Photoelectron spectroscopic investigation of transformation of trifluoroacetate precursors into superconducting YBa2Cu3O7−δ films

X-ray photoelectron spectroscopy (XPS) has been used to investigate the evolution of surface chemistry of YBa₂Cu₃O_7−δ (Y123) films prepared by the metalorganic deposition (MOD) process using trifluoroacetate (TFA) precursors. Detailed XPS core-level spectra obtained from the samples quenched from various points during the calcining and firing stages have been reported for the first time and are used to identify surface species. The XPS data show evidence of formation of intermediate phases such as Y-O-F, BaF₂, and CuO during the calcining process, which are the decomposition products of yttrium, barium, and copper trifluoroacetates, respectively. The TFA precursors are completely decomposed at the end of calcination. The change of binding energies for Y 3d_5/2, Ba 3d_5/2, and O 1s during the firing process indicates that Y123 starts to form at 800 °C after 0.5 h firing. Based on the experimental results, an alternative mechanism of the chemical evolution from precursor to final film in the TFA-MOD process is proposed.     

Die Änderung des Brechungsindex bei der Koagulation von Mangandioxyd-Sol. Nachweis eines „Stufeneffektes“ bei der Änderung

Zusammenfassung Es wurden die ?nderungen der Lichtbrechung bei der Koagulation von Mangandioxyd-Sol durch HCl-, Li₂SO₄-, NaCl-, KCl-, NH₄Cl-, BaCl₂-, AlCl₃-, Ce(NO₃)₄ und Th(NO₃)₄-L?sungen untersucht. Die tats?chliche ?nderung des Brechungsindexμ w?hrend des Verlaufs der Koagulation h?ngt von der spezifischen Beschaffenheit des Koagulators und seiner Konzentration ab. Es zeigte sich, da? dieμ-Zeit-Kurve in allen untersuchten F?llen unstetig oder stufenartig verlief. Dieser Stufeneffekt wird besonders deutlich bei langsamen Koagulationen. übersetzt von A. Siehr (Leipzig).     

Intermolecular Forces of Sugars in Water

Apparent molar volume and viscosities of fructose, glucose, mannose, and sucrose have been measured in dilute aqueous solution, concentration range 0.028–0.336 M at 293 K. The viscosity coefficient B and A were calculated from the viscosity data using the Jones-Dole equation for all the studied sugars. The data were also analysed for Stauarding equation. The structure making behavior was obtained for all the sugars. A modified Jone-Dole equation was proposed by using ratio of mole fractions of solute and solvent in place of concentrations of solute.     

Role of host liquid in optical limiting in ink suspensions

Optical limiting of 532 nm, 15 ns duration laser pulses in suspensions made by diluting black ink in water, ethanol, and isopropanol was studied and the strength of limiting was found to be quite different for the three suspensions. Microscopic investigations showed that the sizes of suspended aggregates were different for different host liquids. The suspension with largest aggregate was found to exhibit strongest optical limiting. Our work thus shows that host liquid influences optical limiting in suspensions not only through its thermodynamic properties but also by determining the particle size which has a strong effect on limiting strength.     

Synthetic Studies of a Didemnin B Analog Based on a 2,3‐Diamino Sugar Scaffolding

Reductive amination, amide formation using BOP [(1H‐1,2,3‐benzotriazol‐1‐yloxy)tris(dimethylamino)‐phosphonium hexafluorophosphate] and esterification via DCC (dicyclohexylcarbodiimide) were the key synthetic steps to generate an advanced intermediate in the preparation of a didemnin B analog based on a sugar scaffolding ( 2 ). This analog should provide insight into the bioactive conformation of didemnin B.     

2,4,6-Trichloro-1,3,5-triazine Catalyzed Chemoselective Transthioacetalization of Aldehyde Acetals and Oxathioacetals

A mild and efficient transthioacetalization of aldehyde acetals and oxathioacetals was carried out using 2,4,6-trichloro-1,3,5-triazine as a mild and inexpensive catalyst. Chemoselective transacetalization is impressive as aldehyde O,O- and O,S-acetals are converted into the corresponding S,S-acetals in the presence of ketones or their acetals and oxathiocetals in nearly quantitative yields.     

Axisymmetric buckling of laminated, moderately thick shallow conical cap

Summary  Axisymmetric buckling and postbuckling analysis is presented for a moderately thick, laminated shallow conical cap under static transverse load. Marguerre-type, first-order shear deformation shallow-shell theory is formulated in terms of transverse deflection w, the rotation ψ of the normal to the midsurface and the stress function Φ. The governing equations are solved by the orthogonal point-collocation method. Clamped conical caps and simple supports with movable and immovable edge conditions are considered. Typical numerical results are presented, illustrating the effect of various parameters. The dependence of the effect of the shear deformation on the thickness parameter, boundary conditions, ratio of Young's moduli and cap height is investigated. Received 10 February 2000; accepted for publication 3 May 2000     

Quaternionic quantum mechanics is consistent with complex quantum mechanics

Quaternionic quantum mechanics is investigated in the light of the great success of complex quantum mechanics. It is shown that to reproduce the results of complex quantum mechanics, quaternionic quantum mechanics must contain complex quantum mechanics.     

A probabilistic approach to antigen-antibody recognition

Expressions for the expected value and the variance of the longest matched segment on the surfaces of two random shapes are obtained. Applications of these estimates to antibody-antigen pattern recognition during immune response are considered. Methods of estimation of the involved probabilities are presented with relevant computational results.