Stages of Filamentary Carbon Growth from Hydrocarbons on Nickelcontaining Catalysts and Causes of their Deactivation

Methane decomposition to carbon and hydrogen has been studied using the Ni/Al2O3, Ni-Cu/Al2O3 and Ni-Cu/MgO catalysts at 550 °C. The S-shaped kinetic curves of carbon formation from methane exhibit the following periods: induction, acceleration, stationary state and deactivation. The induction period is characterized by oversaturation of metal or alloy particles with carbon atoms and predominant formation of the graphite phase at the (111) faces of the catalyst particles. After formation of the graphite crystallization centers, the acceleration period is accompanied by the growth of graphite filaments and simultaneous reconstruction of the metal particles. After termination of the above processes, the carbon deposition rate becomes constant. Deactivation of the catalyst is caused by blocking of the front side of the metal particle with a carbon film. When the reaction temperature increases to 700 °C, deactivation of the nickel-containing catalyst follows a different mechanism. During the growth of the filamentary carbon, the metal particle becomes viscous-flowing. This fact allows for its partial capturing by the inner filament channel. As a result, the formed carbon filament has an internal channel filled either with metal or its alloy. Hydrogen addition to methane leads a decrease in the carbon formation rate on the catalyst and a change in the filamentary carbon morphology: now it contains a hollow channel

Measurement properties of the Minimal Insomnia Symptom Scale (MISS) in an elderly population in Sweden

<p>Abstract</p> <p>Background</p> <p>Insomnia is common among elderly people and associated with poor health. The Minimal Insomnia Symptom Scale (MISS) is a three item screening instrument that has been found to be psychometrically sound and capable of identifying insomnia in the general population (20-64 years). However, its measurement properties have not been studied in an elderly population. Our aim was to test the measurement properties of the MISS among people aged 65 + in Sweden, by replicating the original study in an elderly sample.</p> <p>Methods</p> <p>Data from a cross-sectional survey of 548 elderly individuals were analysed in terms of assumptions of summation of items, floor/ceiling effects, reliability and optimal cut-off score by means of ROC-curve analysis and compared with self-reported insomnia criteria.</p> <p>Results</p> <p>Corrected item-total correlations ranged between 0.64-0.70, floor/ceiling effects were 6.6/0.6% and reliability was 0.81. ROC analysis identified the optimal cut-off score as ≥7 (sensitivity, 0.93; specificity, 0.84; positive/negative predictive values, 0.256/0.995). Using this cut-off score, the prevalence of insomnia in the study sample was 21.7% and most frequent among women and the oldest old.</p> <p>Conclusions</p> <p>Data support the measurement properties of the MISS as a possible insomnia screening instrument for elderly persons. This study make evident that the MISS is useful for identifying elderly people with insomnia-like sleep problems. Further studies are needed to assess its usefulness in identifying clinically defined insomnia.</p