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Climate change and rising temperatures is a well-known problem. To tackle global warming a transition from fossil fuels to renewable and reliable energy sources is necessary. Hydrogen, in fuel cells, is proposed to replace diesel and gasoline in the transport sector. Hydrogen is a pure fuel and the fuel cells only emit water and heat as a byproductbyproduct. Combined with electric motors, the hydrogen fuel cell can be 2-3 times more efficient compared to combustion engines fueled by gasoline. The performance of the fuel cell is affected by how the individual parts of the cell are designed. There are some difficulties in manufacturing complex geometries which requires require a forming in more than one step.  The goal isis to investigate, with the help of COMSOL Multiphysics software, how the performance of the fuel cell is affected by the shaped geometry at the cathode side of the flow plate. A numerical model is developeding will be made with varying parameters on the measurement of the cross-sections of the channels where pressure drop and flow distribution for ten different geometries isarewill be investigated. The model iswas built in the COMSOL Multiphysics 6.1 Software and includes a three-dimensional geometry consisting of a gas channel and a gas diffusion layer. The flow is laminar and the gas diffusion layer is set as a porous medium.  The results show that geometries with less sharp edges have lower pressure drops and more uniform flow distribution compared to geometries with sharper edges. The geometry with the sharpest edges has the highest pressure drop of 4.8 Pa/mm and the geometry with rounder edges has the lowest of 3.8 Pa/mm. A relationship between pressure drop and cross-sectional area can be found. With increasing radius and increasing cross-sectional area will the pressure drop decrease. The Reynolds number is higher for sharper geometries since the average velocity in the channels is higher, which also gives a lower friction factor. The length of the top flat becomes less for rounder geometries, which positively affects uniform flow distribution. The geometries with rounder edges have the most uniform distribution at the top of the gas diffusion layer and the sharpest geometry has the least uniform distribution. The deviation from the mean velocity is lower for sharper geometries, mainly because the velocities in the gas diffusion layer are lower. Sensitivity analysis was made over the mass flow rate and mesh, showing that the pressure drop is proportional to the mass flow rate and it becomes higher with less fine mesh.  Less fine mesh also gives lower velocities in the gas diffusion layer. Further studies can be made on how the gas diffusion layer behaves in the fuel cell when adding clamping force to the stack when putting it together and investigate if and how it affects pressure drop and flow distribution. The environmental benefit can be crucial if the performance of the fuel cells improves and motivates the investments which is are needed for, among other things, the infrastructure. / Klimatförändringar och stigande temperaturer är ett välkänt problem. För att ta itu med den globala uppvärmningen är en övergång från fossila bränslen till förnybara och pålitliga energikällor nödvändigt. Vätgas,  går bland annat att användas ii bland annat bränsleceller och , skulle kunna ersätta diesel och bensin inom transportsektorn. Vätgas är ett rent bränsle och bränslecellerna släpper bara ut vatten och värme som biprodukter. I kombination med elmotorer kan vätgasbränslecellen vara 2–3 gånger mer effektiva jämfört med förbränningsmotorer som drivs av bensin. Bränslecellens prestanda påverkas av hur de enskilda delarna av cellen är utformade. Det finns vissa svårigheter att tillverka komponenter med komplexa geometrier som kräver formning i fler än ett steg. Målet är att med hjälp av programvaran COMSOL Multiphysics undersöka hur bränslecellens prestanda påverkas av den formade geometrin på katodsidan av flödesplattan. En numerisk modellering kommer att utförasgöras utifrån med varierande parametrar därpå måtten hos kanalernas tvärsnitt varieras. Tdär tryckfall och flödesfördelning hos tio olika geometrier kommer att undersökas. Modellen byggdes i COMSOL Multiphysics 6.1 Software och inkluderar en tredimensionell geometri bestående av en gaskanal och ett gasdiffusionsskikt. Flödet är laminärt och gasdiffusionsskiktet antas vara ett poröst medium. Resultaten visar att geometrier med mindre skarpa kanter ger lägre tryckfall och jämnare flödesfördelning jämfört med geometrier med skarpare kanter. Geometrin med skarpast kanter har det högsta tryckfallet på 4.8 Pa/mm och geometrin med rundare kanter har ett tryckfall på 3.8 Pa/mm. Ett samband mellan tryckfall och tvärsnittsarea kan hittas då ökad radie och ökad tvärsnittsarea ger en minskning i tryckfall. Reynoldstalet är högre för skarpare geometrier eftersom medelhastigheten i kanalerna är högre, vilket också ger en lägre friktionsfaktor. Längden på toppen av kanalerna blir mindre för rundare geometrier, vilket påverkar flödesfördelningen positivt. Geometrierna med rundare kanter har den mest jämna fördelningen i toppen av gasdiffusionsskiktet och den skarpaste geometrin har den minst jämna fördelningen. Avvikelsen från medelhastigheten är lägre för skarpare geometrier, främst på grund av att hastigheterna i gasdiffusionslagret är lägre. Känslighetsanalys gjordes över storleken på massflödet och noggrannheten i meshen, vilket visar att tryckfallet är proportionellt mot massflödet och att det blir högre med mindre noggrann mesh. Mindre noggrann mesh ger också lägre hastigheter i gasdiffusionsskiktet. Ytterligare studier kan göras om hur gasdiffusionslagret beter sig i bränslecellen vid sammanpressning av alla delar i cellen och undersöka om och hur det påverkar tryckfall och flödesfördelning. Fördelen för miljönMiljönyttan kan vara stor om bränslecellernas prestanda förbättras och på så vis kan motivera de investeringar som behövs för utbyggnaden av bland annat infrastrukturen.

Background. Past research shows that anxiety disorders can impair work performance, but there are no national studies examining the relationship between anxiety disorder subtypes and low work performance. In a representative sample of employed US adults, we examined the association between low work performance and three types of anxiety disorders--generalized anxiety disorder (GAD), panic disorder (PD), and post-traumatic stress disorder (PTSD). Methods. We analyzed data collected in 2001-2003 on 4,418 employed US adults participating in the National Comorbidity Survey Replication (NCS-R). DSM-IV diagnostic criteria were used to determine the 12-month prevalence of GAD, PD, and PTSD. Low work performance was classified as a score of ≤7 on a 10-point scale in response to a single question (i.e. “What number describes your overall job performance on the days you worked during the past 30 days?”). Logistic regression predicting low work performance adjusted for age, gender, education, financial stress, having children, weekly work hours, race/ethnicity, and geographic region. Results. The prevalence of low work performances was 18.5%, while the prevalences of GAD, PD, and PTSD were 3.0%, 3.6%, and 4.2%, respectively. The prevalence of low work performance among those with GAD, PD, PTSD, or no anxiety disorder were 25.3%, 20.6%, 27.6%, and 18.0%, respectively. After adjustment for covariates, PTSD was the only anxiety disorder associated with a significantly higher risk of low performance (adjusted odds ratio = 1.44, 95 % confidence interval = 1.05, 1.98). Conclusion. Not all types of anxiety disorders may be associated with low work performance. Future research should examine these associations prospectively and by subtype of anxiety disorder. / Epidemiology

Design thinking ability is vital for engineers who are tasked with solving society's toughest sustainable development challenges. Prior research identified that the percentage of design thinkers among freshmen engineering students is greater than the percentage among the general population. However, engineering education's lack of attention to fostering creative ability may cause the design thinking ability of senior engineering students to suffer. The research addressed in this thesis compares the design thinking ability of engineering students across age groups, and compares design thinking ability between the design disciplines of engineering and architecture. To draw design thinking comparisons between these groups, a survey with a nine item design thinking instrument was distributed nationally to freshmen engineering students (n= 2,158), senior engineering students (n= 1,893), and senior architecture students (n= 336). The survey instrument was validated by conducting confirmatory factor analysis on the senior engineering and senior architecture samples' data. The Analysis of Variance (ANOVA) test was utilized to statistically compare scores across sample groups. Both the freshmen engineering students (2.80) and senior architecture students (3.30) scored significantly higher on the design thinking scale than senior engineering students (2.59). These results have important implications for engineering educators as engineering education may contribute to a decrease in design thinking among senior engineering students. A lower design thinking score among seniors was consistent across all engineering sub-disciplines and should be of concern to engineering educators, since design thinking skills are critical for the development of engineering solutions to grand societal challenges. / Master of Science / Design thinking is a way of thinking about the design process which places the user at the center of the design. Thinking about design in this way is a vital ability for engineers and other design professionals to develop because it enables them to solve “wicked” problems like sustainable development challenges. Wicked problems are those which are difficult to solve due to the number of conflicting components involved. Prior research has found that design thinkers are more prevalent among engineering students in their first year of study than among students in other majors. However, engineering education does not attribute much attention to the development of creative ability which could cause the design thinking ability of engineering students in their final year of study to be worse than the ability of those in their first year, as well as worse than the ability of students who study other design disciplines like architecture. This study compared the design thinking abilities of engineering students in their final year of study to engineering students in their first year and to architecture students in their final year. The goal of making these comparisons was to explore if engineering education helps or hinders the development of design thinking. A survey with nine questions related to design thinking was distributed nationwide. The data from the survey was collected and statistically analyzed. The results showed that the design thinking ability of engineering students in their final year was significantly lower than the ability of first year engineering students and significantly lower than the ability of final year architecture students. A decrease in design thinking ability between freshmen and senior year must be addressed by engineering educators. The National Academy of Engineers and industry leaders are calling for the development of engineers who are design thinkers, and the results of this paper suggest that some changes may need to occur within the engineering education curriculum to accommodate this need.

No / Rational, aim, and objectives: A positive patient safety culture in maternity units is linked to higher quality of care and better outcomes for mothers. However, safety culture varies across maternity units. Analyses of variation in safety culture using statistical process control (SPC) methods may help provider units to learn from each other's performance. This study aims to measure patient safety culture across maternity units in Oman using SPC methods. Methods: The 36-item Safety Attitude Questionnaire (SAQ) was distributed to all doctors, nurses, and midwifes working in ten maternity care units in Oman's hospitals and analysed using SPC methods. The SAQ considers six domains: job satisfaction, perception of management, safety climate, stress recognition, teamwork, and work condition. Results: Of the 892 targeted participants, 735 (82%) questionnaires were returned. The overall percentage of positive safety responses in all hospitals ranged from 53% to 66%, but no hospital had the targeted response of above 75%. Job satisfaction had the highest safety score (4.10) while stress recognition was the lowest (3.17). SPC charts showed that the overall percentage of positive responses in three maternity units (H1, H7, and H10) was above and one (H4) was below the control limits that represent special cause variation that merits further investigation. Conclusion: Generally, the safety culture in maternity units in Oman is below target and suggests that considerable work is required to enhance safety culture. Several maternity units showed evidence of high/low special cause variation that may offer a useful starting point for understanding and enhancing safety culture.

nÃo hà / Unit root tests have been widely used to validate or reject economic modelâs hypotheses. Because of this, many authors have created different versions of this kind of test in order to generate statistics which are more precise in identifying the presence of a unit root. Some authors have increased the power of these statistics using panel data. However, the use of panel data brings the possibility of dependence between cross-sections, this has been initially handled by the independence between cross-sections hypothesis. Only the second generation tests consider dependence between cross-sections. Nevertheless, in the literature there is no test which allows changes in the dependence between cross-sections over time. Thus, this paper uses Monte Carlo experiments to analyze the small sample properties of some statistics used to identify the presence of a unit root. It is noticed that the size of these statistics has a large distortion when the level of dependence between cross-sections changes. / Teste de raiz unitÃria tem sido muito importante no sentido de validar ou rejeitar as hipÃteses dos modelos econÃmicos. Devido essa importÃncia, diversos autores tÃm criado diferentes versÃes desse teste, a fim de gerar estatÃsticas que sejam mais precisas em identificar a presenÃa de raiz unitÃria. Usando dados em painel, alguns autores conseguiram aumentar o poder dessas estatÃsticas. No entanto, o uso de dados em painel trÃs a possibilidade de dependÃncia cross-section nos dados, fato esse inicialmente tratado pela hipÃtese de independÃncia cross-section. Somente nos testes chamados de segunda geraÃÃo à que se trata dependÃncia cross-section. Entretanto, nÃo hà na literatura nenhum teste que permita mudanÃas nesse nÃvel de dependÃncia ao longo do tempo. Com isso, esse trabalho pretende avaliar, por meio de um experimento de Monte Carlo, as propriedades de pequenas amostras de algumas estatÃsticas usadas para identificar a presenÃa de raiz unitÃria. Percebe-se que o tamanho dessas estatÃsticas sofre uma grande distorÃÃo para as situaÃÃes de mudanÃa no nÃvel de dependÃncia cross-section.

Made available in DSpace on 2015-03-05T19:11:30Z (GMT). No. of bitstreams: 0 Previous issue date: 29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O propósito desta dissertação foi verificar se o Modelo de Precificação de Ativos de Capital baseado no Consumo (CCAPM) é consistente com os dados de quatro países latino-americanos: Brasil, Chile, Colômbia e México. Para alcançar este objetivo foi realizada uma regressão cross-sectional dos prêmios de risco médios sobre os betas de consumo de cada ativo em cada país analisado. Adicionalmente, de forma análoga a Lintner (1965) e Levy (1978), foi verificado se a variável ‘variâncias residuais’ mostrava-se estatisticamente significante nas regressões cross-sectional, o que seria inconsistente com o modelo. Os resultados empíricos, baseados em estimativas corrigidas para o problema dos erros nas variáveis, demonstram que há uma relação estatisticamente significativa entre os prêmios de risco médios e os betas de consumo nos países acima mencionados, com exceção do México. Apesar disto, o poder explicativo do modelo, dado pelo coeficiente de determinação R2 ajustado, foi muito baixo em todos os países. Quanto à v / The purpose of this thesis is to verify whether the Consumption based Capital Asset Pricing Model (CCAPM) is consistent with the data from four Latin-American countries: Brazil, Chile, Colombia, and Mexico. In order to reach this goal, a cross-sectional regression of the consumption betas on the mean excess returns of each asset is performed for each country analyzed. Also, similar to the studies of Lintner (1965) and Levy (1978), it is verified whether the variable ‘residual variance’ has statistical significance in the cross-sectional regressions, which would be inconsistent with the model. Empirical results showed that there is a statistical significant relationship between mean excess returns and consumption betas in the countries cited above, with exception of Mexico. Despite this, the explanatory power of the model, given by the adjusted coefficient of determination (R2), is very small in all countries. Concerning the variable ‘residual variance’, it is statistically significant for the Brazilian and Me