The Ricatti Equation in the M|G|∞ System Busy Cycle Study

The M|G|∞ queue system can be applied to model many social problems: sickness, unemployment, emigration, etc (see, for instance, Ferreira (1995, 1996, 2003a and 2003b)). In these situations it is very important to study the busy cycle length distribution of that queue system. It is shown, in this work, that the problem solution may be in the resolution of a Ricatti equation, following the work of Ferreira (2003

A further note about the Ricatti equation application to the M|G|∞ system busy period study

The M|G|∞ queue system can be applied in the modelation of many social problems: sickness, unemployment, emigration, ...(see, for instance, Ferreira (1995 and 1996)). In these situations it is very important to study the busy period length distribution of that system. We show, in this work, that the solution of the problem may be in the resolution of a Ricatti equation generalizing the work of Ferreira (1998)

Infância e primeiras letras no pensamento de M. A. Ferreira-Deusdado

Neste texto pretendo dar a conhecer o esforço empreendido pelo pedagogo português M. A. Ferreira-Deusdado (1858-1918) no sentido de, entre nós, em finais do século XIX, reabilitar a infância, acompanhando o progresso das ciências, tal como já se fazia, a nível científico, no resto do mundo considerado civilizado. O seu pensamento no que concerne à presente investigação, será analisado a partir dos textos sobre esta temática que assinou na prestigiada Revista de Educação e Ensino, que fundou em 1886 e dirigiu até 1900. Em consequência, então, apresentarei os principais vectores do seu ideário em torno do novo conceito de infância e da reforma educativa que, em seu entender, era necessário que Portugal empreendesse no sentido de adequar a instituição escolar às novas exigências inerentes ao desenvolvimento da criança para que apontava o progresso científico do qual brotavam novos saberes, tais como a pedagogia

M. A. Ferreira Deusdado (1858-1918)

Estudo biobibliográfico de M. A. Ferreira-Deusdad

M|G|∞ queue systems busy period and logistics

In the M|G|∞ queueing systems customers arrive according to a Poisson process at rate . Each of them receives immediately after its arrival a service whose length is a positive random variable with distribution function G(.) and mean value a . An important parameter of the system is the traffic intensity . The service of a customer is independent of the services of the other customers and of the arrival process. The busy period of a queueing system begins when a customer arrives there, finding it empty, and ends when a customer leaves the system letting it empty. During the busy period there is always at least one customer in the system. Therefore in a queueing system there is a sequence of idle and busy periods. For these systems with infinite servers the busy period length distribution is difficult to derive, except for a few exceptions. But we present formulas that allow the calculation of some of the busy period length parameters for the M|G|∞ queueing system. These results can be applied in logistics. For instance to the failures that occur in the operation of a fleet of aircraft, of shipping or of trucking. The customers are the failures. And its service time is the time that goes from the instant at which they occur till the one at which they are completely repaired. Here a busy period is a period in which there is at least one failure waiting for reparation or being repaired. The formulas referred allow the determination of measures of the system performance

U m precedente do critério de falseabilidade de Popper: críticas a astrología na Inglaterra, no século XVII

Se verificarmos os comentários dirigidos a astrologm na Inglaterra no século XVII, poderemos notar que os pontos abordados nas críticas eram bastante variados. É bem verdade que boa parte desses argumentos já existía desde a Antigüidade e o século XVII pouco se dedicou a aprofundar essas questoes (ver Ferreira, 2005)

Looking at nothing facilitates memory retrieval

When processing visual objects, we integrate visual, linguistic and spatial information to form an episodic trace. Re-activating one aspect of the episodic trace of an object re-activates the entire bundle making all integrated information available. Using the blank screen paradigm [1], researchers observed that upon processing spoken linguistic input, participants tended to make eye movements on a blank screen, fixating locations that were previously occupied by objects mentioned in the linguistic utterance or were related. Ferreira and colleagues [2] suggested that 'looking at nothing' facilitated memory retrieval. However, this claim lacks convincing empirical support. In Experiment 1, Dutch participants looked at four-object-displays. Three objects were related to a spoken target word. Given the target word 'beker' (beaker), the display featured a phonological (a bear), a shape (a bobbin), a semantic (a fork) competitor, and an unrelated distractor (an umbrella). Participants were asked to name the objects as fast as possible. Subsequently, the objects disappeared. Participants fixated the center of the screen and listened to the target word. They had to carry out a semantic judgment task (indicating in which position an object had appeared that was semantically related to the objects) or a visual shape similarity judgment (indicating the position of the object similar in shape to the target). In both conditions, we observed that participants re-fixated the empty target location before responding. The set-up of Experiment 2 was identical except that we asked participants to maintain fixating the center of the screen while listening to the spoken word and responding. Performance accuracy was significantly lower in Experiment 2 than in Experiment 1. The results indicate that memory retrieval for objects is impaired when participants are not allowed to look at relevant, though empty locations. [1] Altmann, G. (2004). Language-mediated eye movements in the absence of a visual world: the 'blank screen paradigm'. Cognition, 93(2), B79-B87. [2] Ferreira, F., Apel, J., & Henderson, J. M. (2008). Taking a new look at looking at nothing. Trends Cogn Sci, 12(11), 405-410