5,508 research outputs found
SC author and illustrator Kate Salley Palmer signing book
No full textPhotograph of SC author and illustrator Kate Salley Palmer signing boo
Book signing by SC author and illustrator Kate Salley Palmer
No full textPhotograph of Book signing by SC author and illustrator Kate Salley Palme
Addressing non-adherence in cluster randomised trials using instrumental variable-based methods
No full textRandomised trials are viewed as the gold standard for evaluating interventions. Depending on the intervention as well as other logistical factors, individuals or group of individuals may be randomised. The former is known as individual randomised controlled trials (RCTs) and the latter as cluster randomised trials (CRTs). CRTs offer advantages such as administrative convenience and reduction of contamination between trial groups but analysis is more complex than that for RCTs, because of the correlations between participants in the same cluster. When non-adherence to treatment occurs in the sense that some participants do not receive the randomly assigned treatment, confounding may exist as there may be common factors influencing treatment received and outcome. Consequently, the intention-to-treat approach, which compares outcomes between the groups as randomised, assesses the effect of being randomised to treatment rather than the causal treatment effect (effect of receiving the treatment). Ad-hoc methods often used to attempt to estimate the causal effect of treatment received such as per-protocol (PP) and as-treated (AT) approaches are likely to provide biased estimates because the assumptions necessary for those approaches to be unbiased are in general implausible. There exists extensive literature on estimating causal treatment effects from RCTs with non-adherence, but not as much for CRTs. Instrumental variables (IV) methods have the advantage, over other causal methods, of accommodating settings where there are unmeasured confounders when making causal inference. This thesis contributes to the literature on the estimation of causal treatment effects in CRTs where there is non-adherence to treatment and focuses on IV-based methods. I first ascertained the current practice of reporting and addressing nonadherence when causal treatment effects are of interest in CRTs via a systematic review of 123 CRT reports. Non-adherence was reported in about half of the CRTs, of which a third were interested in the causal treatment effect. All of the reviewed CRTs that reported adherence-adjusted estimates performed either PP or AT, without discussing the plausibility of the very strong assumptions necessary for such analyses to result in unbiased causal treatment estimates. No study estimated the local average treatment effect (LATE), that is the average treatment effect on those that would comply with the random allocated treatment, or any other appropriate statistical methods for unbiased causal estimation. In many clinical settings, the relevant causal question is whether treatment has an effect among those who are willing to take it, which would be quantified by the LATE. Hence the thesis focuses on this estimand, starting with an introduction and assessment of the performance of IV-based methods for estimating LATE at either cluster level (CL) or individual level (IL) through simulations under the required identification assumptions for LATE. I also perform sensitivity analyses for IL-LATE estimation and illustrate those methods using two real CRTs. The methods include two-stage least squares (TSLS) based on CL outcome summaries and the Wald estimator with the Schochet-Chiang standard error to estimate CL-LATE, and the Wald estimator, TSLS with robust cluster standard errors, TSLS with Moulton's standard errors and the Bayesian multilevel mixture modelling for estimating ILLATE. I conduct extensive simulations and illustrate the methods using real CRTs data. I demonstrate that TSLS is attractive for the estimation of CL-LATE and IL-LATE but is inefficient. This inefficiency may be reduced through covariate adjustment. The Bayesian multilevel mixture modelling is also attractive due to its flexibility and performs well particularly when non-adherence is at the individual level and the intracluster correlation coefficient for outcome is large. Stata and R codes are provided to facilitate implementation by trial investigators. I conclude by making some recommendations about how to estimate CL-LATE and IL-LATE to improve the quality of analysis when estimating causal treatment effects in the presence of non-adherence in CRTs
High-resolution clean-sc
No full textIn this paper a high-resolution extension of CLEAN-SC is proposed: HR-CLEAN-SC. Where CLEAN-SC uses peak sources in “dirty maps” to define so-called source components, HR-CLEAN-SC takes advantage of the fact that source components can likewise be derived from points at some distance from the peak, as long as these “source markers” are on the main lobe of the Point Spread Function (PSF). This is very useful when sources are closely spaced together, such that their PSFs interfere. Then, alternative markers can be sought in which the relative influence by PSFs of other source positions is minimised. For those markers the source components better agree with the actual sources, which allows for better estimation of their locations and strengths. This paper outlines the theory needed to understand this approach and discusses applications to 2D and 3D microphone array simulations with closely spaced sources
SC author and illustrator Kate Salley Palmer talking to event attendees
No full textPhotograph of SC author and illustrator Kate Salley Palmer talking to Rita Lewi
Ca-modified Al–Mg–Sc alloy with high strength at elevated temperatures due to a hierarchical microstructure
No full textAl-Mg alloys are normally prone to lose part of their yield and tensile strength at high temperatures due to insufficient thermal stability of the microstructure. Here, we present a Ca-modified Al–Mg–Sc alloy demonstrating high strength at elevated temperatures. The microstructure contains Al4Ca phases distributed as a network along the grain boundary and Al3(Sc,Zr) nano-particles dispersed within the grains. The microstructure evolution and age-hardening analysis indicate that the combination of an Al4Ca network and Sc-rich nano-particles leads to excellent thermal stability even upon aging at 300 °C. The tensile strength of the alloy for temperatures up to 250 °C is significantly improved by an aging treatment and is comparable with the commercial heat-resistant aluminum alloys, i.e., A356 and A319. At a high temperature of 300 °C, the tensile strength is superior to the above-mentioned commercial alloys, even more so when expressed as the specific strength due to the low density of Ca-modified Al–Mg–Sc alloy. The excellent high-temperature strength results from a synergistic effect of solid solution strengthening, grain boundary strengthening and nanoparticle order strengthening.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Novel Aerospace Material
SC-Square: Overview to 2021.
No full textThis extended abstract was written to accompany an invited talk at the 2021 SC-Square Workshop, where the author was asked to give an overview of SC-Square progress to date. The author first reminds the reader of the definition of SC-Square, then briefly outlines some of the history, before picking out some (personal) scientific highlights
SC-Square: Overview to 2021.
No full textThis extended abstract was written to accompany an invited talk at the 2021 SC-Square Workshop, where the author was asked to give an overview of SC-Square progress to date. The author first reminds the reader of the definition of SC-Square, then briefly outlines some of the history, before picking out some (personal) scientific highlights
Supply Chain (SC) Network Optimization
No full textSupply chain network design and optimization is one of the most important strategic decisions that an organization has to make. SC network design decisions are strategic-level SC decisions because they have long-lasting effect on the firms' supply chain performance and the decisions cannot be changed in a short period. In this chapter, the author aims to introduce the concept of SC network optimization to the managers of medium-sized enterprises. The chapter also explains the importance of the SC network optimization studies, educates readers about how they can benefit from the concept, and tries to show how the implementation of SC network optimization/design will improve the competitiveness of these organizations. The readers are also guided through the four steps of SC network optimization process. Finally, the chapter provides a brief review of the SC network optimization literature and proposes future research directions. </jats:p
The turbulence structure of 3D separation (Stall Cells) over an airfoil
No full textThe flow over airfoils that experience separation of the trailing edge type becomes three-dimensional at angles of attack around maximum lift and Stall Cells (SCs) form. SCs are large scale coherent structures of separated flow that consist of two counter-rotating vortices. In the present study the turbulence structure of a SC over a rectangular wing is investigated using Stereo PIV measurements. It is found that the turbulence characteristics of the flow are highly anisotropic and that the Boussinesq approximation is invalid. High values of normal Reynolds stresses in the SC vortices and the separation shear layer region indicates a wandering motion of the former and a flapping motion of the latter. Based on the available data the relation between Reynolds stresses, their production terms and the mean flow gradients is examined. It is found that at the centre of the SC, between the two vortices, the flow characteristics resemble those of a double shear layer while at the vortex region the effect of the vortices leads to double peaks in production terms
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