Showing papers on "Water flow published in 2001"

Impact of climate change on hydrological regimes and water resources management in the Rhine basin

Abstract: The International Commission for the Hydrology of the Rhine basin (CHR) hascarried out a researchproject to assess the impact of climate change on the river flow conditionsin the Rhine basin. Along abottom-up line, different detailed hydrological models with hourly and dailytime steps have beendeveloped for representative sub-catchments of the Rhine basin. Along atop-down line, a water balancemodel for the entire Rhine basin has been developed, which calculates monthlydischarges and which wastested on the scale of the major tributaries of the Rhine. Using this set ofmodels, the effects of climatechange on the discharge regime in different parts of the Rhine basin werecalculated using the results ofUKHI and XCCC GCM-experiments. All models indicate the same trends in thechanges: higher winterdischarge as a result of intensified snow-melt and increased winterprecipitation, and lower summerdischarge due to the reduced winter snow storage and an increase ofevapotranspiration. When the resultsare considered in more detail, however, several differences show up. These canfirstly be attributed todifferent physical characteristics of the studied areas, but different spatialand temporal scales used in themodelling and different representations of several hydrological processes(e.g., evapotranspiration,snow melt) are responsible for the differences found as well. Climate changecan affect various socio-economicsectors. Higher temperatures may threaten winter tourism in the lower wintersport areas. The hydrologicalchanges will increase flood risk during winter, whilst low flows during summerwill adversely affectinland navigation, and reduce water availability for agriculture and industry.Balancing the required actionsagainst economic cost and the existing uncertainties in the climate changescenarios, a policy of `no-regretand flexibility' in water management planning and design is recommended, whereanticipatory adaptivemeasures in response to climate change impacts are undertaken in combinationwith ongoing activities.

The Energy Harvesting Eel: a small subsurface ocean/river power generator

Abstract: The Energy Harvesting Eel (Eel) is a new device that uses piezoelectric polymers to convert the mechanical flow energy, available in oceans and rivers, to electrical power. Eel generators make use of the regular trail of traveling vortices behind a bluff body to strain the piezoelectric elements; the resulting undulating motion resembles that of a natural eel swimming. Internal batteries are used to store the surplus energy generated by the Eel for later use by a small, unattended sensor or robot. Because of the properties of commercially available piezoelectric polymers, Eels will be relatively inexpensive and are easily scaleable in size and have the capacity to generate from milli-watts to many watts depending on system size and flow velocity of the local environment. A practical Eel structure has been developed that uses the commercially available piezoelectric polymer, PVDF. Future Eels may use more efficient electrostrictive polymer. Every aspect of the system from the interactions between the hydrodynamics of the water flow and structural elements of the Eel, through the mechanical energy input to the piezoelectric material, and finally the electric power output delivered through an optimized resonant circuit has been modeled and tested. The complete Eel system, complete with a generation and storage system, has been demonstrated in a wave tank. Future work on the Eel will focus on developing and then deploying a small, lightweight, one-watt power generation unit, initially in an estuary and then subsequently in the ocean. Such Eels will have the ability to recharge batteries or capacitors of a distributed robotic group, or remote sensor array, thus extending the mission life indefinitely in regions containing flowing water.

Fluid particle accelerations in fully developed turbulence

Abstract: The motion of fluid particles as they are pushed along erratic trajectories by fluctuating pressure gradients is fundamental to transport and mixing in turbulence. It is essential in cloud formation and atmospheric transport, processes in stirred chemical reactors and combustion systems, and in the industrial production of nanoparticles. The concept of particle trajectories has been used successfully to describe mixing and transport in turbulence, but issues of fundamental importance remain unresolved. One such issue is the Heisenberg-Yaglom prediction of fluid particle accelerations, based on the 1941 scaling theory of Kolmogorov. Here we report acceleration measurements using a detector adapted from high-energy physics to track particles in a laboratory water flow at Reynolds numbers up to 63,000. We find that, within experimental errors, Kolmogorov scaling of the acceleration variance is attained at high Reynolds numbers. Our data indicate that the acceleration is an extremely intermittent variable--particles are observed with accelerations of up to 1,500 times the acceleration of gravity (equivalent to 40 times the root mean square acceleration). We find that the acceleration data reflect the anisotropy of the large-scale flow at all Reynolds numbers studied.

Structural determinants of glomerular permeability.

Abstract: Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the endothelial glycocalyx and epithelial slit diaphragm to the overall hydraulic resistance and macromolecule selectivity and the nanostructural basis for the observed permeability properties of the GBM.

Preferential Flow Paths: Biological Hot Spots in Soils

Abstract: The objective of this study was to investigate whether preferential flow paths have higher microbial biomass and different microbial community structures than the rest of the soil. The organic C concentrations in the preferential flow paths were 10 to 70% higher than in the matrix. The organic N concentrations were also enriched in the preferential flow paths, as well as the effective cation exchange capacity and the base saturation. Microbial biomass was 9 to 92% higher in the preferential flow paths than in the matrix, probably due to the better nutrient and substrate supply. The DNA concentrations and direct cell counts showed a similar pattern, while domain-specific genetic fingerprints did not reflect the differences between flow regions. However, Pseudomonas displayed different population structures between preferential flow paths and soil matrix. This indicated that possibly only few populations with a broad acceptance for substrates and aerobic as well as anaerobic growth specifically profit from the favourable conditions in the preferential flow paths.

The Southern Ocean Limb of the Global Deep Overturning Circulation

Abstract: Nine hydrographic sections are combined in an inverse box model of the Southern Ocean south of ;128S. The inclusion of independent diapycnal flux unknowns for each property and air‐sea (heat, freshwater, and momentum) fluxes make it possible to estimate the three-dimensional deep water circulation. The authors find a vigorous 50 3 106 m3 s21 deep overturning circulation that is dominated by an equatorward flow of Lower Circumpolar Deep Water and Antarctic Bottom Water and poleward flow of upper deep water including Indian and Pacific Deep Water below 1500 dbar. In the subtropical Indian and Pacific Oceans the deep overturning cell is essentially isolated from the thermocline and intermediate waters of the subtropical gyre. The southward flowing upper deep water shoals south of the Antarctic Circumpolar Current, where air‐sea fluxes convert outcropping upper deep water to Antarctic surface water and drive a net air‐sea transformation of 34 3 106 m3 s21 to lighter intermediate water. It is the outcropping of upper deep water and transformation by air‐sea fluxes that connects the deep and intermediate circulation cells. The significant poleward transport of relatively light (i.e., above all topography at the latitude of Drake Passage) upper deep water, as required here to balance lateral and diapycnal divergence and air‐sea exchange, provides observational evidence that advection by standing and transient eddies carries significant meridional transport in the Southern Ocean.

Circulation, Renewal, and Modification of Antarctic Mode and Intermediate Water

Abstract: Nine hydrographic sections are combined in an inverse box model of the Southern Ocean south of ;128S. The inverse model has two novel features: the inclusion of independent diapycnal flux unknowns for each property and the explicit inclusion of air‐sea fluxes (heat, freshwater, and momentum) and the water mass transformation they drive. Transformation of 34 3 106 m3 s21 of Antarctic Surface Water by air‐sea buoyancy fluxes, and cooling and freshening where Subantarctic Mode Water outcrops, renews cold, fresh Antarctic Intermediate Water of the southeast Pacific and southwest Atlantic. Relatively cold, fresh mode and intermediate water enter the subtropical gyres, are modified by air‐sea fluxes and interior mixing, and return poleward as warmer, saltier mode and intermediate water. While the zonally integrated meridional transport in these layers is small, the gross exchange is approximately 80 3 106 m3 s21. The air‐sea transformation of Antarctic surface water to intermediate water is compensated in the Southern Ocean by an interior diapycnal flux of 32 3 106 m3 s21 of intermediate water to upper deep water. The small property differences between slightly warmer, saltier intermediate water and cold, fresh Antarctic Surface Water results in a poleward transfer of heat and salt across the Polar Front zone. Mode and intermediate water are crucial participants in the North Atlantic Deep Water overturning and Indonesian Throughflow circulation cells. The North Atlantic Deep Water overturning is closed by cold, fresh intermediate water that is modified to warm, salty varieties by air‐sea fluxes and interior mixing in the Atlantic and southwest Indian Oceans. The Indonesian Throughflow is part of a circum-Australia circulation. In the Indian Ocean, surface water is converted to denser thermocline and mode water by air‐sea fluxes and interior mixing, excess mode water flows eastward south of Australia, and air‐sea fluxes convert mode water to thermocline water in the Pacific.

Water-flow rates and passive diffusion partially explain differential survival of corals during the 1998 bleaching event

Abstract: In the western Pacific during 1998, coral bleach- ing, or the paling of corals through loss of pigmentation or loss of symbiotic algae (zooxanthellae), coincided with some of the warmest sea-surface temperatures (SSTs) on record. How- ever, there was considerable spatial variation in coral sur- vivorship; for example, corals of the same species at different locations around the Ryukyu Islands (Japan), within kilome- ters of each other, showed vastly different responses. Some locations experienced 100% coral mortality while other loca- tions, nearby, suffered little coral mortality. Here we show experimental evidence for high survivorship of Acropora dig- itifera coral colonies that were subjected to both high SSTs (ranging from 26.22 to 33.65°C) and high-water flow (50 to 70 cm s -1 ), while corals that were subjected to both high SSTs and low-water flow (2 to 3 cm s -1 ) showed low survivorship. All experiments were conducted under high irradiance (~95% photosynthetically active radiation). We also empiri- cally show that no coral mortality occurred when SSTs were below 30°C (ranging from 26.64 to 29.74°C) under similar flow regimes. The spatial differences in coral mortality during the 1998 bleaching event may have been, in part, a result of differences in water-flow rates that induced differential rates of passive diffusion, which varied among habitats.

Measurement of Particle Accelerations in Fully Developed Turbulence

Abstract: We use silicon strip detectors (originally developed for the CLEO III high energy particle physics experiment) to measure fluid particle trajectories in turbulence with temporal resolution of up to 70,000 frames per second. This high frame rate allows the Kolmogorov time scale of a turbulent water flow to be fully resolved for 140 = 500. The acceleration flatness is found to increase with Reynolds number, and to exceed 60 at R_lambda = 970. The coupling of the acceleration to the large scale anisotropy is found to be large at low Reynolds number and to decrease as the Reynolds number increases, but to persist at all Reynolds numbers measured. The dependence of the acceleration variance on the size and density of the tracer particles is measured. The autocorrelation function of an acceleration component is measured, and is found to scale with the Kolmogorov time tau_eta.

One-, two-, and three-dimensional root water uptake functions for transient modeling

Abstract: Although solutions of multidimensional transient water flow can be obtained by numerical modeling, their application may be limited as root water uptake is generally considered to be one- or two-dimensional only. This is especially the case for trees. The first objective of this paper is to test the suitability of a three-dimensional root water uptake model for the simultaneous simulation of transient soil water flow around an almond tree. The soil hydraulic and root water uptake parameters were optimized by minimizing the residuals between measured and simulated water content data. Water content was measured in a three-dimensional grid around a sprinkler-irrigated almond tree for a 16 day period, following irrigation. A second objective was to compare the performance and results of the three-dimensional flow model with one- and two- dimensional root water uptake models. For this purpose, measured water contents were aggregated in the x and y direction in the one-dimensional case and in the radial direction for the two-dimensional uptake model. For the estimation of root water uptake model parameters a genetic algorithm was used to estimate the approximate global minimum of the parameter space, whereas final parameters were determined using the Simplex optimization algorithm. With the optimized root water uptake parameters, simulated and measured water contents during the 16-day period were in excellent agreement for all root water uptake models. Most significantly, the spatial variation in flux density below the rooting zone decreased when reducing multidimensional root water uptake to fewer dimensions, thereby justifying the proposed multidimensional approach.

Calibration of a two-dimensional root water uptake model

Abstract: mates of the temporal and spatial root water uptake patterns are needed. Quantification of root water exAlthough solutions of multidimensional transient water flow can traction rates also contributes to an improved underbe obtained by numerical modeling, their application may be limited in part as root water uptake is generally considered to be one-dimen- standing of chemical fluxes in the vadose zone in both sional only. The objective of this study was to develop and test a two- ecological and hydrological studies (Somma et al., 1998), dimensional root water uptake model, which can be incorporated as well as their control by vegetation. Water uptake by into numerical multidimensional flow models. The two-dimensional rooting systems can control the timing and the amount uptake model is based on the model by Raats, but is extended with of chemical pollutant loadings to the groundwater a radial component. Subsequently, the root water uptake model was through elimination of preferential flow patterns of waincorporated into a two-dimensional flow model, and root water up- ter and chemicals, or by regulation of absorption of take parameters were optimized, minimizing the residuals between nutrients or trace elements, thereby reducing their conmeasured and simulated water content data. Water content was meacentration levels in the deep vadose zone or groundwasured around a sprinkler-irrigated almond tree (Prunus laurocerasus ter (Clothier and Green, 1994). Moreover, the rhizoM.J.Roem) for a 16-d period at 25 locations, following irrigation. To calibrate the flow and root water uptake model, a genetic algorithm sphere might be responsible for accelerated breakdown (GA) was used to find the approximate global minimum of the opti- of organic chemicals by biodegradation (Walton and mized parameter space. The final fitting parameters were determined Anderson, 1990). using the Simplex algorithm (SA). With the optimized root water Actual root water uptake not only depends on the uptake parameters, simulated and measured water contents during root distribution and its functioning, but also on soil the 16-d period were in excellent agreement, with R

Decreasing overflow from the Nordic seas into the Atlantic Ocean through the Faroe Bank channel since 1950

Abstract: The overflow of cold, dense water from the Nordic seas, across the Greenland-Scotland ridge and into the Atlantic Ocean is the main source for the deep water of the North Atlantic Ocean. This flow also helps drive the inflow of warm, saline surface water into the Nordic seas. The Faroe Bank channel is the deepest path across the ridge, and the deep flow through this channel accounts for about one-third of the total overflow. Previous work has demonstrated that the overflow has become warmer and less saline over time. Here we show, using direct measurements and historical hydrographic data, that the volume flux of the Faroe Bank channel overflow has also decreased. Estimating the volume flux conservatively, we find a decrease by at least 20 per cent relative to 1950. If this reduction in deep flow from the Nordic seas is not compensated by increased flow from other sources, it implies a weakened global thermohaline circulation and reduced inflow of Atlantic water to the Nordic seas.

Hydraulic conductivity of rice roots

Abstract: A pressure chamber and a root pressure probe technique have been used to measure hydraulic conductivities of rice roots (root Lpr per m 2 of root surface area). Young plants of two rice (Oryza sativa L.) varieties (an upland variety, cv. Azucena and a lowland variety, cv. IR64) were grown for 31–40 d in 12 h days with 500 mmol m � 2 s � 1 PAR and dayunight temperatures of 27 8C and 22 8C. Root Lpr was measured under conditions of steady-state and transient water flow. Different growth conditions (hydroponic and aeroponic culture) did not cause visible differences in root anatomy in either variety. Values of root Lpr obtained from hydraulic (hydrostatic) and osmotic water flow were of the order of 10 � 8 ms � 1 MPa � 1 and were similar when using the different techniques. In comparison with other herbaceous species, rice roots tended to have a higher hydraulic resistance of the roots per unit root surface area. The data suggest that the low overall hydraulic conductivity of rice roots is caused by the existence of apoplastic barriers in the outer root parts (exodermis and sclerenchymatous (fibre) tissue) and by a strongly developed endodermis rather than by the existence of aerenchyma. According to the composite transport model of the root, the ability to adapt to higher transpirational demands from the shoot should be limited for rice because there were minimal changes in root Lpr depending on whether hydrostatic or osmotic forces were acting. It is concluded that this may be one of the reasons why rice suffers from water shortage in the shoot even in flooded fields.

Advanced dtm generation from lidar data

Abstract: The introduction of laser scanning has triggered o a revolution in topographic terrain capturing, especially in the generation of digital terrain models (DTM). In this article refined methods for the restitution of airborne LIDAR data are presented which have been developed at the Institute of Photogrammetry and Remote Sensing (Institut f¨ Photogrammetrie und Fernerkundung, I.P.F.) at Vienna University of Technology. First, a technique for the calibration of laser scanner data is introduced. The (height) discrepancies between overlapping strips, as well as control points with known co-ordinates are utilised for a simultaneous adjustment and transformation of all strips into a state wide co-ordinate system. The next step of LIDAR data processing are the filtering (elimination of vegetation and building points, generally o-terrain points) and the interpolation of the (bald earth) surface. The method, developed at the I.P.F., distinguishes itself in the integration of filtering and terrain interpolation in one process (advantage: even in steep terrain ground points are classified correctly) as well as in the application of data pyramids (advantage: even in very dense forest areas and on large buildings, o-terrain points are eliminated). In order to generate a terrain model with high geo-morphological quality, methods are required for deriving structural line information (e.g. break lines) from laser scanner data. The first method which will be presented, proceeds by a simulation of rain fall over the preliminary DTM (water flow analysis). This yields an identification of the pits with their pit base and the outflow (overflow) point. Subsequently, the terrain shape is changed in order to eliminate the pits. In a further method 3D break lines are derived from the original laser scanner points. The precondition is that the ground plan of the break line is known approximately. The result of this step are 3D-splines which are integrated in the hybrid DTM, combining raster and vector data. KURZFASSUNG

Whole-lake mineralization of allochthonous and autochthonous organic carbon in a large humic lake (Örträsket, N. Sweden)

Abstract: Organic carbon mineralization was studied. in a large humic lake (Lake Ortrasket) in northern Sweden during a well-defined summer stratification period following high water flow during snowmelt. Se ...

Baroclinic transport variability of the Antarctic Circumpolar Current south of Australia (WOCE repeat section SR3)

Abstract: Baroclinic transport variability of the Antarctic Circumpolar Current (ACC) near 140°E is estimated from six occupations of a repeat section occupied as part of the World Ocean Circulation Experiment (WOCE section SR3). The mean top-to-bottom volume transport is 147±10 Sv (mean ±1 standard deviation), relative to a deep reference level consistent with water mass properties and float trajectories. The location and transport of the main fronts of the ACC are relatively steady: the Subantarctic Front carries 105±7 Sv at a mean latitude between 51° and 52°S; the northern branch of the Polar Front carries 5±5 Sv to the east between 53° and 54°S; the southern Polar Front carries 24±3 Sv eastward at 59°S; and two cores of the southern ACC front at 62° and 64°S carry 18±3 and 11±3 Sv, respectively. The variability in net property transports is largely due to variability of currents north of the ACC in particular, an outflow of 8±13 Sv of water from the Tasman Sea and a deep anticyclonic recirculation carrying 22±8 Sv in the Subantarctic Zone. Variability of net baroclinic volume transport is similar in magnitude to that measured at Drake Passage. In density layers, transport variability is small in deep layers, but significant (range of 4 to 16 Sv) in the Subantarctic Mode Water. Variability of eastward heat transport across SR3 is significant (range of 139°C Sv, or 0.57 x 10 15 W, relative to 0°C) and large relative to meridional heat flux in the Southern Hemisphere subtropical gyres. Heat transport changes are primarily due to variations in the westward flow of relatively warm water across the northern end of the section. Weak (strong) westward flow and large (small) eastward heat flux coincides with equatorward (poleward) displacements of the latitude of zero wind stress curl.

Soil Physics Companion

Abstract: Introduction, A.W. Warrick Physical Properties of Primary Particles, J.M. Skopp Particle Density Particle Shape Particle Size Distribution Specific Surface Area Bulk Density and Porosity References Dynamic Properties of Soil, R. Horn and T. Baumgartl Introduction Processes in Aggregate Formation Determination of Mechanical Parameters Effect of Soil Structure and Dynamics on Strength and Stress/Strain Processes Further Dynamic Aspects in Soils Modeling Dynamic Coupled Processes Conclusions References Soil Water Content and Water Potential Relationships, D. Or and J.M. Wraith Introduction Soil Water Content Soil Water Energy Soil Water Content-Energy Relationships Resources References Soil Water Movement, D.E. Radcliffe and T.C. Rasmussen Introduction Flow in Saturated Soil Flow in Unsaturated Soil Measurement of Hydraulic Parameters Numerical Models of Water Flow Concluding Remarks References Water and Energy Balances at Soil-Plant-Atmosphere Interfaces, S.R. Evett Introduction Energy Balance Equation Water Balance Equation References Solute Transport, F.J. Leij and M.Th. van Genuchten Introduction The Advection-Dispersion Equation Solutions of the Advection-Dispersion Equation Stream Tube Models References Soil Structure, B.D. Kay and D.A. Angers Characteristics, Significance, and Measurement of Soil Structure Soil Factors Influencing Structure Other Factors Influencing Soil Structure Interpreting Data on Soil Structure References Soil Gas Movement in Unsaturated Systems, B.R. Scanlon, J.P. Nicot, and J.M. Massmann General Concepts Related to Gas Movement Transport of a Homogeneous Gas Multicomponent Gas Transport Methods Applied Numerical Modeling Applications of Gas Transport Theory Derivation of Equations References Soil Spatial Variability, D.J. Mulla and A.B. McBratney Variability in Soil Properties from Soil Classification Classical Measures of Variability Geostatistics Sampling Design References

The Arctic Ocean Boundary Current along the Eurasian slope and the adjacent Lomonosov Ridge: Water mass properties, transports and transformations from moored instruments

Abstract: Year-long (summer 1995 to 1996) time series of temperature, salinity and current velocity from three slope sites spanning the junction of the Lomonosov Ridge with the Eurasian continent are used to quantify the water properties, transformations and transport of the boundary current of the Arctic Ocean. The mean flow is cyclonic, weak (1 to 5 cm s−1), predominantly aligned along isobaths and has an equivalent barotropic structure in the vertical. We estimate the transport of the boundary current in the Eurasian Basin to be . About half of this flow is diverted north along the Eurasian Basin side of the Lomonosov Ridge. The warm waters (>1.4°C) of the Atlantic layer are also found on the Canadian Basin side of the ridge south of 86.5°N, but not north of this latitude. This suggests that the Atlantic layer crosses the ridge at various latitudes south of 86.5°N and flows southward along the Canadian Basin side of the ridge. Temperature and salinity records indicate a small (0.02 Sv), episodic flow of Canadian Basin deep water into the Eurasian Basin at , providing a possible source for an anomalous eddy observed in the Amundsen Basin in 1996. There is also a similar flow of Eurasian Basin deep water into the Canadian Basin. Both flows probably pass through a gap in the Lomonosov Ridge at 80.4°N. A cooling and freshening of the Atlantic layer, observed at all three moorings, is attributed to changes (in temperature and salinity and/or volume) in the outflow from the Barents Sea the previous winter, possibly caused by an observed increased flow of ice from the Arctic Ocean into the Barents Sea. The change in water properties, which advects at along the southern edge of the Eurasian Basin, also strengthens the cold halocline layer and increases the stability of the upper ocean. This suggests a feedback in which ice exported from the Arctic Ocean into the Barents Sea promotes ice growth elsewhere in the Arctic Ocean. The strongest currents recorded at the moorings (up to ) are related to eddy features which are predominantly anticyclonic and, with a few exceptions, are of two main types: cold core eddies, confined to the upper 100–300 m, probably formed on the shelf, and warm core eddies of greater vertical extent, probably related to instabilities of an upstream front.

Continuous hydrothermal synthesis of inorganic materials in a near-critical water flow reactor; the one-step synthesis of nano-particulate Ce1 − xZrxO2 (x = 0–1) solid solutions

Abstract: Ce1 − xZrxO2 solid solutions are produced continuously by hydrolysis of mixtures of cerium ammonium nitrate and zirconium acetate in near-critical water at ca. 300 °C and 25 MPa using a flow reactor. Rapid hydrothermal coprecipitation leads to nano-particulate Ce1 − xZrxO2 (x = 0–1), the composition of which is largely determined by the initial relative concentrations of Ce4+ and Zr4+ ions in the starting solution. The freshly prepared materials are crystalline, possess very small particle sizes, and have high surface areas. The effects of calcining the products in air at high temperature have been studied. Apart from the 1∶1 Ce∶Zr solid solution, the phases of Ce1 − xZrxO2 remain stable on calcining to 1000 °C, but the particles sinter and the surface areas decrease significantly. The materials have been characterised by Powder X-ray Diffraction (PXD), IR and Raman Spectroscopy, microanalysis, Thermogravimetric Analysis (TGA), X-ray Fluorescence (XRF) and BET (surface area measurements). In selected cases, high resolution Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images were recorded to examine the particle morphology.

Atlantic inflow to the Nordic Seas: current structure and volume fluxes from moored current meters, VM-ADCP and SeaSoar-CTD observations, 1995–1999

Abstract: This study deals with the inflow of warm and saline Atlantic water to the Nordic Seas, an important factor for climate, ecology and biological production in Northern Europe. The investigations are carried out along the Svinoy standard hydrographic section, which cuts through the Atlantic inflow to the Norwegian Sea just to the north of the Faroe–Shetland Channel. In the Svinoy section, we consider the Atlantic inflow as water with salinity above 35.0, corresponding to temperatures above 5°C. Current measurements for the period April 1995 to February 1999, positioned on the continental slope in water depths between 490 and 990 m, are combined with VM-ADCP, SeaSoar-CTD and CTD transects to estimate long-term transports and spatial features of the Atlantic inflow. A well-defined two-branched Norwegian Atlantic Current was revealed with an eastern and a western branch. The eastern branch appears as a narrow, topographically trapped, near barotropic, 30–50 km wide current, with a maximum speed of 117 cm/s. The western branch is also about 30–50 km wide, and appears as an unstable frontal jet about 400 m deep with a maximum speed of 87 cm/s. Between these two prominent branches, the observations show an average eddy field with a recirculation to the southwest. Transport estimates from the current records in the eastern branch show an annual mean inflow of 4.2 Sv (1 Sv=10 6 m 3 /s) with variation on a 25 h time scale ranging from −2.2 to 11.8 Sv, and between 2.0 and 8.0 Sv on a monthly time scale. The current record in the core of the eastern branch mirrors the estimated transport on a monthly time scale with a correlation coefficient of 0.86. Except for the year 1995–1996, this nearly four-year current record shows evidence of a systematic annual cycle with summer to winter variations in the proportion of 1 to 2. Comparison between the North Atlantic Oscillation (NAO) index and the current record on a three-month time scale shows a strong connection for most of the period. This reflects the strong coupling between the westerly winds and the inflow. The baroclinic transport west of the eastern branch, including the frontal jet, is inferred from hydrography in combination with VM-ADCP transects, and has a total mean of 3.4 Sv. Thus, investigations to date indicate a yearly mean Atlantic inflow of 7.6 Sv in the Svinoy section.

Visualization of a water-selective pore by electron crystallography in vitreous ice

Abstract: The water-selective pathway through the aquaporin-1 membrane channel has been visualized by fitting an atomic model to a 3.7-A resolution three-dimensional density map. This map was determined by analyzing images and electron diffraction patterns of lipid-reconstituted two-dimensional crystals of aquaporin-1 preserved in vitrified buffer in the absence of any additive. The aqueous pathway is characterized by a size-selective pore that is approximately 4.0 +/- 0.5A in diameter, spans a length of approximately 18A, and bends by approximately 25 degrees as it traverses the bilayer. This narrow pore is connected by wide, funnel-shaped openings at the extracellular and cytoplasmic faces. The size-selective pore is outlined mostly by hydrophobic residues, resulting in a relatively inert pathway conducive to diffusion-limited water flow. The apex of the curved pore is close to the locations of the in-plane pseudo-2-fold symmetry axis that relates the N- and C-terminal halves and the conserved, functionally important N76 and N192 residues.

Flow rate dependence of soil hydraulic characteristics

Abstract: The rate dependence of unsaturated hydraulic characteristics was analyzed using both steady state and transient flow analysis. One-step and multistep outflow experiments, as well as quasi-static experiments were performed on identical, disturbed samples of a sandy and a loamy soil to evaluate the influence of flow rate on the calculated retention and unsaturated hydraulic conductivity curves. For the sandy soil, a significant influence of the flow rate on both the retention and unsaturated hydraulic conductivity characteristic was observed. At a given matric potential, more water was retained with greater applied pneumatic pressures. Matric potential differences of 10 to 15 cm (for given saturation) and water content differences of up to 7% (for given potential) could be observed between the slowest and the fastest outflow experiments, predominantly at the beginning of drainage. The hydraulic conductivity also increased with increasing flow rate for higher saturations, while a lower hydraulic conductivity was observed near residual saturation for the higher flow rates. We observed a continuously increasing total water potential gradient in the sandy soil as it drained, especially for high-pressure transient one-step experiments. This indicates a significant deviation from static equilibrium, as obtained under static or steady-state conditions. For the finer textured soil, these flow-rate dependent regimes were not apparent. A number of physical processes can explain the observed phenomena. Water entrapment and pore blockage play a significant role for the high flow rates, as well as lack of air continuity in the sample during the wettest stages of the experiment.

The Mechanosensory Lateral Line System of the Hypogean form of Astyanax Fasciatus

Abstract: The mechanosensory lateral line is a distributed, hair-cell based system which detects the water flow regime at the surface of the fish. Superficial neuromasts densely scattered over the surface of some cave fish detect the pattern of flow over the surface of the body and are important in rheotactic behaviors and perhaps in the localization of small vibrating sources. Canal neuromasts are very likely also involved in the detection of small planktonic prey, but seem also to play an essential role in replacing vision as the major sense by which blind cave-fish perceive their surroundings. The flow-field that exists around a gliding fish is perturbed by objects in the immediate vicinity, these perturbations are detected by the lateral line system. In this way the fish can build up a ‘picture’ of its environment, a process that has been called active hydrodynamic imaging. None of the lateral line behaviors exhibited by blind cave fish are necessarily exclusive to these species, but there is some evidence that their lateral line capabilities are enhanced with respect to their sighted relatives.

Aquarium observations on the deep-water coral Lophelia pertusa (L., 1758) (scleractinia) and selected associated invertebrates

Abstract: Growth and behaviour of Lophelia pertusa and selected associated invertebrates were observed in aquaria with running sea-water. The coral polyps captured food particles by means of nematocyst adhesion. Food items up to 2 cm long were ingested. The polyps discriminated between food and sediment particles when presented separately, probably involving chemoreceptors. When presented together with food, sediment was ingested. Linear skeletal extension occurred in pulses of up to 1.2 mm·day-1 in young polyps (mean = 9.4 mm·yr-1). Factors influencing the linear extension were: food availability, water quality, and patterns of water flow. The highest extension rate was recorded in periods with influx of new water masses to the aquarium water intake, and in parts of the aquaria with a slow water movement and a high sedimentation rate. Settlement and reproduction of the parasitic foraminiferan Hyrrokkin sarcophaga was observed, but no clear negative effects on the coral could be observed. The polychaete Eu...

The Cycle of Turbulent Dissipation in the Presence of Tidal Straining

Abstract: In regions of large horizontal density gradient, tidal straining acts to produce a periodic component of stratification that interacts with turbulent mixing to control water column structure and flow. A 25-h series of measurements of the rate of dissipation of turbulent kinetic energy ( e) in the Liverpool Bay region of freshwater influence (ROFI) have revealed the form of this interaction and indicate substantial differences from regions where horizontal gradients are weak. In the ROFI system there is a pronounced difference between flood and ebb regimes. During the ebb the water column stratifies and strong dissipation is confined to the lower half of the water column. By contrast, during the flood, stratification is eroded with complete vertical mixing occurring at high water and high values of dissipation (3 mW m23) extending throughout the water column. The cycle of dissipation is therefore predominantly semidiurnal in the upper layers whereas, near the bottom boundary, the principal variation is at the M4 frequency as observed in regions of horizontal uniformity. Toward the end of the flood phase of the cycle, tidal straining produces instabilities in the water column that release additional energy for convective mixing. Confirmation of increased vertical motions throughout the water column during the late flood and at high water is provided by measurements of vertical velocity and the error velocity from a bottom-mounted acoustic Doppler current profiler.