Improvement of photoluminescence and electrical properties of porous silicon layer treated with lanthanum

The influence of surface treatment of porous silicon (PS) in lanthanum (La) containing solution during different times on its photoluminescence and electrical properties has been investigated. For this purpose, chemical composition, structural, vibrational, photoluminescence and electrical characteristics of the porous silicon layer with and without lanthanum were examined using X-ray diffractometry (XRD), energy dispersive X-ray (EDX) spectroscopy, Fourier transmission infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy and current–voltage (I–V) measurements. The results indicate that porous silicon layers treated with lanthanum exhibit an enhancement of photoluminescence intensity and show an improvement current intensity compared to untreated porous silicon layer.     

Timed Petri nets and prediction to improve the Chandy–Misra conservative-distributed simulation

The main contribution of this paper shows that distributed simulation of timed Petri nets (TPN) can take advantage of their structure to obtain a significant lookahead which is usually difficult to compute with other models. In this paper, we introduce a conservative-distributed simulation with a reduced number of control messages and without deadlock resolution. This approach is based on a part of optimism computed on the prediction time each logical process can determine for its advancement. Obviously this prediction time must be computed easily according to the structure of the simulated logical process. Timed Petri nets meet these requirements and we use their structure to evaluate the depth of the prediction. In conservative-distributed simulation, it is known that the deeper the prediction, the better the efficiency of the simulation. We present a method we have devised based on channel time prediction. We compare its performance to the Chandy–Misra method and to some related Petri nets approaches (Chiola). Experiments carried out on Sun stations show that there is more parallelism and a reduced number of null messages in the cases of deadlock avoidance. Moreover, considering deadlock detection and resolution technique we observe that in many cases no deadlock occurs with less control messages.     

Structural and optical properties of ZnSe x Te1−-x solid solutions in thin-film form

Solid solutions of ZnSe _x Te_1–x (0. 1 x 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe _x Te_1–x (0.1 x 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10^–4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe _x Te_1–x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE _g andE _g + _so The variations in bothE _g andE _g + _so, withx indicate that ZnSe _x Te_1–x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.     

Chromatographic study on the uranium uptake from nitrate solution by different ion exchangers

Chromatographic column investigations were performed for the recovery of uranium from aqueous medium of pH 1.0 and ionic strength of 0.6M/NaNO₃/, which is comparable /in its chemical activity/ to certain high active waste solutions. Six different active beds were tested and compared in terms of their capacity for uranium, height equivalent to theoretical plate and their numbers. The main uranium species present in the medium were elucidated.     

Über Pterinchemie 76. Mitteilung [1] Eine einfache Synthese von Leucovorin

A Convenient Synthesis of Leucovorin The synthesis of leucovorin, a 5-formyl-(6R or S)-5,6,7,8-tetrahydropteroyl-L -glutamic acid (II) is described. The L -folic acid was first reduced to (6R, S)-tetrahy-dro-L -folic acid (I); formylation with methyl-formate in DMSO gave directly leucovorin (as a diastereomeric mixture) in good yields. To demonstrate, that the formylation occurred regiospecifically at N (5) and not at N (10), N (10)-nitroso-(6 R, S)-tetrahydro-L -folic acid was formylated under the same conditions. Reductive elimination of the N (10)-nitrosogroup gave the identical leucovorin as in the previous case. The synthetic leucovorin was biologically as active as the natural product with Streptococcus faecalis ATCC 8043 and Pediococcus cerevisiae ATCC 8081.     

Electrometric titrations with the gold electrode

Summary Massive gold because of the passivity of the oxide formed on its surface can be used as a substitute for platinum in electrometric titrations including acid-base and oxidation-reduction systems. The end points are attended with large jumps on the curves and coincide satisfactorily with those obtained using the hydrogen or platinum electrode or by other method.     

The acid-base properties of Fast Grey R. A.

Summary The acid-base properties of Fast Grey R. A. have been studied with reference to the mode of chelation of the dye with different valent metals. The pK values of 3.83, 10.53 and 10.70 corresponding to the three steps of ionization of the free acid were evaluated by the aid of the relation between log [acid]/[salt] and p_H values obtained during the course of the potentiometric titration of the free acid with a free base.     

Syntheses and Properties of Some New Polyamides. Part II

Interfacial condensation of decamethylenediamine and acid chlorides I, II, and III yielded polyamides the thermal stability of which decreased in the order III, I, II, a finding reasserted by calculating activation energy decomposition temperatures. Irradiation of these polyamides does not appreciably affect their properties, and thus they can be considered satisfactorily γ-irradiation resistant.

It appears that there are only few papers dealing with syntheses and properties of polyamidoarylates. Cleaver and Pratt [1] prepared polyamidoesters by the polymerization of bisoxazolones with glycols. Korshak and others [2], however, obtained a polyamidoester by the aminolysis of polyethylene-sebacate with hexamethylenediamine.

In a previous investigation [3] a few polyamidoarylates were obtained by the condensation of aminophenols with aromatic acid chlorides.

In this work we obtained some new polyamidoarylates by the inter-facial condensation of equimolar ratios of decamethylenediamine with     

1,3,4-Triarylpyrazoles Containing 2-Thioxoimidazolidinones and Different Fused Systems: Synthesis and Antimicrobial Activity

Russian Journal of General Chemistry - A group of new analogs of 1,3,4-trisubstituted pyrazoles functionalized 2-thioxoimidazolidinones and fused heterocyclic systems are synthesized. Their tests...