Rheological properties of partially hydrolyzed ethylene–vinyl acetate copolymers

Studies have been made of steady-shear and dynamic viscosities for melts of two ethylene–vinyl acetate copolymers and their partially hydrolyzed derivatives using a Weissenberg rheogoniometer over the temperature range of 123–150°C with some tests at 160°C. The flow activation energy of all samples studied was essentially independent of shear stress. The introduction of hydroxyl groups in controlled concentrations, however, produced a complicated flow behavior. At low concentrations, there is a marked increase in Newtonian viscosity, flow activation energy, and shear dependence of viscosity. In contrast to previous reports, a further increase in all three functions was not observed with increasing vinyl alcohol concentration. Dynamic viscosities, in contrast, show monotonic increases with increasing hydroxyl group content, as do activation energies derived from the temperature dependence of the dynamic viscosity. These data may result from an increased chain cohesion due to hydrogen bonding of hydroxyl groups.     

A rheological study of long branching in polyethylene by blending

Steady shear viscosities, dynamic viscosities and moduli, and the corresponding activation energies for flow were examined for a branched polyethylene, a linear polyethylene, and three of their blends at 150° and 190°C. The polyethylenes were chosen to have closely matched molecular weights and distributions. An R-17 Weissenberg rheogoniometer and an Instron capillary rheometer were used. At lower stress, the branched polymer had a higher viscosity than the linear one, possibly because of the contribution of long branches to entanglements. At high stress, this contribution is reduced and the inherently smaller coil dimensions likely become responsible for the lower viscosity of the branched polymer. The activation energy for the branched polymer is high and decreases with stress, in contrast to the low and almost-constant value for the linear polymer. The effects here of pressure on compression are considered. The entanglements of long branches may also decrease with increasing temperature. With decreasing stress, the activation energy for branched polymer tends to become constant, corresponding to an absence of pressure effects and an equilibrium entanglement of long branches for a given temperature range. The linear relationship between activation energy and blend composition problably means that any compressional effects, like free volume, are additive and that long-branch entanglements rearrange with added linear molecules. The linearity may be the result, in part, of a broad distribution for the lengths of long branches.     

Synthesis,Photochemistry, Computational Study and Potential Application of New Styryl-Thiophene and Naphtho-Thiophene Benzylamines

In this research, the synthesis, photochemistry, and computational study of new cis- and trans-isomers of amino-thienostilbenes is performed to test the efficiency of their production and acid resistance, and to investigate their electronic structure, photoreactivity, photophysical characteristics, and potential biological activity. The electronic structure and conformations of synthesized thienostilbene amines and their photocyclization products are examined computationally, along with molecular modeling of amines possessing two thiophene rings that showed inhibitory potential toward cholinesterases. New amino-styryl thiophenes, with favorable photophysical properties and proven acid resistance, represent model compounds for their water-soluble ammonium salts as potential styryl optical dyes. The comparison with organic dyes possessing a trans-aminostilbene subunit as the scaffold shows that the newly synthesized trans-aminostilbenes have very similar absorbance wavelengths. Furthermore, their functionalized cis-isomers and photocyclization products are good candidates for cholinesterase inhibitors because of the structural similarity of the molecular skeleton to some already proven bioactive derivatives.     

A correction of E-model in quality estimation of packetized speech signal

This letter presents correction of E-model for the quality estimation of the packetized speech signal in the case of burst packet loss. The current estimation depends on the method of calculation, i.e. on the duration of speech signal segment, which is to be packetized by one packet. This inconsistency in estimation is described, and the correction of this imperfection is proposed. It is explained that the Packet-loss Robustness Factor is dependent, besides coder, on the duration of speech signal segment, which is packetized by one packet.     

Design of optimal controllers for spatially invariant systems with finite communication speed

We consider the problem of designing optimal distributed controllers whose impulse response has limited propagation speed. We introduce a state-space framework in which all spatially invariant systems with this property can be characterized. After establishing the closure of such systems under linear fractional transformations, we formulate the H₂ optimal control problem using the model-matching framework. We demonstrate that, even though the optimal control problem is non-convex with respect to some state-space design parameters, a variety of numerical optimization algorithms can be employed to relax the original problem, thereby rendering suboptimal controllers. In particular, for the case in which every subsystem has scalar input disturbance, scalar measurement, and scalar actuation signal, we investigate the application of the Steiglitz–McBride, Gauss–Newton, and Newton iterative schemes to the optimal distributed controller design problem. We apply this framework to examples previously considered in the literature to demonstrate that, by designing structured controllers with infinite impulse response, superior performance can be achieved compared to finite impulse response structured controllers of the same temporal degree.     

The viscosity effect on autoacceleration of the rate of free radical polymerization

The reaction kinetics at 70°C were investigated for the suspension polymerization of methyl methacrylate initiated by benzoyl peroxide in the presence of variable amounts of dodecyl mercaptan. A dilatometric method designed to follow a suspension polymerization was used. It showed that the autoacceleration of the rate of polymerization begins at higher conversions and becomes less pronounced as the concentration of chain transfer agent is increased. The investigations focused on the determination of the viscosities of the reaction mixtures at the onset of autoacceleration. It was concluded from the flow curves obtained for different reaction mixtures that there exists a critical solution viscosity at which the autoacceleration begins, which supports the accepted theory about the nature of this phenomenon. Measured at a shear rate of 10,000 s^?1 and at 25°C this viscosity was found to equal 0.6 poise regardless of the molecular weight of the growing polymer.     

Evaluation and improvement of antioxidant and antibacterial activities of supercritical extracts from clove buds

For the first time, extracts from clove buds obtained by supercritical carbon dioxide extraction were screened for antioxidant and antibacterial activities. Additionally, antioxidant and antibacterial activities of extracts obtained by the supercritical extraction of the clove bud–oregano leaf mixtures were studied. Supercritical extract of pure clove had the highest eugenol (64%) and total phenolic content (530.56 mg GAE/g_extract). All extracts had antioxidant activity comparable to synthetic antioxidants against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and formation of peroxides. Presence of 0.6% and 5% of oregano extract in the clove extracts obtained from the clove–oregano plant mixtures improved their antioxidant activity with respect to the extract from pure clove. Clove extract showed moderate antibacterial activities against selected Staphylococcus and Enterococcus bacterial strains. Presence of 50% of the oregano extract improved antibacterial activity of clove extract against all tested strains and resulted in a synergistic antibacterial activity against Methicillin-resistant Staphylococcus haemolyticus strain (MIC ? 1.25 μg/mL). Study demonstrated great potential of supercritical clove extract as natural functional ingredient and the possibility of increasing its antioxidant and antibacterial efficiencies in order to apply lower concentrations and to reduce undesirable flavour notes and toxicological effects in final products.     

Chemical composition and antimicrobial activity of Vitex agnus-castus L. fruits and leaves essential oils

The following study deals with the chemical composition, antimicrobial activity of essential oils of Vitex agnus-castus L. and their main constituents in vitro and in vivo. The main compounds in the oil of unripe fruits were sabinene (17.8%) and 1,8-cineole (17.5%), while in the oil of the ripe fruits dominant compounds were 1,8-cineole (16.3%) and sabinene (13.4%). The leaves oil contained an abundance of 1,8-cineole (22.0%), as well. All of the oils tested were rich sources of α-pinene (12.2%, 9.4% and 9.4%, respectively). Antimicrobial activity was tested using bacterial and fungal strains by the microdilution method. Using the same technique 1,8-cineole and α-pinene showed very high antimicrobial potency as well. As 1,8-cineole was the predominant constituent of the oils, we have chosen to test it further in an in vivo experiment. Randomly chosen apples were treated with 1,8-cineol solution and infected with Aspergillus niger in order to provoke Aspergillus rot in apples. Disease incidence was recorded.     

In vitro control of multiplication of some food-associated bacteria by thyme, rosemary and sage isolates

Antibacterial activity of thyme, rosemary and sage isolates obtained by supercritical fluid extraction and hydrodistillation was investigated on Geobacillus stearotermophillus, Bacillus cereus, Bacillus subtilis var. niger, Enterococcus faecium, Salmonella enteritidis and Escherichia coli strains. Bacillus species were the most susceptible to all tested isolates. The thyme isolates showed the strongest antibacterial activity against tested bacteria with MIC values of 40-640 μg/ml, followed by rosemary (MIC = 320-1280 μg/ml) and sage (MIC = 160-2560 μg/ml) isolates. Therefore, the antibacterial activity of the most abundant components found in the thyme isolates, thymol, p-cymene and their mixture was investigated as well. The thyme isolates, especially supercritical extract, showed stronger antibacterial activity against Bacillus strains compared to the single components and their mixture, which indicated synergetic effect of the other components. Results of this study indicated thyme as a valuable source of natural antibacterial agents and supercritical fluid extraction as an efficient isolation method.