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Mean Speed (mean + speed)

Distribution by Scientific Domains

Life Sciences	33%

Selected Abstracts

Estimating the mean speed of laminar overland flow using dye injection-uncertainty on rough surfaces

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2001
David Dunkerley
Abstract A common method for estimating mean flow speeds in studies of surface runoff is to time the travel of a dye cloud across a measured flow path. Motion of the dye front reflects the surface flow speed, and a correction must be employed to derive a value for the profile mean speed, which is always lower. Whilst laminar flow conditions are widespread in the interrill zone, few data are available with which to establish the relationship linking surface and profile mean speeds, and there are virtually none for the flow range 100,<,Re,<,500 (Re,=,Reynolds number) which is studied here. In laboratory experiments on a glued sand board, mean flow speeds were estimated from both dye speeds and the volumetric flow relation v,=,Q/wd with d measured using a computer-controlled needle gauge at 64 points. In order to simulate conditions applicable to many dryland soils, the board was also roughened with plant litter and with ceramic tiles (to simulate surface stone cover). Results demonstrate that in the range 100,<,Re,<,500, there is no consistent relation between surface flow speeds and the profile mean. The mean relationship is v,=,0·56 vsurf, which departs significantly from the theoretical smooth-surface relation v,=,0·67 vsurf, and exhibits a considerable scatter of values that show a dependence on flow depth. Given the inapplicability of any fixed conversion factor, and the dependence on flow depth, it is suggested that the use of dye timing as a method for estimating v be abandoned in favour of precision depth measurement and the use of the relation v,=,Q/wd, at least within the laminar flow range tested. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Tracking larval insect movement within soil using high resolution X-ray microtomography

ECOLOGICAL ENTOMOLOGY, Issue 1 2004
Scott N. Johnson
Abstract., 1. In contrast to above-ground insects, comparatively little is known about the behaviour of subterranean insects, due largely to the difficulty of studying them in situ. 2. The movement of newly hatched (neonate) clover root weevil (Sitona lepidus L. Coleoptera: Curculinidae) larvae was studied non-invasively using recently developed high resolution X-ray microtomography. 3. The movement and final position of S. lepidus larvae in the soil was reliably established using X-ray microtomography, when compared with larval positions that were determined by destructively sectioning the soil column. 4. Newly hatched S. lepidus larvae were seen to attack the root rhizobial nodules of their host plant, white clover (Trifolium repens L.). Sitona lepidus larvae travelled between 9 and 27 mm in 9 h at a mean speed of 1.8 mm h,1. 5. Sitona lepidus larvae did not move through the soil in a linear manner, but changed trajectory in both the lateral and vertical planes. [source]

Representation of accuracy in the dorsal premotor cortex

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2000
Jose E. Gomez
Abstract The endpoint accuracy of a reaching movement strongly affects kinematics, particularly during the final phases of movement. However, where and how accuracy is represented in the central nervous system remains unknown. In this study, the discharge of 150 neurons located primarily in the dorsal premotor cortex (PMd), were recorded from monkeys performing an instructed delay, centre-out reaching task in which movement direction and target size were systematically varied. Linear regression analyses were used to assess the dependence of movement kinematics and cell discharge on target direction, size and tangential velocity (i.e. speed). The speed and timing of the movement were dependent on both direction and target size. Initially direction was the dominant predictor whilst target size became more important as the hand reached the target. A temporal multiple linear regression analysis found significant correlations with target size in 99 of 150 cells. The discharge of 134 cells was directionally tuned and 83 cells modulated with mean speed. Significant correlations of discharge with target size occurred throughout the task as did correlations with direction. However, correlations with direction preferentially occurred early in the task, prior to movement onset, whilst correlations with target size tended to occur late, well after movement onset. This temporal dependency of the firing in relationship to target direction and size mirrored that observed for the kinematics. We conclude that the discharge of PMd cells is highly correlated with the accuracy requirement of the movement. The timing of the correlations suggest that accuracy information is available for the planning and for the on-line control of endpoint accuracy. [source]

Driving speed changes and subjective estimates of time savings, accident risks and braking

APPLIED COGNITIVE PSYCHOLOGY, Issue 4 2009
Ola Svenson
Participants made decisions between two road improvements to increase mean speed. Time saved when speed increased from a higher driving speed was overestimated in relation to time saved from increases from lower speeds. In Study 2, participants matched pairs of speed increases so that they would give the same time saving and repeated the bias. The increase in risk of an accident with person injury was underestimated and the increase in risk of a fatal accident grossly underestimated when speed increased. The increase of stopping distance when speed increased was systematically underestimated. In Study 3, the tasks and results of Study 2 were repeated with engineering students. When forming opinions about speed limits and traffic planning, drivers, the public, politicians and others who do not collect the proper facts are liable to the same biases as those demonstrated in the present study. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Development of a Disposable Maglev Centrifugal Blood Pump Intended for One-Month Support in Bridge-to-Bridge Applications: In Vitro and Initial In Vivo Evaluation

ARTIFICIAL ORGANS, Issue 9 2009
Takeshi Someya
Abstract MedTech Dispo, a disposable maglev centrifugal blood pump with two degrees of freedom magnetic suspension and radial magnetic coupling rotation, has been developed for 1-month extracorporeal circulatory support. As the first stage of a two-stage in vivo evaluation, 2-week evaluation of a prototype MedTech Dispo was conducted. In in vitro study, the pump could produce 5 L/min against 800 mm Hg and the normalized index of hemolysis was 0.0054 ± 0.0008 g/100 L. In in vivo study, the pump, with its blood-contacting surface coated with biocompatible 2-methacryloyloxyethyl phosphorylcholine polymer, was implanted in seven calves in left heart bypass. Pump performance was stable with a mean flow of 4.49 ± 0.38 L/min at a mean speed of 2072.1 ± 64.5 rpm. The maglev control revealed its stability in rotor position during normal activity by the calves. During 2 weeks of operation in two calves which survived the intended study period, no thrombus formation was seen inside the pump and levels of plasma free hemoglobin were maintained below 4 mg/dL. Although further experiments are required, the pump demonstrated the potential for sufficient and reliable performance and biocompatibility in meeting the requirements for cardiopulmonary bypass and 1-week circulatory support. [source]