Temperature-induced thickening of sodium carboxymethylcellulose and poly(N-isopropylacrylamide) physical blends in aqueous solution

This study describes the synthesis of poly(N-isopropylacrylamide) (PNIPAM) via free radical polymerization, the preparation of physical blends containing sodium carboxymethylcellulose (CMC) and PNIPAM in aqueous solution, at total polymer concentrations of 2 and 6?g/L in different compositions, and applies rheology to investigate interactions between PNIPAM and CMC compared to pure polymers, in aqueous solution. Rheological measurements indicated thermothickening behavior for the 50?% PNIPAM–50?% CMC physical blend in aqueous solution, at 6?g/L, as viscosity rose when temperature was increased to a range of 25–40?°C. Similar thermothickening behavior was observed for the 25?% CMC–75?% PNIPAM physical blend in solution, at a total polymer concentration of 2?g/L. These results provide new information for preparing physical blends in aqueous solutions exhibiting thermothickening behavior, indicating that this behavior depends on total polymer concentration and composition of the mixture.     

Phenol removal from wastewater using eco-friendly hybrid hydrogels

The intent of this study was to evaluate the ability of low-cost polyacrylamide/starch hybrid hydrogels in removing organic pollutants from wastewater, using phenol as a model compound, besides of investigating the adsorption/desorption behavior as a function of hydrogels composition. The results indicated that the hydrogel with the lowest amount of starch and crosslinking agent exhibited the maximum phenol adsorption capacity, 21 mg g⁻¹. The adsorption isotherm data were described by Langmuir and Freundlich adsorption isotherm models. According to linear regression analysis, the Freundlich isotherm model was the best fit among the isotherm models for the adsorption process. Furthermore, desorption study revealed a minimum of about 60% of phenol release, indicating reusability to wastewater treatment.     

Covalently-Bonded “Onion Type” Double Fullerenic Carbon Cages

Three “onion type” double carbon cages (consisting of an inner sp³-hybridized C₆₀ buckminsterfullerene skeleton and an outer larger carbon cage with icosahedral symmetry, with covalent bonds between the carbon atoms of the 5-membered rings) are described and their strain energies are discussed: (i) when the outer cage is a C₁₂₀ cage derived from buckminsterfullerene by replacing each bond between two six-membered rings by an acetylenic group, the strain is smallest.; (ii) when the same derivation concerns each bond between 5- and 6-membered rings leading to a C₁₈₀ outer cage, the strain is largest.; (iii) when the outer cage is C₁₈₀ with benzenoid rings, the strain is intermediate.     

Dual diversity combining and equalization in digital cellularmobile radio

The performance of digital data transmission over frequency-selective fading channels is investigated. For statistically independent diversity paths, estimates of average attainable error rates and outage probabilities as functions of system parameters are provided. The dependences among the important system parameters are exhibited graphically for several examples, including quaternary phase-shift keying (QPSK). In the optimized uncoded QPSK with 1.5 b/s/Hz, two orders of magnitude in outage probability can be gained by diversity reception. When one compares the uncoded average probability of error for the optimized mean squared error (MSE) systems one finds at most an order-of-magnitude difference among the different equalizers investigated except for the zero-forcing equalizer, whose performance is drastically inferior to the others. Again, dual diversity can provide two orders of magnitude improvement in the average error rate or in outage probability for the uncoded optimized systems     

Comparison between a polyacrylamide and a hydrophobically modified polyacrylamide flood in a sandstone core

Polymer flooding in oil reservoirs to enhance oil recovery (EOR) has been used worldwide. However, the polymers applied, such as partially hydrolyzed polyacrylamides and xanthan gum, show a number of limitations related to their low salt tolerance and biological degradation, respectively. Therefore, the polymeric properties must be improved to maximize their application. With this goal in mind, a new class of polymers, named “hydrophobically modified water-soluble polymers”, has been developed. These polymers are very similar to conventional polymers used in EOR, except that they have a small number of hydrophobic groups incorporated into the polymer backbone. At incorporation levels of less than 1 mol% these hydrophobic groups can change polymer performance. In this work, a water-soluble polymer made of acrylamide and N,N-dihexylacrylamide was obtained. After characterization of the copolymer, its performance in a porous medium was evaluated through core flood experiments in Botucatu sandstone. In the presence of sodium chloride, the amphiphilic copolymer exhibited a significant increase in viscosity at low polymer concentrations, in addition to resistance factor and residual resistance factor values higher than those of a commercial polyacrylamide. This behavior can increase oil recovery, mainly in high salinity and high-permeability reservoirs, by improving waterflood sweep efficiency.     

Volatile wood extractives of black pine (Pinus nigra Arnold) grown in Eastern Thrace

Pinus nigra.

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Pinus nigra an diesem Standort k?nnte demnach zu einem anderen Taxon geh?ren.

     

Optimum diversity combining and equalization in digital datatransmission with applications to cellular mobile radio. I. Theoreticalconsiderations

A comprehensive theory for Nth-order space diversity reception combined with various equalization techniques in digital data transmission over frequency-selective fading channels is developed. The channels are characterized by N arbitrary impulse responses possessing random parameters as well as N additive Gaussian noise sources. Various combiner-equalizers that minimize the mean-squared error are determined. Formulas are presented for the attainable least-mean-squared errors and upper bounds on average probabilities of error. The theory is applied to optimize system parameters and to predict performance for QAM data transmission operating over a model for the mobile radio channel. For this model, estimates of average attainable error rates and outage probabilities are provided as functions of system parameters. In the channel models the uncoded data rates as well as Shannon capacity are regarded as random variables     

Analytical chromatography for recovery of small amounts of staphylococcal enterotoxins from food

Sample preparation is an important element in the detection of toxins in food samples. In this work, a simple analytical sample preparation method for recovery of small amount of staphylococcal enterotoxin B (SEB) and staphylococcal enterotoxin A (SEA) in food samples was developed. Cation exchanger carboxymethylcellulose (CM) was used for small-scale batch chromatography isolation of SEB from infant formula and from mushrooms spiked with SEB. The resulting materials were analyzed for SEB by Western immunoblotting. Nearly all of the extraneous substances in the sample were removed by this procedure with no significant loss of the toxin. Using this method, even small amounts of SE (0.75 ng/g) can be recovered and immunologically analyzed by Western blotting or by ELISA with a very low background. Because this method is effective, rapid, simple and inexpensive, it has the potential to be a general method for the preparation of samples used for analysis of SEs.     

A Continuous High Pressure Carbon Dioxide System for Microbial Reduction in Orange Juice

ABSTRACT: A continuous high-pressure carbon dioxide system, run at ambient conditions, was tested on its performance in reducing both natural and inoculated microbial loads. The prototype system continuously processes orange juice with carbon dioxide (CO₂) at high pressures. A central composite design was originally used to examine the variables of pressure, residence time, and CO₂/juice ratio. For microbial reduction, residence time was the major factor followed by pressure. The CO₂/juice ratio showed no influence on microbial load, and in this equipment, was difficult to control. The unit was able to cause a 5-log reduction of the natural flora in spoiled juice, and could attain a 5-log decrease in numbers of pathogenic Escherichia coli O157:H7, Salmonella typhimurium , and Listeriamonocytogenes . No viable cells of E . coli O157:H7 orS. typhimurium were cultured after the treated juices were stored at room temperature (22 °C) for 14 d. Thus, non-thermal pathogen reduction is possible with this system.