Chromatic and opto-mechanical dispersion of some characteristic parameters of optical fiber undergoing macrobending

Bending of optical fiber leads to an induced-anisotropy in the index profile that influences many important guiding fiber parameters. An analytical method is described for the measurement of refractive-index-wavelength dispersion in bent optical fibers. Multiple-beam Fizeau fringes technique at transmission is used to analyze the opto-mechanical properties and induced-index anisotropy in a standard single-mode fiber undergoes pure mechanical macrobending. The shift in Fizeau fringes is employed to evaluate the dispersion of the cladding material of the bent fiber. The radial variations in Cauchy’s coefficients and the associated variations of some fiber parameters due to macrobending are carried out. The radial profiles of some material parameters such as oscillation energy, dispersion energy, lattice energy and material dispersion are measured as well. The presented method is capable to achieve quantitative and qualitative measurements, which is not available with other methods. The method has a good index resolution in the order of 10⁻⁴ and spatial resolution of 1.3 μm.     

Optimal stopping problems by two or more decision makers: a survey

A review of the optimal stopping problem with more than a single decision maker (DM) is presented in this paper. We classify the existing literature according to the arrival of the offers, the utility of the DMs, the length of the sequence of offers, the nature of the game and the number of offers to be selected. We enumerate various definitions for this problem and describe some dynamic approaches. Fouad Ben Abdelaziz is on leave from the Institut Superieur de Gestion, University of Tunis, Tunisia e-mail: foued.benabdelaz@isg.run.tn.     

Solid reactions in Rubidium Carbonate-Vanadium Pentoxide system

The reactions between rubidium carbonate and vanadium pentoxide were performed at different high temperatures. Four reaction products of the compositions: I. Rb₂O · V₂O₅; II. 2 Rb₂O · V₂O₅; III. 3 Rb₂O · V₂O₅; and IV. Rb₂O · 4 V₂O₅ were obtained. According to the determination of Rb and the X-ray powder photographs of the products the existence of rubidium metavanadate (RbVO₃) and rubidium pyrovanadate (Rb₄V₂O₇) was confirmed. On the other hand, the preparation of a pure rubidium orthovanadate (Rb₃VO₄) and rubidium tetravanadate (Rb₂O · 4 V₂O₅) was not successful. The diffraction pattern of Rb₂O · V₂O₅ obeys hexagonal indexing with lattice dimensions a = 7.347 and c = 13.608 Å.     

Rapid synthesis of 2,5‐disubtituted 1,3,4‐thiadiazoles under microwave irradiation

The one pot, three‐components condensation of aromatic aldehydes, hydrazine and sulfur in ethanol under microwave irradiation provided symmetrically 3,5‐disubstituted 1,3,4‐thiadiazoles in high yields and good purity. This reaction must be conducted under pressure of hydrogen sulfide produced in‐situ. The structure of the compounds was confirmed by ¹H, ¹³C NMR, MS and elemental analysis.     

Chemistry of Phosphorus Ylides. Part 22 [1]. Effect of Newly Synthesized Niclosamide Mannich Bases, Phosphopyranones, Phosphoranylidenes, and Oxaphosphinin on Some Metabolic Aspects of Biomphalaria Alexandrina

Niclosamide reacts with secondary amines and formaldehyde under the condition of Mannich reaction, to give new Mannich bases. The reaction of these niclosamide Mannich bases with active phosphacumulene ylides affords the corresponding phenyliminopyranone, pyranone, and pyranthione, respectively. When Wittig reaction was carried out on the pyranone, using p-nitrobenzaldehyde, a new arylidene and triphenylphosphine oxide were obtained. On the other hand, stabilized phosphonium ylides affect the transylidation of niclosamide Mannich bases to the corresponding phosphoranylidenes. When diphenylmethylenetriphenylphosphorane reacts with a niclosamide Mannich base, an oxaphosphinin was obtained. The molluscicidal potency of the newly synthesized derivatives against Biomphalaria alexandrina was studied, too.     

Kryometrische Untersuchungen. IV. Lösungen von oxidischen Mo6+- und Cr6+-Verbindungen in geschmolzenem K2Cr2O7 und KNO3

The depression of freezing point of molten K₂Cr₂O₇ and KNO₃ as solvents was measured after addition of small concentrations of the following compounds: to K₂Cr₂O₇: MoO₃, CrO₃, (NH₄)₂CrO₄, K₂MoO₄, Na₂MoO₄, Li₂MoO₄, and Na₂Mo₂O₇, respectively; to KNO₃: CrO₃, (NH₄)₂Cr₂O₇ K₂Cr₂O₇, K₂CrO₄ and MoO₃, (NH₄)₆(Mo₇O₂₄) · 4 H₂O, K₂Mo₂O₇, K₂MoO₄, Na₂MoO₄ and Li₂MoO₄, respectively. It could be concluded from the measured values of the freezing point depression if a reaction between solvent and solute took place.     

Synthesis and characterization of maleimide polymers with pendant pyrazole groups. IV. Copolymerization of pyrazole-modified maleimides with vinyl ethers

The synthesis of maleimides that have pyrazolic or bipyrazolic pendant groups is described. Their homopolymerization and their copolymerization with 2-chloroethyl vinyl ether (CEVE) is reported. The homopolymerizations of such maleimides were performed under various conditions and led to low molecular-weight polymers. However, alternating copolymers were obtained from CEVE as comonomers whatever the monomers feed compositions. A similar behavior was also observed for maleimides that do not exhibit any spacer, whereas for bulky vinyl ethers, random copolymers were produced. A comparison of the thermal behavior between these copolymers (glass transition temperatures, T_g, and decomposition temperatures) and other copolymers having different spacers between the nitrogenated cycles and the chain are related. Thus, an important decrease of T_g, was observed when C₃H₆CO₂CH₂ groups were used as the spacer instead of methylene groups. Moreover, the thermal weakness of these copolymers may come from the substituents of the vinyl ether and is discussed. © 1994 John Wiley & Sons, Inc.     

Catalytic activity and stability of anionic and cationic water soluble cobalt(II) tetraarylporphyrin complexes in the oxidation of 2-mercaptoethanol by molecular oxygen

The catalytic activity and stability of anionic cobalt(II) porphyrin complexes: 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinatocobalt(II), 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5disulfonatophenyl)porphyrinatocobalt(II) and the cationic cobalt(II) porphyrin: 5,10,15,20-tetrakis[4-(diethylmethylammonio)phenyl]porphyrinatocobalt(II) tertraiodide have been investigated in the oxidation of 2-mercaptoethanol by dioxygen. All complexes were efficient catalysts for the auto-oxidation of 2-mercaptoethanol. The cationic cobalt(II) porphyrin has been found to be the most reactive catalyst. The rate of auto-oxidation of 2-mercaptoethanol catalysed by 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5disulfonatophenyl)porphyrinatocobalt(II) has been found to increase with increasing the pH from 7 to 9 then decreased at higher pH. The rate constants of auto-oxidation reaction showed linear dependence on catalyst concentration and saturation kinetics in both 2-mercaptoethanol concentrations and dioxygen pressure. Anionic cobalt(II) porphyrin complexes showed higher stability than the cationic catalyst in repeat oxidation reactions. Immobilizing the anionic catalysts on ion exchange resin and supporting the cationic catalyst on clay mineral montmorillonite improved their stabilities towards oxidation.     

Physicochemical characterization of degradable thermosensitive polymeric micelles

Amphiphilic AB block copolymers consisting of thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) and poly(ethylene glycol), pHPMAmDL-b-PEG, were synthesized via a macroinitiator route. Dynamic light scattering measurements showed that these block copolymers form polymeric micelles in water with a size of around 50 nm by heating of an aqueous polymer solution from below to above the critical micelle temperature (cmt). The critical micelle concentration as well as the cmt decreased with increasing pHPMAmDL block lengths, which can be attributed to the greater hydrophobicity of the thermosensitive block with increasing molecular weight. Cryogenic transmission electron microscopy analysis revealed that the micelles have a spherical shape with a narrow size distribution. 1H NMR measurements in D2O showed that the intensity of the peaks of the protons from the pHPMAmDL block significantly decreased above the cmt, indicating that the thermosensitive blocks indeed form the solidlike core of the micelles. Static light scattering measurements demonstrated that pHPMAmDL-b-PEG micelles with relatively large pHPMAmDL blocks possess a highly packed core that is stabilized by a dense layer of swollen PEG chains. FT-IR analysis indicated that dehydration of amide bonds in the pHPMAmDL block occurs when the polymer dissolved in water is heated from below to above its cmt. The micelles were stable when an aqueous solution of micelles was incubated at 37 degrees C and at pH 5.0, where the hydrolysis rate of lactate side groups is minimized. On the other hand, at pH 9.0, where hydrolysis of the lactic acid side groups occurs, the micelles started to swell after 1.5 h of incubation and complete dissolution of micelles was observed after 4 h as a result of hydrophilization of the thermosensitive block. Fluorescence spectroscopy measurements with pyrene loaded in the hydrophobic core of the micelles showed that when these micelles were incubated at pH 8.6 and at 37 degrees C the microenvironment of pyrene became increasingly hydrated in time during this swelling phase. The results demonstrate the potential applicability of pHPMAmDL-b-PEG block copolymer micelles for the controlled delivery of hydrophobic drugs.     

Cryoscopic studies on some Tungstates and Vanadates in Molten KNO3

The depression of the freezing point of molten KNO₃, as solvent, was measured after the addition of small concentrations of the solutes: 1. WO₃, K₂WO₄, K₂W₂O₇ and 2. V₂O₅, Cs₂V₆O₁₆ and Rb₂V₆O₁₆. DTA-apparatus was used in the measurements. The results showed that the investigated tungstates and vanadates were dissociated in the melt with the formation of monotungstate (WO₄)^2? and orthovanadate (VO₄)^3?-ions.