Showing papers on "Water flow published in 1981"

A heat balance method for measuring water flux in the stem of intact plants

Abstract: This paper describes the method and apparatus for measuring the flow rate of water in intact plant stems, on the basis of heat balance of a stem segment. Under stationary conditions, the heat energy supplied continuously to a segment of plant stem is partitioned into three components such as conduction, mass flow and convection [see Eq. (1)]. By predetermining both heat losses due to conduction in the stem and convection from the segment surface into ambient air, it is possible to evaluate the heat loss due to mass flow of water in the stem, that is, the water flow rate equivalent to the transpiration stream. The water flow rate evaluated by this method is compared with the transpiration loss of water determined directly by weighing potted soybean and sunflower plants and measured by using a chamber method. The comparison shows there is a good agreement between them. This indicates that the newly developed method can be applied for determining transpiration rates of intact plants under laboratory and field conditions.

Water repellent soils: a state-of-the-art

Abstract: Water repellency in soils was first described by Schreiner and Shorey (1910), who found that some soils in California could not be wetted and thereby were not suitable for agriculture. Waxy organic substances were responsible for the water repellency. Other studies in the early 1900's on the fairy ring phenomenon suggested that water repellency could be caused by fungi. These fairy rings created unsightly, circular shaped areas in otherwise healthy turf and lawn. Bayliss (1911) reported on such water repellency and referred to earlier work in 1875 by Gilbert and Laws at Rothamsted which described the same phenomenon. Later, Shantz and Piemeisel (1917) confirmed that soil dryness was associated with fairy rings on grasslands in eastern Colorado.

Structure in turbulent mixing layers and wakes using a chemical reaction

Abstract: Plane turbulent mixing between two streams of water which contained dilute chemical reactants was studied in a new blow-down water tunnel. In a diffusion-limited reaction, a pH indicator, phenolphthalein, in one stream mixed and reacted with a base, sodium hydroxide, in the other stream to form a visible reaction product. The product was found to exist, as expected, in concentrated regions associated with the large, span-wise-coherent structures of the turbulence. A transition in the mixing was observed in which the aqueous mixing product increased by an order of magnitude. The transition is a consequence of the appearance and development of small-scale three-dimensional motions in the flow. Downstream of the transition, the amount of mixing product was independent of Reynolds number (for an order-of-magnitude increase in the latter) and at most only weakly dependent on Schmidt number.

Copepod feeding currents: Food capture at low Reynolds number1

Abstract: High-speed motion pictures of dye streams around feeding calanoid copepods revealed that these important planktonic herbivores do not strain algae out of the water as previously described. Rather, a copepod flaps four pairs of feeding appendages to propel water past itself and uses its second maxillae to actively capture parcels of that water containing food particles. The feeding appendages of Eucalanus pileatus operate at Reynolds numbers of only 10−2 to 10−1. In the viscous world of a feeding copepod, water flow is laminar, bristled appendages behave as solid paddles rather then open rakes, particles can neither be scooped up nor left behind because appendages have thick layers of water adhering to them, and water and particle movement stops immediately when an animal stops beating its appendages.

Role of Organic Debris Dams in Regulating the Export of Dissolved and Particulate Matter from a Forested Watershed

Abstract: An organic debris dam is an accumulation of organic matter in a stream which obstructs water flow. Debris dams trap sediments in the pool formed upstream from them and the dam structure itself collects particulate organic matter. This study was done at the Hubbard Brook Experimental Forest, in New Hampshire, to examine the relative importance of these structures in retention of sediment and organic matter in a small stream ecosystem. An experimental approach was used in which all organic debris dams were re- moved from a 175-m section of second-order stream, just above a gauging weir. The material being exported from the watershed was separated into three size categories: dissolved matter ( 1 mm). Export of each size fraction was monitored for at least 1 yr prior to dam removal, and for 1 yr following removal. Following dam removal, export of dissolved matter increased slightly due to an increase in the concentration of dissolved organic carbon in the stream water during periods of high discharge. Fine particulate matter export increased dramatically at high discharges following dam removal; concen- trations in some instances achieved values five times higher than any observed before dam removal. Coarse particulate matter export also was greatly increased. Calculating dissolved matter and particulate matter export from the watershed, with and without organic debris dams, showed that dam removal brought about a 6% increase in the export of dissolved matter and a 500% increase in the export of both fine particulate and coarse particulate matter.

Water flow in soil macropores ii. a combined flow model

Abstract: Summary This paper presents a one-dimensional model of bulk flow in a combined micropore/macropore system, which has been developed as a result of the experimental work described in Part I. The problems posed by the presence of macropores to model development and validation are discussed and one exploratory model formulation is described. The results of several simulations are presented and used to demonstrate the effect of macropores on infiltration rates in soils of different hydraulic conductivity.

Water flow in soil macropores i. an experimental approach

Abstract: Summary A method is proposed by which the volume of the macropore system and its effect on the infiltration capacity can be estimated using a soil water potential concept. The macropore systems of two large and undisturbed soil samples were investigated. The volumes of macropores were 0.01 and 0.045 of the sample volumes, respectively. When the samples were drained from full saturation to the point where it may be assumed that there was no more water in the macropore system, the hydraulic conductivity decreased by factors of 18 and 4.3 respectively.

Pore networks in Holocene carbonate sediments

Abstract: Permeabilities of Holocene carbonate sediments from Florida and the Bahamas, determined for 74 samples by water flow rates in a "variable-head" permeameter, range from 0.6 to 57,000 millidarcies. Porosities range from 40 to 78 percent. These parameters are related to depositional texture as follows: Table The muddiest sediments (i.e., the finest-grained) have the highest porosities but lowest permeabilities; this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks, even as young as Pleistocene. High porosity and low permeability in sediments show a strong correlation with percentage of fines (<62 µm). From capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 µm in diameter, at least after drying. Measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation; the calculated rates would require excessive time to produce the degree of cementation seen in Late Pleistocene rocks of Florida and the Bahamas. The amounts of rainfall and evaporation are the most important factors in the degree of cementation.

Downhole steam generator with improved preheating, combustion and protection features

Abstract: An apparatus for generation of steam in a borehole for penetration into an earth formation wherein feedback preheater means are provided for the fuel and water before entering the combustor assembly. First, combustion gases are conducted from the combustion chamber to locations in proximity to the water and fuel supplies. Secondly, both hot combustion gases and steam are conducted from the borehole back to the water and fuel supply. The water used for conversion to steam is passed in a countercurrent manner through a plurality of annular water flow channels surrounding the combustion chamber. In this manner, the water is preheated, and the combustion chamber is cooled simultaneously, thereby minimizing thermal stresses and deterioration of the walls of the combustion chamber. The water is injected through slotted inlets along the combustion chamber wall to provide an unstable boundary layer and stripping of the water from the wall for efficient steam generation. Pressure responsive doors are provided at the steam outlet of the combustor assembly. The outlet doors and fluid flow functions may be controlled by a diagnostic/control module. The module is positioned in the water flow channel to maintain a relatively constant, controlled temperature.

Convective and pore scale dispersive solute transport in unsaturated heterogeneous fields

Abstract: Transport of an inert solute in unsaturated horizontally heterogeneous field soils, which differs from that in laboratory conditions, is investigated. Four solute transport factors and their variabilities have been examined: (1) convection by vertical velocity V, which changes in plane because of variability in soil properties, (2) recharge R, applied on the surface, constant in time but varying in plane, (3) pore scale dispersivity λ, variable in the field, and (4) average dispersivity λ, with field condition value. The variables V, R, λ, and solute concentration C are regarded as random. Closed form equations (requiring a numerical quadrature at most) for the probability distribution of C are derived by using several simplifying assumptions concerning the water flow regime. The mathematical solutions are capable of determining detailed statistical information about solute distribution in the field. Two soils are examined: (1) Panoche soil (150 hectares in area) with low average saturated conductivity and relatively large variance and (2) Bet Dagan soil (0.8 hectare in area) with larger average conductivity and a smaller variance. It is found that for both soils the variability of λ has very little influence and that adopting the value of λ for the entire field is sufficient. The variability of R when it is moderate has a modest effect. The three major factors are the variability in soil hydraulic conductivity, average values of rate of recharge R, and pore scale dispersion λ. It is concluded that (1) average concentration profile in the heterogeneous field cannot be modeled as the solution of convective-diffusion equation with constant coefficients and (2) if λ is taken at its laboratory-measured value, its effect upon solute distribution is negligible compared with that of soil variability, but if the large field value is adopted, it has an impact upon solute distribution. The dominant spreading mechanism in Panoche soil is heterogeneity combined with convection. Accounting for both mechanisms is warranted in most cases.

Transport properties of toad kidney epithelia in culture.

Abstract: The characteristics of a continuous line of toad kidney epithelial cells (A6) are described. These cells form a monolayer epithelium of high transepithelial electrical resistance (about 5,000 omega . cm2). The cells generate a transepithelial potential difference (apical surface negative) of about 9 mV. The short-circuit current is equivalent to net sodium flux. Net sodium flux is stimulated by aldosterone and by analogues of cAMP. The stimulation is readily reversible. Neither urea permeability nor osmotic water flow is altered by analogues of cAMP. Amiloride eliminates 90% of the short-circuit current. Thus A6 cells form an epithelium with several differentiated properties including hormonal regulation of transport.

Integrated actions of renal medullary prostaglandins in the control of water excretion

Abstract: The renal medulla is a rich source of prostaglandins. Two cell types, the collecting tubule epithelium and the interstitial cell, have the enzymatic machinery necessary to make prostaglandins. As a result of this localized production and the proximity to highly specialized medullary structures, the prostaglandins can exert potent effects on several aspects of medullary function. At least three physiologic effects have been clearly documented: reduction of vasopressin-dependent osmotic water permeability of the collecting tubule epithelium, enhancement of medullary blood flow, and inhibition of NaCl absorption from the thick ascending limb of Henle's loop. These three functions are the functions that primarily regulate axial solute content and water excretion. The effect of increasing medullary prostaglandin production is to reduce medullary solute content and increase water excretion. Each action in this regard. The medullary prostaglandins thus antagonize the ultimate action of vasopressin. In addition to the direct antagonistic effect on vasopressin-dependent osmotic water flow across the collecting tubule, prostaglandins and vasopressin may have antagonistic effects at other sites. These actions of medullary prostaglandins provide an integrated mechanism for the "fine tuning" of water excretion.

Water status of soil and vegetation in a shortgrass steppe.

Abstract: In an attempt to describe some major relationships between soil and plant compartments in a shortgrass steppe, the process of water loss from the system and plant water relations throughout a drying cycle were studied. The water supply was manipulated and some soil and plant variables monitored throughout a drying cycle. Leaf conductance and leaf water potential of blue grama (Bouteloua gracilis) were measured periodically at predawn and noon. Soil water content and water potential of different layers were also monitored.Three different periods were distinguished in the water loss process throughout a drying cycle. These distinctions were made taking into account the relative contribution of different soil layers. Leaf conductance and water potential at noon slowly declined throughout the first 50 days of plant growth. After that, they rapidly decreased, reaching values of 0.29 mm s-1 and-5.0 MPa, respectively. The predawn leaf water potential remained unchanged around-0.5 MPa during the first 45 days, then rapidly decreased. This occurred when soil water of the wettest soil layer was near depletion.Predawn leaf water potentials were highly correlated with water potentials of the wettest layer. Leaf conductance and water potential at noon were correlated with effective soil water potential (soil water potential weighted by the root distribution in the profile). We concluded that root surface area limited the water flow through an important part of the day in this semiarid ecosystem. Axial root resistance did not appear important in determining the equilibrium status between leaves and the wettest soil layer.

Analysis of the dynamic and steady-state responses of growth rate and turgor pressure to changes in cell parameters

Abstract: The physical analysis of plant cell enlargment is extended to show the dependence of turgor pressure and growth rate under steady-state conditions on the parameters which govern cell wall extension and water transport in growing cells and tissues, and to show the dynamic responses of turgor and growth rate to instantaneous changes in one of these parameters. The analysis is based on the fact that growth requires simultaneous water uptake and irreversible wall expansion. It shows that when a growing cell is perturbed from its steady-state growth rate, it will approach the steady-state rate with exponential kinetics. The half-time of the transient adjustment depends on the biophysical parameters governing both water transport and irreversible wall expansion. When wall extensibility is small compared to hydraulic conductance, the growth rate is controlled by the yielding properties of the cell wall, while the half-time for changes in growth rate is controlled by the water transport parameters. The reverse situation occurs when hydraulic conductance is lower than wall extensibility. The analysis also shows explicitly that turgor pressure is tightly coupled with growth rate when growth is controlled by both water transport and wall yielding parameters.In growing tissue where the resistance to water flow is distributed throughout the tissue, the physical analysis is more complicated because gradients in water potential (and hence turgor pressure) are required to sustain high growth rates. However, the analysis of growth in such tissues shows that the turgor and time-course relations are similar to that in single cells. These turgor and time-course relations provide experimentally useful ways for determining (a) whether growth is limited by water uptake, and (b) whether an agent which alters the growth rate does so by affecting the water transport or wall yielding properties or both.

Water temperature and flow rate selection display and control system and method

Abstract: Apparatus and method for selecting, displaying and automatically controlling water flow rates and temperatures at the outlets of devices used in plumbing fixtures such as sinks, bathtubs, showers, or lavatories; the apparatus includes a temperature sensor at the water output, a control panel for selecting desired output water temperatures and flow rates, a comparator for comparing the selected temperature to the output temperature, and for generating signals to control separate hot and cold water valves to achieve and automatically maintain, within limits, any desired combination of flow rate and temperature. In one embodiment the comparator is embodied in a microprocessor which receives a digital signal representative of the actual water temperature, and generates a modified signal to adjust hot and cold water flow to the output means until the actual output temperature matches the selected temperature within a small error range while maintaining flow rate at a constant level.

Fish mucus: in situ measurements of polymer drag reduction

Abstract: The external layer of mucus on fish was investigated as a drag reducing polymer. Comparing velocity profiles for water flow over rainbow trout (Salmo gairdneri) and wax models of trout with and without hydrodynamically smooth surfaces revealed that the integumental mucous secretion can significantly reduce the rate of momentum transfer through the boundary layer. The difference in momentum transfer is expressed as a reduction in friction drag and discussed in view of the overall drag experienced by fish.

Osmotic water permeability of human red cells.

Abstract: The osmotic water permeability of human red cells has been reexamined with a stopped-flow device and a new perturbation technique. Small osmotic gradients are used to minimize the systematic error caused by nonlinearities in the relationship between cell volume and light scattering. Corrections are then made for residual systematic error. Our results show that the hydraulic conductivity, Lp, is essentially independent of the direction of water flow and of osmolality in the range 184-365 mosM. the mean value of Lp obtained obtained was 1.8 +/- 0.1 (SEM) X 10-11 cm3 dyne -1 s-1.

Carbonate sand bodies along contrasting shallow bank margins facing open seaways in northern Bahamas.

Abstract: High-resolution seismic profiling, bottom sampling, and aerial and space imagery show that widely contrasting carbonate sand bodies are present along the shallow windward, leeward, and tide-dominated margins of Little and Great Bahama Banks which face open seaways--the Northwest Providence Channel and the northern Straits of Florida. This high diversity in sand bodies and their associated bank margins is due to variations in the level, duration, and magnitude of the physical energy flux across the edges of the platforms. In the Bahamas, the dominant winds, waves, and currents are from the east; hence easterly facing margins are windward, westerly facing margins are leeward. Where strong tidal currents are present (because of adjacent basin shape) the windward and leeward effects are diminished. Thus, bank-margin orientation relative to the climatic energy patterns appears to assert the major controls upon sedimentation. Antecedent topography in the form of islands or subtidal rock ridges creates energy barriers which can control the direction and volume of sediment flux on or off the banks. Along windward margins, energy barriers such as large islands not only block the bankward transport of sands but appear to augment offbank transport by setting up seaward flows. In contrast, along leeward margins, energy barriers prevent the vigorous offbank sand transport that normally occurs when these margins are open and water flow is unrestricted. In addition, sand-body geometry and grain type are controlled by bank-margin orientation. Along windward, open margins, skeletal sands accumulate in the lee of low-relief, mostly relict reefs. These margins are generally sediment-barren, having only a sporadic, thin veneer of sand. Along leeward, open margins a broad (10 × 10 km), thick (12 m), bankward-thinning blanket of sand rich in nonskeletal components (peloids, composite grains) lies on top of rock ridges and reefs. Large, asymmetric sand waves superimposed on this sand body indicate net offbank sand transport. Along the tide-dominated margin, large, broad, oolitic sand lobes have migrated onto adjacent lagoonal muddy sands and indicate net bankward transport. We suggest the following classification of modern, shallow, carbonate bank margins: (1) windward open; (2) windward protected; (3) leeward open; (4) leeward protected; (5) tide dominated. This classification seems to fit many ancient analogs and may be useful in paleoenvironmental reconstructions.

Prior mannitol and furosemide infusion in a model of ischemic acute renal failure

Abstract: Tubular transport abnormalities have recently been characterized in a rabbit model of ischemic acute renal failure (ARF). These studies demonstrated severe observable morphologic and functional changes in the proximal nephron together with functional changes in the distal nephron. Tubular debris was often produced by perfusion of proximal nephron segments. In the present study, agents used to prevent ARF were tested in this rabbit model of ARF. Rabbits were infused with either 5% body wt 5% manitol or 20 micrograms . kg-1 . min-1 furosemide in 5% body wt normal saline for the 60 min preceding 60 min of total renal ischemia. Mannitol 1) prevented the development of ARF, 2) maintained fluid reabsorption in the proximal convoluted tubule (PCT) (0.59 +/- 0.03 vs. 0.52 +/- 0.1 nl . mm-1 . min-1) and proximal straight tubule (PST) (0.34 +/- 0.05 vs. 0.39 +/- 0.07 nl . mm-1 . min-1), 3) depressed NaCl reabsorption in the cortical thick ascending limb of Henle's loop (TALH), and 4) did not prevent a decrease in ADH-mediated osmotic water flow in the cortical collecting tubule (CCT). Furosemide 1) partially preserved renal function, 2) partially protected the PCT (0.63 +/- 0.05 vs. 0.38 +/- 0.04 nl . mm-1 . min-1) and PST (0.32 +/- 0.04 vs. 0.22 +/- 0.02 nl . mm-1 . min-1), and 3) did not change the transport capacity of the TALH or the ADH response of the CCT. Preservation of proximal nephron integrity was also reflected by the absence of debris formation. There is a direct relation between an agent's ability to protect the functional integrity of the cells of the proximal nephron and its ability to preserve renal function.

Diversity of swimming behavior in hydromedusae as related to feeding and utilization of space

Abstract: Feeding behaviors of the following 4 species of hydromedusae are described from field and laboratory observations: Probosidactyla flavicirrata, Stomotoca atra, Phialidium gregarium and Polyorchis penicillatus. Feeding efficiency of medusae has previously been considered equivalent to fishing with a given amount (combined tentacle length) of adhesive “fishing line”; however, detailed observation shows that behavior of medusae greatly modifies the fishing capacity of each species. It is hypothesized that in addition to (1) tentacle number and length, the following factors strongly influence feeding efficiency: (2) tentacle posture, (3) velocity of tentacles moving through water (4) swimming pattern of medusa, (5) streamlining effects of medusa bell on water flow, (6) diameter of prey, (7) swimming pattern and velocity of prey. Each species of hydromedusa utilizes the above factors in different combinations.

A Comprehensive Wellbore Stream/Water Flow Model for Steam Injection and Geothermal Applications

Abstract: A mathematical model describing the phenomena around and inside a well bore during the vertical flow of a 2-phase mixture of steam and water was developed, based upon the equations for mass, momentum, and energy balances in the conduit, heat transfer in the well bore, and heat conduction in the formation To examine the validity of the mathematical model, comparisons were conducted with actual field data, and also with previously reported models for steam injection as well as geothermal production Good agreement between the published field data and the results from the present model established the validity of the model, and show that it can be employed for studying well-bore phenomena during steam injection as well as geothermal production 17 references

Mathematical Model of Shallow Water Flow over Porous Media

Abstract: A conjunctive mathematical model for a surface-subsurface flow system is developed. The unsteady surface flow is explored by a set of one-dimensional dynamic wave equations for shallow water, which are solved by using a four-point implicit finite-difference scheme. The transient subsurface flow is two-dimensional, with potential gradients in the vertical direction as well as the surface flow direction. The porous medium may be saturated or unsaturated or both, and it can be nonhomogeneous and anisotropic. The subsurface flow equation is solved by employing a successive line over-relaxation implicit finite-difference scheme. The surface and subsurface flow components are coupled at the ground surface considering the mass conservation and pressure relationships. The model is verified by using existing experimental data and analytical solutions for special cases.

Water flow in soil macropores iii. a statistical approach

Abstract: Summary Two regression equations describing water movement in saturated macropores in the field are compared with a theoretical expresion of the form Qmaα e2ma where Qma is the saturated volume flux density through a macropore system of porosity ema. The theoretical exponent of 2 agrees fairly well with the analyses of two very different sets of field experiments by Burger (1922–1940) and Ehlers (1975). It is suggested that the relationship Qma= Q*e2ma may be a useful first approximation to predict macropore flow, where Q* is an empirical coefficient that is expected to depend on the hydraulic connectivity, geometrical structure, tortuosity, roughness and other properties of the macropore system.

Effects of trifluoperazine on function and structure of toad urinary bladder. Role of calmodulin vasopressin-stimulation of water permeability.

Abstract: Calcium ion plays a major regulatory role in many hormone-stimulated systems. To determine the site of calcium's action in the toad urinary bladder, we examined the effect of trifluoperazine, a compound that binds specifically to the calcium binding protein, calmodulin, and thereby prevents activation of enzymes by the calcium- calmodulin complex. 10 microM trifluoperazine inhibited vasopressin stimulation of water flow, but did not alter vasopressin's effects on urea permeability or short-circuit current. Trifluoperazine also blocked stimulation of water flow by cyclic AMP and methylisobutylxanthine, implying a "postcyclic AMP" site of action. Consistent with these results, trifluoperazine did not decrease epithelial cyclic AMP content or the cyclic AMP-dependent protein kinase activity ratio. Assay of bladder epithelial supernate demonstrated calmodulin-like activity of 1.5 U/microgram protein. Morphologic studies of vasopressin-treated bladders revealed that trifluoperazine did not alter the volume density of cytoplasmic microtubules or significantly decrease the number of fusions between cytoplasmic, aggregate-containing, elongated vesicles and the luminal membrane. Nonetheless, the frequency of luminal membrane aggregates, structures that correlate well with luminal membrane water permeability, was decreased by greater than 50%. Thus, trifluoperazine appears to inhibit the movement of intramembranous particle aggregates from the fused intracellular membranes to the luminal membrane, perhaps by blocking an effect of calcium on microfilament function.

Modeling Nitrogen Transport And Transformations In Soils: 1. Theoretical Considerations1

Abstract: We developed a numerical model to simulate water and nitrogen transport and transformations through water-unsaturated, multilayered soil profiles. The nitrogen transformation processes considered were nitrification, denitrification, immobilization, mineralization, and ionic exchange of ammonium. Plant uptakes of water and nitrogen were also included. We used an explicit-implicit finite difference approximation method to solve the nitrogen transport and transformation equations simultaneously with the water flow equation. Model evaluation and sensitivity analysis for a wide range of values for the rate of nitrification, distribution coefficient for ammonium exchange, and rate of N uptake were investigated.