Comparison of stress-based and strain-based creep failure criteria for severe accident analysis

We conducted a parametic analysis of stress-based and strain-based creep failure criteria to determine if there is a significant difference between the two criteria for SA533B vessel steel under severe accident conditions. Parametric variables include debris composition, system pressure, and creep strain histories derived from different testing programs and mathematically fit, with and without tertiary creep. Results indicate significant differences between the two criteria. Stress gradient plays an important role in determining which criterion will predict failure first. Creep failure was not very sensitive to different creep strain histories, except near the transition temperature of the vessel steel (900 K to 1000 K). Statistical analyses of creep failure data of four independent sources indicate that these data may be pooled, with a spline point at 1000 K. We found the Manson-Haferd parameter to have better failure predictive capability than the Larson-Miller parameter for the data studied.     

Numerical studies of multiphase mixing with application to some small-scale experiments

Numerous experimental and modelling studies of the premixing stage of a steam explosion are underway world-wide. While there is encouraging agreement between model results and experimental data for medium-scale tests, the agreement for small-scale tests has been less encouraging. In this paper, we show that this discrepancy can be accounted for by the need to use higher order differencing schemes for the convection terms in the conservation equations. When such schemes are used, the features of the experiment are reproduced. We present results obtained using various total variation diminishing schemes, quantify the effect of added mass and lift forces, and investigate the effect of interfacial drag modelling.     

A case study of real-world tailpipe emissions for school buses using a 20% biodiesel blend

Numerous laboratory studies report carbon monoxide, hydrocarbon, and particulate matter emission reductions with a slight nitrogen oxides emission increase from engines operating with biodiesel and biodiesel blends as compared to using petroleum diesel. We conducted a field study on a fleet of school buses to evaluate the effects of biodiesel use on gaseous and particulate matter fuel-based emission factors under real-world conditions. The field experiment was carried out in two phases during winter 2004. In January (phase I), emissions from approximately 200 school buses operating on petroleum diesel were measured. Immediately after the end of the first phase measurement period, the buses were switched to a 20% biodiesel blend. Emission factors were measured again in March 2004 (phase II) and compared with the January emission factors. To measure gaseous emission factors we used a commercial gaseous remote sensor. Particulate matter emission factors were determined with a combination of the gaseous remote sensor, a Lidar (light detection and ranging), and transmissometer system developed at the Desert Research Institute of Reno, NV, U.S.A. Particulate matter emissions from school buses significantly increased (up to a factor of 1.8) after the switch from petroleum diesel to a 20% biodiesel blend. The fuel used during this campaign was provided by a local distributor and was independently analyzed at the end of the on-road experiment. The analysis found high concentrations of free glycerin and reduced flash points in the B 100 parent fuel. Both measures indicate improper separation and processing of the biodiesel product during production. The biodiesel fuels used in the school buses were not in compliance with the U.S.A. ASTM D6751 biodiesel standard that was finalized in December of 2001. The U.S.A. National Biodiesel Board has formed a voluntary National Biodiesel Accreditation Program for producers and marketers of biodiesel to ensure product quality and compliance with the ASTM standard. The results of our study underline the importance of the program since potential emission benefits from biodiesel may be reduced or even reversed without appropriate fuel quality control on real-world fuels.     

Numerical Modeling of Flow Dynamics in The Aluminum Smelting Process: Comparison Between Air–Water and CO2–Cryolite Systems

Metallurgical and Materials Transactions B - Air–water models have been widely applied as substitutes for CO2–cryolite systems in the study of the complex bubble dynamics and...     

In vivo and in vitro antilipolytic effects of some various substituted homocysteine-thiolactone-nicotinamides: Structure-activity study

The antilipolytic activity of homocysteine-thiolactone-nicotinamide (ST22) and its 2-chloro (ST71), 6-chloro (ST82) and 6-hydroxy (ST90) derivatives was investigated by evaluation of serum free fatty acids (FFA) and triglycerides (TG) (in vivo) and FFA release from adipose tissue (in vitro). Increased FFA levels in 17-hr fasted rats at 60 min following treatment with 7·10⁻⁴ mol kg⁻¹ p.o. were reduced by 70% (ST22), 60% (ST82) and 18% (ST71), whereas ST90 provoked no change; TG levels showed similar changes. Basal FFA release from epididymal rat adipose tissue at 60 min following treatment with 7·10⁻⁴ mol kg⁻¹ p.o. of ST22 and ST82 was reduced by 79 and 45%, respectively. Lipid mobilization induced by noradrenaline (NA) was diversely affected by the compounds according to the tests employed: with in vivo experiments, serum FFA levels were reduced by 60, 70, 10 and 5% at 60 min following treatment with ST22, ST82, ST71 and ST90, respectively (7·10⁻⁴ mol kg⁻¹ p.o.; NA bitartrate, 2 mg kg⁻¹ s.c.); in vitro, ST22 produced no change, whereas the other compounds induced a significant mobilization of FFA. The results suggest that: (a) antilipolytic activity can be greatly modified when various substituents capable of influencing either the inductive (-I) or the resonance (+M) effect are introduced into the different positions of the pyridine ring; and (b) the lipolysis experiments did not evince any direct relationship between the effects obtained by the in vivo tests and those obtained by the in vitro tests.     

Empfehlungen des Arbeitskreises 6.1 “Geotechnik der Deponiebauwerke” der Deutschen Gesellschaft für Geotechnik e. V. (DGGT)

Recommendations of the DGGT Committee “Geotechnics of Landfill Structures“. The Committee “Geotechnics of Landfill Structures”, formerly “Geotechnics of Landfills and Contaminated Land”, published up to now 75 recommendations. The series is continued by the revised recommendations E2‐18 “Geotechnical aspects of gascollektion” and some more recommendations concerning the use and quality insurance of geosynthetics. Other subjects and recommendations revised during this year are reported.