Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

The Earths climate is changing at a higher rate, i.e between 1861 and 1994 the annual mean temperature in Scandinavia increased with 0,68º C and according to recent climate models the annual mean temperature is likely to rise with another 3º C during this century. A warmer climate in many ways is associated with changing conditions for lake ecosystems. An expected higher water temperature and a stronger summer stratification of the water column increases the risk of anoxic conditions at the lake bottom. Thus anoxic conditions are likely to cause a phosphate leakage from the sediment, i.e. a higher internal loading of phosphate. In this project, the extremely warm summer of 2002 has been used as an example for a possible scenario for a future climate. By comparing levels of phosphorus in the summer of 2002 with a ten-year median value, a phosphorus related sensitivity to climate change has been analyzed for 55 Swedish lakes. This sensitivity has then been related to several parameters of which in particular the lake morphometry and the land use in the catchment of the lake influenced the climatic sensitivity of the lake to climatic change. / Jordens klimat förändras i en allt snabbare takt. Mellan 1861 och 1994 steg årsmedeltemperaturen i Skandinavien med 0,68º C. Enligt aktuella klimatmodeller förväntas årsmedeltemperaturen i Skandinavien öka med ytterligare 3º C det närmaste seklet. Ett varmare klimat innebär på flera sätt nya förutsättningar för ekosystemen. Genom höjda vattentemperaturer och en starkare stratifikation sommartid ökar risken för syrefria förhållanden i sjöar. Då sedimentet under syrefria förhållanden kan läcka fosfat innebär detta en ökad internbelastning av fosfor. I detta projekt har den extremt varma sommaren 2002 använts som ett möjligt framtida klimat. Genom att jämföra fosforhalter sommaren 2002 med ett medianvärde för 10 år har den fosforrelaterade känsligheten för klimatförändringar kunnat analyseras för 55 svenska sjöar. Denna känslighet har sedan relaterats till diverse parametrar så som sjöns morfometri och avrinningsområdets sammansättning.

Reinforced Concrete (RC) bridge piers, RC columns along exterior of buildings or those located in parking garages are designed to support large compressive axial loads but are vulnerable to transverse out-of-plane loadings, such as those arising from impacts or explosions. To address a lack of understanding regarding blast and impact response of RC members and the need for retrofit techniques to address deficiencies in existing structures, a multi-disciplinary team including various institutes of the National Research Council and the University of Ottawa has initiated work towards developing a fibre reinforced polymer composite protection system for RC columns subjected to extreme shocks. This thesis will focus on the impact program of the aforementioned project. An extensive literature review was conducted to gain a better understanding of: impact loading and associated dynamic effects; experimental testing of RC members subjected to impact; experimental testing of axially loaded members; and retrofit methods for the protection of RC under impact loading. Five half-scale RC columns were constructed and tested using a drop-weight impact machine and two additional specimens were tested under static loading. Deflections, strain distributions within the columns, impact loads and reaction loads were measured during the testing of the built RC members. Comparisons of experimental datum were established between members with differing levels of axial load and between a retrofitted and a non-retrofitted member. Single-degree-of-freedom analysis was used to obtain the predicted response of certain columns under impact loading allowing for comparisons with experimental data.

In vitro studies have shown that the major membrane phospholipid phosphatidylcholine (PC) can positively influence the incorporation of cholesterol in lipid membranes. The influence of PC on the cellular trafficking of LDL-derived free cholesterol was investigated. Sterol regulatory-defective (SRD)-4 cells are Chinese hamster ovary (CHO)-derived fibroblasts that display vastly elevated rates for the synthesis and catabolism of PC. SRD-4 cells harbor two known gene mutations: a mutation in the functional allele for SCAP, resulting in defective feedback suppression of cholesterol biosynthesis; and a loss-of-function mutation in the functional allele for acyl-CoA:cholesterol acyl transferase (ACAT), an endoplasmic reticulum (ER)-localized enzyme that esterifies free cholesterol. Incubation of SRD-4 cells with 50 µg/ml low density lipoprotein (LDL) for 18 h resulted in lysosomal accumulation of free cholesterol as revealed by filipin staining. This accumulation was not evident following LDL treatment of parental CHO7 cells, and was blunted in SRD-2 cells that express a constitutively-active form of SREBP-2 and overproduce cholesterol but have functional ACAT activity. Treatment of SRD-2 cells with LDL in the presence of an ACAT inhibitor 58-035 resulted in robust lysosomal cholesterol accumulation that was reversible upon drug washout, supporting that cholesterol trafficking in cholesterol-loaded cells is dependent on ACAT activity and, more specifically, ER free cholesterol levels. Lysosomal accumulation of LDL-derived cholesterol was prevented in SRD-4 cells supplemented with lyso-PC (50 µM), a substrate for PC synthesis through the reacylation pathway, and also in cells treated with bromoenol lactone (BEL), an inhibitor of phospholipase A2 implicated in bulk PC turnover. In a counter study, lysosomal LDL-derived cholesterol accumulation was induced in parental CHO-7 cells using R-propranolol, which inhibits the conversion of phosphatidic acid to diacylglycerol (DAG), a substrate in the CDP-choline pathway. This blockage was also relieved through co-treatment with lyso-PC. These studies support that PC to free cholesterol ratios in downstream organellar membranes can influence cholesterol trafficking out of lysosomal compartments in cholesterol-loaded cells.

No description available.

<p>Soil compaction is an inevitable result of agricultural practices. It alters physical properties of soil and tends to be undesirable as it adversely affects water and nutrient penetration. Furthermore, additional energy is spent to till the soil. Although a tremendous amount of research has been conducted in the area of soil compaction, the focus has been primarily on surface soil displacement.</p> <p>Realizing that the observed soil displacement is the cumulative effect from the compaction of subsurface layers, this research discusses the displacement and distributed pressure through the soil from a surface load. A given volume of soil of known density and moisture content was loaded at the surface with a slowly applied force using an Instron® testing machine. The distribution of the pressure and displacement profile from the surface to depth was measured to provide insight into the formation of the subsurface soil structures. The nonlinear exponential decay of the soil displacement (compaction) from the surface to a given depth converges to zero at the location of a hard, compact layer or a point where no soil movement occurs, regardless of the initial soil compaction. By increasing soil moisture content and decreasing soil bulk density, the vertical soil displacement increased at the surface and within the soil profile, and the pressure distribution decreased with depth. Changing the shape of loading surface had minimal effect on soil displacement.</p>

<p>Soil compaction is an inevitable result of agricultural practices. It alters physical properties of soil and tends to be undesirable as it adversely affects water and nutrient penetration. Furthermore, additional energy is spent to till the soil. Although a tremendous amount of research has been conducted in the area of soil compaction, the focus has been primarily on surface soil displacement.</p> <p>Realizing that the observed soil displacement is the cumulative effect from the compaction of subsurface layers, this research discusses the displacement and distributed pressure through the soil from a surface load. A given volume of soil of known density and moisture content was loaded at the surface with a slowly applied force using an Instron® testing machine. The distribution of the pressure and displacement profile from the surface to depth was measured to provide insight into the formation of the subsurface soil structures. The nonlinear exponential decay of the soil displacement (compaction) from the surface to a given depth converges to zero at the location of a hard, compact layer or a point where no soil movement occurs, regardless of the initial soil compaction. By increasing soil moisture content and decreasing soil bulk density, the vertical soil displacement increased at the surface and within the soil profile, and the pressure distribution decreased with depth. Changing the shape of loading surface had minimal effect on soil displacement.</p>

This thesis reports on the investigations of resistive-capacitive (RC) loaded bow-tie antennas with special emphasis on impulse ground penetrating radar applications. Impulse radiation for ground penetrating radar is a challenging research topic because of the unique problem arising from impulse radiation: late-time ringing, which usually masks the important echo signals from the targets. While resistive loading is a common solution for eliminating late-time ringing, use of resistive loading typically sacrifices the radiation efficiency. In this thesis, a resistive-capacitive loading technique is investigated for a circular bow-tie antenna in the attempt to reduce/suppress the late-time ringing as well as to maintain a relatively high radiation efficiency. To implement the system, a microstrip differentiator, which converts a monopulse into a Gaussian-like monocycle to be used as input impulse, is presented. Further, specially designed coplanar waveguide/coplanar strip (CPW/CPS) baluns embedded with Chebyshev transformers of characteristic impedance up to 120 have been constructed and tested. To evaluate the system, instead of using the conventional peak voltage value of the radiated waveform, average radiated energy, average ringing energy, relative radiation efficiency and relative ringing efficiency are utilized and these metrics are easily established using low-cost low-sensitivity probes. Measurement results show that the RC-loading scheme is functioning as expected and the impulse system as a whole is capable of reducing the late-time ringing energy to 50% while maintaining average radiation energy as 83% when compared with capacitive loading cases. / October 2006

Heterogeneities at the meso-scale strongly influence the shock compression response of composite materials. These heterogeneities arise from both structural variations and differing physical/mechanical properties between constituents. In mixtures of reactive materials, such as Ni and Al, the meso-scale heterogeneities greatly affect component mixing and activation, which, in turn, can induce a chemical reaction. Cold-rolled multilayered composites of Ni and Al provide a unique system for studying the effects of material heterogeneities on a propagating shock wave, due to their full density, periodic layering, and intimate particle contacts. Computational analysis of the shock compression response of fully dense Ni/Al multilayered composites is performed with real, heterogeneous microstructures, obtained from optical microscopy, using the Eulerian hydrocode CTH. Changes in the orientation, density, structure, and strength of the material interfaces, as well as the strength of the constituents, are used to understand the influence microstructure plays on the multilayered composite response at high strain rates. The results show a marked difference in the dissipation and dispersion of the shock wave as the underlying microstructure varies. These variations can be attributed to the development of two-dimensional effects and the nature of the wave reflections and interactions. Validation of the computational results is then obtained through time-resolved measurements (VISAR, PDV, and PVDF stress gauges) performed during uniaxial strain plate-on-plate impact experiments. The experimental results prove that the computational method accurately represents the multilayered composites, thereby justifying the conclusions and trends extracted from the simulations. The reaction response of cold-rolled multilayer composites is also investigated and characterized using uniaxial stress rod-on-anvil impact experiments through post-mortem microscopy and x-ray diffraction. This extensive understanding of the shock compression response of the multilayers systems is contrasted with other composites of Ni and Al, including shock consolidated and pressed (porous) powder compacts. A comprehensive design space is then developed to assist in the understanding and design of Ni/Al composites under conditions of high pressure shock compression. Research funded by ONR/MURI grant No. N00014-07-1-0740.

No description available.