88 research outputs found
AMICO galaxy clusters in KiDS-DR3: The impact of estimator statistics on the luminosity-mass scaling relation
No full textContext. As modern-day precision cosmology aims for statistical uncertainties of the percent level or lower, it becomes increasingly important to reconsider estimator assumptions at each step of the process, along with their consequences on the statistical variability of the scientific results.
Aims. We compare L1 regression statistics to the weighted mean, the canonical L2 method based on Gaussian assumptions, to infer the weak gravitational shear signal from a catalog of background ellipticity measurements around a sample of clusters, which has been a standard step in the processes of many recent analyses.
Methods. We use the shape measurements of background sources around 6925 AMICO clusters detected in the KiDS third data release. We investigate the robustness of our results and the dependence of uncertainties on the signal-to-noise ratios of the background source detections. Using a halo model approach, we derive lensing masses from the estimated excess surface density profiles.
Results. The highly significant shear signal allows us to study the scaling relation between the r-band cluster luminosity, L200, and the derived lensing mass, M200. We show the results of the scaling relations derived in 13 bins in L200, with a tightly constrained power-law slope of ∼1.24 ± 0.08. We observe a small, but significant, relative bias of a few percent in the recovered excess surface density profiles between the two regression methods, which translates to a 1σ difference in M200. The efficiency of L1 is at least that of the weighted mean and increases with higher signal-to-noise shape measurements.
Concluions. Our results indicate the relevance of optimizing the estimator for inferring the gravitational shear from a distribution of background ellipticities. The interpretation of measured relative biases can be gauged by deeper observations, and the increased computation times remain feasible
Monopile installation assessment: A critical assessment of an oscillating monopile during offshore installation
No full textAn offshore wind turbine requires a stable support structure to support the tower and nacelle. The support structure in the form of a monopile is lowered to the seabed and hammered in the soil. During the lowering process the monopile may show excessive motions, that occur on an irregular basis. The cause for this is unknown. This thesis is devoted to find the cause, to prevent this from happening in future operations. First off a literature study and analysis of the environmental conditions is carried out. A study in the mechanical behaviour of the system will provide a good perspective on the situation. Finally, the cause is verified with model tests and a numerical model is validated. From the environmental conditions wind and current are expelled as (main) contributor. Data analysis and system analysis conclude that waves are the main cause for the problem. In the model tests this cause is validated together with the mechanical behaviour (natural frequency) of the system. The natural frequency of the monopile is depending on the waterlevel. Wave frequencies (in the spectrum) close to the natural frequency cause a resonance phenomenon, with large monopile motions as consequence. A numerical model, based on a mechanical system and the Morison's equation is validated. The numerical model is a good and fast solution for modeling monopile motions, from wave conditions. The model can be used to predict future scenarios to prevent excessive monopile motions to occur, a (potential) tool for engineering purposes (determining workability)
Analysing the Relation Between Gaze Location and Gap Acceptance Decisions During Highway Merges
No full textBackground: Merging on a highway is a complex driving task that requires a lot of interaction with other road users. During these tasks, a driver is required to evaluate gaps in space and time between the themselves and other road users and obstacles in order to arrive at the right moment to merge onto the highway. To improve safety and increase road efficiency, it is necessary to understand the decision process during merging decisions. A way of achieving this, is to understand what visual information humans use during this decision process. This study investigated the relation between gaze location and gap acceptance decisions during highway merges.Methods: An experiment was performed in which 26 participants monitored an automated vehicle (AV) that was driving on a highway on-ramp. The participants were given the task to train the AV in whether or not to merge in front of an upcoming vehicle that was already driving on the highway. An eye tracker was used to measure gaze data, which was used to find the relation between gaze behaviour and decision outcomes and response times. A mixed-effects logistic model was used for a statistical analysis with decision outcomes as a dependent variable and different gap sizes as predictor variables. A mixed-effects linear model was used to find the relation between response times and dwell times and the different gap sizes and decision outcomes as predictor variables. For both the decision outcome and response time model, dwell time was later included to find the effect on the predictive validity.Results: The results show that a larger time and distance gap to the upcoming vehicle relate to a higher merging probability. For larger time gaps to the on-ramp, the probability of merging was found to be smaller. It was also found that time gaps to the end of the on-ramp significantly relate to response times, with an increase of 55ms per 1s. Larger time gaps to the upcoming vehicle significantly relates to larger response times, with an increase of 64ms per 1s. No significant relation was found between response time and distance gaps to the upcoming vehicle. The response time was found to be 0.60s longer for rejected gap decisions. The time gap to the end of the on-ramp significantly relates to dwell time, with an increase of 0.56% per 1s. The distance gap to the upcoming vehicle significantly relates to dwell time, with an increase of 0.60% per 10m. The time gap to the upcoming vehicle significantly relates to dwell time, with an increase of 0.52% per 1s. The presented results show as well that a significant relation exists between gaze behaviour and decision outcomes and response times. When analysing decision outcomes and response times, the interaction between dwell time and gap sizes should be taken into account. This improved the predictive validity of the used regression models.Conclusion: Several pieces of evidence suggest that gaze behaviour assist in understanding the human decision making process during merging. This study can serve as a basis for cognitive models that can investigate how the relation between gaze behaviour and gap sizes, decision outcomes and response times can help to understand and potentially predict gap acceptance decisions.Mechanical Engineering | Vehicle Engineering | Dynamics and Control
The Whale: Cultural centre Holesovice
No full textThe cultural centre will provide the city of Prague with a community centre combined with several large scale amenities (a cinema, a club, a big event hall and a skybar) to complement and, at the same time, relieve pressure on the inner city. The building is situated in a green, livable, accessible and diverse new area (outside of the clogged inner city) for both tourists and Praguers to experience and enjoy. Pedestrians are placed on a pedestal and find themselves in an unprecedented new inviting and exiting public space. The cultural centre will work on a city scale and a quarter scale. The goal should be to bring together different social groups. It will function as a community centre for the to be developed urban area as well as the existing neighborhoods (Letná and Holesovice). A place where they can meet, relax and use the wide variety of amenities. Concomitantly the building will give the Praguer an additional place to relax/go out during the weekend
Technical feasibility of a quick bridge replacement strategy with minimal traffic hindrance: On the retainment of existing foundations and the application of Advanced Cementitious Materials in an Accelerated Bridge Construction method
No full textBridges are a crucial part of the dense Dutch highway network. Almost 50% of the current bridges are built between 1960 and 1980 for an intended service life of 50 years and thus they might reach the end of their lifetime in the near future. This strongly indicates that a large challenge can be expected regarding infrastructural replacement.In current practice, the replacement of bridges within the highway network often leads to substantial traffic hindrance, which has a large negative impact on the Dutch economy. Therefore reduction of traffic hindrance – together with sustainability – is generally an important quality criteria in MEAT-procedures (Most Economic Advantageous Tender) for tender assignments. In order to prepare for the upcoming replacement challenge, there is a need for contractors, the government and product suppliers to invest in the development of a sustainable tender strategy now.The main objective of this thesis was to propose a tender strategy that incorporates sustainability and in particular the reduction of traffic hindrance into a technically feasible design. An extensive literature review has led to a quick bridge replacement strategy consisting of three time-reducing actions, listed according to their potential profit in construction time:1. Select the Accelerated Bridge Construction (ABC) approach:By means of lateral sliding or transportation by SPMTs (Self-Propelled Modular Transporters) entire superstructures can be constructed off-site and transported to their final location in a matter of hours.2. Retain the existing foundations:In terms of on-site construction time it would be beneficial to retain the existing foundations. Additionally, theory suggests that a profit in bearing capacity can be obtained compared to the current design codes, which might lead to the total elimination of additional foundation elements required.3. Avoid intermediate supports:Less elements are required if intermediate supports are avoided in the new bridge design. This does however lead to longer spans, and to prevent additional groundwork activities from an increase in deck height a higher slenderness must be obtained. Furthermore, the new superstructure design must be as light as possible, not only to allow for foundation retainment, but also to facilitate transportation and speed of erection.In particular, the technical feasibility of these actions - both separately and combined - required more research. A case study considering a two-span plate bridge was used to investigate these strategy actions. Research was done into the obtainable profit in retained pile foundations and the application of UHPC in a slender and lightweight bridge concept.It was concluded that the proposed tender strategy has a high potential. Not only is the on-site reduction time diminished but the retainment of the existing foundations and the application of UHPC in a slender and lightweight superstructure may also lead to a highly sustainable design.<br/
Finding the Operating Limits and Optimal Configuration of an Electrically Assisted Turbofan
No full textHybrid electric propulsion is a promising new technology to reduce emissions and fuel consumption of an aircraft. In this study a parallel hybrid electric configuration is considered. Since electric motors supply power in the most demanding take-off and climb phases to achieve the required thrust, the turbofan can be redesigned.It was found that the cruise thrust specific fuel consumption could be improved, even though no electric power is supplied in that phase. The hybrid-electric aircraft shows potential to save fuel over a complete mission. Most of these savings are however achieved due to fully electric taxiing. The weight of the electrical system largely offsets the efficiency improvements of the gas turbine during flight. Given that optimistic technology levels are used for these results, parallel hybrid electric propulsion is not expected to be used in the coming decade on short haul flights with narrow-body aircraft.Aerospace Engineering | Flight Performance and Propulsio
Nieuwenhuysenbuurt Futureproof: Minimizing the construction waste released by the demolition of Dutch post-war social housing
No full textMoving towards the Dutch circularity goals of 2050, this project aims to diminish the amount of construction waste released by the demolition of 282 post-war dwellings in the Nieuwenhuysenbuurt in Amsterdam West (1954). Through the use of a flexible and demountable building system, construction waste is diminished now and in the future.Architecture, Urbanism and Building Sciences | Building Technolog
SLOWLY: A digital reflection tool to help Dutch nurses tell their story.
No full textThe extraordinary working conditions caused by the first wave of COVID-19 patients caused stress, anxiety and lack of sleep in frontline nurses. This negatively impacted their psychological well being which is important for providing optimal care and maintaining long-term employability (Schoonhoven & Trappenburg, 2020). There is a lack of accessible and low-threshold support tools such as online peer support platforms for nurses. While storytelling driven online peer support is a promising tool, it is unclear how it should be designed. This project aimed to design a storytelling tool, specific to the psychological needs of the Dutch nurses, that best facilitates online peer support. This report describes the research, design and evaluation activities as part of the design process of SLOWLY - A tool that helps nurses reflect on their experiences, preparing them to write a story to be shared as part of online peer support. A context and target group analysis lead to the assessment of the thirteen fundamental needs (Desmet & Fokkinga, 2020). Fulfilment of autonomy, competence and relatedness, as part of self determination theory (Deci & Ryan, 2000), was found to be critically low. This was the primary source for the design requirements of SLOWLY. After using the design requirements to access a wide variety of design interventions, SLOWLY proved to be the most promising concept due to its potential to provide understanding about an experience in an accessible, low-threshold and safe manner. A detailed digital prototype was created, which used five storytelling prompts (character, setting, plot, conflict and theme) to guide nurses in a five day reflection process. Their responses were shown to them during the writing process to help them write stories with more details relevant to their experience. SLOWLY was found to provide increased understanding of the experience based on user testing with seven participants. It showed potential to fulfil all three critically affected fundamental needs. An additional expert review with one nurse yielded a positive response to the likeability, ease of use, clarity and benefit of SLOWLY. The results of this project provided insight into the potential role of storytelling in facilitating online peer support for nurses. Further research is recommended to evaluate longitudinal effects and possible interactions as a result of story sharing.Design for Interactio
Designing Product Presentation and Communication to Enhance Product Experience at G-Star RAW’s Physical Retail Stores and Shops in 2023
No full textPreviously to the start of this project a research in fifteen monobrand stores of G-Star Raw has been conducted. During this research four major insights of the current consumer experience in the G-Star stores were derived which led to the following problem definition:Currently, G-Star RAW’s products are not experienced in full potential by the consumers since the product stories and features are communicated and presented unclear and inconsistent across their various physical stores and shops. For this reason, consumers are not able to value the full potential of the products. This is considered as an influencer of missing out on sales potential. G-Star believes that the physical stores and shops are fulfilling an important role in the coming 5 years (until 2023) to enable consumers to experience their products and therefore their role needs to be researched.To research this problem definition the Vision in Product Design method is used. This approach is used to deconstruct the current context and interactions to be able to design a new vision which functions as a starting point to reconstruct a new context and interactions.The most important outcome of the deconstruction phase is that G-Star is trying to set up a new identity to appear more emphatic to the consumer. This new appearance is toning down the other values of G-Star and therefore the identity of the brand is experienced less strong by the consumer. Besides that, are the services that G-Star provides in their stores focussed on making instant sales are therefore not matching the needs of the current consumer.To find out how G-Star can improve their service to the consumer in the coming five years, a research to formulate a new retail vision is executed during the reconstruction phase. In the envisioned context consumers are constantly dealing with an overload of influences in a world where they are always connected to others. This provokes the insecurity of how to express their individual identity. To take this insecurity away from consumers the following statement has been created for G-Star:I want G-Star to empower people to stand out individually and to express their unique values by approaching them in an assuring way.To be assuring to the consumer the interaction should contain the following qualities: clarifying, fascinating, evaluating and unconstrained. To enable this interaction in their physical brand environments G-Star should appear as unpretentious and bold. The design that is created to facilitate this interaction is called a physical identity environment. In these environments are consumer able to mold their own identity with identity expressions of G-Star. The products of G-Star will be presented in ‘attitude areas’ and therefore they will be able to value the G-Star products by relating the attitudes to their own identity.Design for Interactio
Chasing the peak: optimal statistics for weak shear analyses
No full textContext. Weak gravitational lensing analyses are fundamentally limited by the intrinsic distribution of galaxy shapes. It is well known that this distribution of galaxy ellipticity is non-Gaussian, and the traditional estimation methods, explicitly or implicitly assuming Gaussianity, are not necessarily optimal.
Aims. We aim to explore alternative statistics for samples of ellipticity measurements. An optimal estimator needs to be asymptotically unbiased, efficient, and robust in retaining these properties for various possible sample distributions. We take the non-linear mapping of gravitational shear and the effect of noise into account. We then discuss how the distribution of individual galaxy shapes in the observed field of view can be modeled by fitting Fourier modes to the shear pattern directly. This allows scientific analyses using statistical information of the whole field of view, instead of locally sparse and poorly constrained estimates.
Methods. We simulated samples of galaxy ellipticities, using both theoretical distributions and data for ellipticities and noise. We determined the possible bias Δe, the efficiency η and the robustness of the least absolute deviations, the biweight, and the convex hull peeling (CHP) estimators, compared to the canonical weighted mean. Using these statistics for regression, we have shown the applicability of direct Fourier mode fitting.
Results. We find an improved performance of all estimators, when iteratively reducing the residuals after de-shearing the ellipticity samples by the estimated shear, which removes the asymmetry in the ellipticity distributions. We show that these estimators are then unbiased in the absence of noise, and decrease noise bias by more than ~30%. Our results show that the CHP estimator distribution is skewed, but still centered around the underlying shear, and its bias least affected by noise. We find the least absolute deviations estimator to be the most efficient estimator in almost all cases, except in the Gaussian case, where it’s still competitive (0.83 < η < 5.1) and therefore robust. These results hold when fitting Fourier modes, where amplitudes of variation in ellipticity are determined to the order of 10-3.
Conclusions. The peak of the ellipticity distribution is a direct tracer of the underlying shear and unaffected by noise, and we have shown that estimators that are sensitive to a central cusp perform more efficiently, potentially reducing uncertainties by more than 50% and significantly decreasing noise bias. These results become increasingly important, as survey sizes increase and systematic issues in shape measurements decrease.</jats:p
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