Computational prediction of the refinement of oxide agglomerates in a physical conditioning process for molten aluminium alloy

Physically conditioning molten scrap aluminium alloys using high shear processing (HSP) was recently found to be a promising technology for purification of contaminated alloys. HSP refines the solid oxide agglomerates in molten alloys, so that they can act as sites for the nucleation of Fe-rich intermetallic phases which can subsequently be removed by the downstream de-drossing process. In this paper, a computational modelling for predicting the evolution of size of oxide clusters during HSP is presented. We used CFD to predict the macroscopic flow features of the melt, and the resultant field predictions of temperature and melt shear rate were transferred to a population balance model (PBM) as its key inputs. The PBM is a macroscopic model that formulates the microscopic agglomeration and breakage of a population of a dispersed phase. Although it has been widely used to study conventional deoxidation of liquid metal, this is the first time that PBM has been used to simulate the melt conditioning process within a rotor/stator HSP device. We employed a method which discretizes the continuous profile of size of the dispersed phase into a collection of discrete bins of size, to solve the governing population balance equation for the size of agglomerates. A finite volume method was used to solve the continuity equation, the energy equation and the momentum equation. The overall computation was implemented mainly using the FLUENT module of ANSYS. The simulations showed that there is a relatively high melt shear rate between the stator and sweeping tips of the rotor blades. This high shear rate leads directly to significant fragmentation of the initially large oxide aggregates. Because the process of agglomeration is significantly slower than the breakage processes at the beginning of HSP, the mean size of oxide clusters decreases very rapidly. As the process of agglomeration gradually balances the process of breakage, the mean size of oxide clusters converges to a steady value. The model enables formulation of the quantitative relationship between the macroscopic flow features of liquid metal and the change of size of dispersed oxide clusters, during HSP. It predicted the variation in size of the dispersed phased with operational parameters (including the geometry and, particularly, the speed of the rotor), which is of direct use to experimentalists optimising the design of the HSP device and its implementation.This research is financially supported by the EC FP7 project “High Shear Processing of Recycled Aluminium Scrap for Manufacturing High Performance Aluminium Alloys” (Grant No. 603577)

Influence of real-time information provision to vacant taxi drivers on taxi system performance

This paper assumes that all taxi drivers adopt a profit maximization strategy when searching for customers. Some taxi drivers are provided with real-time information on customer and taxi queue lengths at all taxi stands while others have no information at all. The questions to be investigated are: (1) will equipped taxi drivers earn a higher profit compared to the uninformed taxi drivers? (2) What is the impact of real-time information provision to a portion of all the taxi drivers on the overall taxi system performance? To find answers to these questions, a case study is conducted by assuming a hypothetical linear city with a single city centre, ten taxi stands and twenty residential zones. A discrete-event dynamic simulation model is adopted to simulate the movements of taxis and to estimate various taxi system performance characteristics, such as taxi operation profit and customer waiting time. The time period simulated is a 3-hour morning commune. The taxi fleet size, fare structure, taxi operation cost and customer demand pattern are all assumed given. The simulation model is used to investigate the variation of taxi system performance with the proportion of informed taxi drivers in the taxi fleet.published_or_final_versionThe 12th World Conference of Transport Research (WCTR 2010), Lisbon, Portugal, 11-15 July 2010

Determination of optimal successor function in phase-based control using neural network

A phase-based method for fixed-time signal control of traffic improves significantly the junction performance over conventional stage-based method of control due to the higher flexibility in specification of signal timings, where the control variables comprise the start and duration of green phases and the cycle time at which the junction is operated. The cycle-structure is specified by a successor function, a combination of 0 and 1 for all incompatible pairs of phases, which indicates the order of phases in a cycle. Normal procedure optimises the timings for each of these successor functions to determine the best timing plan. The computing time is found to be approximately proportional the number of such functions. To reduce the computational requirement, and hence enhance its applicability to real-time actuated control, a neural network is employed in this paper to help identify the optimal successor function for further optimization of timings. Encouraging results are obtained.published_or_final_versio

The Hong Kong second parking demand study

This paper describes the background, objectives, surveys, models, findings and recommendations of the Hong Kong second parking demand study. This study aims to give strategic directions to guide the planning and management of parking facilities in Hong Kong. It comprises extensive surveys to determine the parking inventory, parking characteristics and driver behaviour. Demand models were developed to predict the future night-time and daytime parking demand over a planning horizon of 15 years. All types of vehicle, including private cars, taxis, motorcycles, coaches and goods vehicles, were included in the analysis. The recommendations of a previous parking demand study have been reviewed, and new recommendations are given.published_or_final_versio

Development of a transport model for East Kowloon, Hong Kong

After the relocation of the airport, much land-use change and redevelopment is expected in the East Kowloon District in the city of Hong Kong. Consequently, a comprehensive review of the land-use and transportation plans for the district was required. In the study, a sub-regional transport model for the district was developed. This model was used to forecast the vehicular, public transport and pedestrian demands arising from land-use and transportation system changes in and around the district. This paper describes the modelling approach and validation results. | After the relocation of the airport, much land-use change and redevelopment is expected in the East Kowloon District in the city of Hong Kong. Consequently, a comprehensive review of the land-use and transportation plans for the district was required. In the study, a sub-regional transport model for the district was developed. This model was used to forecast the vehicular, public transport and pedestrian demands arising from land-use and transportation system changes in and around the district. This paper describes the modelling approach and validation results.published_or_final_versio

The Hong Kong parking demand study

This paper describes the objectives, methodology, findings, recommendations and implementation programme of a parking demand study which was conducted in Hong Kong during the period 1993-1995. The study comprises extensive surveys to establish parking characteristics and parking inventory, a stated preference survey to estimate the influence of parking space availability on modal choice, development of parking demand models for private cars and goods vehicles, identification of problems related to parking, and formulation of remedial measures.published_or_final_versio

Herba Epimedii: Anti-oxidative properties and its medical implications

Herba Epimedii is a Chinese herbal medicine with proven efficacy in treating cardiovascular diseases and osteoporosis, and in improving sexual and neurological functions. This efficacy is found to be related to the potent anti-oxidative ability of Herba Epimedii and its flavonoid components, with icarrin as the main effective constituent, along with polysaccharides and vitamin C. These ingredients have been proven to be effective against oxidative-stress related pathologies (cardiovascular diseases, Alzheimer's disease and inflammation) in animal rodent models and in vitro studies. Their antioxidative properties are found to be related to an inductive effect on endogenous freeradical scavenging enzymes such as catalase and glutathione peroxidase and the inherent electron-donating ability of flavonoids. © 2010 licensee MDPI, Basel, Switzerland.published_or_final_versio

Advancement of the annual traffic census in Hong Kong

This paper summarises the process, findings and recommendations of a recently completed joint university consultancy project that reviewed the annual traffic census (ATC) in Hong Kong. The results of a survey that assessed the usefulness of the census report are presented, together with an overview of the existing traffic data collection process and traffic detection equipment. Areas for improvement are then identified, including the sampling strategies for the collection of vehicle classification and occupancy data, the procedure for the development of group scaling factors, the method for the selection of core and coverage stations, the approaches to developing growth factors and traffic flow estimation, the presentation method and database structure of the census framework, and the manpower requirements. Based on these identified areas, a new computer program is developed to integrate all of the tasks of the census report and to produce the results in CD-ROM format. Finally, concluding remarks are given together with recommendations for further study.published_or_final_versio

Evidence for the existence of powder sub-populations in micronized materials : Aerodynamic size-fractions of aerosolized powders possess distinct physicochemical properties

This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.Purpose: To investigate the agglomeration behaviour of the fine ( 12.8 µm) particle fractions of salmeterol xinafoate (SX) and fluticasone propionate (FP) by isolating aerodynamic size fractions and characterising their physicochemical and re-dispersal properties. Methods: Aerodynamic fractionation was conducted using the Next Generation Impactor (NGI). Re-crystallized control particles, unfractionated and fractionated materials were characterized for particle size, morphology, crystallinity and surface energy. Re-dispersal of the particles was assessed using dry dispersion laser diffraction and NGI analysis. Results: Aerosolized SX and FP particles deposited in the NGI as agglomerates of consistent particle/agglomerate morphology. SX particles depositing on Stages 3 and 5 had higher total surface energy than unfractionated SX, with Stage 5 particles showing the greatest surface energy heterogeneity. FP fractions had comparable surface energy distributions and bulk crystallinity but differences in surface chemistry. SX fractions demonstrated higher bulk disorder than unfractionated and re-crystallized particles. Upon aerosolization, the fractions differed in their intrinsic emission and dispersion into a fine particle fraction (< 5.0 µm). Conclusions: Micronized powders consisted of sub-populations of particles displaying distinct physicochemical and powder dispersal properties compared to the unfractionated bulk material. This may have implications for the efficiency of inhaled drug deliveryPeer reviewe

Associations of apolipoprotein E exon 4 and lipoprotein lipase S447X polymorphisms with acute ischemic stroke and myocardial infarction

Background: Because apolipoprotein E (apoE) and lipopoprotein lipase (LPL) polymorphisms interact with each other and with other factors to affect lipid metabolism, we sought to determine their separate and combined effects in association with ischemic vascular disease. Methods: We performed a case-control study of 816 subjects: 246 acute ischemic stroke patients, 234 acute myocardial infarction patients, and 336 controls. APOE exon 4 and LPL S447X genotypes were determined. Results: APOE ε2 and ε4 homozygotes were increased in stroke (4.5% vs. 1.0%, p = 0.008), while in myocardial infarction the ε4 allele was increased (12.6% vs. 9.5%, p = 0.006) but ε2 was decreased (3.7% vs. 12.1%, p = 0.000006). For subjects with either APOE ε2 or ε4 alleles, LPL X alleles were increased in vascular disease (OR = 2.2, p = 0.01). LPL X alleles displayed opposite tendencies toward association with disease when subjects were divided by sex, smoking, or APOE genotype. Meta-analysis and regression analysis of previous studies supported the sex and smoking dichotomies. Conclusion: This is the first report of an association of vascular disease with an interaction of APOE exon 4 and LPL S447X genotypes. Therefore, APOE genotypes and LPL S447X interactions with apoE, sex, and smoking may affect the risk of myocardial infarction and ischemic stroke. © 2006 by Walter de Gruyter.published_or_final_versio