On the expansion wave problem in a long pipe with wall friction

The method of matched asymptotic expansions is used to study the flow out of a long tube or pipeline caused by a sudden rupture. The flow in the tube generated by the expansion wave propagating into the tube from the break point is shown to be modified substantially by the presence of wall friction. This depends primarily on the fact that, when there is wall friction, the velocity derivative along the tube becomes singular at the broken end exit for all times, as long as the flow is critical at the exit.

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Résumé Le débit provenant d'un long tube ou d'un pipeline, suite à une rupture subite, a été étudié en employant la méthode des raccordements asymptotiques. On démontre que l'écoulement à l'intérieur du tube, généré par l'onde de détente qui se propage dans le tube à partir du point de rupture, subit une modification importante due au frottement pariétal. Ceci résulte principalement du fait qu'en cas de frottement pariétal, la dérive de vitesse le long du tube, à n'importe quel moment, devient singulière au point de rupture à condition que le débit soit critique à la sortie.

     

Highly unusual effects of pi-conjugation extension on the molecular linear and quadratic nonlinear optical properties of ruthenium(II) ammine complexes

We have used several techniques, including hyper-Rayleigh scattering and Stark spectroscopy, to investigate the effects of polyene chain length on the optical properties of complexes containing ruthenium(II) electron donor groups and pyridinium electron acceptors. In marked contrast with all other known donor-acceptor polyenes, conjugation extension beyond a single double bond in the dipolar complexes studied leads to blue-shifting of the intramolecular charge-transfer absorptions. Furthermore, the static first hyperpolarizabilities beta0 become maximized with trans-1,3-butadienyl linkages and then decrease in complexes with three CH=CH bonds. Our results clearly demonstrate that the molecular engineering criteria for metal-containing nonlinear optical chromophores can differ dramatically from those for purely organic compounds.     

Syntheses and spectroscopic and quadratic nonlinear optical properties of extended dipolar complexes with ruthenium(II) ammine electron donor and N-methylpyridinium acceptor groups

In this paper, we describe the extremely unusual optical properties of Ru(II)-based electron donor-acceptor (D-A) polyene and some closely related chromophores. For three different polyene series, the intense, visible d-->pi* metal-to-ligand charge-transfer bands unexpectedly blue-shift as the number of E-ethylene units (n) increases from 1 to 3, and the static first hyperpolarizabilities beta(0) determined via hyper-Rayleigh scattering and Stark spectroscopy maximize at n = 2, in marked contrast to other known D-A polyenes in which beta(0) increases steadily with n. Time-dependent density-functional theory and finite field calculations verify these empirical trends, which arise from the orbital structures of the complexes. This study illustrates that transition metal-based nonlinear optical chromophores can show very different behavior when compared with their more thoroughly studied purely organic counterparts.     

Chiral 2-Aryl-2-methyl-2H-1-benzopyrans: Synthesis,characterization of enantiomers,and barriers to thermal racemization

The ease of thermal breaking of the C(sp³)? O bond of the 2-aryl-2-methyl-2H-1-benzopyrans 1 – 9 was evaluated by measuring the free energy (ΔG) of the racemization reaction of optically active compounds. The variation of ΔG of the thermal ring opening in terms of structural modifications is discussed. The synthesis of the studied compounds, the preparative separation of enantiomers by liquid chromatography, the determination of enantiomeric purity, the circular dichroism of enriched enantiomers, and the measurement of rate constants of enantiomerization by monitoring the decrease of the polarimetric angle of rotation at suitable temperatures are described.     

The isoindolobenzazepine alkaloids

Three Chilean barberries, $\text{Berberis}$$\text{actinacantha}$ Mart. ex Schult., $\text{B}$. $\text{darwinii}$ Hook and [ulbar|B. $\text{valdiviana}$Phil. (Berberidaceae), have yielded several new isoindolobenzazepine and protoberberine alkaloids. Novel isoindolobenzazepines are (±)-13-deoxychilenine ($\text{a}$), pictonamine ($\text{10}$), chileninone ($\text{12}$), (±)-chileniimi ($\text{18}$) and (±)-palmanine ($\text{19}$). Highly oxidized protoberberines of particular interest include (±)-O-methylprechilenine ($\text{6}$) and (±)-prepseudopalmanine ($\text{21}$), together with 13-methoxy-8-oxyberberine ($\text{8}$). Isoindolobenzazepine alkaloids arise biogenetically from the rearrangement of highly oxidized protoberberines.     

Some group IVB derivatives of 1,6-methano[10]annulene. Synthesis, substituent effects and reactivity

Certain Group IVB derivatives of 1,6-methano[10]annulene have been synthesised, and their ¹³C nuclear magnetic resonance spectra recorded and assigned, to provide a measure of the substituent effects exerted by metalloid-containing groups in this non-benzenoid aromatic system. Comparisons are made with the corresponding naphthalene and some anthracene derivatives. Protiodemetallations of a number of arylsilanes and -stannanes have been examined, and in protiodestannylation by CH₃CO₂H/dioxane at 27°C (an electrophilic aromatic substitution) the - (or 2-) position of 1,6-methano[10]annulene is ca. 35 times as reactive as the (or 1-) position of naphthalene, whereas in protiodesilylation by CF₃CO₂H/CH₃CO₂H at 27°C it is ca. 700 times the more reactive.     

Oberflächenvorgänge beim Übergang der Silberhalogenide ineinander

Zusammenfassung Beim Anlauf von Silberchlorid in Bromidlösungen entsteht intermediär ein Mischkristall AgCl-AgBr, der schließlich in Silberbromid übergeht. Er ist als instabiler Zwischenzustand aufzufassen.Die über das Gleichgewicht solcher Mischkristalle mit der überstehenden Lösung vorliegenden Kenntnisse werden röntgenographisch bestätigt. Aus ihnen folgt die Instabilität obiger Mischkristalle. Aus ihnen folgt ferner, daß auch Silberbromid in Chloridlösungen (stabile) Mischkristalle bildet, was bestätigt wird. Diese Reaktion ist ein Beispiel der Stabilisierung instabiler Stoffe durch Mischkristallbildung.Dieser Mischkristall wächst in paralleler Orientierung auf das Gitter des Silberbromids auf, obgleich er eine kleinere Gitterkonstante hat als dieses.Beim Anlauf von Silberbromid in Chlorwasser tritt er ebenfalls auf. Hier vermittelt er sogar eine orientierte Bildung von Silberchlorid auf Silberbromid, die auf trocknem Wege wegen der Gitterschrumpfung nicht möglich ist.Alle vorstehenden Erscheinungen können verstanden werden als Fällungen, die im Gleichgewicht mit den örtlichen Konzentrationen in der Diffusionsschicht vor der Oberfläche stehen.     

Squaraine dyes for photodynamic therapy: study of their cytotoxicity and genotoxicity in bacteria and mammalian cells

Halogenated squaraine dyes are characterized by long wavelength absorption (>600 nm) and high triplet yields and therefore represent new types of photosensitizers that could be useful for photodynamic therapy. We have analyzed the cytotoxicity and genotoxicity of the bromo derivative 1, the iodo derivative 2 and the corresponding nonhalogenated dye 3 in the absence and presence of visible light. At concentrations of 1-2 microM, 1 and 2 reduced the cloning efficiency of AS52 Chinese hamster ovary cells to less than 1% under conditions that were well tolerated in the dark. Similarly, the proliferation of L5178Y mouse lymphoma cells was inhibited by photoexcited 1 and 2 with high selectivity. The squaraine 3 was much less efficient. Both 1 and 2 induced only few mutations in the gpt locus of the AS52 cells in the presence of light and were not mutagenic in the dark. No mutagenicity with and without irradiation was observed in Salmonella typhimurium TA100 and TA2638. However, both 1 and 2 plus light increased the frequency of micronuclei in AS52 cells. The results indicate that halogenated squaraines exhibit photobiological properties in vitro that are favorable for photodynamic therapeutical applications.