448 research outputs found
A spectral deferred correction strategy for low Mach number reacting flows subject to electric fields
We propose an algorithm for low Mach number reacting flows subjected to
electric field that includes the chemical production and transport of charged
species. This work is an extension of a multi-implicit spectral deferred
correction (MISDC) algorithm designed to advance the conservation equations in
time at scales associated with advective transport. The fast and nontrivial
interactions of electrons with the electric field are treated implicitly using
a Jacobian-Free Newton Krylov approach for which a preconditioning strategy is
developed. Within the MISDC framework, this enables a close and stable coupling
of diffusion, reactions and dielectric relaxation terms with advective
transport and is shown to exhibit second-order convergence in space and time.
The algorithm is then applied to a series of steady and unsteady problems to
demonstrate its capability and stability. Although developed in a
one-dimensional case, the algorithmic ingredients are carefully designed to be
amenable to multidimensional applications
Direct numerical simulation of a high-pressure hydrogen micromix combustor: flame structure and stabilisation mechanism
A high-pressure hydrogen micromix combustor has been investigated using
direct numerical simulation with detailed chemistry to examine the flame
structure and stabilisation mechanism. The configuration of the combustor was
based on the design by Schefer [1], using numerical periodicity to mimic a
large square array. A precursor simulation of an opposed jet-in-crossflow was
first conducted to generate appropriate partially-premixed inflow boundary
conditions for the subsequent reacting simulation. The resulting flame can be
described as a predominantly-lean inhomogeneously-premixed lifted jet flame.
Five main zones were identified: a jet mixing region, a core flame, a
peripheral flame, a recirculation zone, and combustion products. The core
flame, situated over the jet mixing region, was found to burn as a thin
reaction front, responsible for over 85% of the total fuel consumption. The
peripheral flame shrouded the core flame, had low mean flow with high
turbulence, and burned at very lean conditions (in the distributed burning
regime). It was shown that turbulent premixed flame propagation was an
order-of-magnitude too slow to stabilise the flame at these conditions.
Stabilisation was identified to be due to ignition events resulting from
turbulent mixing of fuel from the jet into mean recirculation of very lean hot
products. Ignition events were found to correlate with shear-driven
Kelvin-Helmholtz vortices, and increased in likelihood with streamwise
distance. At the flame base, isolated events were observed, which developed
into rapidly burning flame kernels that were blown downstream. Further
downstream, near-simultaneous spatially-distributed ignition events were
observed, which appeared more like ignition sheets. The paper concludes with a
broader discussion that considers generalising from the conditions considered
here
Possible Association of APOE Genotype with Working Memory in Young Adults
Possession of the ε4 allele of the Apolipoprotein E (APOE) gene is associated with an increased risk of Alzheimer's disease. Early adult life effects of ε4 are less well understood. Working memory has been relatively little studied (compared to episodic memory) in relation to APOE genotype despite its importance in cognitive functioning. Our hypothesis was that ε4 would lead to an impairment in working memory in young adults.We studied working memory using a computerised n-back task in the Avon Longitudinal Study of Parents and Children (ALSPAC) at age 18. Data was available for 1049-1927 participants and for the 2- and 3-back versions of the task. Using multiple and multi-level regression controlling for important confounders we examined the association between APOE genotype on accuracy and reaction times.There was no evidence of a genotype effect on accuracy when the two difficulty levels were examined separately. There was some evidence to support a deleterious effect of the ε4 allele on n-back accuracy in the multi-level regression. There was weak evidence that the ε22 group were less accurate but the numbers were very low in this group. The ε34 group had faster reaction times than the reference ε33 group in all adjusted analyses but the ε44 group were only faster in the 3-back condition in multi-level analyses.There was no evidence of benefit in ε4 carriers, but there was some evidence of a detrimental effect on working memory in this large study
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Numerical Simulation of a Laboratory-Scale Turbulent SlotFlame
We present three-dimensional, time-dependent simulations ofthe flowfield of a laboratory-scale slot burner. The simulations areperformed using an adaptive time-dependent low Mach number combustionalgorithm based on a second-order projection formulation that conservesboth species mass and total enthalpy. The methodology incorporatesdetailed chemical kinetics and a mixture model for differential speciesdiffusion. Methane chemistry and transport are modeled using the DRM-19mechanism along with its associated thermodynamics and transportdatabases. Adaptive mesh refinementdynamically resolves the flame andturbulent structures. Detailedcomparisons with experimental measurementsshow that the computational results provide a good prediction of theflame height, the shape of the time-averaged parabolic flame surfacearea, and the global consumption speed (the volume per second ofreactants consumed divided by the area of the time-averaged flame). Thethickness of the computed flamebrush increases in the streamwisedirection, and the flamesurface density profiles display the same generalshapes as the experiment. The structure of the simulated flame alsomatches the experiment; reaction layers are thin (typically thinner than1 mm) and the wavelengths of large wrinkles are 5--10 mm. Wrinklesamplify to become long fingers of reactants which burn through at a neckregion, forming isolated pockets of reactants. Thus both the simulatedflame and the experiment are in the "corrugated flameletregime.
Zirconium tetraazamacrocycle complexes display extraordinary stability and provide a new strategy for zirconium-89-based radiopharmaceutical development
89 Zr–Tetraazamacrocycle complexes display extraordinary stability
Researching AI Legibility Through Design
Everyday interactions with computers are increasingly likely to involve elements of Artificial Intelligence (AI). Encompassing a broad spectrum of technologies and applications, AI poses many challenges for HCI and design. One such challenge is the need to make AI’s role in a given system legible to the user in a meaningful way. In this paper we employ a Research through Design (RtD) approach to explore how this might be achieved. Building on contemporary concerns and a thorough exploration of related research, our RtD process reflects on designing imagery intended to help increase AI legibility for users. The paper makes three contributions. First, we thoroughly explore prior research in order to critically unpack the AI legibility problem space. Second, we respond with design proposals whose aim is to enhance the legibility, to users, of systems using AI. Third, we explore the role of design-led enquiry as a tool for critically exploring the intersection between HCI and AI research
Sensitivity and specificity of lung cancer screening using chest low-dose computed tomography
Lung cancer screening programmes using chest X-ray and sputum cytology are routinely performed in Japan; however, the efficacy is insufficient. Screening using low-dose computed tomography (CT) is a more effective approach and has the potential to detect the disease more accurately. A total of 7183 low-dose CT screening tests for 4689 participants and 36 085 chest X-ray screening tests for 13 381 participants were conducted between August 1998 and May 2002. Sensitivity and specificity of lung cancer screening were calculated by both the detection method and the incidence method by linkage of the screening database and the Cancer Registry database. The preclinical detectable phase was assumed to be 1 year. Sensitivity and specificity by the detection method were 88.9 and 92.6% for low-dose CT and 78.3 and 97.0% for chest X-ray, respectively. Sensitivity of low-dose CT by the incidence method was 79.5%, whereas that of chest X-ray was 86.5%. Lung cancer screening using low-dose CT resulted in higher sensitivity and lower specificity than traditional screening according to the detection method. However, sensitivity by the incidence method was not as high as this. These findings demonstrate the potential for overdiagnosis in CT screening-detected cases
Associations with photoreceptor thickness measures in the UK Biobank.
Spectral-domain OCT (SD-OCT) provides high resolution images enabling identification of individual retinal layers. We included 32,923 participants aged 40-69 years old from UK Biobank. Questionnaires, physical examination, and eye examination including SD-OCT imaging were performed. SD OCT measured photoreceptor layer thickness includes photoreceptor layer thickness: inner nuclear layer-retinal pigment epithelium (INL-RPE) and the specific sublayers of the photoreceptor: inner nuclear layer-external limiting membrane (INL-ELM); external limiting membrane-inner segment outer segment (ELM-ISOS); and inner segment outer segment-retinal pigment epithelium (ISOS-RPE). In multivariate regression models, the total average INL-RPE was observed to be thinner in older aged, females, Black ethnicity, smokers, participants with higher systolic blood pressure, more negative refractive error, lower IOPcc and lower corneal hysteresis. The overall INL-ELM, ELM-ISOS and ISOS-RPE thickness was significantly associated with sex and race. Total average of INL-ELM thickness was additionally associated with age and refractive error, while ELM-ISOS was additionally associated with age, smoking status, SBP and refractive error; and ISOS-RPE was additionally associated with smoking status, IOPcc and corneal hysteresis. Hence, we found novel associations of ethnicity, smoking, systolic blood pressure, refraction, IOPcc and corneal hysteresis with photoreceptor thickness
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