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Publications

Publications by José Sarsfield Cabral

1994

Dynamic calibration of price-trend parameters for commodity futures trading

Authors
Sarsfield Cabral, JA; Guimarães, RC;

Publication
Journal of the Operational Research Society

Abstract
This paper addresses the problem of buying commodities through the futures markets and deals specifically with a heuristic rule developed for the scenario described as ‘purchasing under a deadline’. The rule is based on a short-term forecasts produced by Taylor’s price-trend model. In a previous study applied to the Chicago Board of Trade (CBOT) corn futures market the price-trend parameters of the stochastic process generating the daily returns were shown to be nearly stable over time and hence could be estimated using a static procedure. However, the analysis presented in this paper concerning the CBOT soybean futures market strongly suggests that those parameters were unstable, impairing the successful application of the purchasing rule. The authors recommend the continuous CUSUM monitoring of the purchasing results and propose a procedure for dynamically calibrating the price-trend and buying parameters. Under this procedure the price-trend parameter estimates are derived from exponentially smoothed sample autocorrelation coefficients of the rescaled daily returns. The procedure was developed and tested using the 1972-87 series of CBOT daily soybean futures closing prices. The results suggest that it leads to an improvement on the purchasing results derived from the static parameter calibration procedure formerly adopted. © 1994 Operational Research Society Ltd.

2007

Understanding attitudes towards public transport and private car: A qualitative study

Authors
Beirao, G; Cabral, JAS;

Publication
TRANSPORT POLICY

Abstract
This paper presents the results of a qualitative study of public transport users and car users in order to obtain a deeper understanding of travellers' attitudes towards transport and to explore perceptions of public transport service quality. The key findings indicate that in order to increase public transport usage, the service should be designed in a way that accommodates the levels of service required by customers and by doing so, attract potential users. Furthermore, the choice of transport is influenced by several factors, such as individual characteristics and lifestyle, the type of journey, the perceived service performance of each transport mode and situational variables. This suggests the need for segmentation taking into account travel attitudes and behaviours. Policies which aim to influence car usage should be targeted at the market segments that are most motivated to change and willing to reduce frequency of car use.

2006

Enhancing service quality in public transport systems

Authors
Beirao, G; Cabral, JS;

Publication
Urban Transport XII: Urban Transport and the Environment in the 21st Century

Abstract
Public transport systems face the challenge of attracting users to fight the lost in market share, mostly due to the increasing use of private cars. Therefore, the concepts of 'quality' and 'customer' must change and the focus must be on meeting people's needs. At the same time, transport systems should be flexible enough to respond to changes in people's requirements and needs. Thus, the aim for public transport must be enhancing quality of the service. This requires a clear understanding of travel behaviour and consumer needs and expectations. Accordingly, there is an increasing awareness of the importance of including service quality indicators and quality specifications in contracts between operators and public transport authorities. The development of quality measures in the designing of contracts for public transport raises important aspects that must be considered. This paper examines issues concerning the definition of service quality measures for public transport. This will give a better understanding of pertinent questions and of improvement strategies open to public transport management. Next, it outlines some critical aspects that must be considered when including such measures in contracts between operators and public transport authorities.

2008

Market Segmentation Analysis Using Attitudes Toward Transportation Exploring the Differences Between Men and Women

Authors
Beirao, G; Cabral, JS;

Publication
TRANSPORTATION RESEARCH RECORD

Abstract
Traveler attitudes and preferences as well as demographic variables are important components of travel behavior. By using travel attitudes, factor and cluster analyses were conducted to segment the sample. Six distinct groups were extracted: transit enthusiasts, anxious status seekers, carless riders, green cruisers, frugal travelers, and obstinate drivers. The segments showed unique combinations of attitudes with distinct travel behaviors and various degrees of intention to use public transportation. Gender differences were then investigated, and the results suggest that women and men exhibit differences in attitudes, preferences, and behaviors. The design of strategies to promote alternatives to car use should target the market segments that are most motivated to change, focusing on the attitudes that can induce a change, such as pro transit or sensibility to the environment.

2008

A new conceptual framework based on the ECSI model to support Axiomatic Design

Authors
Ferreira, I; Cabral, JS; Saraiva, P;

Publication
VIRTUAL AND RAPID MANUFACTURING: ADVANCED RESEARCH IN VIRTUAL AND RAPID PROTOTYPING

Abstract
According with Axiomatic Design (AD) theory, the world of design is made up of four domains: the customer domain, the functional domain, the physical domain and the process domain. Therefore, to proceed in the design process, firstly, it's necessary to determine the Customer's Attributes (CAs), established in the Customer domain, and translate them into specific requirements, the Functional Requirements (FRs), formalized in the functional domain. This task is considered essential because a major reason for customer dissatisfaction is that the design specifications quite often do not adequately link to customer use of the product, a fact which is being pointed out as the most common cause for product design failures [1-2]. The European Customer Satisfaction Index (ECSI), as a Structural Equation Model (SEM), links customer satisfaction to its main drivers and consequences in terms of causal relationships. We will therefore introduce in this paper a new conceptual framework, aimed at addressing the development and validation of a model based on ECSI that supports the determination of the critical-to-satisfy (CTS) requirements, which are then used to determine the FRs. In order to validate the proposed approach, it was applied to the Portuguese plastic injection moulds sector.

2005

The influence of genes on the aging process of mice: A statistical assessment of the genetics of aging

Authors
de Magalhaes, JP; Cabral, JAS; Magalhaes, D;

Publication
GENETICS

Abstract
Genetic interventions that accelerate or retard aging in mice are crucial in advancing our knowledge over mammalian aging. Yet determining if a given intervention affects the aging process is not straightforward since, for instance, many disease-causing mutations may decrease life span without affecting aging. In this work, we employed the Gompertz model to determine whether several published interventions previously claimed to affect aging in mice do indeed alter the aging process. First, we constructed age-specific mortality tables for a number of mouse cohorts used in longevity experiments and calculated the rate at which mortality increases with age. Estimates of age-independent mortality were also calculated. We found no statistical evidence that GHRHR, IGF1R, INSR, PROP1, or TRX delay or that ATM + TERC, BubR1, klotho, LMNA, PRDX1, p53, WRN + TERC, or TOP3B accelerate mouse aging. Often, changes in the expression of these genes affected age-independent mortality and so they may prove useful to other aspects of medicine. We found statistical evidence that C/EBP, MSRA, SHC1, growth hormone, GHR, PIT1, and PolgA may influence aging in mice. These results were interpreted together with age-related physiological and pathological changes and provide novel insights regarding the role of several genes in the mammalian aging process.

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