Irreversible Absorption Research Articles

Reactivation behaviour of TiFe hydride

The reactivation of TiFe by means of heating—absorption—desorption cycling in pure hydrogen was investigated. An interesting irreversible hydrogen absorption—desorption was observed, i.e. the deactivated sample is found to absorb pure hydrogen to its full capacity at room temperature after an incubation period when heated to 300 °C in pure hydrogen, but the desorption is much less. With increasing cycle number the incubation period becomes shorter and shorter, the amount of hydrogen desorbed increases, the evolution temperature of retained hydrogen decreases and finally the irreversibility disappears. During heating, the change in the surface chemical state was examined by X-ray photoelectron spectroscopy. It is believed that the metallic Fe and suboxidized Ti formed during the heat treatment catalyse the hydrogen dissociation-association and that the hydrogen permeability in the surface layer improves with increasing reductility of Ti. The irreversible hydrogen absorption—desorption was ascribed to the various surface strain states which give rise to different permeabilities in the hydriding and dehydriding processes.

Purification of C60 and C70 by selective complexation with calixarenes

MOLECULAR complexation of fullerenes in host–guest complexes has the potential to afford efficient large-scale purification of fullerenes1. This method would avoid the losses inherent in the chromatographic techniques currently in use, which arise from irreversible absorption on the stationary phase2. Several host-guest interactions have been reported for C60, including the formation of complexes with 1,4-hydroquinone3,4, azacrown compounds5, certain water-soluble macrocycles such as γ-cyclodextrin6–8, and complexation between C60 and an iridium phosphine in which pendant groups attached to a phosphorus atom form a cradle for an adjacent C60 molecule9. Other relevant studies are the inclusion of C60 into a microporous aluminophosphate10 and the formation of a charge-transfer complex between C60 and a thiafulvalene11. Here we show that both C60 and C70 will form discrete complexes with calixarenes, bowl-shaped macrocycles with hydrophobic cavities. Complexation of p-Bu'-calix[8]arene with a mixture of the toluene extract of 'crude' fullerene soot, followed by a series of recrystallizations, affords >99.5% pure C6. Our approach could lead to a substantial reduction in the cost of purifying C60 and C70.

Exact solutions for nonlinear diffusion with first-order loss

Exact solutions are developed for nonlinear diffusion with first-order loss (e.g. by reaction, irreversible absorption, biological degradation, or radioactive decay) from an instantaneous source. The diffusivity is proportional to a positive power of concentration. The solutions are for an arbitrary number of dimensions s > 0, with s = 1,2,3 in physical applications. All solutions give the slug radius exponentially approaching a finite maximum, with concentration decreasing exponentially to zero. Applications include the gravity spreading, and ultimate extinction, of liquid lenses on solid, or immiscible liquid, surfaces. The corresponding exact solutions for first-order gain, not loss, are also given.

Epithelial Transport of Drugs in Cell Culture. VIII: Effects of Sodium Dodecyl Sulfate on Cell Membrane and Tight Junction Permeability in Human Intestinal Epithelial (Caco-2) Cells

This study demonstrates how the common pharmaceutical wetting agent sodium dodecyl sulfate (SDS) increases the absorption of drugs and peptides across the human intestinal epithelium. First, an assay that could follow the reversible and irreversible time-dependent effects of SDS on the permeability of Caco-2 cell monolayers with high reproducibility was developed. SDS (0.40 mM) exposure for 20min resulted in reversible absorption enhancement of mannitol (Mr, 182 g/mol), l-deamino-8-o-arginine-vasopressin (Mr, 1071 g/mol), and polyethylene glycol (Mr, 4000 g/mol). A longer (2 h) exposure to SDS resulted in irreversible absorption enhancement. Second, transepithelial electrical resistance measurements (TEER) together with fluorescence and transmission electron microscopy were used to study the effects of SDS on epithelial integrity, cell membranes, intracellular calcium concentration, cytoskeleton, and tight junctions. The effect of SDS (0.40 mM) on epithelial integrity was immediate. A significant decrease in transepithelial electrical resistance measurements was obtained within 1min after exposure to SDS that was concomitant with increases in the permeability of the apical cell membranes and intracellular calcium concentration. SDS shortened the microvilli of the cells and produced apical (but not basolateral) membrane wounds, actin disbandment, disorganization of the terminal web, and structural separation of the tight junctions. The absorption enhancement was not reduced after repair of the apical cell membranes, indicating that SDS enhances drug and peptide absorption across the intestinal epithelium by the paracellular pathway.

Flow induced polymer‐filler interactions: Bound polymer properties and bound polymer‐free polymer phase separation and subsequent phase inversion during mixing

AbstractThe irreversible absorption of macromolecules on to solid filler particles during mixing in the melt is investigated. The molecular weight and concentration dependence of the absorbed layer thickness are evaluated and the chemical and morphological nature of the irreversibly absorbed polymer (bound polymer) are determined. It is found that the thickness of the bound polymer is not only dependent on the filler concentration but also dependent on polymer molecular weight. Bound polymer in high density polyethylene/colloidal silica systems is more amorphous and contains higher concentration of oxidation products (which are induced by a mechanochemical reaction during mixing) when compared with free polymer. As a result of bound polymer formation, flow induced crystallization and polymer entrapment during mixing, a phase separation between bound polymer and free polymer takes place which eventually leads to a liquid to solid phase inversion when the phase volume of the solids exceed a critical value under isothermal conditions. If the mixing is continued after phase inversion, the particle size of the newly formed powder is reduced and particle size distribution, is narrowed. This process of phase inversion and subsequent size reductions are termed as crumbling which can take place at filler concentrations well below the expected maximum packing fraction of solids, if the filler particle size is small and/or the molecular weight of the polymer is high. Crumbling phenomena are utilized in the agglomeration of fine powders and microencapsulation of solids and/or liquids.

Irreversibility behavior investigated with microwave absorption in the high-T c Bi(Pb)-Sr-Ca-Cu-O superconducting ceramics

Reversible and irreversible microwave absorption is observed as a function of temperature and field in the high-T c phase of a Pb doped Bi-Sr-Ca-Cu-O superconductor. The difference between zero-field-cooled and field-cooled absorption behaviors is related to the flux-pinning property. The irreversibility temperature T irr scales with the applied field as H 1 3 , in accord with an exponent for a Tl-based superconductor, but in contrast to H 2 3 power law in the Y-based superconductor or spin glasses.

A Mathematical Model for 137Cs Uptake and Release by Filamentous Algae

AbstractA mathematical model of the dynamics of radiocaesium transport in the aquatic phase—algae system is suggested in this work. Allowance is made for algae growth and for both reversible and irreversible absorption of this radionuclide by the algae. The algae biomass is divided hypothetically into two compartments with different exchange kinetics. The parameters of the model are time dependent. The model is quantified using experimental data for the concentrations of 137Cs in Cladophora glomerata filamentous algae and in water, obtained in situ in the environment of a nuclear power station. The model fits the data reasonably well and can be applied, for example, in bioindication of radioactivity in aquatic recipients in the environment of nuclear power stations.

Analysis of paired serum, urine and filter paper blood specimens for presence of filarial antigen by immunoradiometric assay.

Paired serum, urine, and finger-prick whole blood dried on filter paper were analyzed by immunoradiometric assay (IRMA) for filarial antigen using Brugia malayi-specific rabbit antibody. Nine sera and 6 urines from the 10 paired serum-urine samples obtained from individuals with microfilaremia contained IRMA detectable filarial antigen. In contrast, all serum and urine specimens from patients with chronic infections, endemic and non-endemic controls were negative. Whole blood eluted from filter paper spots contained IRMA detectable material; their degree of positivity agreed well with IRMA binding levels obtained with paired urines. Reduced recovery of antigen dried on filter paper was observed at antigen levels less than 10 ng/ml equivalents, presumably due to irreversible absorption onto the filter paper. Urine and finger-prick filter paper blood specimens can be used in the diagnosis of microfilaremic infections that have been associated with circulating antigen in the blood.

A particle interaction model of reversible organic chemical sorption

Understanding the factors governing irreversible and reversible sorption is essential to predict the influence of sediment on contaminant fate and transport in surface waters. This study used sediment of an urban water body to demonstrate irreversible accumulation and reversible absorption of perfluoroalkyl acids (perfluorooctane sulfonate (PFOS), perfluorononanoic (PFNA) and perfluorodecanoic acid (PFDA)) during two sorption–desorption (S–D) cycles. Absorption and desorption isotherms were consistent with sorption to irreversibly absorbing glassy sediment organic carbon (SOC) and liquid–liquid like partitioning to rubbery SOC. The observed absorption isotherms and the desorption isotherms were adequately fitted linear models. Irreversible absorption showed signs of saturation and the reversible partitioning diminished during the 2nd S–D cycle causing the composite sorption capacity to decrease. Results suggest that under the conditions tested, surface water sediment can act as sink for the studied PFAAs. Rubbery SOC can potentially release or absorb contaminants, thus acting as a concentration buffer. S–D cycling can cause irreversible absorption concentration to increase even when exposure occurs at lower concentrations (i.e. 5μg/L). logKOC values of sediment that underwent S–D cycling overlaps with the range of field date, suggesting that the sediment of surface water may have experienced some degree of S–D cycling.

Investigations on the storage life of oxygen electrodes by means of electrolytic catalysts based on CoTAA

When electrolytic catalysts preferred by pyrolysis of cobalt tetraazaannulenes on active carbon are stored in air, a decrease of the electrolytic activity is observed. This deterioration is the result of irreversible absorption of oxygen from air. This oxidation of electrode materials which are very active in the cathodic reduction of oxygen can only be prevented by storage under a protective atmosphere or by immediate application.

Keeping a light-driven proton pump under control

Although proton pumping by bacteriorhodopsin is driven by the (presumably) irreversible absorption of a photon, it is inhibited by its ‘product’, the electrochemical potential difference of the proton. Apparently, this control property (reminiscent of respiratory control) is so important for the overall control characteristics of energy metabolism that bacteriorhodopsin acquired (or retained) a special catalytic mechanism: its photocycle appears to be branched into a pumping and a non-pumping pathway.

Complete and reversible absorption of radiation

Kirchhoff's law has caused confusion in the discussion about the theoretical maximum work from radiation because it permits only infinitesimal or irreversible absorption. With the aid of an optical circulator, non-Kirchhoff behaviour is possible in principle which permits at the same time complete and reversible radiation absorption. The key to overcome Kirchhoff's law seems to be the magnetic field, a condition explicitly excluded by Kirchhoff. The work extracted in complete reversible conversion of radiation is calculated. The irreversibilities connected with the emission process are discussed.

Laser induced irreversible absorption changes in alkali halides at 10.6 μm

Laser induced irreversible changes in the absorption of alkali halides has been observed by using repetitively pulsed laser calorimetry. These changes occur at intensities below that required for laser induced breakdown and necessitate a change in the definition of laser damage threshold. A simple model is proposed to explain these observations based on the accumulation of microscopic failures as a result of each pulse.

Abnormal effects, accompanying metamagnetic transition in a longitudinal pulse field

It is shown that a system undergoing metamagnetic transition under adiabatic conditions, “is moving” in a phase space along the first-order phase transition line. In the vicinity of the tricritical point the system is no longer adiabatic due to a sharp increase of an irreversible absorption of the low-frequency external field energy. Comparison is made of the results of present work with experimental data obtained for siderite FeCO 3.

Light‐Induced Absorption Changes in Etiolated Coleoptiles

AbstractBlue (or green) light induced reversible and irreversible absorption changes in etiolated wheat (Triticum aestivum) coleoptiles. Immediately after a 10 s pulse of blue light there was an absorbance increase at 440 nm and a decrease at 420 nm. The absorbance at 440 nm returned to the original level in a biphasic way, with first‐order rate constants of 0.05 s−1 and 0.006 s−1 at 25°C. The change at 440 nm was partly, but not completely, inhibited by iodide. In the 500–600 nm region complex changes occurred, indicating the participation of at least two different cytochromes, one of which was oxidized during a 10 s light pulse and the other oxidized more slowly during the following dark period.

Determination of irreversible absorption of water by cellulose filters

Using cellulose filters instead of glass fiber for the determination of the total suspended particulates by the “High-Vol” method may cause significant positive errors. Because of their hygroscopic nature, cellulose filters absorb a large quantity of water during sampling which is not entirely lost on equilibration at constant humidity. For short period samples, the amount of water irreversibly absorbed, strongly depends on the atmospheric humidity. For a 1-h filter taken on a foggy day, this amount of water may be of the same order or even higher as an average particulate load obtained by commercial “High-Vol” samplers in urban areas. For 24-h sampling periods, a mean correction factor was determined during various atmospheric conditions. This value amounted to 4.2 ± 2.4 mg on the average for an 11 cm dia. Whatman 41 filter (0.8 g of cellulose) at a mean atmospheric humidity of 90 per cent.

Axial and Transnodal Movement of14C,22Na, and36Cl inNitella translucens

The time courses of axial movement in Nitella translucens of a number of 14C-labelled compounds and of 36C1 and 22Na have been determined together with simultaneous microscopical observations of the rates of visible protoplasmic streaming. In general, the translocation profiles suggest the irreversible absorption of tracer though there are examples of reversible absorption. The coupling between visible streaming and the front of the axial transport is weak. Light, DCMU (dichlorophenyldimethylurea), and temperature affect the translocation but visible streaming is affected only by temperature and the passage of an action potential. There is evidence, from a number of compounds, of a faster-thari-streaming translocation of small amounts of tracer in the form of ‘pulses’ which are completely detached from the main body of tracer. Either vesicles or microperistaltic packets are thought to account for this rapid moiety. Observations of transnodal transfer suggest that an active mechanism is involved in the transference of carbonate, urea, acetate, and chloride. The influxes of the various compounds have been calculated and shown to be in good agreement with existing published values. Action potentials reduce the influx of carbonate, chloride, and possibly acetate, as do lack of light and DCMU. It is suggested that the influx of these anions is coupled with the active anion pump and with loading sites on the plasma membrane which become inoperative during and immediately following an action potential.

Effect of relative humidity on the disappearance of ozone and sulphur dioxide in contained systems

The decay of sulphur dioxide and ozone concentrations has been observed in two different containers. The decay is first order in both cases indicating irreversible absorption on the walls. Relative values are considered in terms of deposition velocities ( v g ) and these are shown to be very sensitive to the humidity of the system. In the case of sulphur dioxide at high humidities, v g values are high and come very close to the maximum value for the system as measured by Thorium B disappearance. In the case of ozone, v g is much smaller but the increase with humidity is sufficiently large to affect overall ozone concentrations in experiments simulating photochemical smog formation.

Studies of the rickettsial plaque assay technique.

A plaque assay system for pathogenic rickettsiae, which utilizes primary chick embryo tissue cultures, is described. It proved to be a highly reproducible measure of infectiousness for Rickettsia rickettsi and R. typhi, which were employed in most studies; as well as for R. canada, R. prowazeki, R. sibirica, R. akari, R. conori, and Coxiella burneti. Plaque-forming units (PFU) were compared to direct rickettsial counts and to 50% infectious dose (ID(50)) values for embryonated eggs, mice, and guinea pigs. Plaque size, appearance, and number were influenced by diluent, incubation temperature after nutrient overlay, centrifugation of inoculated tissue cultures, and number of host cells planted initially in each flask. The most critical factors in plaque formation were diluent used in making rickettsial suspensions and incubation temperature (32 C) after nutrient overlay. Brain Heart Infusion was the only diluent capable of preventing significant delay in plaque formation and decreases in PFU and mouse ID(50). Plaque formation was unaffected by genetic background of host cells, volume of inoculum, temperature and length of incubation period before nutrient overlay, and rapid freezing and thawing of rickettsial seed. Centrifugation of inoculated cultures at 600 x g resulted in 100% irreversible absorption of rickettsiae to host cells within 5 min, whereas without centrifugation at least 4 hr was required to achieve the same effect.

Superhigh temperature gas chromatography

At red heat temperatures and higher, the conditions of gas chromatographic separation change essentially, since the separated components, packing and even the column and detector walls are in a state of higher chemical activity. When designing an apparatus for superhigh temperature gas chromatography, the detector problem is the most difficult. Many kinds of detectors used at present are unsuitable under these conditions and considerable modifications of others are necessary. Pneumatic detectors are the most useful for superhigh temperature detection. At temperatures between 500 and 1000° the separation is often complicated by chemical reactions which can take place in the column. For instance, irreversible absorption of metallic K and Na, and PbCl 2 and SnCl 2 with many materials, destruction of CdI 2, reaction between S and Se on introduction of such a mixture into the column have been observed. However, the successful separation of some metals and halides and good results for the direct quantitative analysis of ZnCd binary alloys allows us to hope that further investigation in this field will give interesting results.