138 research outputs found
Boundary Layer Flashback of Turbulent Premixed Hydrogen/DNG/Air Flames produced by a Bunsen Burner
No full textDue to the growing energy demand and global warming renewable energy is currently of interest. To deal with the production intermittency of renewable energy, energy might be stored in hydrogen. Hydrogen can be converted into electricity with a fuel cell or by combusting hydrogen in a gas turbine. Gas turbines are more suitable for large power outputs. Large power outputs require large volumetric flow rate through the gas turbine. The large volumetric flow rate causes high gas velocities and results in a turbulent flow. Using hydrogen instead of natural gas as energy resource changes the stable operating regime and increases flame flashback propensity. Current studies done at the Technical University of Munich and the Technical University of Delft suggest flame confinement, burner wall temperature and velocity fluctuations are vital to the flashback process. Des-pite the recent studies flashback is yet not completely understood. \\ This research focuses on premixed turbulent hydrogen and hydrocarbon combustion to further investigate the possibilities of using hydrogen in a gas turbine. The aim of this research is to gain more insight in the flashback process by varying velocity fluctuations while keeping the bulk velocity constant. The first objective is to gain insight in the relation between bulk velocity at flashback and velocity fluctuations. The second objective is to gain insight in the relation between bulk velocity at flashback and low velocity streaks upstream the flame front. The third research objective is to gain insight in the relation between flame front, boundary layer obstruction and bulk velocity at flashback. \\ All experiments were conducted with a Bunsen burner. A screw, acting as boundary layer obstruction, was placed below the burner rim to locally disturb the flow. The influence of the local disturbance on bulk velocity at flashback was investigated by mapping flashback propensity and by examining non-reacting and reacting pipe flow with planar Particle Image Velocimetry (PIV). The fuel compositions studied in this research are DNG, hydrogen and mixtures containing 20, 40, 60 or 80 volumetric percentage . \\ The flashback maps show that bulk velocity at flashback increases with obstruction height for all gas mixtures. The obstruction height is the height from burner wall to screw tip. The results obtained through the non-reacting field experiment confirmed that the flow was fully-developed and turbulent. Furthermore, the results showed that obstruction height locally increased velocity fluctuations. The average velocity downstream the obstruction slightly decreased with increasing obstruction height. The reacting field was examined during flashback and during stable operation to relate flashback propensity and time-averaged flow characteristics with statistical analysis. The results showed flame front axial distance from the burner rim decreases with increasing obstruction height, indicating that a flame produced by a burner with boundary layer obstruction is more prone to flashback. The flow characteristics just upstream the flame front were analyzed because once the conditions upstream the flame front are suitable, flashback occurs. \\ A flashback prediction model developed at the TU Munich was modified to account for the obstruction height. The modelled results indicate that, in an unconfined set-up, flashback might be described with time-averaged flow characteristics and that the turbulent burning velocity is strongly correlated to the bulk velocity at flashback. Histograms of the instantaneous velocity showed that obstruction height has no influence on low velocity streaks and thus it seems low velocity streaks are not dominant in the flashback process of premixed unconfined flames. The absence of low velocity streaks for different obstruction heights indicates that flashback of unconfined flames is a different process than flashback of confined flames
De kracht van onbewust gepercipieerde gezichtskenmerken.
No full textNon-profit organisaties maken gebruik van fondswervingsadvertenties. Er is echter weinig aandacht voor de invloed van de gezichtskenmerken van de afgebeelde persoon op de effectiviteit van de fondswervingsadvertentie. Het huidige onderzoek richtte zich daarom op de mogelijke invloed van emotie, leeftijd en tranen op de effectiviteit van fondswervingsadvertenties. Doormiddel van een experiment met binnenproefpersoonontwerp werd onderzocht of de gepercipieerde hulpbehoefte van de afgebeelde persoon en de intentie om te helpen en te doneren en de hoogte van de potentiele donatie van de proefpersoon werden beïnvloed door de gezichtskenmerken van de afgebeelde persoon. Het bleek dat de proefpersonen meer zouden doneren aan een droevig persoon dan aan een neutraal persoon. Hiernaast bleek dat het effectiever is om een niet huilende volwassene af te beelden dan een niet huilend kind en dat wanneer er een huilend persoon afgebeeld moet worden het effectiever is om een kind af te beelden dan een volwassene
On embryo implantation
No full textHomburg, R. [Promotor]Hompes, P.G.A. [Copromotor]Lambalk, C.B. [Copromotor
Als u de trap opsjouwt met de wasmand. Een membership categorisation analysis van patiënt-huisartsconsulten.
No full textDit onderzoek had als doel om inzicht te bieden in hoe artsen en patiënten elkaar of zichzelf categoriseren als man of vrouw (gendercategorisatie) en wat de consequenties hiervan zijn op het verloop van het consult. Uit voorgaand onderzoek blijkt dat zowel sekse als gender van zowel de patiënt als de arts van invloed kunnen zijn op de kwaliteit van zorg. In totaal zijn 70 huisartsconsulten uit de regio Nijmegen kwantitatief en middels membership categorisation analysis (MCA) geanalyseerd op gendercategorisatie. Drie typen gendercategorisatie bleken het meest voorkomend in deze huisartsconsulten en zijn daarom geselecteerd voor de analyse middels MCA. De drie typen zijn de hypothetische situatie, de gegenderde verklaring en de gegenderde smalltalk. Het huidige onderzoek toont hiermee aan dat hoewel dit medisch gezien niet noodzakelijk is, zowel de arts als de patiënt op verschillende manieren gecategoriseerd worden op basis van hun gender wat invloed heeft op het verloop het consult
Is aspirin effective in women undergoing in vitro fertilization (IVF)? Results from an individual patient data meta-analysis (IPD MA)
No full textBACKGROUND Aspirin is believed to improve the outcome of IVF, but previous conventional meta-analyses on the subject are conflicting. Therefore, we performed a meta-analysis with individual patient data (IPD MA) of randomized clinical trials (RCTs) on the subject. METHODS A systematic literature search was conducted to identify RCTs assessing the effectiveness of aspirin in IVF. Authors were asked to share their original data. In a one step meta-analytic approach, the treatment effect of aspirin was estimated with odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression, based on the intention to treat principle. RESULTS Ten studies fulfilled the inclusion criteria. Authors of six studies provided IPD, including 1119 patients (562 placebo and 557 aspirin). There were 160 clinical pregnancies in the aspirin (28.8%) and 179 (31.9%) in the placebo group [OR 0.86, 95% CI (0.69–1.1)]. There were 129 ongoing pregnancies in the aspirin (23.6%) and 147 in the placebo group (26.7%) [OR 0.85, 95% CI (0.65–1.1)]. Whereas the conventional meta-analysis limited to studies that could provide IPD showed an OR of 0.89 (95% CI 0.69–1.2), the conventional meta-analysis limited to the eight studies of which method of randomization could be confirmed showed an OR of 0.94 (95% CI 0.76–1.17) and the conventional meta-analysis including all 10 eligible RCTs identified with our search changed the OR to 1.07 (95% CI 0.81–1.41). This difference in direction of effect, derived from the studies not able to share IPD of which quality of randomization could not be confirmed. CONCLUSIONS Aspirin does not improve pregnancy rates after IVF.E. Groeneveld, K.A. Broeze, M.J. Lambers, M. Haapsamo, K. Dirckx, B.C. Schoot, B. Salle, C.I. Duvan, R. Schats, B.W. Mol, and P.G.A. Hompes, for the IPD MARIA study grou
Mineral Nutrition Of Campos Rupestres Plant Species On Contrasting Nutrient-impoverished Soil Types
No full textIn Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic nutrient-impoverished soils, which are particularly low in phosphorus (P). Despite recognition of the campos rupestres as a global biodiversity hotspot, little is known about the diversity of P-acquisition strategies and other aspects of plant mineral nutrition in this region. To explore nutrient-acquisition strategies and assess aspects of plant P nutrition, we measured leaf P and nitrogen (N) concentrations, characterized root morphology and determined the percentage arbuscular mycorrhizal (AM) colonization of 50 dominant species in six communities, representing a gradient of soil P availability. Leaf manganese (Mn) concentration was measured as a proxy for carboxylate-releasing strategies. Communities on the most P-impoverished soils had the highest proportion of nonmycorrhizal (NM) species, the lowest percentage of mycorrhizal colonization, and the greatest diversity of root specializations. The large spectrum of leaf P concentration and variation in root morphologies show high functional diversity for nutritional strategies. Higher leaf Mn concentrations were observed in NM compared with AM species, indicating that carboxylate-releasing P-mobilizing strategies are likely to be present in NM species. The soils of the campos rupestres are similar to the most P-impoverished soils in the world. 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JaJakarta - The anarchistic factory as an alternative for squatting
No full textJabodetabek, the urban agglomeration consisting of DKI Jakarta, Bogor, Depok, Tangerang and Bekasi, is the second fastest growing megacity on the planet (Robinson, 2011). Current projections show that Jabodetabek’s population will reach 38 million people in 2030 (Jakarta municipality, 2014). However, this growth will take place in a city that is facing major problems; all these issues are deeply interconnected and are seriously jeopardizing the city’s livability. (Kusno, 2010; Robinson, 2011; Silver, 2007). We believe these problems should be tackled with a radical reconsideration of Jakarta’s urban fabric. We propose the double the amount of inhabitants, going from Jakarta to Jajakarta. In 2030 Jakarta will have expended so much due to migration and population growth, and in this process overtaken many adjacent cities, that it will be called Jabodetabekasepususesuci (Jakarta municipality, 2014). An unpronounceable name for a megacity that has become so addictive to growth that it will become uncontrollable. The municipality will be left incapable in effectively managing the dramatically enlarged city. Stopping the urban sprawl will mean that the city center, known as DKI Jakarta, should increase its density; both in its inhabitants as in floor space, in order to be able to house the majority of the expected growth for all income classes. This change will require a new kind of urban fabric, in which the kampung is intensified.The Why FactoryArchitectureArchitecture and The Built Environmen
Development of surrogate-based multidisciplinary optimization methodology with flutter constraints for aircraft conceptual design
No full textAircraft concepts with high aspect ratio wings have been investigated more extensively in the recent past, as such configurations would reduce the induced drag significantly. At the same time, the high aspect ratio challenges the wing’s aero-structural stability (flutter). Therefore there is a need to perform aero-structural analysis already within the conceptual design phase, preferably in an automated fashion to enable the execution of multidisciplinary design optimization (MDO). This study has investigated methods to directly incorporate flutter speed predictions as constraints in an automated optimization process for conceptual design of aircraft. The computationally expensive flutter calculations have been modelled using different surrogate models (SM) to reduce calculation time in the automated design process. The combination of different surrogate and design of experiments (DOE) methods have been investigated and compared. Each combination of SM and DOE provides an indication of the trade-off between computation time and precision. The MultiFit software tool, developed by the Netherlands Aerospace Centre, was used to set up the different SMs. Artificial neural networks have shown the best capabilities in representing the behaviour of the flutter speed. Furthermore, surrogate-based optimization (SBO) methods have been able to find the same optimum design point at lower computational cost compared to the classical (non-surrogate) multidisciplinary feasible (MDF) MDO architecture. In an attempt to reduce optimization time even further, an adaptive surrogate modelling approach has been incorporated in the surrogate-based optimization method. The proposed method starts with a small DOE to create an initial SM. Then, an SBO is performed on this model. The value of the resulting optimum is recalculated using the complete multidisciplinary analysis and this new design point is then added to the DOE. A new surrogate model is created and an SBO is performed using the earlier found optimum as a starting point. This process is repeated until the process converges. The case study in this research has shown that adaptive surrogate-based optimization can be an efficient method to find the optimum of the objective function at a low computational cost, although more advanced enrichment and convergence criteria are recommended to improve the algorithm.Aerospace EngineeringAerodynamics, Wind Energy & Propulsio
Sensitivity and control of a pneumatic force transducer: A proof of principle
No full textCurrent upper-limb prostheses are often rejected as a result of high activation forces that are needed for control. Another reason for rejection is the absence of appropriate proprioceptive feedback. In this study, a pneumatic control system was designed that decreased the activation forces and where proprioceptive feedback was provided. The system was placed on the back of the user and was actuated by shoulder movements. The design has been evaluated on two aspects, namely the sensitivity, determined by the Just Noticeable Difference (JND) and the Weber Fraction (WF), and the displacement (re-)production accuracy (e.g. opening/closing of the prosthetic hand). Ten healthy, right-handed male subjects performed both experiments. The sensitivity was assessed by a reminder task where two forces were compared. Four reference force levels were used: 2, 4, 6, and 8N. This resulted in WF values of: 18% for 2N, 4% for 4N, 3% for 6N, and 2% for 8N. The results for the three higher forces agreed with literature. To evaluate the displacement accuracy the Absolute Displacement Error (ADE), the Relative Displacement Error (RDE), and the Displacement Variability (DV) were measured for three different reference displacements: 5mm, 10mm, and 20mm. The results show that the control of the system is accurate enough for object manipulation and the relative error was lower than 1% for each reference displacement. This design may be the next step in controlling prosthetic hands
Design of a 3D printer for healthcare in Sub-Saharan Africa
No full textWith the introduction of the RepRap 3D printers, capable of printing most of its own parts, the cost of 3D printers dropped radically, making it an affordable and accessible technology, even for low resource settings. It is said that 3D printing can greatly increase accessibility to medical equipment in low resource settings because it enables local production and radically reduces costs. Within the Delft Global Initiative there are several research teams experimenting with the use of 3D printing for local production of low cost medical equipment in Sub-Saharan Africa. They quickly discovered that 3D printing in this setting is not as easy as it might sound. For one, the operating conditions were found to be much harsher in African, than in Western settings. According to researchers from Penn State University, current 3D printers lack in user-friendliness and robustness required to impact rural healthcare. Therefore, the goal of this project was to (1) identify the challenges for 3D printing in Sub-Saharan Africa, and (2) develop a final design proposal for a 3D printer for healthcare in this setting. The project started with an extensive analysis phase, where Kenya was chosen as a case study of a Sub-Saharan African country. The goal of this phase was to get a deep and qualitative understanding of the context of Kenya, and identify important implications for the design. In the design phase, an extensive amount of time and effort has gone into finding solutions for the challenges identified during the analysis. Solutions were developed to make the printer (1) able to operate on an unstable grid, (2) able to deal with excessive dust and high temperatures, (3) maintain a maximum printing uptime, (4) allow the printer to be used by anyone and finally (5) to allow the printer to be compactly transported. The first deliverable is a list of valuable insights that provides a deep and qualitative understanding in the context of Kenya in relation to 3D printing. This can primarily be used for the development of a 3D printer for low resource settings, but might also be valuable for initiatives working on closely related products in a similar setting. The second deliverable, in the form of a final design proposal, consists of a Prusa i3 printer adapted to fit the context of Kenya. It features a flexible power supply with backup battery, protection against dust and high temperatures, an automatic part ejection system, easy use through smartphone and lastly it is can be compactly transported and quickly assembled. The design proposal was evaluated by a panel of experts from Kenya and the US. They rated the final design to fit the intended user and context very well, but also stressed that it could be tailored more to the healthcare sector. The proposal was considered a better solution than what is currently on the market. More work should be done in the field of usability.Integrated Product Desig
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