A Model of Human Muscle Energy Expenditure

A model of muscle energy expenditure was developed for predicting thermal, as well as mechanical energy liberation during simulated muscle contractions. The model was designed to yield energy (heat and work) rate predictions appropriate for human skeletal muscle contracting at normal body temperature. The basic form of the present model is similar to many previous models of muscle energy expenditure, but parameter values were based almost entirely on mammalian muscle data, with preference given to human data where possible. Nonlinear phenomena associated with submaximal activation were also incorporated. The muscle energy model was evaluated at varying levels of complexity, ranging from simulated contractions of isolated muscle, to simulations of whole body locomotion. In all cases, acceptable agreement was found between simulated and experimental energy liberation. The present model should be useful in future studies of the energetics of human movement using forward dynamic computer simulation.     

First selenosteid placoderms from the eastern Anti‐Atlas of Morocco; osteology,phylogeny and palaeogeographical implications

Abstract: A new placoderm assemblage is reported from the Kellwasser facies of the eastern Anti‐Atlas, Morocco. This is the first record of an abundant Frasnian placoderm assemblage from Africa. The following new selenosteid taxa are described: Draconichthys elegans gen. et sp. nov., Enseosteus marocanensis sp. nov. and Walterosteus lelievrei sp. nov. In addition, material of Rhinosteus cf. parvulus is figured and described for the first time from Gondwana. The genera Enseosteus, Rhinosteus and Walterosteus are reviewed. ‘Wildungenichthys’ is regarded as a junior subjective synonym of Walterosteus. The new material and a revision of the taxa from Bad Wildungen, Germany, are the basis for a new phylogenetic analysis of the selenosteid arthrodires. The monophyly of the selenosteids is confirmed. The North American selenosteids are a sister group of Moroccan and European selenosteids, excluding Pachyosteus. The Moroccan vertebrate assemblage resembles that of Bad Wildungen. This supports the close palaeogeographical positions of Gondwana and Laurussia during the Late Devonian and indicates that biogeographical barriers for placoderms that could have separated the two assemblages were absent.     

Characteristics and utilization of old Black Woodpecker Dryocopus martius holes by hole-nesting species

Old nest holes made by the Black Woodpecker Dryocopus martius were examined in two study areas in Sweden. We found a large variation in nest hole characteristics and that the height in the tree and depth of the hole were important factors in the choice of nest hole by secondary hole nesters. A large proportion of old nest holes remained unoccupied. Many holes were probably of poor quality due to shallow depth, low height or narrow entrance. Nest holes in the vicinity of farmland (<200 m from the field-forest edge) were more often occupied than nest holes deeper into the forest. This was because Jackdaws Corvus monedula , the numerically dominant species, only used nest holes near farmland. Jackdaws usually used the best nest holes, while other subordinate species had to use inferior holes near fields or nest holes in areas with less competition, deeper in the forest. Besides birds, some mammals and bees were found using old Black Woodpecker holes.     

Multi-element and multi-site isotopic analysis of nicotine from tobacco leaves

The carbon, nitrogen and hydrogen stable-isotope contents of nicotine extracted from tobacco leaves were determined by Isotope Ratio Mass Spectrometry (overall ²H, ¹³C and ¹⁵N contents) and by the SNIF-NMR method (site-specific deuterium content). In addition, nicotine was chemically degraded into nicotinic acid so that the intramolecular distribution of carbon and nitrogen isotopes could be studied. A prerequisite for reliable measurements is the use of experimental procedures free of isotopic fractionation. Therefore, it was ensured that isotopic integrity was maintained throughout extraction, purification and chemical degradation steps. The multi-element and multi-site information provided is tentatively interpreted in terms of biochemical isotopic effects on intramolecular distribution patterns and of the influence of environmental factors on nicotine isotopic parameters.     

Plasma Membrane Turnover in Plant Cells

Steer, M. W. 1988. Plasma membrane turnover in plant cells.—J.exp. Bot. 39: 987–996. Plasma membrane turnover in plant cells occurs as a consequenceof secretion, which incorporates new membrane into the cellsurface and endocytosis, which internalizes surface membrane.Development of methods that provide estimates of the rate ofnew membrane flow to the cell surface has allowed the estimationof turnover times for the plasma membrane. These times rangefrom 10 min for a non-expanding secretory cell to 3 h for anelongating epidermal cell. At least part, if not all, of thereturn route into the cell is via endocytotic vesicles. Quantitativestudies are required to establish the precise level of flowthrough this route. However, turnover times estimated from theabundance of coated patches on the plasma membrane are comparableto those estimated from secretion studies. The effect of thesehigh turnover rates on a number of plasma membrane functionsare discussed and assessed. Key words: Plasma membrane, endocytosis, secretion, plant cells