In this study, we investigate the fundamental mechanisms defining the approach for addressing tribological challenges in mechanical systems via the use of the tribocatalytically active coating. The coating is designed using an electrodeposition process and consists of a hard amorphous cobalt-phosphorous matrix with the incorporation of tribocatalytically-active nickel and copper. Our focus is on understanding the effect of the tribocatalytic elements, Cu vs Ni, on the coating's performance in high-contact stress conditions, generating local heating, shear, and compression. By optimizing the relative composition and mechanical characteristics of the coating, we aim to enhance its tribological performance in the presence of a hydrocarbon environment. Through extensive characterization of the wear tracks using SEM/EDS and Raman analyses, we identify the formation of a protective carbon-based tribofilm on the coating's surface during sliding as the key factor behind its excellent performance. Our findings not only contribute to the understanding of material transformations in the contact but also offer a robust and versatile approach to addressing tribological challenges in mechanical systems. The development of this innovative coating opens up new possibilities for promoting the formation of protective tribofilms and improving the performance of mechanical components operating in low-viscosity fuels and synthetic oils.

Nonlinear optics represents a significant area of research and technology concerned with the modification of material optical properties using light. The interaction between light and such materials gives rise to a multitude of nonlinear optical effects, including second har-monic generation, third harmonic generation, high harmonic generation, and sum frequency generation. This thesis focuses on a specific and relevant nonlinear phenomenon within this field, namely the nonlinear Kerr effect, which involves the modification of a material’s re-fractive index through the exposure to an intense beam of light. The nonlinear Kerr effect holds promise for various applications, such as self-phase modulation in laser technology and the utilization of optical solitons in telecommunications. However, the limited availability of materials with sufficiently strong Kerr effects often restricts the practical application of this effect across different industries. Concurrently, optical time-varying systems play crucial roles in modern technologies, in-cluding optical modulators, LiDAR systems, and adaptive cameras. These systems involve the dynamic modification of optical properties. To achieve ultra-fast modulation of light properties, it is beneficial to explore materials with ultra-fast modulation speeds of the op-tical refractive index for integration into time-varying systems. While electro-optical effects represent the most common methods for achieving high-speed modulation of the effective refractive index, the utilization of all-optical methods, such as the nonlinear Kerr effect, presents an alternative approach. Nevertheless, the absence of simultaneous high speed and large nonlinear Kerr response in the majority of well-established materials restricts the utilization of the Kerr effect in time-varying systems.This thesis focuses on the study of a group of materials known as epsilon-near-zero (ENZ) materials, where the real part of the permittivity vanishes at a specific wavelength referred to as the ENZ wavelength. Specifically, indium-tin-oxide (ITO), a transparent conducting oxide, is investigated, with its ENZ wavelength falling within the infrared region of the elec-tromagnetic spectrum. ITO has been shown to possess a record-breaking large nonlinear Kerr effect with sub-picosecond response times, making it an excellent candidate for all-optical time-varying systems. The primary objective of this research is to investigate the applications of this large, fast nonlinear response and, where possible, enhance its effective-ness. One notable application of rapid and substantial modifications in the refractive index of a material is adiabatic wavelength conversion of light. In one project, a thin layer of ITO is subjected to a pump-probe setup, where an intense pump beam of light triggers the nonlinear response of ITO, causing the refractive index to rapidly change while a probe beam passes through the modulated system. Consequently, the wavelength of the probe beam undergoes conversion. Furthermore, it has been demonstrated that the nonlinear response of ITO can be sig-nificantly enhanced in the presence of a plasmonic metasurface. Metasurfaces consist of two-dimensional arrays of sub-wavelength scattering objects capable of manipulating the vectorial properties of light. In another project, we design a gradient metasurface composed of gold placed over ITO, enabling the diffraction of incident light into various diffraction orders depending on the ratio between the wavelength of light and the periodicity of the metasurface. This unique property is utilized to dynamically steer the diffraction orders of the probe beam, achieving wavelength conversion by exciting the nonlinear response of the ITO substrate with a second pump beam. Additionally, we investigate the interaction of resonance modes in an amorphous silicon metasurface, known as Mie modes, with an inherently dark mode in a thin layer of ITO known as the ENZ mode. Through experimental and analytical approaches, we demonstrate that two fundamental Mie modes, electric dipole resonance and magnetic dipole resonance, can strongly couple with the ENZ mode. This strong coupling creates a highly complex system with a large and rapid nonlinear response, enabling the manipulation of light on sub-picosecond timescales. In our final main project, we delve into investigating the nonlinear response of ITO nanoparticles. To accomplish this, we put forth a numerical recursive approach that allows us to incorporate the significant nonlinear Kerr effect of ITO into inherently linear simulation environments. Subsequently, we employ this proposed method to extract the scattering pattern of sub-wavelength antennas fabricated from ITO in both linear and nonlinear optical regimes. Our objective is to explore the potential applications of ITO nanoantennas in various fields. Moreover, this thesis encompasses other projects related to ENZ materials. We investi-gate the nonlinear response of an artificially created ENZ medium by stacking subsequent layers of materials with negative and positive permittivities within the visible range of the electromagnetic spectrum. Additionally, we explore the nonlinear response of nanoparticles made of ITO. Lastly, we present our investigations into the strong coupling of the ENZ mode in a thin layer of ITO with surface plasmon polaritons in a layer of gold in contact with ITO.

This thesis investigates the relationship between product market competition and zero leverage behavior within firms, aiming to uncover how these dynamics interact. Additionally, it explores whether firms characterized by higher earnings volatility exhibit a more pronounced positive relationship between product market competition and the likelihood of adopting a zero-leverage strategy. To carry out this investigation, we employed product market competition data (Fluidity) from the Hoberg-Phillips Data Library and financial data from the Compustat (North America) database, spanning from 1989 to 2019. As product market competition intensifies, the probability of firms adopting a zero leverage policy increases. Furthermore, our research illuminates that the positive impact of heightened product market competition on the likelihood of zero leverage policies is accentuated in firms characterized by elevated levels of earnings volatility. This finding corroborates our initial hypothesis, substantiating the notion that increased competition significantly influences a company's earnings volatility. We also strengthened our analysis with insights from existing literature, underscoring how heightened earnings volatility intensifies the propensity to embrace a zero leverage policy. This study contributes insights to the literature, notably as the first to employ the interaction term between product market competition and earnings volatility in exploring these financial dynamics.

Wireless networks are vulnerable to adversarial devices by spoofing the digital identity of valid wireless devices, allowing unauthorized devices access to the network. Instead of validating devices based on their digital identity, it is possible to use their unique "physical fingerprint" caused by changes in the signal due to deviations in wireless hardware. In this thesis, the physical fingerprint was validated by performing classification with complex-valued neural networks (NN), achieving a high level of accuracy in the process. Additionally, zero-shot learning (ZSL) was implemented to learn discriminant features to separate legitimate from unauthorized devices using outlier detection and then further separate every unauthorized device into their own cluster. This approach allows 42\% of unauthorized devices to be identified as unauthorized and correctly clustered

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.