Performance of Low Earth Orbit Satellite Systems with Coding

The effect of block, convolutional and Turbo coding on the probability of error and the capacity are investigated for CDMA Low Earth Orbit (LEO) Satellite systems. The model employed assumes a contaminated Gaussian traffic model to be more compatible with different population areas. The conventional Gaussian distribution can be considered as a special case.     

Infrared and chemical durability studies of some binary PbO and ZnO phosphate glasses and their corresponding sodium metaphosphate derivatives

Abstract. Structural conclusions are obtained for glasses in the binary PbO and ZnO phosphate systems by IR spectroscopy. Alterations in bands, frequencies and intensities as a function of chemical composition are interpreted and these indicate various types of interlink between Pb²⁺ and Zn²⁺ cations and the host network, especially, when they are incorporated as NWF’s. Moreover, the metaphosphate structure, theoretically possible to be achieved in the structure of glasses with equimolar compositions 50M(II)O·50P₂O₅ (mol%) (where M is Zn or Pb), is not confirmed by their spectral patterns. However, this structure is confirmed to be achieved in the structure of glasses with 20Na₂O·30PbO·50P₂O₅ and 40Na₂O·10ZnO·50P₂O₅ (mol%). The dissolution rates of most of the studied glasses were measured as a function of pH and variation in chemical composition. The results are discussed in light of the conclusions obtained from the IR study, structural model of phosphate glasses (Van Wazer) and the previously suggested mechanisms for dissolution of phosphate glasses.     

Gas phase esterification of acetic acid with ethanol over MoO3 supported on AlPO4 and the effect of modification with phosphomolybdic acid and Ce4+ ions

A series of AIPO₄–MoO₃ (APM) systems with various molybdena loadings (5–50) mol %, same modified with phosphomolybdic acid (PMA) and cerium ions, were prepared by an impregnation method and calcined at 400 °C, except for the samples modified with PMA which were calcined at 350 °C for 4 h. The catalysts were characterized by TG/DTG, XRD, IR spectroscopy, N₂ adsorption and electrical conductivity measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of isopropyl alcohol. The catalytic esterification of acetic acid with ethanol was carried out in a convention fixed bed reactor. The results clearly revealed that the catalyst with a composition of 10 mol % MoO₃ (APM10) was the most active and selective catalyst for the production of ethyl acetate. Moreover, the yield of ethyl acetate increases on addition of PMA into APM10 while it decreases on the addition of Ce⁴⁺ ions. These results were correlated with structure, semiconductivity and the acid–base properties of the prepared catalysts. Copyright © 2003 Society of Chemical Industry     

Supramolecular host–guest systems constructed of pyrrole derivatives and 3D-coordination polymers

Pyrrole derivatives have been shown to be completely or partially oxidized within the expandable channels of the 3D-coordination polymers [(R₃Sn)₃Fe(CN)₆] _n and [(R₃Sn)(R₃^′Sn)₂Fe(CN)₆] _n , R and R′ = Me, n-Bu, or Ph, to give novel class of supramolecular host–guest systems. The structures and physical properties of these host–guest systems depend on the reaction time, nature of the host and guest, the space empty within the network of the 3D-coordination polymers. Pyrrole undergoes oxidative polymerization in the channels of the 3D-coordination polymers to form semiconducting diamagnetic supramolecular host–guest systems. Whereas N-methylpyrrole and 2,5-dimethylpyrrole are not polymerized under these experimental conditions, but give paramagnetic charge transfer (CT) supramolecular host–guest systems.     

Ultrasonic investigation of some rubber blends

Compression ultrasonic velocity, longitudinal ultrasonic absorption, and heat of mixing for NR-BR, NR, NBR, and NR-IIR rubber blends were measured. Results show the applicability of examining the compatibility degree by using longitudinal ultrasonic absorption techniques. Results showed that NR-BR blends are compatible, whereas NR-NBR and NR-IIR blends are semicompatible and incompatible, respectively.     

Effect of some thermal and chemical pretreatments on smoked Oyster mushroom quality

The effect of different thermal and chemical pretreatments on quality and enzyme activities of smoked mushroom was investigated. Mushrooms were blanched (water and steam) and dipped in different concentrations of sulphites (SO₂), hydrogen peroxide (H₂O₂), ethylene‐di‐amine tetra‐acetic acid (EDTA) and citric acid for 10 min before smoking. Enzyme activities, colour characteristics, microbiological and sensory examinations were carried out every 2 weeks up to 8 weeks of storage in refrigerator at 4 °C. Results could be concluded that smoked mushroom pretreated with SO₂, H₂O₂ and steam blanching had the best colour values, the better score for all sensory characteristics and lower non‐enzymatic browning compared with other pretreatments. The most effective pretreatment against total aerobic bacteria and yeast & moulds were citric acid, EDTA and steam, and then smoking of mushroom can be attributed to the reduction of microbial counts. The most effective pretreatments on quality and safety of smoked mushrooms were H₂O₂ and steam. It can be concluded that thermal and chemical treatments, rather than smoking of mushroom, reduce enzyme activities and are suitable to preserve mushrooms.     

Electrochemical studies on the effect of pyrazolo‐containing compounds on the corrosion of carbon steel in 1 M sulphuric acid

The effect of some synthesized pyrazolo containing compounds on the corrosion of carbon steel in 1 M H₂SO₄ was investigated. The investigation involved electrochemical polarization methods (potentiodynamic, Tafel extrapolation and the determination of the polarization resistance). A significant decrease in the corrosion rate of carbon steel was observed in the presence of the investigated compounds. The results show that these compounds act as mixed type inhibitors, but the cathode is more preferentially polarized. The relative inhibition efficiency of these compounds depends on both the nature and concentrations of the investigated compounds. Compounds are found to adsorb on the carbon steel surface according to the Langmuir adsorption isotherm.