estimator, we first calculate the productivity levels of companies, and then check for any unusual fluctuation in this performance variable. We find that in 2002 there has been a significant drop in TFP. The paper is an invitation for further research in this field, given the possible important effects of safeguard measures on exporters.

Does role clarity explain employee-perceived service quality? A study of antecedents and consequences in call centres

Purpose – Role clarity of frontline staff is critical to their perceptions of service quality in call centres. The purpose of this study is to examine the effects of role clarity and its antecedents and consequences on employee-perceived service quality. Design/methodology/approach – A conceptual model, based on the job characteristics model and cognitive theories, is proposed. Key antecedents of role clarity considered here are feedback, autonomy, participation, supervisory consideration, and team support; while key consequences are organizational commitment, job satisfaction and service quality. An internal marketing approach is adopted and all variables are measured from the frontline employee's perspective. A structural equation model is developed and tested on a sample of 342 call centre representatives of a major commercial bank in the UK. Findings – The research reveals that role clarity plays a critical role in explaining employee perceptions of service quality. Further, the research findings indicate that feedback, participation and team support significantly influence role clarity, which in turn influences job satisfaction and organizational commitment. Research limitations/implications – The research suggests that boundary personnel in service firms should strive for more clarity in perceived role for delivering better service quality. The limitations are in sample availability from in-house transaction call centres of a single bank. Originality/value – The contributions of this study are untangling the confusing research evidence on the effect of role clarity on service quality, using service quality as a performance variable as opposed to productivity estimates, adopting an internal marketing approach to understanding the phenomenon, and introducing teamwork along with job-design and supervisory factors as antecedent to role clarity.

Abordagem rítmica probabilística aplicada em análises de fluxo e estabilidade de taludes

Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Programa de Pós-Graduação em Geotecnia, 2015.

Asociación de anemia ferropenica y rendimiento escolar en niños de 2º A 7º año de Educación Básica Escuela 12 DE OCTUBRE TAMBO. 2015

Anemia ferropénica, enfermedad común en niños afecta su desarrollo psicomotriz y cognitivo, se ha asociado a una disminución en su rendimiento escolar. OBJETIVO GENERAL Determinar la asociación entre la anemia ferropénica y rendimiento escolar en niños de 2º a 7º año de educación básica de la escuela “12 de Octubre” del cantón el Tambo, 2015. DISEÑO METODOLÓGICO Estudio tipo analítico transversal, a una población de 92 escolares de 2º a 7º año de educación básica, matriculados en el año lectivo 2015 – 2016. Previo a su inclusión representantes de los escolares firmaron consentimiento informado, luego llenaron un formulario que determinó variables como edad, sexo, año escolar, lugar de residencia. Un análisis sanguíneo permitió establecer la presencia de la variable anemia ferropénica; y la variable rendimiento escolar fue tomada de los libros de registro de calificaciones. Recolectada la información se ingresó al ordenador para un análisis ulterior en los programas Microsoft Office Excel 2010 y SPSS V22. RESULTADOS De los 92 escolares investigados, el 53,3% fueron mujeres y el 46.7% hombres. El promedio de edad fue de 9,38 (DS 2,10). El mayor número según grupo de edad fue entre 10 y 11 años con el 43,48%. Se presentó anemia por deficiencia de hierro en 25% de los escolares, la relación con el rendimiento escolar fue no significativa (RP 0,6 IC 95 0,14-2,51, valor de p=0,51)

Variable effects of larval size on post-metamorphic performance in the field

Larval quality may be capable of explaining much of the variation in the recruitment and subsequent population dynamics of benthic marine invertebrates. Whilst the effects of larval nutritional condition on adult performance have received the most attention, recent work has shown that larval size may also be an important and ubiquitous source of variation in larval quality. We examined the effects of variation in larval size on the post-metamorphic survival and growth of Watersipora subtorquata in 2 very different habitats - experimental substrata and pier pilings. We found strong effects of larval size on colony performance, although these varied among experiments. For colonies on experimental substrata, larval size positively affected adult survival and, initially, growth. However, after 3 wk in the field, there was no relationship between larval size and colony size, possibly because colonies were completely surrounded by newly settled organisms. Larval size also positively affected post-metamorphic growth of colonies on pier pilings, but, surprisingly, colonies that came from larger larvae had lower survival than colonies from smaller larvae. Overall, variation in larval size will strongly affect the recruitment and subsequent performance of adults in this species, although this may vary among different habitats. This study highlights the importance of examining the effects of larval quality on adult performance in as realistic conditions as possible, because of the strong interaction between larval size effects and the environment.

Comparative study of power converter topologies and control strategies for the harmonic performance of variable-speed wind turbine generator systems

Power converters play a vital role in the integration of wind power into the electrical grid. Variable-speed wind turbine generator systems have a considerable interest of application for grid connection at constant frequency. In this paper, comprehensive simulation studies are carried out with three power converter topologies: matrix, two-level and multilevel. A fractional-order control strategy is studied for the variable-speed operation of wind turbine generator systems. The studies are in order to compare power converter topologies and control strategies. The studies reveal that the multilevel converter and the proposed fractional-order control strategy enable an improvement in the power quality, in comparison with the other power converters using a classical integer-order control strategy. (C) 2010 Elsevier Ltd. All rights reserved.

A comparative performance study of four-pole induction motors and synchronous reluctance motors in variable speed drives

Design aspects of the Transversally Laminated Anisotropic (TLA) Synchronous Reluctance Motor (SynRM) are studied and the machine performance analysis compared to the Induction Motor (IM) is done. The SynRM rotor structure is designed and manufactured for a30 kW, four-pole, three-phase squirrel cage induction motor stator. Both the IMand SynRM were supplied by a sensorless Direct Torque Controlled (DTC) variablespeed drive. Attention is also paid to the estimation of the power range where the SynRM may compete successfully with a same size induction motor. A technicalloss reduction comparison between the IM and SynRM in variable speed drives is done. The Finite Element Method (FEM) is used to analyse the number, location and width of flux barriers used in a multiple segment rotor. It is sought for a high saliency ratio and a high torque of the motor. It is given a comparison between different FEM calculations to analyse SynRM performance. The possibility to take into account the effect of iron losses with FEM is studied. Comparison between the calculated and measured values shows that the design methods are reliable. A new application of the IEEE 112 measurement method is developed and used especially for determination of stray load losses in laboratory measurements. The study shows that, with some special measures, the efficiency of the TLA SynRM is equivalent to that of a high efficiency IM. The power factor of the SynRM at rated load is smaller than that of the IM. However, at lower partial load this difference decreases and this, probably, brings that the SynRM gets a better power factor in comparison with the IM. The big rotor inductance ratio of the SynRM allows a good estimating of the rotor position. This appears to be very advantageous for the designing of the rotor position sensor-less motor drive. In using the FEM designed multi-layer transversally laminated rotor with damper windings it is possible to design a directly network driven motor without degrading the motorefficiency or power factor compared to the performance of the IM.

Doubly fed wind turbine performance in variable grid conditions

Wind turbines based on doubly fed induction generators (DFIG) become the most popular solution in high power wind generation industry. While this topology provides great performance with the reduced power rating of power converter, it has more complicated structure in comparison with full-rated topologies, and therefore leads to complexity of control algorithms and electromechanical processes in the system. The purpose of presented study is to present a proper vector control scheme for the DFIG and overall control for the WT to investigate its behavior at different wind speeds and in different grid voltage conditions: voltage sags, magnitude and frequency variations. The key principles of variable-speed wind turbine were implemented in simulation model and demonstrated during the study. Then, based on developed control scheme and mathematical model, the set of simulation is made to analyze reactive power capabilities of the DFIG wind turbine. Further, the rating of rotor-side converter is modified to not only generate active rated active power, but also to fulfill Grid Codes. Results of modelling and analyzing of the DFIG WT behavior under different speeds and different voltage conditions are presented in the work.

Performance and radial distribution profiles of a variable flow rate sprinkler developed for precision irrigation

Variable rate sprinklers (VRS) have been developed to promote localized water application of irrigated areas. In Precision Irrigation, VRS permits better control of flow adjustment and, at the same time, provides satisfactory radial distribution profiles for various pressures and flow rates are really necessary. The objective of this work was to evaluate the performance and radial distribution profiles of a developed VRS which varies the nozzle cross sectional area by moving a pin in or out using a stepper motor. Field tests were performed under different conditions of service pressure, rotation angles imposed on the pin and flow rate which resulted in maximal water throw radiuses ranging from 7.30 to 10.38 m. In the experiments in which the service pressure remained constant, the maximal throw radius varied from 7.96 to 8.91 m. Averages were used of repetitions performed under conditions without wind or with winds less than 1.3 m s-1. The VRS with the four stream deflector resulted in greater water application throw radius compared to the six stream deflector. However, the six stream deflector had greater precipitation intensities, as well as better distribution. Thus, selection of the deflector to be utilized should be based on project requirements, respecting the difference in the obtained results. With a small opening of the nozzle, the VRS produced small water droplets that visually presented applicability for foliar chemigation. Regarding the comparison between the estimated and observed flow rates, the stepper motor produced excellent results.

The Quiet Eye and motor performance – Introducing fixation duration as an independent variable

Evidence suggests a strong relation between superior motor performance and the duration of the last fixation before movement initiation (called Quiet Eye, QE). Although this phenomenon proves to be quite robust, to date, only little is known about its functional role. Therefore, in two experiments, a novel paradigm is introduced, testing the QE as independent variable by experimentally manipulating the duration of the last fixation in a throwing task. In addition, this paradigm allowed for the manipulation of the predictability of the target position. Results of the first study revealed an increase in throwing accuracy as function of experimentally prolonged QE durations. Thus, the assumption that the QE does not surface as a mere by-product of superior performance could be confirmed. In the second study, this dependency was found only under high task-demand conditions in which the target position was not predictable. This finding confirms the hypothesis that it is the optimization of information processing which serves as the crucial mechanisms behind QE effects.

The relation between cognitive and motor performance and their relevance for children’s transition to school: A latent variable approach

Both theoretically and empirically there is a continuous interest in understanding the specific relation between cognitive and motor development in childhood. In the present longitudinal study including three measurement points, this relation was targeted. At the beginning of the study, the participating children were 5-6-year-olds. By assessing participants' fine motor skills, their executive functioning, and their non-verbal intelligence, their cross-sectional and cross-lagged interrelations were examined. Additionally, performance in these three areas was used to predict early school achievement (in terms of mathematics, reading, and spelling) at the end of participants' first grade. Correlational analyses and structural equation modeling revealed that fine motor skills, non-verbal intelligence and executive functioning were significantly interrelated. Both fine motor skills and intelligence had significant links to later school achievement. However, when executive functioning was additionally included into the prediction of early academic achievement, fine motor skills and non-verbal intelligence were no longer significantly associated with later school performance suggesting that executive functioning plays an important role for the motor-cognitive performance link.

Electrochemical performance of carbon gels with variable surface chemistry and physics

This study describes the electrochemical characterization of N-doped carbon xerogels in the form of microspheres and of carbon aerogels with varied porosities and surface oxygen complexes. The interfacial capacitance of N-doped carbon xerogels decreased with increased micropore surface area as determined by N2 adsorption at −196 °C. The interfacial capacitance showed a good correlation with the areal NXPS concentration, and the best correlation with the areal concentration of pyrrolic or pyridonic nitrogen functionalities. The gravimetric capacitance decreased with greater xerogel microsphere diameter. The interfacial capacitance of carbon aerogels increased with higher percentage of porosity as determined from particle and true densities. The interfacial capacitance showed a linear relationship with the areal oxygen concentration and with the areal concentrations of CO- and CO2-evolving groups.