Economic growth is the increase in the inflation-adjusted market value of the goods and services produced by an economy over time. The total output is the quantity of goods or servicesproduced in a given time period within a country. Sweden was affected by two crises during the period 2000-2010: a dot-com bubble and a financial crisis. How did these two crises affect the economic growth?     The changes of domestic output can be separated into four parts: changes in intermediate demand, final domestic demand, export demand and import substitution. The main purpose of this article is to analyze the economic growth during the period 2000-2010, with focus on the dot-com bubble in the beginning of the period 2000-2005, and the financial crisis at the end of the period 2005-2010. The methodology to be used is the structural decomposition method.     This investigation shows that the main contributions to the Swedish total domestic output increase in both the period 2000-2005 and the period 2005-2010 were the effect of domestic demand. In the period 2005-2010, financial crisis weakened the effect of export. The output of the primary sector went from a negative change into a positive, explained mainly by strong export expansion. In the secondary sector, export had most effect in the period 2000-2005. Nevertheless, domestic demand and import ratio had more effect during the financial crisis period. Lastly, in the tertiary sector, domestic demand can mainly explain the output growth in the whole period 2000-2010.

Energy shortages around the world necessitated research into alternative energy sources especially for domestic applications to reduce the load on conventional energy sources. This resulted in research done on the possibility of integrating solar energy with an aqua-ammonia diffusion absorption cycle specifically for domestic applications. The bubble pump can be seen as the heart of the diffusion absorption cycle, since it is responsible, in the absence of a mechanical pump, to circulate the fluid and to desorb the refrigerant (ammonia) from the mixture. It is thus of paramount importance to ensure that the bubble pump is designed efficiently. Various bubble pump simulation models have been developed over the years, but it was found that none of the existing models served as a good basis for application-specific design. Most of the models constrained too many parameters from the outset which made the investigation of the effects of certain parameters on the bubble pump’s performance impossible. According to the research, no bubble pump model investigated the effect of such a wide variety of factors including tube diameter, heat flux, mass flux, generator heat input and system pressure on the bubble pump’s lift height. A simulation model for a bubble pump for integration with a solar-driven aqua-ammonia diffusion absorption cycle was developed. It serves as a versatile design model to optimise the bubble pump for a large variety of conditions as well as changes in parameters. It was achieved by constraining the bubble pump dimensions and parameters as little as possible. A unique feature of this model was the fact that the bubble pump tube was divided into segments of known quality which made the length of the pipe completely dependent on the flow inside the pipe. It also made the demarcation of the flow development inside the tube easier. The model attempted to incorporate the most appropriate correlations for pressurised two-phase aqua-ammonia flow. The most appropriate void fraction correlation was found to be Abstract The design and optimisation of a bubble pump for an aqua-ammonia diffusion absorption heat pump the Rouhani-Axelsson (Rouhani I) correlation. It was mainly due to its exclusive use of thermophysical properties and the vapour quality. The most appropriate heat transfer coefficient that predicted the most realistic wall temperature, was the correlation from Riviera and Best (1999) which was the only correlation found in the literature developed with aqua-ammonia in mind. It was found that the published correlation could not reproduce their experimental results, and a modification of their correlation was made after which the simulation model’s results correlated well with the experimental values of Riviera and Best (1999). The main goal of the simulation model was to determine the height that the bubble pump was capable of lifting at the slug to churn flow transition under various conditions. The effect of varying a variety of parameters on the bubble pump lift height was also investigated. The results from Shelton & White Stewart (2002) were compared to the outputs of the simulation model, and it was found that their constraining of the submergence ratio limited their outputs, and that their heat inputs under different conditions was a bit optimistic. The simulation model’s outputs correlated well at higher tube diameters with the results from Shelton & White Stewart (2002), but at the lower diameters which was used in their study it was impossible to compare data, since their diameters was already in mini flow and micro flow regions. The temperatures also correlated well, all within 2% of the results from Shelton & White Stewart (2002). It was found that there couldn’t be just one set of optimised conditions and values for the bubble pump, but that each cycle with differing specifications and operating conditions would yield a unique set of optimised parameters. It was for that reason very important not to constrain parameters beforehand without investigating its effect on the bubble pump first. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

Energy shortages around the world necessitated research into alternative energy sources especially for domestic applications to reduce the load on conventional energy sources. This resulted in research done on the possibility of integrating solar energy with an aqua-ammonia diffusion absorption cycle specifically for domestic applications. The bubble pump can be seen as the heart of the diffusion absorption cycle, since it is responsible, in the absence of a mechanical pump, to circulate the fluid and to desorb the refrigerant (ammonia) from the mixture. It is thus of paramount importance to ensure that the bubble pump is designed efficiently. Various bubble pump simulation models have been developed over the years, but it was found that none of the existing models served as a good basis for application-specific design. Most of the models constrained too many parameters from the outset which made the investigation of the effects of certain parameters on the bubble pump’s performance impossible. According to the research, no bubble pump model investigated the effect of such a wide variety of factors including tube diameter, heat flux, mass flux, generator heat input and system pressure on the bubble pump’s lift height. A simulation model for a bubble pump for integration with a solar-driven aqua-ammonia diffusion absorption cycle was developed. It serves as a versatile design model to optimise the bubble pump for a large variety of conditions as well as changes in parameters. It was achieved by constraining the bubble pump dimensions and parameters as little as possible. A unique feature of this model was the fact that the bubble pump tube was divided into segments of known quality which made the length of the pipe completely dependent on the flow inside the pipe. It also made the demarcation of the flow development inside the tube easier. The model attempted to incorporate the most appropriate correlations for pressurised two-phase aqua-ammonia flow. The most appropriate void fraction correlation was found to be Abstract The design and optimisation of a bubble pump for an aqua-ammonia diffusion absorption heat pump the Rouhani-Axelsson (Rouhani I) correlation. It was mainly due to its exclusive use of thermophysical properties and the vapour quality. The most appropriate heat transfer coefficient that predicted the most realistic wall temperature, was the correlation from Riviera and Best (1999) which was the only correlation found in the literature developed with aqua-ammonia in mind. It was found that the published correlation could not reproduce their experimental results, and a modification of their correlation was made after which the simulation model’s results correlated well with the experimental values of Riviera and Best (1999). The main goal of the simulation model was to determine the height that the bubble pump was capable of lifting at the slug to churn flow transition under various conditions. The effect of varying a variety of parameters on the bubble pump lift height was also investigated. The results from Shelton & White Stewart (2002) were compared to the outputs of the simulation model, and it was found that their constraining of the submergence ratio limited their outputs, and that their heat inputs under different conditions was a bit optimistic. The simulation model’s outputs correlated well at higher tube diameters with the results from Shelton & White Stewart (2002), but at the lower diameters which was used in their study it was impossible to compare data, since their diameters was already in mini flow and micro flow regions. The temperatures also correlated well, all within 2% of the results from Shelton & White Stewart (2002). It was found that there couldn’t be just one set of optimised conditions and values for the bubble pump, but that each cycle with differing specifications and operating conditions would yield a unique set of optimised parameters. It was for that reason very important not to constrain parameters beforehand without investigating its effect on the bubble pump first. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

This dissertation focuses on mortgage defaults in Southern California during the housing bubble of the 2000s. The rapid decline in the housing market that precipitated the current recession has been accompanied by an unprecedented number of loan defaults and foreclosures. Recent studies have identified two major theories of default--the "double trigger" hypothesis, where negative equity and an income shock are necessary conditions for default--and "strategic default" where negative equity is a sufficient condition for default. This paper adds to the default literature by adding short sale as another possible outcome of mortgage default. The primary goal is to analyze the determinants of mortgage default to assist in understanding the conditions under which strategic behavior of home sales is most likely to occur. Data from Los Angeles County was analyzed from 2007 to 2010 for every closed sale, then coded into three possible sales outcomes: 1) Organic 2) Short Sale 3) Real Estate Owned (REO). A multinomial probit model was used to model homeowner decision-making based on the sale outcome. The model rejected the "double trigger" hypothesis, as it was found that income shocks do no have a significant effect on impacting the predicted probability for distressed sales. Education levels, the sales price of homes, credit card debt, and market price reductions were found to be significant variables in determining distressed sales outcomes, thereby confirming the strategic default hypothesis. The next section studied spatial association of short sales and REO to see if any contagion effects were present. It was found that both short sales and REO form into clusters of hot and cold spots. Social stigma is believed to impact consumer behavior, the theory was confirmed through the findings of contagion and spatial lag. The final section constructed a hedonic price model to capture the price effects that distressed sales have on neighborhood pricing. Foreclosures were found to have three times the negative impact on neighborhood pricing compared to short sales.

Syfte: Syftet med denna studie var att se hur och varför volatiliteten påverkades i DJIA, S&P 500 och NASDAQ Composite under IT-bubblan. Metod: Års- och månadsvolatiliteten för DJIA, S&P 500 och NASDAQ Composite har beräknats under 1995-2004 med hjälp av data från Yahoo Finance. Empiri: Resultatet visar att volatiliteten var väsentligt högre i NASDAQ Composite än vad den var i S&P 500 och DJIA som i sin tur höll en liknande volatilitet i förhållande till varandra. Analys: I analysen framträdde det att volatiliteten blev väsentligt högre i samband med att bubblan sprack under maj 2000 fram till dess att paniken lade sig kort efter maj 2002. Det fanns en hög överensstämmelse mellan denna rapport och övriga tidigare studier. Teorierna var mestadels väl applicerbara. Slutsats: Volatiliteten för DJIA, S&P 500 och NASDAQ Composite var som högst mellan 2000 och 2002 under undersökningsperioden 1995-2004. IT-bubblan uppstod samt sprack till följd av irrationellt investeringsbeteende bland investerarna på aktiemarknaden och paniken som uppstod efteråt gjorde att volatiliteten på aktiemarknaden höll sig förhållandevis hög fram tills den lade sig kort efter maj 2002. NASDAQ Composite hade högst volatilitet till följd av IT-bubblan medan DJIA och S&P 500 hade likvärdig volatilitet. Samtliga index följde ett liknande mönster, detta var troligtvis på grund av att företag från NASDAQ Composite kunde återfinnas i S&P 500 samt DJIA. / Purpose: The purpose of this thesis is to see how and why the volatility was affected in DJIA, S&P 500 and NASDAQ Composite during the Dot-com bubble. Method: The yearly and monthly volatility of DJIA, S&P 500 and NASDAQ Composite were computed with data from a period spanning 1995-2004, which were collected from Yahoo Finance. Empiricism: The results illustrate that the volatility was vastly higher in NASDAQ Composite than in DJIA and S&P 500 which in turn yielded a comparable volatility in relation to each other. Analysis: The analysis extracted the fact that the volatility rose considerably after the bubble burst during May 2000 and started waning after the panic died out circa May 2002. There were a relatively high harmony between the results of this report and the earlier studies which it was compared to. Conclusion: The volatility for DJIA, S&P 500 and NASDAQ 500 was higher between 200 and 2002 than during the rest of the observed period. The Dot-com bubble arose due to irrational investment behavior among investors and the panic which arose afterwards contributed to the increasing volatility which maintained a high level until it subsided after May 2002. NASDAQ Composite had the highest volatility during the Dot-com bubble while DJIA and S&P 500 had a similar volatility. All indexes followed a similar pattern, this was probably due to that companies from NASDAQ Composite reasonably should be found in S&P 500 and DJIA.

The rise velocity of injected air phase from the injection point toward the vadose zone is a critical factor in in-situ air sparging operations. It has been reported in the literature that air injected into saturated gravel rises as discrete air bubbles in bubbly flow of air phase. The objective of this study is to develop a quantitative technique to estimate the rise velocity of an air bubble in coarse porous media. The model is based on the macroscopic balance equation for forces acting on a bubble rising in a porous medium. The governing equation incorporates inertial force, added mass force, buoyant force, surface tension and drag force that results from the momentum transfer between the phases. The momentum transfer terms take into account the viscous as well as the kinetic energy losses at high velocities. Analytical solutions are obtained for steady, quasi-steady, and accelerated bubble rise velocities. Results show that air bubbles moving up through a porous medium equilibrate after a short travel time and very iv short distances of rise. It is determined that the terminal rise velocity of a single air bubble in an otherwise water saturated porous medium cannot exceed 18.5 cm/sec. The theoretical model results compared favorably with the experimental data reported in the literature. A dimensional analysis conducted to study the effect of individual forces indicates that the buoyant force is largely balanced by the drag force for bubbles with an equivalent radius of 0.2-0.5 cm. With increasing bubble radius, the dimensionless number representing the effect of the surface tension force decreases rapidly. Since the total inertial force is quite small, the accelerated bubble rise velocity can be approximated by the terminal velocity.

The objective of this thesis was to develop a novel understanding of the mechanics of two phase gas-liquid flows and sprays injected through industrial effervescent nozzles. This was done using detailed experimental investigations and scaling for two-phase flows and sprays. This study helps to quantify near-field liquid and gas phase statistics that are challenging and impossible to measure in the reactors due to inaccessibility restrictions. The development of nozzles is generally performed on air-water systems. My plan was to begin with the study of small-scale sprays (air and water) to compare to full scale industrial conditions at pilot operation (air-water) or at commercial operation (steam-bitumen), to determine size scaling relationships. The relationship between the lab scale air-water experiments and real industrial scale steam-bitumen has never been fully examined. Knowledge from this thesis will make the development of future nozzles with much less dependent on trial and error. This thesis was an attempt to establish fundamental scaling relationships for the prediction of two-phase spray behavior that can be applied directly to full scale industrial size nozzles that would be of very significant value to industries and to the scientific community in general. Understanding the performance of two phase nozzles through established scaling laws will aid in optimizing the two phase nozzle flow conditions and will serve as a major tool in nozzle design and development for future generation nozzles for many industrial applications.

Effervescent atomization has been a topic of considerable investigation in the literature due to its important advantages over other atomization mechanisms. This work contributes to the development of both effervescent atomizers and also laser-based techniques for spray investigation In order to develop non-intrusive measurement techniques for spray applications, a procedure is suggested to characterize the shape of droplets using image-based droplet analyzers. Image discretization which is a major source of error in droplet shape measurement is evaluated using a simulation. The accuracy of StereoPIV system in conducting droplet velocity measurement in a spray field is also investigated. To assist in the design of effervescent atomizers, bubble formation during gas injection from a micro-tube into liquid cross-flow is investigated using a Shadow-PIV/PTV system. The generated spray fields of two effervescent atomizers which operate using a porous and a typical multi-hole air injector are compared using qualitative images and Shadow-PTV measurement.

Co-rotating twin-screw extruders are unique and versatile machines that are used widely in the plastics and food processing industries. Due to the large number of operating variables and design parameters available for manipulation and the complex interactions between them, it cannot be claimed that these extruders are currently being optimally utilised. The most significant improvement to the field of twin-screw extrusion would be through the provision of a generally applicable dynamic process model that is both computationally inexpensive and accurate. This would enable product design, process optimisation and process controller design to be performed cheaply and more thoroughly on a computer than can currently be achieved through experimental trials. This thesis is divided into three parts: dynamic modelling, measurement and control. The first part outlines the development of a dynamic model of the extrusion process which satisfies the above mentioned criteria. The dynamic model predicts quasi-3D spatial profiles of the degree of fill, pressure, temperature, specific mechanical energy input and concentrations of inert and reacting species in the extruder. The individual material transport models which constitute the dynamic model are examined closely for their accuracy and computational efficiency by comparing candidate models amongst themselves and against full 3D finite volume flow models. Several new modelling approaches are proposed in the course of this investigation. The dynamic model achieves a high degree of simplicity and flexibility by assuming a slight compressibility in the process material, allowing the pressure to be calculated directly from the degree of over-fill in each model element using an equation of state. Comparison of the model predictions with dynamic temperature, pressure and residence time distribution data from an extrusion cooking process indicates a good predictive capability. The model can perform dynamic step-change calculations for typical screw configurations in approximately 30 seconds on a 600 MHz Pentium 3 personal computer. The second part of this thesis relates to the measurement of product quality attributes of extruded materials. A digital image processing technique for measuring the bubble size distribution in extruded foams from cross sectional images is presented. It is recognised that this is an important product quality attribute, though difficult to measure accurately with existing techniques. The present technique is demonstrated on several different products. A simulation study of the formation mechanism of polymer foams is also performed. The measurement of product quality attributes such as bulk density and hardness in a manner suitable for automatic control is also addressed. This is achieved through the development of an acoustic sensor for inferring product attributes using the sounds emanating from the product as it leaves the extruder. This method is found to have good prediction ability on unseen data. The third and final part of this thesis relates to the automatic control of product quality attributes using multivariable model predictive controllers based on both direct and indirect control strategies. In the given case study, indirect control strategies, which seek to regulate the product quality attributes through the control of secondary process indicators such as temperature and pressure, are found to cause greater deviations in product quality than taking no corrective control action at all. Conversely, direct control strategies are shown to give tight control over the product quality attributes, provided that appropriate product quality sensors or inferential estimation techniques are available.

The exchange of mass (gases, water & salts) between the oceans and the atmosphere is vital to the maintenance of life on earth. At high wind velocities most of this exchange is attributable to breaking wave entrained air bubbles. A vertical supported planar plunging jet experiment was used to model the entrainment process. The bubbles were detected with a dual tip conductivity probe and a video camera. At plunging jet velocities below 1.0m/s there is no bubble entrainment. This inception velocity appears to have a Froude and Weber number scaling for large rough turbulent jets. At jet velocities up to 5m/s air appeared to be entrained via intermittent air cavities at the jet - plunge pool intersection. The entrained air packets subsequently break in the two phase free shear layer under the entrainment point. At higher jet velocities there may be partial penetration of the aerated jet surface via pulsating induction cavities plus air entrainment via jet self aeration before impact. Plunging jet air flow data displays the different types of entrainment mechanisms. Mono-phase diffusion models can be successfully adapted to describe the shear layer developing zone. The diffusion of the air bubbles is approximately a Gaussian self similar process. The mean bubble velocity profiles can be modelled using the Goertler Error function or Hyperbolic Tangent models. The bubble spectra is approximately Lognormal with a geometric mean diameter of 1.0-2.0mm for a range of jet velocities. A bubble Weber number is found to model the maximum bubble size of approximately 10mm diameter. An original adaptation of the potential flow solution for the vortex sheet is shown to be a simple and reasonably accurate finite amplitude model for water surface gravity waves, especially in deep water. This model has some interesting features, such as both vertical and horizontal asymmetry and standing wave water profile modelling. A simple and possibly insightful model of wave growth due to the wind is introduced, using a constant sea surface Reynolds number U*.sqrt(L.F)/Gamma , where U* = wind friction velocity, L = wavelength, F = fetch, and Gamma = wave field vortex circulation per wavelength. The results may have application in the modelling of air - sea gas exchanges, predicting breaking wave forces on structures and the use of the planar plunging jet as an aeration device in industry.