STUDY OF TRAPPING EFFECTS IN ALGAN/GAN MOSHEMTS

Ph.DDOCTOR OF PHILOSOPH

Biocompatibility of implantable materials: an oxidative stress viewpoint

Oxidative stress occurs when the production of oxidants surpasses the antioxidant capacity in living cells. Oxidative stress is implicated in a number of pathological conditions such as cardiovascular and neurodegenerative diseases but it also has crucial roles in the regulation of cellular activities. Over the last few decades, many studies have identified significant connections between oxidative stress, inflammation and healing. In particular, increasing evidence indicates that the production of oxidants and the cellular response to oxidative stress are intricately connected to the fate of implanted biomaterials. This review article provides an overview of the major mechanisms underlying the link between oxidative stress and the biocompatibility of biomaterials. ROS, RNS and lipid peroxidation products act as chemo-attractants, signalling molecules and agents of degradation during the inflammation and healing phases. As chemo-attractants and signalling molecules, they contribute to the recruitment and activation of inflammatory and healing cells, which in turn produce more oxidants. As agents of degradation, they contribute to the maturation of the extracellular matrix at the healing site and to the degradation of the implanted material. Oxidative stress is itself influenced by the material properties, such as by their composition, their surface properties and their degradation products. Because both cells and materials produce and react with oxidants, oxidative stress may be the most direct route mediating the communication between cells and materials. Improved understanding of the oxidative stress mechanisms following biomaterial implantation may therefore help the development of new biomaterials with enhanced biocompatibility

Modulation of the immune response following myocardial infarction utilizing biomaterial-based therapeutic delivery strategies

In 2015, American Heart Association (AHA) reported that 1 in 9 deaths are attributed to Heart failure (HF), the number one killer in the world. While advancements in interventional cardiology in conjunction with pharmacotherapies have significantly reduced the rate of mortality following MI, there has been a corresponding rise in chronic heart failure (CHF) in surviving patients, largely attributed to the limited regenerative capacity of the heart and the inadequate healing response. Myocardial ischemic injury triggers an exuberant local and systemic inflammation, and the extent and quality of the cardiac wound healing process is intricately tied to the delicate equilibrium of this inflammatory response. While cardiac regeneration is an important goal, it is imperative in the meantime to explore therapeutic strategies that target these inflammatory mediators of early cardiac repair. These interventions to influence and improve cardiac wound healing can represent a new therapeutic window to halt the progression of heart failure between the few hours that may be used to limit infarct size by reperfusion and an irreversible non-contractile cardiac scar. This dissertation examines three therapeutic delivery strategies aimed at modulating the immune response to enhance cardiac repair in rodent models MI: 1) Polyketal nanoparticles as siRNA delivery vehicles for antioxidant therapy; 2) Spherical nucleic acid particles for anti-inflammatory therapy and; 3) Bioactive PEG (polyethyleneglycol)-based hydrogel for immunomodulation. The work presented here applies novel nucleic acid delivery strategies for cardiac gene silencing and has contributed to new knowledge with regard to modulating the immune response following MI.Ph.D

Non-perturbative phenomena and the electroweak phase transition

The aim of this thesis is to investigate various non-perturbative phenomena within and beyond the standard model and their implications on the electroweak phase transition. The perturbative spectrum of the standard model is well-known and its properties have been measured to great precision. However, the same cannot be said for the non-perturbative spectrum. We first show the existence of electroweak monopoles with finite energy in a Born-Infeld extension of the standard model. We calculate this mass and discuss experimental constraints from light by light scattering and vector boson scattering processes. We also show that these monopoles are a source of B+L - and CP-violation which could potentially provide a novel method of detecting them. We then propose a new mechanism of baryogenesis through B+L - and CP-violating monopole-antimonopole annihilation processes. The phenomenon of scale invariance is an elegant solution to the hierarchy problem. We consider a model in which the standard model is a low energy effective theory with a UV completion that exhibits scale invariance. We compute the thermal effective potential for this model and show that the electroweak phase transition is dramatically different in this theory, only occurring after the QCD chiral phase transition. We also discuss phenomenological implications of this scenario. Finally, we inspect the role of gravity in quantum electrodynamics. We show that quantum gravity effects driven by electrically charged gravitational instantons give rise to a topologically non-trivial vacuum structure resulting in important phenomenological consequences like the violation of CP and the quantisation of electric charge. These models demonstrate that the detailed study of non-perturbative phenomena can yield interesting and significant results and can be the key to answering the unanswered questions in particle physics and cosmology

Impact of Google searches and social media on digital assets’ volatility

Abstract Advanced digitalization and financial technology have of recent times become among the most crucial tools. Data mining and sentiment analysis have revealed the importance of digitalization in modern times. This study examines the influence of Google search activity on the volatility of digital assets. We analyzed six digital asset prices for Bitcoin, Bitcoin Cash, Ethereum, Ethereum Classic, Litecoin, and Ripple from the Coinmarketcap database. We used tweets on Twitter to survey users’ sentiment by using the Twitter search Application Programming Interface and Google trend search from web searches, news searches, and YouTube searches data using RStudio software. The study spanned 1 September 2019 to 31 January 2020 and employed the Vector Autoregression (VAR) approach for analysis. The VAR estimation revealed that Google search variables have significantly influenced the volatility of Bitcoin, Ethereum, Litecoin, and Ripple, as supported by the Granger causality test and impulse response function. The results of this study could be useful for investors and policymakers in drawing up strategies to reduce market volatility. These results should thus be useful to investors in developing profitable investment strategies to mitigate the impact of market turbulence

Band alignment of HfAlO/GaN (0001) determined by X-ray photoelectron spectroscopy: Effect of in situ SiH4 passivation

The energy band alignment between HfAlO and GaN (0001) was characterized using high-resolution X-ray photoelectron spectroscopy (XPS). The HfAlO was deposited using a metal-organic chemical vapor deposition (MOCVD) gate cluster. A valence band offset of 0.38 eV and a conduction band offset of 2.22 eV were obtained across the HfAlO/GaN heterointerface without any passivation. With in situ SiH4 passivation (vacuum anneal + SiH4 treatment) on the GaN surface right before HfAlO deposition, the valence band offset and the conduction band offset across the HfAlO/GaN heterointerface were found to be 0.51 eV and 2.09 eV, respectively. The difference in the band alignment is believed to be dominated by the core level up-shift or chemical shift in the GaN substrate as a result of different interlayers (ILs) formed by the two surface preparations. (C) 2015 Elsevier B.V. All rights reserved

Bioactive nanoparticles improve calcium handling in failing cardiac myocytes

AimsTo evaluate the ability of N-acetylglucosamine (GlcNAc) decorated nanoparticles and their cargo to modulate calcium handling in failing cardiac myocytes (CMs).Materials & methodsPrimary CMs isolated from normal and failing hearts were treated with GlcNAc nanoparticles in order to assess the ability of the nanoparticles and their cargo to correct dysfunctional calcium handling in failing myocytes.Results & conclusionGlcNAc particles reduced aberrant calcium release in failing CMs and restored sarcomere function. Additionally, encapsulation of a small calcium-modulating protein, S100A1, in GlcNAc nanoparticles also showed improved calcium regulation. Thus, the development of our bioactive nanoparticle allows for a 'two-hit' treatment, by which the cargo and also the nanoparticle itself can modulate intracellular protein activity

AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistor with polarized P(VDF-TrFE) Ferroelectric polymer gating

10.1038/srep14092Scientific Reports51409