Interfacial effects in carbon-epoxies

The work of fracture has been measured, using the Izod test, for short-fibre laminates. The fibres were 2mm long and in one series of experiments were aligned, and in a second series of experiments they were random in the plane of the laminate. The work of fracture increased monotonically with increasing fibre content and fibre critical length, but values were less than expected on the basis of established fibre pull-out theory. The low values were probably due to the high resistance to debonding of these composites, since the fibre pull-out lengths at the fracture surfaces were very much smaller than the fibre critical lengths.     

Simplified design and analysis method for a waveguide iris filter

A simplified method for design and analysis of a direct coupled waveguide iris filter suitable for computer aided design implementation is presented. A curve fit formula for calculating the aperture dimensions of an iris as a function of normalized shunt inductor values is given. The analysis of the entire filter response is calculated using ABCD parameters. Using proposed equations a five section iris filter at X band has been designed and tested. Comparison between measured and theoretical results is shown. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 150–154, 1999     

Cobalt selenide thin film: photovoltaic and impedance spectral studies by simple chemical grown technique

A thin film of cobalt selenide is deposited on the fluorescence tin oxide-coated glass surface material using a simple chemical growth technique. In this article, we report on the study of photoelectrochemical characteristics (PEC), including current–voltage, capacitance–voltage characteristics, photovoltaic power output, and spectral response in dark and light conditions. For the above parameter study, we prepared using cobalt selenide and carbon electrode (using polysulfide as electrolyte), the battery configuration is expressed as n-CoSe/NaOH (1 M)?+?Na₂S (1 M)?+?S (1 M)/C (graphite). The performance of the cobalt selenide thin film material the resulted values of respective series (R_S) and shunt (R_Sh) resistance 2.280 kΩ and 1.224 Ω, respectively. The efficiency and fill factor of these PEC cells were found to be 0.899 and 28.72%. The junction ideality value are found to be (n_D) is 0.69 in the dark and 2.72 in the light (n_L). The M–S plots are constructed using C^?2 against applied bias voltage (with respect to SCE) for CoSe PEC cell. The positive slope of the M–S plot confirms n-type conductivity of the CoSe films. The carrier density values of the samples obtained from the M–S plots varied from 3.48?×?10¹⁴ cm^?3.

     

Interphase effects on the mechanical and physical aspects of natural fiber composites

The interaction and adhesion between the fiber and matrix has a significant effect in determining the mechanical and physical behavior of fiber composites. The effect of the interface and interphase depends on several factors such as chemical composition (functional groups), molecular structure characteristics (branching, molecular weight distribution, cross-linking), and details of its physical state (above or below T_g, nature and degree of crystallinity). Natural fibers have complex and varying chemical structures that have uneven surface topographies. This creates difficulties in using single fiber composite testing to accurately evaluate the interfacial shear strengths, except for comparisons. A review of our interphase related research in natural fiber composites is presented. When using coupling agents it is well known that the tensile and flexural strengths increase dramatically in natural fiber reinforced composites. However, in the case of modulus, the results are more complex. For two ethylene-propylene impact copolymers, the uncoupled systems had much higher Young's moduli than the coupled systems. The dynamic storage moduli of the uncoupled impact polymers were higher than the coupled composites at temperatures up to about 50°C. At higher temperatures the presence of the coupling agent resulted in higher storage moduli. Transcrystallinity may play an important role in this phenomenon. Creep and other long-term properties are also affected by the quality of the interphase, although the level of improvement decreases with an increase in the molecular weight of the matrix polymer. Coupling agents reduced the rate of water absorption and the moduli were less affected in blends with a higher concentration of coupling agents.     

Lipids of dermatophytes. III. Sterol-induced changes in the lipid composition and functional properties ofEpidermophyton floccosum

Sterol supplementation, alone or in the presence of cerulenin, resulted in an increase in the total sterol content ofEpidermophyton floccosum. While the total phospholipid levels ofE. floccosum exhibited only marginal changes with sterol supplementation, the fatty acid profiles of these phospholipids were highly varied. In the presence or absence of cerulenin, the oleic acid content of phospholipids were increased significantly by cholesterol supplementation, whereas linoleic acid levels were enhanced by ergosterol supplementation. These variations resulted in higher unsaturated/saturated phospholipid fatty acid ratios in sterol-supplemented cells. The uptake of labeled amino acids (aspartic acid, lysine, glycine) was influenced by sterol supplementation. Alterations in the number of binding sites for the membrane probe, 1-anilino-naphthalene-8-sulfonate (ANS), were seen based on Scatchard plot calculations. The results indicate a correlation between sterol-induced changes in membrane lipid composition and function.     

Synthesis and characterization of Cd0.7Pb0.3Se thin films for photoelectrochemical solar cell

Optimum composition Cd_0.7Pb_0.3Se thin films have been deposited using the chemical bath containing cadmium sulfate octahydrate, lead nitrate, tartaric acid, potassium hydroxide, ammonia, and sodium selenosulfate onto fluorine-doped tin oxide glass substrate. The various deposition parameters such as composition of reactive bath, pH of the solution, deposition temperature, deposition time, speed of rotation, etc. have been optimized for obtaining good quality film. X-ray diffraction studies revealed the polycrystalline nature of sample with the solid solution of lead (II) ions in CdSe host lattice, having a hexagonal phase structure. Scanning electron micrograph suggested that the grains were non-uniformly distributed over the substrate surface. Film composition was determined by atomic absorption spectroscopy as well as energy dispersive X-ray atomic spectroscopy. Optical absorption data showed the presence of direct transition with energy band gap 1.80 eV for the deposited thin films. The dark specific conductance of Cd_0.7Pb_0.3Se thin films was found to the order of 10⁻⁶ (Ω cm)⁻¹ having n-type semiconducting nature. Photoelectrochemical characterization was carried out using sulfide/polysulfide electrolyte with 1.401% efficiency.     

Evaluation of wood-thermoplastic-interphase shear strengths

A macroscopic pull-out technique has been developed to determine the interphase properties in wood/low-molecular-weight-thermoplastic systems. Experimental variables affecting the shear properties of these types of composites were first identified so that the test could be used to compare the effect of different surface treatments on the interfacial properties. The relationship between the debonded force,F, and embedded length,L, was not linear, suggesting a failure mechanism that was different from interfacial yielding. Low embedded lengths provide useful comparative data on the maximum interfacial-shear strength of the system. The test is also useful for evaluating the quality of the fibre-matrix bond after exposure to water, since dimensional stability is an important consideration for wood-fibre-based composites. The test can be used to screen the effects of modifications on the lignocellulosic and/or the thermoplastic matrix on adhesive bonding for the development of composites. The use of lignocellulosic fibres (recycled wood fibres and natural fibres such as jute) in combination with recycled plastics could find applications in the automotive, furniture and building-materials industry.     

Mobile Software-Agenten in der Telekommunikation

The future evolution of telecommunication will be characterised by decentralised high-speed communication systems in distributed environments. These systems enable the dynamic provision of various information- and communication services, where information will be accessible any time, at any place, in any form. The development of a new technology, which customises the existing telecommunication services, is very significant for the competitiveness of network- and service providers. This article introduces the technology of intelligent agents, in particular mobile agents, and its application in telecommunications. The use of mobile agents enables dynamic provision of multimedia services, decentralisation of network management, and efficient resource management.     

Fuel pellets from biomass: The importance of the pelletizing pressure and its dependency on the processing conditions

The aim of the present study was to identify the key factors affecting the pelletizing pressure in biomass pelletization processes. The impact of raw material type, pellet length, temperature, moisture content and particle size on the pressure build up in the press channel of a pellet mill was studied using a single pellet press unit. It was shown that the pelletizing pressure increased exponentially with the pellet length. The rate of increase was dependent on biomass species, temperature, moisture content and particle size. A mathematical model, predicting the pelletizing pressure, was in good accordance with experimental data. It was shown that increasing the temperature resulted in a decrease of the pelletizing pressure. Infrared spectra taken from the pellets surface, indicated hydrophobic extractives on the pellet surface, for pellets produced at higher temperatures. The extractives act as lubricants, lowering the friction between the biomass and the press channel walls. The effect of moisture content on the pelletizing pressure was dependent on the raw material species. Different particle size fractions, from below 0.5 mm up to 2.8 mm diameter, were tested, and it was shown that the pelletizing pressure increased with decreasing particle size. The impact of pelletizing pressure on pellet density was determined, and it was shown that a pelletizing pressure above 200 MPa resulted only in minor increase in pellet density.