Effects of ultrasonic disintegration on sludge microbial activity and dewaterability

Ultrasonic treatment can disintegrate sludge, enhance microbial activity and improve sludge dewaterability at different energy inputs. To find their relationship, the three phenomena during ultrasonic treatment were investigated synchronously, and an experimental model was established to describe the process of ultrasonic sludge disintegration. Analysis results showed that the changes of sludge microbial activity and dewaterability were dependent on sludge disintegration degree during ultrasonic treatment. When sludge disintegration degree was lower than 20%, sludge flocs were disintegrated into micro-floc aggregates and the microbial activity increased over 20%. When sludge disintegration degree was over 40%, most cells were destroyed at different degree, and sludge activity decreased drastically. Only when sludge disintegration degree was 2-5%, sludge dewaterability was improved with the conditioning of FeCl(3). It was also found that the sonication with low density and long duration was more efficient than sonication with high density and short duration at the same energy input for sludge disintegration, and a transmutative power function model can be used to describe the process of ultrasonic disintegration.     

Effect of Alloy Composition and Exposure Conditions on the Selective Oxidation Behavior of Ferritic Fe–Cr and Fe–Cr–X Alloys

Selective oxidation behavior of ferritic martensitic Fe–Cr base alloys, exposed in various atmospheres containing combinations of O₂, CO₂, and H₂O, were studied at various temperatures relevant to oxy-fuel combustion. This paper begins with a discussion of the required Cr content to form a continuous external chromia scale on a simple binary Fe–Cr alloy exposed in oxygen or air based on experiments and calculations using the classic Wagner model. Then, the effects of the exposure environment and Cr content on the selective oxidation of Fe–Cr alloys are evaluated. Finally, the effects produced by alloying additions of Si, commonly present in various groups of commercially available ferritic steels, are described. The discussion compares the oxide scale formation on simple binary and ternary Fe–Cr base model alloys with that on several commercially available ferritic steels.     

Mean-delay approximation for cyclic-service queueing systems

This paper investigates mean delays in a single-server queueing model with cyclic service. An approximate analysis is performed for an arbitrary number of queues, constant switch-over time, exhaustive service discipline, Poisson arrival processes, and general service-time distributions. Neither inter-arrival nor service-time distributions have to be identical for the different queues. A major value of our approximation lies in the simplicity of its numerical evaluation for an arbitrary number of queues and any traffic pattern. Extensive comparisons with simulation results show the high accuracy of the approximation over a wide range of parameters.     

On fracture mechanics under complex stress

The majority of linear elastic fracture mechanics investigations since the pioneering work of Irwin and Paris have been carried out under tension-tension loading conditions in sheet metal. However, built up structures have generally been under complex stress conditions and to date very scanty information is available on fracture mechanics parameters under complex stress conditions. The current stale of the art for mixed mode crack tips deformation is reviewed.In order to use linear elastic fracture mechanics methodology to predict crack growth rate in shear webs, an experimental program was initiated. Initial tests on 7075-T6 Aluminum alloy sheet, using a picture frame type specimen, were conducted. The critical stress intensity factors and the rate of crack growth under aforementioned condition are established.     

Token-ring local-area networks and their performance

The major technical concepts underlying token-ring technology are examined, and performance issues arising in the design of such local-area networks (LANs) are detailed. Following a survey of analytical queuing models to describe the basic token-ring operation, three topics are discussed in detail: (1) the IEEE 802.5 token ring and its performance; (2) the ANSI fiber distributed data interface (FDDI) token ring and its performance; and (3) architecture and performance issues arising in the interconnection of token-ring networks with regard to the various components of a multiring architecture demonstrating which congestion-control problems can arise in such a network and how they can be overcome. The author concludes with a number of open questions concerning the understanding of the quantitative behavior of token-ring-based LANs     

Integrated sequential fuzzy logic search models for simulating wastewater treatment plants missing influent parameters

Aiming at achieving optimum operations of wastewater treatment plant (WWTP) processes, it is essential to develop accurate predictive models for expected influent pollutant loads. To overcome limited timespan data and model complexity, this study is devoted to propose an integration of inputs' sequential search with the adaptive neuro-fuzzy inference system (ANFIS) for reducing the modelling complexity. The input data included nine influent parameters measured bi-weekly for 12 years at a WWTP, South Africa (SA). The sequential search process was used for input optimization to select the most representative inputs in modelling four parameters. The obtained results indicated a strong correlation with R² and NSE above 0.85 for the four targeted influent parameters. After validating the developed models using different criteria, the missing records were predicted throughout the study period. The integration of sequential search input optimization and ANFIS modelling was able to provide a high performance in modelling WWTP datasets.