Yes / With the advent of Wireless Sensor Networks (WSN) and its immense popularity in a wide range of applications, security has been a major concern for these resource-constraint systems. Alongside security, WSNs are currently being integrated with existing technologies such as the Internet, satellite, Wi-Max, Wi-Fi, etc. in order to transmit data over long distances and hand-over network load to more powerful devices. With the focus currently being on the integration of WSNs with existing technologies, security becomes a major concern. The main security requirement for WSN-integrated networks is providing end-to-end security along with the implementation of in-processing techniques of data aggregation. This can be achieved with the implementation of Homomorphic encryption schemes which prove to be computationally inexpensive since they have considerable overheads. This paper addresses the ID-issue of the commonly used Castelluccia Mykletun Tsudik (CMT) [12] homomorphic scheme by proposing an ID slotting mechanism which carries information pertaining to the security keys responsible for the encryption of individual sensor data. The proposed scheme proves to be 93.5% lighter in terms of induced overheads and 11.86% more energy efficient along with providing efficient WSN scalability compared to the existing scheme. The paper provides analytical results comparing the proposed scheme with the existing scheme thus justifying that the modification to the existing scheme can prove highly efficient for resource-constrained WSNs.

No / Regular Network Data Envelopment Analysis (NDEA) models deal with evaluating the performance of a set of decision-making units (DMUs) with a two-stage construction in the context of a deterministic data set. In the real world, however, observations may display a stochastic behavior. To the best of our knowledge, despite the existing research done with different data types, studies on two-stage processes with stochastic data are still very limited. This paper proposes a two-stage network DEA model with stochastic data. The stochastic two-stage network DEA model is formulated based on the satisficing DEA models of chance-constrained programming and the leader-follower concepts. According to the probability distribution properties and under the assumption of the single random factor of the data, the probabilistic form of the model is transformed into its equivalent deterministic linear programming model. In addition, the relationship between the two stages as the leader and the follower, respectively, at different confidence levels and under different aspiration levels, is discussed. The proposed model is further applied to a real case concerning 16 commercial banks in China in order to confirm the applicability of the proposed approach at different confidence levels and under different aspiration levels.

Yes / So far, the dominant comparative studies of competing distress prediction models (DPMs) have been restricted to the use of static evaluation frameworks and as such overlooked their performance over time. This study fills this gap by proposing a Malmquist Data Envelopment Analysis (DEA)-based multi-period performance evaluation framework for assessing competing static and dynamic statistical DPMs and using it to address a variety of research questions. Our findings suggest that (1) dynamic models developed under duration-dependent frameworks outperform both dynamic models developed under duration-independent frameworks and static models; (2) models fed with financial accounting (FA), market variables (MV), and macroeconomic information (MI) features outperform those fed with either MVMI or FA, regardless of the frameworks under which they are developed; (3) shorter training horizons seem to enhance the aggregate performance of both static and dynamic models.

Grid-connected inverters have wide application in the field of distributed generation and power quality. As the power level demanded by these applications increase, the design and performance evaluation of these converters become important. In the present work, a 50 kVA three-phase back-to-back connected inverter with output LCL filter is built to study design and performance evaluation aspects of grid-connected inverters. The first part of the work explores the split-capacitor resistive-inductive (SC-RL) passive damping scheme for the output LCL filter of a three-phase grid-connected inverter. The low losses in the SC-RL scheme makes it suitable for high power applications. The SCRL damped LCL filter is modelled using state space approach. Using this model, the power loss and damping are analysed. A method for component selection that minimizes the power loss in the damping resistors while keeping the system well damped is proposed. Analytical results show the losses to be in the range of 0.05-0.1% and the quality factor to be in the range of 2.0-2.5. These results are validated experimentally. In the second part of the work, a test method to evaluate the thermal performance of the semi-conductor devices of a three-phase grid-connected inverter is proposed. The method eliminates the need for high power sources, loads or any additional power converters for circulation of power. Only energy corresponding to the losses is consumed. The capability of the method to evaluate the thermal performance of the DC bus capacitors and the output filter components is also explored. The method can be used with different inverter configurations -three-wire or four-wire and for different PWM techniques. The method has been experimentally validated at a power level of 24kVA. In the third part of the work, the back-to-back connected inverter is programmed as a hardware grid simulator. The hardware grid simulator emulates the real-time grid and helps create grid disturbances often observed at the point of common coupling in an ac low voltage grid. A novel disturbance generation algorithm has been developed, analysed and implemented in digital controller using finite state machine model for control of the grid simulator. A wide range of disturbance conditions can be created using the developed algorithm. Experimental tests have been done on a linear purely resistive load, a non-linear diode-bridge load and a current-controlled inverter load to validate the programmed features of the grid simulator.

Current SME performance models suffer from a number of disadvantages. The models use intensively a business ratio approach, they look at SMEs as a homogenous group, they consider firms to be closed systems, they do not directly incorporate the impact of an enterprise’s innovation activities, and finally they are complex and rely on sophisticated statistical refining methods making them unpractical to use by SME managers. There are four major challenges when one tries to build SME performance models that lack these deficiencies. The first challenge is that the desired performance evaluation model must optimally incorporate both quantitative and qualitative input. The second challenge is that the model must incorporate non-financial input parameters, such as firm size and age (among others), in the performance evaluation models. The third is that the model must consider the variety of SMEs as concerns their business sectors, nationalities, sizes, and ages. The final challenge is that the model must be able to utilize existing limited information available from the SMEs bookkeeping practices in an optimal way. The thesis addresses three questions related to constructing a better SMEperformance model, namely (1) What are the advantages and disadvantages of the existing models used in evaluating SME performance? (2) What characterizes a comprehensive model for measuring SME performance with acknowledgement of the firm’s innovation activities? (3) How can a firm’s innovation activities be enhanced in relation to the firm’s external environment? To construct a model that copes with these challenges, I used a literature-based selection of parameters as well as a theory-based selection. I used both a conceptual approach and an empirical approach to discuss and propose a model, the Survival Index Value (or SIV) model, as an alternative to the existing performance models for SMEs. The major contributions of this thesis to the field of SME performance can be summarized in three outcomes: the SIV model as a new model of SME performance evaluation, the ASPEM as a new tool for strategic utilization of SME performance models, and a new approach to account for innovation in relation to the external environment of the firm using the IBAM tool. The work adds to the theory of the firm, as it presents a new way of evaluating firm performance. It also contributes to bridging the theory of the firm to organizational theory, by elevating the significance of networking and its impact on SME efficiency.

Thesis (MBA)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: People management, as a differentiating factor for an organisation in a competitive environment, has become a reality. This report focuses on practical best practices in making human capital the differentiating factor in any organisation. Eight topics are discussed, after positioning them against existing models and showing their relationship to the MARDEN diagnostic model of change management. The topics are: • Ensuring that your organisation's people management strategy delivers tangible results. • Entrenching a workplace culture that delivers optimum performance. • Creating high performance workplace practices. • Achieving growth through competency-based people performance and development. • Leveraging superior performance through team based leadership. • Strategy processes in developing supply chains and workplaces into major competitive advantages. • Transforming knowledge into power by becoming a true learning organisation. • Enabling your organisation to implement a successful change and transformation process. The topics are each evaluated in further detail, in order to drill down into specific practices and issues that need to be addressed by organisations. This ensures that practical best practices are positioned to ensure that the human capital, as a major intangible asset, is nurtured into high performing teams and a cohesive group. / AFRIKAANSE OPSOMMING: Mensebestuur as 'n differensierende faktor vir 'n organisasie in 'n mededingende omgewing is 'n realiteit. Hierdie verslag fokus op praktiese beste praktyke vir die versekering om mense-kapitaal as die differensiasie faktor te vestig in enige organisasie. Daar word agt onderwerpe bespreek teen die agtergrond van bestaande modelle, asook die verwantskap met die MARDEN diagnostiese model van veranderingsbestuur as evaluerings basis. Die onderwerpe is: • Versekering dat die organisasie se mense-bestuur strategie tasbare resultate lewer. • Vestiging van 'n werkplek kultuur wat optimale resultate verseker. • Vestiging van hoë verrigting werkplek praktyke. • Groei stimulasie deur bevoegdheid gebasseerde mense-prestasie en ontwikkeling. • Hefkrag van buitengewone prestasie deur span gebasseerde leierskap. • Strategiese prosesse deur die ontwikkeling van waardekettings en werkplek tot mededingende voordele. • Omskakeling van kennis in mag deur 'n ware lerende organisasie. • Bemagtiging van 'n organisasie deur die implimentering van suksesvolle veranderings en transformasie prosesse. Elke onderwerp word verder ondersoek in meer praktyke en detail wat deur organisasies geadresseer moet word om te verseker dat die beste praktyke toegepas word. Sodoende word die organisasie by gestaan om mense-kapitaal te posisioneer as die belangrikste ontasbare bate en ontwikkel in hoë prestasie spanne en 'n samehorige groep.

Recent research has indicated that although security systems are developing, illegal intrusion to computers is on the rise. The research conducted here illustrates that improving intrusion detection and prevention methods is fundamental for improving the overall security of systems. This research includes the design of a novel Intrusion Detection System (IDS) which identifies four levels of visibility of attacks. Two major areas of security concern were identified: speed and volume of attacks; and complexity of multistage attacks. Hence, the Multistage Intrusion Detection and Prevention System (MIDaPS) that is designed here is made of two fundamental elements: a multistage attack engine that heavily depends on attack trees and a Denial of Service Engine. MIDaPS were tested and found to improve current intrusion detection and processing performances. After an intensive literature review, over 25 GB of data was collected on honeynets. This was then used to analyse the complexity of attacks in a series of experiments. Statistical and analytic methods were used to design the novel MIDaPS. Key findings indicate that an attack needs to be protected at 4 different levels. Hence, MIDaPS is built with 4 levels of protection. As, recent attack vectors use legitimate actions, MIDaPS uses a novel approach of attack trees to trace the attacker's actions. MIDaPS was tested and results suggest an improvement to current system performance by 84% whilst detecting DDOS attacks within 10 minutes.

The growing demand on the variety of internet applications requires management of large scale networks by efficient Quality of Service (QoS) routing, which considerably contributes to the QoS architecture. The biggest contemporary drawback in the maintenance and distribution of the global state is the increase in communication overheads. Unbalancing in the network, due to the frequent use of the links assigned to the shortest path retaining most of the network loads is regarded as a major problem for best effort service. Localised QoS routing, where the source nodes use statistics collected locally, is already described in contemporary sources as more advantageous. Scalability, however, is still one of the main concerns of existing localised QoS routing algorithms. The main aim of this thesis is to present and validate new localised algorithms in order to develop the scalability of QoS routing. Existing localised routing, Credit Based Routing (CBR) and Proportional Sticky Routing (PSR), use the blocking probability as a factor in selecting the routing paths and work with either credit or flow proportion respectively, which makes impossible having up-to-date information. Therefore our proposed Highest Minimum Bandwidth (HMB) and Highest Average Bottleneck Bandwidth History (HABBH) algorithms utilise bandwidth as the direct QoS criterion to select routing paths. We introduce an Integrated Delay Based Routing and Admission Control mechanism. Using this technique Minimum Total Delay (MTD), Low Fraction Failure (LFF) and Low Path Failure (LPF) were compared against the global QoS routing scheme, Dijkstra, and localised High Path Credit (HPC) scheme and showed superior performance. The simulation with the non-uniformly distributed traffic reduced blocking probability of the proposed algorithms. Therefore, we advocate the algorithms presented in the thesis, as a scalable approach to control large networks. We strongly suggest that bandwidth and mean delay are feasible QoS constraints to select optimal paths by locally collected information. We have demonstrated that a few good candidate paths can be selected to balance the load in the network and minimise communication overhead by applying the disjoint paths method, recalculation of candidate paths set and dynamic paths selection method. Thus, localised QoS routing can be used as a load balancing tool in order to improve the network resource utilization. A delay and bandwidth combination is one of the future prospects of our work, and the positive results presented in the thesis suggest that further development of a distributed approach in candidate paths selection may enhance the proposed localised algorithms.

Over recent years, wireless communication systems have been experiencing a dramatic and continuous growth in the number of subscribers, thus placing extra demands on system capacity. At the same time, keeping Quality of Service (QoS) at an acceptable level is a critical concern and a challenge to the wireless network designer. In this sense, performance analysis must be the first step in designing or improving a network. Thus, powerful mathematical tools for analysing most of the performance metrics in the network are required. A good modelling and analysis of the wireless cellular networks will lead to a high level of QoS. In this thesis, different analytical models of various handoff schemes and resource re-allocation in homogeneous and heterogeneous wireless cellular networks are developed and investigated. The sustained increase in users and the request for advanced services are some of the key motivations for considering the designing of Hierarchical Cellular Networks (HCN). In this type of system, calls can be blocked in a microcell flow over to an overlay macrocell. Microcells in the HCN can be replaced by WLANs as this can provide high bandwidth and its users have limited mobility features. Efficient sharing of resources between wireless cellular networks and WLANs will improve the capacity as well as QoS metrics. This thesis first presents an analytical model for priority handoff mechanisms, where new calls and handoff calls are captured by two different traffic arrival processes, respectively. Using this analytical model, the optimised number of channels assigned to II handover calls, with the aim of minimising the drop probability under given network scenarios, has been investigated. Also, an analytical model of a network containing two cells has been developed to measure the different performance parameters for each of the cells in the network, as well as altogether as one network system. Secondly, a new solution is proposed to manage the bandwidth and re-allocate it in a proper way to maintain the QoS for all types of calls. Thirdly, performance models for microcells and macrocells in hierarchical cellular networks have been developed by using a combination of different handoff schemes. Finally, the microcell in HCN is replaced by WLANs and a prioritised vertical handoff scheme in an integrated UMTS/WLAN network has been developed. Simulation experiments have been conducted to validate the accuracy of these analytical models. The models have then been used to investigate the performance of the networks under different scenarios.

The Best PhD Thesis in the Faculties of Architecture, Arts, Business & Economics, Education, Law and Social Sciences (University of Hong Kong), Li Ka Shing Prize, 2005-2006. / published_or_final_version / abstract / Real Estate and Construction / Doctoral / Doctor of Philosophy