Julia and Mandelbrot sets for dynamics over the hyperbolic numbers

Julia and Mandelbrot sets, which characterize bounded orbits in dynamical systems over the complex numbers, are classic examples of fractal sets. We investigate the analogs of these sets for dynamical systems over the hyperbolic numbers. Hyperbolic numbers, which have the form $x+\tau y$ for $x,y \in \mathbb{R}$, and $\tau^2 = 1$ but $\tau \neq \pm 1$, are the natural number system in which to encode geometric properties of the Minkowski space $\mathbb{R}^{1,1}$. We show that the hyperbolic analog of the Mandelbrot set parameterizes connectedness of hyperbolic Julia sets. We give a wall-and-chamber decomposition of the hyperbolic plane in terms of these Julia sets.Comment: 7 page

Investigation of Ti64 sheathed cellular anatomical structure as a tibia implant

In order to reduce stress shielding following a segmental bone replacement surgery requires stiffness matching strategies between the host bone and the implant are required. Carefully engineered implant geometry that can mimic the mechanical performance of the host bone is required to achieve this. The development of Additive Layer Manufacturing (ALM) techniques such as Direct Metal Laser Sintering (DMLS) allows for the fabrication of complex geometries that can achieve targeted mechanical performance. Consequently, this work introduces a sheathed Ti6Al4V additively manufactured tibial implant that mimics the circumferential anatomy of the host bone. Performance evaluation of the implant was carried using experimental and numerical technique under axial compression. Furthermore, the influence of sheathing strategy and sheath thickness on the compressive performance of the implant is parametrically analysed. The results of this study shows a promising sheathed implant that can replace a defective tibia bone segment. The implant is superior to conventional porous implants as it allows for easy implantation in surgical operation and allows for the reduction of stress shielding

Ultrasound-Assisted Peripheral Venous Access in Young Children: A Randomized Controlled Trial and Pilot Feasibility Study

OBJECTIVES: Intravenous (IV) access in children treated in the emergency department (ED) is frequently required and often difficult to obtain. While it has been shown that ultrasound can be useful in adults for both central and peripheral venous access, research regarding children has been limited. We sought to determine if the use of a static ultrasound technique could, a) allow clinicians to visualize peripheral veins and b) improve success rates of peripheral venous cannulation in young children in the ED.METHODS: We performed a randomized clinical trial of children < 7 years in an academic pediatric ED who required IV access and who had failed the first IV attempt. We randomized patients to either continued standard IV attempts or ultrasound-assisted attempts. Clinicians involved in the study received one hour of training in ultrasound localization of peripheral veins. In the ultrasound group, vein localization was performed by an ED physician who marked the skin overlying the target vessel. Intravenous cannulation attempts were then immediately performed by a pediatric ED nurse who relied on the skin mark for vessel location. We allowed for technique cross-over after two failed IV attempts. We recorded success rate and location of access attempts. We compared group success rates using differences in 95% confidence intervals (CI).RESULTS: We enrolled 44 children over a one-year period. The median age of enrollees was 9.5 months. We visualized peripheral veins in all patients in the ultrasound group (n=23) and in those who crossed over to ultrasound after failed standard technique attempts (n= 8). Venipuncture was successful on the first attempt in the ultrasound group in 13/23 (57%, CI, 35% to 77%), versus 12/21 (57%, CI, 34% to 78%) in the standard group, difference between groups 0.6% (95% CI -30% to 29%). First attempt cannulation success in the ultrasound group was 8/23 (35%, CI, 16% to 57%), versus 6/21 (29%, CI, 11% to 52%) in the standard group, difference between groups 6% (95% CI -21% to 34%).CONCLUSION: Ultrasound allows physicians to visualize peripheral veins of young children in the ED. We were unable to demonstrate, however, a clinically important benefit to a static ultrasound aided vein cannulation technique performed by clinicians with limited ultrasound training over standard technique after one failed IV attempt in an academic pediatric ED

Acoustic metamaterials for sound absorption and insulation in buildings

© 2024 The Authors. Published by Elsevier. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1016/j.buildenv.2024.111250Despite the emergence of acoustic metamaterials with superior sound absorption and transmission loss, their adoption for building sound insulation has been limited. Sound insulation design in buildings is still informed by the acoustic performance of conventional materials, where the mass law contradicts light weighting when it comes to acoustic design. In any case buildings close to noisy environments such as motorways, railway lines and airports still suffer from significant low frequency noise pollution. Although the limited working bandwidth of acoustic metamaterials is a major issue limiting its application, combining meta-units that interact at various frequencies alongside multi-layer conventional solutions can deliver superior sound insulation in buildings. The review put forwards acoustic metamaterials, specifically emphasising superior sound absorption and transmission/insertion loss as critical properties for effective building sound insulation. The paper reveals a variety of acoustic metamaterials that can be adopted to compliment conventional sound insulation approaches for acoustically efficient building design. The performance of these metamaterials is then explained through their characteristic negative mass density, bulk modulus or repeating or locally resonating microstructure. The review is also extended to air transparent acoustic metamaterials that can be used for sound insulation of building ventilation. Lastly the prospects and challenges regarding the adoption of acoustic metamaterials in building insulation are also discussed. Overall, tuneable, and multifunctional acoustic metamaterials when thoughtfully integrated to building sound insulation can lead to significant acoustic comfort, space-saving and light-weighting.Published versio

Melt Pool Monitoring and X-ray Computed Tomography-Informed Characterisation of Laser Powder Bed Additively Manufactured Silver–Diamond Composites

In this study, silver (Ag) and silver–diamond (Ag-D) composites with varying diamond (D) content are fabricated using laser powder bed fusion (L-PBF) additive manufacturing (AM). The L-PBF process parameters and inert gas flow rate are optimised to control the build environment and the laser energy density at the powder bed to enable the manufacture of Ag-D composites with 0.1%, 0.2% and 0.3% D content. The Ag and D powder morphology are characterised using scanning electron microscopy (SEM). Ag, Ag-D0.1%, Ag-D0.2% and Ag-D0.3% tensile samples are manufactured to assess the resultant density and tensile strength. In-process EOSTATE melt pool monitoring technology is utilised as a comparative tool to assess the density variations. This technique uses in-process melt pool detection to identify variations in the melt pool characteristics and potential defects and/or density deviations. The resultant morphology and associated defect distribution for each of the samples are characterised and reported using X-ray computed tomography (xCT) and 3D visualisation techniques. Young’s modulus, the failure strain and the ultimate tensile strength of the L-PBF Ag and Ag-D are reported. The melt pool monitoring results revealed in-process variations in the build direction, which was confirmed through xCT 3D visualisations. Additionally, the xCT analysis displayed density variations for all the Ag-D composites manufactured. The tensile results revealed that increasing the diamond content reduced Young’s modulus and the ultimate tensile strength

3D printed CoCrMo personalised load-bearing meta-scaffold for critical size tibial reconstruction

© 2024 The Authors. Published by Elsevier. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1016/j.stlm.2024.100163Porous scaffolds have evolved, allowing personalised 3D-printed structures that can improve tissue reconstruction. By using scaffolds with specific porosity, Poisson's ratio and stiffness, load-bearing tissues such as tibial reconstruction can be improved. Recent studies suggest the potential for negative Poisson's ratio (-ν) meta-scaffolds in mimicking the behaviour of natural tissue, leading to improved healing and tissue reintegration. This study reveals a porous meta-scaffold that offers high -ν and can be personalised to match desired stiffness. By using laser powder bed fusion (L-PBF) of CoCrMo, a porous structure was created, characterised by its ability to achieve heightened -ν. Prototype testing and numerical modelling unveiled a proxy-model capable of predicting and personalising the porosity, yield strength, elastic modulus, and -ν of the tibial meta-scaffold representing a novel contribution to the field. The surrogate model also aids characterising the impact of design variables such as of the scaffold on the key performance requirements of the tibial scaffold. This approach enables the fabrication of porous biomaterials with personalised properties, specifically suited for load-bearing tibial reconstruction. The resulting meta-scaffold offers -ν ranging from -0.16 to -0.38, porosity between 73.46% and 85.36%, yield strength of 30–80 MPa, and elastic modulus ranging from 8.6 to 22.6 GPa. The optimised architecture feature -ν of 0.223 and a targeted elastic modulus of 17.53 GPa, while also showcasing yield strength and porosity of 57.2 MPa and 76.35%, respectively. By combining 3D printing with tailored scaffolds, this study opens doors to mass customisation of improved load-bearing porous biomaterials that of negative Poisson's ratio and stiffness matching.Accepted versio

A scoping review of augmented/virtual reality health and wellbeing Interventions for older adults: redefining Immersive virtual reality

Augmented and virtual reality (AR/VR) technologies are regularly used in psychology research to complement psychological interventions and to enable an individual to feel as if they are in an environment other than that of their immediate surroundings. A scoping review was performed to identify how AR/VR was being used with older adult populations to impact their physical and mental health. The review also sought to determine whether the terminology used in AR/VR research was consistent. The results show that 65 studies have been published in the last 20 years that meet the inclusion criteria (virtual/augmented reality) technology to impact older adults’ physical/mental health and wellbeing. Participants included healthy, physically, and cognitively impaired, and emotionally vulnerable older adults. We argue that over 70% of the studies included in this review were mislabeled as VR and only six papers included fully immersive VR/AR. The remaining studies use less immersive variants of virtual reality with their populations, and only one study made use of AR, which prompted the suggestion of a new definition for virtual reality. This paper also calls for an updated taxonomy of augmented and virtual reality definitions to address the lack of consistency found in studies that identify themselves as AR/VR when they are using less immersive technical set-ups, including displaying non-interactive videos on 2D screens

3D printed CoCrMo personalised load-bearing meta-scaffold for critical size tibial reconstruction

Porous scaffolds have evolved, allowing personalised 3D-printed structures that can improve tissue reconstruction. By using scaffolds with specific porosity, Poisson's ratio and stiffness, load-bearing tissues such as tibial reconstruction can be improved. Recent studies suggest the potential for negative Poisson's ratio (−υ) meta-scaffolds in mimicking the behaviour of natural tissue, leading to improved healing and tissue reintegration. This study reveals a porous meta-scaffold that offers high −υ and can be personalised to match desired stiffness. By using laser powder bed fusion (L-PBF) of CoCrMo, a porous structure was created, characterised by its ability to achieve heightened −υ. Prototype testing and numerical modelling unveiled a proxy-model capable of predicting and personalising the porosity, yield strength, elastic modulus, and −υ of the tibial meta-scaffold representing a novel contribution to the field. The surrogate model also aids characterising the impact of design variables such as of the scaffold on the key performance requirements of the tibial scaffold. This approach enables the fabrication of porous biomaterials with personalised properties, specifically suited for load-bearing tibial reconstruction. The resulting meta-scaffold offers −υ ranging from -0.16 to -0.38, porosity between 73.46% and 85.36%, yield strength of 30–80 MPa, and elastic modulus ranging from 8.6 to 22.6 GPa. The optimised architecture feature −υ of 0.223 and a targeted elastic modulus of 17.53 GPa, while also showcasing yield strength and porosity of 57.2 MPa and 76.35%, respectively. By combining 3D printing with tailored scaffolds, this study opens doors to mass customisation of improved load-bearing porous biomaterials that of negative Poisson's ratio and stiffness matching

Developments and prospects of additive manufacturing for thermoelectric materials and technologies

© 2024 The Authors. Published by Elsevier B.V. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1016/j.susmat.2024.e01008In view of the increased demand for electricity and the associated environmental and financial concerns, there is an urgent need to develop technological solutions that can improve the efficiency of engineering systems and processes. Thermoelectric (TE) technologies, with their capability of direct conversion of thermal energy into electrical energy, are promising technologies for green power generation through using them as energy harvesting devices for waste heat recovery in industrial processes and power generation systems. To date, TE technologies are still not commercialized on a large scale due to various economic and technical obstacles. The majority of previous research on TE technologies concentrated on improving the TE properties, such as electronic transport and figure-of-merit, while limited attempts were made to identify the best material processing techniques or reduce the cost of manufacturing. Conventional Manufacturing (CM) of TE materials and devices is multi-stage, complex, labour-intensive, time-consuming, and has high energy requirements. Thus, manufacturing challenges are considered key contributors toward limited industrial adoption of TE technologies. The rapid advent of advanced Additive Manufacturing (AM) processes, in recent years, caused dramatic changes in engineering design thinking and created opportunities to solve manufacturing challenges. With its significant capabilities, AM can be the route to address the shortcomings of CM of the thermoelectric technologies. In this regard, this paper presents an in-depth review of the literature studies on using AM technologies, such as selective laser melting, fused deposition modelling, direct ink writing, stereo lithography, etc., for manufacturing TE materials and devices. The benefits and challenges of each AM technology are discussed to identify their merits and the required future research. This paper demonstrates the role of AM in advancing green materials and technologies for solving some of the outstanding energy and environmental issues.Accepted versio

Targeted mechanical and energy absorption properties of 3D printed aluminium metamaterials

© 2024 The Authors. Published by Elsevier. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1016/j.nxmate.2024.100356The potential of 3D-printed AlSi10Mg auxetic structures for diverse mechanical and energy-absorbing needs remains untapped. This article reveals a multi-criteria framework for the laser powder bed fused (L-PBF) - v architecture considering elastic modulus (E), yield strength (Oy), specific energy absorption (SEA), peak crush force (PCF) and crush force efficiency (CFE). The framework seamlessly combines trial data, multi-criteria decision-making, and performance indicators. Five auxetic structures were 3D-printed, characterised for mechanical and energy absorption traits within a 0.17–0.26 relative density range. The outcomes revealed a range of values for various parameters, including the Poisson’s ratio (−0.03 to −0.22), porosity (80.87–87.60 %), CFE (33–83 %), elastic modulus (100–632 MPa), yield strength (1.8–10 MPa), and SEA (0.5–6.8 kJ/kg). The reliability of these structures was ensured through a meticulous selection process based on an extensive literature review and empirical validation. To address the limitations of theoretical models, our work goes beyond theoretical predictions by experimentally validating these properties and integrating advanced methodologies such as the ‘analytic hierarchy process’ (AHP) and the ‘technique for order of preference by similarity to ideal solution’ (TOPSIS). This allows us to determine the best-performing auxetic architecture. The decision-making process was informed by five user-defined parameters prioritised in the order of CFE> -v > E> Oy > SEA based on their relative closeness identifying AUX5 as the best performing auxetic architecture. This study introduces an innovative method for crafting scenario-based auxetic architectures with varying performance levels based on their relative importance.This project was supported by the Elite Centre for Manufacturing Skills (ECMS) project number GD026, United Kingdom.Accepted versio