Semipermeable Layer Research Articles

Seed enhancements

AbstractSeed enhancements may be defined as post-harvest treatments that improve germination or seedling growth, or facilitate the delivery of seeds and other materials required at the time of sowing. This definition includes three general areas of enhancements: pre-sowing hydration treatments (priming), coating technologies and seed conditioning. Pre-sowing hydration treatments include non-controlled water uptake systems (methods in which water is freely available and not restricted by the environment) and controlled systems (methods that regulate seed moisture content preventing the completion of germination). Three techniques are used for controlled water uptake: priming with solutions or with solid particulate systems or by controlled hydration with water. These priming techniques will be discussed in this paper with reference to methodology, protocol optimization, drying and storage. Coating technologies include pelleting and film coating, and coatings may serve as delivery systems. Seed conditioning equipment upgrades seed quality by physical criteria. Integration of these methods can be performed, and a system is described to upgrade seed quality inBrassicathat combines hydration, coating and conditioning. Upgrading is achieved by detecting sinapine leakage from nonviable seeds in a coating material surrounding the seeds. Seed-coat permeability directly influences leakage rate, and seeds of many species have a semipermeable layer. The semipermeable layer restricts solute diffusion through the seed coat, while water movement is not impeded. Opportunities for future seed enhancement research and development are highlighted.

Combined 14C and δ13C Monitoring of in Situ Biodegradation of Petroleum Hydrocarbons

Measurements of the stable carbon isotope ratios (δ13C) of microbial metabolic end products presents a promising method for monitoring in situ bioremediation of petroleum hydrocarbons. Differences between the δ13C values of hydrocarbons and indigenous carbon sources (e.g., plant matter, soil carbonates) can be exploited to trace the origins of metabolic end products. However, in zones of methanogenesis and/or where the δ13C values of endogenous plant matter overlap those of hydrocarbons, δ13C measurements can produce ambiguous results. In such cases, simultaneous measurement of the radiocarbon (14C) contents of metabolic end products can be used to determine their sources. This method was applied at a gasoline station spill site where hydrocarbons were the only source of 14C-free carbon. Combined δ13C and 14C measurements of soil gas CO2 and dissolved inorganic carbon in groundwater enabled quantification of carbon inputs. Furthermore, low 14C contents of high δ13C CO2 were crucial in establishing that the soil gas CO2 was derived from methanogenesis of hydrocarbons and not shell dissolution. In addition, low 14C content coupled with a 16‰ drop in the δ13C values of CO2 across a semipermeable layer beneath the gas station building confirmed that microbial oxidation of methane was occurring within this zone.

Role of adsorbed fluoride ions on the dissolution of synthetic hydroxyapatite

The dissolution kinetics at 37°C and for constant pH values of 5.0 and 6.0 are studied for calcium hydroxyapatite (HAp) equilibrated at pH 7.0 in the presence of 1 or 10 ppm of F-. Experiments are realized using an automatic setup which allows a continuous record of proton uptake and calcium or fluoride activities in solution using specific electrodes. It is shown that the presence of fluoride ions affects the dissolution kinetics in two ways. Their presence at the HAp interface reduces the final solubility of HAp, but accelerates the initial dissolution rates. Both observations are fully interpreted using the HAp dissolution model recently developed. According to this model, apatite dissolution is auto-inhibited by the adsorption at the solid interface of calcium ions forming a cationic semi-permeable layer. Adsorbed fluoride ions interact with this natural cationic layer, decrease its ionic capacity and accelerate the dissolution process.

Geostatistical characterization of a complex semi-permeable layer : Engineering geology of quaternary sediments. Proc. symposium, Delft, 1994, ed N. Rengers, (Balkema), 1994, symposium, Delft, 1994, ed N. Rengers, (Balkema), 1994, pp 73–92

Presents a study to quantify the lithofacies distribution of a complex semi-permeable layer consisting of fluvial and organic deposits. In a small study area in the central Rhine-Meuse delta a large number of drillings were made in a semi-permeable layer overlying shallow permeable aquifers. Detailed cross sections and semivariogram analysis are used to quantify the spatial variability of fluvial overbank deposits in the semi-permeable layer and to determine minimal drilling distances for detailed mapping of the lithofacies. Conditional indicator simulation is applied to obtain simulated stochastic images of the semi-permeable layer. These images may serve as analogues for similar layers found at greater depths. -Authors

Mechanism of Action of Adsorbed Fluoride Ions on the Dissolution Kinetics of Apatite Powder

The kinetics of dissolution of calcium hydroxyapatite powder (HAP) is studied at 37°C at a constant pH 5 or 6 in the presence of 1 or 10 ppm fluoride ions. Experiments were carried out with an automatic setup which recorded continuously the proton uptake and the concentrations of calcium and fluoride in solution, using specific electrodes. We demonstrate that fluoride ions have a dual action. Their presence at the interface reduces the apatite solubility, and, as a consequence, the equilibrium is attained earlier. However, the adsorption of fluoride ions onto the apatite surface accelerates the initial dissolution process. Both processes are fully interpreted using the quantitative model recently proposed for HAP dissolution. According to this model, apatite dissolution is autoinhibited by the adsorption of calcium ions at the solid interface, thus forming a cationic semipermeable layer. Fluoride ions interact with this layer and decrease its autoinhibiting ability, especially in the case of higher fluoride concentrations where interfacial CaF 2 is formed.

Adsorption of Neutral and Anionic Polyacrylamides on Hydroxyapatite and Human Enamel: Influence on the Dissolution Kinetics

The adsorption of polyacrylamide fractions of different molecular weights and degrees of hydrolysis on hydroxyapatite and dental enamel, as well as their influence on the kinetics of dissolution of the latter, are studied at a constant pH under well controlled conditions. It is shown that the adsorbed polymers can slow down the dissolution process. The intensity of the inhibition effect follows the characteristics of the adsorption layer. The inhibition increases with the molecular weight of the polymers and their degree of hydrolysis. These behaviors are well interpreted with the model of apatite dissolution recently proposed, which supposes the formation of a cationic semipermeable layer, formed by the adsorption of calcium ions at the apatite interface.

Inhibition of dissolution of hydroxyapatite powder by adsorbed anionic polymers

The effect of the presence in solution of neutral or anionic hydrosoluble polymers on the kinetics of dissolution of hydroxyapatite powder (HAP) is analysed at a constant pH of 5 and under well-controlled conditions. Four polymers are studied. It is shown that the polymers that are able to be adsorbed induce a decrease in the rate of dissolution which strongly depends on the chemical structure of the polymers. Chemical groups with the ability to bind calcium ions, such as phosphate and phosphonate groups, are particularly efficient. The results are interpreted with the use of a recently proposed apatite dissolution model which assumes the formation, at the apatite interface, of an ionic semipermeable layer produced by the adsorption of calcium ions. According to this model, adsorbed polymers increase the ionic capacity of the interface.

Endothelium-derived biologically active substance: von Willebrand factor and endothelin

Endothelial cells from the inner lining of the vascular wall and create a continuous nonthrombogenic and semipermeable layer. They are capable of regulating vascular tone, haemostasis, inflammation etc. by synthesis and secretion of various biologically active substances like substance P, acetylcholine, ABO-antigens, endothelium-derived relaxing factor (EDRF), endothelium-derived contracting factor (EDCF), NO, endothelins, thrombospondin, von Willebrand factor and others. In the following review we describe briefly the biology of von Willebrand factor (vWF), a potent adhesive glycoprotein, and the constrictor peptide endothelin, recently isolated from endothelial cell cultures. vWF is the major constituent of FVIII/vWF complex. It is synthesized by endothelial cells and megakaryocytes. Endothelial cell Weibel-Palade bodies act as storage compartments of the large multimeric forms of vWF. Its unique secretion is maintained by constitutive and regulated pathway. vWF is secreted into the lumen and periendothelial matrix and mediates adhesion of platelets to the subendothelium after vascular injury. Structurally defective or immature subunits circulate in the plasma of patients, suffering from von Willebrand disease. Endothelins are a group of 21-aminoacidpeptides secreted mainly by endothelial cells. Synthesis of peptides of the endothelin family is located also in nonendothelial cells like pulmonary and tracheal epithelium, dorsal root ganglia etc. They act as potent vasoactive substances causing sustained elevation of blood pressure as well as powerful bronchoconstrictors, via two distinct receptors. Judging from their physiological effects, they may take part in various diseases like atherosclerosis, hypertension and asthma. The clinical relevance of this is also discussed. Biomedical Reviews 1992; 1: 39-45.

難透水層を挟む成層帯水層における海岸地下水の挙動

本研究は,被圧帯水層内に一層の難透水層を想定し,二次元定常移流分散モデルによる数値解析を行い,この難透水層の存在が海水侵入にどのような影響をもたらすかについて考察を行ったものである。分散係数として,2種類のケースを想定した。1つは帯水層内のどの場所でもすべて一様とした場合,もう1つは難透水層内の分散係数を透水係数と同じく2オーダ小さくした場合である。得た結果を要約すれば次のようである。濃度分布を調べた結果,水位勾配が大きい場合には,難透水層の存在は下部透水層においては塩水の侵入を抑える効果がある。難透水層内では一様な分散係数の場合には上下透水層に比べて,より侵入した濃度分布を示すが,難透水層の分散係数を小さくすると侵入は抑えられる。しかし,水位勾配が小さい場合には,.一様な分散係数では難透水層の効果は際だって現れないが,難透水層の分散係数を小さくすると,上部透水層ではかなり侵入が抑えられ,逆に下部透水層では促進される。また,流速分布を調べた結果,帯水層出口付近において上下の透水層で循環流がみられ,その規模は上部の方が大きい。また,難透水層内の流れは出口付近では上向きであり,この流れは,透水層の水位勾配が大きいほど大きい。さらに,塩の移動を調べた結果,上下透水層で塩の循環流が顕著に現れる。

SEAWATER INTRUSION AFFECTED BY BOUNDARY CONDITIONS IN UNCONFINED AQUIFERS

The characteristics of seawater intrusion are examined on the various aquifer conditions. Numerical positions of fresh-saltwater interface are obtained with using Residual Flow Procedure that was proposed originally to solve unconfined groundwater flow. A simulated result of fresh-saltwater interface is confirmed by sand model test in case of two-layered aquifer. From the simulated results, the followings are clarified, that is; seawater easily intrude to the two-layered aquifers in case that the high permeable layer overlies on the low permeable layer. The intruded saltwater region is relatively small in case of both the stratified aquifers separated by a semi-permeable layer and the anisotropic aquifers having low permeability in vertical direction, but that is relatively large in both the two-layered aquifer and the stratified aquifer of which the upper layer is closed by the impermeable wall.

Reverse water level fluctuations in semiconfined aquifer systems — “rhade effect”

Pumping tests in semiconfined aquifer systems near Dorsten (F.R.G.) caused anomalous reverse water level fluctuations in observation wells tapping the overlying confining bed (aquitard) at different depths (multilevel piezometer). Whenever water is pumped from a well that is screened in the aquifer of the “Halterner Sande”, the piezometric surface in the aquitard (“Bottroper Mergel”) rises. After that increase, the water level falls according to the drawdown of head within the pumped aquifer (Noordbergum effect according to Verruijt, 1969). Conversely, the piezometric surface in the aquitard falls whenever the pump is shut off (Rhade effect). The anomalous water level reactions propagate with decreasing amplitude from the aquifer-aquitard boundary to the top of the semipermeable layer. Such water level fluctuations (“swelling effects”) may be explained by the capability of a water-saturated, compacted material to change volume when subjected to sudden pressure changes. On a practical basis, the Noordbergum and Rhade effects must be taken into consideration for evaluating long-term changes in chemical and hydraulic properties in pumped, semiconfined aquifer systems.

Derivation of conditions describing transport across zones of reduced dynamics within multiphase systems

Equations for describing flow and transport in multiphase systems can be derived within the context of averaging theory. In some subsurface systems, the balance equations must be three dimensional in one portion of a domain of interest but need be only one or two dimensional in other regions (e.g., across clay lenses or within fractures). Conditions linking the dynamic processes among the different regions are typically obtained heuristically. Here a general framework is presented within which the needed conditions may be derived systematically. Particular conditions for mass, momentum, chemical species, and heat transfer are illustrated between main porous media domains and both a permeable fracture and a semipermeable layer.

An enzymic creatinine assay and a direct ammonia assay in coated thin films.

We developed a thin-film enzymic assay for creatinine that makes use of creatinine iminohydrolase (EC 3.5.4.21) to convert creatinine to N-methylhydantoin and ammonia. The ammonia diffuses through a semipermeable layer and is quantitated by reaction with bromphenol blue. A paired analysis of the sample on a separate coating without the enzymic reaction measures endogenous ammonia and, for samples with normal concentrations of ammonia, allows accurate determination of serum creatinine to 150 mg/L without dilution. Results of this assay (y) compare well with those by a liquid-chromatographic comparison assay (x) by linear regression (slope = 0.935, intercept = 1.13 mg/L, r2 = 0.995). It is insensitive to many substances, such as ketones and keto acids, that interfere with conventional assays. Results of the ammonia assay (y) correlate well with those by a semi-automated enzymic assay (x) based on glutamate dehydrogenase (slope = 1.068, intercept = 17.3 mumol/L, r2 = 0.985).

Identification of Recharge Areas Using Geochemical Factor Analysis

ABSTRACTFactor analysis is useful for interpreting commonly collected ground‐water quality data and relating those data to specific hydrogeologic processes. One hundred nine ground‐water quality samples from wells completed in the upper Floridan Aquifer near Live Oak, Florida were analyzed for major dissolved constituents. R‐mode factor analysis was used to separate those chemical variables that reflect areally‐significant recharge processes from those related strictly to the dissolution of aquifer materials. Areas impacted by direct, rapid, artificial recharge through drainage wells and sinkholes, as well as by slow, natural recharge into the Floridan Aquifer, were delineated. Four factors which represent different chemical processes were identified and their relative areal impact determined. These processes are: (1) regional dissolution of the aquifer limestone, (2) dissolution and ion exchange in the discontinuous, semipermeable layer that overlies portions of the aquifer, (3) and (4) recharge from local, urban and agricultural runoff.

Composite hollow fiber membranes

AbstractComposite polysulfone hollow fibers consisting of a polysulfone porous substrate coated with crosslinked polyethyleneimine (PEI) or furan resin are reported. These composite hollow fibers are analogous to the flat‐sheet composite membranes known as NS‐100 and NS‐200. The surface structure of the porous substrate was rigorously studied before and after coating. Scanning electron microscope observations and reverse osmosis transport studies showed that the support fiber must have surface pore diameters of less than 0.2 μm to obtain a durable composite hollow fiber membrane. The curing process would normally follow in situ condensation of the PEI or the cationic polymerization of the furfuryl alcohol. However, since both the dense layer and surface of the porous substrate contract when exposed to the curing temperature (110–150°C), it was found to be profitable to cure the hollow fiber before applying the coating. When tested in a reverse osmosis rig, PEI/TDI‐coated polysulfone hollow fiber bundles displayed 98% salt rejection and a flux of 5–7 gfd for a feed solution of 10,000 ppm NaCl at a hydraulic pressure of 400 psi. A new method of depositing furan resin on the polysulfone hollow fiber is described. The furfuryl alcohol is instantaneously polymerized by exposing the alcohol‐soaked fiber to a 60% solution of concentrated sulfuric acid. It has been demonstrated that in such a polymerization procedure a dense, semipermeable layer is formed on top of the porous substrate; the resulting composite hollow fiber membrane yields salt rejections higher than 98% when tested under the above reverse osmosis conditions.

Intracellular Membranes

ABSTRACT Spheres that stain with neutral red in cephalopod neurons show changes with variations in the tonicity of the surrounding medium. In hypertonic solutions the surface becomes shrunken and the stainable matter restricted to crescents or granules at the side of the sphere. These processes are reversible. They may be interpreted by considering that the surface of the spheres consists of material with properties partly analogous to those of a semi-permeable layer and partly to a membrane, that is to say a layer with tangential cohesive forces. These analogies are not perfect, however, and in particular the cohesive properties of the ‘membrane’ are limited and its material tends to flow together to form drops when the inner pressure is reduced. The appearances produced by the classical methods for staining the Golgi apparatus are a result of distortions of these droplets similar to those produced by changes in tonicity. The outer more osmiophil or argentophil component adopts forms reminiscent of those shown by the component that stains more deeply with neutral red.