Climate change and its accompanying environmental issues have caused the building industry to use more environmentally friendly building materials. Wood have always been a buildingmaterial but due to the renewed interest in imparting sustainability and renewability, its usage has increased over the recent years. With a rising interest in wood, it is of great importance to enhance the knowledge of its burning behaviour in order to predict and prevent fire hazards. Fire development is often characterized in terms of heat release rate (HRR) as a function oftime. Therefore, HRR is considered one of the most important variables in the evaluation of material fire hazards. This study aims to generate greater knowledge of the HRR curve of wood when exposed to heating in the cone calorimeter and how the curve can be described quantitatively. Furthermore, it was attempted to comprehend the properties and functions of char and its effects on HRR during combustion. The study is based on laboratory tests carried out with a cone calorimeter and a Scanning Electron Microscope (SEM). The cone calorimeter was set to generate a heat flux of 35 kWm-2. Spruce wood samples of three thicknesses were analysed, namely 10, 20 and 30mm. The samples were assembled with one of three types of material on the rear side of the samples, which were Kaowool, steel plates and aluminium foil wrapped around wood. The different materials were used as they are greatly dissimilar in their thermal properties. Wood with both low and normal moisture content was also analysed. Char was analysed with SEM. The results show that there are four major points of interest in the HRR curve of wood. The first point is the initial peak heat release rate (PHRR) that occurs when the sample surface ignites causing great production of heat which increases the HRR. The second point of interest is the vast decrease in HRR soon after the first PHRR, this is due to char formation, which acts as a protective barrier preventing the exchange of volatile gases and oxygen. The third point of interest is a second PHRR close to the end of the combustion that occurs as a response to sample burn through, which means that the heat gradient reaches the rear side of the sample. The second PHRR is highly dependent on the boundary condition defined by the rear material, which determines the heat losses at the rear side of the specimen, and consequently the temperature of the specimen. The higher is the specimen temperature, the higher is the pyrolysis rate, and therefore also the higher the second PHRR. Moreover, high moisture content delays the time of occurrence of the second PHRR as more water needs to undergo phase change, which requires a high amount of energy. The final point of interest is the final decrease in HRR as a result of fuel depletion leading to the sample smouldering or the fire being extinguished. Char, formed by mainly lignin and some cellulose in wood, affects the overall HRR. The SEM analysis showed that the char cracks grew wider during the second PHRR. It is, however, observed that char cracking has no significance in the time of occurrence of the second PHRR as this is based on sample burn through, and it was difficult to determine to what extent char cracking affected the intensity of the PHRR. This systematic study is considered adequate to justify the research questions and aim of this study. It has also created new questions for further study in the area as well as provided a deeper understanding of the fundamental burning behaviour of wood. / Klimatförändringen och dess medföljande miljöfrågor har fått byggbranschen att använda mer hållbara och miljövänliga byggmaterial. Trä har alltid varit ett byggmaterial men på grund av ett förnyat intresse för hållbarhet och förnybarhet har användningen av materialet ökat under de senaste åren. Med ett stigande intresse för trä är det av stor vikt att öka kunskapen om dess förbränningsbeteende för att kunna förutse och förebygga brandrisker. Brandutveckling karakteriseras ofta i termer av värmeavgivningshastighet (HRR) som funktion av tid. Det är därför en av de viktigaste variablerna i utvärderingen av brandrisker. Denna studie syftar till att skapa större kunskap om HRR-kurvan för trä när det utsätts för värme i konkalorimetern och hur kurvan kan beskrivas kvantitativt. Vidare, att studera kollagrets egenskaper och funktioner samt hur det påverkar HRR under förbränning. Studien bygger på laborativa försök utförda med en konkalorimeter och ett svepelektronmikroskop (SEM). Konkalorimetern genererade strålning med intensitet 35 kWm-2. Tre tjocklekar av granprover testades, 10, 20 och 30 mm. Proverna placerades ovanpå en av tre typer av material i en provform, Kaowool, stålplattor och trä invirat i aluminiumfolie. Materialen användes då deras termiska egenskaper skiljer sig åt. Vidare testades även trä av både låg och normal fukthalt. Kollagret analyserades med SEM. Resultatet visar att det finns fyra intressanta områden på HRR-kurvan för trä. Det första är den initiala maximala värmeavgivningshastigheten (PHRR) som inträffar när provytan antänder vilket orsakar en stor värmeproduktion som ökar HRR. Det andra är en kraftig minskning av HRR strax efter den första PHRR. Detta beror på att kol börjat bildas på provytan, kollagret fungerar som en skyddande barriär som förhindrar utbyte av flyktiga gaser och syre. Det tredje är en andra PHRR som inträffar nära brandprovets slut. Detta sker till följd av provkroppsgenombränning som innebär att värmegradienten når provets baksida. Intensitetenav PHRR är starkt beroende av materialet bakom provet. Det bestämmer värmeförlusten på provets baksida och därmed även provkroppens temperatur. Ju högre provkroppstemperaturenär, desto högre är pyrolyshastigheten vilket leder till en högre andra PHRR. Hög fukthalt fördröjer även tidpunkten för uppkomsten av den andra PHRR eftersom fasomvandling av vatten kräver en stor mängd energi. Det sista och fjärde området av intresse är en minskning av HRR efter den andra PHRR, detta sker när allt bränsle förbränts och det som kvarstår är endast ett glödande prov. Kollagret, som främst bildas av lignin och en del cellulosa i träet, påverkar den totala HRR. SEM-analysen visade att sprickorna i kollagret blev bredare under den andra PHRR. Däremot observerades det att sprickbildningen inte har någon betydelse för tidpunkten av den andra PHRR uppkomst då denna enbart är baserad på provets genombränning. Det är även svårt att avgöra i vilken utsträckning sprickbildningen påverkar intensiteten av PHRR. Metoden som används för att besvara frågeställningarna och syftet anses vara adekvat. Studien har öppnat upp för ytterligare frågeställningar och idéer till fortsatta försök inom området. Vidare har även studien gett en djupare förståelse om förbränningsbeteendet av trä.

Aneurysms are a deadly asymptomatic cardiovascular disease that may occur especially where there are bends and bifurcations in the cerebral vasculature. A region where these features are especially prominent is the Circle of Willis (COW) in the brain, where aneurysms are known to occur. In the carotid artery, which feeds into the COW, the Reynolds number of blood flow is typically around 200-500. Even with such a low Reynolds number, turbulent-like flow, or tortuous flow, can occur due to bends, bifurcations and highly pulsatile flow which lower the effective Reynolds number where tortuous flow can occur. Highly pulsatile flow is unsteady flow that is high in magnitude and changes over time. Endothelial cells (ECs) line the inner wall of the blood vessel and experience the friction force of blood flow. This work is focused on designing a device that can expose ECs to forces they would undergo in an aneurysm-susceptible site. This is accomplished by exposing ECs to physiologically relevant Wall Shear Stress (WSS) and vibrations simultaneously. Vibrations in the body occur due to flow separation at the vessel wall, which leads to pressure changes. These pressure changes induce vibrations onto ECs. The fluid flow in the designed Parallel Plate Flow Chamber (PPFC) is laminar to induce a predictable WSS onto the cells, while the vibrations will induce a rapid cyclical force to simulate pressure fluctuations that may occur in vivo. The aneurysm-susceptible flow will simulate a more turbulent-like flow in the carotid artery; higher maximum WSS (around 2.2 Pa) with vibrations. The aneurysm-protective flow will have a lower WSS maximum (around 0.5 Pa). The PPFC, made of polycarbonate, is small and light enough to be conveniently vibrated using an electromagnetic vibration stage. The PPFC can be driven by a syringe or peristaltic pump, allowing for either steady or transient waveforms. The PPFC’s fluid domain will not change upon vibration, isolating the effect of vibration on the cells. Also, two side-by-side glass slide slots were included to allow for both protein and mRNA quantification from the same experiment, increasing experimental efficiency and flow-related consistency between the two cell areas. Simulations using ANSYS Fluent verified the flow field and WSS waveform on the cells for the designed geometry for 3D and 2D cases, as well as verified equal WSS values throughout all areas of ECs. Then, Particle Image Velocimetry (PIV) was done to verify the predicted flow rate in the machined PPFC given a steady flow rate driven by a syringe pump. Preliminary cell experiments were performed in an incubator under flow and vibration conditions to demonstrate cell survivability.

No abstract available

In recent years, interest in sustainability and being environmentally friendly has increased. Wood is a durable and renewable building material, which is becoming more common in the constructions industry. In 2002, the government in Sweden adopted a national strategy to promote an increased use of wood in buildings. However, the usage of wood in construction has a potential risk – wood is ignitable and has fire-spreading properties.  The aim of this project was to investigate whether a ZnO coating can reduce the risk of ignition on wooden surfaces exposed to a radiative heat source, focusing on the time to ignition of the wood. ZnO possess a wide combination of physical properties, such as ability to reflect infrared radiation and being thermally stable at extremely high temperatures. The study has been carried out through a literature review and laboratory experiments. In the laboratory experiments, a cone calorimeter was used and the tests were performed according to ISO 5660-1. In the cone calorimeter, two different amounts of ZnO applied to the wood surface were tested, 0.5 and 1 g ZnO per dm2 and an untreated piece of wood as a reference. The test was carried out in three different heat fluxes: 20, 35 and 50 kWm-2. After completed tests, the change in the wood’s morphology was examined in a scanning electron microscopy (SEM). The result shows that an application of ZnO on a wooden surface significantly increases the time to ignition for the wood. An application of 0.5 g ZnO per dm2increased the time to ignition by 26-33 % for the three different heat fluxes. On the other hand, 1 g of ZnO per dm2 created an increase of 37-40 %. The trend of the increase of time to ignition was similar for all heat fluxes. The result showed no clear tendency that the smoke production rate was reduced with the application of ZnO. The heat release rate was not affected by the addition of ZnO, which was expected because ZnO delays the time to ignition, but once it catches fire, the wood burns. The SEM images before and after combustion showed that there is no change in the morphology of ZnO, although some ZnO has agglomerated but remains intact after combustion. The conclusion of this study is that ZnO has the potential to protect wood from fireby increasing the time to ignition. But when the wood has ignited, there is no clear tendency for ZnO to affect the growth of the fire. The study has shown that in the future ZnO could be applied to a wooden surface to reduce the risk of fire ignition. Further studies are required to find effective methods to implement the usage of ZnO, as applying ZnO on vertical wooden surfaces.

Abaco Island is located on Little Bahama Bank at the northwestern extent of the Bahamian Archipelago. Karst features on Abaco include: flank margin caves, karren, blue holes, pit caves, banana holes, and cone karst. As part of this study all known flank margin caves on Abaco were GPS located and surveyed. The presence and locations of the other karst features were recorded as part of the karst inventory of Abaco. The cone karst is of particular interest because cone karst has not been documented on other Bahamian islands. These cones form from the dissection of an eolianite ridge due to karst, fire, and vegetative processes. Tafoni-like recesses, originally believed to be high flank margin caves, were formed during cliffing of an eolianite ridge during the OIS 5e highstand. The geologic evolution of representative depositional sequences on Abaco fits within the accepted Bahamian stratigraphy.

After over a decade of its discovery, the Electroretinogram (ERG) still remains the objective tool that is conventionally used in assessment of retinal function in health and disease. Although there is ongoing research in developing ERG recording techniques, interpretation and clinical applications, there is still a limited understanding on how each photoreceptor class contribute to the ERG waveform and their role and/or susceptibilities in various retinal diseases still remains unclear. Another limitation with currently used conventional testing protocols in a clinical setting is the requirement of an adaptation period which is time consuming. Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs using sine- and square- wave temporal profiles. The ERGs achieved in this manner were shown to be photoreceptor-selective. Furthermore, these responses did not only provide the functional index of photoreceptors but their contributions to their successive postreceptoral pathways. We believe that the substitution stimuli used in this thesis could be a valuable tool in functional assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation. / Bradford School of Optometry and Vision Sciences scholarship

No description available.

No description available.

No description available.

No description available.