Pulsed laser deposition of Eu:Y2O3 thin films on (0001) α-Al2O3

This paper focuses on the preparation and characterization of crystalline thin films of rare-earth-doped sesquioxides (Y₂O₃, Lu₂O₃) grown by pulsed laser deposition on single-crystal (0001) sapphire substrates. X-ray diffraction measurements show that the films with thicknesses between 1 nm and 500 nm were highly textured along the 111 direction. Using Rutherford backscattering analysis, the correct stoichiometric composition of the films was established. The emission and excitation spectra of europium-doped films with a thickness 100 nm look similar to those of the corresponding crystalline bulk material, whereas films with a thickness 20 nm show a completely different emission behavior. PACS 68.55.Jk; 78.66.Nk; 81.15.F     

Breaking a chaos-noise-based secure communication scheme

This paper studies the security of a secure communication scheme based on two discrete-time intermittently chaotic systems synchronized via a common random driving signal. Some security defects of the scheme are revealed: 1) The key space can be remarkably reduced; 2) the decryption is insensitive to the mismatch of the secret key; 3) the key-generation process is insecure against known/chosen-plaintext attacks. The first two defects mean that the scheme is not secure enough against brute-force attacks, and the third one means that an attacker can easily break the cryptosystem by approximately estimating the secret key once he has a chance to access a fragment of the generated keystream. Yet it remains to be clarified if intermittent chaos could be used for designing secure chaotic cryptosystems.     

Visualization of the dynamics of an optimization process in chemical kinetics by pseudo-three-dimensional diagrams

A series of pseudo-three-dimensional diagrams illustrating the dynamics of an optimization process and the discrimination between two solutions corresponding to the kinetic system of two consecutive reactions were treated by a computer program.

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Gas phase thermolysis of sulfur compounds. II. Ditertiary butyl sulfide

The pyrolysis of di-tert-butyl sulfide has been investigated in static and stirred-flow systems at subambient pressures. The rate of consumption of the sulfide was measured in some experiments, and the rate of pressure increase was followed in others. The results suggest that the reaction is essentially homogeneous in a seasoned reactor and proceeds through a free radical mechanism. In the initial stages, the decomposition rate follows first-order kinetics, and the rate coefficient in the absence of an inhibitor is given by between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately.     

Gas phase thermolysis of cyanomethyl t-butyl sulfide and cyanomethyl t-butyl ether

The pyrolyses of cyanomethyl t-butyl sulfide and its oxygen homologue have been studied in a stirred-flow system over the temperature range 490–540°C and pressures between 5 and 14 Torr. In both cases, isobutene is formed as product in over 97% yield. Hydrogen sulfide is obtained in about half the amount of isobutene in the pyrolysis of the sulfide. Hydrogen cyanide is formed in the pyrolysis of the ether. The first-order rate coefficients for the consumption of the reactants followed the Arrhenius equations Cyanomethyl t-butyl sulfide: Cyanomethyl t-butyl ether: A molecular mechanism involving polar four-centered cyclic transition states is proposed for both reactions, with the CN group stabilizing the partial negative charge developed at the S and O atoms.     

On-column interactions in the direct GLC assay of hexetidine

Summary Gas chromatography was used for the direct assay of hexetidine and triamine in a pharmaceutical formulation. During this work we came across a strong oncolumn interaction, in such a way that the GLC retention, selectivity and response parameters were seriously modified relative to the injections of hexetidine and triamine standard solutions. The interaction was traced to the coinjected hydrochloride form of a major component of the sample and in practical terms points to the potential quantitation errors that may be associated to similar systems.     

SN2 vs. E2 on quaternary centres: an application to the synthesis of enantiopure beta2,2-amino acids

S(N)2 and E2 competing reactions in cyclic sulfamidates can be modulated by the change of an amide group to an ester group attached to the quaternary carbon activated for the nucleophilic attack, allowing an easy approach to enantiopure alpha,alpha-disubstituted beta-amino acids.     

Laser techniques in the study of drug photochemistry

This review describes the application of different laser time-resolved techniques, such as time-resolved fluorescence, phosphorescence and laser flash photolysis, to elucidate the mechanism of drug photodegradation. The assignment of transient species based on their luminescence or absorption spectra and based on their reactivity to various quenchers is illustrated. The mathematical expressions used in fitting measured transient decays over time are also discussed. Practical situations found in the literature and relevant to drug photodegradation illustrate different examples. The importance of laser power, concentration and absorbance of the ground state, as well as other parameters intrinsic to laser techniques are discussed.