Behaviour of mesogenic side group polyacrylates in dilute and semidilute regime

The solution behaviour of a new mesogenic side group polyacrylate in tetrahydrofuran and toluene has been investigated by static and dynamic light scattering. In the dilute regime the polymer behaves as typical polydisperse linear chains in good solvent and the dynamics is dominated by a single fast mode. Cluster formation was detected starting at a concentration around 50 g l⁻¹. It seems to be independent of the solvent as well as of polymer molecular weight. In the semidilute regime, the behaviour of the reduced osmotic modulus leads to the conclusion that repulsion between the chains is stronger than in linear macromolecules. The appearance of larger clusters was revealed above a characteristic concentration and is slightly dependent on the polyacrylate molecular weight. The dynamics was generally characterised by a fast mode related to the cooperative diffusion and by a slow mode associated with large clusters. The existence of a network of multiconnected clusters is envisaged with increasing solution concentration.     

Viscometric and transmitted light investigation of agarose and agarose-guar water systems

Summary Agarose water solutions of different concentrations and agarose-guar water solutions of 1% (w/w) total concentration and varied compositions were submitted to viscometric and turbidimetric measurements as function of the temperature. Phase diagrams for both systems are compared. For agarose solutions, phase separation occurs prior to gelation within a certain concentration range, and network formation seems to take place by the connectivity of the polymer-rich domains. For the mixed agarose-guar system, the homogeneous solutions gel directly.     

The toxicity of IDPN on the vestibular system of the rat: new insights on its effects on behavior and neurofilament transport

3,3'-Iminodipropionitrile (IDPN) causes a permanent syndrome of abnormalities in spontaneous behavior and a deficit in the axonal transport of neurofilaments (NF). Male Long-Evans rats were given IDPN (0, 200, 400, 600, or 1000 mg/kg, ip, in saline) and assessed for behaviors indicative of vestibular function at 1 week post-dosing. The morphology of the peripheral vestibular system in animals dosed with 0, 200, 400, 600, 800, or 1000 mg/kg of IDPN was assessed at 4 days post-dosing by light microscopy on semithin sections. Animals receiving 1000, 1500, or 2000 mg/kg of IDPN were assessed for morphological alterations in the vestibular ganglion at 8 days post-dosing. Behavioral data indicated a dose-dependent loss of vestibular function after IDPN, the vestibular deficits first appearing at the 400 mg/kg dose level. IDPN exposure was also observed to result in degeneration of the vestibular sensory hair cells. Degenerative changes were already found at the 400 mg/kg dose level, and were extensive after 1000 mg/kg. In the ganglion neurons, no effects were observed after 1000 mg/kg of IDPN, but perikaryal accumulations of NF were found after 1500 or 2000 mg/kg. In conclusion, the data showed that low doses of IDPN are toxic to the vestibular hair cells, and suggest a link between this action and the effects of the chemical on spontaneous behavior. In addition, doses of IDPN larger than those required for toxicity to the vestibular sensory cells, induced accumulations of NF in the myelinated cell bodies of the vestibular ganglion neurons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Production of single and multi-walled carbon nanotubes using natural gas as a precursor compound

In this work, the Catalytic Chemical Vapor Deposition (CCVD) technique was used to synthesize carbon nanotubes (CNT). Natural gas (NG) was employed as a carbon source for the growing of CNT, while magnesium oxide was used as a catalyst support for the nanotubes synthesis. Two systems were utilized. The Fe–Mo/MgO system was obtained by the impregnation technique through the dispersion of iron oxide, which is the catalyst, over magnesia (with molybdenum additions). This system was tested intending to optimize the parameters for the production of single-walled carbon nanotubes (SWCNT). Moreover, Mg_1−x Fe _x MoO₄, which was prepared by the combustion synthesis method, was tested to produce multi-walled carbon nanotubes (MWCNT). The Fe-Mo/MgO tests were carried out under H₂/GN and Ar/GN atmospheres at 950 °C, whereas the Mg_1−x Fe _x MoO₄ was submitted to 1,000 °C under H₂/GN atmosphere. The Fe–Mo/MgO catalyst produced better results regarding number of CNT and their diameters under Ar/NG atmospheres than under H₂/NG atmospheres. The system Mg_1−x Fe _x MoO₄ produced MWCNT according to the expectations.     

Carbon based electronic materials: applications in electron field emission

The influence of the different types of bonding present in a range of carbon based materials is discussed as a precursor to describing the field emission characteristics of carbon cold cathode materials. Some of the controlling factors which govern electron emission from carbon based cathodes are discussed. It is shown that from disordered carbon films the interplay between the clustered sp² phase and the insulating sp³ matrix is important. The transition from a ‘back contact’ to ‘front surface’ controlled emission mechanism is described in terms of the sp² content and field penetration. A possible reason for high field enhancement factors found in disordered films also is provided. It is further shown that changes to the sp² phase by current stressing can improve the field emission characteristics. Emission from carbon nanotubes is also discussed and the prospects for new types of nanotube – polymer composite based cathodes are also considered.     

Relationship between seizure frequency and costs and quality of life of outpatients with partial epilepsy in France, Germany, and the United Kingdom

PURPOSE: The relationship between seizure frequency and both health care costs and quality of life (QOL) was investigated in a retrospective, cross-sectional, multicenter study in France, Germany, and the United Kingdom. METHODS: Three hundred outpatients with stable partial epilepsy were approximately evenly distributed among five seizure-frequency groups, ranging from seizure-free in the last 3 months (group 1) to daily seizures (group 5). Economic data, obtained through patient interviews and record abstraction, comprised direct medical costs, direct nonmedical costs, and indirect costs for the preceding 3 months. Total societal costs in the three countries were pooled and converted to United States dollar equivalents. QOL was assessed through a self-administered questionnaire, the Functional Status Questionnaire (FSQ). RESULTS: Mean total costs increased from $780 in group 1 to $2,171 in group 5 (p = 0.0001), with significant increases in each cost category as seizure frequency increased. Greater seizure frequency also significantly (p = 0.0270) correlated with lower employment rates, which ranged from 57% in group 1 to 30% in group 5. QOL declined as seizure frequency increased. Particularly affected were basic and intermediate activities of daily living (ADL), mental health, social activity, and feeling about health. CONCLUSIONS: The study results show that higher seizure frequencies are associated with higher direct and indirect costs and with reduced QOL for patients with epilepsy.     

Rheological behaviour of processed avocado pulp emulsions

Shear rate vs. shear stress data were obtained on avocado pulp in water emulsions using a concentric cylinder rheometer and fitted to a power law model. Dilution, as volume fraction of water, had a pronounced effect on the apparent viscosity of the pulp emulsions and the Richardson equation, (η_R= exp.( a φ) for the emulsion viscosity fitted the data well. A mean slope coefficient, a , of 4.57 can be used as a first approximation. Enzymatic treatment (40°C, 1 h), is slightly more effective than thermal treatment (65°C, 1 h), in reducing the initial apparent viscosity of the pulp-water emulsions     

The microbiology of mixed salad containing raw and cooked ingredients without dressing

Growth of aerobic mesophilic bacteria in mixed salad without dressing, containing cooked sweet corn and raw endive, was similar to that of raw endive alone. At 9°C, sweet corn permitted the growth of the lactic acid bacterium Leuconostoc mesenteroides , whenever the bacterium was present on raw endive, whereas no growth of lactic acid bacteria was recorded on raw endive alone. Listeria monocytogenes , artificially inoculated in the samples, grew more in the mixed salad than in the raw endive alone, for products stored at 6°C and 9°C. Acidification of sweet corn to pH 5.0 was proposed to reduce the development of L. monocytogenes in the mixed salad to a level similar to that recorded in the raw endive alone. Acidification with citric acid reduced spoilage of sweet corn, whereas acetic acid caused necrosis on the leaves of raw endive.     

Synthesis method for testable electrical networks using 1st order building blocks

This work presents a method for synthesizing testable continuous-time linear time-invariant electrical networks using 1st order blocks for the implementation of analog linear circuits. A functional-structural fault model for the block, and a fault dictionary are proposed together with a simple set of test vectors. The method allows, also, the fault grade evaluation for the modeled faults. The results obtained from the two application examples have shown the suitability of the approach as a design for test method for analog circuits.