Maximum Rate Of Absorption Research Articles

Biosorbents for wastewater treatment

Biosorption is a promising technology for removing various pollutants from industrial wastewater, which consists in the use of secondary plant raw materials (e.g., agro-industrial waste) to solve environmental pollution problems. The purpose of this study is to evaluate the potential of nut shells as a biosorbent, to study the effect of alkaline modification of shells on their properties and to study the use of spent biosorbents as additives in cement. The influence of the fractional composition of the initial material on its sorption capacity and the influence of the modification of shells with alkaline solution on the properties of the obtained biosorbents are investigated. The yield of the final products was determined gravimetrically as the ratio of the mass of the product to the mass of the raw material. The sorption capacity was studied using model solutions. The concentration of sodium hydroxide solutions was determined by titration, and the cationic dye by spectrophotometric method. Methylene blue was used as a test dye. The studies have shown that the fractional composition of the material largely determines its sorption properties. Reducing the particle size of the nut shells leads to an increase in the sorption efficiency of methylene blue from 17.2% for the fraction with a size of 1.5-2.0 mm to 39.2% for the fraction with a size of 0.5-1.0 mm. The static exchange capacity increases by an average of 30 % for each subsequent fraction. To improve the sorption properties of the initial material, along with grinding, it is advisable to use chemical modification. The method of alkaline modification was used, which is accompanied by partial destruction of the aromatic component of raw materials and low molecular weight polysaccharides and by removal of extractives of different nature, which leads to the formation of a more porous structure. The maximum sorption efficiency of methylene blue (80 %) corresponds to the biosorbent obtained from nut shells (fractional composition 0.5-1.0 mm) by modifying with 5 % NaOH solution for 180 min at a temperature of 100 oC. Alkaline treatment significantly improves the adsorption capacity of the biosorbent to the cationic dye compared to the initial material. The sorption capacity of nut shells and biosorbent based on shells was studied as a function of pH of aqueous dye solution and duration of contact. It was found that pH of the aqueous solution had a significant effect on the sorption of the dye and the maximum value was reached at pH 6. This is due to the electrokinetic properties of the surface of lignocellulosic materials - the ability to change charge depending on pH (positive in acidic, negative in neutral and alkaline), due to the presence of different functional groups. The study of kinetics showed that the maximum rate of absorption of methylene blue corresponded to the first 30 minutes of contact. Sorption equilibrium is achieved within 240 minutes of contact. Sorption kinetics was also studied using pseudo-first and pseudo-second order models, as well as a diffusion model. The pseudo-second order kinetic model (R2 = 0.99) best describes the absorption kinetics of the cationic dye and suggests that the fixation of methylene blue on the surface of the biosorbent occurs due to various mechanisms. The problem of further use of spent sorption materials is no less important than the efficiency of sorbents in creating an effective integrated water treatment technology. Spent biosorbent was used as an additive to the composition of cement type I/500. The use of plant material in the amount of 5% will not lead to a significant deterioration of the physical and mechanical properties of cement. This indicates the prospects of such an approach in the utilization of spent sorbents. In further research, it is planned to investigate various modification options for plant materials for obtaining highly effective biosorbents of multipurpose function for the solution of environmental problems.

Effect of Complex Structural Material Coated the Flight Body to Measure the Absorption of Radar Radiation at Different Elevations of Flight Latitude

Avoiding radar detection is a prime importance in several fields. We design multi reinforced polymeric materials to absorb radar waves, these materials have low density, high elastic modulus, high tensile strength good erosion resistance and good fatigue strength. Composite materials are made by three principle techniques, injection, spraying and compression. Jet technique was used to measure materials resistance for erosion. We find that polytetrafluroethylene with multi mixtures has the best specification than other polymeric materials. We manufacture twenty-one alloys (A, B, C, D, E, F…..W) used in this work. Composite materials (A-W) are making by adding fillers to matrices. Absorption coefficient of fillers and matrices was evaluated and measured alone or as a composite. Dynamic and static radar cross section shapes (eight shapes)were studied in this work. The better shapes for absorption waves are (spherical, conical, cylindrical, and parabolic). All parameters controlled reflectivity and absorption were studied. We found that the maximum rate of absorption is more than (70%), this percent observed in certain coating layers. Metallurgical and mechanical work on composite materials have been investigated. Model designed to compute multi variables affecting on absorption and reflection.

FORMULATION DEVELOPMENT AND EVALUATION OF SR MATRIX TABLETS OF PEFLOXACIN

The basic objective in dosage form design is to optimize the delivery of medication to achieve the control of therapeutic eff ect in the fa ce of uncertain fluctuation in the system in which drug release takes place. This is usually concerned with the maximum drug availability by attempting to attain a maximum rate and extent of drug absorption, however ; control of drug action through formulat ion also implies controlling the bioavailability to reduce drug absorption rates. So in the present study, an attempt has been made to formulate sustained release matrix tablets of Pefloxacin. Tablets were prepared using a direct compression method employi ng natural sustain ed release polymer such as Xanthum gum in different concentrations . The tablets were evaluated for physical characteristic like hardness, weight variation, friability and drug content. In - vitro release of drug was performed in phosphate b uffer pH 6.8 for fourteen hours, percent friability 0.22 % and disintegration time 2.20 h. All the physical characters of the fabricated tablet were within the acceptable limits . The data obtained from in vitro dissolution studies were fitted in different models viz. Zero order, first order, Higuchi and Korsmeyer - Peppas equation. It was also observed that the highest correlation was for Korsmeyer - Peppas profile (R 2 = 0 . 9938). A value of n for all matrices studied here was ranged between 0.4339 to 0.4840; indicating an anomalous behavior corresponding to swelling, diffusion and erosion mechanism .

Light intensity distribution in multi-lamp photocatalytic reactors

A computational fluid dynamics approach has been used to investigate the effect of lamp separation (Xlamp) on the radiation intensity distribution in a multiple-lamp photocatalytic reactor. The optical parameters (absorption and scattering coefficients) of Aeroxide® P25 titanium dioxide (TiO2) were determined by performing experiments using a single lamp system. Since the optical properties are wavelength dependent, the range of wavelength from the UV lamp was divided into 4 bands, and optical properties in each of the bands were determined by matching the experimental observations with simulated values. Simulations were then carried on multiple-lamp (2 and 4 lamps) photoreactors as a function of lamp separation and catalyst loadings. In case of 2-lamp system, the maximum local volumetric rate of energy absorption (〈LVREA〉) occurred at Xlamp=40mm, and it was independent of the catalyst loading. With 4 lamps however, optimum Xlamp was dependent on the catalyst loading. At low loads (up to Wcat=0.06gL−1), the optimum Xlamp was 80mm but as the catalyst concentration increased, the value of the optimum lamp separation decreased considerably, with 30mm for Wcat=0.07gL−1 and decreasing further as the concentration further increased. Because of the high absorption coefficient of the catalyst, the wall emissivity had a negligible effect on the 〈LVREA〉 for both configurations, even when the lamps were close to the wall. Finally, in both cases, the optimum lamp separation was independent of the lamp emissive power.

Enhanced Bioavailability and Dissolution of Atorvastatin Calcium from Floating Microcapsules Using Minimum Additives

Atorvastatin calcium, a lipid-lowering drug, is much less bioavailable because of reduced solubility in acidic media. Multiple-unit floating microcapsules of Atorvastatin calcium (ATC) were developed to expand the gastric residence time of the drug, as ATC has maximum rate of absorption in the upper GI tract. Floating microcapsules were prepared by Emulsion-solvent evaporation technique through incorporation of dioctyl sodium sulphosuccinate (DSS) as a dissolution enhancer. The microcapsules were assessed for shape, size, drug entrapment efficiency, stability and in-vitro drug dissolution rate and were subjected to SEM, DSC and PXRD studies. The ATC-loaded floating microcapsules were spherical in shape and had the particle size of about 28.10 μm and drug-loading efficiency of about 96.55 %. The floating microspheres containing DSS had significantly higher drug dissolution rates than those without DSS. The best formulation, AT4, consisting of Ethyl cellulose, DSS and Poly Ox®, had a maximum drug dissolution rate of 97.86 %, as compared to Storvas 80 mg (Ranbaxy Ltd, as a reference) which had a rate of only 54% during a period of 12 h in acidic media. A pharmacokinetic study performed on albino rabbits illustrates that the bioavailability of AT4 floating microcapsules significantly increased to nearly 1.7 times that of Storvas 80 mg. The present study indicates that the use of multi-unit floating microcapsules for delivery of ATC can improve its bioavailability.

Competition between selenomethionine and methionine absorption in the intestinal tract of green sturgeon ( Acipenser medirostris)

l-Selenomethionine (SeMet) is a dominant form of selenium (Se) found in organisms at all levels of aquatic food chains and a key source of Se bioaccumulation and ecotoxicity. In mammals, intestinal absorption of SeMet is at least partly via the Na +-dependent neutral amino acid transporter. The mechanism of SeMet absorption and competitive effects of other dietary components on SeMet absorption in fish are unknown. Thus the in vitro uptake rates of l-methionine (Met) and the competitive effect of SeMet on Met absorption, an indicator that SeMet uses the same nutrient transporter(s) for absorption, in the various regions of the green sturgeon ( Acipenser medirostris) intestine were investigated using intact tissues (a modified everted sleeve method). Intestinal tissue was incubated in Ringer's solution containing 0–10 mmol L −1 Met or SeMet ( n = 5 for each substrate's concentration and intestinal region), respectively, as well as constant tracer levels of isotope-labeled Met. The data indicate that SeMet uptake was mediated by the same transporter(s) as Met and that the absorption kinetics were similar for both substrates. When there were differences in absorption they appeared to be mostly due to higher permeability (passive uptake) of the tissue for Met than for SeMet, particularly in the pyloric caeca (PC) and distal intestine (DI). Maximum rates of absorption, on the other hand, tended to be higher for SeMet than Met in the mid intestine and DI, whereas differences in affinity for the transporters varied between these tissues but were very similar in the PC. These differences may be due to differences in regional intestinal characteristics such as amount of mucus secreted and degree of tissue contraction, and/or substrate differences regarding solubility in and movement through the mucus, influence on tissue contraction, permeability through membranes or between cells, intracellular metabolism, as well as basolateral transport. Interestingly, an increasing proximal-to-distal gradient for rates of methionine and putative SeMet absorption was observed in green sturgeon which differs from the declining gradient usually observed for substrate absorption in other fish species and mammals.

Nonlinear intestinal absorption kinetics of cefuroxime axetil in rats.

Cefuroxime is commercially available for parenteral administration as a sodium salt and for oral administration as cefuroxime axetil, the 1-(acetoxy)ethyl ester of the drug. Cefuroxime axetil is a prodrug of cefuroxime and has little, if any, antibacterial activity until hydrolyzed in vivo to cefuroxime. In this study, the absorption of cefuroxime axetil in the small intestines of anesthetized rats was investigated in situ, by perfusion at four concentrations (11.8, 5, 118 and 200 microM). Oral absorption of cefuroxime axetil can apparently be described as a specialized transport mechanism which obeys Michaelis-Menten kinetics. Parameters characterizing absorption of prodrug in free solution were obtained: maximum rate of absorption (Vmax) = 289.08 +/- 46.26 microM h-1, and Km = 162.77 +/- 31.17 microM. Cefuroxime axetil transport was significantly reduced in the presence of the enzymatic inhibitor sodium azide. On the other hand, the prodrug was metabolized in the gut wall through contact with membrane-bound enzymes in the brush border membrane before absorption occurred. This process reduces the prodrug fraction directly available for absorption. From a bioavailability point of view, therefore, the effects mentioned above can explain the variable and poor bioavailability following oral administration of cefuroxime axetil. Thus, future strategies in oral cefuroxime axetil absorption should focus on increasing the stability of the prodrug in the intestine by modifying the prodrug structure and/or targeting the compound to the absorption site.

Glomerular filtration and saturable absorption of iohexol in the rat isolated perfused kidney.

1. The renal handling of iohexol was examined in the rat isolated perfused kidney (IPK) over a perfusate concentration range of 5-20 micrograms ml-1. 2. At a concentration of 5 micrograms ml-1, a ratio of renal clearance over clearance by glomerular filtration (ClR/GF) of 0.63 +/- 0.06 could be determined. This ratio increased until 1.02 +/- 0.06 at 20 micrograms ml-1, indicating that a saturable mechanism is involved in the luminal disappearance of the drug. 3. Pretreatment of the kidneys with polylysine, probenecid or diatrizoate resulted in a significantly enhanced clearance of iohexol, probably due to inhibition of membrane binding. Renal clearance data were fitted to a kinetic model including filtration into the primary urine followed by saturable absorption at the luminal membrane. An absorption constant, KA, of 7.3 +/- 1.3 micrograms ml-1, and a maximum rate of absorption, VA,Max, of 1.4 +/- 0.1 micrograms min-1 were determined. 4. Iohexol accumulated in kidney tissue, reaching a concentration of 2 to 7.5 times the perfusate concentration. In freshly isolated proximal tubular cells and kidney cortex mitochondria, iohexol reduced the uncoupled respiratory rate at a concentration comparable to the highest tissue concentration found in the IPK. 5. In conclusion, iohexol is not only filtered by the kidney but also reabsorbed via a saturable mechanism, which results in tubular accumulation. Intracellularly sequestered iohexol may affect mitochondrial oxidative metabolism. Our results indicate that iohexol is not a true filtration marker.

Glucose absorption by isolated perfused rat proximal straight tubules

Glucose absorption was investigated in isolated perfused proximal straight tubules from rats by use of a newly developed ultramicrofluorometric assay. This assay takes advantage of the increase in fluorescence associated with the reduction of NAD to NADH while glucose is degraded to 6-phosphogluconate. When tubules were perfused at 6.70 +/- 0.42 nl.mm-1.min-1, the mean rate of glucose absorption was 11.0 +/- 1.0 pmol.mm-1.min-1, and the mean rate of fluid absorption was 0.61 +/- 0.06 nl.mm-1.min-1. Glucose transport is generally due to Na-glucose cotransport in the proximal nephron. In the rat proximal straight tubule, glucose absorption also appeared to be primarily due to Na-glucose cotransport, since 10(-4) M phlorizin inhibited absorption by 100%, as did inhibition of Na(+)-K(+)-ATPase by K removal. To determine the maximum rate of transport, tubules were perfused at rates greater than 20 nl.mm-1.min-1 with a solution containing 5.5 mM glucose. The maximum rate of glucose absorption was approximately 20 pmol.mm-1.min-1 under these conditions. The concentration of glucose that supports 50% of the maximum rate of absorption, Km, was 0.6 mM. When tubules were perfused at flow rates of less than or equal to 2 nl.mm-1.min-1, the luminal glucose concentration reached a limiting value of 0.47 mM with 5.5 mM glucose in the bath. The glucose permeability was 3.1 X 10(-6) cm/s.

Simulation studies on the kinetics of intestinal absorption

1. 1. A model has been used to simulate the absorption of solutes from perfused intestines. The model makes possible the numerical solution of the differential equations describing absorption processes along the length of the intestine which cannot be solved analytically. It allows for water absorption and the non-linear fall in solute concentration down the intestine. It can be modified easily to include other features, e.g. a change in V (maximum rate of absorption) or K (solute concentration at V/2) along the intestine. 2. 2. 90 perfect data sets have been simulated using the model. The Michaelis-Menten equation was fitted to a quarter of them using different algebraic expressions for the apparent solute concentration. The fit of the equation was very good in every case and it was not possible to explain the poorness-of-fit encountered during an earlier survey (Atkins, G.L. and Gardner, M.L.G. (1977) Biochim. Biophys. Acta 468, 127–145) in terms of the fall in solute concentration described above. 3. 3. The equation was also fitted to all the data sets in order to compare the use of several algebraic expressions for the apparent solute concentration. It has been shown that the current practice of using either the initial concentration or the effluent concentration can lead to estimates of V and K up to almost twice their true value. It has been shown that in one situation (glucose absorption by perfused rat intestine) it is possible to use an empirical expression that will reduce the errors considerably. 4. 4. It is also possible, and perhaps preferable, to use a computer program for fit the model directly to data from the simulated experiments and obtain precise estimates of V and K . 5. 5. In order to show that the model can be easily modified to incorporate other characteristics of perfused intestines, simulations were performed in which V decreased linearly down the intestine. In this example, it was concluded that an inhomogeneity due to non-constancy of V cannot be detected by single-pass perfusions.

A comparison between the balance method and radiotracer methods for measuring calcium absorption in treated and untreated patients with osteoporosis

Measurements of calcium absorption by the balance method and by the double tracer, multiple blood sampling radiocalcium tracer method were synchronized in 48 studies in 35 patients with osteoporosis. In the patients who were studied twice, results were obtained before and during treatment. Significant correlations were obtained between fractional dietary calcium absorption and three measures of the rate of 47Ca absorption : the maximum rate of absorption (M.A.R.) and mean rate of absorption ( AR ), both calculated by deconvolution analysis from the results of the double tracer study ; and the mean rate of absorption calculated from the oral tracer appearance curve using Marshall and Nordin's (1969) method (L.A.R.). None of these correlations were sufficiently good for the radiocalcium absorption test to be able to replace the expensive and time-consuming balance technique in the detailed study of absorption of calcium from the diet or calcium balance in individual patients with osteoporosis. Only a small part of this lack of correspondence could be accounted for by methodological uncertainties. The most sensitive radiocalcium absorption tests appear to be those which measure rates of absorption and they appear best suited to studying patients in homogeneous groups rather than individually.

Colostral Immunoglobulin Transfer in Calves II. The Rate of Absorption

The rate and pattern of colostral immunoglobulin absorption, based upon increase in concentration of immunoglobulin in serum in calves, has been determined from the interaction of three factors: starting age of colostral feeding, amount of colostrum fed, and time after feeding. All immunoglobulin classes show common characteristics of absorption following a rapid transfer during the first 4h after feeding. An analysis of three-dimensional response surface for each of the three immunoglobulin classes indicated positive linear trend in the amount fed up to 2 liters. Rates of absorption in succeeding time periods following the initial feeding had decreasing linear trends. That is, age at first feeding had an inverse effect on rate of absorption. A linear-by-linear interaction between amount fed and starting age was shown for all three classes. Only immunoglobulin IgM had a significant quadratic response for amount fed.Concentration of immunoglobulin in the pooled colostrums fed had no influence on rate of absorption. Evidence is that 2 liters of colostrum fed to Holstein calves may be optimum in the range studied for maximum pinocytotic activation of absorptive cells and maximum rate of absorption.

Disposition of zinc pyrithione in the rat

The pharmacokinetic profile of orally administered [2,6- 14C]-labelled zinc pyrithione (ZPT) was defined in male and female rats and was used to predict the blood concentrations of 14C at steady state correlating with the skeletal-muscle weakness observed in long-term feeding tests and mechanism studies. The 14C concentration was determined in blood, urine and faeces as a function of time following oral administration of doses of 0·5, 1·25 and 12·5 mg [ 14C]ZPT/kg. The major route of elimination from the body was the urine, in which all the ZPT appeared as metabolites. Mass-spectroscopic analysis of the urine indicated that a minor metabolite was 2-mercaptopyridine- N-oxide and the major metabolites were S-glucuronides of 2-mercaptopyridine- N-oxide. Radioassay of tissues indicated that ZPT was rapidly excreted and was not retained in the body to any significant degree. A two-compartment open model was used to describe the dynamics of ZPT in males and females given 0·5, 1·25 or 12·5 mg/kg. Kinetic constants for the same dose indicated sex differences in plasma elimination, renal clearance, time required for attainment of maximum blood concentration and rate of absorption. The ratio for 14C binding in red blood cells and plasma, respectively, was 5:1 at 96 hr and increased to ⩾ 45:1 at 240 hr, a probable reason for the low renal clearance rates. No sex difference in the concentration of 14C in blood at steady-state levels (maximum and minimum) was seen with the 0·5 mg/kg dose, but a significant difference was apparent at 1·25 mg/kg, the concentration being higher in the females. The significantly lower blood concentration of 14C in the males, in conjunction with the apparent higher rate of metabolism in the male, provide a reasonable explanation for the demonstrated sex difference in the dietary level of ZPT capable of producing an effect.

Study of the thermal oxidation of polyolefins—III: Pressure and temperature dependence of the rate of oxygen absorption

The kinetics of oxygen absorption by high pressure polyethylene (PE) have been studied between 8 and 650 torr oxygen pressure and in the temperature range 140 to 180°. The mechanism of thermal oxidation has been described and the equation for the rate of oxygen absorption has been derived. The rate equation has been studied in the initial stage and at points of the maximum rate of oxygen absorption. Some rate constant combinations (characteristic of the process) and their temperature dependence have been determined from experimental data. The pressure dependence of the initial and maximum rates of oxygen absorption, in the pressure range investigated, is well described by the proposed mechanism.

Intestinal calcium absorption: concurrent use of oral and intravenous tracers and calculation by the inverse convolution method.

Abstract Serum calcium specific activity curves following concurrent oral and intravenous doses of 2 radioisotopes of calcium were obtained in 20 normal women averaging 41 years of age, and in 10 osteoporotics averaging 65 years. Calcium absorption rate was calculated over a 4 hour period using an inverse convolution function of the 2 specific activity curves. The maximum rate of absorption occurred at an average of 15.6 minutes after ingestion and decreased monoexponentially thereafter. This finding is consistent with animal studies indicating that calcium absorption occurs maximally in the first part of the small intestine. Fractional absorption of the test load was calculated from integration of the absorption rate curve and was found to be identical both to the average equilibrium quotient, 47 Ca/ 45 Ca, observed in the blood and urine samples collected from these patients over several days, and to absorption estimated from external recovery of the oral tracer. Absorption was higher in the normal women than in 6 untreated osteoporotics, but 5 osteoporotics given ethane-1-hydroxy-1,1-diphosphonate had a higher rate than either group. Neither of these differences was statistically significant.

Transcapillary fluid movement in human calf after drinking hypertonic saline.

1. Transcapillary absorption of interstitial fluid was demonstrated with a pressure plethysmograph applied to the human calf after the ingestion of 200 ml. hypertonic (5.1%) saline. Capillary absorption began within 15 min after ingestion and lasted for about 2 hr. The maximum rate of absorption (0.019 ml./min. 100 ml. tissue) was attained 30-75 min after ingestion.2. The total amount of fluid absorbed into capillary blood vessels in the calf was 1.11 ml./100 ml. tissue. The amount of fluid thus absorbed in the whole body was estimated to be 677 ml.3. The capillary filtration coefficient (CFC) of the calf was also measured by the pressure plethysmograph. This was 0.0038 ml./min. mm Hg. 100 ml. tissue.4. The peak value of capillary absorption pressure was 5.2 mm Hg.5. The total osmotic pressure of the plasma rose by 12.6 m-osmole/kg H(2)O after ingestion. This rise was accompanied by transcapillary fluid absorption.6. The plasma protein concentration and packed cell volume were almost unchanged by ingestion, indicating that the plasma volume was unaltered.7. It was estimated that the net shift of fluid between intracellular and interstitial compartments during the period of transcapillary fluid absorption was very small.8. It is concluded that the volume of fluid moving from plasma into intestinal lumen is the same as that flowing from interstitial fluid into plasma, and that the transcapillary absorption is caused by a difference in osmotic pressure between the plasma and the interstitial fluid.

Design and performance characteristics of an X-ray target for electron accelerators

A simple inexpensive and convenient X-ray target has been developed for use with commercial electron accelerators. Measurements made at 3.0 MeV with an unscanned electron beam indicate a flux equivalent to 1.04 kr/min per mA of beam current at one meter from the target. The maximum practical rate of energy absorption for small samples under the above conditions is about 20 Mrad/hr, using a 5 in. scan.

The Absorbency of Terry Towels

Samples from eleven undyed cotton terry towels, ranging from 9.7 to 14.8 oz. per square yard, were laundered up to 100 times in a household type washer. Their weights, maximum rates of absorption, and ultimate absorptions were determined after various numbers of laundering and drying cycles. The unlaundered samples had the lowest values for both rate and ultimate absorption. Both values increased markedly with successive launderings up to about 10; after that the increase, were slight. At 100 laundering the rate had passed maximum, but the ultimate absorption was still increas ing. Ultimate absorption correlates well with fabric weight, but the rate shows no such correlation. The absorption per gram of cotton was somewhat greater for the lighter weight fabrics.