Wireless Internet Security

Immer kleiner, immer schneller, immer mobiler – Wireless LANs (WLANs) haben Einzug in Unternehmen und Hochschulen gehalten und GPRS soll den Mobilfunk revoluzionieren.     

Biohybrid Carbon Nanotube/Agarose Fibers for Neural Tissue Engineering

We report a novel approach for producing carbon nanotube fibers (CNF) composed with the polysaccharide agarose. Current attempts to make CNF's require the use of a polymer or precipitating agent in the coagulating bath that may have negative effects in biomedical applications. We show that by taking advantage of the gelation properties of agarose one can substitute the bath with distilled water or ethanol and hence reduce the complexity associated with alternating the bath components or the use of organic solvents. We also demonstrate that these CNF can be chemically functionalized to express biological moieties through available free hydroxyl groups in agarose. We corroborate that agarose CNF are not only conductive and nontoxic, but their functionalization can facilitate cell attachment and response both in vitro and in vivo. Our findings suggest that agarose/CNT hybrid materials are excellent candidates for applications involving neural tissue engineering and biointerfacing with the nervous system.     

Polymer/carbon nanotube composites for liquid sensing: Model for electrical response characteristics

Electrically conductive polymer composites (CPCs) based on carbon nanotubes (CNTs) and polycarbonate were investigated regarding their electrical resistance change in different solvents like tetrahydrofuran, acetone, and ethyl acetate. CPCs containing 0.086 to 2.778 vol.% CNT were melt mixed using a twin-screw extruder under optimised conditions and subsequently compression-moulded.All sensing experiments revealed a resistance increase of CPCs having a U-shaped sample geometry during solvent immersion. Light microscopy investigations have shown that the diffusion of solvents into CPCs can be monitored in terms of a pronounced diffusion front, separating a swollen skin from the dry core. Based on this observed skin-core morphology, a model allowing the calculation of the time depending relative resistance change has been proposed considering several factors like diffusion parameters, composite characteristics, and geometrical values.Simulated response curves based on the model were compared with experimental data obtained on the CPCs and very good agreement was observed. Using this model the influence of CNT content and kind of solvent could be described exactly.     

Ryegrass uptake of carbamazepine and ibuprofen applied by urine fertilization

Human urine is a potential alternative fertilizer for agriculture. However, its usage is associated with a risk of spreading pharmaceutical residues to fields. The individual and combined behavior of carbamazepine and ibuprofen was investigated by GC/MS analysis in a greenhouse experiment using ryegrass fertilized with pharmaceutical-spiked urine. Only carbamazepine could be detected in soil, roots, and aerial plant parts. Fifty-three per cent of carbamazepine originally present in the urine was recovered in soil samples taken after three months. Additionally, 34% of carbamazepine was found in aerial plant parts and 0.3% in roots. Model calculations showed that neither roots nor Casparian strip posed a considerable barrier to uptake. Carbamazepine transport was clearly driven by transpiration. Ibuprofen was not detected in the soil or in any plant parts after three months. This was assumed to be due to biodegradation of ibuprofen. Carbamazepine and ibuprofen, singly or in combination, did not adversely affect the growth of ryegrass.     

Comparison of numerical methods for solving population balance equations incorporating aggregation and breakage

This paper presents a comparison of numerical results obtained by two different approaches, the sectional methods and finite volume methods, of solving population balance equations. In particular, the cell average technique, recently proposed by the authors [J. Kumar et al. 2006, Improved accuracy and convergence of discretized population balance for aggregation: the cell average technique. Chemical Engineering Science, 61, 3327–3342] and the finite volume scheme developed by Filbet and Laurençot [2004, Numerical simulation of the Smoluchowski coagulation equation. SIAM Journal on Scientific Computing, 25:2004–2028] are considered. The advantages and disadvantages are pointed out between the two different approaches of solving the population balance equations. It is concluded that the finite volume scheme predicts more accurate results for particle number density on fine grids, on the other hand quite reasonable results for number density as well as for its moments can be obtained using the cell average scheme even on coarse grids.     

A sensitive enzyme immunoassay (EIA) for the determination of melengestrol acetate (MGA) in adipose and muscle tissues

The development of a sensitive screening method of MGA residues in bovine perirenal fat and muscle based on a competitive microtitration plate enzyme immunoassay is described. The samples were extracted with petroleum ether and purified with octadecyl-silica-cartridges. The detection limit for fat was 0.4ng/g and for muscle tissue 0.05ng/g, much lower than required for reliable detection of positive samples. The mean recovery rates of fortified samples amount to 75%, the mean intraassay variations to 7% and the interassay variation to 13%. Determination limits were validated for fat at 2ng/g and for muscle at 0.1ng/g. The efficiency of the new screening method was successfully demonstrated by the direct comparison to GC-MS and LC-MS methods performed at natural positive samples originating from an animal experiment in which the labelled dose (0.5mg per animal and day) with and without a 48h withdrawal period or 3-fold or 10-fold the amount of MGA, respectively, was fed to Holstein Frisian heifers. In conclusion, this new screening method can be used for sensitive determination of MGA residues in adipose tissues even after low treatment doses or longer withdrawal periods.     

Investigation into the mechanism of bacterial adhesion to hydrogel-coated surfaces

As a model for hydrogel-coated biomaterials, self-assembled monolayers of polyoxyethylene (POE) derivatives on sheets of polymeric biomaterials were prepared. The POE derivatives consisted of hydrophilic chains with different lengths and a long-chain alkyl group that served as an anchor function. The coatings obtained were analyzed with XPS and contact angle measurements showing hydrophilic chains of different lengths extending away from the surface. Bacterial adhesion was measured with a clinically relevant Klebsiella pneumoniae type strain and measurements reproduced 12 times. Bacterial adhesion decreased markedly with increasing hydrophilic chain length. Based upon these findings a new model for bacterial adhesion to hydrogel-coated surfaces is suggested: steric repulsion effects that increase with increasing chain length of grafted hydrophilic chains play an important role in bacterial adhesion to hydrogel-coated surfaces. © 1999 Kluwer Academic Publishers     

Tensile strength of spruce glulam

Comparative tests on spruce glulam members subject to tension and bending, respectively, were numerically simulated to determine the tensile-to-bending-strength ratio. Nine different grading methods were applied to cover a wide strength range. They are based on visual inspection and mechanical determination of density and MOE. The simulated tensile and bending strength values result in an almost constant tensile-to-bending-strength ratio of 0.88. The ratio is valid for fifth percentile values and for standardized tests with prescribed member sizes. It is independent of the grading method used. In addition the size effect in glulam tension members was numerically studied. The results show a strong dependence of the glulam tensile strength upon the length subject to tension in case of short members. The dependence slowly wears off in case of long members. The tensile strength for members 150 mm in length is 140 percent of the reference value. The limit strength for a quasi-infinite length is about 80 percent.