Spatiotemporal networks in addressable excitable media

Spatiotemporal networks are studied in a photosensitive Belousov-Zhabotinsky medium that allows both local and nonlocal transmission of excitation. Local transmission occurs via propagating excitation waves, while nonlocal transmission takes place by nondiffusive jumps to destination sites linked to excited sites in the medium. Static, dynamic, and domain link networks are experimentally and computationally characterized. Transitions to synchronized behavior are exhibited with increasing link density, and power-law relations are observed for first-coverage time as a function of link probability.     

Polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3

We report polarized Raman scattering in single crystals of Nd_0.7Sr_0.3MnO₃. The temperature dependence of the MnO₆ octahedral bending and stretching modes observed in the XX spectra points to the existence of local lattice distortions, possibly polarons. The XY spectra have been analyzed using a collision-dominated model, which allows the extraction of the carrier scattering rate.     

Use of a liquid ion-exchanger in the solvent extraction and atomic-absorption determination of trace copper in waters

Copper in the 10-100 ppM range has been determined by a solvent extraction and atomic-absorption procedure involving the use of the liquid ion-exchanger Amberlite LA 2 in thiocyanate form. The procedure is rapid and gives results of good precision, and uses stable reagents and standard instrumentation.     

A parallel hp-adaptive discontinuous Galerkin method for hyperbolic conservation laws

This paper describes a parallel adaptive strategy based on discontinuous hp-finite element approximations of linear, scalar, hyperbolic conservation laws. The paper focuses on the development of an effective parallel adaptive strategy for such problems. Numerical experiments suggest that these techniques are highly parallelizable and deliver super-linear rates of convergence, thereby yielding efficiency many times superior to conventional schemes for hyperbolic problems.     

Host-guest interactions at self-assembled monolayers of cyclodextrins on gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding.     

Quantitative magnetic resonance (QMR) method for bone and whole-body-composition analysis

Objective: to evaluate the applicability, precision, and accuracy of the new EchoMRI quantitative magnetic resonance (QMR) method for in-vitro bovine bone analysis and in-vivo whole-body-composition analysis of conscious live mice. Research methods and procedures: bovine tibia bone samples were measured by QMR and dual-energy X-ray adsorptiometry (DEXA). Repeated measures of whole-body composition were made using live and dead mice with different levels of fat by QMR and DEXA and by classic chemical analysis of the mouse carcass. Results: bone-mineral density (BMD) and bone-mineral content (BMC) measured in bovine tibia by QMR and DEXA were highly correlated. Precision of fat and lean measurement in mice was found to be better for QMR than for DEXA. The coefficient of variation (CV) for fat was 0.34–0.71% for QMR compared with 3.06–12.60% for DEXA. Discussion: QMR offers more specific parameters of bone structure than does DEXA. QMR and DEXA did not differ in the total amount of fat detected in live mice but QMR had improved precision. QMR was superior to DEXA in measuring fat in very small mice. Conclusions: in bone tissue there is a strong correlation between hydrogen NMR signal and bone-mineral density as measured by X-ray. QMR provides a very precise, accurate, fast, and easy to use method for determining fat and lean mass of mice without the need for anesthesia. Its ability to detect differences and monitor changes in body composition in mice with great precision should be of great value in characterizing phenotypes and studying drugs affecting obesity.     

Thermal analysis of manganese dioxide in controlled atmospheres

TG and DTA curves of-MnO₂ have been obtained in nitrogen, air and oxygen. The reactions MnO₂Mn₂O₃ and Mn₂O₃ Mn₃O₄ were observed in the ranges 450° to 600° and 750° to 1100° respectively, and the decomposition temperatures are affected by the partial pressure of oxygen. The endotherm at 1200° is unaffected by the atmosphere and is not accompanied by weight loss. It is, therefore, due to a polymorphic transformation of Mn₃O₄ rather than formation of MnO. Reaction to form MnO was observed by TG in nitrogen above 1400°, but did not occur on heating in oxygen to 1500°.

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Zusammenfassung Die TG und DTA Kurven von-MnO₂ wurden in Stickstoff, Luft und Sauerstoff ermittelt. Die Umwandlungen MnO₂ Mn₂O₃ und Mn₂O₃ Mn₃O₄ wurden im Temperaturbereich von 450° bis 600° bzw. 750° bis 1100° beobachtet. Die Zersetzungstemperaturen werden durch den partiellen Sauerstoffdruck beeinflußt. Der endendothermische Vorgang von 1200° bleibt von der Atmosphäre unbeeinflußt, ist mit keinem Gewichtsverlust verbunden. Er ist eher einer polymorphen Umwandlung von Mn₃O₄ als der Bildung von MnO zuzuschreiben. Die Bildung von MnO wurde thermogravimetrisch in Stickstoff oberhalb 1400° beobachtet, nicht jedoch in Sauerstoff bis zu 1500°.

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Résumé Etude de-MnO₂ par TG et par ATD, dans l'azote, dans l'air et dans l'oxygène. Entre 450 et 600° on observe la réaction MnO₂Mn₂O₃ et entre 750 et 1100° Mn₂O₃ Mn₃O₄. La pression partielle de l'oxygène influence la température de la décomposition. A 1200°, il apparaît un phénomène endothermique undépendant de la nature de l'atmosphère et qui ne s'accompagne d'aucune variation de poids. C'est pourquoi il est attribué à une transformation polymorphique de Mn₃O₄ plutôt qu'à la formation de MnO. Celle-ci s'observe en TG au-dessus de 1400°, dans l'azote, mais ne se produit pas par chauffage dans l'oxygène jusqu'à 1500°.

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, -MnO₂. , MnO₂ Mn₂O₃ Mn₂O₃ Mn₃O₄ 450°–600° 750°–1100°, , . 1200° . , n₃₄, MnO. MnO 1400°, , 1500° .

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The authors wish to thank Dr. D. Dollimore and Dr. R. C. Mackenzie for suggesting the problem, and the S.R.C. for a research assistantship to D.M.T.