A Model of Subdiffusive Interface Dynamics with a Local Conservation of Minimum Height

We define a new model of interface roughening in one dimension which has the property that the minimum of interface height is conserved locally during the evolution. This model corresponds to the limit q of the q-color dimer deposition-evaporation model introduced by us earlier [Hari Menon and Dhar, J. Phys. A: Math. Gen. 28:6517 (1995)]. We present numerical evidence from Monte Carlo simulations and the exact diagonalization of the evolution operator on finite rings that growth of correlations in this model is subdiffusive with dynamical exponent z2.5. For periodic boundary conditions, the variation of the gap in the relaxation spectrum with system size appears to involve a logarithmic correction term. Some generalizations of the model are briefly discussed.     

Kinetics and thermal decomposition of Fe(III) and UO2(II) complexes with embelin (2,5-dihydroxy-3-undecyl-P-benzoquinone)

The thermal decomposition of the complexes: [Fe(C₁₇H₂₄O₄)_1.5·2H₂O]_n and [UO₂(C₁₇H₂₄O₄·2H₂O]_n, and evaluation of kinetic parameters (E, Z andS) by making use of Piloyan-Novikova, Coats-Redfern and Horowitz-Metzger equations are reported. The complexes are found to decompose in three well defined steps involving random nucleation mechanism. The intermediates formed during decomposition usually undergo further decomposition without remaining stable over a considerable range of temperature.

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Zusammenfassung Es wird über die thermische Zersetzung der Komplexe [Fe(C₁₇H₂₄O₄)_1.5·2H₂O]_n und [UO₂(C₁₇H₂₄O₄)·2H₂O]_n und über die Ermittlung der kinetischen Parameter durch Anwendung der Piloyan-Novikova, der Coats-Redfern und der Horowitz-Metzger-Gleichungen berichtet. Die Komplexe werden in drei gut definierten Stufen mit Random-Keimbildungsmechanismus zersetzt. Die während der Zersetzung gebildeten Zwischenprodukte unterliegen stets einer weiteren Zersetzung, ohne in einem erheblichen Temperaturbereich Stabilität zu zeigen.

     

Glycosylidene Carbenes Part 12. A new synthesis and some reactions of spirooxiranes

The diazirine 1 , upon thermolysis or photolysis in either acetone or cyclohexanone, at different concentrations, yield the spiro epoxides 2 and 3 , and 4 and 5 , respectively (Scheme 1). Yield of 2 and 3 depended both on the temperature and the concentration, and correlated inversely with the yield of the major by-product, the enol-derived glycoside 6 . Other by-product were the benzyloxglycal 7 and the lactone azines 8 . ZnCl₂-Promoted methanolysis of 2 under mild condition yielded mixture of the uloside 9 and 10 (1.2:1); similarly, 4 yielded 11 and 12 (1.8:1; Scheme 2). More strongly acidic conditions converted 11 into 12 , evidencing that ZnCl₂-promoted methanolysis proceeds under kinetic control, which is rationalized. The diazirine 13 , upon thermolysis of Photolysis in either acetone of cyclohexanone, yielded the α-D -configurated spiro epoxides 14 and 16 , and the α-D -configurated dihydrooxazoles 15 and 17 , respectively (Scheme 3), which are either formed by ring-opening of ß-D -epoxides, by competitive interception of the initially formed, hypothetical addition products of the intermediate carbene to the ketones. The glycosylidene carbenes, derived from 1 or 13 are not very reactive towards ketones, yields are good only when sterically unhindered ketones are used in large excess.     

Direct synthesis of β-FeSi2 by ion beam mixing of Fe/Si bilayers

The iron di-silicide #-FeSi₂ is a promising direct band gap semiconductor but difficult to produce. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 450 to 550 °C is reported. The obtained single-phase #-FeSi₂ layers and their structure are confirmed by Rutherford backscattering spectrometry, X-ray diffraction and conversion electron Mössbauer spectroscopy.     

Dense-Kondo antiferromagnetism in (CePd3)8Ge

We report the existence of (CePd₃)₈Ge and (LaPd₃)₈Ge, and find them to have the same cubic superstructure as reported for (CePd₃)₈T (T=Ga, In, Sn, Sb, Pb and Bi) by Gordon and co-workers [1 and 2]. The cerium ions in (CePd₃)₈Ge are trivalent and undergo an antiferromagnetic transition below 5 K with a dense-Kondo-lattice behaviour.     

An improved method of controlling rare earth incorporation in optical fiber

The process parameters involved at various stages of solution doping method for fabricating rare earth (RE) doped optical fiber have been systematically investigated to optimize the process conditions and achieve better control over RE incorporation. It is observed that the RE concentration, uniformity and the overall fiber quality are strongly influenced by the solution properties and dipping parameters. The soaking solution needs to be judiciously selected depending on the porous layer characteristics to improve the fiber quality and process efficiency. An interesting observation not hitherto reported is the influence of Al ion concentration in the solution on RE incorporation into the core. The investigation helps to obtain the optimum conditions necessary to produce fibers of given specification and achieve greater reproducibility.     

Direct introduction of glycine/mercaptoacetic acid units into electron-poor alkenes: a novel route to functionally rich α-amino/α-mercapto acids

The first example of an operationally simple direct introduction of glycine/mercaptoacetic acid units into electron-poor alkenes is reported. In this protocol, Lewis acid-catalyzed Michael addition of activated glycine or mercaptoacetic acid, that is 2-phenyl-1,3-oxazol-5-one or 2-methyl-2-phenyl-1,3-oxathiolan-5-one, to various electron-poor alkenes in water/1,4-dioxane (1:2, v/v) solvent system diastereoselectively affords the corresponding functionally rich α-amino acids or α-mercapto acids, respectively, in high yields at ambient temperature.     

Cathodoluminescence during epitaxy in Rb-ion irradiated α-quartz

Implanting photoactive ions into quartz or silica is a simple and efficient way to tune the luminescence light used for various optoelectronic applications. However, such ion implantation damages or even destroys the crystalline order in quartz. We report here on cathodoluminescence of α-quartz after 175 keV Rb-ion implantation and epitaxial growth when annealing the samples in air or ¹⁸ O ₂. In the cathodoluminescence spectra taken at room temperature, five bands were identified. In addition to three intrinsic bands at 2.40, 2.79, and 4.30 eV, which are related to the quartz and/or silica matrix, two strong violet sub-bands at 3.25 and 3.65 eV were observed, which appear to be strongly correlated with the presence of alkali ions and/or the degree of epitaxy of the matrix. Their properties and origin are discussed in relation to similar bands observed after Ba, Ge, and Na ion implantation. PACS 61.80.Jh; 81.15.Np; 42.70.Ce     

Conservation laws in stochastic deposition-evaporation models in one dimension

An infinite number of conservation laws is identified for a stochastic model of deposition and evaporation of trimers on a linear chain. These laws can be encoded into a single nonlocal invariant, the irreducible string, which uniquely lables an exponentially large number of kinetically disconnected sectors of phase space. This enables the number and sizes of sectors to be determined. The effects of conservation laws on some thermodynamic properties are studied.