In this work, the peroxide-initiated degradation of polypropylene (PP) in co-rotating intermeshing twin-screw extruders (COITSEs) is analyzed by means of numerical simulations. This reactive extrusion (REX) operation is simulated by implementing (i) a one-dimensional and (ii) a three-dimensional (3D) modeling approach. In the case of the 1D modeling, a REX mathematical model previously developed and implemented as a computer code is used for the evaluation of two scale-up rules for COITSEs of various sizes. The first scale-up rule which is proposed in this work is based on the concept of thermal time introduced by Nauman (1977), and the second one is based on specific energy consumption (SEC) requirements. The processing parameters used in testing the previously referred to scale-up approaches are the mass throughput, the screw rotating speed, and the peroxide concentration, whereas the extruder screw configuration and the barrel temperature profiles are kept constant. The results for the simulated operating conditions show that when the REX operation is scaled-up under constant thermal time, very good agreement is obtained between the weight-average molecular weight (Mw) and poly-dispersity index (PDI) from the larger extruders and the values of these parameters corresponding to the reference extruder. For the constant SEC approach, on the other hand, more significant variations are observed for both of the aforementioned parameters. In the case of the implemented constant thermal time procedure, a further analysis of the effect of the mass throughput and screw speed of the reference device on the scaled-up operation is performed. It is observed that when the lower mass throughput is implemented for the smaller extruder keeping a constant screw speed, the predicted residence times of extrusion for the larger extruders are lower, in general terms, than those corresponding to the reference device, and a converse situation occurs for the higher implemented value of the mass throughput. Also, in general terms, the higher increase of the reaction temperature on the scaled-up operation corresponds to the lower mass throughputs and higher screw speeds specified for the reference extruder. For the 3D modeling approach, two different case studies are analyzed by means of a commercial FEM software package. The REX simulations are performed under the assumption of steady-state conditions using the concept of a moving relative system (MRS). To complement the information obtained from the MRS calculations, simulations for selected conditions (for non-reactive cases) are performed considering the more realistic transient-state (TS) flow conditions. The TS flow conditions are associated to the time periodicity of the flow field inside the conveying elements of COITSEs. In the first case study, the peroxide-initiated degradation of PP is simulated in fully-filled screw elements of two different size COITSEs in order to evaluate scale-up implications of the REX operation. In the second case, the reacting flow is simulated for a conventional conveying screw element and a conveying screw element having a special design and corresponding to the same extruder size. For both of the analyzed cases, the effects of the initial peroxide concentration and mass throughput on the final Mw and PDI of the degraded resin are studied. The effect of the processing conditions is discussed in terms of the residence time distribution (RTD), the temperature of reaction, and the distributive mixing capabilities of the REX system. When analyzing the scale-up case, it is found that for the implemented processing conditions, the final Mws and PDIs are very close to each other in both of the analyzed flow geometries when the specified flow is close to that corresponding to the maximum conveying capabilities of the screw elements. For more restrictive flow conditions, the final Mws and PDIs are lower in the case of the screw element of the larger extruder. It is found that the distributive mixing ability of the reactive flow is mainly related to the specified mass throughput and almost independent of the specified peroxide concentration for a particular extruder size. For the analyzed screw elements, the conveying element corresponding to the small size extruder shows a slightly better distributive mixing performance. For this same case study, a further evaluation of the proposed scale-up criterion under constant thermal time confirms the trend of the results observed for the 1D simulations. In the second case study, the special type of screw element consists of screws rotating at different speeds which have different cross sections. In this case, the outer and inner diameters of both the special and the conventional type of screw elements are specified to be the same. As in the previous case study, the distributive mixing capabilities appear to be independent of the specified peroxide concentrations but dependent on the mass flow rate. It is speculated from the simulation results, from both the transient- as well as the steady-state flow conditions, that the screw element with the special design would yield lower final values of the PDI and Mw. Also, this screw element appears to have improved distributive mixing capabilities as well as a wider RTD.

A twin-buck converter with zero-voltage-transition (ZVT) is proposed in this thesis. The converter comprises two identical buck conversion units connected in parallel by an interleaved inductor. The ZVT is accomplished by the resonating the currents between the interleaved inductor and the parasitic capacitances of the power MOSFETs. The circuit efficiency can be further improved by introducing synchronous rectification to reduce the condition loss on the diodes. The detailed circuit analysis and operation characteristics are provided. A laboratory circuit rated at 300 W is designed and tested. Experimental results show that the switching losses can be effectively reduced by smoothly transiting the currents of the active power switches.

The schools located in many township and rural areas of South Africa struggle to provide a high standard of education because many of the inhabitants of these areas are very poor and there is thus a lack of the funding required for the necessary educational equipment. The Afri Twin project, started by Jayne Martin from the UK, addresses this problem. The project is collaboration between a British school, a South African town/city school, and a school from a poor township or rural community in South Africa. This article reports on a research project that made use of a qualitative case study approach, to focus on the collaboration between Wellacre Technology College, Ferrum High School, and Siyalungelwa High School as part of the Afri Twin project. The objectives of the research project are to determine the benefits of the Afri Twin project for the schools involved; to investigate the unique interaction between Wellacre, Ferrum, and Siyalungelwa; and to determine the cultural enrichment of learners and the multi-cultural interaction between the three schools. Data was collected through focus group interviews, in-depth interviews, and questionnaires. Data analysis led to the emergence of four major themes with categories and subcategories. The conclusion underlined the cultural tolerance that is established through the Afri Twin project, as well as the importance of financial support for promoting an improved learning environment. / Thesis (M.A. (Psychology)--North-West University, Potchefstroom Campus, 2009.

The schools located in many township and rural areas of South Africa struggle to provide a high standard of education because many of the inhabitants of these areas are very poor and there is thus a lack of the funding required for the necessary educational equipment. The Afri Twin project, started by Jayne Martin from the UK, addresses this problem. The project is collaboration between a British school, a South African town/city school, and a school from a poor township or rural community in South Africa. This article reports on a research project that made use of a qualitative case study approach, to focus on the collaboration between Wellacre Technology College, Ferrum High School, and Siyalungelwa High School as part of the Afri Twin project. The objectives of the research project are to determine the benefits of the Afri Twin project for the schools involved; to investigate the unique interaction between Wellacre, Ferrum, and Siyalungelwa; and to determine the cultural enrichment of learners and the multi-cultural interaction between the three schools. Data was collected through focus group interviews, in-depth interviews, and questionnaires. Data analysis led to the emergence of four major themes with categories and subcategories. The conclusion underlined the cultural tolerance that is established through the Afri Twin project, as well as the importance of financial support for promoting an improved learning environment. / Thesis (M.A. (Psychology)--North-West University, Potchefstroom Campus, 2009.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The purpose of this study was to explore the relation between anxiety symptoms and victimization experiences. It was expected that anxiety (both at age 5 and follow-up) and victimization (both overt and relational subtypes) would be heritable. It was also expected that early anxiety would predict future victimization experiences and that these experiences would be correlated with concurrent anxiety. Finally, it was predicted that early anxiety and high risk genotypes of the 5-HTTLPR serotonin transporter and DRD2 dopamine receptor genes would serve as diatheses, which upon experiencing the stressor of victimization, would put an individual at a multiplicatively greater risk for experiencing anxiety symptoms. Sixty-five children from the Southern Illinois Twins and Siblings Study (SITSS) were examined longitudinally. Parent-reported anxiety was obtained at age 5. Then during a follow-up study when the children were aged 6-16 years, parent- and self-report measures of anxiety and a self-report measure of victimization experiences were collected. Results indicated that the genetic influences on parent-reported anxiety at age 5 and total victimization were significant, with practically no influence of the shared environment. However, self-reported anxiety appeared to be largely due to the non-shared environment. A diathesis stress framework was not supported in this study, as early anxiety and high-risk genotype did not put an individual at greater risk for developing subsequent anxiety after being victimized. Although significant heritability was demonstrated for early anxiety and victimization, high risk alleles for both of the genes examined in this study (5-HTTLPR and DRD2) were not significant contributors to the demonstrated genetic underpinnings. Likewise, early anxiety did not serve as a diathesis for subsequent anxiety. However, age 5 and follow-up measures were positively correlated when both were reported by a parent, a result that did not remain true when measures were taken from different informants. The relation between anxiety symptoms and victimization also varied by informant and time. Early anxiety, as reported by a parent, was predictive of overt victimization specifically, whereas youth reports of anxiety were significantly related to both subtypes of victimization (both of which were measured at follow-up). However, parent-reported anxiety at follow-up was not significantly associated with any form of victimization. These results indicate that the relation between anxiety symptoms and victimization is complex and dependent on the type of victimization and reporter of anxiety symptoms. Understanding the maladaptive consequences of experiencing peer victimization as well as the psychological factors that put children at risk for being bullied will inform teachers, parents, and counselors how to effectively prevent and handle these maladaptive interactions. Given that peer victimization is a very common phenomenon, research in this field will generalize to a large portion of the population.

Accurate predictions of ground-borne vibration levels in the vicinity of an underground railway are greatly sought after in modern urban centers. Yet the complexity involved in simulating the underground environment means that it is necessary to make simplifying assumptions about this system. One such commonly made assumption is to ignore the effects of nearby embedded structures such as piled foundations and neighbouring tunnels. Through the formulation of computationally efficient mathematical models, this dissertation examines the dynamic behaviour of these two particular types of structures. The effect of the dynamic behaviour of these structures on the ground-borne vibration generated by an underground railway is considered. The modelling of piled foundations begins with consideration of a single pile embedded in a linear, viscoelastic halfspace. Two approaches are pursued: the modification of an existing plane-strain pile model; and the development of a fully three-dimensional model formulated in the wavenumber domain. Methods for adapting models of infinite structures to simulate finite systems using mirror-imaging techniques are described. The interaction between two neighbouring piles is considered using the method of joining subsystems, and these results are extended to formulate models for pile groups. The mathematical model is validated against existing numerical solutions and is found to be both accurate and efficient. A building model and a model for the pile cap are developed, and are attached to the piled foundation. A case study is used to illustrate a procedure for assessing the vibration performance of pile groups subject to vibration generated by an underground railway. The two-tunnel model uses the superposition of displacement fields to produce a fully coupled model of two infinitely long tunnels embedded in a homogeneous, viscoelastic fullspace. The significance of the interactions occurring between the two tunnels is quantified by calculating the insertion gains that result from the existence of a second tunnel. The results show that a high degree of inaccuracy exists in any underground-railway vibration prediction model that includes only one of the two tunnels present.

Ca(1-x)Nd2x/3TiO3 and MgTiO3-Ca0.61Nd0.26TiO3 composite ceramics were prepared by the mixed oxide route and characterised in terms of their structure, microstructure and properties. Ceramics sintered at 1450-1500oC achieved better than 95% of the theoretical density. X-Ray diffraction (XRD) revealed that Ca(1-x)Nd2x/3TiO3 ceramics were single phase for all compositions. For x ≤ 0.39 the structure was Pbnm with lattice parameters of a = b = √2ac and c = 2ac and a tilt system of a-a-c+. Compositions with x ≥ 0.48 could be better described by a C2/m structure with lattice parameters of a = b = c = 2ac. Scanning electron microscopy (SEM) revealed that the ceramics had grain sizes in the 5-70 μm range with abnormal grain growth for Nd3+ rich compositions. Images revealed that the twin domains in CaTiO3 were needle shaped and on addition of Nd3+ the domain morphology becomes more complex. The needle domain morphology returns for Ca0.43Nd0.38TiO3. High resolution electron microscopy (HAADF-STEM and electron diffraction) was used to probe cation-vacancy ordering (CVO) in the lattice. It was found that there was no CVO for x < 0.48 whilst at x = 0.48 there was evidence of a transition to a short range CVO. A transition to long range ordering is almost complete for the Ca0.1Nd0.6TiO3. The structural characteristics of Ca(1-x)Nd2x/3TiO3 ceramics as a function of temperature were investigated using in-situ XRD and Raman spectroscopy. All compositions were found to have the same structure across the entire temperature range. The Raman spectroscopy as a function of temperature indicated a possible transition with similar characteristics to a Curie temperature in a ferroelectric ceramic. The transition temperature was dependent on the cation ordering with the ceramics with greatest degree of disorder having the lowest transition temperature. The microwave dielectric properties of the samples were measured by a cavity resonance method in the 2-4GHz range. The relative permittivity (εr) was found to decrease from 180 for CaTiO3 to approximately 80 for Ca0.1Nd0.6TiO3 with an exponential dependence between the composition and the property. The temperature coefficient of resonant frequency (τf) ranged from +770ppmK-1 for CaTiO3 to +200ppmK-1 for Ca0.1Nd0.6TiO3. The Q x f for CaTiO3 was found to be 6000GHz and this increased to a maximum of 13000GHz for Ca0.7Nd0.2TiO3. After the Ca0.7Nd0.2TiO3 composition, the Q x f decreased to approximately 1100GHz for Ca0.1Nd0.6TiO3. The εr and τf were found to be mainly dependent on the composition of the ceramics whilst the Q x f value was more complex being dependent on the width of the twin domains in the grains. CaTiO3 samples fabricated by spark plasma sintering at 1150oC and above achieved better than 95% of the theoretical density. XRD revealed only a single phase with an orthorhombic Pbnm structure at room temperature and a tilt system of a-a-c+. SEM confirmed that the samples were single phase with grain size between 500nm-5μm. Transmission electron microscopy (TEM) of specimens sintered at 1150oC showed evidence of both (011) and (112) type domains. The τf of the ceramics was shown to be dependent on the volume of the unit cell, in agreement with the Bosman-Havinga equations. The ceramic sintered at 1150oC showed improvement in the Q x f value compared to samples prepared by conventional sintering. The structure, microstructure and properties of composite ceramics based on the MgTiO3-Ca0.61Nd0.26TiO3 system were investigated. Optimum properties were achieved at a composition of 0.8MgTiO3-0.2Ca0.61Nd0.26TiO3 with τf = -0.1ppmK-1, Q x f of 39000GHz and εr of 25.4. XRD revealed the presence of 3 phases including Ca0.61Nd0.26TiO3, MgTiO3 and MgTi2O5. The grain size of the ceramics was typically 5μm. The Q x f value was sensitive to the cooling rate and these changes could be related to changes in the vibrational properties of the lattice through changes in the lattice parameters.

The Digital Twin (DT) is a concept that is gaining more and more attention. A DT is a virtualversion of a physical product, which can be used in monitoring and developing said physical product.In this report we have discussed how a DT of a Transportable Culture Cabinet (TCC) could beimplemented, and its framework. The TCC is being developed at Q-linea and will be used for culturingblood samples for faster diagnosis of sepsis. A DT of a TCC could be used to monitor the statusof the sample and the physical product itself. Data from the TCC could also be used by the DTto detect and predict failures of the TCC such as malfunctioning batteries. The TCC can also bereferred to as a physical twin and will exist in the physical space, while the DT will exist in thevirtual space. An information processing layer (IPL) will connect the physical space and the virtualspace. A Digital Twin can either be a Digital Twin Prototype (DTP), a Digital Twin Environment(DTE), a Digital Twin Instance (DTI), or a Digital Twin Aggregate (DTA), which is an aggregationof all the DTIs. In this paper, we have solely focused on DTIs and DTAs. The Digital Twin ofthe Transportable culture cabinet will be a DTI, and by aggregating all the existing DTIs, or allDTIs belonging to the same hospital, a DTA will be created. Both DTIs and DTAs can be appliedwith different levels of complexity. Hence, we have proposed three levels of complexity of DTIs and DTAs. There are challenges of using a DT for a TCC. The user interface have to be user friendly forstaff that have little IT knowledge. Another challenge is the synchronisation between the TCC and DT.Since the TCC is mobile, a stable internet connection cannot be guaranteed. The TCC should thereforebe able to store the most important data.

In these challenging times caused by the COVID-19, technology that leverages Artificial Intelligence potential can help people cope with the pandemic. For example, people looking to perform physical exercises while in quarantine. We also find another opportunity in the widespread adoption of mobile smart devices, making complex Artificial Intelligence (AI) models accessible to the average user. Taking advantage of this situation, we propose a Smart Coaching experience on the Edge with our Digital Twin Coaching (DTC) architecture. Since the general population is advised to work from home, sedentarism has become prevalent. Coaching is a positive force in exercising, but keeping physical distance while exercising is a significant problem. Therefore, a Smart Coach can help in this scenario as it involves using smart devices instead of direct communication with another person. Some researchers have worked on Smart Coaching, but their systems often involve complex devices such as RGB-Depth cameras, making them cumbersome to use. Our approach is one of the firsts to focus on everyday smart devices, like smartphones, to solve this problem. Digital Twin Coaching can be defined as a virtual system designed to help people improve in a specific field and is a powerful tool if combined with edge technology. The DTC architecture has six characteristics that we try to fulfill: adaptability, compatibility, flexibility, portability, security, and privacy. We collected training data of 10 subjects using a 2D pose estimation model to train our models since there was no dataset of Coach-Trainee videos. To effectively use this information, the most critical pre-processing step was synchronization. This step synchronizes the coach and the trainee’s poses to overcome the trainee's action lag while performing the routine in real-time. We trained a light neural network called “Pose Inference Neural Network” (PINN) to serve as a fine-tuning architecture mechanism. We improved the generalist 2D pose estimation model with this trained neural network while keeping the time complexity relatively unaffected. We also propose an Angular Pose Representation to compare the trainee and coach's stances that consider the differences in different people's body proportions. For the PINN model, we use Random Search Optimization to come up with the best configuration. The configurations tested included using 1, 2, 3, 4, 5, and 10 layers. We chose the 2-Layer Neural Network (2-LNN) configuration because it was the fastest to train and predict while providing a fair tradeoff between performance and resource consumption. Using frame synchronization in pre-processing, we improved 76% on the test loss (Mean Squared Error) while training with the 2-LNN. The PINN improved the R2 score of the PoseNet model by at least 15% and at most 93% depending on the configuration. Our approach only added 4 seconds (roughly 2% of the total time) to the total processing time on average. Finally, the usability test results showed that our Proof of Concept application, DTCoach, was considered easy to learn and convenient to use. At the same time, some participants mentioned that they would like to have more features and improved clarity to be more invested in using the app frequently. We hope DTCoach can help people stay more active, especially in quarantine, as the application can serve as a motivator. Since it can be run on modern smartphones, it can quickly be adopted by many people.