Medium Water Content Research Articles

Actual Performance versus Theoretical Advantages of Polyacrylamide Hydrogel throughout Bedding Plant Production

An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca2+ and Mg2+). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.

Enzymatic synthesis of l-ascorbyl linoleate in organic media

A novel L-ascorbyl fatty acid ester, L-ascorbyl linoleate was successfully prepared by enzymatic esterification and transesterification in a non-aqueous medium using immobilized lipase as biocatalyst. Changes in enzymatic activity and product yield were studied for the following variable: the nature of the fatty acid, the fatty acid concentration and water content. The yield of synthesis for the C18 unsaturated fatty acids were higher than for the C18 saturated fatty acid. Initial enzyme concentration does not affect the equilibrium of the reaction. And the product yield (33.5%) in the transesterification was higher than that of the esterification (21.8%) at a high-substrate concentration 0.3 M. The medium water content was found to have a distinct influence on the L-ascorbyl linoleate synthesis.

Novel Characteristics of Bifidobacterium bifidum in Solid State Fermentation System

The characteristics of Bifidobacterium bifidum grown in solid state fermentation (SSF) system (water content of media 54.5 and 68.8%) was compared with the submerged fermentation (SmF) system (water content of medium: 89.8%). Besides lactic acid (lactate) and acetic acid (acetate), the bacterium was able to secrete propionic acid (propionate) and butyric acid (butyrate) under SSF conditions. However, it only produced lactate and acetate under SmF conditions. The ratio of lactate to acetate was 1.26–1.62:1 in SSF but it was 1:2 in SmF. A higher content of C16:0 and C18:1 as well as a lower content of C18:0 cell membrane fatty acids were observed in SSF than in SmF. There was a lower growth rate, a lower viable count and a longer logarithmic growth phase for B. bifidum cultivated in SSF than in SmF.

Comparison of Soil Hydraulic Parameterizations for Mesoscale Meteorological Models

AbstractSoil water contents, calculated with seven soil hydraulic parameterizations, that is, soil hydraulic functions together with the corresponding parameter sets, are compared with observational data. The parameterizations include the Campbell/Clapp–Hornberger parameterization that is often used by meteorologists and the van Genuchten/Rawls–Brakensiek parameterization that is widespread among hydrologists. The observations include soil water contents at several soil depths and atmospheric surface data; they were obtained within the Regio Klima Projekt (REKLIP) at three sites in the Rhine Valley in southern Germany and cover up to 3 yr with 10-min temporal resolution. Simulations of 48-h episodes, as well as series of daily simulations initialized anew every 24 h and covering several years, were performed with the “VEG3D” soil–vegetation model in stand-alone mode; furthermore, 48-h episodes were simulated with the model coupled to a one-dimensional atmospheric model. For the cases and soil types considered in this paper, the van Genuchten/Rawls–Brakensiek model gives the best agreement between observed and simulated soil water contents on average. Especially during episodes with medium and high soil water content, the van Genuchten/Rawls–Brakensiek model performs better than the Campbell/Clapp–Hornberger model.

Vulnerability of Bavarian silty loam soil to compaction under heavy wheel traffic: impacts of tillage method and soil water content

Soil compaction caused by traffic of heavy vehicles and machinery has become a problem of world-wide concern. The aims of this study were to evaluate and compare the changes in bulk density, soil strength, porosity, saturated hydraulic conductivity and air permeability during sugar beet ( Beta vulgaris L.) harvesting on a typical Bavarian soil (Regosol) as well as to assess the most appropriate variable factors that fit with the effective controlling of subsequent compaction. The field experiments, measurements and laboratory testing were carried out in Freising, Germany. Two tillage systems (conventional plough tillage and reduced chisel tillage) were used in the experiments. The soil water contents were adjusted to 0.17 g g −1 ( w 1 ), 0.27 g g −1 ( w 2 ) and 0.35 g g −1 ( w 3 ). Taking the increase in bulk density, the decrease in air permeability and reduction of wide coarse pore size porosity (−6 kPa) into account, it seems that CT (ploughing to a depth of 0.25 m followed by two passes of rotary harrow to a depth 0.05 m) of plots were compacted to a depth of at least 0.25 m and at most 0.40 m in high soil water ( w 3 ) conditions. The trends were similar for “CT w 1 ” (low soil water content) plots. However, it seems that “CT w 1 ” plots were less affected than “CT w 3 ” plots with regard to bulk density increases under partial load. In contrast, diminishments of wide coarse pores (−6 kPa) and narrow (tight) coarse pores (−30 kPa) were significantly higher in “CT w 1 ” plots down to 0.4 m. Among CT plots, the best physical properties were obtained at medium soil water ( w 2 ) content. No significant increase in bulk density and no significant decrease in coarse pore size porosity and total porosity below 0.2 m were observed at medium soil water content. The soil water content seemed to be the most decisive factor. It is likely that, CS (chiselling to a depth of 0.13 m followed by two passes of rotary harrow to a depth 0.05 m) plots were less affected by traffic treatments than CT plots. Considering the proportion of coarse pore size porosity (structural porosity) and total porosity, no compaction effects below 0.3 m were found. Medium soil water content ( w 2 ) provides better soil conditions after traffic with regard to wide coarse pore size porosity (−6 kPa), air permeability (at 6 and 30 kPa water suction), total porosity and bulk density. Proportion of wide coarse pores, air permeability and bulk density seems to be suitable parameters to detect soil compaction under the conditions tested.

Gel-immobilized enzymes as promising biocatalysts: Results from Indo-Russian collaborative studies

Abstract Chemo-enzymatic methods constitute a promising approach to obtain various biologically active compounds, including enantiomerically pure substances. Entrapment in gels is one of the most convenient methods to stabilize enzymes for their application in water/organic media. Proteases and lipases are widely used for enantioselective transformations of various organic compounds in water-poor media. In this study, chymotrypsin was entrapped into a composite poly(N-vinyl caprolactam)-calcium alginate (PVCL-CaAlg) and covalently attached to poly(vinyl alcohol) (PVA) cryogel beads. Lipase was immobilized by covalently attaching to aldehyde-bearing PVA cryogel beads. The activities of the entrapped biocatalysts were studied. Both entrapped α-chymotrypsin and lipase retained high activity in acetonitrile/water medium (water content 0.5–20 %) and displayed high storage stability for several months. The high operational stability of immobilized α-chymotrypsin and lipase in a cyclic process (up to 912 h in total) was also demonstrated. Gel-immobilized enzymes were successfully used to obtain optically pure L-phenylalanine (ee 98.6 and 83 % in the case of α-chymotrypsin and lipase, respectively) by enantioselective hydrolysis of Schiff’s base of amino acid ethyl ester in an acetonitrile/water system.

Inverse Mobile-Immobile Modeling of Transport During Transient Flow: Effects of Between-Domain Transfer and Initial Water Content

Mobile–immobile models (MIM) have rarely been used for inverse simulation of measurements of variably saturated water flow and contaminant transport. We evaluated two MIM approaches with water transfer across the mobile and immobile regions either based on relative saturation (Se) differences, MIM(Se), or pressure head ( h ) differences, MIM( h ), for inverse simulation of transient water flow and Br − transport in aggregated soil. Six undisturbed Ap soil columns (14.7-cm length and diameter) at wet, medium, and dry initial water contents were subjected to application of 0.005 L Br − solution of 1000 mg L −1 and subsequent irrigation of 1 cm h −1 for 3 h. Two similar irrigations were applied after 7 and 14 d. Measurements comprised pressure heads at depths of 2.8 and 12.8 cm, average soil column water contents, outflow, and effluent solute concentrations. This experimental information was used for simultaneous optimization of van Genuchten soil hydraulic parameters for mobile and immobile regions, the dispersivity, and the first-order rate coefficients for water and solute transfer. In total, eight parameters were estimated for MIM(Se) and 10 parameters for MIM( h ). The inverse MIM approaches described the various hydraulic and transport data adequately. Physical nonequilibrium was more pronounced for wet and dry than for intermediate initial moisture, while initial moisture had no obvious effect on the total Br − lost. For wet and dry initial conditions, parameter estimates seemed fairly reliable, with the exception of the highly correlated saturated water contents in mobile and immobile regions. MIM( h ) yielded parameters that appeared physically more consistent with observations, but required smaller time steps than MIM(Se) to overcome oscillations of pressure heads. Both MIM approaches were found to be suitable for inverse simulation of physical nonequilibrium transport during variably saturated flow.

Inverse Mobile–Immobile Modeling of Transport During Transient Flow: Effects of Between‐Domain Transfer and Initial Water Content

Mobile–immobile models (MIM) have rarely been used for inverse simulation of measurements of variably saturated water flow and contaminant transport. We evaluated two MIM approaches with water transfer across the mobile and immobile regions either based on relative saturation (Se) differences, MIM(Se), or pressure head (h) differences, MIM(h), for inverse simulation of transient water flow and Br− transport in aggregated soil. Six undisturbed Ap soil columns (14.7‐cm length and diameter) at wet, medium, and dry initial water contents were subjected to application of 0.005 L Br− solution of 1000 mg L−1 and subsequent irrigation of 1 cm h−1 for 3 h. Two similar irrigations were applied after 7 and 14 d. Measurements comprised pressure heads at depths of 2.8 and 12.8 cm, average soil column water contents, outflow, and effluent solute concentrations. This experimental information was used for simultaneous optimization of van Genuchten soil hydraulic parameters for mobile and immobile regions, the dispersivity, and the first‐order rate coefficients for water and solute transfer. In total, eight parameters were estimated for MIM(Se) and 10 parameters for MIM(h). The inverse MIM approaches described the various hydraulic and transport data adequately. Physical nonequilibrium was more pronounced for wet and dry than for intermediate initial moisture, while initial moisture had no obvious effect on the total Br− lost. For wet and dry initial conditions, parameter estimates seemed fairly reliable, with the exception of the highly correlated saturated water contents in mobile and immobile regions. MIM(h) yielded parameters that appeared physically more consistent with observations, but required smaller time steps than MIM(Se) to overcome oscillations of pressure heads. Both MIM approaches were found to be suitable for inverse simulation of physical nonequilibrium transport during variably saturated flow.

Water properties of soft contact lens materials

The properties of water in soft contact lenses such as the water content, free-to-bound water ratio, and the extent to which soft lenses dehydrate during wear, are key determinants of their in eye performance and oxygen transmissibility characteristics. This study describes clinical and laboratory experiments that were conducted in order to examine the state of water in eight soft contact lenses manufactured from different materials. Specifically, lenses made from the following eight materials (and nominal water contents) were used: HEMA/VP 40%, HEMA/VP 55%, HEMA/VP 70%, VP/MMA 55%, VP/MMA 70%, HEMA 40%, HEMA/MAA 55% and HEMA/MAA 70% [HEMA = 2-hydroxy-ethyl methacrylate, VP = vinyl pyrrolidone, MMA = methyl methacrylate, MAA = methacrylic acid]. Differential scanning calorimetry (DSC) was used for measuring the free water content in the materials listed above. Some noticeable differences in water properties among soft contact lens materials having approximately the same water contents were revealed. Low water content materials exhibited a simple endotherm and all water melted around 0 °C. On the other hand, medium and high water content materials exhibited multiple melting endotherms, representing a broad range of interactions between water and the polymer. Low water content soft contact lenses have approximately the same amount of bound water as those with much higher water contents. Six subjects were then fitted with the same lenses for one day. In vitro measurements of water content and oxygen transmissibility were taken at 35 °C, both before lens fitting and after 6 h of lens wear. Water content and oxygen transmissibility were correlated with the water properties of the soft contact lens materials. The relative change in lens water content (%ΔWC) and relative change in lens oxygen transmissibility (%ΔDk/ t) were calculated and correlated with the water properties of the eight soft contact lens materials. It was concluded that (a) oxygen transmissibility, free water content and free-to-bound water ratio are increased when the water content of a contact lens is increased and (b) water content, free water content and free-to-bound water ratio cannot be used for the prediction of soft contact lens dehydration in vivo.

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VIII. Thermodynamic of Interactions of Na+Ion with 15-Crown-5 and Benzo-15-Crown-5 Ethers in the Mixtures of Water with Hexamethylphosphortriamide at 298.15 K

The equilibrium constants of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15 K. The thermodynamic functions of complex formation of 15-crown-5 and benzo-15-crown-5 ethers with the sodium cation in the mixtures of water with hexamethylphosportriamide at 298.15 K have been calculated. The extent of complex formation in this mixed solvent depends on the enthalpic effect. In water–hexamethylp- hosportriamide mixtures with medium and low water content, the complex of crown ethers with the sodium cation is not formed because of the strong solvation of sodium cation and crown ethers molecules; this implies that the entropy of complex formation is more negative than the enthalpy of complex formation.

Characterisation of avocado (Persea americana Mill) honeys by their physicochemical characteristics

AbstractThe quality of 12 avocado (Persea americana Mill) honeys from Spain was evaluated. Eight common physicochemical parameters were analysed, namely water content, pH, acidity (free, lactonic and total), sugar content, ash content and electrical conductivity. In addition, the honey samples were analysed using inductively coupled plasma optical emission spectrometry (ICP‐OES), and six minerals were quantified for each honey, namely potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), phosphorus (P) and sulphur (S). Most samples showed proper maturity considering the medium water content (mean 17.7%). The total acidity (below 50 meq kg−1 except for one sample) indicated absence of undesirable fermentation; also, the mean pH of around 4.77 is usual in this kind of honey. The values for ash content and electrical conductivity were high (0.77% and 798 µS cm−1 respectively) and typical of dark honeys. K was the predominant mineral (accounting for 73% of the total minerals quantified), followed by Na (10%). Copyright © 2004 Society of Chemical Industry

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents: Part VII . Enthalpy of solution of 15-crown-5 and benzo-15-crown-5 in the mixtures of water with acetone at 298.15 K

Enthalpy of solution of crown ethers (15-crown-5 and benzo-15-crown-5) in water–acetone mixtures have been measured within the whole range of mole fraction at 298.15 K. The obtained data have been compared with those of the solution enthalpy of both crown ethers in the mixtures of water with dimethyl sulfoxide. The replacement of SO group with CO in the molecule of the organic solvent brings about an increase in the exothermic effect of the solution of 15-crown-5 and benzo-15-crown-5 ethers, especially in the mixtures with a medium water content. The observed effect is connected with the preferential solvation of the molecules of both crown ethers by acetone molecules in the water–acetone mixtures. The process of preferential solvation of 15-crown-5 and benzo-15-crown-5 ethers does not take place in the water–dimethyl sulfoxide mixture.

Phenology and diameter increment in seedlings of European beech ( Fagus sylvatica L.) as affected by different soil water contents: variation between and within provenances

The effect of different soil water levels on phenology and growth of 14 provenances of European beech ( Fagus sylvatica L.) was investigated in a glasshouse experiment. The genetic variation within one provenance was further studied by including 10 half-sib families from a Danish stand in the experiment. Flushing and the time for onset of diameter growth were significantly different between provenances. Length of the growing season varied significantly among provenances and was highly affected by the soil water content. Root collar diameter increment during the experimental treatment was reduced by 43% in plants at low compared to plants at medium and high soil water content. The corresponding reduction in height was 53%. Differences between provenances and the interaction between provenances and the soil water treatments were significant for growth response. This interaction term was not significant in the material of 10 half-sib families. Linear geographic and clinal trends were revealed for growth and phenological parameters, but these relationships depended on the soil water levels. The provenances from northern Europe had a fairly homeostatic expression on a low growth level across the soil water gradient, whereas the southern provenances showed a much stronger positive response to increase in soil water content. Consequently, the south European provenances had a greater adaptability to the changing growth conditions. The genetic variation in growth response within one Danish provenance was comparable with the variation between provenance under dry soil conditions, whereas this was not the case under moist and wet soil conditions. The results indicate that a substantial gain in evolutionary adaptability is possible for north European forestry by choice of material from central and southern Europe or by mixing autochton plant material with more southern seed sources.

Pressure pulsation in solid-phase fermentation.

Inadequate dissipation of heat generated by biologic activities has prevented the use of solid-phase fermentation in large-scale applications. This study deals with the cooling effects of pressure pulsation on solid, porous beds. Pressure pulsation also enhances evaporation of medium moisture, which is also described. Computer software has been developed for on-line control of heat accumulation and moisture loss involving automatic variation in pressure pulsation frequency and airflow direction as well as replenishment of water. Aspergillus niger NRRL3 was cultivated on a moist, solid medium made of wheat bran and ground corncobs to produce cellobiase. During 100 h of fermentation, the maximum temperature inside the solid bed was kept under 40 degrees C, and the medium water content was successfully maintained between 61 and 65%, which was optimal for cell growth. Cells grew heavily on the solid-phase substrate and distributed uniformly. With good on-line control of temperature and moisture, the 12-L fermentor provided a better environment for enzyme production than 250 mL flasks did.

Electrokinetic Remediation Using Surfactant-Coated Ceramic Casings

Electrokinetic remediation is an emerging technique that can be used to remove metals from saturated or unsaturated soils. In unsaturated soils, control of the medium's water content is essential. Previously used electrode designs have caused detrimental soil wetting due to excess electroosmotic flow out of ceramic-encased anodes. We tested a method to reverse the electroosmotic flow at the anode by treating the ceramic casing with the cationic surfactant hexadecyltrimethylammonium (HDTMA). Laboratory tests showed the untreated ceramic had an electroosmotic permeability of 2.4 × 10−5 cm2 V−1 s−1. Ceramic treated with HDTMA had an electroosmotic permeability of −1.3 × 10−5 cm2 V−1 s−1. Under an applied electric potential, electroosmotic flow was reversed in the HDTMA-treated ceramic, indicating a reversed zeta potential due to formation of an HDTMA bilayer on the ceramic surface. Field tests conducted over a 6-month period showed negligible water loss from HDTMA-treated ceramic (0.03 L h−1) compared to untreated ceramics (up to 6 L h−1). The results indicated that a surfactant treatment to the anode ceramic casing can greatly improve the application of electrokinetics in unsaturated environments.

Assessment of postmortem blood alcohol concentrations by ethanol levels measured in fluids from putrefactive blisters

It was the aim of the present study to investigate whether the postmortem blood alcohol concentration (BAC) can be assessed by means of ethanol values measured in fluids from putrefactive blisters. Fluids from one or two putrefactive blisters were collected in 45 putrefied corpses (postmortem interval: 3–23 days, graduation of the degree of decomposition into four stages) and compared with femoral vein blood or femoral muscle. Ethanol and so-called putrefactive alcohols were determined in all samples by double GC-measurements. The results were converted to the medium water content of blood of 80%. The investigations revealed a significant correlation between the ethanol values of femoral blood/muscle and putrefactive blister fluid (PBF) ( r=0.725, P<0.001). With the exception of one case, PBF values of 0.11% or more ( n=11) corresponded to minimum blood/muscle concentrations of 0.085%; PBF values of more than 0.15% ( n=8) corresponded to blood/muscle levels of at least 0.159%. Regression analysis revealed the formula BAC (in %)=0.785×ethanol (PBF) +0.011. Relevant concentrations of putrefactive alcohols such as 1- and 2-propanol and 1-butanol only occurred in cases with far advanced decomposition. Ethanol levels determined in fluids from different putrefactive blisters of the same body also demonstrated a significant correlation ( r=0.791, P<0.001). Ethanol concentrations determined in PBF must be judged with caution, but PBF values >0.15% point to corresponding blood levels with a high degree of probability, at least where advanced putrefaction is excluded.

Fertilizer Diffusion in Container Medium

The process of fertilizer diffusion was examined using KBr and NaBr salts placed at the top of columns filled with a container medium at an initial water content of 4.0, 2.5, or 1.0 g·g-1 (mass of water/mass of medium). Columns were sealed to create a protected diffusion zone (PDZ) shielding the system from water infiltration and evaporation. Bromide and water distributions were determined after 5, 10, 25, and 120 days. Using a Fickian diffusion model, effective diffusion coefficients calculated for Br- in the medium at 2.5 g·g-1 ranged from 2.7 to 4.6 × 10-6 cm2·s-1, which is 3 to 9 times less than the diffusion coefficient in water alone. Diffusion rates increased with increasing medium water content. Differences in the hygroscopicity and solubility of KBr and NaBr affected the distribution of water and diffusion rates in the columns. Redistribution of water was driven to a significant degree by vapor-phase transport, caused by large gradients in osmotic potential, and was most apparent at low water content. At high water content, water redistribution was affected by solution density gradients in the system. This significantly complicates the mathematical modeling of the system, which renders a simple Fickian diffusion model of limited predictive value in high and low water content media.

EFFECT OF WATER STRESS ON HEAT STRESS TOLERANCE IN GERANIUM

This study evaluated the effect of reversible water stress on heat stress tolerance (HST) in greenhouse-grown geraniums. Water stress was imposed by withholding irrigation until pots reached ≈30% (by weight) of well-watered (control) plant pots, and maintaining this weight for 7 days. Control plants were watered to just below field capacity, every other day. Leaf xylem water potential (LXWP, MPa), leaf-relative water content (LRWC,%), media water content (MWC, % fresh weight), and heat stress tolerance (HST, LT50) were determined for control and stressed plants. HST (LT50), defined as temperature causing half-maximal percent injury, was based on electrolyte leakage from leaf disks subjected to 25 to 60C. Control-watering was restored in stressed plants and above measurements made after 7 days of recovery. Data indicate: 1) LXWP, LRWC, and MWC in control and stressed plants were –0.378 and –0.804 MPa, 92.31% and 78.69% and 82.86% and 15.5%, respectively; 2) HST increased significantly in stressed as compared to control plants (LT50 of 55C vs. 51C); 3) control plants were near maximally injured by 53C treatment and sustained more than 3-fold greater injury than stressed plants at 53C. In recovered plants, LXWP and RWC reversed back to control levels, paralleled by loss of higher HST.

Heat and mass transfer along a wetted porous plate in an air stream

AbstractThis experimental study examines 2‐D effects on long plate drying due to heat and moisture transfer through boundary layers and porous medium interaction. Many innovative techniques are used to measure accurately boundary layers (velocity, temperature, moisture), the wall surface (infrared sensors for temperature and moisture), and the medium (water content). Gradual decrease in surface saturation measured for several kinds of materials shows that their behavior is more complex than described by the Suzuki–Maeda model, which does not predict the mass exchange sufficiently. Based on the analysis of the transfer between the surrounding air and the porous medium at the scale of the pore on a rough surface, a flow classification is defined and other characteristics are proposed. The drying rate depends on the mass‐transfer coefficient, which varies along the plate with the air flow. The study of boundary layers gives the corresponding profiles with an acceptable accuracy. The laminar‐to‐turbulent transition increases mass‐transfer rates resulting in two drying fronts. The diffusive model proposed here predicts a gradual change in the drying rate along the plate similar to the experimental one.

AEROMEDICAL ASPECTS OF CONTACT LENSES (SOFT AND SEMISOFT)

A comprehensive clinical study on the effects of various aviation stresses on soft and semisoft contact lenses was carried out to find out their compatibility in aviation environment. Twenty subjects (11 aircrew and 9 non air-crew) participated in the study. Twelve of them were given soft lenses of water contents of 38%, 50% and 78% and rest 8 were given semisoft lenses of daily wear and extended wear type. The environmental trial consisted of exposure to hypoxia, rapid decompression, acceleration, pressure breathing, vibration and high temperature. On successful completion of environmental trials on ground simulators, the inflight trials on high performance aircraft, transport aircraft, passenger aircraft and helicopters were conducted. The soft lenses with low, medium and high water contents and extended wear semisoft lenses (large diameter) were found compatible with all types of aircraft flying.