Constrained multi-item inventory systeṁs an implicit approach

This paper examines the N-item deterministic inventory model subject to a single linear constraint. Functional relationships between the Lagrangian multipliers and shifts occurring simultaneously in multiple system parameters are identified and used to establish effective initial bounds on the optimal multiplier, Φ^*, in closed form. A recursive process which rapidly converges to Φ^* is also presented. Finally, a comparative analysis highlighting the efficiency of the proposed process in relation to existing algorithms is exhibited.     

The sociobiology of bereavement: A reply to Littlefield and Rushton.

This article offers a critique of Littlefield and Rushton's (1986) application of sociobiological principles to bereavement following the death of a child. The following general issues are considered: (a) whether behavior is always adaptive and (b) the distinction between proximate and ultimate explanations. It is argued that grief is a maladaptive by-product of another, adaptive feature and that hypotheses about the severity of grief are best derived from proximate considerations rather than genetic relatedness. The use of a single-item rating scale to measure grief is questioned, and it is noted that interspouse reliabilities reported in the article were low, a problem not solved (as claimed) by aggregation. Criticisms are made of the specific hypotheses, notably in terms of their origins in sociobiological theory. It is argued that functional hypotheses are not alternatives to proximate mechanisms, but enable some proximate mechanisms to be viewed from the perspective of evolutionary biology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Well reservoir model identification using translation and scale invariant higher order networks

This paper describes the use of higher order neural networks to identify well reservoir response models from test data. Well reservoir response models are characterised by a family of parametrically related curves. Neural networks can in principle offer an interesting approach to the identification problem as data are often uncertain and incomplete. However, it turns out that the well reservoir model, viewed as a curve in two dimensions, is invariant with respect to translation and changes of scale of the axes. This poses severe problems for a standard backpropagation network using the two-dimensional plot as an input retina. This difficulty can be overcome by using a higher order network in which the output is forced to be invariant with respect to the required transformations of the retina. In this way, the potentially huge number of weights is significantly reduced using the invariance condition as a constraint which acts so as to divide the weights into equivalence classes within which they are equal. The resulting network can then be trained using standard techniques. We contrast this network approach with classical methods of model identification.     

Kinetics of the methanogenic fermentation of acetate

The kinetics of methanogenesis from a stirred batch-fed calcium acetate enrichment culture have been studied. A detailed kinetic analysis of the culture allowed four distinct phases to be distinguished. Phase 1 was a period of very rapid increase (from low initial values) in the rate of methanogenesis upon addition of acetate, and was not thought to be associated with cell growth. In Phase 2 the rate of methanogenesis increased exponentially with time reflecting exponential growth. Phase 3 was characterised by an approximately constant rate of methane production, and is discussed in relation to the uncoupling of growth and methanogenesis. Phase 4 is a period of rapid decline associated with depletion of acetate. The apparent size of the population of the acetate-utilising methanogenic bacteria subsequently declined, with a specific decay constant of 0.4 ± 0.1 d^?1. The significance of these phases, in particular 2 and 3, for industrial anaerobic digestion is discussed.     

Comportement du nitrure de niobium cubique δ en atmosphere d'oxygene

The oxidation of cubic δ NbN_.87 plates and NbN_.90 powder in oxygen at pressures of 25–730 Torr in the temperature range 425–600°C obeys pressure independent sigmoïdal kinetics. There is formation of a low temperature form of Nb₂O₅. The reaction is governed by an inner interface process, the shape of the curves being associated to a chain fragmentation of the nitride substrate.     

Waiting list dropouts in a university counseling center.

Surveyed 59 clients at a university counseling center who had been placed on a waiting list and subsequently decided not to renew their request for counseling. Ss were asked why they did not renew their request and whether they were still interested in counseling. Responses were analyzed in terms of type of problem, time on the waiting list, and degree of urgency. Most Ss did not report negative reactions or effects from their placement on the waiting list, although Ss in the highest urgency category tended to report that the wait was too long. 30 Ss stated that the intake interview was enough or that the problem had been resolved, while 23 were still interested in counseling. It is suggested that (1) high-urgency clients should be given priority at university counseling centers, (2) directive crisis-intervention approaches can be used to resolve issues at intake sessions, (3) assessment should identify clients whose motivation for counseling is related to developmental issues that need to be dealt with immediately, and (4) alternative treatments such as groups or workshops should be made available to waiting-list clients. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photogalvanic cells—I. The potential of zero current

A general treatment is developed for calculating the change in potential at the point of zero current when a photogalvanic cell which contains two electrochemical redox couples (such as the iron-thionine system) is illuminated. The treatment does not depend upon the exact form of the transport to the electrode or of the photochemical kinetics. The change in potential on illumination, from a thermodynamic dark potential to a mixed potential, may be positive, negative or zero, depending on the balance between the electrode kinetics of the two couples in the solution. The rate of transport to the electrode and of homogeneous back reaction in solution also affect the magnitude of the potential shift. The implications with respect to obtaining electric work from photogalvanic cells are discussed, with some illustrative examples from the literature.