Effect of γ-alumina crystallinity on the state of rhodium during high-temperature treatments in oxygen and hydrogen

Rhodium catalysts, supported on six γ-Al₂O₃ supports with different crystallinities, were exposed to sequential treatments in hydrogen at 500°C, in oxygen at 760°C, in hydrogen at 500°C and at 760°C, respectively. Samples were characterized by X-ray diffraction and hydrogen chemisorption at various stages in the sequential treatment. Based on the characterization results, it is concluded that the formation of crystalline Rh₂O₃ is a function of γ-Al₂O₃ crystallinity; formation of crystalline Rh₂O₃ increased with increasing crystallinity of γ-Al₂O₃ during treatment in oxygen at 760°C. The crystalline Rh₂O₃ formed during treatment in oxygen at 760°C was reduced to Rh metal by hydrogen at 500°C, but most of the Rh did not adsorb hydrogen at room temperature. Subsequent treatment in hydrogen at 760°C increased the hydrogen adsorption capacity by as much as a factor of three. X-ray line broadening measurements showed that oxygen treatment of reduced Rh/γ-Al₂O₃ at 760°C followed by hydrogen reduction at 500°C resulted in significant increases in Rh crystal size; further treatment in hydrogen at 760°C resulted in additional sintering of Rh.     

Isotopenhydrologische Methoden (2H, 18O) zur Bestimmung der Grundwasserneubildung in Trockengebieten: Potenzial und Grenzen

Grundwasser - Die Quantifizierung der Grundwasserneubildung in Trockengebieten stellt aufgrund klimatischer Gegebenheiten, mächtiger ungesättigter Zonen sowie hochangepasster Vegetation...     

聚乙烯压力管的质量控制

简述PE压力管对原材料的技术要求。采用先进可靠的专用生产设备,和通过验证定型的工艺方案,确保从原材料选择到产品出厂全过程必须处于受控状态,且要求PE压力管生产企业应具有综合服务能力。     

The Sintering of Supported Metal Catalysts

Metal catalysts are commonly employed in the form of metal dispersed as small crystallites on high surface area supports. The use of these supported metal catalysts increases the utilization of the metal as a catalyst since a large fraction of the metal atoms are at the surface of the small metal crystallites. Another important function of the support is to physically separate the small metal crystallites and thereby hinder the agglomeration of the small metal crystallites into larger crystallites. This agglomeration would decrease the number of surface metal atoms per unit mass of metal, and thereby decrease the utilization of the metal and the activity of the catalyst.     

Dopamine and Cognitive Control: The Influence of Spontaneous Eyeblink Rate and Dopamine Gene Polymorphisms on Perseveration and Distractibility.

One fundamental problem of intelligent organisms pursuing goal-directed behavior is how to dynamically regulate the balance between maintenance and flexibility. The authors show that central dopaminergic activity, as indicated by spontaneous eyeblink rate and dopamine gene polymorphisms, plays an important role in the modulation of this balance. Seventy-two young adults were examined. Participants with high blink rates showed increased cognitive flexibility but decreased cognitive stability compared with participants with low blink rates. This pattern of results was even more pronounced for carriers of the DRD4 exon III 4/7 genotype, even though no main effects were found for DRD4 and COMT polymorphisms. Results converge with neuropsychological models that suggest a modulatory role of prefrontal dopaminergic activity for processes of cognitive control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Health-related quality of life measured by the SF12 in working populations: Associations with psychosocial work characteristics.

This study investigated the contribution of psychosocial work characteristics (decision latitude, job demand, social support at work, and effort-reward imbalance) to health-related quality of life. Data were derived from 2 aircraft manufacturing plants (N = 1,855) at the start of a longitudinal study. Regression analysis showed that work characteristics (1st model) explained 19% of the variance in the mental summary score of the Short Form-12 Health Survey. R2 change for work characteristics decreased to 13%, accounting for demographics, socioeconomic status, body mass index, and medical condition (5th model). Including health behavior and personality factors (full model), R2 change for work characteristics remained significant. Psychosocial work characteristics account for relevant proportions in the subjective perception of mental health beyond a wide array of medical variables and personality factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hydrogen adsorption measurements by the dynamic pulse method

Hydrogen adsorption uptakes by supported metal catalysts are commonly measured by the dynamic pulse technique. The pulse technique has several experimental advantages over the conventional static method, but the hydrogen uptakes measured by the pulse method are not easily interpreted. The measured pulse adsorption uptakes are influenced by the desorption of weakly adsorbed hydrogen. We found that the desorption of hydrogen at room temperature depends on the metal and the metal dispersion. We also found that hydrogen uptake measurements by the dynamic pulse method under well defined conditions are very reproducible.     

Research and innovation in higher education: empirical evidence from research and patenting in Brazil

Scientometrics - The encyclicals, also known as papal letters, are documents that have a profound influence on the Catholic Church and, as a result, on the West. This research seeks to explore the...     

Groundwater Recharge Assessment for the Kalahari Catchment of North-eastern Namibia and North-western Botswana with a Regional-scale Water Balance Model

Groundwater is the only source of drinking water for the inhabitants of the Kalahari. Thus understanding spatial and temporal variations in groundwater recharge is very important and a regional-scale water balance model has therefore been set up for a 209,149 km² catchment in north-eastern Namibia and north-western Botswana. The model has a spatial resolution of 1.5 × 1.5 km, daily model time-steps, and climatic input parameters for 19 years are used. The distributed, GIS-based, process-oriented, physical water balance model (MODBIL) used in this study considers the major water balance components: precipitation, evapotranspiration, groundwater recharge, and surface runoff/interflow. Mean precipitation for the study area is 409 mm a⁻¹, while mean actual evapotranspiration is 402 mm a⁻¹ and mean groundwater recharge is 8 mm a⁻¹ (2% of mean annual precipitation). The recharge pattern is mainly influenced by the distribution of soil and vegetation units. Groundwater recharge shows a high inter- and intra-annual variability, but not only the sum of annual precipitation is important for the development of groundwater recharge; a large amount of precipitation in a relatively short period is more important. Published independent data from the Kalahari in Namibia, Botswana and the Southern African region under similar climatic conditions are used to verify the modelling results.     

Backward inhibition as a means of sequential task-set control: Evidence for reduction of task competition.

Endogenously initiated transitions between tasks are associated with inhibition of the attentional set for the task preceding the transition, as demonstrated by slowed reactions to a task most recently switched away from (U. Mayr & S. W. Keele, 2000). Using an altered methodological approach, the authors found that this backward inhibition counteracts perseverative tendencies when switching to a new task in that it selectively reduces interference exerted by the preceding task set. The reduction of interference was dependent on endogenous preparation for the new task and did not occur for unpredictable task switches or for task switches that were precued without information about the identity of the new task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)