Water Release Rate Research Articles

Poly(MAA-co-AN) hydrogels with improved mechanical properties for theophylline controlled delivery

A hydrophobically improved copolymer hydrogel was constructed and developed based on methacrylic acid (MAA) and acrylonitrile (AN) monomers. The swelling investigations indicated that the hydrogels were highly sensitive to the pH and ionic strength of the surrounding environment. The swelling ratios of the gels in stimulated intestinal fluids (SIF, pH 7.4) were higher than those in stimulated gastric fluids (SGF, pH 1.4), and followed a non-Fickian and a Fickian diffusion mechanism, respectively. The results match well with scanning electron microscopy observations showing that mesh sizes in hydrogels in SGF are larger and more patulous than in SIF. It is believed that the phenomena are concerned with the electrostatic repulsion originating from the formation and dissociation of carboxyl groups, as well as a charge screening effect of the cations leading to the reduction of osmotic pressure. A dynamic mechanical analyzer revealed that the addition of hydrophobic AN units notably improved the compression mechanical properties of the control sample. With an increase in AN concentrations, the ability for the copolymers to resist compression deformation enhanced in distilled water and the compression strains have almost the same values in SIF environments. Differential scanning calorimetry was used to analyze the state of water and to determine the amounts of freezing and non-freezing water. The controlled release examination based on the theophylline model drug showed that the release rate in distilled water was faster than that in SIF or SGF. The introduction of the hydrophobic AN decreased the theophylline release rates in both SIF and SGF, and the release rate variation in SIF was notably larger than that in SGF. The drug release behavior of the AN-modified P(MAA-co-AN) copolymer hydrogel deviates from the Fickian diffusion control mechanism. This hydrogel is expected to be used as an excellent material in oral drug controlled release.

Dynamic Relationship Between Neurostimulation and N-Acetylaspartate Metabolism in the Human Visual Cortex

N-acetyl-l-aspartic acid (NAA), an amino acid synthesized and stored primarily in neurons in the brain, has been proposed to be a molecular water pump (MWP) whose function is to rapidly remove water from neurons against a water gradient. In this communication, we describe the results of a functional (1)H proton magnetic resonance spectroscopy (fMRS) study, and provide evidence that in the human visual cortex, over a 10-min period of visual stimulation, there are stimulation-induced graded changes in the NAA MRS signal from that of a preceding 10-min baseline period with a decline in the NAA signal of 13.1% by the end of the 10-min stimulation period. Upon cessation of visual stimulation, the NAA signal gradually increases during a 10-min recovery period and once again approaches the baseline level. Because the NAA MRS signal reflects the NAA concentration, these changes indicate rapid focal changes in its concentration, and transient changes in its intercompartmental metabolism. These include its rates of synthesis and efflux from neurons and its hydrolysis by oligodendrocytes. During stimulation, the apparent rate of NAA efflux and hydrolysis increased 14.2 times, from 0.55 to 7.8 micromol g(-1) h(-1). During recovery, the apparent rate of synthesis increased 13.3 times, from 0.55 to 7.3 micromol g(-1) h(-1). The decline in the NAA signal during stimulation suggests that a rapid increase in the rate of NAA-obligated water release to extracellular fluid (ECF) is the initial and seminal event in response to neurostimulation. It is concluded that the NAA metabolic cycle in the visual cortex is intimately linked to rates of neuronal signaling, and that the functional cycle of NAA is associated with its release to ECF, thus supporting the hypothesis that an important function of the NAA metabolic cycle is that of an efflux MWP.

Water release rate from corn kernel affected by cropping intensity

The average field kernel drying rate (water release rate) was not the identical in all growing seasons. Similar kernel drydown rates in the field are observed in 2002 and 2003 and they were much slower than drydown rates in the field in 2001. Although in the IPS the kernel moisture loss in the field is faster, the difference between production systems was not significant. All the hybrids, except Bc Jumbo 48, had the fastest average kernel drydown rate in 2001. Also, all the hybrids, except Bc Jumbo 48, had the fastest average kernel drydown rate in the IPS. Chosen hybrids had a significant kernel drydown rates in the field and responded differently in drydown rate under the impact of climatic conditions in growing seasons.

Effect of drainage systems on the water release rate in the process of drying wheat and corn grain

AbstractThe basic aim of this research is to determine the influence of various types of pipe drainage upon the water release rate in the process of drying wheat and corn kernels grown on a hydromorphic type of soil. The research was conducted during a period of three years (1998–2001). Seven different types of drainage systems were built on pseudogleyic‐gleyic soil (various spacings of drainage pipes with gravel used or not used in the drainage trench above the pipes). Based on soil moisture measurement data (to a soil depth of 60 cm), acquired by means of the gravitational method in the period of vegetation, it is clear that the most favourable humidity occurred on soil with spacing of drainage pipes being 25 m, gravel used, with both cultures. The yield gained also shows that this drainage type is the most favourable. The process of drying the kernels to the storage humidity value took the shortest time with this type of drainage.Results of this research contribute to energy savings in the process of drying wheat and corn crops. Additionally, the results can be used for selecting systems of drainage in dealing with excess water on hydromorphic soil types. Copyright © 2007 John Wiley & Sons, Ltd.

On the relationship between visual magnitudes and gas and dust production rates in target comets to space missions

In this paper, we report the results of a cometary research, developed during the last 10 years by us, involving a criterious analysis of gas and dust production rates in comets directly associated to recent space missions. For the determination of the water release rates we use the framework of the semi-empirical model of observed visual magnitudes [Newburn Jr., R.L. A semi-empirical photometric theory of cometary gas and dust production. Application to P/Halley’s production rates, ESA–SP 174, 3, 1981; de Almeida, A.A., Singh, P.D., Huebner, W.F. Water release rates, active areas, and minimum nuclear radius derived from visual magnitudes of comets – an application to Comet 46P/Wirtanen, Planet. Space Sci. 45, 681–692, 1997; Sanzovo, G.C., de Almeida, A.A., Misra, A. et al. Mass-loss rates, dust particle sizes, nuclear active areas and minimum nuclear radii of target comets for missions STARDUST and CONTOUR, MNRAS 326, 852–868, 2001.], which once obtained, were directly converted into gas production rates. In turn, the dust release rates were obtained using the photometric model for dust particles [Newburn Jr., R.L., Spinrad, H. Spectrophotometry of seventeen comets. II – the continuum, AJ 90, 2591–2608, 1985; de Freitas Pacheco, J.A., Landaberry, S.J.C., Singh, P.D. Spectrophotometric observations of the Comet Halley during the 1985–86 apparition, MNRAS 235, 457–464, 1988; Sanzovo, G.C., Singh, P.D., Huebner, W.F. Dust colors, dust release rates, and dust-to-gas ratios in the comae of six comets, A&AS 120, 301–311, 1996.]. We applied these models to seven target comets, chosen for space missions of “fly-by”/impact and rendezvous/landing.

Involvement of Gypsum (CaSO4 · 2H2O) in Water Treatment Sludge Dewatering: A Potential Benefit in Disposal and Reuse

This research assessed the use of gypsum (CaSO4 · 2H2O) as a skeleton builder for sludge dewatering since polymer conditioning of sludge affected only the rate of water release, not the extent of dewatering. The use of gypsum as a physical conditioner, in association with a polymer, could improve sludge filterability. More significantly, gypsum serves as a skeleton builder, forming a permeable and rigid lattice structure that can remain porous under high positive pressure during the compression step after the cake growth of the filtration, thereby maintaining the size of the micro‐passages through which water is expressed. Experiments using a high pressure cell apparatus showed that a further decrease of two to seven percent of the equilibrium moisture content of the sludge cake was achieved, for sludge thicknesses for dewatering of 1 to 10 cm, by the addition of gypsum with 60% of the original sludge solids when compared to the single polymer conditioning. The importance of the addition of gypsum in alum sludge dewatering is not only the improvement in the extent of dewatering, but also the potential application of transforming dewatered alum sludge from “waste” for landfill to useful “fertilizer” or to be used as a filter medium/adsorbent for wastewater treatment engineering.

Synthesis and swelling behavior of thermosensitive poly(N‐isopropyl acrylamide‐co‐sodium‐2‐acrylamido‐2‐methyl propane sulfonate) and poly(N‐isopropyl acrylamide‐co‐sodium‐2‐acrylamido‐2‐methyl propane sulfonate‐co‐glycidyl methacrylate) hydrogels

AbstractThe crosslinked copolymers and terpolymers of N‐isopropyl acrylamide (NIPAm) with sodium‐2‐acrylamido‐2‐methyl propane sulfonate (NaAMPS) and glycidyl methacrylate (GMA) were prepared in the presence of N,N′‐methylene bisacrylamide (NMBA) as crosslinker by free radical solution polymerization at 4°C. Potassium persulfate (KPS) and potassium bisulfide (KBS) were used as initiator and accelerator, respectively. While molar percentages of NaAMPS in copolymers feed were varied as 1, 2, and 3; NaAMPS and GMA were used in the molar percentages of 1 : 1, 2 : 2, and 3 : 3, respectively, for the terpolymer preparation. NMBA contents were kept constant as 1 or 1.5 mol % of total monomer moles in feed composition. The effects of the comonomer type, feed composition, and the crosslinker contents on the lower critical solution temperatures (LCST), equilibrium swelling values (Q) of polymers, swelling kinetics in water at room temperature, and deswelling kinetics at 55°C were investigated. The results indicated that the higher the NaAMPS content in NIPAm/NaAMPS copolymer, the higher the Q and water uptake rate, but less the water release rate. However, the presence of hydrophobic GMA comonomer in the terpolymer of NIPAm/NaAMPS/GMA decreased the Q values, it increased both the water uptake and the water release rates. It was also observed that NIPAm/NaAMPS and NIPAm/NaAMPS/GMA polymers exhibit continuous phase transition behavior between 40 and 50°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 428–438, 2006

Preparation and Physical Properties of Hollow Polyester Filaments with High Breathability, Water Absorption and Release Rates

This paper reports the preparation of hollow polyester filaments with high water absorption and release rates, and the study of their physical properties using differential scanning calorimetry, thermogravimetric analysis, density gradient, gel permeation chromatography, rheometry and statistical regression analysis. Four readily soluble poly(ethylene glycol)-modified cationic dyeable poly(ethylene terephthalate) (PEG-CDPET) polymers were prepared, with 3 mol % of the sodium salt of dimethyl 5-sulfo-isophthalate (SIPM). The poly(ethylene glycol) (PEG) contents were 3 and 6 wt% and the number-average molecular weights ([Formula: see text]) of the PEG were 600 and 8000 (g/mol). Blends of regular PET and PEG-CDPET were spun into hollow filaments. These hollow filaments were then drawn and treated with aqueous sodium hydroxide. The crystallinity of the PEG-CDPET polymers declined as the PEG content increased, given a fixed SIPM content. Furthermore, the crystallinity of the PEG-CDPET polymers declined as the [Formula: see text] of the PEG increased for the same SIPM and PEG contents. The SIPM and PEG segments did not change the original PET unit cell. The sodium sulphonate (–SO3Na) functional groups and the PEG molecules were only on the crystal surface and in the amorphous regions. Obviously, the rate constants for alkaline hydrolysis were in the order: PEG-CDPET polymer<<CDPET polymer<regular PET polymer. The water-absorption and release and the heat retention properties of alkali treated PET/PEG-CDPET polyblend hollow filaments were better than those of the regular PET filaments. The porous nature of the large filaments (from 0.02-1 μm in diameter) was observed after alkali treatment of the PET/PEG-CDPET polyblend hollow filaments. Additionally, the hollowness of the PET/PEG-CDPET polyblend filaments was observed to increase from 40 to 42% after alkali treatment.

Microencapsulation of l-menthol by spray drying and its release characteristics

The microencapsulation of l-menthol was studied by spray drying, using gum arabic (GA) and modified starch (CAPSUL, HI-CAP 100) as capsule materials. The results showed a higher retention of l-menthol with the increasing of initial solid concentration. HI-CAP 100, showed a higher retention than the other capsule materials. However, it also showed a higher residue of l-menthol on the surface of powder especially at the high concentration of l-menthol in the feed emulsion. That might be from the interaction between the wall materials and l-menthol which can re-crystallize to form whisker after the spray drying. Furthermore, the release characteristics of l-menthol were also investigated. The release rate increased upon elevation of relative humidity and temperature. The activation energies of the release of l-menthol from GA wall matrices at 75 and 83%RH were 140 and 48 kJ/mol, respectively. Industrial relevance Controlled release of food constituents is currently receiving highest interest. This study aimed to better understand some of the processing and storage conditions. Decrease in emulsion droplet size led to increased flavor retention during spray drying. Interesting electron-micrographs of the spray dried capsules are provided as well as data on water absorption isotherms and release rate constants vs. storage temperatures. Clear industrially relevent data regarding capsule size, matrix, material, water activity and temperature during storage are provided.

A non‐invasive stress assay based upon measurement of free cortisol released into the water by rainbow trout

A procedure previously used for sex steroids was adapted to extract free cortisol and cortisone from water samples taken from rainbow trout Oncorhynchus mykiss tanks. Both corticosteroids could be readily detected by radioimmunoassay (RIA), with cortisol being predominant. All stages of the sampling, extraction and RIA procedure were validated for cortisol. An intermittent problem with poor replication was traced to the use of diethyl ether during the extraction procedure, and was overcome by the use of ethyl acetate. Other modifications were also introduced to speed up the procedure. The concentration and time course of release of both corticosteroids were shown to be related to the degree of stress that the fish had been subjected to. It was confirmed that cortisol concentrations in water and estimated cortisol release rates increased in response to handling stress, and that both were correlated with plasma cortisol concentrations. The potential for using water cortisol concentration and release rates to assess the primary stress response of fishes as a non‐invasive alternative to blood sampling is discussed.

Drug release from carbomer:carbomer sodium salt matrices with potential use as mucoadhesive drug delivery system

In vitro mucoadhesion, water uptake, and drug release of nystatin (N) from matrices of carbomer (C) and lyophilized carbomer sodium salt (CNa L) mixtures were evaluated. Matrices with different ratios C:CNa L were prepared by direct compression. Commercial C as well as lyophilized powder (C L) were used. In vitro mucoadhesion increased as the proportion of C in the matrix was raised. The same effect was observed when C was replaced by C L. Matrices in which C was replaced by C L showed an increase of both water uptake and release rates. Besides, the release of N from matrices C L:CNa L exhibited a kinetics with Super Case II ( n>1) mechanism. However, for C:CNa L matrices, drug release was slower and exhibited a biphasic profile with a first stage characterized by either an anomalous ( n<1, for C≥50%) or a Case II ( n ∼ 1.0, C<50%) mechanisms. After that period, the mechanism changed to Super Case II transport ( n>1).

Origin of the Dual Structural Transformation of Trehalose Dihydrate upon Dehydration

Upon dehydration, trehalose dihydrate transforms either toward a glassy amorphous state or toward a polymorphic crystalline phase depending on the dehydration protocol. Although this duality is now admitted, its origin remains an open question. We present here calorimetric and thermogravimetric experiments clearly showing that the main pertinent physical parameter governing this duality is the instantaneous rate of water release and not the thermal treatment used to dehydrate the sample. The latter, by acting on the rate of water loss, has only an indirect influence on the structure of the dehydrated product. A threshold rate of water removal, above which dehydration produces an amorphous state and below which it produces a polymorphic phase, is also defined.

Average cost under the PMλ, τ policy in a finite dam with compound Poisson inputs

We consider the policy in a finite dam in which the input of water is formed by a compound Poisson process and the rate of water release is changed instantaneously from a to M and from M to a (M &gt; a) at the moments when the level of water exceeds λ and downcrosses τ (λ &gt; τ) respectively. After assigning costs to the changes of release rate, a reward to each unit of output, and a cost related to the level of water in the reservoir, we determine the long-run average cost per unit time.

Average cost under the P M λ, τ policy in a finite dam with compound Poisson inputs

We consider the policy in a finite dam in which the input of water is formed by a compound Poisson process and the rate of water release is changed instantaneously from a to M and from M to a (M &amp;gt; a) at the moments when the level of water exceeds λ and downcrosses τ (λ &amp;gt; τ) respectively. After assigning costs to the changes of release rate, a reward to each unit of output, and a cost related to the level of water in the reservoir, we determine the long-run average cost per unit time.

Integrated effects of applied pressure, time, and polymer doses on alum sludge dewatering behaviour

In this study, combinations of applied pressure, pressing time and polymer dose were examined in an air pressure plate apparatus to explore their integrated influence on the dewatering of an alum sludge. Results of the investigation demonstrated that dewatering can be enhanced by increases in pressure and time. However, a point is reached at which continued increases in pressure and time offer little benefit. The data also confirmed that polymer affects the rate of water release rather than the extent of dewatering. Increased rates of water release due to increasing polymer dose can be attributed to the aggregation of sludge particles by polymer addition. It was also evident in this study that the initial sludge depth has a major impact on the average cake moisture content at a given dewatering time. It was apparent that once the initial sludge thickness exceeds about 2 cm, the water release follows a fairly similar pattern, which can be represented by a simple empirical model.

Paclitaxel-loaded crosslinked hyaluronic acid films for the prevention of postsurgical adhesions.

Post surgical adhesion formation results in significant morbidity for surgical patients. The purpose of this study was to investigate the use of paclitaxel (PTX) as an inhibitor of adhesion formation in rats and to design and characterize a controlled release film formulation of the drug for application to exposed surgical sites. The rat cecal side wall abrasion model was used to investigate the anti-adhesion properties of PTX. The drug was administered by either intraperitoneal injection (i.p.), as the cremophor formulation (Taxol) or by application of carbodiimide crosslinked hyaluronic acid (HA) films containing PTX. The HA films were also characterized by measurements of elasticity, degree of swelling in water and drug release rates. Taxol administered by i.p. injection at 4 mg/kg on a daily basis for between 3 and 5 days resulted in a significant reduction in adhesion formation. All animals in the control group (n = 10) had some form of adhesion following abrasion whereas the percent of animals without adhesions significantly increased and the mean incidence of adhesion formation decreased in the three Taxol treated groups. The application of 5% PTX loaded HA films had a similar significant effect in increasing both the % of animals without adhesions and in reducing the mean incidence of adhesions. Paclitaxel is an effective inhibitor of adhesion formation in rats. HA crosslinked with 2 mM water soluble carbodiimide and containing 10% glycerol and 5% PTX are flexible, mucoadhesive, biocompatible controlled release films suitable for application to surgical sites for the prevention of adhesion formation.

Water Quality Issues Associated With Composite Tailings (CT) Technology for Managing Oil Sands Tailings

In the oil sands industry, composite tails (CT) is a tailings management approach in which the fines or clay fraction of extraction tailings are mixed with the coarse sand fractions, such that, with the addition of a coagulant aid, a non-segregating deposit is produced. Various coagulant aids have been shown to be effective. In the process of coagulation, the fine solids aggregate. Under self-weight consolidation (aided by high proportion of sand grains), particle-free water is released from the deposit leaving the fines solids and some water trapped within the voids of the coarse solids matrix. The rate and degree of water release determines when the resulting deposit can be classed as a “dry” landscape for reclamation. The coagulation of the clays has been demonstrated with a variety of chemicals, both organic and inorganic. Depending on the particular coagulant aid, various changes in pH, salinity, cation and anion levels, buffering capacity and toxicity have been observed. The impacts of some of these coagulant aids on water quality are described and the potential influence of the CT release waters on operational aspects of oil sands operations and on eventual reclamation options are discussed.

Mass-loss rates, dust particle sizes, nuclear active areas and minimum nuclear radii of target comets for missions STARDUST and CONTOURP

Observed visual magnitudes of the short-period comets 2P/Encke, 81P/Wild 2, 6P/d'Arrest and 73P/Schwassmann–Wachmann 3 and the long-period comet C/1984 V1 Levy–Rudenko are converted into water release rates. These H2O release rates are used to derive the nuclear surface areas, minimum nuclear radii and gas mass loss of these comets. Combined with estimated gas release rates, we make an uniform and systematic analysis of the observed continuum fluxes in the comae of these comets with the objective to find dust release rates, effective dust particle sizes and total mass release rates. The nuclei of Comets 2P/Encke, 6P/d'Arrest and 73P/Schwassmann–Wachmann 3, which has split into as many as four fragments, are potential targets for the flyby of the CONTOUR (COmet Nucleus TOUR) spacecraft, scheduled for launch in 2002 July, while Comet 81P/Wild 2 has been chosen as a target by the NASA spacecraft STARDUST, which was launched on 1999 February 7.

A modified capillary suction time apparatus for measuring the filterability of super-flocculated sludges

The capillary suction time (CST) test provides a quantitative measure of the rate of water release from a sludge and has the advantage of being simple to run. The test consists of allowing sludge water to filter into and penetrate a filter paper by capillary force. Although the CST works well for the majority of sludges, it is not a useful test for measuring the filterability of highly flocculated sludges or sludges conditioned by other methods such as freeze-thaw. The escape of water from the sludge in such cases is too fast and the rate-limiting step becomes the movement of water through the filter paper instead of the release of water from the sludge. There is a need to improve the CST apparatus so it can be used to measure the degree of filterability for super flocculated sludges as well. Such a device is described in this paper. It consists of first draining the free water from the well-flocculated sludge and only then allowing the flocculated sludge to come in contact with the filter paper.The results of our study show that the filterability of super-flocculated sludges can be measured with acceptable precision using the modified CST apparatus.

Phosphorus release from coated monoammonium phosphate: Effect of coating thickness, temperature, elution medium, soil moisture and placement method

Coating fertilizer granules with a polymer slows the release of nutrients over a long period of time, so that the fertilizer uptake by plants may be enhanced. Two laboratory experiments were conducted to determine the effects of coating thickness, temperature, soil moisture, and placement method on the release rate of P from coated monoammonium phosphate (MAP) in soil; to compare the release rate of P from coated MAP in soil and in water; and to evaluate different kinetic equations for simulating the release of P from coated MAP. In exp. 1, release of P from 10 pre-weighed granules of a non-coated MAP and three polymer-coated MAP fertilizers (Coated I, 4%; Coated II, 4.5%; and Coated III, 5%) was determined in water at 10 and 23°C. In exp. 2, release of P from the four MAP fertilizers in soil was determined at two temperatures (10 and 23°C), two moisture levels (90 and 60% field capacity) and two placement methods (incorporation and banding). Four kinetic equations, i.e., simple Elovich, Parabolic diffusion, Power function, and First order kinetics, were evaluated to simulate the release of P from coated MAP. Activation energy of P release was calculated using the P release versus ln time plots of the simple Elovich equation. The release rate of P from coated MAP was strongly affected by coating thickness and temperature but was not affected by method of P placement and soil water content. The release of P from coated MAP was slower in soil than in water, and it decreased markedly with increasing thickness of polymer coating on MAP, whereas it increased with increasing temperature. The simple Elovich equation best described the release of P from coated MAP in both water and soil. The activation energy was not affected by elution medium and coating thickness but it was lower at the higher temperature. In conclusion, the test of P release rate from coated MAP in water may not represent the true release rate of P from coated MAP in soil, as it is influenced by elution medium, temperature and coating thickness. The simple Elovich equation best described the P release kinetics from coated MAP in soil and in water. Key words: Coating thickness, monoammonium phosphate, P release rate in water and soil, P release kinetics, placement method, soil moisture content, temperature