Is it Possible to Derive the Dresdner Correction Formula Using a Finite Element Program? / Lässt sich die Dresdner Korrekturformel durch Daten aus einem Finite-Elemente-Programm wiederfinden?

INTRODUCTION: The aim was to construct a model cornea by CAD and finite element software to find out how the intraocular pressure compares to the forces for applanation at the outside of the model cornea. These data were to be compared to the Dresdner correction formula. Thereby, it was possible to find out whether the model was plausible and to find hints as to why a correction for how the intraocular pressure depends on the corneal thickness is necessary at all. METHODS: Using the open-source software FreeCad and geometrical data for the cornea of the literature, an average cornea was constructed. On this average cornea, a finite element analysis was performed using the free software z88aurora. The intraocular pressure was measured by applanation of the outer cornea. The necessary forces were analysed. RESULTS: In this model, the intraocular pressure had to be corrected depending on the corneal thickness. The correction factor was kmean; finite elements = 19.17 - 0.0334*corneal thickness. The necessary correction did not exclusively depend on the relation between the endothelial area and the area of the outer cornea: for this relation alone the correction would have been karea-relation = 1.0361 - 0.0006*corneal thickness. DISCUSSION: The model correction formula was close to the Dresdner formula. The relation between endothelial area and the area of the outer cornea could only explain about half of the necessary correction.

Removal of Trace Organic Contaminants by Parallel Operation of Reverse Osmosis and Granular Activated Carbon for Drinking Water Treatment.

In response to increasingly stringent restrictions for drinking water quality, a parallel operation of two common technologies, low-pressure reverse osmosis (LPRO) and activated carbon filtration (ACF), was investigated in a comprehensive five-month pilot study for the removal of 32 typical trace organic contaminants (TrOCs) from Rhine bank filtrates employing a semi- technical plant. TrOCs have been divided into three groups: polyfluorinated aliphatic compounds; pharmaceuticals, pesticides and metabolites; in addition to volatiles, nitrosamines and aminopolycarboxylic acids, which were also examined. The net pressure behavior, normalized salt passage and rejection of TrOCs by LPRO were investigated and compared with ACF operation. In addition, autopsies from the leading and last membrane modules were performed using adenosine triphosphate (ATP), total organic carbon (TOC), ICP-OES and SEM-EDX techniques. Generally, rather stable LPRO membrane performance with limited membrane fouling was observed. TrOCs with a molecular weight of ≥ 150 Da were completely retained by LPRO, while the rejection of di- and trichloro compounds improved as the filtration progressed. ACF also showed significant removal for most of the TrOCs, but without desalination. Accordingly, the ACF and LPRO can be operated in parallel such that the LPRO permeate and the ACF-treated bypass can be mixed to produce drinking water with adjustable hardness and significantly reduced TrOCs.

Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration.

Humic acids (HAs) content of raw water is an important analytical parameter in water treatment facilities because HAs in the presence of chlorine may lead to the formation of dangerous by-products (e.g., trihalomethanes). The concentration of HAs in water is not directly accessible by common analytical methods due to their heterogeneous chemical structure. The aim of this study was to compare two methods to assess humic acids (HAs) in surface water namely absorbance of ultraviolet light at 254 nm (UV(254)) and total organic carbon (TOC), as well as to evaluate the effects of calcium and magnesium concentrations, pH and sample filtration on the methods' results. An aqueous solution of a commercial HA with 10 mg L(-1) was used in the present work. Quantification of the HA was carried out by both UV(254) and TOC (combustion-infrared method) measurements. UV(254) results were converted to TOC using a calibration curve. The effects of calcium (0-136.3 mg L(-1)) and magnesium (0-34.5 mg L(-1)) concentrations, pH (4.0, 7.0 and 9.0) and sample filtration on UV(254) and TOC measurements of the HA suspension were evaluated. More accurate TOC values of HA suspensions were obtained by the combustion-infrared method than by the UV(254) absorbance method. The higher differences of TOC values between unfiltered and filtered samples were detected in the presence of calcium at pH 9.0 using the spectrophotometric method.

Enzyme-assisted vitrectomy in enucleated pig eyes: a comparison of hyaluronidase, chondroitinase, and plasmin.

PURPOSE: Facilitation of vitrectomy by vitreolytic enzymes may be of great value in complicated or office-procedure vitreo-retinal surgery. In this study, we quantified and compared the effect of hyaluronidase, chondroitinase, and plasmin pre-incubation on vitrectomy rate and explored potential retinal damage. METHODS: Freshly enucleated pigs eyes were incubated (1 or 3 hours) with an intravitreally injected enzyme or control solution. Enzyme doses were 100 and 1000 U for hyaluronidase, 1 and 2 U for chondroitinase, 3 and 30 U for plasmin. The eyes were weighed before and after 10 minutes of one-port vitrectomy, the difference representing the amount of removed vitreous. Light microscopy was used to assess potential damage to the retina. RESULTS: All enzymes significantly increased the amount of removed vitreous at all doses and incubation periods. The highest increase was found with hyaluronidase 1000 U, 3 hours, the lowest with chondroitinase 1 U, 1 hour. Damage occasionally occurred to the internal limiting membrane and very rarely to the nerve fiber layer. No damage at all was seen in the 100 and 1000 U hyaluronidase (1-hour incubation) groups. CONCLUSIONS: Hyaluronidase, chondroitinase, and plasmin are good candidates for enzyme-assisted vitrectomy. Although retinal structural damage was very rarely seen, safety concerns will have to be investigated further.

Removal of industrial cutting oil from oil emulsions by polymeric ultra- and microfiltration membranes.

The utilization of micro- and ultrafiltration with polymeric membranes for treatment of industrial cutting oil emulsion was investigated. The performance of 14 different membranes with pore sizes in the range of 1-800 nm, representing 8 different materials and varying hydrophobicity, was determined experimentally. Membrane permeances between 1.6 and 939 L m 2 h(-1) bar(-1) have been observed for the different samples as well as oil rejections between 3.42% and 99.99%. Membrane pore size and contact angle showed little influence on both values, while an interesting correlation is displayed to the individual membranes' capillary pressures. A possible explanation for this phenomenon is suggested based on the formation of oil films on the membrane surface. From the investigated membranes, the best-suited one for cutting oil treatment was selected and subjected to further experiments. The effect of process temperatures between 22 and 43 degrees C and of feed oil concentrations between 0 and 20 vol % on the removal performance was determined. The results correspond to the explanation suggested previously.