Physics Commons^™

Study Of Weakly Bound Cluster Anions Using Self Interaction Corrected Density Functional Scheme, Peter Obinna Ufondu

Open Access Theses & Dissertations

The Kohn–Sham formulation of density functional theory (DFT) is a widely used quantum mechanical theory to study chemical and materials properties. The practical application of DFT requires an approximation to the exchange–correlation (XC) functional. These approximations suffer from self-interaction errors due to the incomplete cancellation of the self-Coulomb energy with the approximate self-exchange and correlation energy for one-electron densities. Systems with weakly-bound electrons impose great challenges to semi-local density functional approximations. We use recently developed local scaled self-interaction correction (LSIC) by Zope et al and the Perdew-Zunger SIC method using the Fermi-Löwdin orbitals to calculate the vertical detachment energies (VDEs) …

High Frequency Electron Spin Resonance Investigations On Quasi-Two-Dimensional Chromium Halide Magnets, Christian Saiz

Open Access Theses & Dissertations

Broadening the knowledge and understanding on the magnetic correlations in van der Waals layered magnets is critical in realizing their potential next-generation applications in devices such as spintronics. In this study, we employ high frequency (ν = 120 GHz, 240 GHz) electron spin resonance (ESR) spectroscopy on plate-like CrX3 (where X = Cl, Br, I) to gain insight into the magnetic interactions as a function of temperature (200 – 4.4 K) and the angle of rotation θ (degrees). We find that the temperature dependence of the ESR linewidth is well described by the Ginzburg-Landau critical model, indicative of antiferromagnetic correlations …

Impact Of Various Hydrophobic Cargoes On The Structural Properties Of Pluronic-F127 Based Micelles Near The Standard Critical Transition Zone, Tahmida Raheen Iqbal

Open Access Theses & Dissertations

Pluronic F-127 is a triblock copolymer (PEO-PPO-PEO) that can form a micelle at critical micelle concentration (CMC). CMC for Pluronic F-127 is 0.7% at 25 0C. Micelles are lipid molecules that can arrange themselves in a spherical form in an aqueous solution with a hydrophobic core and hydrophilic shell. Pluronic F-127 can encapsulate poor water-soluble drugs and administrate the medicine to the targeted area with a controlled drug release rate and low toxicity. The purpose of this study is to understand the structural variation in Pluronic F-127 micelles after loading with different hydrophobic cargoes (alkanes, fatty acids, anticancer therapeutic agents). …

A Study Of The Frustrated Honeycomb Battery Material Na2ni2teo6, Nathan Christopher Episcopo

Open Access Theses & Dissertations

The P2-type layered hexagonal compound Na2Ni2TeO6 with Ni2+ on a honeycomb lattice was synthesized by the standard solid-state route. Structural characterization chemical phase purity was confirmed by Rietveld refinement of laboratory and synchrotron data. The crystal structure refines well in the P63/mcm space group. Single crystal growth trials using the self-flux-melt method were conducted with limited success. The magnetic transition temperature pertaining to Ni2+ lattice was confirmed by analysis of specific heat capacity to be . The magnetic susceptibility remains largely unchanged in magnetic field of and external pressure of . There is an almost linear response in isothermal magnetization …

Two Developments For Efficient And Accurate Density Functional Theory Calculations, Zachary John Buschmann

Open Access Theses & Dissertations

Density functional theory (DFT) has long been the workhorse of quantum chemists and materials scientists. As the ability of modern DFT codes to address larger and more complex molecular systems has grown, so too has the computational cost, with cutting edge simulations requiring thousands of hours of wall time on the worldâ??s fastest supercomputers.For this reason, efficiency in both memory and time is critical at every step of the process. In fact, the increasing scope of physical systems that can be modeled is as much a function of computational elegance as of the physical fidelity of the simulation. The continuing …

Examining The Quality Of Life In Transgender Women Following Gender Affirming Voice Treatment, Georgina L. Salas

Open Access Theses & Dissertations

Transgender women are reported to have a lower quality of life. Gender affirming voice treatment is reported to increase quality of life in transgender women. This study examined 3 participants and their quality of life after gender affirming voice treatment. The results of this study indicated gender affirming therapy did not improve participants' quality of life.

Mathematical Modeling Of Microemulsification Processes, Numerical Simulations And Applications To Drug Delivery, Ogochukwu Nneka Ifeacho

Open Access Theses & Dissertations

Microemulsion systems are a great pharmaceutical tool for the delivery of formulations containing multiple hydrophilic and hydrophobic ingredients of varying physicochemical properties. These systems are gaining popularity because of its long shelf life, improved drug solubilisation capacity, easy preparation and improvement of bioavailability. Despite the advantages associated with the use of microemulsion systems in pharmaceutical industries, the major challenge impeding their use has been and continues to be the lack of understanding of these systems.

Microemulsions can be mathematically modeled by an initial boundary value problem involving a sixth order nonlinear time dependent equation. In this Thesis, we present a …

Density Functional Calculations On Single Molecular (1d) And Van Der Waals Bi -Layered (2d) Magnets., Md Shamsul Alam

Open Access Theses & Dissertations

Low-dimensional magnetic materials show novel properties that is not seen in bulk magnets. The weak interactions such as spin-orbit interactions, electron correlation, van der Waals interaction in case magnetic bi-layers, play an important role in determining the properties of the system. Using density functional theory, we computationally investigated two categories of magnetic material- 1: Single Molecular Magnets (SMM) 2: Van der Waals layered Cr-Halide magnets. We used different classes of density functionals to examine the spin ordering and magnetic anisotropy barriers in several single molecule magnets - Mn12, Co4, Ni4, V15. We find that the magnetic anisotropy barrier significantly depends …

Some Fermi-Lowdin Orbital Self-Interaction Correction Studies On Atomic Systems, Christopher Alexis Ibarra

Open Access Theses & Dissertations

Density Function Theory (DFT) is a popular quantum chemistry calculation method with many appeals but also deficiencies. Many modification and additions to the method have been made over the years, such as self-interaction corrections and new density functional approximations. We review here the theoretical background needed for a basic understanding of quantum chemistry calculations. In addition, we present the quantum chemistry calculation method used in this paper called Fermi-Lowdin Self-Interaction Correction (FLOSIC), including the base code it was implemented on, the Naval Research Laboratory Molecular Orbital Library (NRLMOL) Code, and the resulting modified code simply called FLOSIC. Furthermore, we explore …

Development Of Software Tools And Experimental In Situ Electron Spin Resonance For Characterizing The Magnetic And Electrocatalytic Properties Of Transition Metal Chalcogenide Crystals, Jose Armando Delgado

Open Access Theses & Dissertations

Studying the magnetic properties and crystal defects of transition metal chalcogenide crystals is of paramount importance for utilizing them for next generation spintronics devices and hydrogen evolution reaction catalysts. Hydrothermally grown transition metal chalcogenide nanocrystals (MoS2, Ru2S3, Rh2S3, Co2S8) were chosen as catalysts for the hydrogen evolution reaction due to their low dimensionality and previous utilization as catalysts for hydrodesulfurization. The relationship between crystal defect sites and catalytic activity must be discerned to maximize the efficiency of hydrogen production during the hydrogen evolution reaction. ESR spectroscopy was utilized as a spin sensitive technique to study the defects and local changes …

Independent And Simultaneous Control Of Electromagnetic Wave Properties In Self-Collimating Photonic Crystals Using Spatial Variance, Jesus Javier Gutierrez

Open Access Theses & Dissertations

Photonic crystals are engineered periodic structures that provide great control over electromagnetic waves. One of these mechanisms is self-collimation, in which the electromagnetic wave travels through the photonic crystal along an axis of the lattice without diffracting or spreading. This mechanism of self-collimation is a dispersion phenomenon, which is dependent on the unit cell's physical and geometrical characteristics. An algorithm for generating spatially variant lattices (SVL) was developed that can change geometrical properties in photonic crystals as a function of position, like unit cell orientation, fill fraction, symmetry, and others in a manner that is smooth, continuous, and virtually free …

Development And Assesment Of Local Scaled Self-Interaction Corrected Density Functional Method With Simple Scaling Factor, Selim Romero

Open Access Theses & Dissertations

The Hohenberg-Kohn-Sham (HKS) density functional theory (DFT) is widely used to compute electronic structures of atoms, molecules, and solids. It is an exact theory in which ground state electron density plays the role of basic variable, same as the wavefunction does in quantum mechanics. The total ground state energy is a functional of electron density. The practical application of HKS DFT require approximation to the exchange-correlation energy functional. Many density functional approximations (DFAs) with various degree of sophistication and complexities have been developed. Depending on the complexity, these functionals include electron density, density gradients, density Laplacian, kinetic energy densities, Hartree-Fock …

Comparative Experimental And Theoretical Study Of Dopamine And Serotonin Interaction, Jose A. Guerrero

Open Access Theses & Dissertations

To accurately identify and measure the concentrations of dopamine (DA) and serotonin (5-HT) in mixtures of these neurotransmitters without labeling, a comprehensive, comparative computational and Raman experimental analysis is provided. While the distinction between these two analytes may be accomplished for concentrations in the millimolar range of these mixtures, their accurate quantification remains unattainable. As shown for the first time in this study, potential creation of a new composite resulting from their interactions with each other could be a reason for this lack of quantification.

Although this new hydrogen-bonded complex greatly complicates future analyte differentiation and quantification at concentrations typical …

Planar Motion Control Of A Cube Satellite Using Cold Gas Thrusters, Christian Lozoya

Open Access Theses & Dissertations

This Thesis presents a mathematical model developed for the computational simulation ofCubeSat movement using four thrusters that permit uniaxial translation and rotation. Arbitrary functions are fit to boundary conditions to simulate the force, acceleration, velocity, and displacement of the CubeSat along a plane. The model is used to derive a motion control algorithm assuming constant pressure and mass. A single model describes both translation and rotation. This Thesis also explores the relationship between propellant consumption and the time required to complete a displacement implied by the model.

Study Of Blinking Statistics In Silver Coated Cobalt Ferrite Single Nanoprticle Using Two-Photon Fluorescence Microscopy, Rajen Kumar Goutam

Open Access Theses & Dissertations

Two-photon fluorescence microscopy is a powerful tool to study the molecular and cellular interactions. This technology is a non-invasive approach with the advantage of three-dimensional imaging up to submicron resolution. Two-photon excitation process is the result of simultaneous absorption of two photons that has special features of reduced photodamaged and elongated penetration depth on samples. In this work, blinking statistics of silver-coated Cobalt ferrite (CoFe2O4) single nanocrystal is studied using two-photon fluorescence microscopy. By defining the intensity threshold, the observed fluorescence is divided into two distinct stages: OFF and ON states. Both of these states followed the inverse power law. …

Phase Diagram Of Nuclear Matter, Adrian Gaytan Terrazas

Open Access Theses & Dissertations

Nowadays it is well known that nuclear matter has a liquid and a gas phase, as well as a coexistence of phases region. Symmetric nuclear matter (same number of protons and neutrons) exhibit phase transitions from the gas phase to a liquid-gas mixture. A useful tool to represent such phases and transitions is through diagrams that show the necessary conditions of density and temperature to be in either of the phases.

Now the question is, what if we extend the traditional phase diagram for symmetric matter to the asymmetric

cases (different number of protons and neutrons)?

This study uses classical …

Near Room Temperature Magnetocaloric Materials For Magnetic Refrigeration, Eduardo Martinez Teran

Open Access Theses & Dissertations

Magnetic refrigeration (MR) is a cooling process based on the magnetocaloric effect (MCE) that is present to some extent in all magnetic materials, and the ones in which this effect is more appreciable are called magnetocaloric materials (MCM). The implementation of new designs and materials for the construction of cooling systems is a must do, being essential that these improved designs will reduce the environmental impact and increase the efficiency of their predecessors. In this thesis, the magnetocaloric effect theory is presented from a thermodynamic point of view and also the synthesis and study to a new Heusler alloy (MnFe2Ga) …

Computational Studies On Perovskite-Metallofullerene Interface And Magnetic Properties Of Mn-Based Mixed Olivines, Bethuel Omutiti Khamala

Open Access Theses & Dissertations

Methyl ammonium lead halide (MAPbX3) perovskite based solar cells have recently emerged as promising class of materials for photovoltaic applications with efficiencies reaching over 22%. Designing interfaces with strong binding is vital to developing efficient, high-performing solar cells. Fullerene-based materials are widely employed as efficient electron acceptors and can serve as electron transporting layer in perovskite based solar cells. We have studied interfaces of methyl ammonium lead iodide MAPbI3 with Sc3N@C80 fullerene and Sc3N@C80PCBM fullerene derivate within the density functional formalism. Different surface terminations and orientations of the methyl ammonium are examined for binding of the fullerene layer. Our calculated …

Spectroscopic Analysis Of Calcium Oxalate Kidney Stone Inhibition By Nordihydroguaiaretic Acid (Ndga), Mahendra Subedi

Open Access Theses & Dissertations

This current study provides information regarding the inhibition of calcium oxalate type of kidney stones by the use of nordihydroguaiaretic acid (NDGA). Around 80% of kidney stones found in patients are principally made of calcium oxalate and calcium phosphate. NDGA is an antioxidant compound that is chemically extracted from the desert bush Larrea tridentata. This work is a logical continuation of a previous research, where different concentrations of Larrea tridentata extract were used for such inhibition. Size and morphological changes from a calcium oxalate monohydrate (COM) structure to a calcium oxalate dihydrate (COD) structure were previously reported.

In the current …

A Study Of Solvent Effects On The Ground And Excited States Of Endohedral Tri-Scandium Nitride C80 Fullerene Coupled With Zinc Phthalocyanine And Metal-Free Phthalocyanine Using Dft-Pcm Method, Timilsina Prasad Timlsina

Open Access Theses & Dissertations

The photovoltaic active materials composed of endohedral metafullerene and phthalocyanine derivatives are known as excellent electron donor-acceptor pairs. The tri-metallic nitride endohedral C80 fullerene exhibits high absorption coefficients in the visible region of the spectrum and has similar electron-accepting abilities as that of C60 fullerene, which can allow for higher efficiencies in OPV devices. In this study, we examine the effect of solvent on the charge transfer excitation energies of Sc3N@C80-ZnPc and Sc3N@C80-H2Pc donor-acceptor molecular complexes. Three different solvents with different polarity - water, toluene, and acetone are used. The solvent is modeled as a polarizable continuum as implemented in …

Non Linear Optics For Materials Fabrication And Medical Instrumentation, Aurelio Paez

Open Access Theses & Dissertations

Two-photon absorption is a nonlinear optical process where two photons are absorbed by a molecule simultaneously. The probability of this quantum phenomenon is proportional to the quadratic excitation of light intensity. It has many applications in biomedical and materials research, such as two-photon fluorescence microcopy. The first project is to apply two-photon absorption induced bond cleavage in photoreactive materials for engineering 3D tissue scaffolds. The major challenge for growing thick 3D tissues is the lack of vasculature, where nutrients and oxygen can be delivered to the growing cells. Our collaborators have synthesized a novel polypeptide that is composed of 34-mer …

Quasi-Harmonic And Anharmonic Entropies In Transition Metals, Bimal K C

Open Access Theses & Dissertations

Density functional theory (DFT) employing the quasi-harmonic approximation (QHA) is a robust method for evaluating thermal properties of solids. In the case of transition metals however, the method yields high values of the thermal pressure when compared to experimental data or with more direct methods like quantum-molecular dynamics (QMD) simulations. Surprisingly, there has not been to date, a systematic study aimed at understanding the reasons for these large discrepancies, particularly at low temperature, i.e. below the Debye temperature of the solid. Using Tantalum as a test model for which a lot of experimental data exist, thermal properties were evaluated employing …

Magnetic Nanoparticles For Hyperthermia For Cancer Treatment, Bianca Paola Meneses Brassea

Open Access Theses & Dissertations

Fe3O4 and NixCu4-x magnetic nanoparticles were synthesized using supercritical conditions of liquids and wet chemistry, respectively. Characterization methods (VSM, SEM, TEM, and magnetic hyperthermia) yielded results that prove feasibility for magnetic hyperthermia for cancer treatment.

Dimensionality Of Magnetism In Trirutile Cota2o6 And Its Derivatives, Raju Baral

Open Access Theses & Dissertations

In this thesis, we addressed the question of low dimensionality of trirutile compound CoTa2O6 and studied how the low dimensionality evolved with doping of Mg on Co-site. In order to study low dimensionality in CoTa2O6 and its derivative compounds Co1-xMgxTa2O6 (x = 0.1, 0.3, 0.5, 0.7, and 1), we used different techniques: X-ray diffraction, magnetic susceptibility, magnetization, specific heat and elastic neutron diffraction. We have addressed the question of low dimensional magnetism of CoTa2O6 by preparing phase-pure samples of the compound. In CoTa2O6 a broad feature is observed in magnetic susceptibility at 10 K and an antiferromagnetic phase transition is …

Study Of D-Electron Systems With Fermi-Lowdin Orbital Self-Interaction Correction, Prakash Mishra

Open Access Theses & Dissertations

Density Functional Theory (DFT) is one of the very popular and versatile methods for calculations to study electronic structure, and the accuracy of DFT depends on the approximation used in the exchange-correlation functional. One of the known problems with the approximation is that the widely used density functional approximations (DFA) suffer self-interaction errors. Systems with d-electrons such as transition metal oxides often show deviation of DFT predicted behavior from experimental result. SIE tends to unphysically lower the energies of fractionally occupied state which leads to deviation from piece-wise linear behavior of total energy between two integer occupations. This leads to …

Novel Maximum Entrophy Method For The Average Survival Time Differences Between Two Groups, Joscelyne Guzman - Gonzalez

Open Access Theses & Dissertations

We suggest a Maximum Likelihood estimator for the Average Survival Time Difference between two groups, based on the extra time in which should be added to one group to produce the maximum entropy of the result. The estimator is calculated only from time to event data, does not assume hazard proportionality and provides directly the magnitude of the clinical differences between the groups. Our Monte Carlo simulations show that, even at low sample numbers the estimator is a reliable predictor for the clinical differences between the groups, and therefore can be used to estimate from preliminary data whether or not …

Nonlinear Optics For Nanoparticle Tracking And Materials Characterization, Angela Christina Aguilar

Open Access Theses & Dissertations

A high-speed 3D imaging method is developed by integrating ultrafast laser pulse shaping, temporal focusing microscopy and defocused imaging. This system does not require mechanical movement of either the stage or laser beam. Axial scanning is achieved by manipulation of group velocity dispersions on the femtosecond laser spectrum via pulse shaping method by applying modulation functions on an acoustic optical modulator which diffracts the laser spectrum. The scanning depth becomes only dependent on electronic signals which can be tuned to kHz speeds. The volumetric high-speed scanning capability was demonstrated on fluorescent microspheres suspended in a volume of 100 x100 x …

Using Two-Photon Microscopy To Analyze Arabidopsis Thaliana Leaves Under Autophagy Conditions And Second Harmonic Generation In Collagen, Andres Martin Reyes

Open Access Theses & Dissertations

Two-photon microscopy has emerged as a highly efficient and effective imaging tool for biological samples. This can be utilized in studying recently emerging technologies and conditions such as the autophagy process in arabidopsis thaliana leaves and second harmonic generation in collagen. Both of these areas of study utilize the two-photon microscopy practice effectively in uncovering more information of the biological nature of examined samples.

Electron Binding Energy Of Polar Molecules Using Fermi Löwdin Orbital Self Interaction Corrected Density Functional Scheme, Peter Obinna Ufondu

Open Access Theses & Dissertations

Density functional theory (DFT) has become a standard method for electronic structure calculations in physics. The standard approximate density functional usually do not bind this class of anions, due to self-interaction error (SIE). We apply the recently developed Fermi Löwdin orbitals based self-interaction correction method (FLOSIC) with long-range diffuse Gaussian functions to study dipole bound anions and negatively charged water clusters. These calculations are carried out using Perdew-Wang (1992) local spin density PW91-LDA, Perdew-Burke-Ernzerhof PBE-GGA, and the recently developed Strongly Constrained and Appropriately Normed SCAN-meta-GGA functional which satisfies all the known constraints for exchange-correlation functional. Plot from FLOSIC density difference …

Experimental Laser Powder Bed Fusion System For Difficult To Process Metallic Materials, Syed Zia Uddin

Open Access Theses & Dissertations

The focus of this research was twofold, such as development of defect free fabrication parameters for laser powder bed fusion (LPBF) processing of crack prone or difficult to process metallic materials, and study of the temperature dependence of emissivity for some commonly used metal alloy powders in LPBF process. The later objective extends to the implementation of multiwavelength (MW) pyrometer technology for in situ true surface temperature measurement in LPBF process. LPBF is an additive manufacturing (AM) process capable of layer-by-layer manufacturing by successive laser melting of each layer according to CAD data. AM manufacturing has the inherent advantages of …