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Relative Speed (relative + speed)
Selected AbstractsBipedal locomotion in ratites (Paleognatiform): examples of cursorial birdsIBIS, Issue 4 2000ANICK ABOURACHID The gaits of five Ostriches Struthio camelus, seven Emus Dromaius novaehollandiae, two Greater Rheas Rhea americana, two Southern Cassowaries Casuarius casuarius and one Brown kiwi Apteryx australis were filmed at zoological parks. Locomotor parameters were measured using footprints on sandy tracks and video records. Osteological measurements were made on skeletons of the pelvic limbs. All of these terrestrial birds shift from wallking to running at a relative speed below 1. However, they show two different locomotor patterns: the Brown Kiwi increases its speed by increasing its stride length, mainly by increasing the protraction angle. Its hindlimbs make a flexed jointed chain system, its centre of mass is anterior, its femurs are long and the knees act in yield whereas the distal joints act in propulsion. Other ratites, particularly Ostriches, increase their speed by increasing frequency. Their centre of mass is close to the hip, their hindlimbs have an extended jointed chain system with a short erect femur, maximizing a gravity-powered system. [source] Evolutionary relationships of sprint speed in Australian varanid lizardsJOURNAL OF ZOOLOGY, Issue 4 2009C. J. Clemente Abstract Ecomorphological studies often seek to link morphology and performance to relevant ecological characteristics. Varanid lizards are unique in that species can vary in body size by almost four orders of magnitude within a single genus, and a question of considerable interest is whether similar ecomorphological relationships exist when constraints on body size are reduced. We studied sprint speed in relation to size, shape and ecology for 18 species of varanid lizards. Maximal speed scaled positively with mass0.166 using least squares regression, and mass0.21 using reduced major-axis regression. However, a curvilinear trend better described this relationship, suggesting an optimal mass of 2.83 kg with respect to speed. Including data for the komodo dragon Varanus komodoensis moves the optimum mass to 2.23 kg. We use this relationship to predict the sprint speed of the Komodo's giant extinct relative Varanus (Megalania) prisca to be 2.6,3 m s,1 similar to that of extant freshwater crocodiles Crocodylus johnstoni. When differences in speed were compared to ecological characteristics, species from open habitats were significantly faster than species from semi-open or closed habitat types, and remained so after correction for size and phylogeny. Thus, despite large variation in body size, varanids appear to share similar associations between performance and ecology as seen in other lizard groups. Varanids did, however, differ in morphological relationships with sprint speed. Differences in relative speed were not related to relative hindlimb length, as is commonly reported for other lizard groups. Instead, size-free forefoot length was negatively related to speed as was the size-free thorax,abdomen length. While shorter forefeet were thought to be an adaptation to burrowing, and thus open habitats, rather than speed per se, the reduction in the thorax,abdomen length may have significant advantages to increasing speed. Biomechanical models predicting this advantage are discussed in relation to a trade-off between speed and manoeuvrability. [source] A multivariate time series approach to projected life tablesAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 6 2009Dorina Lazar Abstract The method of mortality forecasting proposed by Lee and Carter describes a time series of age-specific log-death rates as a sum of an independent of time age-specific component and a bilinear term in which one of the component is a time-varying factor reflecting general change in mortality and the second one is an age-specific parameter. Such a rigid model structure implies that on average the mortality improvements for different age groups should be proportional, regardless of the calendar period: a single time factor drives the future death rates. This paper investigates the use of multivariate time series techniques for forecasting age-specific death rates. This approach allows for relative speed of decline in the log death rates specific to the different ages. The dynamic factor analysis and the Johansen cointegration methodology are successfully applied to project mortality. The inclusion of several time factors allows the model to capture the imperfect correlations in death rates from 1 year to the next. The benchmark Lee,Carter model appears as a special case of these approaches. An empirical study is conducted with the help of the Johansen cointegration methodology. A vector-error correction model is fitted to Belgian general population death rates. A comparison is performed with the forecast of life expectancies obtained from the classical Lee,Carter model. Copyright © 2009 John Wiley & Sons, Ltd. [source] An adaptive load balancing scheme for web serversINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 1 2002Dr. James Aweya This paper describes an overload control scheme for web servers which integrates admission control and load balancing. The admission control mechanism adaptively determines the client request acceptance rate to meet the web servers' performance requirements while the load balancing or client request distribution mechanism determines the fraction of requests to be assigned to each web server. The scheme requires no prior knowledge of the relative speeds of the web servers, nor the work required to process each incoming request. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||