Coherent flow structures in a depth-limited flow over a gravel surface : the role of near-bed turbulance and influence of Reynolds number

In gravel bed rivers, the microtopography of the bed exerts a significant effect on the generation of turbulent flow structures. Although field and laboratory measurements have indicated that flows over gravel beds contain coherent macroturbulent flow structures, the origin of these phenomena, and their relationship to the ensemble of individual roughness elements forming the bed, is not quantitatively well understood. Here we report upon a flume experiment in which flow over a gravel surface is quantified through the application of digital particle imaging velocimetry, which allows study of the downstream and vertical components of velocity over the entire flow field. The results indicate that as the Reynolds number increases (1) the visual distinctiveness of the coherent flow structures becomes more defined, (2) the upstream slope of the structures increases, and (3) the turbulence intensity of the structures increases. Analysis of the mean velocity components, the turbulence intensity, and the flow structure using quadrant analysis demonstrates that these large-scale turbulent structures originate from flow interactions with the bed topography. Detection of the dominant temporal length scales through wavelet analysis enables calculation of mean separation zone lengths associated with the gravel roughness through standard scaling laws. The calculated separation zone lengths demonstrate that wake flapping is a dominant mechanism in the production of large-scale coherent flow structures in gravel bed rivers. Thus, we show that coherent flow structures over gravels owe their origin to bed-generated turbulence and that large-scale outer layer structures are the result of flow-topography interactions in the near-bed region associated with wake flapping

Microsatellite development for the genus Guibourtia (Fabaceae, Caesalpinioideae) reveals diploid and polyploid species

Premise of the study: Nuclear microsatellites (nSSRs) were designed for Guibourtia tessmannii (Fabaceae, Caesalpinioideae), a highly exploited African timber tree, to study population genetic structure and gene flow. Methods and Results: We developed 16 polymorphic nSSRs from a genomic library tested in three populations of G. tessmannii and two populations of G. coleosperma. These nSSRs display three to 14 alleles per locus (mean 8.94) in G. tessmannii. Cross-amplification tests in nine congeneric species demonstrated that the genus Guibourtia contains diploid and polyploid species. Flow cytometry results combined with nSSR profiles suggest that G. tessmannii is octoploid. Conclusions: nSSRs revealed that African Guibourtia species include both diploid and polyploid species. These markers will provide information on the mating system, patterns of gene flow, and genetic structure of African Guibourtia species

Instrument for bone mineral measurement using a microprocessor as the control and arithmetic element

A self-contained instrument for the determination of bone mineral content by photon absorptometry is described. A high-resolution detection system allows measurements to be made at up to 16 photon energies. Control and arithmetic functions are performed by a microprocessor. Analysis capability and limitations are discussed. (auth

Arteriography during ex vivo renal perfusion A complication

A case of bilateral renal-cell carcinoma unsuccessfully treated with bench surgery is reported. The reason for failure was apparently the toxicity of the contrast media used during the ex vivo arteriographic studies. © 1973

Assessment of fine scale population genetic diversity and regeneration in Congo basin logged forests

In the Congo Basin most of the light-demanding timber tree species display a deficit of natural regeneration which is a major handicap for sustainable production and certification. Whilst the majority of scientists investigate abiotic and biotic factors explaining that pattern, we hypothesize that tree population density or individual spatial isolation may also affect the tree fitness through inbreeding. In this study, we integrate ecological and genetic approaches to characterize the regeneration potential of a set of priority timber species by (i) estimating pollen dispersal distances at various tree population densities, and (ii) evaluating the impact of increasing spatial isolation on mating characteristics and tree fitness. The ultimate goal is the proposal of minimum population density that prevents inbreeding consequences. Method This ongoing study focuses on 10 timber species (Pericopsis elata, Milicia excelsa, Baillonella toxisperma, Entandrophragma cylindricum, E. utile, E. angolense, E. candollei, Afzelia bipindensis, Erythrophleum suaveloens, Terminalia superba). The data collection was carried out in the logging concession granted to Pallisco in Cameroon. We established two 400-ha plots, where all individuals (DBH > 10 cm) of the target species were inventoried and mapped. A sample of leave or cambium was collected for each of these individuals, as well as for seedlings to characterize patterns of gene flow using genetic tools (nuclear microsatellites). Dispersal agents were identified by direct observations and camera traps. Germination success was characterized in nursery for seeds collected on trees under an increasing isolation gradient. Results Main dispersal agents (wind, bat, rodent) and predators (rodent) were identified for all the species. The gene flow and germination data is still being analyzed and the main results will be presented in the poster. Conclusion Our data will allow characterizing the reproductive biology of a set of important timber species from the Congo basin. These information will strengthen sustainable forest management and the application of certification by adjusting harvesting norms through the use of scientifically-relevant data. In particular, we will tentatively define a maximum distance to be maintained between two adults to allow a qualitative reproduction

Complex-valued Burgers and KdV-Burgers equations

Spatially periodic complex-valued solutions of the Burgers and KdV-Burgers equations are studied in this paper. It is shown that for any sufficiently large time T, there exists an explicit initial data such that its corresponding solution of the Burgers equation blows up at T. In addition, the global convergence and regularity of series solutions is established for initial data satisfying mild conditions

Sturmian morphisms, the braid group B_4, Christoffel words and bases of F_2

We give a presentation by generators and relations of a certain monoid generating a subgroup of index two in the group Aut(F_2) of automorphisms of the rank two free group F_2 and show that it can be realized as a monoid in the group B_4 of braids on four strings. In the second part we use Christoffel words to construct an explicit basis of F_2 lifting any given basis of the free abelian group Z^2. We further give an algorithm allowing to decide whether two elements of F_2 form a basis or not. We also show that, under suitable conditions, a basis has a unique conjugate consisting of two palindromes.Comment: 25 pages, 4 figure

Absolute values of the London penetration depth in YBa2Cu3O6+y measured by zero field ESR spectroscopy on Gd doped single crystals

Zero-field electron spin resonance (ESR) of dilute Gd ions substituted for Y in the cuprate superconductor YBa$_2$Cu$_3$O$_{\rm 6+y}$ is used as a novel technique for measuring the absolute value of the low temperature magnetic penetration depth $\lambda(T\to 0)$. The Gd ESR spectrum of samples with $\approx 1$ substitution was obtained with a broadband microwave technique that measures power absorption bolometrically from 0.5 GHz to 21 GHz. This ESR spectrum is determined by the crystal field that lifts the level degeneracy of the spin 7/2 Gd$^{3+}$ ion and details of this spectrum provide information concerning oxygen ordering in the samples. The magnetic penetration depth is obtained by relating the number of Gd ions exposed to the microwave magnetic field to the frequency-integrated intensity of the observed ESR transitions. This technique has allowed us to determine precise values of $\lambda$ for screening currents flowing in the three crystallographic orientations ($\hat a$, $\hat b$ and $\hat c$) in samples of Gd$_{\rm x}$Y$_{\rm 1-x}$Ba$_2$Cu$_3$O$_{6+{\rm y}}$ of three different oxygen contents ${\rm y}=0.993$ ($T_c = 89$ K), ${\rm y}=0.77$ ($T_c=75$ K) and ${\rm y}=0.52$ ($T_c=56$ K). The in-plane values are found to depart substantially from the widely reported relation $T_c\propto 1/\lambda^2$.Comment: 14 pages, 12 figures; version to appear in PR

Exploring the relationship between hydrograph characteristics and the time evolution of sand bed morphology

The development of sand bed morphology in response to steady uniform flow is well described by phase diagrams. This includes the predications of bedform spacing, and individual bedform characteristics, both important parameters on describing flow resistance. However during time varying flow such as that experienced during the passage of a flood wave, the implicit assumption that bed form adjustment tracks changes to flow does not hold true with evidence of bed form hysteresis in flood cycles. Consequently there is a need to understand which characteristics of unsteady flow drive the disequilibrium between bedform geometries and the hydraulic conditions. This paper describes a series of experiments set up to identify the impacts of hydrograph characteristics on the morphodynamic evolution of alluvial dunes. A series of mobile bed experiments were undertaken in a 16m long, 1.6m wide flume, using a uniform sediment of medium sand (D50 of 450μm). Sediment was water worked under steady flow until quasi equilibrium bed conditions were met whereupon a hydrograph consisting of a rising and falling rising limb was applied. At the end of the hydrograph a period of steady flow was once again run until equilibrium conditions were attained. During the experiments profiles of bed morphology were measured continuously along a 5m long, 0.6m wide transect taken along the channel centreline using ultrasonic sensors. Flow was measured with a suite of Acoustic Doppler Velocimeters and suspended sediment with Acoustic Backscatter Sensors. Results are reported for two different hydrographs applied to two different initial starting conditions. The impact of the differing rising-limb characteristics are discussed in terms of differences between equilibrium bed morphologies, flow field characteristics and suspended sediment concentrations

What do young athletes implicitly understand about psychological skills?

One reason sport psychologists teach psychological skills is to enhance performance in sport; but the value of psychological skills for young athletes is questionable because of the qualitative and quantitative differences between children and adults in their understanding of abstract concepts such as mental skills. To teach these skills effectively to young athletes, sport psychologists need to appreciate what young athletes implicitly understand about such skills because maturational (e.g., cognitive, social) and environmental (e.g., coaches) factors can influence the progressive development of children and youth. In the present qualitative study, we explored young athletes’ (aged 10–15 years) understanding of four basic psychological skills: goal setting, mental imagery, self-talk, and relaxation. Young athletes (n = 118: 75 males and 43 females) completed an open-ended questionnaire to report their understanding of these four basic psychological skills. Compared with the older youth athletes, the younger youth athletes were less able to explain the meaning of each psychological skill. Goal setting and mental imagery were better understood than self-talk and relaxation. Based on these findings, sport psychologists should consider adapting interventions and psychoeducational programs to match young athletes’ age and developmental level