16 research outputs found
Prediction of composition-dependent self-diffusion coefficients in binary liquid mixtures: The missing link for Darken-based models
No full textMutual diffusion coefficients can be successfully predicted with models based on the Darken equation. However, Darken-based models require composition-dependent self-diffusion coefficients which are rarely available. In this work, we present a predictive model for composition-dependent self-diffusion coefficients (also called tracer diffusion coefficients or intradiffusion coefficients) in nonideal binary liquid mixtures. The model is derived from molecular dynamics simulation data of Lennard-Jones systems. A strong correlation between nonideal diffusion effects and the thermodynamic factor is observed. We extend the model by McCarty and Mason (Phys. Fluids 1960, 3, 908-922) for ideal binary gas mixtures to predict the composition-dependent self-diffusion coefficients in nonideal binary liquid mixtures. Our new model is a function of the thermodynamic factor, the self-diffusion coefficients at infinite dilution, and the self-diffusion coefficients of the pure substances, which are readily available. We validate our model with experimental data of 9 systems. For both Lennard-Jones systems and experimental data, the accuracy of the predicted self-diffusion coefficients is improved by a factor of 2 compared to the correlation of McCarty and Mason. Thus, our new model significantly expands the practical applicability of Darken-based models for the prediction of mutual diffusion coefficients.Accepted Author Manuscript (the title slightly differs from the publishers version)Engineering Thermodynamic
TEDx Event center: Connecting the Binnengasthuis area and the city of Amsterdam
No full textTransformation of the Binnengasthuis area in Amsterdam to a place of connectivity.Heritage & ArchitectureArchitectureArchitecture and The Built Environmen
CoBaPreM Component-Based Predictive Maintenance to reduce unscheduled occurrences: A new strategy to improve reliability practices
No full textCosts associated to unscheduled and excessively prudent maintenance can contribute significantly to an airline's expenditure. Due to the complex nature of aviation related operations, reliability practices have been limited. In an attempt to improve component reliability, i.e. reduce maintenance-related costs, a new strategy was proposed which pursuits new avenues w.r.t. reliability modelling. The strategy focusses on identifying operational factors affecting component reliability and assessing whether these can be used to reduce the number of unscheduled occurrences (i.e. failures). Currently, reliability models are limited to exponential distributions, which assume hazard rates remain constant throughout the component's operational life. Studies have shown that time-independent Proportional Hazard Models (PHMs) could improve overall reliability, however, due to poor data, this was not verified. In this solution, the benefits of both time-independent and -dependent PHMs are assessed. Furthermore, underlying hazard functions were supplemented by introducing: normal, log-normal, logistic, exponential, Weibull, and gamma distributions. To address repairables, restoration events were simulated using Kijima type II General Repair Processes (GRPs). This project would not have been possible without the cooperation of QantasLink that supplied the data required. Results obtained from analysing historical data of the top ten components w.r.t. unscheduled removals indicated that adopting new maintenance schedules, derived from the proposed reliability models, could reduce the number of unscheduled occurrences by approximately 37% while limiting the increase in Mean Time Till (next) Repair (MTTRep). The variables identified by the solution were validated using literature, however, due to variable reduction and data limitations, the exact nature of component failures is yet to be established. Undeniably the potential benefits of adopting the proposed strategy are extensive. Nonetheless, numerous assumptions were introduced to overcome challenges imposed by the complex nature of the data. To overcome these challenges, recommendations and suggestions were proposed for the future development of airline reliability practices.Air Transport and OperationsControl and OperationsAerospace Engineerin
Istruzione e formazione: da beni di consumo a capitali di investimento
No full textIn this paper the promotion of education and training, i.e. workers’ employability is examined in theoretical and
practical terms. The author highlights the phenomenon of under-investment in general and firm-specific
human capital, and argues that training is a risky investment. Due to market failures – characterized as the
prisoner’s dilemma, free-riding, hold up and liquidity constraints – the vocational training of adult
employees fails to reach the optimal level. It is argued that cooperation and agreements between the social
partners and the extension of collective labour agreements provide solutions to these market failures. In
decision-making and accounting practice not only private enterprises, but also national governments treat
education and training as consumption goods and not as investment goods. Some practical policy solutions
are suggested to treat education and training more like real investments and to bridge the gap between human
capital theory and accounting practice, and to improve the quality of decision-making relating to education
and training
Component-Based Data-Driven Predictive Maintenance to Reduce Unscheduled Maintenance Events
No full textCosts associated with unscheduled and preventive maintenance can contribute significantly to an airline's expenditure. Reliability analysis can help to identify and plan for maintenance events. Reliability analysis in industry is often limited to statistically based approaches that incorporate failure times as the primary stochastic variable, with additional strict assumptions regarding independence of events and underlying distributions of failure phenomena. This foregoes the complex nature of aircraft operations, where a whole range of operational factors may influence the probability of occurrence of a maintenance event. The aim of this research is to identify operational factors affecting component reliability and to assess whether these can be used to reduce the number of unscheduled occurrences (i.e. failures). To do so, a data-driven approach is adopted where historical operational and maintenance data is gathered and analysed to identify operational factors with a measurable influence on maintenance event occurrence. Both time-independent and time-dependent Proportional Hazard Models (PHMs), models which incorporate operational factors as covariates, are employed to generate reliability estimates. Results obtained from analysing historical data of a set of ten components with respect to unscheduled removals indicates that adopting new maintenance schedules, derived from the proposed reliability models, could reduce the number of unscheduled occurrences by approximately 37%. The potential benefits of adopting the proposed strategy are extensive. Nonetheless, numerous assumptions have been introduced to overcome challenges imposed by the complex nature of the data. To overcome these challenges, recommendations are made for future development of the proposed approachAir Transport & Operation
Evaluating Risk Management Strategies for Third Party Payment Networks
No full textLike most consumers, you probably take the payment process when checking out at your favorite webshop, for granted. Regardless of which payment method you select, chances are big that the schemes of one of the few players within the payment industry - i.e. MasterCard or Visa - are used. We refer to this part of the industry as the card network. In order to create more competition for the card network, the European Commission is working on Payment Service Directive II (PSDII) which introduces the third party payment (TPP) network. Although there seems to be quite some potential for the TPP network, challenges are present. The new TPP network is less mature than the established card network that has dominated the payment industry for decades. Whereas one of the main challenges in the card network is the cost effective management of chargebacks, a similar challenge is present in the TPP network. Practice has shown that merchants that make use of payment methods in the TPP network are confronted with reversed payments - i.e. the TPP has provided an authorization, however no settlement has been received. We refer to these transactions as non-payments. There is a lack of knowledge about the reasons of the occurrence of the non-payments. In our research we have aimed to understand how big the financial risk of the occurrence of non-payments is and what could be strategies a payment service provider (PSP) can use to manage this risk. With our research, we have made four contributions. First, we described the payment process as it is organized in the TPP network and contrasted it with the card network. Second, we identified patterns in transaction data from the TPP network, that let us distinguish payments from non-payments. Third, we designed and evaluated risk management strategies that can be used to manage the non-payment risk. And fourth, we compared the merchant's transaction costs in the card and TPP networks to verify if the TPP network can become a cost competitor of the card network. The results of our research show that the TPP network is a cost competitor of the card network when considering the merchant's transaction costs.Economics of CybersecurityTechnology, Policy and Managemen
Schema van de fabricage van huishoudelijk aardewerk
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
The influence of the Sand Engine on the Delfland coastal cell
No full textThe Sand Engine is an example of a feeder nourishment that is intended to nourish coastal systems. This strategy is based on placing sediments highly concentrated at one location, from which it is expected to spread alongshore over large distances on decadal timescales.Here the morphological development of the Sand Engine mega feeder nourishment and the adjacent coastal sections is presented. This study is based on 37 high-resolution topographical surveys, spanning a coastal cell of 17 km alongshore. These data are explored to examine the alongshore spreading in the first five years after construction in 2011, as well as the response at different depth contours in the coastal profile.The analysis shows that the highly concentrated nourishment supplies sediment to a stretch of coast that is several times the initial length of the nourishment, as the size of the Sand Engine peninsula increased from 2.2 to 5.8km alongshore. The plan-form shape of the peninsula is found to gradually extend alongshore, while reducing in cross-shore extent. This behaviour is found to vary strongly with depth contours. The strongest response was found around the mean sea level iso-bath in contrast to the deeper parts and Aeolian parts of the Sand Engine. This variability in response over depth results in different profile slope development in accretive and erosive areas. In coastal sections which are eroding the sub-tidal slope decreases, while accretive profiles experience a profile slope increment over time. The cross shore extent of the morphologic response shows limited morphodynamic activity below the -8m NAP depth contour and confirms earlier assessments of closure depth at this coast.The current findings at the Sand Engine imply that mega feeder nourishments can be beneficial to the sediment budget of a larger coastal cell. However, volumes that are deposited around or below the depth of closure (around 15 % for the Sand Engine) may react on much longer time-scales than intended. Therefore, the feeding characteristics of mega feeder nourishments on time-scales of years should be assessed using the nourished volumes above the depth of closure rather than the total volume.Abstract to the presentation given at the NCK days 2018.Coastal Engineerin
Women's rights agenda and fragmented advocacy for safe abortion in Kenya
No full textRestrictive abortion laws resulting in unsafe abortions form one of the key causes of maternal morbidity and mortality in Kenya. Despite the existence of several Women's Rights Organisations (WROs), advocacy for safe abortions against restrictive laws does not have the momentum the subject deserves. This research draws on agenda-setting literature to explore factors that impede advocacy initiatives of WROs against restrictive abortion laws in Kenya. Using qualitative methods, the article shows that women's rights agenda results from existing societal norms, funding priorities, state legislation, and lack of solidarity among WROs.Policy AnalysisSanitary Engineerin
Why My Payment Got Rejected: A Method to Mine Payment Refusal Clues
No full textA significant amount of payments fail for seemingly ‘mysterious’ reasons when refused by an issuer (i.e. cardholder’s bank). The technical and social complexities, such as a principal-agent problem, hinder the development of policies or information architectures, which impose an issuer to share its ‘honest’ reason. In this thesis we propose a method to induce the authorisation decision rules which an issuer uses to refuse certain payments. We evaluate the method on a large database with payment transactions. Experts confirm the correctness and the completeness of the found rules. We experiment with strategies to act on the rules, which shows there is significant business value in the results. The results signal that there is a large potential which justifies further research to improve the method.Information- and Communication TechnologyEngineering Systems and ServicesTechnology, Policy and Managemen
