The Mechanism of Aromatization of 7-Norbornadiene Acetals. Evidence for Norcaradiene Formation

Dicarbomethoxy-tetraehloronorbornadienone aeetal le rearranges spontaneously to hemimelitate 3c while the corresponding anhydride 14 is stable up to 200oC. This result supports the hypothesis that the thermal rearrangement of substituted norbornadienes to aromatic products occurs by rate determining formation of norcaradiene intermediates

Kvantitativna analiza tragova manganovih iona korištenjem voltametrijske redukcije manganova dioksida akumuliranog na površini radne elektrode: ispitivanje svojstava grafitne elektrode s radnom površinom okomitom na slojeve grafita i mogućnosti njene primjene u analizi prirodnih voda

The determination of trace levels of manganese via cathodic stripping voltammetry at an edge plane pyrolytic graphite electrode (eppge) was evaluated for use in environmental analysis. The response of the eppge is compared with boron-doped diamond electrodes under quiescent conditions where the former is observed to have a three times higher sensitivity. Using this protocol with a stirred accumulation period, a detection limit of 14.2 nmol dm–3 and a sensitivity of 14.2 mol dm–3 A–1 is achieved with linearity from 25 to 250 nmol dm–3, based on a 120 seconds accumulation period. The response at a carbon paste electrode is also compared under the same conditions with the eppge found to be superior in terms of sensitivity, detection limits and reproducibility. The efficacy of the protocol utilising the eppge was assessed in the determination of manganese in a certified seawater reference material, NASS-5, from the National Research Council Canada, which was found to be in excellent agreement with the independently verified sample.Istražena je mogućnost određivanja koncentracije manganovih iona u prirodnim vodama korištenjem grafitne elektrode s radnom površinom okomitom na slojeve grafita u kombinaciji s voltametrijskom metodom koja se zasniva na redukciji manganova dioksida akumuliranog na površini radne elektrode. Ako se MnO2 akumulira iz mirne otopine, osjetljivost grafitne elektrode je tri puta veća od osjetljivosti dijamantne elektrode dopirane borom. Kada se akumulacija provodi tokom 120 sekundi uz miješanje otopine, osjetljivost metode je 14,2 mol dm–3 A–1, granica detekcije mangana je 14,2 nmol dm–3, a odziv je linearna funkcija koncentracije mangana u rasponu od 25 do 250 nmol dm–3. Grafitna elektroda osjetljivija je i pouzdanija i od elektrode sačinjene od žitke smjese čađi i mineralnog ulja. Točnost metode potvrđena je mjerenjem koncentracije manganovih iona u referentnom uzorku morske vode (NASS-5, Nacionalni istraživački savjet Kanade)

Universal hidden order in amorphous cellular geometries

Partitioning space into cells with certain extreme geometrical properties is a central problem in many fields of science and technology. Here we investigate the Quantizer problem, defined as the optimisation of the moment of inertia of Voronoi cells, i.e., similarly-sized ‘sphere-like’ polyhedra that tile space are preferred. We employ Lloyd’s centroidal Voronoi diagram algorithm to solve this problem and find that it converges to disordered states associated with deep local minima. These states are universal in the sense that their structure factors are characterised by a complete independence of a wide class of initial conditions they evolved from. They moreover exhibit an anomalous suppression of long-wavelength density fluctuations and quickly become effectively hyperuniform. Our findings warrant the search for novel amorphous hyperuniform phases and cellular materials with unique physical properties

Universal hidden order in amorphous cellular geometries

Partitioning space into cells with certain extreme geometrical properties is a central problem in many fields of science and technology. Here we investigate the Quantizer problem, defined as the optimisation of the moment of inertia of Voronoi cells, i.e., similarly-sized ‘sphere-like’ polyhedra that tile space are preferred. We employ Lloyd’s centroidal Voronoi diagram algorithm to solve this problem and find that it converges to disordered states associated with deep local minima. These states are universal in the sense that their structure factors are characterised by a complete independence of a wide class of initial conditions they evolved from. They moreover exhibit an anomalous suppression of long-wavelength density fluctuations and quickly become effectively hyperuniform. Our findings warrant the search for novel amorphous hyperuniform phases and cellular materials with unique physical properties