The deterioration in heat transfer to fluids at super-critical pressure and high heat fluxes

Introduction: Several supercritical steam generators in the American Electric Power system have shown evidence of tube overheat in the lower furnance at the point where the water bulk temperature is about 670 0 F. The evidence is of two kinds. First thermal fatigue has occurred and caused tube failures long before a failure of any kindwas to be expected. Second, pairs of cordal thermocouples have shown very high wall temperatures and, extrapolating back to the inside of the tube, evidence reduced inside heat transfer coefficients. It was suspected that a possible cause of the high tube temperature was a supercritical "burnout". The primary purpose of this investigation is to determine the cause and conditions leading to a supercritical "burnout" such as might occur in a supercritical steam generator. Before focusing on this aspect of the problem it is worthwhile to mention several other possible causes for the high tube wall temperatures which have been observed. In this context high means higher than the design temperature. Let us just list these possibilities. 1. Scale inside the boiler tubes. 2. Hot spot factors in the design procedure which are too low. 3. Higher heat transfer from the combustion gases than expected. Better design procedures or better control of the water purity might be sufficient to cause the problem to disappear without changing the water flow conditions inside the tube. Because the three factors which are listed above are really rather vague, it appeared that the most promising approach is to eliminate the excessive temperatures inside the tube at supercritical pressure is to eliminate the "burnout". Therefore, only the burnout aspect of the problem has been studied here. The undesirable behavior of the Nusselt number, which is of interest, is indicated in Fig. 1. In particular we want to find out when the supercritical Nusselt number is less than one would expect from the affects of simple porperty variations alone.Sponsored by American Electric Power Service Corp

Computational fact checking from knowledge networks

Traditional fact checking by expert journalists cannot keep up with the enormous volume of information that is now generated online. Computational fact checking may significantly enhance our ability to evaluate the veracity of dubious information. Here we show that the complexities of human fact checking can be approximated quite well by finding the shortest path between concept nodes under properly defined semantic proximity metrics on knowledge graphs. Framed as a network problem this approach is feasible with efficient computational techniques. We evaluate this approach by examining tens of thousands of claims related to history, entertainment, geography, and biographical information using a public knowledge graph extracted from Wikipedia. Statements independently known to be true consistently receive higher support via our method than do false ones. These findings represent a significant step toward scalable computational fact-checking methods that may one day mitigate the spread of harmful misinformation

Coping with stress in medical students: results of a randomized controlled trial using a mindfulness-based stress prevention training (MediMind) in Germany

BACKGROUND: High prevalence rates of psychological distress in medical training and later professional life indicate a need for prevention. Different types of intervention were shown to have good effects, but little is known about the relative efficacy of different types of stress management interventions, and methodological limitations have been reported. In order to overcome some of these limitations, the present study aimed at evaluating the effect of a specifically developed mindfulness-based stress prevention training for medical students (MediMind) on measures of distress, coping and psychological morbidity. METHODS: We report on a prospective randomized controlled trial with three study conditions: experimental treatment (MediMind), standard treatment (Autogenic Training) and a control group without treatment. The sample consisted of medical or dental students in the second or eighth semester. They completed self-report questionnaires at baseline, after the training and at one year follow-up. Distress (Trier Inventory for the Assessment of Chronic Stress, TICS) was assessed as the primary outcome and coping (Brief COPE) as a co-primary outcome. Effects on the psychological morbidity (Brief Symptom Inventory, BSI) as a secondary outcome were expected one year after the trainings. RESULTS: Initially, N = 183 students were randomly allocated to the study groups. At one year follow-up N = 80 could be included into the per-protocol analysis: MediMind (n =31), Autogenic Training (n = 32) and control group (n = 17). A selective drop-out for students who suffered more often from psychological symptoms was detected (p = .020). MANCOVA’s on TICS and Brief COPE revealed no significant interaction effects. On the BSI, a significant overall interaction effect became apparent (p = .002, η2partial = .382), but post hoc analyses were not significant. Means of the Global Severity Index (BSI) indicated that MediMind may contribute to a decrease in psychological morbidity. CONCLUSION: Due to the high and selective dropout rates, the results cannot be generalized and further research is necessary. Since the participation rate of the trainings was high, a need for further prevention programs is indicated. The study gives important suggestions on further implementation and evaluation of stress prevention in medical schools. TRIAL REGISTRATION: This trial is recorded at German Clinical Trials Register under the number DRKS00005354 (08.11.2013)

Studies on Rare Earth Exchanged Zeolites: Part I – Sorption Properties of Rare Earth Exchanged Zeolites

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