Biomedical subjects

c

Publications and source records attributed to c.

3 recordsLinked to original sources

PubMed1998

A computational fluid dynamic study of hawkmoth hovering

A computational fluid dynamic (CFD) modelling approach is used to study the unsteady aerodynamics of the flapping wing of a hovering hawkmoth. We use the geometry of a Manduca sexta-based robotic wing to define the shape of a three-dimensional 'virtual' wing model and 'hover' this wing, mimicking accurately the three-dimensional movements of the wing of a hovering hawkmoth. Our CFD analysis has established an overall understanding of the viscous and unsteady flow around the flapping wing and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading-edge vortex with axial flow was detected during translational motions of both the up- and downstrokes. The attached leading-edge vortex causes a negative pressure region and, hence, is responsible for enhancing lift production. The axial flow, which is derived from the spanwise pressure gradient, stabilises the vortex and gives it a characteristic spiral conical shape. The leading-edge vortex created during previous translational motion remains attached during the rotational motions of pronation and supination. This vortex, however, is substantially deformed due to coupling between the translational and rotational motions, develops into a complex structure, and is eventually shed before the subsequent translational motion. Estimation of the forces during one complete flapping cycle shows that lift is produced mainly during the downstroke and the latter half of the upstroke, with little force generated during pronation and supination. The stroke plane angle that satisfies the horizontal force balance of hovering is 23.6 degrees , which shows excellent agreement with observed angles of approximately 20-25 degrees . The time-averaged vertical force is 40 % greater than that needed to support the weight of the hawkmoth.

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PubMed1998

Thermal control of metabolic cold defence in pigeons columba livia

Metabolic rate (MR) and various body temperatures were recorded in pigeons Columba livia during gradual lowering of the ambient temperature (Ta) and during cold exposure (-10 degrees C) for an entire circadian cycle. The aim was to study how changes in MR accorded with the observed body temperature displacements and our knowledge of regional cold sensitivity. When Ta was lowered from 28 to -10 degrees C, the threefold increase in MR was accompanied by a significant increase in deep-body and spinal cord temperatures. Cold exposure also resulted in a distinct rise in breast skin temperature, whereas the skin temperatures of the neck, back and leg decreased significantly. Thus, during acute cold exposure of pigeons, peripheral thermosensors seem to have the primary effect in mediating metabolic cold defence, while internal thermosensors are apparently of minor importance. By using differential weightings of various skin areas, cold-sensitivity values of between -3.9 and -14. 7 W kg-1 degrees C-1 were estimated. These values indicate a much higher skin thermosensitivity of birds than has been previously suggested. When cold-exposed for an entire circadian cycle, the pigeons usually maintained a low leg skin temperature. However, during these experiments, the pigeons showed regular distinct increases in leg skin temperature, obviously due to cold-induced vasodilatations (CIVDs). The flushing of cold peripheral blood through the body in connection with these CIVDs resulted in a decrease in deep-body temperature (Tb), to which the pigeons responded with a distinct increase in MR. From the concomitant changes in MR and Tb, a total body cold sensitivity of -8.0 W kg-1 degrees C-1 was calculated, a value that is close to the previously published cold-sensitivity value of pigeons. This shows that, at least under some naturally occurring conditions, internal thermosensors will provide a significant error signal in the control of metabolic cold defence. Furthermore, the results of our study show that the relative importance of various thermosensitive sites in the control of metabolic cold defence is contextual.

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PubMed1996

Electrophysiological and endocrinological evidence that F-series prostaglandins function as priming pheromones in mature male Atlantic salmon (Salmo salar parr

Previous work has demonstrated that the urine from mature female salmonids contains a priming pheromone that significantly enhances the reproductive physiology of receiving males. The chemical identity of the pheromone(s) has not yet been identified. The present study investigated the possibility that F-type prostaglandins (PGFs) may have a pheromonal role in Atlantic salmon by measuring the olfactory sensitivity of male salmon to PGFs, the effect of waterborne PGFs on male reproductive physiology and the PGF content of mature female urine. Electrophysiological studies demonstrated that the olfactory epithelium of mature male salmon parr was acutely sensitive to PGF1[alpha] and PGF2[alpha], with detection threshold concentrations of 10(-11) mol l-1. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF2[alpha] (threshold 10(-8) mol l-1), but did not detect a further metabolite, 13,14-dihydro-15-ketoPGF2[alpha]. Sensitivity to both PGF1[alpha] and PGF2[alpha] increased as the reproductive season progressed. Exposure of mature male parr to waterborne PGF1[alpha] and PGF2[alpha] (10(-8) mol l-1) resulted in significant increases in levels of expressible milt and in the plasma concentrations of 17,20ss-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. Urine from ovulated female salmon also contained large quantities (18 ng ml-1) of immunoreactive PGFs, whereas urine from mature males and non-ovulated mature females contained significantly smaller amounts (<1 ng ml-1). The results support the theory that PGFs function as priming pheromones in Atlantic salmon and are released in the urine of ovulated female salmon. The involvement of these pheromones in synchronising male-female salmon spawning is discussed.

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