The control theory of nonlinear systems has been receiving increasing attention in recent years, both for its technical importance as well as for its impact in various fields of application. In several key areas, such as aerospace, chemical and petrochemical industries, bioengineering, and robotics, a new practical application for this tool appears every day. System nonlinearity is characterized when at least one component or subsystem is nonlinear. Classical methods used in the study of linear systems, particularly superposition, are not usually applied to the nonlinear systems. It is necessary to use other methods to study the control of these systems. For a wide class of nonlinear systems, a rather important structural feature comes from the strong nonlinearity appearing as coupling between spectrally decoupled parts of the system. Even in the case of low frequencies, where lumped models can still be employed the nonlinear coupling between parts of the system requires specific treatment, using advanced mathematical tools. In this context, an alternative, frequency domain approach is pursued here. In the rest of this work, a specific system form of linearly decoupled but nonlinearly coupled subsystems is examined. The mathematical toolbox of the Hilbert transform is appropriately introduced for obtaining two low-pass subsystems that form an equivalent description of the essential overall system dynamics. The nonlinear coupled dynamics is investigated systematically by partitioning the coupled system state vector in such a way as to fully exploit the low-pass and the band-pass intrinsic features of free dynamics. In particular, by employing the Hilbert Transform, a low-pass equivalent system is derived. Then, a typical case is investigated thoroughly by means of numerical simulation of the original coupled low and band-pass, real-state-variable system and the low-pass-equivalent, complex-state-variable derived one. The nonlinear model equations considered here pave the way for a systematic investigation of nonlinear feedback control options designed to operate mechatronic transducers in energy harvesting, sensing or actuation modes.

Transition metal oxides have attracted widespread attention due to their broad range of fascinating exotic phenomena such as multiferroicity, superconductivity, colossal magnetoresistance and metal-to-insulator transition. Due to the interplay between spin, charge, lattice and orbital degrees of freedom of strongly correlated d electrons, these physical properties are extremely sensitive to the external perturbations such as magnetic field, charge carrier doping and pressure, which provide a unique chance in search for novel exotic quantum states. Ruthenate systems are a typical strongly correlated system, with rich ordered states and their properties are extremely sensitive to external stimuli. Recently, the experimental observation of spin-orbit coupling induced Mott insulator in Sr2IrO4 as well as the theoretical prediction of topological insulating state in other iridates, have attracted tremendous interest in the physics of strong correlation and spin-orbit coupling in 4d/5d compounds. We observe an itinerant ferromagnetic ground state of Ca2RuO4 film in stark contrast to the Mott-insulating state in bulk Ca2RuO4. We have also established the epitaxial strain effect on the transport and magnetic properties for the (Ca,Sr)2RuO4 thin films. For Sr2IrO4 thin films, we will show that the Jeff = 1/2 moment orientation can be modulated by epitaxial strain. In addition, we discovered novel Ba7Ir3O13+x thin films which exhibit colossal permittivity. / acase@tulane.edu

Weak bonds such as hydrogen bond, pi-pi stacking and van der Waals interaction are much weaker in the strength but play a more important role for the existence of various lives. For example, they are the major intermolecular interactions in the liquid and solid structure of water and determine the 3 dimensional structure of protein and DNA, which are the crucial organic molecules in lives. As a result, studying these weak bonds can lead to the better understanding of fundamental knowledge of lives. Kohn-Sham (K-S) Density Functional Theory (DFT) is an accurate and effect way to investigate the fundamental properties for many-body systems, in which, only the exchange-correlation energy as a functional of electron density need to be approximated. However, weak interaction system is still a challenge problem for KS-DFT. In this dissertation work, several standard density functionals are used to study these weak interactions in the solid state structure ice as long as nucleic bases molecules in the biologic system. It is found that the hydrogen bond can be well described by most semilocal functionals: the mismatch problem of ice Ih and AgI for GGA functional can be solved by using the higher level meta-GGA functionals and the binding length and energy between nucleic bases in DNA can be well described. However, the more accurate dispersion correction is strongly needed for van der Waals interactions and pi stacking for super-high pressure ice phases and large size biologic molecules, where van der Waals interaction takes major role. Finally, the basic structural properties of various phases of ice and DNA can be understood based on the investigation with appropriate functionals. / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

Density functional theory (DFT) is a widely used quantum mechanical method for the simulation of the electronic structure of atoms, molecules, and solids. The only part that needs to be approximated is the exchange-correlation energy as a functional of the electron density. After many-year development, there is a huge variety of exchange-correlation functionals. According to the ingredients, an exchange-correlation functional can be classified as a semi-local functional or beyond. A semi-local functional can be nonempirical or empirical and only uses locality information, such as electron density, gradient of the density, Laplacian of the density, and kinetic energy density. Unlike a non-local functional that uses non-locality information, a semi-local functional is computationally efficient and can be applied to large systems. The meta-generalized gradient approximation (meta-GGA), which is the highest-level semi-local functional, has the potential to give a good description for condensed matter physics and quantum chemistry. We built the self-consistent revised Tao-Perdew-Staroverov-Scuseria (revTPSS) meta-GGA into the band-structure program BAND to test the performances of some self-consistent semi-local functionals on lattice constant with a 58-solid test set. The self-consistent effect of revTPSS was also discussed. The vibration of a crystal has a contribution to the ground state energy of a system, which is the zero-point energy at zero temperature. It has anharmonicity at the equilibrium geometry. The standard DFT doesn’t consider the zero-point energy of a crystal. We used density functional perturbation theory (DFPT), which is a powerful and flexible theoretical technique within the density functional framework, to study the zero-point energy and make a correction to the lattice constant. The method was compared to a traditional zero-point anharmonic expansion method that is based on the Debye and Dugdale-MacDonald approximations. We also tested some new meta-GGA functionals (revTPSS, regularized revTPSS, and meta-GGA made simple) on a big molecular test set - GMTKN30 - that is composed of 30 smaller test sets and covers a large cross section of chemically relevant properties. The performances of these new meta-GGAs were compared with some other popular functionals or meta-GGAs. / acase@tulane.edu

<p>Chemical gas sensors can be used in a variety of applications such as process control, security systems and medical diagnosis. In the research for new functions and new sensing materials a “breadboard” would be useful. A technique that has been investigated for such a purpose is the grid-gate device which is a metal-oxide-semiconductor (MOS) based gas sensor. It is a MOS capacitor consisting of a passive grid-gate with depositions of sensing materials overlapping the grid. The measuring is carried out with a light addressable method called scanning light pulse technique (SLPT) which enables the detection of spatially distributed gas response.</p><p>A development of the grid-gate sensor would be to separate the sensing materials from the chip. In this thesis the aim was to see if this was possible by depositing the sensing material on a slide of micro pillars which was put on top of a biased grid-gate chip.</p><p>The test was made with palladium depositions in an ambient of synthetic air and 2500 ppm hydrogen, and the measuring technique was SLPT as for the preceding device.</p><p>The result of the test was that the new device showed a combined gas response of both charge content shift at flat-band voltage and at inversion voltages. The conclusion is therefore that the sensing material can be separated from the grid-gate chip and that the response will be caused by several mechanisms. The two-dimensional image response utilized for the preceding grid-gate device will instead be a multi-dimensional response consisting of the curve for the charge content shift at every measuring position.</p>

<p>Nickel based coatings were deposited on copper substrates by two different sputtering techniques from a nickel alloy based target. The substrates used were commercially available copper based substrates for low duty electrical contacts. The coatings were analyzed and evaluated as copper diffusion barriers for electrical contact applications. In addition two types of commercially available electroplated nickel coatings (referred to as type A electroplated coatings and type B electroplated coatings) were characterized for comparison. The Technique I sputtered coatings were deposited using three different substrate bias voltages and two different working gas pressures. The Technique II coatings were deposited using two different substrate bias voltages and two different working gas pressures. All sputtered coatings were deposited at a temperature of 200° C. The quality of the barriers was investigated by analyzing their composition, microstructure, stress, mechanical properties , and surface roughness. The results show that sputtered coatings have polycrystalline structures while the two plated films had (200) orientation and (111) orientation. Both plated coatings contained impurities that originate from chemicals used in the plating baths. The surface of the sputtered coatings reflects the substrate surface, while the electroplated samples on the same substrate (type A coatings) show a smooth mirror like surface and the type B electroplated coatings show a rough surface.</p><p>Technique II sputtered coatings showed the highest hardness in the amount of 13 GPa, followed by electroplated type A coatings with a hardness of about 9 GPa while the Technique I coatings showed hardness of 6-8 GPa. All sputtered coatings exhibited compressive stress while the electroplated type A coatings exhibited tensile stress of almost twice the magnitude.</p><p>In this study it is shown that sputtered nickel based coatings sputtered nickel based coatings are a promising more environmental friendly alternative to electroplated nickel coatings.</p>

<p>An active optical shutter for infrared light (3-5 μm) has been designed, exploiting the phase transition in thermochromic vanadium dioxide (VO₂). A spin coating processing route for VO₂ films has been adapted to manufacture reproducible depositions onto sapphire (Al₂O₃) substrates. The VO₂ films have been characterized by X-ray powder diffraction (XRPD) and infrared spectroscopy (FTIR), showing 55 % transmittance in the open mode and 0.1 % in the closed mode.</p><p>The VO₂ film temperature determines the operating mode of the shutter, and a resistive circuit of gold was deposited on top of the film for heating purposes. Switching times from the open to the closed mode down to 15 ms have been measured.</p><p>This work is a part of a comprehensive project at the Swedish Defence Research Agency (FOI), aiming to improve active components for protection against lasers. The shutter within this work is at this stage an early prototype, and needs further development and complementary systems such as a control unit to be implemented in an optical system.</p>

<p>The option of communicating via SMS messages can be considered available in all GSM networks. It therefore constitutes a almost universally available method for mobile communication.</p><p>The Tiger XS, a device for secure communication manufactured by Sectra, is equipped with an encrypted text message transmission system. As the text message service of this device is becoming increasingly popular and as options to connect the Tiger XS to computers or to a keyboard are being researched, the text message service is in need of upgrade.</p><p>This thesis proposes amendments to the existing protocol structure. It thoroughly examines a number of options for source coding of small text messages and makes recommendations as to implementation of such features. It also suggests security enhancements and introduces a novel form of stegangraphy.</p>