2,954 research outputs found

    CFD Modelling of the Mixture Preparation in a Modern Gasoline Direct Injection Engine and Correlations with Experimental PN Emissions

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    A detailed 3D CFD analysis of a modern gasoline direct injection (GDI) engine is carried out to reveal the connections between pre-combustion mixture indicators and PN emissions. Firstly, a novel calibration methodology is introduced to accurately predict the widely used characteristics of the high-pressure fuel spray. The methodology utilised the Siemens STAR-CD 3D CFD software environment and employed a combination of statistical and optimization methods supported by experimental data. The calibration process identified dominant factors influencing spray properties and established their optimal levels. The two most used models for fuel atomisation were investigated. The Kelvin–Helmholtz/Rayleigh–Taylor (KH–RT) and Reitz–Diwakar (RD) break-up models were calibrated in conjunction with the Rosin–Rammler (RR) mono-modal droplet size distribution. RD outperformed KH–RT in terms of prediction when comparing numerical spray tip penetration and droplet size characteristics to the experimental counterparts. Then, the modelling protocol incorporated droplet-wall interaction models and a multi-component surrogate fuel blend model. The comprehensive digital model was validated using published data and applied to a modern small-capacity GDI engine. The study explored various engine operating conditions and highlights the contribution of fuel mal-distribution and liquid film retention at spark timing to Particle Number (PN) emissions. Finally, a novel surrogate model was developed to predict the engine-out PN. An extensive CFD analysis was conducted considering part-load operating conditions and variations of engine control variables. The PN surrogate model was developed using an Elastic Net (EN) regression technique, establishing relationships between experimental PN emission levels and modelled, pre-combustion, air-fuel mixture quality indicators. The approach enabled the reliable prediction of engine sooting tendencies without relying on complex measurements of combustion characteristics. These research efforts aim to enhance engine efficiency, reduce emissions, and contribute to the development of a reliable and cost-effective digital toolset for engine development and diagnostics

    Authentication enhancement in command and control networks: (a study in Vehicular Ad-Hoc Networks)

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    Intelligent transportation systems contribute to improved traffic safety by facilitating real time communication between vehicles. By using wireless channels for communication, vehicular networks are susceptible to a wide range of attacks, such as impersonation, modification, and replay. In this context, securing data exchange between intercommunicating terminals, e.g., vehicle-to-everything (V2X) communication, constitutes a technological challenge that needs to be addressed. Hence, message authentication is crucial to safeguard vehicular ad-hoc networks (VANETs) from malicious attacks. The current state-of-the-art for authentication in VANETs relies on conventional cryptographic primitives, introducing significant computation and communication overheads. In this challenging scenario, physical (PHY)-layer authentication has gained popularity, which involves leveraging the inherent characteristics of wireless channels and the hardware imperfections to discriminate between wireless devices. However, PHY-layerbased authentication cannot be an alternative to crypto-based methods as the initial legitimacy detection must be conducted using cryptographic methods to extract the communicating terminal secret features. Nevertheless, it can be a promising complementary solution for the reauthentication problem in VANETs, introducing what is known as “cross-layer authentication.” This thesis focuses on designing efficient cross-layer authentication schemes for VANETs, reducing the communication and computation overheads associated with transmitting and verifying a crypto-based signature for each transmission. The following provides an overview of the proposed methodologies employed in various contributions presented in this thesis. 1. The first cross-layer authentication scheme: A four-step process represents this approach: initial crypto-based authentication, shared key extraction, re-authentication via a PHY challenge-response algorithm, and adaptive adjustments based on channel conditions. Simulation results validate its efficacy, especially in low signal-to-noise ratio (SNR) scenarios while proving its resilience against active and passive attacks. 2. The second cross-layer authentication scheme: Leveraging the spatially and temporally correlated wireless channel features, this scheme extracts high entropy shared keys that can be used to create dynamic PHY-layer signatures for authentication. A 3-Dimensional (3D) scattering Doppler emulator is designed to investigate the scheme’s performance at different speeds of a moving vehicle and SNRs. Theoretical and hardware implementation analyses prove the scheme’s capability to support high detection probability for an acceptable false alarm value ≤ 0.1 at SNR ≥ 0 dB and speed ≤ 45 m/s. 3. The third proposal: Reconfigurable intelligent surfaces (RIS) integration for improved authentication: Focusing on enhancing PHY-layer re-authentication, this proposal explores integrating RIS technology to improve SNR directed at designated vehicles. Theoretical analysis and practical implementation of the proposed scheme are conducted using a 1-bit RIS, consisting of 64 × 64 reflective units. Experimental results show a significant improvement in the Pd, increasing from 0.82 to 0.96 at SNR = − 6 dB for multicarrier communications. 4. The fourth proposal: RIS-enhanced vehicular communication security: Tailored for challenging SNR in non-line-of-sight (NLoS) scenarios, this proposal optimises key extraction and defends against denial-of-service (DoS) attacks through selective signal strengthening. Hardware implementation studies prove its effectiveness, showcasing improved key extraction performance and resilience against potential threats. 5. The fifth cross-layer authentication scheme: Integrating PKI-based initial legitimacy detection and blockchain-based reconciliation techniques, this scheme ensures secure data exchange. Rigorous security analyses and performance evaluations using network simulators and computation metrics showcase its effectiveness, ensuring its resistance against common attacks and time efficiency in message verification. 6. The final proposal: Group key distribution: Employing smart contract-based blockchain technology alongside PKI-based authentication, this proposal distributes group session keys securely. Its lightweight symmetric key cryptography-based method maintains privacy in VANETs, validated via Ethereum’s main network (MainNet) and comprehensive computation and communication evaluations. The analysis shows that the proposed methods yield a noteworthy reduction, approximately ranging from 70% to 99%, in both computation and communication overheads, as compared to the conventional approaches. This reduction pertains to the verification and transmission of 1000 messages in total

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    The 2023 terahertz science and technology roadmap

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    Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a 'snapshot' introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation

    Spatial frequency domain imaging towards improved detection of gastrointestinal cancers

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    Early detection and treatment of gastrointestinal cancers has been shown to drastically improve patients survival rates. However, wide population based screening for gastrointestinal cancers is not feasible due to its high cost, risk of potential complications, and time consuming nature. This thesis forms the proposal for the development of a cost-effective, minimally invasive device to return quantitative tissue information for gastrointestinal cancer detection in-vivo using spatial frequency domain imaging (SFDI). SFDI is a non-invasive imaging technique which can return close to real time maps of absorption and reduced scattering coefficients by projecting a 2D sinusoidal pattern onto a sample of interest. First a low-cost, conventional bench top system was constructed to characterise tissue mimicking phantoms. Phantoms were fabricated with specific absorption and reduced scattering coefficients, mimicking the variation in optical properties typically seen in healthy, cancerous, and pre-cancerous oesophageal tissue. The system shows accurate retrieval of absorption and reduced scattering coefficients of 19% and 11% error respectively. However, this bench top system consists of a bulky projector and is therefore not feasible for in-vivo imaging. For SFDI systems to be feasible for in-vivo imaging, they are required to be miniaturised. Many conditions must be considered when doing this such as various illumination conditions, lighting conditions and system geometries. Therefore to aid in the miniaturisation of the bench top system, an SFDI system was simulated in the open-source ray tracing software Blender, where the capability to simulate these conditions is possible. A material of tunable absorption and scattering properties was characterised such that the specific absorption and reduced scattering coefficients of the material were known. The simulated system shows capability in detecting optical properties of typical gastrointestinal conditions in an up-close, planar geometry, as well in a non-planar geometry of a tube simulating a lumen. Optical property imaging in the non-planar, tubular geometry was done with the use of a novel illumination pattern, developed for this work. Finally, using the knowledge gained from the simulation model, the bench top system was miniaturised to a 3 mm diameter prototype. The novel use of a fiber array producing the necessary interfering fringe patterns replaced the bulky projector. The system showed capability to image phantoms simulating typical gastrointestinal conditions at two wavelengths (515 and 660 nm), measuring absorption and reduced scattering coefficients with 15% and 6% accuracy in comparison to the bench top system for the fabricated phantoms. It is proposed that this system may be used for cost-effective, minimally invasive, quantitative imaging of the gastrointestinal tract in-vivo, providing enhanced contrast for difficult to detect cancers

    The role of AD protective variant PLCγ2P522R in modulating microglia mediated clearance and synaptic pruning

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    PLCG2-P522R, a rare coding variant in the Phospholipase C gamma-2 (PLCG2) gene, has been found to be protective against late onset Alzheimer's disease (AD). Within the central nervous system, PLCγ2 is most abundantly expressed in microglia, and microglial mediated neuroinflammatory system has emerged as a major contributor to the molecular and phenotypic changes observed in the AD brain. However, the mechanism by which the P522R variant of PLCγ2 reduces AD pathology is still unknown. BV2 (mouse microglia) cells and human induced pluripotent stem-cells (hiPSC) derived microglia were used in this thesis work to evaluate the role of PLCγ2 in modifying various disease-relevant microglia functions. PLCγ2WT and PLCγ2P522R expression constructs were transfected into BV2 cells to examine the effects of PLCγ2 overexpression on various microglia functions including amyloid beta (Aβ) clearance and synaptic targeting, and various transcriptional changes linked to AD. hiPSCs were genome edited using CRISPR/Cas9 to generate both heterozygous and homozygous forms of the PLCG2_P522R variant in healthy controls. These hiPSC derived microglia were used to explore the effects of the PLCγ2P522R basal level on disease-relevant processes, such as microglial capacity to uptake Aβ and synapses. Microglia transcriptional changes were examined using targeted qPCR analysis to investigate changes in expression of key microglial genes. Mitochondrial function and calcium level changes were also investigated in these microglia cells to determine their metabolic fitness. In addition, the microglia were subjected to acute and chronic treatment of oligomeric Aβ to examine the impact of PLCγ2P522R on microglia's ability to respond to acute and chronic stress. As a result, the effects of Aβ oligomers on lysosomal biogenesis and phagocytic capacities of these microglia were examined further. As a result of PLCγ2 overexpression, Aβ uptake and other immune- provoking cargoes like zymosan were significantly increased. In contrast, the uptake of synaptosomes in BV2 cells overexpressing PLCγ2 was considerably reduced. Similarly, microglia generated from hiPSCs also showed enhanced clearance of Aβ and preservation of synapses by PLCγ2P522R variants. In the PLCγ2P522R microglia variants, the expression of multiple genes, including IL-10 and CX3CR1, as well as mitochondrial function, cytoplasmic calcium flux, and cellular motility were all increased. It was found that the protective effect of PLCγ2P522R was vitally dependent on 'allelic-dose', as homozygous cells displayed a lower preservation of synapse and a distinct gene expression profile compared to heterozygous cells. Similarly, microglia with the protective mutation PLCγ2P522R displayed higher inflammatory cytokine IL-1β level, and better response to acute treatment with Aβ oligomers. PLCγ2P522R appeared to resist the quiescence that was seen in WT microglia variants, by increasing cytokine production and lysosomal biogenesis. My findings suggest that the P522R variant in PLCγ2 increases microglia capacity to clear toxic aggregates such as Aβ while preserving synapses. Furthermore, my findings suggests that PLCγ2P522R contributes to greater microglial surveillance, as well as microglia priming towards a pro-inflammatory state, along with an increased capacity to adapt to growing energy demands. This, however, also shows the delicate balance of this system, as increasing the 'dosage' of PLCγ2P522R may result in diminished favourable benefits

    Development of Novel Therapeutic Strategies to Target Therapy Resistance and Cancer Stem Cells

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    This thesis focuses on the core issues of multidrug resistance (MDR) in cancer, a process that hinders the success of chemotherapeutic treatments. MDR involves various mechanisms, including the upregulation of ABC transporter pumps, like MRP1, and increased cancer stemness, which contributes to malignancy and recurrence. The thesis comprises seven chapters: a literature review (Chapter 1), methodology (Chapter 2), results (Chapters 3-5), and discussions on findings and future studies (Chapters 6) and final discussion and overall summary (Chapter 7). Chapter 3 delves into the novel roles of MRP1 in cellular iron metabolism and proliferation, its interaction with c-Myc, and the effects on cellular proliferation. Silencing and inhibition studies reveal MRP1's role in regulating iron regulatory proteins through c-Myc. Chapter 4 investigates the role of ABC transporters in cancer stemness, revealing their connection with stemness states in different tumor types. Chapter 5 explores strategies for targeting drug-resistant cancer cells, demonstrating how doxycycline reduces the stemness marker SOX2 across multiple tumor types through a unique pathway. Chapter 6 examines the alteration of metabolism and stemness in drug-resistant cancer cells and strategies for targeting the cysteine metabolism pathway. The findings provide insights into cancer stemness regulation and potential therapeutic strategies, improving the efficacy of chemotherapeutics. The work reported in this thesis reveals an underlying and unique mechanism in regulation of SOX2-mediated cancer stemness. Moreover, the use of DXC to remove stemness was demonstrated to be a promising therapeutic strategy in combination with other common chemotherapeutics agents. These findings presented in this thesis enables us to understand cancer stemness better and improve the efficacy of current chemotherapeutics, which ultimately improve overall quality of life
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