Periodic solutions of a nonlinear propagation equation via a fixed point argument

In this work the initial value problem for the equation $$u_t + \beta u_x + yf(u)_x - \delta u_{xxt} = g,\forall x \in R, \forall t \in [0,T],$$ with periodic boundary conditions is interpreted in the sense of periodic distributions and studied via fixed point arguments. Weak solutions exist iff∈C ⁰ (R) andg∈L ^∞(L ²(0,1)). Moreover, regularity inf, g and the initial data implies regularity of solutions.     

Interdiffusion in the Co-Ni system-I concentration penetration curves and interdiffusion coefficients

The interdiffusion in the Co-Ni system has been investigated in the temperature range of 950 to 1150 °C, by means of diffusion specimens of pure Co and Ni. The concentration curvesN(x, t) obtained with the aid of an JXA-3 A JEOL electron microprobe were evaluated using the smoothing cubic spline method by means of the Boltzmann-Matano equation. The obtained interdififusion coefficient values ¯D increase with the increasing Ni concentration and satisfy the Arrhenius equation at temperaturesH 990 °C. At lower temperatures the influence of high diffusivity paths may be effective, resulting in higher ¯D values. No expressive influence of atomic (Ni₃Co) or magnetic order on the interdiffusion has been detected. The activation enthalpyH values were found almost concentration independent. A Kirkendall effect study has been carried out with positive results which are presented in Part II of this paper. A new method for the determination of diffusants concentration in the Kirkendall plane was proposed. With the use of this method and of Darken equations the intrinsic diffusion coefficients were calculated. These results are given in Part III.     

A model of oxide film originating at thermal oxidation of GaAs

In this paper an approximative procedure to determine of the most probable model of oxide film originating at thermal oxidation of GaAs single-crystal samples within the temperature range 480–530 °C is proposed. It is shown that the system presented is more complicated if compare with that presumed previously.     

Optimization of the Microwave-Assisted Saponification and Extraction of Organic Pollutants from Marine Biota Using Experimental Design and Artificial Neural Networks

Several improvements in sample pretreatment for the determination of organic pollutants (i.e. n-alkanes, polycyclic aromatic hydrocarbons, PAHs) in marine biota (mussels) are presented. The use of liquid nitrogen and homogenization of the samples are shown to be an alternative to the time consuming liophilization step required for the analysis of biota samples. Microwave-assisted hydrolysis and extraction are combined to isolate organic pollutants (19 n-alkanes and 27 PAHs) from biota matrices. Experimental design (ED) and artificial neural networks (ANNs) were used to optimize the experimental conditions. NIST-CRM 2978 was used to test the validity of the developed method which shows a good agreement with certified values.     

Thermal behaviour of benzenesulfenamides and of their chromium carbonyl complexes

Benzenesulfenamides with the formula R-S-N-(R)₂ (R=C₆H₅ andR=NC₄H₈O, C₇H₇ and C₆H₁₁) and their chromium carbonyl complexes were studied by means of TG and mass spectrometric methods. The thermal behaviour of the compounds the stabilities of free sulfenamides are lower than those observed for the corresponding chromium carbonyl complexes. Combined thermogravimetry — mass spectrometry results suggest that the fragmentation mechanism of the carbonyl complexes involves cleavage of the Cr-S and Cr-CO bonds while that of sulfenamide depends mainly on the dissociation rates of the NR₂ groups.This work was partially supported by the Departamento técnico de Investigation of the Universidad de Chile, Grant Q3280/9324.     

Reaction graphs and a construction of reaction networks

Summary A general definition of reaction graphs is presented. For a pair of isomeric molecular graphs and , related by a chemical transformation , the reaction graph is determined using a maximal common subgraph defined for vertex mapping . A binary operation defined for graphs constructed over the same vertex set enables us to decompose the reaction graph into the sum of prototype reaction graphs. A decomposition of an overall reaction graph can be advantageously used for the construction of a reaction network. An oriented path in this network beginning at and ending at corresponds to a breakdown of the transformation into a sequence of intermediates.     

Gould-Jacobs reaction of 6-amino-2,3-diphenylquinoxaline

Summary Catalytic hydrogenation of 2,3-diphenyl-6-nitroquinoxaline led to the corresponding amine1 which in turn afforded products3a-i on reaction with alkoxymethylene derivatives2a-i. Thermal cyclization of3b and3f yielded substituted pyrazinoquinolones5b and5f, respectively. Optimal conditions for the successful hydrolysis of ester5b were found. The structures of all products were deduced from their IR, UV,¹H, and¹³C NMR spectroscopic data.Dedicated to Prof.F. Sauter on the occasion of his 65th birthday     

Cycloaddition chemistry of 2-vinyl-substituted indoles and related heteroaromatic systems

[reaction: see text] The intramolecular Diels-Alder cycloaddition reaction (IMDAF) of several N-phenylsulfonylindolyl-substituted furanyl carbamates containing a tethered pi-bond on the indole ring were examined as an approach to the iboga alkaloid catharanthine. Only in the case where the tethered pi-bond contained two carbomethoxy groups did the [4 + 2]-cycloaddition occur. Push-pull dipoles generated from the Rh(II)-catalyzed reaction of diazo imides, on the other hand, undergo successful intramolecular 1,3-dipolar cycloaddition across both alkenyl and heteroaromatic pi-bonds to provide novel pentacyclic compounds in good yield and in a stereocontrolled fashion. The facility of the cycloaddition was found to be critically dependent on conformational factors in the transition state. Ligand substitution in the rhodium(II) catalyst markedly altered the product ratio between [3 + 2]-cycloaddition and intramolecular C-H insertion. The variation in reactivity reflects the difference in electrophilicity between the various rhodium carbenoid intermediates. Intramolecular C-H insertion is enhanced with the more electrophilic carbene generated using Rh(II) perfluorobutyrate.     

Comparison of the acidity of residual silanol groups in several liquid chromatography columns

The silanol acidity of Waters Resolve C18, Waters Resolve silica, Waters Symmetry C18, Waters Symmetry silica, Waters XTerra MS C18 and underivatized XTerra columns has been measured from the retention of LiNO3 with a methanol/water (60:40) mobile phase buffered to different pH values. The Li+ cation is retained by cationic exchange with the background cation of the mobile phase (Na+) through the ionized silanols. The number of active silanols increases in the order: XTerra MS C18 < Symmetry C18 < underivatized XTerra < Resolve C18 < Resolve silica approximately equal to Symmetry silica. XTerra MS C18 does not present any residual silanol acidity up to s(s)pH 10.0 (pH in 60% methanol) as measured by LiNO3. The underivatized XTerra packing and Symmetry C18 present active silanols only at s(s)pH values higher than 7.0. For the other three columns, two different types of silanols with different acidity (s(s)pKa values about 3.5-4.6 and 6.2-6.8, respectively) have been observed. Symmetry C18 shows evidence of the presence of active basic sites that retain NO3- by anionic exchange.     

Filipin orientation revealed by linear dichroism. Implication for a model of action

The organization of the polyene antibiotic filipin in membranes containing cholesterol is a controversial matter of debate. Two contradictory models exist, one suggesting a parallel and the other perpendicular organization of filipin with respect to the plane of the membrane. UV-vis linear dichroism, ATR-FTIR, and fluorescence anisotropy decay techniques were combined to study the orientation of filipin in model systems of membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) with and without cholesterol. Filipin's orientation is determined by the presence/absence of cholesterol when it is inserted in gel crystalline phase model membranes. When cholesterol (33%) is present in DPPC bilayers, filipin stands perpendicular to the membrane surface as expected in "pore-forming" models. At variance, absence of cholesterol leaves filipin in an essentially random organization in the lipidic matrix. In liquid crystalline phase bilayers (POPC) filipin's orientation is perpendicular to the membrane surface even in absence of cholesterol. Thus filipin's activity/organization depends not only on cholesterol presence but also in the lipid phase domain it is inserted in. These findings were combined with spectroscopy and microscopy data in the literature, solving controversial matters of debate.