Influence of Specimen Size∕Geometry on Shrinkage Cracking of Rings

This paper presents experimental evidence to show that a size∕geometry dependence is observed in the shrinkage cracking behavior of restrained concrete structures. A theoretical model is developed to explain this behavior. First, a solution is presented to compute the stress and displacement fields of an aging, linear, viscoelastic cylinder by assuming that a uniformly distributed shrinkage strain is perfectly restrained in the radial direction at the internal surface of the cylinder. Second, a fracture mechanics failure criterion is implemented to develop time and geometry-dependent tensile stress resistance (strength) curves. Third, this model is used to illustrate the role of specimen size∕geometry and material composition on the failure response. Finally, experimentally measured ages of cracking are compared with the theoretical modeling predictions.     

Theoretische Untersuchungen zum Zerfallsgleichgewicht des Harnstoffs in Gasphase und in wäßriger Lösung

Theoretical Investigations on the Decomposition Equilibrium of Urea in Gaseous State and Aqueous Solution There is empirical evidence that among the two possible decomposition equilibria of urea in the gaseous and aqueous states the desammonation process prevails. In the present work the thermodynamic and kinetic conditions of desammonation and dehydration based on intramolecular mechanisms were examined by means of quantum chemical methods. The application of MNDO method yields correct structural data, dipole moments and ionisation potentials; the solvation is taken into account using NDDO based solvation and reaction field models. Maximum deviations concerning enthalpies of formation in π-electron rich compounds reach up to 40kJ/mole. A detailed examination of the energy hyperfaces reveals that the dehydration is kinetically hindered by a significantly high activation barrier. This situation is not essentially altered by taking into account nonspecific solvent effects in aqueous solution.     

Validation of coupled codes using VVER plant measurements

A data set of five transients at different VVER type nuclear power plants was collected in order to validate neutron kinetics/thermal hydraulics codes. Two of these transients ‘drop of control rod at nominal power at Bohunice-3’ of VVER-440 type and ‘coast-down of 1 from 3 working MCPs at Kozloduy-6’ of VVER-1000 type, were then utilised for code validation. Eight institutes contributed to the validation with 10 calculations using 5 different combinations of coupled codes. The thermal hydraulic codes were ATHLET, SMABRE and RELAP5 and the neutron kinetic codes DYN3D, HEXTRAN, KIKO3D and BIPR8. The general behaviour of both the transients was quite well calculated with all the codes. Even an elementary modelling of coolant mixing in reactor pressure vessel under asymmetric transients improved correspondence to the measurements. Some differences between the calculations seem to indicate that fuel modelling and treatment of VVER-440 control rods need further consideration. The simultaneous validation interacted with the data collection effort and thus improved its quality. The complexity of data collection systems and sometimes conflicting data, however, called for compromises and interpretation guides that also taught the analysts balanced plant modelling.     

Bandwidth performance of 16-element thinned phased array withtapped delay-line filter

The bandwidth performance of a thinned phased adaptive array with and without a delay-line processor are compared. Five- and nine-jammer scenarios are considered for two EHF bands, 0.125 and 2.0 GHz. The null-depth which was used as the measure of performance was computed over the nulling band for three different delay-line configurations. The simulation results give some insight into the way in which delay-line compensation provides improved performance as the interference bandwidth increases