581 research outputs found
Aerodynamic noise from rigid trailing edges with finite porous extensions
This paper investigates the effects of finite flat porous extensions to
semi-infinite impermeable flat plates in an attempt to control trailing-edge
noise through bio-inspired adaptations. Specifically the problem of sound
generated by a gust convecting in uniform mean steady flow scattering off the
trailing edge and permeable-impermeable junction is considered. This setup
supposes that any realistic trailing-edge adaptation to a blade would be
sufficiently small so that the turbulent boundary layer encapsulates both the
porous edge and the permeable-impermeable junction, and therefore the
interaction of acoustics generated at these two discontinuous boundaries is
important. The acoustic problem is tackled analytically through use of the
Wiener-Hopf method. A two-dimensional matrix Wiener-Hopf problem arises due to
the two interaction points (the trailing edge and the permeable-impermeable
junction). This paper discusses a new iterative method for solving this matrix
Wiener-Hopf equation which extends to further two-dimensional problems in
particular those involving analytic terms that exponentially grow in the upper
or lower half planes. This method is an extension of the commonly used "pole
removal" technique and avoids the needs for full matrix factorisation.
Convergence of this iterative method to an exact solution is shown to be
particularly fast when terms neglected in the second step are formally smaller
than all other terms retained. The final acoustic solution highlights the
effects of the permeable-impermeable junction on the generated noise, in
particular how this junction affects the far-field noise generated by
high-frequency gusts by creating an interference to typical trailing-edge
scattering. This effect results in partially porous plates predicting a lower
noise reduction than fully porous plates when compared to fully impermeable
plates.Comment: LaTeX, 20 pp., 19 graphics in 6 figure
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How to discriminate between computer-aided and computer-hindered decisions: a case study in mammography
Background. Computer aids can affect decisions in complex ways, potentially even making them worse; common assessment methods may miss these effects. We developed a method for estimating the quality of decisions, as well as how computer aids affect it, and applied it to computer-aided detection (CAD) of cancer, reanalyzing data from a published study where 50 professionals (âreadersâ) interpreted 180 mammograms, both with and without computer support.
Method. We used stepwise regression to estimate how CAD affected the probability of a reader making a correct screening decision on a patient with cancer (sensitivity), thereby taking into account the effects of the difficulty of the cancer (proportion of readers who missed it) and the readerâs discriminating ability (Youdenâs determinant). Using regression estimates, we obtained thresholds for classifying a posteriori the cases (by difficulty) and the readers (by discriminating ability).
Results. Use of CAD was associated with a 0.016 increase in sensitivity (95% confidence interval [CI], 0.003â0.028) for the 44 least discriminating radiologists for 45 relatively easy, mostly CAD-detected cancers. However, for the 6 most discriminating radiologists, with CAD, sensitivity decreased by 0.145 (95% CI, 0.034â0.257) for the 15 relatively difficult cancers.
Conclusions. Our exploratory analysis method reveals unexpected effects. It indicates that, despite the original study detecting no significant average effect, CAD helped the less discriminating readers but hindered the more discriminating readers. Such differential effects, although subtle, may be clinically significant and important for improving both computer algorithms and protocols for their use. They should be assessed when evaluating CAD and similar warning systems
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Effects of incorrect computer-aided detection (CAD) output on human decision-making in mammography
To investigate the effects of incorrect computer output on the reliability of the decisions of human users. This work followed an independent UK clinical trial that evaluated the impact of computer-aided detection(CAD) in breast screening. The aim was to use data from this trial to feed into probabilistic models (similar to those used in "reliability engineering") which would detect and assess possible ways of improving the human-CAD interaction. Some analyses required extra data; therefore, two supplementary studies were conducted. Study 1 was designed to elucidate the effects of computer failure on human performance. Study 2 was conducted to clarify unexpected findings from Study 1
Are people experiencing the âpains of imprisonmentâ during the Covid-19 lockdown?
Background: By the end of March 2020, more than a fifth of the worldâs population was in various degrees of âlockdownâ in order to slow the spread of Covid-19. This enforced confinement led some to liken lockdown to imprisonment. We directly compared individualâs experiences of lockdown with prisonersâ experiences of imprisonment in order to determine whether psychological parallels can be drawn between these two forms of confinement.
Method: Online surveys of adults in lockdown in the UK (N = 300) and California (N = 450) were conducted four and five weeks into lockdown in each region, respectively. The UK data was then compared to Souza and Dhamiâs (2010) sample of 267 medium security prisoners in England, and the Californian data was compared to Dhami et al.âs (2007) sample of 307 medium security Federal prisoners in California. We measured the effects of Group (Lockdown v. Prison) on five categories of dependent variables (i.e., activity, social contact, thoughts, feelings, and rule-breaking), controlling for demographic differences between the groups.
Results: In both regions, people in lockdown thought significantly less often about missing their freedom, as well as missing their family and friends living elsewhere than did first-time prisoners. However, people in lockdown in both regions were also significantly less engaged in a range of daily activities than were first-time prisoners. Additionally, in both regions, people in lockdown reported feeling more hopeless than first-time prisoners.
Conclusions: Although Governments introducing lockdown policies do not intend to punish their citizens as courts do when sending convicted offenders to prison, such policies can have unintended adverse consequences. Psychological parallels can be drawn between the two forms of confinement
Effects of ignorance and information on judgments and decisions
We compared Turkish and English studentsâ soccer forecasting for English soccer matches. Although the Turkish students knew very little about English soccer, they selected teams on the basis of familiarity with the team (or its identified city); their prediction success was surprisingly similar to knowledgeable English studentsâconsistent with Goldstein and Gigerenzerâs (1999; 2002) characterization of the recognition heuristic. The Turkish students made forecasts for some of the matches with additional informationâthe half-time scores. In this and a further study, where British students predicting matches for foreign teams could choose whether or not to use half-time information, we found that predictions that could be made by recognition alone were influenced by the half-time information. We consider the implications of these findings in the context of Goldstein and Gigerenzerâs (2002, p. 82) suggestion that â. . . no other information can reverse the choice determined by recognitionâ and a recent more qualified statement (Gigerenzer & Goldstein, 2011
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Use of computer-aided detection (CAD) tools in screening mammography: a multidisciplinary investigation
We summarise a set of analyses and studies conducted to assess the effects of the use of a computer-aided detection (CAD) tool in breast screening. We have used an interdisciplinary approach that combines: (a) statistical analyses inspired by reliability modelling in engineering; (b) experimental studies of decisions of mammography experts using the tool, interpreted in the light of human factors psychology; and (c) ethnographic observations of the use of the tool both in trial conditions and in everyday screening practice. Our investigations have shown patterns of human behaviour and effects of computer-based advice that would not have been revealed by a standard clinical trial approach. For example, we found that the negligible measured effect of CAD could be explained by a range of effects on experts' decisions, beneficial in some cases and detrimental in others. There is some evidence of the latter effects being due to the experts using the computer tool differently from the intentions of the developers. We integrate insights from the different pieces of evidence and highlight their implications for the design, evaluation and deployment of this sort of computer tool
The seductive allure of technical language and its effect on covid-19 vaccine beliefs and intentions
Previous research has demonstrated a âseductive allureâ of technical or reductive language such that bad (e.g., circular) explanations are judged better when irrelevant technical terms are included. We aimed to explore if such an effect was observable in relation to a covid-19 vaccinations and if this subsequently affected behavioural intentions to take up a covid-19 vaccine. Using a between subjects design we presented participants (N=996) with one of four possible types of vignette that explained how covid-19 vaccination and herd immunity works. The explanations varied along two factors: (1) Quality, explanations were either good or bad (i.e., tautological); (2) Language, explanations either contained unnecessary technical language or did not. We measured participantsâ evaluation of the explanations and intentions to vaccinate. We demonstrate a âseductive allureâ effect of technical language on bad vaccine explanations. However, an opposite ârepellent disdainâ effect occurred for good explanations which were rated worse when they contained technical language. Moreover, we show that evaluations of explanations influence intentions to vaccinate. We suggest that misinformation that includes technical language could be more detrimental to vaccination rates. Importantly, however, clear explanatory public health information that omits technical language will be more effective in increasing intentions to vaccinate
Boundary Dissipation in a Driven Hard Disk System
A simulation is performed aiming at checking the existence of a well defined
stationary state for a two dimensional system of driven hard disks when energy
dissipation takes place at the system boundaries and no bulk impurities are
presentComment: 5 pages, 7 figure
RESPOND â A patient-centred programme to prevent secondary falls in older people presenting to the emergency department with a fall: Protocol for a mixed methods programme evaluation.
Background Programme evaluations conducted alongside randomised controlled trials (RCTs) have potential to enhance understanding of trial outcomes. This paper describes a multi-level programme evaluation to be conducted alongside an RCT of a falls prevention programme (RESPOND). Objectives 1) To conduct a process evaluation in order to identify the degree of implementation fidelity and associated barriers and facilitators. 2) To evaluate the primary intended impact of the programme: participation in fall prevention strategies, and the factors influencing participation. 3) To identify the factors influencing RESPOND RCT outcomes: falls, fall injuries and ED re-presentations. Methods/ Design Five hundred and twenty eight community-dwelling adults aged 60â90 years presenting to two EDs with a fall will be recruited and randomly assigned to the intervention or standard care group. All RESPOND participants and RESPOND clinicians will be included in the evaluation. A mixed methods design will be used and a programme logic model will frame the evaluation. Data will be sourced from interviews, focus groups, questionnaires, clinician case notes, recruitment records, participant-completed calendars, hospital administrative datasets, and audio-recordings of intervention contacts. Quantitative data will be analysed via descriptive and inferential statistics and qualitative data will be interpreted using thematic analysis. Discussion The RESPOND programme evaluation will provide information about contextual and influencing factors related to the RCT outcomes. The results will assist researchers, clinicians, and policy makers to make decisions about future falls prevention interventions. Insights gained are likely to be transferable to preventive health programmes for a range of chronic conditions
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