Passive drag is still a good evaluator of swimming aptitude

The passive drag (Dp) of 218 competitive swimmers was studied and related to their performance level. To study this relationship, specific attention was given to anthropometric and joint laxity (JL) variations. The Dp was measured at 1.40 m.s-1, using a mechanical winch and a strain gauge with a load cell connected to a strain bridge. Swimmers were towed in a prone position holding their breath after a maximal inspiration. Buoyancy was evaluated by the hydrostatic lift (HL), i.e., the maximal weight just necessary to maintain the swimmer in a balanced position under the water after a maximal inspiration. The JL was assessed by a standard scoring system. The Dp was related mainly to the surface area (SA) (r = 0.73 and 0.53; P less than 0.01, for males and females, respectively). For a given SA, Dp was inversely related to the performance level. The JL explained 7% of the variability of Dp. On average, Dp measured after a maximal expiration, increases of about 22% SD 3% (P less than 0.01). This increase was related to individual vital capacities (r = 0.86, P less than 0.01). As Dp was mainly related to SA and HL, it is suggested that the body exerts a large pressure effect on the water. The contribution to performance might be related to the gliding phase of swimming.     

Feeding postures of suspension-feeding larval black flies: the conflicting demands of drag and food acquisition

Summary We tested whether larval black flies actively control the positioning of their feeding appendages (labral fans), and if so, whether their posture represents a balance between the conflicting demands of drag and feeding. We compared the postures of live larvae with the postures of larvae killed by heat-shock in three different flow regimes in a laboratory experiment; we assumed that the postures of heat-killed larvae approximated a passive response to drag. The average height of the labral fans above the bed declined significantly in faster flows, and was significantly greater in live than dead larvae. There was also a significant interaction effect, since the difference between the fan heights of live and dead larvae was greater in slower flows. Two mechanisms may contribute to this result. Larvae in slower flows have to increase their fan heights more than larvae living in faster flows to achieve comparable increases in velocity and thus particle flux. In addition, muscular strength may limit the feeding postures larvae can assume. The fan heights of live larvae also varied depending on the concentration of food particles: larvae exposed to low food concentrations held their fans higher above the bed than did larvae exposed to high food concentrations in the same flow regime. This change in posture is due neither to an uneven particle concentration in the boundary layer nor to added drag from particles trapped in the labral fans. Collectively, our results indicate that these suspension feeders actively control their feeding posture, and suggest that these varying postures represent a dynamic balance between the conflicting needs of minimizing drag and maximizing feeding.     

林带中阻力分布的理论与实验研究

推导了风向垂直于林带走向时林带内的阻力分布的解析式,比较了３种所面形状林带的阻力分布特点,并用风洞实验资料进行了验证,简析了在实际生产中的应用．     

Swimming performance is reduced by reflective markers intended for the analysis of swimming kinematics

The present study aimed to clarify whether swimming performance is affected by reflective markers being attached to the swimmer’s body, as is required for a kinematic analysis of swimming. Fourteen well-trained male swimmers (21.1 ± 1.7 yrs) performed maximal 50 m front crawl swimming with (W) and without (WO) 25 reflective markers attached to their skin and swimwear. This number represents the minimum required to estimate the body’s center of mass. Fifty meter swimming time, mid-pool swimming velocity, stroke rate, and stroke length were determined using video analysis. We found swimming time to be 3.9 ± 1.6% longer for W condition. Swimming velocity (3.3 ± 1.8%), stroke rate (1.2 ± 2.0%), and stroke length (2.1 ± 2.7%) were also significantly lower for W condition. To elucidate whether the observed reduction in performance was potentially owing to an additional drag force induced by the reflective markers, measured swimming velocity under W condition was compared to a predicted velocity that was calculated based on swimming velocity obtained under WO condition and an estimate of the additional drag force induced by the reflective markers. The mean prediction error and ICC (2,1) for this analysis of measured and predicted velocities was 0.014 m s⁻¹ and 0.894, respectively. Reducing the drag force term led to a decrease in the degree of agreement between the velocities. Together, these results suggest that the reduction in swimming performance resulted, at least in part, from an additional drag force produced by the reflective markers.     

Reconfiguration as a Prerequisite for Survival in Highly Unstable Flow-Dominated Habitats

Unstable and mechanically demanding habitats like wind-exposed open fields or the wave-swept intertidal require rapid adaptive processes to ensure survival. The mechanism of passive reconfiguration was analyzed in two plant models exposed to irregular flow of water or air, two species of the brown seaweed Durvillaea and the giant reed Arundo donax. Irrespective of the surrounding media and the subsequent Reynolds numbers (Re ~ 10⁵ - 10⁷), reconfiguration seems to be the key strategy for streamlining to avoid overcritical drag-induced loads. This passive mechanism is also discussed in the context of the requirement of a maximized surface area for light interception, so that morphological adaptations to rapid reconfiguration represent at least a bifactorial optimization. Both tested plant models exhibited the same principles in streamlining. At a specific threshold value, the proportionality between drag forces and flow velocity can be reduced from the second power close to an almost linear relation. This empirically derived relation could be characterized by a figure of merit or Vogel number (B). A value close to B = -1, resulting in a linear increase of drag force with velocity, was found at higher velocities for both the seaweeds and the giant reed, as well as for a variety of plants described in the literature. It is therefore concluded that the ability to reduce velocity-dependent drag force to a linear relation is a potentially important adaptation for plants to survive in unstable flow-dominated habitats.     

Tidal-Scale Hydrodynamics within Mangrove Swamps

Both the drag force and the horizontal eddy viscosity play a dominant role in the tidal-scale hydrodynamics in mangrove wetlands. Using field observations and basic fluid mechanics laws, the drag coefficient and the coefficient of dynamic eddy viscosity are found to be predictable as a function of the Reynolds Number based on the characteristic length scale of the vegetation. The characteristic length scale of the vegetation varies greatly with vegetation species, vegetation density and tidal elevation. Both these coefficients decrease with increasing values of the Reynolds Number. At the low range of the Reynolds Number both these coefficients reach much higher values than those typical of vegetation-poor estuaries and rivers. Consequently, the tidal flow within mangrove areas depends to a large degree upon the submerged vegetation density that varies with the tidal stage. These findings may be applied also in other vegetated tidal wetlands, including salt marshes.     

Strength, drag, and dislodgment of two competing intertidal algae from two wave exposures and four seasons

Intertidal macroalgae often experience greater risk of dislodgment with increasing size because of underscaling of breaking force of their stipes relative to drag on their thalli. This ratio (breaking force/drag) indicates safety from breakage at a given flow speed, with values greater than one indicating safety from breakage and values lower than one indicating danger of breakage. We examined this force ratio for the largest thalli of two species of co-dominant, red algae, Chondrus crispus Stackhouse and Mastocarpus stellatus Stack. In With. (Guiry), in four seasons at two wave exposures. During fall and winter, the largest thalli in both populations were dislodged resulting in a decrease in mass of the largest thalli found. This decrease was greater for Chondrus than for Mastocarpus, but their mass-specific force ratios (at 0.55 m s⁻¹) were equal indicating similar size-specific risk of dislodgment. The equality of force ratios was underlain by two similarities: (1) breaking force was independent of mass and not different between species; (2) mass-specific drag was not different between species. These similarities were underlain by dissimilar causes: (i) similarity in breaking force (the product of cross-sectional area and material strength) occurred because greater material strength of Mastocarpus compensated for greater mass-specific cross-sectional area of Chondrus; (ii) similarity in mass-specific drag (a function of planform area and the coefficient of drag) occurred because greater drag coefficients for Mastocarpus compensated for greater mass-specific planform areas of Chondrus. The similarity in force ratio, if it held at season- and site-relevant flow speeds, would suggest that during seasons of minimal growth and high wave exposure, the mass of the largest thalli of both species should be the same. Chondrus, however, had a greater mass at both sites in all seasons. Chondrus experienced greater decreases in mass probably because it grew larger and larger thalli are less safe. Extrapolation of a site-relevant force ratio for Chondrus in the fall revealed (1) that the site-relevant force ratio did not differ between exposures even though the mass-specific force ratio was greater at the protected site, and (2) a paradoxical result that all Chondrus thalli studied ought to have dislodged, but had not. This paradox may be resolved by consideration of the protection conferred by canopies of Chondrus: a canopy may effectively raise its site-relevant force ratio. Perhaps differences in protection conferred by different canopies explain why larger Chondrus persist with Mastocarpus even given a similarity in mass-specific force ratio.     

Drag forces on common plant species in temperate streams: consequences of morphology, velocity and biomass

Swift flow in streams may physically influence the morphology and distribution of plants. I quantified drag as a function of velocity, biomass and their interaction on the trailing canopy of seven European stream species in an experimental flume and evaluated its importance for species distribution. Drag increased at a power of 1.3–1.9 with velocity and 0.59–0.77 with biomass in 75% of the measurements. Velocity and biomass interacted because higher velocity causes reconfiguration and greater internal shelter to unimpeded flow and higher biomass enhances shelter among neighbouring shoots. Increase of drag with velocity did not differ systematically among inherently streamlined or non-streamlined species while increase of drag with biomass was smallest among non-streamlined shoots which provide greater mutual shelter. At low shoot density, inherently streamlined species usually experienced the lowest drag conducive to colonisation and growth in swift flow. At high shoot density, no systematic differences in drag existed between the two morphologies. No clear relationship existed between drag forces, morphology and field distribution of species as a function of current velocity probably because a variety of environmental conditions and plant traits influences distribution. Drag on the trailing canopy usually increased 15- to 35-fold for a 100-fold increase of biomass suggesting that an even distribution of plants at low density across the stream bed offers greater resistance to downstream flow than an uneven distribution with the same biomass confined to dense patches surrounded by open flow channels. Thus, management strategies to ensure a patchy plants distribution should be suitable for combining agricultural drainage and ecological stream quality. Handling editor: S. M. Thomaz     

Increased production of extracellular polysaccharide by Porphyridium cruentum immobilized in foam sheets

Large‐size plate bioreactors were used to compare the production of extracellular polysaccharide by the red microalga Porphyridium cruentum when grown in suspension and in a foam sheet. A well‐defined illuminated area and unidirectional light propagation allowed us to generate information that is better quantified when expressed in terms of illuminated area. This is essential for meaningful comparison of data, especially considering that for a well‐designed and managed bioreactor, the culture production rates are believed to be light limited. At the same level of illumination, the culture immobilized in foam showed double the production rate of extracellular polysaccharide compared with the culture in suspension. The saturation level of biomass density per unit of illuminated area was eight times higher for the immobilized culture compared with the culture in suspension. Despite the increased biomass density for the immobilized culture, an increase in the light level above the optimum found for the culture in suspension reduced the extracellular polysaccharide production, suggesting that the photoinhibition light level was surpassed.     

转运体ABCC4和ABCC5介导的肿瘤多药耐药研究进展

：ABCC4、ABCC5是ABCC（ATP-binding cassette transporter family class C, ABCC）蛋白转运体家族的成员,介导众多内源性代谢产物和外源性药物从细胞内向外转运。ABCC4和ABCC5在体内分布广泛,参与机体对药物和内、外源物质的吸收、分布和排泄等。ABCC4、ABCC5的一些突变会引起转运体表达、功能的改变和机体对药物反应的改变。近年研究发现ABCC4、ABCC5与某些肿瘤的多药耐药相关,转运体的过表达可以引起肿瘤细胞对多种肿瘤化疗药物的耐药性,导致临床化疗效果不佳。本文就转运体ABCC4和ABCC5介导的肿瘤多药耐药研究进展进行综述。