Microstructure evolution during mechanical working of three RS aluminium alloys: Al-4Cr-1Fe,Al-5Cr-2Zr and Al-6.43Cr-1.67Zr

Three Al-Cr alloys containing additions of Zr and Fe have been fabricated via cold compaction and hot extrusion. The decomposition of the powder microstructure and the subsequent coarsening during thermomechanical treatment have been studied. Detailed electron microscopy investigations were performed at different locations of partially extruded billets at 450 °C. The microstructure of the dead metal zone reflects the effect the induction heating exerts on the as-atomized powder microstructure. In the low Cr alloys, Al-4Cr-1 Fe and Al-5Cr-2Zr, decomposition of the rapidly solidified microstructure commences at the rich intercellular network, whereas the microstructure of the Al-6.43Cr-1.67Zr alloy remains relatively unaffected. Within the deformation zone the precipitation kinetics are affected by the shearing and the temperature rise. The cells and the powder particles are aligned along the extrusion direction. Precipitation is taking place within the primary segregation-free areas, observed in Al-4Cr-1 Fe and Al-5Cr-2Zr alloys, whereas in the Al-6.43Cr-1.67Zr alloy, decomposition of the powder microstructure starts at the Cr-rich intermetallic particles. The as-extruded microstructure is fibrous and heterogeneous. The heterogeneity of the as-extruded microstructure is a result of the microstructural variation observed within different size powder particles and within individual ones.     

Integrated modelling under uncertainty in watershed-level assessment and management.

Uncertainty in water quality model predictions is inevitably high due to natural stochasticity, model uncertainty, and parameter uncertainty. An integrated modelling system (modified-BASINS) under uncertainty is described and demonstrated for use in receiving-water quality prediction and watershed management. A Monte Carlo simulation was used to investigate the effect of various uncertainty types on output prediction. Without pollution control measures in the watershed, the concentrations of total nitrogen (T-N) and total phosphorus (T-P) in the Hwaong Reservoir, considering three uncertainty types, would be less than about 4.4 and 0.23 mg L(-1), respectively, in 2012, with 90% confidence. The effects of two watershed management practices, wastewater treatment plants (WWTP) and constructed wetlands (WETLAND), were evaluated. The combined scenario (WWTP + WETLAND) was the most effective at improving reservoir water quality, bringing concentrations of T-N and T-P in the Hwaong Reservoir to less than 3.4 and 0.14 mg L(-1), 24 and 41% improvements, respectively, with 90% confidence. Overall, the Monte Carlo simulation in the integrated modelling system was practical for estimating uncertainty and reliable in water quality prediction. The approach described here may allow decisions to be made based on the probability and level of risk, and its application is recommended.     

Use of biocompatible calcium-phosphate glass ceramic BGC in surgical treatment of maxillary cysts

The possibility of using the granulated form of biocompatible material made of calcium-phosphate glass ceramic BGC for treatment of maxillary cysts was demonstrated.     

Stable operation range for laser diodes with an integrated passivecavity in the presence of external optical feedback

It is shown that a laser diode with an integrated passive cavity yields higher tolerable levels of feedback from distant reflections than an equivalent long solitary laser diode. To ensure this high tolerance for external feedback, the internal feedback level in the integrated passive cavity must be of the order of about 10%. Then the laser diode remains stable up to external feedback levels in excess of 1% even if the internal reflection phase is not carefully adjusted. External reflections from a cleaved fiber end are then not sufficient to drive the laser into coherence collapse, if realistic coupling efficiencies between laser diode and fiber are taken into account. The low feedback sensitivity is explained by the combination of the long effective length of the laser and a high relaxation resonance frequency. Therefore, quantum-well laser diodes with a long length and a high relaxation resonance frequency are likewise expected to exhibit low feedback sensitivity     

Mutagenicity of ambient aerosol collected in an urban and industrial area of The Netherlands

To investigate the influence of the densely populated and heavily industrialized Rijnmond area of The Netherlands on the genotoxicity of the ambient aerosol, aerosol samples were collected at locations within the area, and at a coastal region located upwind. The mutagenicity of extracts of the samples was compared in the Salmonella/microsome test. The dependence of the effects on sampling time and on sampling location was investigated with the aid of a series of simple mathematical models. These models were also used to estimate the increase in mutagenicity above background levels at the sites in the Rijnmond area due to emissions within that area. Application of the models showed that the clear and significant increases are not merely a result of the additions of mutagens emitted, but that possibly interactions between sampling time- and location-dependent factors play a role. Comparison of the results obtained with the different Ames-test variants (different strains, with and without liver homogenate) indicate that the conclusions concerning the time and location dependence of the effect were not dependent on the variant used.     

Analog and Digital Speed Control of DC Drives Using Proportional-Integral and Integral-Proportional Control Techniques

A comparative study of proportional-integral (P-I) and integral-proportional (I-P) control schemes, for the speed control of a dc drive, using both analog-and microprocessor-based digital circuits, is presented. The often-neglected current response is discussed and results are presented. The speed response to step changes in speed reference and load torque, using both the control schemes, is compared to evaluate the merits of I-P control. A brief discussion of sensitivity to controller gains is also given. It is shown that the I-P control scheme offers some distinctive advantages over P-I control. Experimental and simulation results are also presented.