3,029 research outputs found
Optimization using surrogate models and partially converged computational fluid dynamics simulations
No full textEfficient methods for global aerodynamic optimization using computational fluid dynamics simulations should aim to reduce both the time taken to evaluate design concepts and the number of evaluations needed for optimization. This paper investigates methods for improving such efficiency through the use of partially converged computational fluid dynamics results. These allow surrogate models to be built in a fraction of the time required for models based on converged results. The proposed optimization methodologies increase the speed of convergence to a global optimum while the computer resources expended in areas of poor designs are reduced. A strategy which combines a global approximation built using partially converged simulations with expected improvement updates of converged simulations is shown to outperform a traditional surrogate-based optimization
An adjoint for likelihood maximization
No full textThe process of likelihood maximization can be found in many different areas of computational modelling. However, the construction of such models via likelihood maximization requires the solution of a difficult multi-modal optimization problem involving an expensive O(n3) factorization. The optimization techniques used to solve this problem may require many such factorizations and can result in a significant bottle-neck. This article derives an adjoint formulation of the likelihood employed in the construction of a kriging model via reverse algorithmic differentiation. This adjoint is found to calculate the likelihood and all of its derivatives more efficiently than the standard analytical method and can therefore be utilised within a simple local search or within a hybrid global optimization to accelerate convergence and therefore reduce the cost of the likelihood optimization
Response surface model evolution
No full textMethods are presented for reducing time and effort when performing aerodynamic optimisation using response surface models. Significant time savings are made possible by monitoring the convergence of computational fluid dynamics simulations and omitting regions of poor designs. In so doing, optimal regions of the design space can be highlighted and surface refinement commenced early in the convergence of the design point set. A strategy employing surface updates with new data at points of maximum expected improvement is shown to perform more efficiently than reducing the design space to the region of the optimum. The response surface evolution methods are demonstrated through an example two parameter optimisation of a flap track fairing on a commercial airliner wing
Facing the Future: the Changing Shape of Academic Skills Support at Bournemouth University
No full textThis paper explores the potential impact of changes to higher education in England on student expectations, engagement, lifestyles and diversity, and outlines implications for the development of digital literacy within academic skills support at Bournemouth University (BU). We will investigate how tackling resource constraints with organisational change can also enable efficient, centralised provision of support materials that utilise networks to overcome the risk of fragmented support for digital literacy. We will also look at how changing delivery modes for support can accommodate changing student lifestyles whilst tackling a weakness of centralised support for digital literacy: that it can become detached from the student’s subject-focused academic practice. Finally we will explore how involving students in developing support can help us to face changes to student expectations and engagement whilst ensuring that materials are authentic and speak to learners in their own voice
The influence of strut-connectors in stented vessels: a comparison of pulsatile flow through five coronary stents
No full textThe design of coronary stents has evolved significantlyover the past two decades. However, they still face theproblem of in-stent restenosis, formation of neointima within12 months of the implant. The biological response after stentimplantation depends on various factors including the stentgeometry which alters the hemodynamics. This study takesfive different coronary stent designs, used in clinical practice,and explores the hemodynamic differences arising due to thedifference in their design. Of particular interest is the designof the segments (connectors) that connect two struts.Pulsatile blood flow analysis is performed for each stent,using 3-D computational fluid dynamics (CFD), and variousflow features viz. recirculation zones, velocity profiles, wallshear stress (WSS) patterns, and oscillatory shear indices areextracted for comparison. Vessel wall regions with abnormalflow features, particularly low, reverse, and oscillating WSS,are usually more susceptible to restenosis. Unlike previousstudies, which have tried to study the effect of designparameters such as strut thickness and strut spacing onhemodynamics, this work investigates the differences in theflow arising purely due to differences in stent-shape, otherparameters being similar. Two factors, the length of theconnectors in the cross-flow direction and their alignmentwith the main flow, are found to affect the hemodynamicperformance. This study also formulates a design index(varying from 18.81% to 24.91% for stents used in thisstudy) that quantifies the flow features that could affectrestenosis rates and which, in future, could be used foroptimization studies
Dissimilarity is used as evidence of category membership in multidimensional perceptual categorization: a test of the similarity-dissimilarity generalized context model
No full textIn exemplar models of categorization, the similarity between an exemplar and category members constitutes evidence that the exemplar belongs to the category. We test the possibility that the dissimilarity to members of competing categories also contributes to this evidence. Data were collected from two 2-dimensional perceptual categorization experiments, one with lines varying in orientation and length and the other with coloured patches varying in saturation and brightness. Model fits of the similarity-dissimilarity generalized context model were used to compare a model where only similarity was used with a model where both similarity and dissimilarity were used. For the majority of participants the similarity-dissimilarity model provided both a significantly better fit and better generalization, suggesting that people do also use dissimilarity as evidence
Maximizing Research Impact Through Institutional and National Open-Access Self-Archiving Mandates
No full textNo research institution can afford all the journals its researchers may need, so all articles are losing research impact (usage and citations). Articles made “Open Access,” (OA) by self-archiving them on the web are cited twice as much, but only 15% of articles are being spontaneously self-archived. The only institutions approaching 100% self-archiving are those that mandate it. Surveys show that 95% of authors will comply with a self-archiving mandate; the actual expe-rience of institutions with mandates has confirmed this. What institutions and funders need to mandate is that (1) immediately upon acceptance for publication, (2) the author’s final draft must be (3) deposited into the Institutional Repository. Only the depositing needs to be mandated; set-ting access privileges to the full-text as either OA or Restricted Access (RA) can be left up to the author. For articles published in the 93% of journals that have already endorsed self-archiving, access can be set as OA immediately; for the remaining 7%, authors can email the eprint in re-sponse to individual email requests automatically forwarded by the Repository
Gaiman, Neil
No full textA brief description of the main characteristics of the works for children of the British author Neil Gaiman, the themes he privileges in his stories, the way he portrays children and the relationship between children and adults
Jere Nash Interview with Neil McMillen (Part 1 of 2)
No full textInterview conducted by author Jere Nash with University of Southern Mississippi history professor Neil R. McMillen in the process of writing Mississippi Politics: The Struggle for Power, 1976-2006. Topics dicussed include race and politics in Mississippi; southern historians including Dewey Grantham, C. Vann Woodward, Numan V. Bartley, John Boles; segregation in Mississippi and resistance to change; genesis of McMillin\u27s book Dark Journey; fifteenth Freedom Summer reunion at Millsaps and Tougaloo; John Ditmer; contributing to A History of Mississippi edited by Richard Aubrey McLemore and reaction by the public and University of Southern Mississippi officials; hiring of African American faculty at USM; M.M. Roberts; and William D. McCain
Millisecond accuracy video display using OpenGL under Linux
No full textTo measure people’s reaction times to the nearest millisecond, it is necessary to know exactly when
a stimulus is displayed. This article describes how to display stimuli with millisecond accuracy on a
normal CRT monitor, using a PC running Linux. A simple C program is presented to illustrate how this
may be done within X Windows using the OpenGL rendering system. A test of this system is reported
that demonstrates that stimuli may be consistently displayed with millisecond accuracy. An algorithm
is presented that allows the exact time of stimulus presentation to be deduced, even if there are relatively
large errors in measuring the display time
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