Numerical Modelling of Transient and Droplet Transport for Pulsed Pressure - Chemical Vapour Deposition (PP-CVD) Process

The objective of this thesis is to develop an easy-to-use and computationally economical numerical tool to investigate the flow field in the Pulsed Pressure Chemical Vapour Deposition (PP-CVD) reactor. The PP-CVD process is a novel thin film deposition technique with some advantages over traditional CVD methods. The numerical modelling of the PP-CVD flow field is carried out using the Quiet Direct Simulation (QDS) method, which is a flux-based kinetic-theory approach. Two approaches are considered for the flux reconstruction, which are the true directional manner and the directional splitting method. Both the true directional and the directional decoupled QDS codes are validated against various numerical methods which include EFM, direct simulation, Riemann solver and the Godunov method. Both two dimensional and axisymmetric test problems are considered. Simulations are conducted to investigate the PP-CVD reactor flow field at 1 Pa and 1 kPa reactor base pressures. A droplet flash evaporation model is presented to model the evaporation and transport of the liquid droplets injected. The solution of the droplet flash evaporation model is used as the inlet conditions for the QDS gas phase solver. The droplet model is found to be able to provide pressure rise in the reactor at the predicted rate. A series of parametric studies are conducted for the PP-CVD process. The numerical study confirms the hypothesis that the flow field uniformity is insensitive to the reactor geometry. However, a sufficient distance from the injection inlet is required to allow the injected precursor solution to diffuse uniformly before reaching the substrate. It is also recommended that placement of the substrate at the reactor’s centre axis should be avoided

Does prior experience really matter for disaster preparedness?

Climate change and transition toward urbanization had resulted in more frequent and severe disasters in the last decade. While urbanization is potential driver of change and economic growth, climate change had exacerbated resource scarcity and exposed local communities to greater and more frequent disasters. The local communities in Malaysia are of no exception. The most common types of disasters in Malaysia are landslide, flash flood and haze. This study explores the extent to which prior experience affects the level of preparedness among Malaysian communities before occurrence of natural disasters. Although previous studies have proven prior experience aided better handling of preparedness, yet some researchers have not found significant correlation between prior experience and preparedness. Having inconclusive results and with the rise of unexpected disaster events, has lead this present study to investigate the link in the Malaysian context. Questionnaire surveys were distributed to more than 1,000 respondents and face-to-face interviews were conducted with 12 local communities from Klang Valley, Malaysia. The results indicated that prior experience does contribute towards the level of disaster preparedness among the local communities in Malaysia. Hence, the findings of this present study may reduce the impact of disasters and thus could help local communities to effectively cope with the events of disasters

Effects of fermentation time and pH on soursop (Annona muricata) vinegar production towards its chemical compositions

Vinegar is a liquid product that undergoes both alcoholic and acetous fermentation of sugar (carbohydrate) sources. Soursop (Annona muricata) is easily available in Malaysia throughout the year. However, it is also highly perishable and has a short shelf-life. Therefore, in this research, soursop was used in the production of vinegar, to increase its utilisation and reduce wastage. The objectives of this research were to determine the effects of fermentation time and pH on soursop vinegar using a 3 × 5 factorial design and to determine its chemical compositions. It was found that pH and fermentation time showed significant (p0.05). It was evident that the sugar concentration reduces over time and it was inversely proportional to the ethanol and acetic acid concentrations, due to the conversion of sugar to ethanol and subsequently acetic acid. It was found that higher pH (pH5.5) gave significantly (p0.05) effect on ethanol production. There were no significant differences (p>0.05) in vitamin C content in all vinegar samples. Thus, it can be established that at fermentation time of 120 h and pH5.5, more sugar was used and more ethanol and acetic acid were produced

Optimization of torrefaction conditions for high energy density solid biofuel from oil palm biomass and fast growing species available in Malaysia

Without appropriate treatment, lignocellulosic biomass is not suitable to be fed into existing combustion systems because of its high moisture content, low bulk energy density and difficulties in transport, handling and storage. The aim of this study was to investigate the effects of torrefaction treatment on the weight loss and energy properties of fast growing species in Malaysia (Acacia spp., and Macaranga spp.) as well as oil palm biomass (oil palm trunk and empty fruit bunch). The lignocellulosic biomass was torrefied at three different temperatures 200, 250 and 300 °C for 15, 30 and 45 min. Response surface methodology was used for optimization of torrefaction conditions, so that biofuel of high energy density, maximized energy properties and minimum weight loss could be manufactured. The analyses showed that increase in heating values was affected by treatment severity (cumulated effect of temperature and time). Our results clearly demonstrated an increased degradation of the material due to the combined effects of temperature and treatment time. While the reaction time had less impact on the energy density of torrefied biomass, the effect of reaction temperature was considerably stronger under the torrefaction conditions used in this study. It was demonstrated that each biomass type had its own unique set of operating conditions to achieve the same product quality. The optimized torrefaction conditions were verified empirically and applicability of the model was confirmed. The torrefied biomass occurred more suitable than raw biomass in terms of calorific value, physical and chemical properties. The results of this study could be used as a guide for the production of high energy density solid biofuel from lignocellulosic biomass available in Malaysia

Application of an evolutionary algorithm-based ensemble model to job-shop scheduling

In this paper, a novel evolutionary algorithm is applied to tackle job-shop scheduling tasks in manufacturing environments. Specifically, a modified micro genetic algorithm (MmGA) is used as the building block to formulate an ensemble model to undertake multi-objective optimisation problems in job-shop scheduling. The MmGA ensemble is able to approximate the optimal solution under the Pareto optimality principle. To evaluate the effectiveness of the MmGA ensemble, a case study based on real requirements is conducted. The results positively indicate the effectiveness of the MmGA ensemble in undertaking job-shop scheduling problems

Studies on the storage stability of fermented red dragon fruit (Hylocereus polyrhizus) drink

The objective of this work was to study the effect of storage temperatures and duration on the stability of fermented red dragon fruit drink (FRDFD) on its betacyanins content, physicochemical and microbiological qualities (BPM) and determining sensory acceptability. Results showed that both storage temperatures and duration have a significant effect on betacyanins content and physicochemical properties of FRDFD. Aerobic mesophilic and yeast and mold counts were lower than 1 × 103 CFU/mL for FRDFD stored at both temperatures. The loss of betanin (16.53–13.93 g/L) at 4 °C was 15.73% with no significant changes in physicochemical properties from week two onwards compared to 56.32% (16.53–7.22 g/L) of betanin loss at 25 °C. At week eight, FRDFD stored at 4 °C still contained 13.93 g/L betanin with a pH value of 3.46, suggested its potential as a functional drink which is sensory acceptable (mean score > 80% using hedonic test) among consumers

Deep Temporal Convolution Network for Time Series Classification

A neural network that matches with a complex data function is likely to boost the classification performance as it is able to learn the useful aspect of the highly varying data. In this work, the temporal context of the time series data is chosen as the useful aspect of the data that is passed through the network for learning. By exploiting the compositional locality of the time series data at each level of the network, shift-invariant features can be extracted layer by layer at different time scales. The temporal context is made available to the deeper layers of the network by a set of data processing operations based on the concatenation operation. A matching learning algorithm for the revised network is described in this paper. It uses gradient routing in the backpropagation path. The framework as proposed in this work attains better generalization without overfitting the network to the data, as the weights can be pretrained appropriately. It can be used end-to-end with multivariate time series data in their raw form, without the need for manual feature crafting or data transformation. Data experiments with electroencephalogram signals and human activity signals show that with the right amount of concatenation in the deeper layers of the proposed network, it can improve the performance in signal classification

Study on bioaccessibility of betacyanins from red dragon fruit (Hylocereus polyrhizus)

Betacyanins are bioactive dietary phytochemicals which can be found in red dragon fruit (RDF). Therefore, the bioaccessibility of betacyanins that present in fermented red dragon fruit drink (RDFD) and pressed red dragon fruit juice (RDFJ) was accessed in simulated gastric and intestinal digestion. Results disclosed that betacyanins from RDFD and RDFJ suffered minor loss (< 25%) at gastric-like environment but greater loss was observed during the intestinal phase digestion. After subjected to intestinal digestion, RDFD retained 46.42% of betanin while RDFJ retained 43.76%, with betanin concentration of 17.12 mM and 12.37 mM, respectively. Findings also revealed that RDFD exhibited higher antioxidant capacity compared to RDFJ after subjected to intestinal digestion, with values of 0.88 mM Trolox equivalent antioxidant capacity (TEAC) and 0.85 mM TEAC, respectively. The data suggests that betacyanins that present in RDF are bioaccessible while fermentation able to enhance the bioavailability with more betacyanins retained after intestinal digestion

Chemical changes and optimisation of acetous fermentation time and mother of vinegar concentration in the production of vinegar-like fermented papaya beverage

Fermentation has been long used as a method to produce beverage of various health benefits. In this research, ripe papaya (Carica papaya) was fermented through alcoholic fermentation using Saccharomyces cerevisiae, followed by acetous fermentation using Acetobacter spp. from mother of vinegar, to reduce wastage of this highly perishable Malaysian fruit. The papaya juice was pasteurised prior to the fermentation process. Optimisation of acetous fermentation was carried out using the response surface methodology (RSM) with central composite rotatable design (CCRD). Acetous fermentation time had shown significant effect on all the chemical characteristics while mother of vinegar concentration did not significantly effect on all the chemical characteristics. The vinegar-like fermented papaya beverage which was produced at the optimum point (Fermentation time = 70.80 h and concentration = 40% mother of vinegar) contained 0.37 ± 0.01% reducing sugar, 3.54 ± 0.36% ethanol, 2.46 ± 0.07% acetic acid, 327.89 ± 3.60 mg GAE/ L total phenolic, 2.32 ± 0.17 mg/100 mL ascorbic acid and 52.40 ± 0.23% mg AA/100 mL free-radical scavenging activity. In conclusion, vinegar-like fermented papaya beverage was successfully produced and its chemical compositions changed from papaya juice to wine and vinegar-like beverage with increased bioactive compounds and antioxidative activity

Does the Axillary Lymph Node Ratio Have Any Added Prognostic Value over pN Staging for South East Asian Breast Cancer Patients?

10.1371/journal.pone.0045809PLoS ONE79