Adaptive control and synchronization of a coupled dynamo system with uncertain parameters

This paper treats the adaptive control and synchronization of the coupled dynamo system with unknown parameters. Based on the Lyapunov stability technique, an adaptive control laws are derived such that the coupled dynamo system is asymptotically stable and the two identical dynamo systems are asymptotically synchronized. Also the update rules of the unknown parameters are derived. Finally, numerical simulation of the controlled and synchronized systems are presented.     

Pinacol-Pinacolone Rearrangement of 1, 2-Di-(p-methoxyphenyl)-ethane-1, 2-diol and Bis-(4-methoxyphenyl)-acetaldehyde in Acid Media

1, 2-Di-(p-methoxyphenyl)-ethane-1, 2-diol gave in acid media bis-(4-methoxy-phenyl)-acetaldehyde, 4-4′-dimethoxy-deoxybenzoin, and 1, 2-di-(p-methoxyphenyl)-ethylene oxide; their respective yields being influenced by at least 3 factors: (i) the acid, (ii) its concentration, and (iii) the reaction period. Bis-(4-methoxyphenyl)-acetaldehyde rearranged to the deoxybenzoin in boiling sulfuric (50%) or phosphoric (75%) acids (w/w), and to two isomeric 1, 2-diacetoxy-1, 2-di-(p-methoxyphenyl) ethanes when it was heated with acetic anhydride. The mechanisms of these reactions are discussed.     

UV-vis, IR and 1H NMR spectroscopic studies of some mono- and bis-azo-compounds based on 2,7-dihydroxynaphthalene and aniline derivatives

The absorption spectra of mono- and bis-azo-derivatives obtained by coupling the diazonium salts of aromatic amines and 2,7-dihydroxynaphthalene have been studied in six organic solvents. The different absorption bands have been assigned and the effect of solvents on the charge transfer band is also discussed. The diagnostic IR spectral bands and 1H NMR signals are assigned and discussed in relation to molecular structure. Also, semi-empirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory have been performed to investigate the molecular and electronic structures of these compounds. According to these calculations, an intramolecular hydrogen bonding is essential for stabilization of such molecules.     

Thermal stabilities,electronic properties and structures of metformin-metal complexes

The atomic superposition and electron delocalization molecular orbital (ASED-MO) theory was used to calculate structures and relative stabilities of metformin-metal complexes. The relative stabilities and decomposition pathways were discussed in terms of bond order, binding energy and the nature of charge on the central metal atom. The electronic transitions and their energy gaps were also studied. The optimization of the structures shows that the most stable state is distorted from planarity for Co^II and Ni^II complexes.     

Spectrophotometric determination of tetracyclines and cephalosporins with ammonium vanadate

A spectrophotometric method for the determination of some tetracyclines as well as some cephalosporins is described. The drug is boiled with ammonium vanadate solution in sulphuric acid medium for 10 min and the absorbance of the colour developed is measured at 750 nm. The proposed method can be successfully applied to the determination of tetracycline hydrochloride, oxytetracycline hydrochloride, doxycycline hyclate, demeclocycline hydrochloride, chlortetracycline hydrochloride, cephalothin sodium, cephaloridine and cephapirin sodium. These drugs can be determined either in pure form or in pharmaceutical preparations.     

Thermal degradation studies of alkyl-imidazolium salts and their application in nanocomposites

Increasing the thermal stability of organically-modified layered silicates is one of the key points in the successful technical application of polymer-layered silicate nanocomposites on the industrial scale. To circumvent the detrimental effect of the lower thermal stability of alkyl ammonium-treated montmorillonite, a series of alkyl-imidazolium molten salts were prepared and characterized by elemental analysis, thermogravimetry (TGA) and thermal desorption mass spectroscopy (TDMS). The effect of counter ion, alkyl chain length and structural isomerism on the thermal stability of the imidazolium salts was investigated. Alkyl-imidazolium-treated montmorillonite clays were prepared by ion exchange of the imidazolium salts with Na-montmorillonite. These organically-modified clays were characterized by X-ray diffraction (XRD), TDMS and thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR), and compared to the conventional quaternary alkyl ammonium montmorillonite. Results indicate that the counter ion has an effect on the thermal stability of the imidazolium salts, and that imidazolium salts with PF₆⁻, N(SO₂CF₃)₂⁻ and BF₄⁻ anions are thermally more stable than the halide salts. A relationship was observed between the chain length of the alkyl group and the thermo-oxidative stability; as the chain length increased from propyl, butyl, decyl, hexadecyl, octadecyl to eicosyl, the stability decreased. The results also show that the imidazolium-treated montmorillonite has greater thermal stability compared to the imidazolium halide. Analysis of the decomposition products by FTIR provides an insight about the decomposition products which are water, carbon dioxide and hydrocarbons.     

Microdetermination of phosphorus in organic compounds by indirect spectrophotometric reactions

Summary Organo phosphorus compounds are decomposed by closed-flask combustion. The phosphate ions produced are then converted to phosphomolybdic acid and extracted withiso- butyl acetate. The 12molybdate ions associated with each original phosphate ion are spectrophotometrically determined by reactions with alkaline hydrogen peroxide, hydrogen peroxide and benzidine and gallic acid. The colours are measured at 450, 400 and 400nm respectively.

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Zusammenfassung Organische Phosphorverbindungen werden im Schöniger-Kolben mineralisiert. Das Phosphat wird zu Phosphormolybdänsäure umgesetzt, miti-Butylacetat extrahiert und dann spektrophotometrisch bestimmt. Dazu bedient man sich der Reaktionen mit alkalischem Wasserstoffperoxid, mit Wasserstoffperoxid und Benzidin oder mit Gallussäure. Die Messungen erfolgen bei 450 nm im ersten Fall, bei 400 nm im Fall der beiden letztgenannten Farbreaktionen.

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This paper is taken from the Master's Thesis of S. A. I. Thoria.     

Development and validation of routine analysis methods for the determination of essential, nonessential, and toxic minor and trace elements in cereal and cereal flour samples by inductively coupled plasma-atomic emission spectrometry

Various digestion procedures were carefully investigated and accurately evaluated with respect to their effect on the analysis of cereals and cereal flours. Multielement methods were selected and well developed for the determination of essential (Cr, Cu, Fe, Mg, Mn, and Zn), nonessential (Ag, Al, Ba, Bi, In, and Ga), and toxic (Cd and Pb) minor and trace elements by inductively coupled plasma-atomic emission spectrometry. Only Ag could be determined, either with aqueous standard or standard addition calibration methods, while the standard addition methods were more accurate for the determination of other elements. The recoveries were mostly within the range of 84.1-113% for the expected values of all analytes with respect to certified reference material NIST SRM 1586a (rice flour). The results proved that, for cereals and cereal flours, the use of H2O2 for wet digestion and HNO3 for dry ashing were not necessary. Linear regression analysis and Student's paired t-test were applied to evaluate the significant differences between different procedures and type of samples.     

Kinetic studies of cobalt alginate gels

Summary Sodium alginate sol can be converted into ionotropic gels by diffusion of di/or trivalent metal ions. The kinetics of this phase transition is studied by two different methods. It is found that the rate of gel membrane formation at the earlier stages is greater than that of the further gel growth. The kinetic studies of gel formation in the presence of a mixture of Cu²⁺ ions with either Co²⁺ or Ni²⁺ ions show that the exhaust of Co²⁺ and Ni^2- ions is remarkable only at the first stage of gel formation. Meanwhile the Cu²⁺ ions continue exchanging all the time with Na²⁺ ions in the alginate sol. The activation energy of gel formation is found to range between 17–23 kJ mol^–, indicating the diffusion control of the process.With 6 figures and 3 tables     

Modification of the resistance of two epoxy resins to accelerated weathering using calcium sulfate as a photostabilizer

Epoxy-timber composites have received increasing attention during the last decades because there are many advantages related to their uses as construction materials in applications such as timber bridges. However, the durability of epoxy-timber composites under outdoor conditions has become a concern for many epoxy resins. This study evaluated the chemical, thermal, and mechanical properties of two cured epoxies, the product of the diglycidyl ether of bisphenol A with 2,4-trimethyl-1,6-hexanediamine (DGEBA-TMDA) and the analogous resin prepared with the hydrogenated diglycidyl ether of bisphenol A (HDGEBA-TMDA), each mixed with 2?wt. % calcium sulfate (CS). We hypothesized that the use of CS, as an inorganic UV absorber, could decrease undesirable effects arising from exposure to UV light, moisture, and extreme temperatures.

An accelerated aging chamber simulated natural weathering for 1, 2, 3, 4, and 6?months. Chemical changes in cured epoxy systems over time in the presence and absence of CS fillers were determined using Fourier transform infrared spectroscopy (FT-IR). Thermal degradation profiles before and after exposure to accelerated weathering were followed by thermogravimetric analysis (TGA). The glass transition temperatures (T_g) before and after accelerated weathering were measured, and the effect of accelerated weathering on the surface morphology of the epoxy systems was investigated by scanning electron microscopy (SEM). In the presence of CS, after 6?months accelerated weathering the tensile strength of DGEBA-TMDA reduced by 23.8?±?2.4%, compared to 46.5?±?5.5% in its absence, while the corresponding values for HDGEBA-TMDA were 21.4?±?2.1% and 28.7?±?1.8%.