This thesis deals with multi-stage stochastic programming in the context of random process representation. Basic structure for random process is a scenario tree. The thesis introduces general and stage-independent scenario tree and their properties. Scenario trees can be also combined with Markov chains which describe the state of the system and determine which scenario tree should be used. Another structure which enables reduce the complexity of the problem is a scenario lattice. Scenario generation is performed using moment method. Scenario trees are used for representation of random returns as the input to the investment problem.

This thesis deals with multi-stage stochastic programming in the context of random process representation. Basic structure for random process is a scenario tree. The thesis introduces general and stage-independent scenario tree and their properties. Scenario trees combined with Markov chains are also introduced. Markov chains states determine if there is a crisis period or not. Information about historical number of crises helps us to construct a scenario lattice. Scenario generation is performed using moment method. Scenario trees are used as an input to the investment problem.

No description available.

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.

No description available.

Reservoir release patterns are determined by a number of purposes, the most fundamental of which is to manage water resources for human use. Managing our water resources means not only controlling the water in reservoirs but also determining the optimum release rate taking into account factors such as reservoir stability, power generation, water supply for domestic, industrial, and agricultural uses, and the river ecosystem. However, riverbank stability has generally not been considered as a factor, even though release rates may have a significant effect on downstream riverbank stability. Riverbank retreat not only impacts land properties but also damages structures along the river such as roads, bridges and even buildings. Thus, reservoir releases need to also take into account the downstream riverbank stability and erosion issues. The study presented here investigates the riverbank stability and erosion at five study sites representing straight as well as inside and outside channel meander bends located on the lower Roanoke River near Scotland Neck, North Carolina. Extensive laboratory and field experiments were performed to define the hydraulic and geotechnical properties of the riverbank soils at each site. Specifically, soil water characteristic curves were determined using six different techniques and the results compared to existing mathematical models. Hydraulic conductivity was estimated using both laboratory and in situ tests. Due to the wide range of experimentally obtained values, the values determined by each of the methods was used for transient seepage modeling and the modeling results compared to the actual ground water table measured in the field. The results indicate that although the hydraulic conductivities determined by in situ tests were much larger than those typically reported for the soils by lab tests, numerical predictions of the ground water table using the in situ values provided a good fit for the measured ground water table elevation. Shear strengths of unsaturated soils were determined using multistage suction controlled direct shear tests. The test method was validated, and saturated and unsaturated shear strength parameters determined. These parameters, which were determined on the basis of results from both laboratory and field measurements, and the associated boundary conditions, which took into account representative flow rates and patterns including peaking, drawdown and step-down scenarios, were then utilized for transient seepage analyses and slope stability analyses performed using SLIDE, a software package developed by Rocscience. The analyses confirmed that the riverbanks are stable for all flow conditions, although the presence of lower permeability soils in some areas may create excess pore water pressures, especially during drawdown and step-down events, that result in the slope becoming unstable in those locations. These findings indicate that overall, the current reservoir release patterns do not cause adverse impacts on the downstream riverbanks, although a gradual drawdown after a prolonged high flow event during the wet season would reduce unfavorable conditions that threaten riverbank stability. / Ph. D.

El crecimiento de los computadores paralelos basados en redes de altas prestaciones ha aumentado el interés y esfuerzo de la comunidad investigadora en desarrollar nuevas técnicas que permitan obtener el mejor rendimiento de estas redes. En particular, el desarrollo de nuevas técnicas que permitan un encaminamiento eficiente y que reduzcan la latencia de los paquetes, aumentando así la productividad de la red. Sin embargo, una alta tasa de utilización de la red podría conllevar el que se conoce como "congestión de red", el cual puede causar una degradación del rendimiento. El control de la congestión en redes multietapa es un problema importante que no está completamente resuelto. Con el fin de evitar la degradación del rendimiento de la red cuando aparece congestión, se han propuesto diferentes mecanismos para el control de la congestión. Muchos de estos mecanismos están basados en notificación explícita de la congestión. Para este propósito, los switches detectan congestión y dependiendo de la estrategia aplicada, los paquetes son marcados con la finalidad de advertir a los nodos origenes. Como respuesta, los nodos origenes aplican acciones correctivas para ajustar su tasa de inyección de paquetes. El propósito de esta tesis es analizar las diferentes estratégias de detección y corrección de la congestión en redes multietapa, y proponer nuevos mecanismos de control de la congestión encaminados a este tipo de redes sin descarte de paquetes. Las nuevas propuestas están basadas en una estrategia más refinada de marcaje de paquetes en combinación con un conjunto de acciones correctivas justas que harán al mecanismo capaz de controlar la congestión de manera efectiva con independencia del grado de congestión y de las condiciones de tráfico. / Ferrer Pérez, JL. (2012). DESIGN OF EFFICIENT PACKET MARKING-BASED CONGESTION MANAGEMENT TECHNIQUES FOR CLUSTER INTERCONNECTS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18197

Yes / Solar energy, amongst all renewable energies, has attracted inexhaustible attention all over the world as a supplier of sustainable energy. The energy requirement of major seawater desalination processes such as multistage flash (MSF), multi-effect distillation (MED) and reverse osmosis (RO) are fulfilled by burning fossil fuels, which impact the environment significantly due to the emission of greenhouse gases. The integration of solar energy systems into seawater desalination processes is an attractive and alternative solution to fossil fuels. This study aims to (i) assess the progress of solar energy systems including concentrated solar power (CSP) and photovoltaic (PV) to power both thermal and membrane seawater desalination processes including MSF, MED, and RO and (ii) evaluate the economic considerations and associated challenges with recommendations for further improvements. Thus, several studies on a different combination of seawater desalination processes of solar energy systems are reviewed and analysed concerning specific energy consumption and freshwater production cost. It is observed that although solar energy systems have the potential of reducing carbon footprint significantly, the cost of water production still favours the use of fossil fuels. Further research and development on solar energy systems are required to make their use in desalination economically viable. Alternatively, the carbon tax on the use of fossil fuels may persuade desalination industries to adopt renewable energy such as solar.

The Reverse Osmosis (RO) process has been considered to be one of the most widely utilised techniques for brackish water desalination for its capabilities to produce high-quality water. The RO process characterised by its low energy consumption compared to thermal distillation processes, leading to reduced overall water production cost. To systematically understand the transport phenomena of solvent and solutes via the membrane texture, several mathematical models were developed. This interestingly aids to conduct a huge amount of simulation and optimisation studies to judge the influence of control variables on the performance indexes and to adjust the key variables at optimum values to realise optimum production indexes. In this research, a specific accurate model for a single spiral wound RO process has been successfully developed and used to build accurate models for the multistage brackish water RO desalination process of two different designs. The robustness of the model developed was confirmed via validation against the experimental data collected from simple design of RO system and complicated design of RO system of Arab Potash Company (APC). This is followed by a thorough simulation of the RO process to explore the influence of operating conditions on the process performance indicators. Recently, several contributions were made in this thesis that specifically comprises the improvement of the original design of brackish water RO desalination process. The influence of a retentate recycle design is investigated on the process performance. Moreover, evaluation and minimisation of specific energy consumption (expressed in kWh/m3 of freshwater production) is carried out on the simple and complicated designs of RO process by implementing an energy recovery device. Also, the most suitable brand of membranes was explored for the RO system from a set of different brands of membrane to attain the highest-performance rejection at lowest energy consumption compared to the original membrane. Furthermore, a single optimisation framework was developed to mitigate the specific energy consumption of simple and complicated designs of brackish water RO desalination process. Finally, a thermodynamic limitations and exergy analysis of the complicated design of RO system are outlined via a thoroughly study to investigate the locations of high exergy destruction. These contributions were verified as they promoted the separation performance at a significant energy saving. / Mutah University, Jordan

Among many seawater desalination processes, the multistage flash (MSF) desalination process is a major source of fresh water around the world. The most costly design and operation problem in seawater desalination is due to scale formation and corrosion problems. Fouling factor is one of the many important parameters that affect the operation of MSF processes. This thesis therefore focuses on determining the optimal design and operation strategy of MSF desalinations processes under fouling which will meet variable demand of freshwater. First, a steady state model of MSF is developed based on the basic laws of mass balance, energy balance, and heat transfer equations with supporting correlations for physical properties. gPROMS software is used to develop the model which is validated against the results reported in the literature. The model is then used in further investigations. Based on actual plant data, a simple dynamic fouling factor profile is developed which allows calculation of fouling factor at different time (season of the year). The role of changing brine heater fouling factor with varying seawater temperatures (during the year) on the plant performance and the monthly operating costs for fixed water demand and fixed top brine temperature are then studied. The total monthly operation cost of the process are minimised while the operating parameters such as make up, brine recycle flow rate and steam temperature are optimised. It was found that the seasonal variation in seawater temperature and brine heater fouling factor results in significant variations in the operating parameters and operating costs. The design and operation of the MSF process are optimized in order to meet variable demands of freshwater with changing seawater temperature throughout the day and throughout the year. On the basis of actual data, the neural network (NN) technique has been used to develop a correlation for calculating dynamic freshwater demand/consumption profiles at different times of the day and season. Also, a simple polynomial based dynamic seawater temperature correlation is developed based on actual data. An intermediate storage tank between the plant and the client is considered. The MSF process model developed earlier is coupled with the dynamic model for the storage tank and is incorporated into the optimization framework within gPROMS. Four main seasons are considered in a year and for each season, with variable freshwater demand and seawater temperature, the operating parameters are optimized at discrete time intervals, while minimizing the total daily costs. The intermediate storage tank adds flexible scheduling and maintenance opportunity of individual flash stages and makes it possible to meet variable freshwater demand with varying seawater temperatures without interrupting or fully shutting down the plant at any-time during the day and for any season. Finally, the purity of freshwater coming from MSF desalination plants is very important when the water is used for industrial services such as feed of boiler to produce steam. In this work, for fixed water demand and top brine temperature, the effect of separation efficiency of demister with seasonal variation of seawater temperatures on the final purity of freshwater for both cleaned and fouled demister conditions is studied. It was found that the purity of freshwater is affected by the total number of stages. Also to maintain the purity of freshwater product, comparatively large number of flash stage is required for fouled demister.