Showing papers by "National University of Singapore published in 2022"

Mechanism of keyhole pore formation in metal additive manufacturing

Abstract: Abstract During metal additive manufacturing, the porosity of the as-built part deteriorates the mechanical property and even hinders the further application of metal additive manufacturing. Particularly, the mechanisms of keyhole pores associated with the keyhole fluctuation are not fully understood. To reveal the mechanisms of the keyhole pores formation, we adopt a multiphysics thermal-fluid flow model incorporating heat transfer, liquid flow, metal evaporation, Marangoni effect, and Darcy’s law to simulate the keyhole pore formation process, and the results are validated with the in situ X-ray images. The simulation results present the instant bubble formation due to the keyhole instability and motion of the instant bubble pinning on the solidification front. Furthermore, comparing the keyhole pore formation under different laser scanning speeds shows that the keyhole pore is sensitive to the manufacturing parameters. Additionally, the simulation under a low ambient pressure shows the feasibility of improving the keyhole stability to reduce and even avoid the formation of keyhole pores.

A device-independent quantum key distribution system for distant users

Abstract: Device-independent quantum key distribution (DIQKD) enables the generation of secret keys over an untrusted channel using uncharacterized and potentially untrusted devices1-9. The proper and secure functioning of the devices can be certified by a statistical test using a Bell inequality10-12. This test originates from the foundations of quantum physics and also ensures robustness against implementation loopholes13, thereby leaving only the integrity of the users' locations to be guaranteed by other means. The realization of DIQKD, however, is extremely challenging-mainly because it is difficult to establish high-quality entangled states between two remote locations with high detection efficiency. Here we present an experimental system that enables for DIQKD between two distant users. The experiment is based on the generation and analysis of event-ready entanglement between two independently trapped single rubidium atoms located in buildings 400 metre apart14. By achieving an entanglement fidelity of [Formula: see text] and implementing a DIQKD protocol with random key basis15, we observe a significant violation of a Bell inequality of S = 2.578(75)-above the classical limit of 2-and a quantum bit error rate of only 0.078(9). For the protocol, this results in a secret key rate of 0.07 bits per entanglement generation event in the asymptotic limit, and thus demonstrates the system's capability to generate secret keys. Our results of secure key exchange with potentially untrusted devices pave the way to the ultimate form of quantum secure communications in future quantum networks.

General synthesis of high-entropy alloy and ceramic nanoparticles in nanoseconds

Abstract: High-entropy materials, which include high-entropy alloys and high-entropy ceramics, show promise for their use in many fields, yet a robust synthesis strategy is lacking. Here we present a simple and general approach, laser scanning ablation, to synthesize a library of high-entropy alloy and ceramic nanoparticles. The laser scanning ablation method takes only five nanoseconds per pulse to ablate the corresponding nanoparticle precursors at atmospheric temperature and pressure. The ultrarapid process ensures that dissimilar metallic elements combine regardless of their thermodynamic solubility. As a laser pulse confines energy to the desired microregions, the laser scanning ablation method renders a high-entropy material nanoparticle loading on various substrates, which include thermally sensitive substrates. Applied as electrocatalysts for overall water splitting, the as-prepared high-entropy material nanoparticles can achieve an overpotential of 185 mV @ 10 mA cm–2. This versatile strategy enables the preparation of materials useful for a range of fields, such as biomedicine, catalysis, energy storage and sensors.

Machine learning methods for modelling the gasification and pyrolysis of biomass and waste

Abstract: Over the past two decades, the use of machine learning (ML) methods to model biomass and waste gasification/pyrolysis has increased rapidly. Only 70 papers were published in the 2000s compared to a total of 549 publications in the 2010s. However, the approaches and findings have yet to be systematically reviewed. In this work, the machine learning methods most commonly employed for modelling gasification and pyrolysis processes are discussed with reference to their applications, merits, and limitations. Whilst coefficients of determination (R2) can be difficult to compare directly, due to some studies having greatly different approaches and aims, most studies consistently achieved a high prediction accuracy with R2 > 0.90. Artificial neural networks have been most widely used due to their potential to learn highly non-linear input-output relationships. However, a variety of methods (e.g. regression methods, tree-based methods, and support vector machines) are appropriate depending on the application, data availability, model speed, etc. It is concluded that ML has great potential for the development of models with greater accuracy. Some advantages of machine learning models over existing models are their ability to incorporate relevant non-numerical parameters and the power to generate a multitude of solutions for a wide range of input parameters. More emphasis should be placed on model interpretability in order to better understand the processes being studied.

High-ferrite Portland cement with slag: Hydration, microstructure, and resistance to sulfate attack at elevated temperature

Abstract: Among the four mineral components in cement, C4AF has been demonstrated to have satisfactory corrosion resistance to sulfate attack. Here, high-ferrite Portland cement (HFPC) is used to prepare high corrosion-resistance cement-based materials. The hydration mechanisms and pore structures of HFPC pastes containing different slag dosages are studied at 20 °C, 40 °C, and 60 °C. The results indicate that the elevated temperature greatly stimulates the slag activity and significantly promotes the hydration of HFPC/slag blends. As the temperature increases, the heat curve of the cement pastes with high content slag shows a third or fourth exothermic peak. The hydration of pastes with more than 40% slag is controlled by the nucleation of hydrates in the acceleration stage and by the diffusion of ions in the deceleration stage above 40 °C. In addition, the HFPC pastes show excellent mechanical properties in a high-temperature environment. The HFPC pastes exhibit better sulfate attack resistance performance compared with pure ordinary Portland cement (OPC) ones. Therefore, the excellent performance of HFPC-based materials can be applied in the construction of concrete in mass under the environment of the South Sea in China, to solve the problems of high environmental temperature, large temperature differences, and sulfate attack.

A review on 5G technology for smart energy management and smart buildings in Singapore

Abstract: Sustainable and smart building is a recent concept that is gaining momentum in public opinion, and thus, it is making its way into the agendas of researchers and city authorities all over the world. To move towards sustainable development goals, 5G technology would make significant impacts are building construction, operation, and management by facilitating high-class services, providing efficient functionalities. It's well known that the Singapore is one of top smart cities in this world and from the first counties that adopted of 5G technology in various sectors including smart buildings. Based on these facts, this paper discusses the international trends in 5G applications for smart buildings, and R&D and test bedding works conducted in 5G labs. As well as, the manuscript widely reviewed and discussed the 5G technology development, use cases, applications and future projects which supported by Singapore government. Finally, the 5G use cases for smart buildings and build environment improvement application were discussed. This study can serve as a benchmark for researchers and industries for the future progress and development of smart cities in the context of big data.

Metaverse and Virtual Health Care in Ophthalmology: Opportunities and Challenges

Abstract: The outbreak of the coronavirus disease 2019 has further increased the urgent need for digital transformation within the health care settings, with the use of artificial intelligence/deep learning, internet of things, telecommunication network/virtual platform, and blockchain. The recent advent of metaverse, an interconnected online universe, with the synergistic combination of augmented, virtual, and mixed reality described several years ago, presents a new era of immersive and real-time experiences to enhance human-to-human social interaction and connection. In health care and ophthalmology, the creation of virtual environment with three-dimensional (3D) space and avatar, could be particularly useful in patient-fronting platforms (eg, telemedicine platforms), operational uses (eg, meeting organization), digital education (eg, simulated medical and surgical education), diagnostics, and therapeutics. On the other hand, the implementation and adoption of these emerging virtual health care technologies will require multipronged approaches to ensure interoperability with real-world virtual clinical settings, user-friendliness of the technologies and clinical efficiencies while complying to the clinical, health economics, regulatory, and cybersecurity standards. To serve the urgent need, it is important for the eye community to continue to innovate, invent, adapt, and harness the unique abilities of virtual health care technology to provide better eye care worldwide.