Computational Fluid Dynamics of Catalytic Reactors

Today, the challenge in chemical and material synthesis is not only the development of new catalysts and supports to synthesize a desired product, but also the understanding of the interaction of the catalyst with the surrounding flow field. Computational Fluid Dynamics or CFD is the analysis of fluid flow, heat and mass transfer and chemical reactions by means of computer-based numerical simulations. CFD has matured into a powerful tool with a wide range of applications in industry and academia. From a reaction engineering perspective, main advantages are reduction of time and costs for reactor design and optimization, and the ability to study systems where experiments can hardly be performed, e.g., hazardous conditions or beyond normal operation limits. However, the simulation results will always remain a reflection of the uncertainty in the underlying models and physicochemical parameters so that in general a careful experimental validation is required. This chapter introduces the application of CFD simulations in heterogeneous catalysis. Catalytic reactors can be classified by the geometrical design of the catalyst material (e.g. monoliths, particles, pellets, washcoats). Approaches for modeling and numerical simulation of the various catalyst types are presented. Focus is put on the principal concepts for coupling the physical and chemical processes on different levels of details, and on illustrative applications. Models for surface reaction kinetics and turbulence are described and an overview on available numerical methods and computational tools is provided

The effects of melatonin on sleep–wake rhythm of daytime haemodialysis patients: a randomized, placebo-controlled, cross-over study (EMSCAP study)

AIM: The aim of this study was to investigate the effects of exogenous melatonin on sleep-wake rhythm in haemodialysis patients. METHODS: The study design is a randomized, double-blind, placebo-controlled, cross-over study of 3 ¥ 6 weeks melatonin 3 mg at 22.00 h every night. Haemodialysis patients were asked to fill out a sleep questionnaire and to wear an actometer to record their sleep problems objectively. Furthermore, melatonin concentrations in saliva were sampled the night after daytime haemodialysis and the consecutive night. Actometers, the sleep questionnaire and melatonin concentrations were repeated during the study. RESULTS: In total, 20 patients (six female, median age 71 years) completed the investigation. On nights after daytime dialysis, objective sleep onset latency decreased significantly from a median of 44.5 (placebo) to a median of 15.5 min with melatonin (P < 0.01). Sleep efficiency increased from 67.3 to 73.1% with melatonin (P < 0.05). Actual sleep time increased from 376 min (placebo) to 388min with melatonin (P < 0.01), and sleep fragmentation decreased from 4.5 to 3.1 (P < 0.01). Furthermore, subjective sleep parameters improved also. Patients reported less time needed to fall asleep (P < 0.05) and fewer wake periods (P < 0.05) on the nights with and without daytime dialysis and an increase in sleep time on the night of daytime dialysis (P < 0.05). Furthermore, the nocturnal melatonin rise was recovered. CONCLUSION: Treatment with melatonin resulted in an improvement of subjective and objective sleep parameters, as well as a recovered nocturnal melatonin rhythm

Levels of DHES, PRL, LH, and FSH during the day, measured at four-hour intervals for male (left panels) and female (right panels) volunteers.

<p>Time indicates clock time. Values at 8-hr were double plotted to help visualize daily patterns. Data represent mean ±sd.</p

Levels of different lipids during the day, measured at four-hour intervals for male (left panels) and female (right panels) volunteers.

<p>Time indicates clock time. Values at 8-hr were double plotted to help visualize daily patterns. Data represent mean ±sd.</p

Around the clock levels for classical circadian markers cortisol, <i>PER1</i> and <i>BMAL1</i>.

<p>Upper panels show cortisol levels in male (left panels) and female (right panels) volunteers, determined in serum. mRNA expression of <i>BMAL1</i> and <i>PER1</i> in buffy coats are depicted in the lower panels (females subset n = 6). All were measured at 4 hour intervals, where time indicates clock time. Values at 8-hr were double plotted to help visualize daily patterns. Data represent mean ±sd.</p

Cognitive, behavioral, and physiological reactivity to chronic itching: analogies to chronic pain.

Contains fulltext : 50680.pdf (publisher's version ) (Closed access)It is well-known that cognitive, behavioral, and physiological reactivity to pain, such as catastrophizing, avoidance of activity, and increased physiological responses, can unfavorably affect long-term outcomes in patients with chronic pain. In line with similarities between the psychophysiology of pain and itching, corresponding mechanisms may be relevant for the maintenance of chronic itching. The goal of this study was to examine the role of self-reported cognitive, behavioral, and physiological reactivity factors on itching-related outcomes in 235 patients with chronic skin diseases suffering from chronic itching. Sequential regression analyses indicate that all 3 reactivity systems predicted itching-related outcomes. Specifically, more catastrophizing, higher levels of avoidance of activity, and heightened self-reported physiological reactivity predicted more itching, more scratching, and a reduced disease-related quality of life. The results suggest that a psychological model as described for chronic pain is a useful starting point for study of the maintaining mechanisms of chronic itching