Plastic pollution has become of public concern recently and only in the last decades the need of quantifying loads of plastic in the marine environment and identifying their ultimate destination has been urged as a mean to point at where interventions should concentrate. The Arabian seas (Red Sea and Arabian Gulf) have oceanographic features that candidate them as accumulation zones for marine plastics, but, especially the Red Sea, are largely unexplored. The dissertation here presented provides significant advances in the understanding of the marine plastic distribution in the two basins. Despite the initial hypothesis, the Red Sea was found to hold a remarkably low abundance of plastic particles in its surface waters. Similarly, previous assessments have reported the same in the Arabian Gulf. In line with the global estimates, only a small portion of the plastic that is discarded yearly in the marine environment is found in its surface waters, implying the presence of removal processes. However, the unexpectedly low loads of floating plastics in the Arabian seas indicate that sinks are likely more significant here than elsewhere. In the Red Sea, an extensive survey of macroplastic stranded on shores, globally considered a major sink of marine plastic, has indicated that Avicennia marina mangrove forests, through the mesh created by their pneumatophores, contribute significantly more than unvegetated shores in retaining plastics. Loads of plastic in the Arabian Gulf mangrove stands, more impacted by coastal development than stands in the Red Sea, are even larger. The role of mangroves as significant sinks of plastics is further corroborated by the finding that the burial rates of plastic in their sediments follow an exponential increase in line with the global plastic production increase, ultimately demonstrating that plastic is likely sequestered there permanently. Mangrove forests alone are, however, not enough to justify the mismatch between plastic inputs and loads in surface waters. The experimental finding showed here that coral structures can passively trap substantial loads of microplastics and the large extension of reefs, especially in the Red Sea, suggest that reefs might constitute a missing sink of marine plastic in the basin worth exploring.

Global simulations of atmospheric methyl chloride (CH3Cl) are conducted using the GEOS-Chem model in order to understand better its sources and sinks. Though CH3Cl is one of the most abundant organic chlorine species in the stratosphere, not much is known about its sources and the budget remains unbalanced. In addition to the known sources (1.5 Tg yr-1) from ocean, biomass burning, incineration/industry, salt marshes, and wetlands, a hypothetical aseasonal biogenic source of 2.9 Tg yr-1 is added in order to match needed emissions. Observations from 7 surface sites and 8 aircraft field experiments are used to evaluate the model simulations. The model results with a priori emissions and sinks reproduce CH3Cl observations at northern mid and high latitudes reasonably well. However, the seasonal variation of CH3Cl at southern mid and high latitudes is severely overestimated. Simulated vertical profiles show disagreements in the vicinities of major sources, principally reflecting the uncertainties in the estimated distributions of our added pseudo-biogenic and the biomass burning sources. Inverse modeling is applied to obtain optimal source distributions of CH3Cl on the basis of surface and aircraft observations and model results. We resolve the seasonal dependence of the biogenic and biomass burning sources for each hemisphere. The aircraft in situ measurements are found to provide better constraints on the emission sources than surface measurements. The a posteriori emissions result in better agreement with the observations particularly at southern high latitudes. The a posteriori biogenic and biomass burning source decrease by 13 and 11% to 2500 and 545 Gg yr-1, respectively, while the a posteriori net ocean source increases by about a factor of 2 to 761 Gg yr-1. The decrease in biomass burning emissions is largely due to the reduction in the emissions in seasons other than spring in the northern hemisphere. The inversion results indicate that the biogenic source has a clear winter minimum in both hemispheres, likely reflecting the decrease of biogenic activity during that season.

Forced air cooling of electronic packages is enhanced through the use of extended surfaces or heat sinks that reduce boundary resistance allowing heat generating devices to operate at lower temperatures, thereby improving reliability. Unfortunately, the clearance zones or bypass regions surrounding the heat sink, channel some of the cooling air mass away from the heat sink, making it difficult to accurately estimate thermal performance. The design of an "optimized" heat sink requires a complete knowledge of all thermal resistances between the heat source and the ambient air, therefore, it is imperative that the boundary resistance is properly characterized, since it is typically the controlling resistance in the path. Existing models are difficult to incorporate into optimization routines because they do not provide a means of predicting flow bypass based on information at hand, such as heat sink geometry or approach velocity. <br /><br /> A procedure is presented that allows the simultaneous optimization of heat sink design parameters based on a minimization of the entropy generation associated with thermal resistance and fluid pressure drop. All relevant design parameters such as geometric parameters of a heat sink, source and bypass configurations, heat dissipation, material properties and flow conditions can be simultaneously optimized to characterize a heat sink that minimizes entropy generation and in turn results in a minimum operating temperature of an electronic component. <br /><br /> An analytical model for predicting air flow and pressure drop across the heat sink is developed by applying conservation of mass and momentum over the bypass regions and in the flow channels established between the fins of the heat sink. The model is applicable for the entire laminar flow range and any type of bypass (side, top or side and top both) or fully shrouded configurations. During the development of the model, the flow was assumed to be steady, laminar, developing flow. The model is also correlated to a simple equation within 8% confidence level for an easy implementation into the entropy generation minimization procedure. The influence of all the resistances to heat transfer associated with a heat sink are studied, and an order of magnitude analysis is carried out to include only the influential resistances in the thermal resistance model. Spreading and material resistances due to the geometry of the base plate, conduction and convection resistances associated with the fins of the heat sink and convection resistance of the wetted surfaces of the base plate are considered for the development of a thermal resistance model. The thermal resistance and pressure drop model are shown to be in good agreement with the experimental data over a wide range of flow conditions, heat sink geometries, bypass configurations and power levels, typical of many applications found in microelectronics and related fields. Data published in the open literature are also used to show the flexibility of the models to simulate a variety of applications. <br /><br /> The proposed thermal resistance and pressure drop model are successfully used in the entropy generation minimization procedure to design a heat sink with bypass for optimum dimensions and performance. A sensitivity analysis is also carried out to check the influence of bypass configurations, power levels, heat sink materials and the coverage ratio on the optimum dimensions and performance of a heat sink and it is found that any change in these parameters results in a change in the optimized heat sink dimensions and flow conditions associated with the application for optimal heat sink performance.

Forced air cooling of electronic packages is enhanced through the use of extended surfaces or heat sinks that reduce boundary resistance allowing heat generating devices to operate at lower temperatures, thereby improving reliability. Unfortunately, the clearance zones or bypass regions surrounding the heat sink, channel some of the cooling air mass away from the heat sink, making it difficult to accurately estimate thermal performance. The design of an "optimized" heat sink requires a complete knowledge of all thermal resistances between the heat source and the ambient air, therefore, it is imperative that the boundary resistance is properly characterized, since it is typically the controlling resistance in the path. Existing models are difficult to incorporate into optimization routines because they do not provide a means of predicting flow bypass based on information at hand, such as heat sink geometry or approach velocity. <br /><br /> A procedure is presented that allows the simultaneous optimization of heat sink design parameters based on a minimization of the entropy generation associated with thermal resistance and fluid pressure drop. All relevant design parameters such as geometric parameters of a heat sink, source and bypass configurations, heat dissipation, material properties and flow conditions can be simultaneously optimized to characterize a heat sink that minimizes entropy generation and in turn results in a minimum operating temperature of an electronic component. <br /><br /> An analytical model for predicting air flow and pressure drop across the heat sink is developed by applying conservation of mass and momentum over the bypass regions and in the flow channels established between the fins of the heat sink. The model is applicable for the entire laminar flow range and any type of bypass (side, top or side and top both) or fully shrouded configurations. During the development of the model, the flow was assumed to be steady, laminar, developing flow. The model is also correlated to a simple equation within 8% confidence level for an easy implementation into the entropy generation minimization procedure. The influence of all the resistances to heat transfer associated with a heat sink are studied, and an order of magnitude analysis is carried out to include only the influential resistances in the thermal resistance model. Spreading and material resistances due to the geometry of the base plate, conduction and convection resistances associated with the fins of the heat sink and convection resistance of the wetted surfaces of the base plate are considered for the development of a thermal resistance model. The thermal resistance and pressure drop model are shown to be in good agreement with the experimental data over a wide range of flow conditions, heat sink geometries, bypass configurations and power levels, typical of many applications found in microelectronics and related fields. Data published in the open literature are also used to show the flexibility of the models to simulate a variety of applications. <br /><br /> The proposed thermal resistance and pressure drop model are successfully used in the entropy generation minimization procedure to design a heat sink with bypass for optimum dimensions and performance. A sensitivity analysis is also carried out to check the influence of bypass configurations, power levels, heat sink materials and the coverage ratio on the optimum dimensions and performance of a heat sink and it is found that any change in these parameters results in a change in the optimized heat sink dimensions and flow conditions associated with the application for optimal heat sink performance.

This study has two main objectives: The performance evaluation of existing microchannel heat sinks using a CFD model, and the dimensional optimization of various heat sinks by minimizing the total thermal resistance. For the analyses, the geometric modeling is performed using the software GAMBIT while the thermal analysis is performed with FLUENT. The developed model compares very well with those available in the literature. Eight different metal-polymer microchannel heat sinks are analyzed using the model to find out how much heat could be provided to the systems while keeping the substrate temperatures below 85&deg / C under a constant pumping power requirement. Taking the objective function as the total thermal resistance, the optimum geometries have been obtained for the mentioned metal-polymer heat sinks as well as more conventional silicon ones. The results of the optimization code agreed very well with available ones in the literature. In the optimization study, the Intel Core i7-900 Desktop Processor Extreme Edition Series is considered as a reference processor which is reported to dissipate 130 W of heat and to have chip core dimensions of 1.891 cm &times / 1.44 cm. A dimensional optimization study has been performed for various copper and silicon microchannel heat sinks to cool down this processor. To the best of the author&rsquo / s knowledge, this study contributes to the literature in that, as opposed to the available analytical microchannel optimization studies considering constant thermophysical properties at the fluid inlet temperature, the properties are evaluated at the area weighted average of the fluid inlet and iteratively calculated outlet temperatures. Moreover, the effects of the thermal and hydrodynamic entrance regions on heat transfer and flow are also investigated.

The thermal interface layer can be a limiting element in the cooling of microelectronic devices. Conventional solders, pastes and pads are no longer sufficient to handle the high heat fluxes associated with connecting the device to the sink. Carbon nanotubes(CNTs) have been proposed as a possible thermal interface material(TI M), due to their thermal and mechanical properties, and prior research has established the effectiveness of vertically arranged CNT arrays to match the capabilities of the best conventional TIMs. However, to reach commercial applicability, many improvements need to be made in terms of improving thermal and mechanical properties as well as cost and manufacturing ease of the layer. Prior work demonstrated a simple method to transfer and bond CNT arrays through the use of a nanometer thin layer of gold as a bonding layer. This study sought to improve on that technique. By controlling the rate of deposition, the bonding temperature was reduced. By using different metals and thinner layers, the potential cost of the technique was reduced. Through the creation of a patterned array, a phase change element was able to be incorporated into the technique. The various interfaces created are characterized mechanically and thermally.

Reliable prediction of climate change and its impact on and feedbacks from terrestrial carbon cycles requires realistic representation of physiological and ecological processes in coupled climate-carbon models. This is hampered by various deficiencies in model structures and parameters. The goal of my study is to improve model realism by incorporating latest advances of fundamental eco-physiological processes and further to use such improved models to investigate climate-carbon interactions at regional to global scales. I focus on the CO₂ diffusion within leaves (a key plant physiological process) and large-scale disturbances (a fundamental ecological process) as extremely important but not yet in current models. The CO₂ diffusion within plant leaves is characterized by mesophyll conductance (g[subscript m]), which strongly influences photosynthesis. I developed a g[subscript m] model by synthesizing new advances in plant-physiological studies and incorporated this model into the Community Land Model (CLM), a state-of-art climate-carbon model. I updated associated photosynthetic parameters based on a large dataset of leaf gas exchange measurements. Major findings are: (1) omission of g[subscript m] underestimates the maximum carboxylation rate and distorts its relationships with other parameters, leading to an incomplete understanding of leaf-level photosynthesis machinery; (2) proper representation of g[subscript m] is necessary for climate-carbon models to realistically predict carbon fluxes and their responsiveness to CO₂ fertilization; (3) fine tuning of parameters may compensate for model structural errors in contemporary simulations but introduce large biases in future predictions. Further, I have corrected a numerical deficiency of CLM in its calculation of carbon/water fluxes, which otherwise can bias model simulations. Large-scale disturbances of terrestrial ecosystems strongly affect their carbon sink strength. To provide insights for modeling these processes, I used satellite products to examine the temporal-spatial patterns of greenness after a massive ice storm. I found that the greenness of impacted vegetation recovered rapidly, especially in lightly and severely impacted regions. The slowest rebound occurred over moderately impacted areas. This nonlinear pattern was caused by an integrated effect of natural regrowth and human interventions. My results demonstrate mechanisms by which terrestrial carbon sinks could be significantly affected and help determine how these sinks will behave and so affect future climate. / text

No description available.

The aim of this study is to identify the opportunities that currently exist in the Egyptian market in order for Franke to make a decision on the expansion of their business into this market. In order for the Board of Directors to make a quality decision they require good and accurate information. In line with the Franke growth strategy Franke South Africa was given the clear directive to grow the market share on the African continent. With this continent being as diverse as it is and suffering from many years of poverty, a focused strategy is required. With this in hand a study of the African continent was undergone and a couple of markets were identified as targets for either a take-over or new formation. With the information gathered on Egypt it became clear that this would be the ideal market to establish another Franke operation. Egypt has many positive issues that attract a decision like this of which the local market size, geographical position, COMESA membership and the fact that the market is well structured form the backbone. Based on this Business Plan, which researches all the relevant issues required to make a quality decision, an investment could be qualified and supported. It focuses on the possible target as well as elaborates on the medium term forecasted performance of the new setup. / Thesis (MBA)-University of Natal, Durban, 2003.

Climate change has exacerbated environmental degradation processes, causing an imbalance in the natural concentrations in atmospheric greenhouse gases. This has resulted in a myriad of socio–economic effects which have focused global attention on methodologies to reduce these effects, such as carbon sequestration. To achieve long term sustainability and success, community involvement in the technical and social aspects of carbon sequestration projects is necessary and must be acknowledged. One such mitigation methodology which incorporates the ideals of community proactive participation is carbon sink reforestation projects. This study is based on a community perspective of a carbon sink reforestation project, carried out in KwaZulu-Natal, South Africa. The study provides a holistic perspective of the concept of carbon sequestration drawing together technical aspects of carbon sequestration reforestation projects and the inclusion of the role of communities. The methodology comprised of questionnaires with industry experts and a local community, following a thematic data analysis. The current perception from industry is that the South African government lacks significant technology, capacity and finance to effectively manage national forest carbon sequestration regimes. Project participants expressed the view that these types of projects provided a sense of belonging and hope and articulated their gratitude for the environmental knowledge they gained from the project experience. Technical and social aspects of such projects such as carbon calculations and participatory rural appraisal techniques enhance a country’s ability for successful implementation of such projects. Findings reveal a need for technology, capacity building and finance; and the effects participation in these projects has on individuals. This is followed by recommendations and a ‘How To Guide’ developed by the researcher. This guide intends to enhance the collaboration of the technical aspects and involvement of communities throughout the project implementation process. Carbon regimes in this century will continue to grow in size and complexity. Stakeholder participation will be a strong factor in the success or failure of carbon sequestration reforestation projects. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.