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Buoyancy
Terms modified by Buoyancy Selected AbstractsContribution of gravitational potential energy differences to the global stress fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009Attreyee Ghosh SUMMARY Modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics. Both these sources of buoyancies are important in generating the lithospheric stress field. However, these sources and the contribution that they make are dependent on a number of variables, such as the role of lateral strength variation in the lithosphere, the reference level for computing the gravitational potential energy per unit area (GPE) of the lithosphere, and even the definition of deviatoric stress. For the mantle contribution, much depends on the mantle convection model, including the role of lateral and radial viscosity variations, the spatial distribution of density buoyancies, and the resolution of the convection model. GPE differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography. The global lithospheric stress field can thus be divided into (1) stresses associated with GPE differences (including the contribution from radial basal tractions) and (2) stresses associated with the contribution of horizontal basal tractions. In this paper, we investigate only the contribution of GPE differences, both with and without the inferred contribution of radial basal tractions. We use the Crust 2.0 model to compute GPE values and show that these GPE differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes, as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the Earth's plate boundary zones. We argue that GPE differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere; shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection. Deviatoric stress magnitudes arising from GPE differences are in the range of 1,4 TN m,1, a part of which is contributed by dynamic topography. The EGM96 geoid data set is also used as a rough proxy for GPE values in the lithosphere. However, GPE differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators. GPE values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography. Another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating GPE. We also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2-D approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress. [source] Numerical study of influences of buoyancy and solutal Marangoni convection on flow structures in a germanium-silicon floating zoneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2005K. Lin Abstract This paper presents a numerical study of Marangoni flows in a floating zone of germanium-silicon crystals, which was performed by using a commercial finite element program FIDADTM. The numerical results point out that for fluids with a small Pr number the influence of buoyancy forces cannot be ignored in the numerical model. Furthermore, the competition between the thermocapillary (TC) and solutocapillary (SC) flows in the floating zones was qualitatively examined. If the TC flow is as strong as that in the Si-rich floating zone, the SC flow may be restricted to the bottom area near the free surface. Otherwise, the SC flow may overcome the TC flow and induce a surface transfer of species. The numerical predictions agree well with the previous experiment results. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Aquatic exercise for children with cerebral palsyDEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 12 2005Michelle Kelly BScPT MSc Exercise for children with cerebral palsy (CP) is gaining popularity among pediatric physical therapists as an intervention choice. Exercise in water appeals to children with CP because of the unique quality of buoyancy of water that reduces joint loading and impact, and decreases the negative influences of poor balance and poor postural control. In this paper, research of land-based exercise and aquatic exercise for children with CP is reviewed. Clinically relevant considerations for aquatic exercise programming for children with CP are discussed. [source] An evaluation of actual and simulated smoke propertiesFIRE AND MATERIALS, Issue 2 2005Jill Suo-Anttila Abstract Federal regulations require that aircraft cargo compartment smoke detection systems be certified by testing their operation in flight. For safety reasons, only simulated smoke sources are permitted in these certification tests. To provide insight into smoke detection certification in cargo compartments, this research investigates the morphology, transport and optical properties of actual and simulated smoke sources. Experimental data show the morphology of the particulate in smoke from flaming fires is considerably different from simulated smoke. Although the detection of smoldering fires is important as well, only a qualitative assessment and comparison of smoldering sources was possible; therefore, efforts were concentrated on the quantitative comparison of smoke from flaming fires and smoke generators. The particulate for all three different flaming fires was solid with similar morphological properties. Simulated smoke was composed of relatively large liquid droplets, and considerably different size droplets can be produced using a single machine. Transport behavior modeling showed that both the actual and simulated smoke particulates are sufficiently small to follow the overall gas flow. However, actual smoke transport will be buoyancy driven due to the increased temperature, while the simulated smoke temperature is typically low and the release may be momentum driven. The morphology of the actual and simulated smoke were then used to calculate their optical properties. In contrast to the actual smoke from a flaming fire, which is dominated by absorption, all of the extinction for the simulated smoke is due to scattering. This difference could have an impact on detection criteria and hence the alarm time for photoelectic smoke detectors since they alarm based on the scattering properties of the smoke. Copyright © 2004 John Wiley & Sons, Ltd. [source] Process-based model for direct and indirect effects of hydrographic conditions on Central Baltic cod (Gadus morhua) egg mortalityFISHERIES OCEANOGRAPHY, Issue 2 2008K. H. ANDERSEN Abstract A process-oriented model for the mortality of eggs of cod Gadus morhua in the Central Baltic Sea is developed, based on a synthesis of existing knowledge of the effects of salinity, oxygen and predation by sprat Sprattus sprattus. The models show the importance of the vertical and temporal overlap between eggs and predations. Effects related to the changing buoyancy of the eggs due to age and size of the mother fish, batch number and stock structure are not of major importance for the egg survival of this stock. It is demonstrated that under the present high sprat predation pressure, the observed delay in spawning time has increased egg survival. [source] Modelling the effect of buoyancy on the transport of anchovy (Engraulis capensis) eggs from spawning to nursery grounds in the southern Benguela: an IBM approachFISHERIES OCEANOGRAPHY, Issue 3 2003C. Parada Abstract An individual-based model (IBM) was used to investigate the effects of physical and biological variables on the transport via a jet current of anchovy (Engraulis capensis) eggs from spawning to the nursery grounds in the southern Benguela ecosystem. As transport of eggs and early larvae is considered to be one of the major factors impacting on anchovy recruitment success, this approach may be useful to understand further the recruitment variability in this economically and ecologically important species. By coupling the IBM to a 3D hydrodynamic model of the region called Plume, and by varying parameters such as the spatial and temporal location of spawning, particle buoyancy, and the depth range over which particles were released, we could assess the influences of these parameters on transport success. A sensitivity analysis using a General Linear Model identified the primary determinants of transport success in the various experimental simulations, and model outputs were examined and compared with patterns observed in field studies. Model outputs compared well with observed patterns of vertical and horizontal egg distribution. Particle buoyancy and area of particle release were the major single determinants of transport success, with an egg density of 1.025 g cm,3 maximizing average particle transport success and the western Agulhas Bank being the most successful spawning area. This IBM may be useful as a generic prototype for other upwelling ecosystems. [source] Transport and settlement of organic matter in small streamsFRESHWATER BIOLOGY, Issue 2 2010TRENT M. HOOVER Summary 1.,After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (,flexible' red alder leaves and three ,stiff' particle types , Douglas-fir needles, red cedar fronds and Douglas-fir branch pieces). 2.,Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas-fir needles and red cedar fronds, which all reached constant still-water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3.,We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ,riffle' than a slow, deep ,pool'. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4.,These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second-order coastal stream. 5.,When the experimental channel and in-stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams. [source] Subaqueous hydrochory: open-channel hydraulic modelling of non-buoyant seed movementFRESHWATER BIOLOGY, Issue 11 2008SCOTT H. MARKWITH Summary 1. Subaqueous transport may be a significant dispersal and migration mechanism of non-buoyant seeds of aquatic and riparian plants, and also secondary transport of seeds once they have lost buoyancy, but the efficiency of this difficult to observe process is largely unexamined. This study uses hydraulic modelling to establish the discharges that move the non-buoyant seeds of Hymenocallis coronaria as bedload or suspended load; uses stream gauge data to examine the frequency of effective discharges from late June to late September, the seed maturation and germination period; and the potential transport distance of the seeds. 2. The results show that the majority of non-buoyant seeds of H. coronaria can be transported as bedload through entire modelled stream reaches of lengths 10.8, 18 and 14.4 km with the 0.5 year return interval flow. Bedload apparently has the ability to move seeds over great distances, and may be a substantial factor determining the genetic structure, demography and dynamics of populations and communities. However, prolonged movement of non-buoyant seeds in suspension appears to be quite rare. 3. Although insect mediated pollination and biochory occur concurrently with bedload transport, bedload transport alone may be sufficient to account for the established gene flow rate of H. coronaria. The potential transport distance of many of the seeds exceed that between populations, and migration may occur more frequently than the species' generation time. 4. This is the first known study to use open-channel hydraulic modelling and sediment transport analysis to determine the effectiveness of non-buoyant seed transport. This method of analysis shows promise for application in other contexts, and especially where flow management is a critical issue for maintenance of rare species. [source] Contribution of gravitational potential energy differences to the global stress fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009Attreyee Ghosh SUMMARY Modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics. Both these sources of buoyancies are important in generating the lithospheric stress field. However, these sources and the contribution that they make are dependent on a number of variables, such as the role of lateral strength variation in the lithosphere, the reference level for computing the gravitational potential energy per unit area (GPE) of the lithosphere, and even the definition of deviatoric stress. For the mantle contribution, much depends on the mantle convection model, including the role of lateral and radial viscosity variations, the spatial distribution of density buoyancies, and the resolution of the convection model. GPE differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography. The global lithospheric stress field can thus be divided into (1) stresses associated with GPE differences (including the contribution from radial basal tractions) and (2) stresses associated with the contribution of horizontal basal tractions. In this paper, we investigate only the contribution of GPE differences, both with and without the inferred contribution of radial basal tractions. We use the Crust 2.0 model to compute GPE values and show that these GPE differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes, as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the Earth's plate boundary zones. We argue that GPE differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere; shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection. Deviatoric stress magnitudes arising from GPE differences are in the range of 1,4 TN m,1, a part of which is contributed by dynamic topography. The EGM96 geoid data set is also used as a rough proxy for GPE values in the lithosphere. However, GPE differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators. GPE values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography. Another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating GPE. We also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2-D approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress. [source] Subducted slabs and lateral viscosity variations: effects on the long-wavelength geoidGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009Nicola Tosi SUMMARY The characteristic broad local maxima exhibited by the long-wavelength geoid over subduction zones are investigated with a numerical model of mantle flow. In a spherical axisymmetric geometry, a synthetic model of buoyancy driven subduction is used to test the effects on the geoid caused by the depth of penetration of the lithosphere into the mantle, by the viscosity stratification and by lateral viscosity variations (LVV) in the lithosphere, upper and lower mantle. The presence of anomalous slab density in the lower mantle guarantees geoid amplitudes comparable with the observations, favouring the picture of slabs that penetrate the transition zone and sink into the deep mantle. The viscosity of the lower mantle controls the long-wavelength geoid to the first order, ensuring a clear positive signal when it is at least 30-times greater than the upper-mantle viscosity. The presence of LVV in the lithosphere, in the form of weak plate margins, helps to increase the contribution of the surface topography, causing a pronounced reduction of the geoid. Localized LVV associated with the cold slab play a secondary role if they are in the upper mantle. On the other hand, highly viscous slabs in the lower mantle exert a large influence on the geoid. They cause its amplitude to increase dramatically, way beyond the values typically observed over subduction zones. Long-wavelength flow becomes less vigorous as the slab viscosity increases. Deformation in the upper mantle becomes more localized and power is transferred to short wavelengths, causing the long-wavelength surface topography to diminish and the total geoid to increase. Slabs may be then weakened in the lower mantle or retain their high viscosity while other mechanisms act to lower the geoid. It is shown that a phase change from perovskite to post-perovskite above the core,mantle boundary can cause the geoid to reduce significantly, thereby helping to reconcile models and observations. [source] Evaluating MT3DMS for Heat Transport Simulation of Closed Geothermal SystemsGROUND WATER, Issue 5 2010Jozsef Hecht-Méndez Owing to the mathematical similarities between heat and mass transport, the multi-species transport model MT3DMS should be able to simulate heat transport if the effects of buoyancy and changes in viscosity are small. Although in several studies solute models have been successfully applied to simulate heat transport, these studies failed to provide any rigorous test of this approach. In the current study, we carefully evaluate simulations of a single borehole ground source heat pump (GSHP) system in three scenarios: a pure conduction situation, an intermediate case, and a convection-dominated case. Two evaluation approaches are employed: first, MT3DMS heat transport results are compared with analytical solutions. Second, simulations by MT3DMS, which is finite difference, are compared with those by the finite element code FEFLOW and the finite difference code SEAWAT. Both FEFLOW and SEAWAT are designed to simulate heat flow. For each comparison, the computed results are examined based on residual errors. MT3DMS and the analytical solutions compare satisfactorily. MT3DMS and SEAWAT results show very good agreement for all cases. MT3DMS and FEFLOW two-dimensional (2D) and three-dimensional (3D) results show good to very good agreement, except that in 3D there is somewhat deteriorated agreement close to the heat source where the difference in numerical methods is thought to influence the solution. The results suggest that MT3DMS can be successfully applied to simulate GSHP systems, and likely other systems with similar temperature ranges and gradients in saturated porous media. [source] An unsteady flow structure on a heated rotating disk under mixed convectionHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2005Noriyuki Furuichi Abstract A flow field under mixed convection on a heated rotating disk has been measured using an ultrasonic velocity profiler (UVP). The measured velocity field is a spatio-temporal one as a function of radial coordinates and time. The objective of this paper is to clarify the vortex structure caused by the instability between buoyancy and centrifugal force. The vortex appears under typical conditions of Reynolds numbers and Grashof numbers and it moves toward the outside of the disk. This behavior can be classified into two patterns. The size of the vortex structure decreases with an increasing Reynolds number and increases with the Grashof number. The traveling velocity of the vortex increases with the Grashof number. Moreover, it decreases with an increasing Reynolds number in spite of increasing centrifugal force. According to these results, the region dominated by natural, forced, and mixed convection is classified in the relationship between Reynolds and Grashof numbers. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(6): 407,418, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20074 [source] Impact of spatial variations of land surface parameters on regional evaporation: a case study with remote sensing dataHYDROLOGICAL PROCESSES, Issue 9 2001Hussein O. Farah Abstract Most precipitation in watersheds is consumed by evaporation, thus techniques to appraise regional evaporation are important to assess the availability of water resources. Many algorithms to estimate evaporation from remotely sensed spectral data have been developed in the recent past. In addition to differences in the physical parameterization of surface fluxes, these algorithms have different solutions for describing spatial variations of the parameters in the soil,vegetation,atmosphere,transfer (SVAT) continuum. In this study, the necessity to spatially distinguish SVAT parameters for computing surface heat fluxes is analysed for the Naivasha watershed in the Kenyan Rift Valley. Landsat Thematic Mapper (TM) spectral data have been used to first delineate the watershed into 15 hydrological units using surface temperature, normalized difference vegetation index and surface albedo as attributes. Thereafter, semi-empirical relationships between these TM-based parameters and other SVAT parameters have been applied to compute the spatial variation of SVAT parameters and the associated evaporation from the different hydrological units. The impact of using watershed-constant or watershed-distributed SVAT parameters on the fluxes is analysed. The determination of watershed averaged evaporation with area-aggregated SVAT parameters is feasible without significant loss of accuracy. Distributed evaporation in heterogeneous watersheds, however, can be investigated only with remote sensing flux algorithms that can account for spatially variable air temperature, surface roughness, surface albedo and the stability correction of the temperature profile due to buoyancy. Erroneous results can be expected if area-aggregated SVAT parameters are used to calculate local evaporation. As most of the recently developed remote sensing flux algorithms are based on areal constant SVAT parameters, direct applications in watersheds are still limited. Copyright © 2001 John Wiley & Sons, Ltd. [source] Stabilized finite element formulation of buoyancy driven incompressible flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 5 2002S. Aliabadi Abstract Streamline-upwind/Petrov,Galerkin finite element method is developed for buoyancy-driven incom-pressible flows with heat and mass transfer. The stabilized finite element formulations are implemented in parallel using message passing interface libraries. To measure the accuracy of the method, we solve a 2D numerical example of natural convection flows at moderate to high Rayleigh numbers. The 3D applications include the dispersion of smoke from a chimney and within a stadium. Copyright © 2002 John Wiley & Sons, Ltd. [source] Dendritic solidification of binary alloys with free and forced convectionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2005P. Zhao Abstract Dendritic solidification with forced convection and free convection driven by contraction and thermo- solutal buoyancy is simulated in two-dimensional space using a sharp-interface model. Both pure substances and alloys are considered. The model is formulated using the finite element method and works directly with primitive variables. The coupled energy- and solutal concentration-equations, along with the Navier,Stokes equations for incompressible flow, are solved using different meshes. Temperature is solved in a fixed mesh that covers the whole domain (solid + liquid) where the solid,liquid interface is explicitly tracked using marker points. The concentration and momentum equations are solved in the liquid region using an adaptive mesh of triangular elements that conforms to the interface. The velocity boundary conditions are applied directly on the interface. The model is validated using a series of problems that have analytical, experimental and numerical results. Four simulations are presented: (1) crystal growth of succinonitrile with thermal convection under two small undercoolings; (2) dendritic growth into an undercooled pure melt with a uniform forced flow; (3) equiaxial dendritic growth of a pure substance and an alloy with contraction-induced convection; and (4) directional solidification of Pb,0.2 wt% Sb alloy with convection driven by the combined action of contraction, thermal and solutal buoyancy. Some of the simulation results are compared to those reported using other methods including the phase-field method; others are new. In each case, the effects of convection on dendritic solidification are analysed. Copyright © 2005 John Wiley & Sons, Ltd. [source] A mass-conserving Level-Set method for modelling of multi-phase flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2005S. P. van der Pijl Abstract A mass-conserving Level-Set method to model bubbly flows is presented. The method can handle high density-ratio flows with complex interface topologies, such as flows with simultaneous occurrence of bubbles and droplets. Aspects taken into account are: a sharp front (density changes abruptly), arbitrarily shaped interfaces, surface tension, buoyancy and coalescence of droplets/bubbles. Attention is paid to mass-conservation and integrity of the interface. The proposed computational method is a Level-Set method, where a Volume-of-Fluid function is used to conserve mass when the interface is advected. The aim of the method is to combine the advantages of the Level-Set and Volume-of-Fluid methods without the disadvantages. The flow is computed with a pressure correction method with the Marker-and-Cell scheme. Interface conditions are satisfied by means of the continuous surface force methodology and the jump in the density field is maintained similar to the ghost fluid method for incompressible flows. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratiosINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004M. A. Habib Abstract Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time-averaged governing equations of 2-D axi-symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle-tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd. [source] Peat bog restoration by floating raft formation: the effects of groundwater and peat qualityJOURNAL OF APPLIED ECOLOGY, Issue 3 2002Alfons J. P. Smolders Summary 1,A prerequisite for the restoration of desiccated bog remnants is rewetting the peat surface. Frequently in Europe, extensive areas are flooded in order to maximize water retention, and growth of peat mosses is often observed in the shallow zones. In deeper waters, regeneration appears to depend on whether residual peat will become buoyant and form floating rafts. 2,In order to study the initial stages of peat bog regeneration, conditions required for peat buoyancy were studied on peat monoliths collected from three cut-over bog remnants in the Netherlands. The effects of different peat quality and water chemistry on buoyancy of the monoliths, as well as growth of Sphagnum cuspidatum and nutrient availability, were followed in a glasshouse experiment. 3,Both groundwater and peat quality affected the buoyancy of the monoliths and the growth of S. cuspidatum. When groundwater containing bicarbonate (1 mmol l,1 HCO3,, pH 6·0) was applied, the pH of peat monoliths increased from c. 3·5 to c. 4·5 due to acid buffering. As a result, two of the peat types became more buoyant and the concentration, production and emissions of methane (CH4) increased. It was concluded that the increase in CH4 production, induced by the increased pH, was responsible for the buoyancy. 4,When groundwater contained both HCO3, (1 mmol l,1) and sulphate (1 mmol l,1), pH was further increased to approximately pH 5·0 due to alkalinity generated by the SO42, reduction process. CH4 production, however, decreased because of interference from the SO42,, as confirmed in additional incubation experiments. Phosphate concentrations, however, greatly increased in the HCO3,/SO42, addition treatment due to the interaction between sulphide and iron phosphate precipitates. 5,In one of the peat types, treatments did not influence CH4 production and buoyancy, most probably because of its low decomposability. The chemical characteristics of the peat, notably the concentrations of lignin and soluble phenolics as well as C:N, C:P and C:K ratios, were all higher than in the other two peat types. 6,The increase of S. cuspidatum biomass during the experiment appeared to be strongly related to the N:P ratios of the capitula, which differed considerably among the three peat types. 7,We conclude that when bog remnants are inundated the prospects for bog regeneration are largely determined by peat quality and water chemistry. Peat mats with low concentration of lignin and phenolics and low C:N ratios are most likely to become buoyant in water with a higher pH, so providing suitable environments for Sphagnum species. When peat quality is inadequate, either shallow inundation or the addition of suitable peat from elsewhere is indicated. [source] Diving in shallow water: the foraging ecology of darters (Aves: Anhingidae)JOURNAL OF AVIAN BIOLOGY, Issue 4 2007Peter G. Ryan Diving birds have to overcome buoyancy, especially when diving in shallow water. Darters and anhingas (Anhingidae) are specialist shallow-water divers, with adaptations for reducing their buoyancy. Compared to closely-related cormorants (Phalacrocoracidae), darters have fully wettable plumage, smaller air sacs and denser bones. A previous study of darter diving behaviour reported no relationship between dive duration and water depth, contrary to optimal dive models. In this study I provide more extensive observations of African darters Anhinga melanogaster rufa diving in water<5 m deep at two sites. Dive duration increases with water depth at both sites, but the relationship is weak. Dives were longer than dives by cormorants in water of similar depth (max 108 s in water 2.5 m deep), with dives of up to 68 s observed in water<0.5 m deep. Initial dives in a bout were shorter than expected, possibly because their plumage was not fully saturated. Dive efficiency (dive:rest ratio) was 5,6, greater than cormorants (2.7±0.4 for 18 species) and other families of diving birds (average 0.2,4.3). Post-dive recovery periods increased with dive duration, but only slowly, resulting in a strong increase in efficiency with dive duration. All dives are likely to fall within the theoretical anaerobic dive limit. Foraging bouts were short (17.8±4.3 min) compared to cormorants, with birds spending 80±5% of time underwater. Darters take advantage of their low buoyancy to forage efficiently in shallow water, and their slow, stealthy dives are qualitatively different from those of other diving birds. However, they are forced to limit the duration of foraging bouts by increased thermoregulatory costs associated with wettable plumage. [source] Tufted ducks Aythya fuligula do not control buoyancy during divingJOURNAL OF AVIAN BIOLOGY, Issue 3 2005Lewis G. Halsey Work against buoyancy during submergence is a large component of the energy costs for shallow diving ducks. For penguins, buoyancy is less of a problem, however they still seem to trade-off levels of oxygen stores against the costs and benefits of buoyant force during descent and ascent. This trade-off is presumably achieved by increasing air sac volume and hence pre-dive buoyancy (Bpre) when diving deeper. Tufted ducks, Aythya fuligula, almost always dive with nearly full oxygen stores so these cannot be increased. However, the high natural buoyancy of tufted ducks guarantees a passive ascent, so they might be expected to decrease Bpre before particularly deep, long dives to reduce the energy costs of diving. Body heat lost to the water can also be a cause of substantial energy expenditure during a dive, both through dissipation to the ambient environment and through the heating of ingested food and water. Thus dive depth (dd), duration and food type can influence how much heat energy is lost during a dive. The present study investigated the relationship between certain physiological and behavioural adjustments by tufted ducks to dd and food type. Changes in Bpre, deep body temperature (Tb) and dive time budgeting of four ducks were measured when diving to two different depths (1.5 and 5.7 m), and for two types of food (mussels and mealworms). The hypothesis was that in tufted ducks, Bpre decreases as dd increases. The ducks did not change Bpre in response to different diving depths, and thus the hypothesis was rejected. Tb was largely unaffected by dives to either depth. However, diving behaviour changed at the greater dd, including an increase in dive duration and vertical descent speed. Behaviour also changed depending on the food type, including an increase in foraging duration and vertical descent speed when mussels were present. Behavioural changes seem to represent the major adjustment made by tufted ducks in response to changes in their diving environment. [source] Energy density of anchovy Engraulis encrasicolus in the Bay of BiscayJOURNAL OF FISH BIOLOGY, Issue 3 2009J. Dubreuil The energy density (ED) of anchovy Engraulis encrasicolus in the Bay of Biscay was determined by direct calorimetry and its evolution with size, age and season was investigated. The water content and energy density varied seasonally following opposite trends. The ED g,1 of wet mass (MW) was highest at the end of the feeding season (autumn: c. 8 kJ g,1MW) and lowest in late winter (c. 6 kJ g,1MW). In winter, the fish lost mass, which was partially replaced by water, and the energy density decreased. These variations in water content and organic matter content may have implications on the buoyancy of the fish. The water content was the major driver of the energy density variations for a MW basis. A significant linear relationship was established between ED g,1 (y) and the per cent dry mass (MD; x): y =,4·937 + 0·411x. In the light of the current literature, this relationship seemed to be not only species specific but also ecosystem specific. Calibration and validation of fish bioenergetics models require energy content measurements on fish samples collected at sea. The present study provides a first reference for the energetics of E. encrasicolus in the Bay of Biscay. [source] Variation in the diet of the Patagonian toothfish with size, depth and season around the Falkland IslandsJOURNAL OF FISH BIOLOGY, Issue 2 2003A. Arkhipkin The ontogenetic and seasonal variations in the feeding spectrum were studied in 756 specimens of the Patagonian toothfish Dissostichus eleginoides (16,159 cm total length, LT) collected on the shelf, continental slope and bathyal waters (67,1960 m, depth range) around the Falkland Islands between April 1999 and August 2002. On the shelf, small toothfish (<40 cm LT) were active predators taking mostly one relatively large prey item at a time (mainly near-bottom Patagonotothen ramsayi and Loligo gahi). Medium-size toothfish (40,60 cm LT) fed on the same prey, but the number of prey items increased to 1,2 items per fish. Large toothfish (>60 cm LT) switched their diet to other large pelagic fishes occurring near the bottom (Macruronus magellanicus and Micromesistius australis australis), again taking mostly one prey item at a time. The diet of medium-size D. eleginoides on the shelf varied seasonally depending on the abundance and migrations of the major prey species. Patagonotothen ramsayi was abundant in the diet throughout the year, whereas L. gahi appeared only from February to October during its offshore seasonal migrations to the depth range of D. eleginoides. During November to January, L. gahi migrated inshore to spawn and disappeared from the toothfish diet, being substituted by M. australis australis which dispersed on the shelf after spawning. After its ontogenetic descent to the lower part of the continental slope (500,1000 m depths), toothfish took less active (than on the shelf) fishes such as Antimora rostrata whilst also feeding on active near-bottom macrourids and skates. In their deepest habitat (>1000 m depths), toothfish became a typical opportunistic predator, feeding mainly on relatively small and inactive fishes, squids and prawn-like crustaceans Acanthephyra pelagica and Thymops birsteini. Decrease in hunting activity with depth could be related to a specific adaptation to keep neutral buoyancy by increase of lipid content in white muscles of D. eleginoides with size. [source] The role of viscous heating in Barrovian metamorphism of collisional orogens: thermomechanical models and application to the Lepontine Dome in the Central AlpsJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2005J.-P. BURG Abstract Thermal models for Barrovian metamorphism driven by doubling the thickness of the radiogenic crust typically meet difficulty in accounting for the observed peak metamorphic temperature conditions. This difficulty suggests that there is an additional component in the thermal budget of many collisional orogens. Theoretical and geological considerations suggest that viscous heating is a cumulative process that may explain the heat deficit in collision orogens. The results of 2D numerical modelling of continental collision involving subduction of the lithospheric mantle demonstrate that geologically plausible stresses and strain rates may result in orogen-scale viscous heat production of 0.1 to >1 ,W m,3, which is comparable to or even exceeds bulk radiogenic heat production within the crust. Thermally induced buoyancy is responsible for crustal upwelling in large domes with metamorphic temperatures up to 200 °C higher than regional background temperatures. Heat is mostly generated within the uppermost mantle, because of large stresses in the highly viscous rocks deforming there. This thermal energy may be transferred to the overlying crust either in the form of enhanced heat flow, or through magmatism that brings heat into the crust advectively. The amplitude of orogenic heating varies with time, with both the amplitude and time-span depending strongly on the coupling between heat production, viscosity and collision strain rate. It is argued that geologically relevant figures are applicable to metamorphic domes such as the Lepontine Dome in the Central Alps. We conclude that deformation-generated viscous dissipation is an important heat source during collisional orogeny and that high metamorphic temperatures as in Barrovian type metamorphism are inherent to deforming crustal regions. [source] The contribution of the swimbladder to buoyancy in the adult zebrafish (Danio rerio): A morphometric analysisJOURNAL OF MORPHOLOGY, Issue 6 2008George N. Robertson Abstract Many teleost fishes use a swimbladder, a gas-filled organ in the coelomic cavity, to reduce body density toward neutral buoyancy, thus minimizing the locomotory cost of maintaining a constant depth in the water column. However, for most swimbladder-bearing teleosts, the contribution of this organ to the attainment of neutral buoyancy has not been quantified. Here, we examined the quantitative contribution of the swimbladder to buoyancy and three-dimensional stability in a small cyprinid, the zebrafish (Danio rerio). In aquaria during daylight hours, adult animals were observed at mean depths from 10.1 ± 6.0 to 14.2 ± 5.6 cm below the surface. Fish mass and whole-body volume were linearly correlated (r2 = 0.96) over a wide range of body size (0.16,0.73 g); mean whole-body density was 1.01 ± 0.09 g cm,3. Stereological estimations of swimbladder volume from linear dimensions of lateral X-ray images and direct measurements of gas volumes recovered by puncture from the same swimbladders showed that results from these two methods were highly correlated (r2 = 0.85). The geometric regularity of the swimbladder thus permitted its volume to be accurately estimated from a single lateral image. Mean body density in the absence of the swimbladder was 1.05 ± 0.04 g cm,3. The swimbladder occupied 5.1 ± 1.4% of total body volume, thus reducing whole-body density significantly. The location of the centers of mass and buoyancy along rostro-caudal and dorso-ventral axes overlapped near the ductus communicans, a constriction between the anterior and posterior swimbladder chambers. Our work demonstrates that the swimbladder of the adult zebrafish contributes significantly to buoyancy and attitude stability. Furthermore, we describe and verify a stereological method for estimating swimbladder volume that will aid future studies of the functions of this organ. J Morphol., 2008. © 2008 Wiley-Liss, Inc. [source] Development of the swimbladder and its innervation in the zebrafish, Danio rerioJOURNAL OF MORPHOLOGY, Issue 11 2007G.N. Robertson Abstract Many teleosts including zebrafish, Danio rerio, actively regulate buoyancy with a gas-filled swimbladder, the volume of which is controlled by autonomic reflexes acting on vascular, muscular, and secretory effectors. In this study, we investigated the morphological development of the zebrafish swimbladder together with its effectors and innervation. The swimbladder first formed as a single chamber, which inflated at 1,3 days posthatching (dph), 3.5,4 mm body length. Lateral nerves were already present as demonstrated by the antibody zn-12, and blood vessels had formed in parallel on the cranial aspect to supply blood to anastomotic capillary loops as demonstrated by Tie-2 antibody staining. Neuropeptide Y-(NPY-) like immunoreactive (LIR) fibers appeared early in the single-chambered stage, and vasoactive intestinal polypeptide (VIP)-LIR fibers and cell bodies developed by 10 dph (5 mm). By 18 dph (6 mm), the anterior chamber formed by evagination from the cranial end of the original chamber; both chambers then enlarged with the ductus communicans forming a constriction between them. The parallel blood vessels developed into an arteriovenous rete on the cranial aspect of the posterior chamber and this region was innervated by zn-12-reactive fibers. Tyrosine hydroxylase- (TH-), NPY-, and VIP-LIR fibers also innervated this area and the lateral posterior chamber. Innervation of the early anterior chamber was also demonstrated by VIP-LIR fibers. By 25,30 dph (8,9 mm), a band of smooth muscle formed in the lateral wall of the posterior chamber. Although gas in the swimbladder increased buoyancy of young larvae just after first inflation, our results suggest that active control of the swimbladder may not occur until after the formation of the two chambers and subsequent development and maturation of vasculature, musculature and innervation of these structures at about 28,30 dph. J. Morphol., 2007. © 2007 Wiley-Liss, Inc. [source] Kinetics of microbubble,solid surface interaction and attachmentAICHE JOURNAL, Issue 4 2003Chun Yang Microbubble,solid surface interaction and attachment under the influence of hydrodynamic and physicochemical forces were studied experimentally and theoretically. An impinging-jet technique was developed to measure bubble-attachment flux onto a flat solid surface in an impinging-jet stagnation flow. A video imaging system enables direct observation of the attachment behavior of hydrogen microbubbles onto two different collector surfaces: hydrophilic untreated glass and hydrophobic methylated glass. Experimental results showed that the attachment flux depends on both hydrodynamic flow and electrolyte concentration. A mass-transfer model developed computes bubble-attachment flux, considering hydrodynamic convection, Brownian diffusion, migration under gravitational buoyancy, and DLVO surface forces (that is, van der Waals and electric double-layer forces). At high flow rates, the numerical predictions for attachment rates onto methylated glass generally agreed well with the experimental data. However, a difference exists between theoretical and experimentally determined attachment rates for both untreated and methylated glass when the Reynolds number of the flow is low. Several mechanisms are proposed to account for this discrepancy. [source] Design and evaluation of a dry coated drug delivery system with floating,pulsatile releaseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2008Hao Zou Abstract The objective of this work was to develop and evaluate a floating,pulsatile drug delivery system intended for chronopharmacotherapy. Floating,pulsatile concept was applied to increase the gastric residence of the dosage form having lag phase followed by a burst release. To overcome limitations of various approaches for imparting buoyancy, we generated the system which consisted of three different parts, a core tablet, containing the active ingredient, an erodible outer shell and a top cover buoyant layer. The dry coated tablet consists in a drug-containing core, coated by a hydrophilic erodible polymer which is responsible for a lag phase in the onset of pulsatile release. The buoyant layer, prepared with Methocel® K4M, Carbopol® 934P and sodium bicarbonate, provides buoyancy to increase the retention of the oral dosage form in the stomach. The effect of the hydrophilic erodible polymer characteristics on the lag time and drug release was investigated. Developed formulations were evaluated for their buoyancy, dissolution and pharmacokinetic, as well gamma-scintigraphically. The results showed that a certain lag time before the drug released generally due to the erosion of the dry coated layer. Floating time was controlled by the quantity and composition of the buoyant layer. Both pharmacokinetic and gamma-scintigraphic data point out the capability of the system of prolonged residence of the tablets in the stomach and releasing drugs after a programmed lag time. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:263,273, 2008 [source] Exploring teachers' informal formative assessment practices and students' understanding in the context of scientific inquiryJOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 1 2007Maria Araceli Ruiz-Primo This study explores teachers' informal formative assessment practices in three middle school science classrooms. We present a model for examining these practices based on three components of formative assessment (eliciting, recognizing, and using information) and the three domains linked to scientific inquiry (epistemic frameworks, conceptual structures, and social processes). We describe the informal assessment practices as ESRU cycles,the teacher Elicits a question; the Student responds; the teacher Recognizes the student's response; and then Uses the information collected to support student learning. By tracking the strategies teachers used in terms of ESRU cycles, we were able to capture differences in assessment practices across the three teachers during the implementation of four investigations of a physical science unit on buoyancy. Furthermore, based on information collected in a three-question embedded assessment administered to assess students' learning, we linked students' level of performance to the teachers' informal assessment practices. We found that the teacher who more frequently used complete ESRU cycles had students with higher performance on the embedded assessment as compared with the other two teachers. We conclude that the ESRU model is a useful way of capturing differences in teachers' informal assessment practices. Furthermore, the study suggests that effective informal formative assessment practices may be associated with student learning in scientific inquiry classrooms. © 2006 Wiley Periodicals, Inc. J Res Sci Teach [source] Production, Quality, and Low Temperature Incubation of Eggs of Atlantic Cod Gadus morhua and Haddock Melanogrammus aeglefinus in CaptivityJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 1 2000Lawrence J. Buckley Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus broodstock maintained under altered regimens of temperature and photoperiod spawned up to 8 mo per year. The cod broodstock produced viable embryos from October through June. The haddock broodstock produced viable embryos from December through May. Egg diameters were largest during the middle of the spawning season when water temperature was at a minimum, resulting in an inverse relationship between egg diameter and water temperature in both species. Egg quality was high, as evaluated by buoyancy, fertilization rate, regularity of early cleavage, and percent viable hatch. Low temperature incubation of cod and haddock eggs extended the embryonic period. Cod embryos tolerated a wider range of temperatures than haddock. High mortality (1 90%) was observed before hatching in haddock embryos incubated at 1 C. Atlantic cod embryos hatched at temperatures as low as ,1 C, extending the embryonic period to 59 d. At 8 C Atlantic cod and haddock embryos hatched in 11,12 d. To determine if extending the embryo incubation time by using low temperatures had a detrimental effect, embryos were incubated through hatch at either 1 C or 6 C, and the larvae from both groups reared at 6 C. Growth and early survival of larvae were comparable in both treatments. [source] The role of suture complexity in diminishing strain and stress in ammonoid phragmoconesLETHAIA, Issue 1 2008FABIO VITTORIO DE BLASIO Several hypotheses have been put forward to explain the sinuosity and complexity of suture lines in Ammonoidea. At present, the two principal opponent views maintain either that high complexity was a requisite to reinforce the shell in response to hydrostatic pressure, or that complexity augmented the attachment area for muscles. By using finite element calculations and analytical estimates of simplified ammonoid shell geometries, it is shown that complex suture lines reduced dramatically the strain and the stress in the phragmocone. The calculations lend support to the hypothesis that high sinuosity is an evolutionary response to external pressure. Additionally, it is found that without complex septa, the inward deformation of an ammonoid with thin shell would cause it to shrink in response to pressure and to lose buoyancy by a non-negligible amount. [source] | |||||||||||||||||||||||||