Activation Energy Of Water Diffusion Research Articles

Solar drying of oregano leaves (Plectranthus amboinicus, Lour): Analysis of experimental performance under a tropical climate

Despite the multiple applications of the oregano ( Plectranthus amboinicus (Lour)), an important herbaceous plant because of its medicinal and culinary properties, limited research has been conducted on this species’ solar drying. Thus, the experimental drying of oregano leaves in a tropical climate was performed using direct and indirect solar drying and an electric oven in this research work. Also, mathematical modeling of the drying process, moisture diffusivity, activation energy, and colorimetric analysis (as a quality parameter) were accomplished to complement the experimental evaluation and understand the drying process behavior. The results show a shorter drying time obtained with the electric oven with 210 min reached at 65°C; however, the minimum solar drying time (250 min) was achieved with a maximum drying rate of 0.025 g water/g dry matter per minute and minimum final moisture between 0.28 and 0.13 g water/g dry matter was obtained with indirect solar dryer. Moreover, the models that better represented the experimental data were Modified Page, Page, and Logarithmic, with a maximum value of R2 obtained of 0.9980 corresponding to the Logarithmic model. Furthermore, a maximum effective diffusivity value of 1.81E-9 was obtained with direct solar dryer natural convection, while for the electric oven, were 1.14E-10, 2.280E-10, and 1.026E-09 for 45, 55, and 65°C, respectively. The activation energy for water diffusion in oregano leaves was 55.66 and 97.78 kJ/g mol for solar dryers and electric ovens, respectively, which were values very close to those reported in the literature. Finally, the colorimetric analysis exhibited a minimum color change value of 17.1 obtained for the indirect solar dryer, allowing better oregano preservation and maintaining its quality for the market, which makes it ideal for drying oregano in tropical climates and promotes solar drying use for sustainable growth of the region.

Water Sorption by Polyheteroarylenes.

The sorption–diffusion characteristics of rigid-chain glassy polymers based on polyheteroarylenes (PHAs) have been studied in a wide interval of relative humidity and temperatures of thermal treatment of the polymer sorbents. Experimental data on water vapor sorption for polynaphthoyleneimidobenzimidazole (PNIB) and its copolymers with different chemical nature have been obtained. Water diffusion coefficients have been calculated, and parameters of their concentration and temperature dependences have been determined. It was found that water molecules sorbed by PNIB and its copolymers are strongly bounded. Water mobile and cluster states depend on the structure of macromolecules and thermal prehistory of polymer sorbents. It is shown that the translational coefficients of water diffusion for all PHAs are in the range from 10−9 to 10−8 cm2/s. The diffusion coefficients also increase slightly with temperature increasing, and their general dependence on temperature is satisfactorily described by the Arrhenius equation. The average activation energy of water diffusion varies from 24.3 to 25.9 kJ/mol. The hydrate numbers of rigid-chain PHAs functional groups have been determined. The above-mentioned results allow us to predict the sorption properties of heterocyclic macromolecular sorbents with complex chain architecture.

Study on dehydration kinetics of mango kernel

This study was aimed to study the dehydration kinetics of mango kernel with specific reference to sample thickness, drying temperature and mango varieties, and was performed prior to preparation of flour from mango kernel. Kernels of four mango varieties (Boishakhi, Amrapali, Fazli and Ashwina) were separated manually and dried at 65˚C by slicing into 4, 6 and 8 mm thickness to know the thickness effect on drying kinetics. Again, 6 mm thick slices of kernels were dried at 55, 60 and 65˚C to know the temperature effect. Kinetics analysis resulted that drying rate decreased with the increasing of thickness and decreasing of temperature. Ashwina’s kernels having the highest initial moisture content (M0) had the highest drying rate constant (m), while the lowest m was noticed for Boishakhi’s kernels having the lowest M0. The values of power law index (n) of drying model were 0.83, 0.32, 0.31 and 0.70 for kernels of Boishakhi, Amrapali, Fazli and Ashwina mango, respectively. Activation energy of water diffusion was in the range of 7.002-7.515 KCal/g-mole. Conclusively, this study revealed that moisture diffusivity and drying rate are greatly influenced by drying parameters and kernel varieties.

Effect of soaking conditions on properties of Khao Dawk Mali 105

The effects were studied of soaking conditions on the physical properties and water absorption behavior of Khao Dawk Mali 105 (KDML105) paddy. Samples of KDML105 paddy were soaked in water at four temperatures (room temperature (27.8 ± 0.98°C), 30°C, 40°C, 50°C) for 1–12 hr. The soaking conditions (temperature and time) affected the water absorption of KDML105 paddy. However, the soaking temperature had more influence on the water absorption than the soaking time since the water absorption rate of paddy after the first hour increased from 0.117 kg water/hr/kg solids at room temperature of soaking to 0.159 kg water/hr/kg solids at 50°C soaking temperature. The suitable conditions for soaking were 50°C for 9 hr and the resultant moisture content of the paddy was higher than 45% on a dry basis and sufficient for gelatinization and germination of Khao Hang rice. For the same period of soaking, water absorption increased with increasing soaking temperature. The effective water diffusion was influenced by the soaking temperature increasing with temperature from 8.85 × 10-12 m2/s to 1.83 × 10-11 m2/s. An Arrhenius relationship was used to describe the water diffusion dependence on the soaking temperature, and the activation energy for water diffusion was 26.48 kJ/mol. Seven empirical models were developed to explain the hydration behavior of KDML105 paddy. The two-term exponential model produced the best results for goodness-of-fit for any soaking time.

Size-dependent corrosion behavior of graphene oxide coating

Graphene oxide emerges as an effective corrosion resistant coating. However, the influence of graphene oxide sheets size on the corrosion protection remains unclear. In this report, we investigate the effect of different graphene oxide (GO) sheets size in the formation of corrosion resistant coating. We provide valuable input for electrophoretic deposition in which GO sheets in smaller size diffuse faster during deposition to cause more oxygen reduction, thereby forms a coating with higher hydrophobicity, stronger adhesion, and lesser pinholes. Detailed electrochemical impedance analysis shows that the coating formed from GO sheets in smaller size exhibits higher activation energy for water diffusion, causing slower water diffusion rate and lower permeation into the coating. The findings suggest that GO sheets in smaller size produce a reliable coating with excellent corrosion resistance behavior.

Anisotropic diffusion of water molecules in hydroxyapatite nanopores

New insights into the dynamical properties of water in hydroxyapatite (HAP) nanopores, a model system for the fluid flow within nanosize spaces inside the collagen-apatite structure of bone, were obtained from molecular dynamics simulations of liquid water confined between two parallel HAP surfaces of different sizes (20 A ≤ H ≤ 240 A). Calculations were conducted using a core-shell interatomic potential for HAP together with the extended simple point charge model for water. This force field gives an activation energy for water diffusion within HAP nanopores that is in excellent agreement with available experimental data. The dynamical properties of water within the HAP nanopores were quantified in terms of the second-order water diffusion tensor. Results indicate that water diffuses anisotropically within the HAP nanopores, with the solvent molecules moving parallel to the surface twice as fast as the perpendicular direction. This unusual dynamic behaviour is linked to the strong polarizing effect of calcium ions, and the synergic interactions between the water molecules in the first hydration layer of HAP with the calcium, hydroxyl, and phosphate ions, which facilitates the flow of water molecules in the directions parallel to the HAP surface.

Effect of N,N′-ethylenebis(stearamide) on the water absorption and hydrolytic degradation of poly(lactic acid)/halloysite nanocomposites

Poly(lactic acid)/halloysite nanoclay (PLA/HNC) nanocomposites with N, N′-ethylenebis(stearamide) (EBS) were produced by melt mixing. Water absorption behaviors of the PLA nanocomposites were studied at three different temperatures, that is, 30, 40, and 50°C. The water absorption kinetics of PLA/HNC nanocomposites conform to Fickian diffusion behavior at immersion temperatures of 30 and 40°C due to the diffusional exponent ( n) values that were close to 0.5 for all specimens. However, the hydrolysis of PLA occurred for longer time deviations at 50°C. Activation energy of water diffusion ( Ea) for PLA nanocomposites were found to be affected by the HNC and EBS contents. The glass transition temperature ( Tg), cold crystallization temperature ( Tcc), and melting temperature ( Tm) of the PLA sample were shifted to lower temperature after subjected to immersion temperature of 50°C. The carbonyl index of all PLA specimens increased after water absorption at 40 and 50°C due to the formation of higher amount of carboxylic acid end groups during the hydrolysis process.

Epoxidized natural rubber toughened poly(lactic acid)/halloysite nanocomposites with high activation energy of water diffusion

ABSTRACTPoly(lactic acid)/halloysite nanotube (PLA/HNT) nanocomposites were prepared using melt compounding followed by compression molding. Epoxidized natural rubber (ENR) was used to toughen the PLA nanocomposites. The properties of PLA/HNT nanocomposites were characterized by impact tests, thermal analysis (DSC), morphological analysis (FESEM, TEM), and Fourier transform infrared spectroscopy (FTIR). Water absorption tests were performed at three immersion temperature (30, 40, 50°C). The maximum water absorption (Mm), diffusion coefficient (D), and the activation energy of water diffusion (Ea) were determined. The impact strength of PLA/HNT6 nanocomposites was increased significantly to ∼296% by the addition of 15 wt % ENR. The incorporation of HNT and ENR increase its nucleation effect and assist in the crystallization process of PLA. The HNT has good affinity with PLA and ENR, which was revealed by TEM and FTIR. The Mm of PLA was increased in the presence of HNT and ENR. Nevertheless, the D value and the Ea of the PLA nanocomposites were found to be affected by the HNT and ENR contents. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42850.

Arrhenius activation energy for water diffusion during drying of tomato leathers: The concept of characteristic product temperature

The drying kinetics of tomato leathers was studied between 40 and 80 °C and the corresponding thermal histories were recorded. As air and product temperatures were found to be considerably different during the drying runs, the original concept of “characteristic product temperature” was proposed. It is defined as the temperature corresponding to the time at which the instantaneous drying rate is equal to the mean drying rate. Then, the Arrhenius activation energies (Ea) obtained by two methods were compared: (1) correlating the diffusion coefficient (D) with the air temperature and (2) correlating D with the characteristic product temperature. Drying curves comprised a “wet zone”, where moisture content fell almost linearly with time, and a subsequent “dry zone”. In the first zone, the Arrhenius relationship with the air temperature yielded an Ea of 18.6 kJ mol−1 whereas, when utilising the characteristic product temperature the activation energy was 47.3 kJ mol−1, comparable to the enthalpy of water desorption. In the second zone, activation energies were 21.7 and 26.6 kJ mol−1, respectively. Molecular mobility theory suggests a stronger temperature dependence of diffusion-limited phenomena in high moisture content matrices and thus would forecast a higher Ea for the wet zone. Therefore, the characteristic product temperature is more meaningful than the air temperature in the Arrhenius relationship.

Morphology and water permeability of red blood cells from green sea turtle (Chelonia mydas).

The morphology and diffusional water permeability (P d) of red blood cells (RBCs) from green sea turtle (GST) (Chelonia mydas) are presented for the first time. The RBCs had an ellipsoidal shape with full-axis lengths (diameters): D = 14.4μm; d = 10.2μm; h = 2.8μm. The values of P d (cms(-1)) were 5.1 × 10(-3) at 15°C, 5.7 × 10(-3) at 20°C, 6.3 × 10(-3) at 25°C, 6.8 × 10(-3) at 30°C, and 7.9 × 10(-3) at 37°C (i.e., significantly higher than in human RBCs in which it was measured to be 4.2 × 10(-3) at 25°C, 5.0 × 10(-3) at 30°C, and 6.2 × 10(-3) at 37°C). There was a lack of inhibition of P d of GST RBCs by p-chloromercuribenzoate (PCMB), a well-known inhibitor of the RBC water channel proteins (WCPs). The activation energy of water diffusion (E a,d) in GST RBCs was 15.0 ± 1.6kJmol(-1) which is lower than the E a,d for human RBCs (~25kJmol(-1)). These results indicate that in the membrane of GST RBCs, there were no WCPs that were inhibited by the mercurial reagent, while the lipid bilayer of this membrane is unusually permeable to water. This is likely to be a phylogenetically old trait, like that found in amphibians and even the later birds, all of which have nucleated erythrocytes; and it is also likely to be a result of the animal's adaptation to a herbivorous diet (algae and seagrasses).

Water Absorption Kinetics and Hygrothermal Aging of Poly(lactic acid) Containing Halloysite Nanoclay and Maleated Rubber

Poly(lactic acid)/halloysite nanoclay composites (PLA/HNC) containing maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH) were produced using melt compounding followed by compression molding. The effects of hygrothermal aging on the thermal properties and functional groups changes of the HNC reinforced PLA (with and without SEBS-g-MAH) at three different temperatures (i.e., 30, 40 and 50 °C) were analyzed using differential scanning calorimetry and Fourier transform infrared spectroscopy techniques. The diffusion coefficient (D) of PLA was decreased by the incorporation of HNC and SEBS-g-MAH. The activation energy of water diffusion (E a ) of PLA/HNC/SEBS-g-MAH nanocomposites was higher than that of pure PLA. The glass transition temperature (T g ), cold-crystallization temperature (T cc ) and melting temperature (T m ) of the PLA sample were shifted to lower temperature and the effect was more pronounced at 50 °C. The carbonyl index values of all PLA samples increased after immersed in 40 and 50 °C, which is due to the formation of higher amount of carboxyl groups during the hydrolysis process.

Mechanical and water absorption behaviors of carbon nanotube reinforced epoxy/glass fiber laminates

Epoxy laminates were prepared by using hybridization of glass fibers and multiwalled carbon nanotubes. Mechanical behaviors of the epoxy hybrid composites were characterized by using flexural, impact, and fracture toughness tests. Morphological properties of the epoxy hybrid composites were investigated by using field emission scanning electron microscopy. Water absorption tests were performed at three different immersion temperatures, i.e. 30, 60, and 90℃. The flexural properties, impact strength and fracture toughness of the epoxy/glass fiber composites increased significantly by the incorporation of multiwalled carbon nanotubes. The kinetics of water absorption for the epoxy hybrid composites conformed to Fickian law behavior. Adding multiwalled carbon nanotubes increases the equilibrium moisture content ( Mm) and diffusion coefficient ( D), but lowers the activation energy of water diffusion ( Ea) for epoxy/glass fiber composites.

Water Vapor Permeability of Polypropylene

To understand the water vapor transport through a polypropylene film at near ambient temperature, water vapor permeation and sorption measurements were carried out using tritiated water as tracer. The activation energy and frequency factor of the permeability were found to be 11 kJ/mol and 1.5 x 10-10 cm3(STP) cm cm-2 s-1 Pa-1, respectively. The corresponding values of the solubility were determined to be -30 kJ/mol and 2.9 x 10-10 cm3(STP) cm-3 Pa-1. Because the permeation can be described by a one-dimensional diffusion model, the diffusion coefficient was evaluated from the quotient of permeability and solubility. The activation energy of water diffusion through polypropylene was calculated to be 41 kJ/mol.

Comparative NMR studies of diffusional water permeability of red blood cells from different species: XVIII platypus (Ornithorhynchus anatinus) and saltwater crocodile (Crocodylus porosus)

As part of a programme of comparative measurements of Pd (diffusional water permeability) the RBCs (red blood cells) from an aquatic monotreme, platypus (Ornithorhynchus anatinus), and an aquatic reptile, saltwater crocodile (Crocodylus porosus) were studied. The mean diameter of platypus RBCs was estimated by light microscopy and found to be approximately 6.3 microm. Pd was measured by using an Mn2+-doping 1H NMR (nuclear magnetic resonance) technique. The Pd (cm/s) values were relatively low: approximately 2.1 x 10(-3) at 25 degrees C, 2.5 x 10(-3) at 30 degrees C, 3.4 x 10(-3) at 37 degrees C and 4.5 at 42 degrees C for the platypus RBCs and approximately 2.8 x 10(-3) at 25 degrees C, 3.2 x 10(-3) at 30 degrees C, 4.5 x 10(-3) at 37 degrees C and 5.7 x 10(-3) at 42 degrees C for the crocodile RBCs. In parallel with the low water permeability, the Ea,d (activation energy of water diffusion) was relatively high, approximately 35 kJ/mol. These results suggest that "conventional" WCPs (water channel proteins), or AQPs (aquaporins), are probably absent from the plasma membranes of RBCs from both the platypus and the saltwater crocodile.

Comparative NMR studies of diffusional water permeability of red blood cells from different species: XVI Dingo (Canis familiaris dingo) and dog (Canis familiaris)

As part of a programme of comparative measurements of Pd (diffusional water permeability) the RBCs (red blood cells) from dingo (Canis familiaris dingo) and greyhound dog (Canis familiaris) were studied. The morphologies of the dingo and greyhound RBCs [examined by light and SEM (scanning electron microscopy)] were found to be very similar, with regard to aspect ratio and size; the mean diameters were estimated to be the same (approximately 7.2 microm) for both dingo and greyhound RBCs. The water diffusional permeability was monitored by using an Mn2+-doping 1H NMR technique at 400 MHz. The Pd (cm/s) values of dingo and greyhound RBCs were similar: 6.5 x 10(-3) at 25 degrees C, 7.5 x 10(-3) at 30 degrees C, 10 x 10(-3) at 37 degrees C and 11.5 x 10(-3) at 42 degrees C. The inhibitory effect of a mercury-containing SH (sulfhydryl)-modifying reagent PCMBS (p-chloromercuribenzene sulfonate) was investigated. The maximal inhibition of dingo and greyhound RBCs was reached in 15-30 min at 37 degrees C with 2 mmol/l PCMBS. The values of maximal inhibition were in the range 72-74% when measured at 25 degrees C and 30 degrees C, and approximately 66% at 37 degrees C. The lowest value of Pd (corresponding to the basal permeability to water) was approximately 2-3 x 10(-3) cm/s in the temperature range 25-37 degrees C. The Ea,d (activation energy of water diffusion) was 25 kJ/mol for dingo RBC and 23 kJ/mol for greyhound RBCs. After incubation with PCMBS, the values of Ea,d increased, reaching 46-48 kJ/mol in the condition of maximal inhibition of water exchange. The electrophoretograms of membrane polypeptides of the dingo and greyhound RBCs were compared and seen to be very similar. We postulate that the RBC parameters reported in the present study are characteristic of all canine species and, in particular in the two cases presented here, these parameters have not been changed by the peculiar Australian habitat over the millennia (as in the case of the dingo) or over shorter time periods, decades or centuries (as in the case of the domestic greyhound).

Comparative NMR studies of diffusional water permeability of red blood cells from different species: XV. Agile wallaby ( Macropus agilis), red-necked wallaby ( Macropus rufogriseus) and Goodfellow's tree kangaroo ( Dendrolagus goodfellowi)

The water diffusional permeability ( P d) of red blood cells (RBC) from agile wallaby ( Macropus agilis), red-necked wallaby ( Macropus rufogriseus) and Goodfellow's tree kangaroo ( Dendrolagus goodfellowi) was monitored using an Mn 2+-doping 1H nuclear magnetic resonance (NMR) technique at 400 MHz. The P d (cm s − 1 ) values of agile wallaby RBCs were 7.5 × 10 − 3 at 25 °C, 9 × 10 − 3 at 30 °C, 11 × 10 − 3 at 37 °C, and 13 × 10 − 3 at 42 °C. The inhibitory effect of a mercury-containing sulfhydryl (SH)-modifying reagent p-chloromercuribenzoate (PCMB) on agile wallaby RBCs was investigated. The maximal inhibition was reached in 90 min at 37 °C with 2 mmol L − 1 PCMB. The value of maximal inhibition was ~ 63% when measured at 25 °C, ~ 52% at 37 °C and ~ 45% at 42 °C. The lowest value of P d (corresponding to the basal permeability to water) was ~ 3 × 10 − 3 cm s − 1 at 25 °C. For the RBCs from red-necked wallaby ( M. rufogriseus) the values of P d (cm s − 1 ) were 7 × 10 − 3 at 25 °C, 8 × 10 − 3 at 30 °C, 10 × 10 − 3 at 37 °C, and 12 × 10 − 3 at 42 °C. Higher values of P d (cm s − 1 ) were found for the RBCs from Goodfellow's tree kangaroo ( D. goodfellowi): 8.5 × 10 − 3 at 25 °C, 10 × 10 − 3 at 30 °C, 13 × 10 − 3 at 37 °C, and 15 × 10 − 3 at 42 °C. The mean values of the activation energy of water diffusion ( E a,d) were ~ 25 kJ mol − 1 for RBCs from the agile wallaby and tree kangaroo, respectively, and ~ 23 kJ mol − 1 for RBCs from red-necked wallaby. The values of E a,d increased after exposure of agile wallaby RBCs to PCMB, reaching a value of ~ 43–46 kJ mol − 1 when the maximal inhibition of P d was achieved.

Temperature dependence of water self-diffusion through lipid bilayers assessed by NMR

The temperature dependence of the coefficient of water self-diffusion across plane-parallel multib-ilayers of dioleoylphosphatidylcholine oriented on a glass support was studied in the 20–60°C range by pulsed field gradient NMR. The coefficient for transbilayer diffusion of water proved almost four orders of magnitude smaller than for bulk water, and 10 times smaller than that for lateral diffusion of lipid under the same conditions. The temperature dependence obeyed the Arrhenius law with apparent activation energy of 41 kJ/mol, much higher than that for bulk water (18 kJ/mol). The experimental data were analyzed using the “dissolution-diffusion” model, by simulating water passage through membrane channels, and by examining water exchange in states with different modes of translational mobility, including pore channels and bilayer defects. Each approach could take into account the role of bilayer permeability and assess the apparent activation energy for water diffusion in the hydrophobic part of the bilayer, which proved close to the value for bulk water. Estimates were obtained for water diffusion coefficients in the system, coefficients of bilayer permeability for water, and the influence of bilayer defects on the lateral and transverse diffusion coefficients.

Thermal properties and water sorption behaviors of epoxy and bismaleimide composites

In this work, we prepared epoxy/BMI composites by usingN,N′-bismaleimide-4,4′-diphenylmethane (BMI), epoxy resin (diglycidyl ether of bisphenol-A (DGEBA)), and 4,4’-diamino diphenyl methane (DDM). The thermal properties and water sorption behaviors of the epoxy and BMI composites were investigated. For the epoxy/ BMI composites, the glass transition and decomposition temperatures both increased with increasing BMI addition, which indicates the effect of BMI addition on improved thermal stability. The water sorption behaviors were gravimetrically measured as a function of humidity, temperature, and composition. The diffusion coefficient and water uptake decreased and the activation energy for water diffusion increased with increasing BMI content, indicating that the water sorption in epoxy resin, which causes reliability problems in electronic devices, can be diminished by BMI addition. The water sorption behaviors in the epoxy/BMI composites were interpreted in terms of their chemical and morphological structures.

H 2O diffusion in dacitic and andesitic melts

The diffusion of water in dacitic and andesitic melts was investigated at temperatures of 1458 to 1858 K and pressures between 0.5 and 1.5 GPa using the diffusion couple technique. Pairs of nominally dry glasses and hydrous glasses containing between 1.5 and 6.3 wt.% dissolved H 2O were heated for 60 to 480 s in a piston cylinder apparatus. Concentration profiles of hydrous species (OH groups and H 2O molecules) and total water ( C H 2 O t = sum of OH and H 2O) were measured along the cylindrical axis of the diffusion sample using IR microspectroscopy. Electron microprobe traverses show no significant change in relative proportions of anhydrous components along H 2O profiles, indicating that our data can be treated as effective binary interdiffusion between H 2O and the rest of the silicate melt. Bulk water diffusivity ( D H 2 O t ) was derived from profiles of total water using a modified Boltzmann-Matano method as well as using fittings assuming a functional relationship between D H 2 O t and C H 2 O t . In dacitic melts D H 2 O t is proportional to C H 2 O t up to 6 wt.%. In andesitic melts the dependence of D H 2 O t on C H 2 O t is less pronounced. A pressure effect on water diffusivity could not be resolved for either dacitic or andesitic melt in the range 0.5 to 1.5 GPa. Combining our results with previous studies on water diffusion in rhyolite and basalt show that for a given water content D H 2 O t increases monotonically with increasing melt depolymerization at temperatures >1500 K. Assuming an Arrhenian behavior in the whole compositional range, the following formulation was derived to estimate D H 2 O t (m 2/s) at 1 wt.% H 2O t in melts with rhyolitic to andesitic composition as a function of T (K), P (MPa) and S (wt.% SiO 2): log D H 2 O t = ( – 0.757 – 0.0868 ⁢ ⋅ S ) + ( – 14 ,     785 + 131.7 ⁢ ⋅ S )  / T + ( 3 .079 – 0 .0490 ⋅ S ) ⋅ P/T The experimental data (69 in total, covering 803 to 1848 K and 0.1 to 1500 MPa) are reproduced by this relationship with a standard error of 0.12 log units. Using proportionality between water content and bulk water diffusivity, the above equation can also be used to estimate D H 2 O t in rhyolite to dacite containing up to 2 wt.% H 2O t at magmatic temperatures. For andesitic melts the functional relationship between D H 2 O t and C H 2 O t is not known at magmatic temperatures and, hence, application of our model remains uncertain for such conditions. As the activation energy for water diffusion increases from rhyolite to andesite, the diffusivities become similar at intermediate temperatures. Below 1000 K (depending on H 2O content and pressure), water diffusion may be faster in rhyolite than in dacite than in andesite.

Effects of p-chloromercuribenzene sulfonate on water transport across the marsupial erythrocyte membrane.

The effects of exposure of red blood cells (RBC) of three species of marsupial to a mercury-containing sulfhydryl-modifying reagent, p-chloromercuribenzene sulfonate (PCMBS), on the water diffusional permeability ( P (d)) of their membranes were monitored by using an Mn(2+)-doping (1)H nuclear magnetic resonance (NMR) technique at 400 MHz. For koala ( Phascolarctos cinereus), RBC the maximal inhibition was reached at 37 degrees C in 60 min with 1 mmol.l(-1) PCMBS or in 15-30 min with 2 mmol. l(-1) PCMBS. In contrast, in the case of red kangaroo ( Macropus rufus) or swamp wallaby ( Wallabia bicolor) RBC, maximal inhibition required an incubation of 90 min at 37 degrees C with 2 mmol.l(-1) PCMBS. For the RBC of all three species the value of maximal inhibition was very high, being 50-70% when measured at 25 degrees C, 60-80% at 30 degrees C and 60-70% at 37 degrees C. The lowest values of P (d) appeared to be around 2 x 10(-3)-3 x 10(-3) cm.s(-1) in the temperature range of 25-37 degrees C. The mean value of the activation energy of water diffusion ( E (a,d)) was approximately 20-25 kJ.mol(-1) for control and approximately 40 kJ.mol(-1) for PCMBS-inhibited RBCs. These results show that marsupial RBC have a basal permeability to water similar to that previously reported for human RBC, but a higher value of the PCMBS-inhibitable water permeability. This indicates that the higher water permeability of marsupial RBC compared with human RBC is associated with a higher fraction of protein-mediated water permeability.