Numerical experiments in semi-infinite programming

A quasi-Newton algorithm for semi-infinite programming using an L∞ exact penalty function is described, and numerical results are presented. Comparisons with three Newton algorithms and one other quasi-Newton algorithm show that the algorithm is very promising in practice

Virtue and austerity

Virtue ethics is often proposed as a third way in health-care ethics, that while consequentialism and deontology focus on action guidelines, virtue focuses on character; all three aim to help agents discern morally right action although virtue seems to have least to contribute to political issues, such as austerity. I claim: (1) This is a bad way to characterize virtue ethics. The 20th century renaissance of virtue ethics was first proposed as a response to the difficulty of making sense of ‘moral rightness’ outside a religious context. For Aristotle the right action is that which is practically best; that means best for the agent in order to live a flourishing life.There are no moral considerations besides this. (2) Properly characterized, virtue ethics can contribute to discussion of austerity. A criticism of virtue ethics is that fixed characteristics seem a bad idea in ever-changing environments; perhaps we should be generous in prosperity, selfish in austerity. Furthermore, empirical evidence suggests that people indeed do change with their environment. However, I argue that virtues concern fixed values not fixed behaviour; the values underlying virtue allow for different behaviour in different circumstances: in austerity, virtues still give the agent the best chance of flourishing. Two questions arise. (a) In austere environments might not injustice help an individual flourish by, say, obtaining material goods? No, because unjust acts undermine the type of society the agent needs for flourishing. (b) What good is virtue to those lacking the other means to flourish? The notion of degrees of flourishing shows that most people would benefit somewhat from virtue. However, in extreme circumstances virtue might harm rather than benefit the agent: such circumstances are to be avoided; virtue ethics thus has a political agenda to enable flourishing. This requires justice, a fortiori when in austerity

Vascular self-healing within carbon fibre reinforced polymer stringer run-out configurations

Stringer debonding within stiffened, assembled aerospace structures is one of the most critical damage scenarios that can occur in such structures. As a result, a degree of redundancy is inherently built-in to the design process of skin-stringer configurations to mitigate against premature and in-service failure. Introducing a “self-healing” solution for stringer run-out configurations has the benefit of mitigating and controlling damage initiation, and by introducing this concept there is great potential to reduce excessive conservative safety margins that could ultimately lead to more lightweight designs. Vascular self-healing technology has been successfully implemented into a simplified strap lap specimen, showing that the introduction of a vascular microchannel reduces the strength by 15% but has little effect on the stiffness. Upon delivery and cure of epoxy-based self-healing agents full recovery of the mechanical properties was observed. This self-healing approach has been further implemented into industrially relevant, larger stringer run-out panels as a feasibility study, in which no knockdown to mechanical properties caused by the embedded vascular microchannels has been observed, this study has also shown similar promising results in terms of performance recovery.</p

A direct search conjugate directions algorithm for unconstrained minimization

A direct search algorithm for unconstrained minimization of smooth functions is described. The algorithm minimizes the function over a sequence of successively finer grids. Each grid is defined by a set of basis vectors. From time to time these basis vectors are updated to include available second derivative information by making some basis vectors mutually conjugate. Convergence to one or more stationary points is shown, and the finite termination property of conjugate direction methods on strictly convex quadratics is retained. Numerical results show that the algorithm is effective on a variety of problems including ill-conditioned problems

Effect of limited precision on the BFGS quasi-Newton algorithm

Some claim that updating approximate Hessian information via the BFGS formula with a Cholesky factorisation offers greater numerical stability than the more straightforward approach of performing the update directly. Others claim that no such advantage exists and that any such improvement is probably due to early implementations of the DFP formula in conjunction with low accuracy line searches. We find no discernible advantage in choosing factorised implementations (over non-factorised implementations) of BFGS methods when approximate Hessian information is available to full machine precision. However, the type of implementation may have significant effects when approximate Hessian information is only available to limited precision. Furthermore, a conjugate directions factorisation outperforms the other methods explored (including Cholesky factorisation)

A Tablet-based Virtual Environment for Neurosurgery Training

Published in Presence: Teleoperators and Virtual Environments, Spring 2015No. 2, Pages 155-162 Posted Online October 15, 2015. doi:10.1162/PRES_a_00224The requirement for training surgical procedures without exposing the patient to additional risk is well accepted and is part of a national drive in the UK and internationally. Computer-based simulations are important in this context, including neurosurgical resident training. The objective of this study is to evaluate the effectiveness of a custom built virtual environment in assisting training of a ventriculostomy procedure. The training tool (called VCath) has been developed as an app for a tablet platform to provide easy access and availability to trainees. The study was conducted at the first boot camp organized for all year one trainees in neurosurgery in the UK. The attendees were randomly distributed between the VCath training group and the Control group. Efficacy of performing ventriculostomy for both groups was assessed at the beginning and end of the study using a simulated insertion task. Statistically significant changes in performance of selecting the burr hole entry point, the trajectory length and duration metrics for the VCath group, together with a good indicator of improved normalized jerk (representing the speed and smoothness of arm motion), all suggest that there has been a higher level cognitive benefit to using VCath. The app is successful as it is focused on the cognitive task of ventriculostomy, encouraging the trainee to rehearse the entry point and use anatomical landmarks to create a trajectory to the target. In straight-line trajectory procedures such as ventriculostomy, cognitive task based education is a useful adjunct to traditional methods and may reduce the learning curve and ultimately improve patient safety

Identifying key influences on antibiotic use in China: a systematic scoping review and narrative synthesis

INTRODUCTION: The inappropriate use of antibiotics is a key driver of antimicrobial resistance. In China, antibiotic prescribing and consumption exceed recommended levels and are relatively high internationally. Understanding the influences on antibiotic use is essential to informing effective evidence-based interventions. We conducted a scoping review to obtain an overview of empirical research about key behavioural, cultural, economic and social influences on antibiotic use in China. METHODS: Searches were conducted in Econlit, Medline, PsycINFO, Social Science citation index and the Cochrane Database of Systematic Reviews for the period 2003 to early 2018. All study types were eligible including observational and intervention, qualitative and quantitative designs based in community and clinical settings. Two authors independently screened studies for inclusion. A data extraction form was developed incorporating details on study design, behaviour related to antibiotic use, influences on behaviour and information on effect (intervention studies only). RESULTS: Intervention studies increased markedly from 2014, and largely focused on the impact of national policy and practice directives on antibiotic use in secondary and tertiary healthcare contexts in China. Most studies used pragmatic designs, such as before and after comparisons. Influences on antibiotic use clustered under four themes: antibiotic prescribing; adherence to antibiotics; self-medicating behaviour and over-the-counter sale of antibiotics. Many studies highlighted the use of antibiotics without a prescription for common infections, which was facilitated by availability of left-over medicines and procurement from local pharmacies. CONCLUSIONS: Interventions aimed at modifying antibiotic prescribing behaviour show evidence of positive impact, but further research using more robust research designs, such as randomised trials, and incorporating process evaluations is required to better assess outcomes. The effect of national policy at the primary healthcare level needs to be evaluated and further exploration of the influences on antibiotic self-medicating is required to develop interventions that tackle this behaviour

The Use of Stereoscopy in a Neurosurgery Training Virtual Environment

Published in Presence: Teleoperators and Virtual EnvironmentsWe have previously investigated the effectiveness of a custom built virtual environment in assisting training of a ventriculostomy procedure, which is a commonly performed procedure by a neurosurgeon and a core task for trainee surgeons. The training tool (called VCath) was initially developed as a low fidelity app for a tablet platform to provide easy access and availability to trainees. Subsequently we have developed a high fidelity version of VCath that uses a stereoscopic display to immerse the trainee in the virtual environment. This paper reports on two studies that have been carried out to compare the low and high fidelity versions of VCath, particularly to assess the value of stereoscopy. Study 1 was conducted at the second annual boot camp organized for all year one trainees in neurosurgery in the UK. Study 2 was performed on lay people, with no surgical experience. Our hypothesis was that using stereoscopy in the training task would be beneficial. Results from Study 1 demonstrated that performance improved for both the control group and the group trained with the tablet version of VCath. The group trained on the high fidelity version of VCath with a stereoscopic display showed no performance improvement. The indication is that our hypothesis is false. In Study 2, six different conditions were investigated that covered the use of training with VCath on a tablet, a mono display at two different sizes, a stereo display at two different sizes, and a control group who received no training. Results from this study with lay people show that stereoscopy can make a significant improvement to the accuracy of needle placement. The possible reasons for these results and the apparent contradiction between the two studies are discussed

Astrometric and Timing Effects of Gravitational Waves from Localized Sources

A consistent approach for an exhaustive solution of the problem of propagation of light rays in the field of gravitational waves emitted by a localized source of gravitational radiation is developed in the first post-Minkowskian and quadrupole approximation of General Relativity. We demonstrate that the equations of light propagation in the retarded gravitational field of an arbitrary localized source emitting quadrupolar gravitational waves can be integrated exactly. The influence of the gravitational field on the light propagation is examined not only in the wave zone but also in cases when light passes through the intermediate and near zones of the source. Explicit analytic expressions for light deflection and integrated time delay (Shapiro effect) are obtained accounting for all possible retardation effects and arbitrary relative locations of the source of gravitational waves, that of light rays, and the observer. It is shown that the ADM and harmonic gauge conditions can both be satisfied simultaneously outside the source of gravitational waves. Their use drastically simplifies the integration of light propagation equations and those for the motion of light source and observer in the field of the source of gravitational waves, leading to the unique interpretation of observable effects. The two limiting cases of small and large values of impact parameter are elaborated in more detail. Explicit expressions for Shapiro effect and deflection angle are obtained in terms of the transverse-traceless part of the space-space components of the metric tensor. We also discuss the relevance of the developed formalism for interpretation of radio interferometric and timing observations, as well as for data processing algorithms for future gravitational wave detectors.Comment: 43 pages, 4 Postscript figures, uses revtex.sty, accepted to Phys. Rev. D, minor corrections in formulae regarding algebraic sign