143174 research outputs found
Sort by
Patient-specific modelling of pulmonary arterial hypertension: wall shear stress correlates with disease severity
No full textIntroduction: Pulmonary arterial hypertension (PAH) requires an invasive right heart catheter (RHC) procedure for diagnosis. Patients can present with initial symptoms and interact with healthcare institutes for up to three years before referral for diagnosis. Thus, there is a great need to develop noninvasive tools, to better screen patients and improve early diagnosis rates. Methods: seven patients diagnosed and treated for PAH were included in this study. Patient-specific computational fluid dynamics (CFD) models were built for all patients, with all model parameters tuned using non-invasive imaging data, including CT, cardiac MR, echocardiogram, and 4D-flow MRI scanscrucially, a 3D inlet velocity profile was derived from 4D-flow MRI. Results: CFD models were quantitatively and qualitatively well matched with in-vivo 4D-flow hemodynamics. A linear correlation of R 2 = 0.84 was found between CFD derived time-averaged wall shear stress (TAWSS) and RHC measured mean pulmonary pressure (key diagnostic value): low TAWSS correlated with high pressure. Conclusions: This study highlights TAWSS as a potential computational biomarker for PAH. The clinical use of TAWSS to diagnose and stratify PAH patients has the potential to greatly improve patient outcomes. Further work is ongoing to validate these findings in larger cohorts
Design and behaviour of moment resisting precast concrete connections with cast-in shear fasteners
No full textThe paper proposes a novel design procedure for an innovative connector that provides flexural continuity between ribbed precast concrete flooring units. The innovation was driven by the goal of rapid onsite assembly which precluded the use of structural toppings, complex in-situ stitching of projecting bars or onsite welding. Assembly on site is a simple process of bringing the precast elements together on temporary supports and grouting the prefabricated steel connectors into well-voids cast into the member ends. The benefits of the developed connection have been successfully demonstrated within a number of full-scale prototypes. Due to the novel and unconventional form of the proposed connector, physical testing was crucial to provide an in-depth understanding of its response characteristics under serviceability and ultimate loading conditions. Towards this end, three full size specimens were tested to failure under four-point bending. The outcomes of these experiments are used to validate 3-D high-fidelity nonlinear finite element analysis models. These are finally used in a wide-ranging study to demonstrate the applicability of the proposed design procedure for this novel precast concrete connection system
Modelling active travel accessibility at the micro-scale using multi-source built environment data
No full textAccessibility models explore how land use and transport systems interact to facilitate access to activities and daily needs. Existing applications generally model accessibility based on distance or travel time. For pedestrians and cyclists, the street-level environment (e.g., green visibility, streetside amenities, dedicated infrastructure) significantly influences people's willingness and ability to travel. Incorporating these features into accessibility models can help them to be more representative of active travellers' experienced environment.
This study presents a methodology for incorporating the street-level environment into active mode accessibility. First, micro-scale built environment data from multiple sources are harmonised into a high-resolution digital representation of the land use and transport system. Second, a compute-optimised framework is developed for modelling accessibility at the micro-scale (i.e., each dwelling separately) incorporating the street-level environment. The methods build upon the open geodatabase OpenStreetMap and open-source MATSim project, facilitating expandability and transferability to other contexts. We apply this methodology to develop policy-relevant accessibility indicators for Greater Manchester.
In the results, we observe that the street-level environment can cause accessibility indicators to vary at the micro-scale, especially in less connected neighbourhoods where the choice of routes is limited. We also observed that for cyclists, the accessibility advantage over walking reduces substantially when traffic stress is considered. Our findings support further adoption of micro-scale built environment data and high-resolution analysis methods for active travel accessibility modelling in research and practice
Impact of ionomers on porous Fe-N-C catalysts for alkaline oxygen reduction in gas diffusion electrodes
No full textAlkaline exchange membrane fuel cells (AEMFCs) offer a promising alternative to the traditional fossil fuel due to their ability to use inexpensive platinum group metal (PGM)-free catalysts, which could potentially replace Platinum-based catalysts. Iron coordinated in nitrogen-doped carbon (Fe-N-C) single atom electrocatalysts offer the best Pt-free ORR activities. However, most research focuses on material development in alkaline conditions, with limited attention on catalyst layer fabrication. Here, we demonstrate how the oxygen reduction reaction (ORR) performance of a porous Fe-N-C catalyst is affected by the choice of three different commercial ionomers and the ionomer-to-catalyst ratio (I/C). A Mg-templated Fe-N-C is employed as a catalyst owing to the electrochemical accessibility of the Fe sites, and the impact of ionomer properties and coverage were studied and correlated with the electrochemical performance in a gas-diffusion electrode (GDE). The catalyst layer with Nafion at I/C = 2.8 displayed the best activity at high current densities (0.737 ± 0.01 VRHE iR-free at 1 A cm⁻²) owing to a more homogeneous catalyst layer, while Sustainion displayed a higher performance in the kinetic region at the same I/C. These findings provide insights into the impact of catalyst layer optimization to achieve optimal performance in Fe-N-C based AEMFCs
Shapley-PC: constraint-based causal structure learning with a Shapley inspired framework
No full textCausal Structure Learning (CSL), also referred to as causal discovery, amounts to extracting causal relations among variables in data. CSL enables the estimation of causal effects from observational data alone, avoiding the need to perform real life experiments. Constraint-based CSL leverages conditional independence tests to perform causal discovery. We propose Shapley-PC, a novel method to improve constraint-based CSL algorithms by using Shapley values over the possible conditioning sets, to decide which variables are responsible for the observed conditional (in)dependences. We prove soundness, completeness and asymptotic consistency of Shapley-PC and run a simulation
study showing that our proposed algorithm is superior to existing versions of PC
Efavirenz-based highly active antiretroviral therapy disrupts folliculogenesis: evidence from 48 women of reproductive age
No full textIntroduction: Interventions to eliminate mother-to-child transmission of HIV have led to a low vertical transmission rate and improved reproductive outcomes for women living with HIV. There are genuine concerns about the long-term effect of antiretroviral drugs (ARVs) on the future reproductive function of females, as female rodent models have shown impaired folliculogenesis when treated with contemporary ARVs. There is a need to investigate the effect of contemporary ARVs on the ovarian reserve of patients receiving ARVs.
Methods: This cross-sectional study was conducted on women between the reproductive age of 15 and 45 years, forming three study categories. Group 1 comprised HIV-positive patients already on efavirenz-based antiretroviral therapy. Group 2 comprised HIV-positive patients who were naïve to ARVs at the time of recruitment. Group 3 comprised HIV-negative women within the reproductive age range not on ARVs (controls). We used t-test and ANOVA for statistical analysis. The alpha level was significant if the p-value was <0.05.
Results: The average value of follicle-stimulating hormone was significantly higher in the HIV-positive group receiving ARVs, compared to the control group (p = 0.039). The average value of luteinizing hormone was significantly higher in the HIV-positive group receiving ARVs when compared to the HIV-negative group (p = 0.014). The antral follicular count was significantly reduced in the group receiving ARVs, compared to HIV-positive individuals naïve to ARVs and HIV-negative controls (p = 0.009).
Conclusion: Evidence from this study suggests that efavirenz-based antiretroviral medication disrupts follicular development
Engineering aluminosilicates with high surface area extracted from waste concrete to form a viable supplementary cementitious material
No full textAluminosilicate residues can be produced by acid leaching waste concrete. These are pozzolanic and have the potential to be used as a supplementary cementitious material (SCM). However, the workability of cement mixes is seriously compromised when aluminosilicate particles are used, due to their high surface area and excessive water absorption. This negatively influences the compaction and performance of mixes. In this work, aluminosilicates extracted from waste concrete have been heat-treated, and the effects of temperature on their specific surface area, pozzolanic reactivity, and consequently the workability and strength of mortars are reported. Thermal treatment at 900℃ for 1 hour reduces the specific surface area of aluminosilicate particles to values comparable to commercial SCMs such as coal fly ash (FA) and ground granulated blast furnace slag (GGBFS), while retaining significant pozzolanic activity. Mortars containing CEM I replaced by 20 wt% of optimally heat-treated aluminosilicate residue at a 0.56 w/b ratio show improved flow properties compared to untreated residues, and similar compressive strength to mortars containing the same amount of silica fume (SF) or GGBFS. The research shows that aluminosilicates extracted from cement paste can be heat treated to form a viable SCM, and this contributes to the future development of circular concrete
Ratte: Fuzzing for miscompilations in multi-level compilers using composable semantics
No full textMulti-level intermediate representation (MLIR) is a rapidly growing compiler framework, with its defining feature being an ecosystem of modular language fragments called dialects. Specifying dialect semantics and validating dialect implementations presents novel challenges, as existing techniques do not cater for the modularity and composability required by MLIR. We present Ratte,1 a framework for specifying composable dialect semantics and modular dialect fuzzers. We introduce a novel technique for the development of semantics and fuzzers for MLIR dialects, enabling a harmonious cycle where the fuzzer validates the semantics via test-case generation, whilst at the same time the semantics allow the generation of high-quality test cases that are free from undefined behaviour. The composability of semantics and fuzzers allows generators to be cheaply derived to test combinations of dialects. We have used Ratte to find 6 previously-unknown miscompilation bugs in the production MLIR implementation. To our knowledge, Ratte is the first MLIR fuzzer capable of finding such bugs. Our work identified several aspects of the MLIR specification that were unclear, for which we proposed fixes that were adopted. Our technique provides composable reference interpreters for important MLIR dialects, validated against the production implementation, which can be used in future compiler development and testing research
A smart cane-based indoor positioning system for visually impaired people
No full textAutonomous navigation is a crucial aspect of the visually impaired community’s pursuit of independence and social equity. To achieve this goal, Visually Impaired People (VIP) require a navigation and wayfinding system that works both outdoors and indoors. While outdoor navigation can rely on ubiquitous signals such as Global Navigation Satellite System (GNSS), indoor navigation presents a significant challenge, especially in unfamiliar environments. Despite over two decades of research and development, the issue of delivering a high performance and cost-effective indoor positioning solution for VIPs remains unresolved. Bluetooth-based Angle of Arrival (AOA) positioning is a cost-effective method that offers accuracy ranging from upper decimetres to meters. However, it still faces challenges in detecting and mitigating outliers caused by non-line-of-sight (NLOS) and multipath effects during signal propagation. In light of these challenges, this paper proposes a novel dead reckoning aided AOA Bluetooth indoor positioning system that utilises a smart cane. The developed model takes into account the swinging characteristic of the cane, which is integral to visually impaired individuals’ mobility. Furthermore, the paper incorporates a novel outlier detection and exclusion layer to reduce the impact of NLOS and multipath effects. The proposed system’s performance was evaluated through a series of experiments, and the positioning error distribution was analysed. The results showed that the accumulated probability of errors less than 0.5 m was 93.56%, and 99.64% of errors were within 0.7 m. With the demonstrated high level of accuracy, the proposed system presents a promising solution for indoor navigation for VIPs
A thermodynamically equivalent transformation method for the design and performance analysis of absorption cycles
No full textAbsorption cycles are a very promising technology for the provision of heating or cooling. Systems based on such cycles are capable of utilizing environmentally-friendly thermal energy sources such as low-grade solar or waste heat. Increasingly advanced absorption cycles with complex configurations are being proposed to meet the diversified demands of modern energy systems, however, a convenient, rapid yet accurate method for the design and performance analysis of these complex cycles is lacking. In this paper, a thermodynamically equivalent transformation method is proposed which decomposes complex cycles into mutually coupled basic single-stage cycles. Based on the decomposition transformation, a generalized method for the fast calculation of the COP of complex cycles under both ideal and practical conditions was also established and verified. Two case studies on the configuration design, performance analysis and optimization of complex absorption cooling cycles are performed to demonstrate the applicability of the proposed method. The results show that the proposed thermodynamically equivalent transformation method can make the decomposition of complex cycles convenient and effective. Although the present paper focuses on absorption cooling cycles, the method is equally applicable to absorption heat pump cycles. The established fast COP prediction method is computationally efficient and accurate for the performance analysis of absorption cycles with complex configurations. This study provides a powerful tool for the design, performance analysis and optimization of next-generation advanced absorption cycles