Search

In this study, we explore the impact of four alternative indices of reproductive potential (RP) on perceptions of population productivity for eight fish populations across the North Atlantic. The four indices of RP included increasing biological complexity, adding variation in maturation, sex ratio, and fecundity. Perceptions of stock productivity were greatly affected by the choice of index of RP. Population status relative to reference points, RP per recruit, and projections of population size all varied when alternative indices of RP were used. There was no consistency in which index of RP gave the highest or lowest estimate of population productivity, but rather, this varied depending on how much variation there was in the reproductive biology of the population and the age composition. Estimates of sustainable harvest levels and recovery time for depleted populations can vary greatly depending on the index of RP. Nous explorons dans notre etude les effets de quatre indices de rechange du potentiel reproductif (RP) sur la perception de la productivite de la population chez huit populations de poisons provenant de l'Atlantique Nord. Les quatre indices de RP comprennent l'accroissement de la complexity biologique, l'addition de variation dans la maturation, la proportion des sexes et la fecondite. Le choix d'indice de RP affecte considerablement la perception de la productivite des stocks. Le statut de la population en fonction des points de reference, le RP par recrue et les projections de la taille de la population varient tous en fonction de l'indice RP retenu. Il n'y a pas de coherence en ce qui a trait a quel indice donne l'estimation la plus elevee ou la plus base de la productivite de la population, mais il y a plutot des resultats differents selon l'importance de la variation dans la biologie de la reproduction et la composition en age de la population. Les estimations des niveaux admissibles de recolte et du temps necessaire au retablissement des populations epuisees peuvent varier considerablement selon l'indice de RP utilise. [Traduit par la Redaction], Introduction Estimating a population's productivity is key to sustainable management of fisheries. A population's level of productivity will determine the level of fishing mortality (F) that it can sustain as [...]

Elastic-plastic crack front fields in are-shaped tension specimens (C-specimens) were analyzed by a three-dimensional finite element method. The effect of side grooves on the ductile fracture behavior was investigated by studying the J-integral distribution, plane-strain constraint parameter, and development of plastic zones and comparing to experimental data. The applicability of the [eta] factor (derived for use with compact tension specimens) for the calculation of J-integral values for the C-specimen was also investigated. The results show that side grooves promote and establish near plane strain conditions at the crack front in sub-size specimens. It was also found that a two-dimensional plane-strain analysis in conjunction with the standard American Society for Testing and Materials (ASTM) tests was sufficient to determine the fracture toughness values from side-grooved C-specimen. The results indicate the [eta] factor for compact tension specimen as specified in the ASTM standards appears to produce reliable results for the calculation of J of C-specimens. [DOI: 10.1115/1.1762425] Keywords: Arc-Shaped Tension Specimen, Elastic-Plastic Fracture, Three Dimensional, Crack-Front Field, Finite Element Method, Side-Groove, [eta] Factor

The theory of binocular stereopsis is analyzed in terms of its application to a moving object and observer. The disparity that arises from the use of two eyes is complex enough but is ably managed by the visual system to calculate relative distances and shapes. However, this complexity becomes magnified when dealing with moving targets. In this case, neurons which have special filtering qualities.