Synthesis of polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane via polysiloxane‐based macroinitiator in supercritical CO2

Polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane (PDMS‐b‐PS‐b‐PDMS) was synthesized by the radical polymerization of styrene using a polydimethylsiloxane‐based macroazoinitiator (PDMS MAI) in supercritical CO₂. PDMS MAI was synthesized by reacting hydroxy‐terminated PDMS and 4,4′‐azobis(4‐cyanopentanoyl chloride) (ACPC) having a thermodegradable azo‐linkage at room temperature. The polymerization of styrene initiated by PDMS MAI was investigated in a batch system using supercritical CO₂ as the reaction medium. PDMS MAI was found to behave as a polyazoinitiator for radical block copolymerization of styrene, but not as a surfactant. The response surface methodology was used to design the experiments. The parameters used were pressure, temperature, PDMS MAI concentration and reaction time. These parameters were investigated at three levels (?1, 0 and 1). The dependent variable was taken as the polymerization yield of styrene. PDMS MAI and PDMS‐b‐PS‐b‐PDMS copolymers obtained were characterized by proton nuclear magnetic resonance and infrared spectroscopy. The number‐ and weight‐average molecular weights of block copolymers were determined by gel permeation chromatography. Copyright © 2004 Society of Chemical Industry     

Risk factors for isolation of Staphylococcus aureus or Streptococcus dysgalactiae from milk culture obtained approximately 6 days post calving

Milk culture results at approximately 6 d post calving were assessed in a 2-year retrospective single-cohort study in 178 Norwegian herds. A combined teat dipping and selective antibiotic therapy trial was performed in these herds where cows with composite milk somatic cell count (CMSCC) >100,000 cells/ml before drying-off (geometric mean of the last three CMSCC test-days) and isolation of Staphylococcus aureus or Streptococcus dysgalactiae were selected for either short-acting lactation antibiotic treatment or long-acting dry cow antibiotic treatment. Milk culture results at approximately 6 d post-calving were available from 437 treated cows and 3061 non-treated cows before drying-off and separate multivariable logistic regression models were ran for these two groups. Risk factors associated with isolation of Staph. aureus 6 d post calving for non-treated cows were CMSCC >400,000 cells/ml before drying-off v. <400,000 cells/ml (Odd ratio (OR) = 2.4) and clinical mastitis (CM) in the previous lactation v . non-treated (OR=1.5). Risk factors associated with Staph. aureus 6 d post calving for treated cows was a CMS > 200,000 cells/ml before drying-off v. <200,000 cells/ml (OR=2.3) and CM in the previous lactation verus non-treated (OR=1.7). For non-treated cows it was 1.7 times more likely to isolate Str. dysgalactiae 6 d post-calving if the CMSCC was > 50,000 cells/ml compared with <50,000 cells/ml. For treated cows it was 3.7-5.8-times more likely to isolate Str. dysgalactiae 6 d post calving if given short-acting lactation formula at quarter level compared with long-acting dry cow formula used at cow level. Regular use of iodine post-milking teat disinfection (PMTD) did not influence the isolation of Staph. aureus 6 d post calvin, but it was less likely to isolate Str. dysgalactiae 6 d post calving if iodine PMTD was used regularly rather than irregularly. The external teat sealant had no effect on either of the two bacteria. This study indicates that the CMSCC limit for sampling cows before drying-off can be reduced to 50,000 cells/ml in herds with a Str. dysgalactiae problem. Iodine PMTD should also be recommended in these herds. Cows with a CMSCC > 400,000 cells/ml prior to drying-off should receive long-acting dry cow formula irrespective of the milk result.     

Synthesis and in vitro antimicrobial characterization of Boron-PVA Electrospun nanofibers

Polyvinyl alcohol (PVA) electrospun nanofibers and boric acid (BA) complexes of these nanofibers were synthesized with and without using TritonX-100(TX-100) as a water soluble surfactant (PVA, PVA/BA, PVA/TX-100, PVA/TX-100/BA). The electrospun nanofibers were characterized by SEM, FTIR and TGA. Preliminary results showed that certain amount of boric acid decreased the number of Stapylococcus aureus from 6,8x10⁷(CFU/mL) to 3x10⁷(CFU/mL). In the preparation of polymer, boric acid was used as a crosslinker and antimicrobial agent whereas TX-100 was used as surfactant. The viscosity and conductivity measurements indicated that the BA increased viscosity but decreased conductivity. In contrast, TX-100 increased conductivity without considerable effect on viscosity, which affects the production and resulting nanofiber properties such as diameter and bead formation. The antimicrobial activities of the nanofibers were assayed in vitro by Gram-negative (E. coli) and Gram-positive(S. aureus) bacteria. It was observed that PVA/TX-100/BA showed better antibacterial activity against S.aureus bacteria compared to PVA and PVA/TX-100 nanofibers.     

Biosorption of chromium(VI), nickel(II) and Remazol blue by Rhodotorula muciloginosa biomass

The passive removal of commonly used reactive dye and two heavy metals, from aqueous solutions by inexpensive biomaterial, yeast Rhodotorula muciloginosa biomass, termed biosorption, was studied with respect to pH, initial dye concentration and initial metal ion concentration. The biomass exhibited maximum dye and chromium(VI) uptake at pH 5 and pH 6 for nickel(II) in media containing 50 mg/L heavy metal and 50 mg/L remazol blue. It was found that the highest chromium(VI) removal yields measured were 31.3% for 49.0 mg/l initial chromium(VI) concentrations. The nickel(II) removal yield was 32.5% for 22.3 mg/L. Higher R. Blue removal yields were obtained, such as 77.1% for 117.5 mg/L. The maximum dye biosorption yield was investigated in medium with a constant dye (approximately 50 mg/L) and increasing heavy metal concentration. In the medium with 48.8, 103.8 and 151.8 mg/L chromium(VI) and constant dye concentration, the maximum chromium(VI) biosorption was 7.4, 9.3 and 17.1%, whereas the maximum dye biosorption was 61.6, 56.6 and 55.9%. The maximum nickel(II) biosorptions in the medium with dye were 38.1, 22.1 and 8.8% at 23.7, 37.7 and 60.1 mg/L nickel(II) concentrations. In these media, dye biosorptions were 93.9, 86.4 and 93.3%, respectively.     

Hydroxyapatite-chitosan biocomposites synthesized in the simulated body fluid and their drug loading studies

Hydroxyapatite (HAp) is a bioceramic applied in the biomedical areas, such as matrices for drug release control. Chitosan (CTS), a natural polymer, is another material has been widely investigated for its potential use in the drug delivery systems. In this study, the composites of HAp-CTS are produced in order to investigate their drug loading and release studies. First of all, HAp-CTS composites are produced in the presence of simulated body fluid (SBF). Analysis confirmed the structure of HAp-CTS composites. Secondly, composites are encapsulated with 5-Fluorouracil (5-FU). The weight ratio of CTS is varied to realize its effect on drug loading of 5-Fluorouracil, a cancer drug, for the ratios of 1:1, 1:2 and 1:4 of HAp-CTS. The weight ratio giving the greatest drug load efficiency is selected for the last step of the study. Crosslinking agent, glutaraldehyde, are changed from 0 to 5% on the selected sample, then, drug loading is examined again in various environment owing different pH. Furthermore, drug release studies are conducted. To understand the structure and morphology of the samples, XRD, FTIR, SEM and Uv-Spectrum are applied. It is observed that weight ratio of polymer and crosslinking agent can be manipulated to adjust drug loading. Release kinetics are shown the Fickian diffusion. This new produced material can be applicable for drug delivery.     

The Circuit Implementation of a Wavelet Function Approximator

This paper describes the analog synthesis of a wavelet function approximator using sigmoidal mother wavelet. Any finite energy multivariate function can be approximated by this analog circuit using the multiresolution approximation property of the wavelet decomposition. The approximator circuit includes bipolar junction transistors, operational amplifiers and linear passive circuit elements.     

Organic micropollutants in a Norwegian water-course

A Norwegian water-course has been investigated for the content of organic micropollutants. The investigation was performed using liquid—liquid extractions and analysed by GC and GC-MS using capillary columns. Both qualitative and semi-quantitative results were obtained.The dominating components from the main downstream station were mostly n-alkanes, aromatic hydrocarbons and fatty acids. The main sources for the hydrocarbons are probably runoff from roads and atmospheric fallout, while the fatty acids originate from natural sources. Phenol and cresols together with some unidentified compounds were also present in minor amounts. These compounds probably originate from a large industrial effluent in the region.