Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Iowa State University

Retrospective Theses and Dissertations

Discipline
Keyword
Publication Year

Articles 1 - 30 of 731

Full-Text Articles in Physics

Magneto-Optical Study Of The Intermediate State In Type-I Superconductors: Effects Of Sample Shape And Applied Current, Jacob Ray Hoberg Jan 2008

Magneto-Optical Study Of The Intermediate State In Type-I Superconductors: Effects Of Sample Shape And Applied Current, Jacob Ray Hoberg

Retrospective Theses and Dissertations

The magnetic flux structures in the intermediate state of bulk, pinning-free Type-I superconductors are studied using a high resolution magneto-optical imaging technique. Unlike most previous studies, this work focuses on the pattern formation of the coexisting normal and superconducting phases in the intermediate state. The influence of various parameters such as sample shape, structure defects (pinning) and applied current are discussed in relation to two distinct topologies: flux tubes (closed topology) and laminar (open topology). Imaging and magnetization measurements performed on samples of different shapes (cones, hemispheres and slabs), show that contrary to previous beliefs, the tubular structure is the ...


Study Of Left-Handed Materials, Jiangfeng Zhou Jan 2008

Study Of Left-Handed Materials, Jiangfeng Zhou

Retrospective Theses and Dissertations

Left handed materials (LHMs) are artificial materials that have negative electrical permittivity, negative magnetic permeability, and negative index of refraction across a common frequency band. They possess electromagnetic (EM) properties not found in nature. LHMs have attracted tremendous attention because of their potential applications to build the perfect lens and cloaking devices. In the past few years there has been ample proof for the existence of LHMs in the microwave frequency range. Recently, researchers are trying hard to push the operating frequency of LHMs into terahertz and the optical regime.;In this thesis, we start with the theoretical prediction of ...


Magnetic Properties Of Rt2zn20 R = Rare Earth, T = Fe, Co , Ru, Rh , Os And Ir, Shuang Jia Jan 2008

Magnetic Properties Of Rt2zn20 R = Rare Earth, T = Fe, Co , Ru, Rh , Os And Ir, Shuang Jia

Retrospective Theses and Dissertations

Single crystals of RT2Zn20 compounds were grown from Zn self-flux. Thermodynamic and transport measurements indicated that YFe2Zn20 is closer to the Stoner criteria. As a result of local moments embedded in this highly polarizable Fermi liquid, remarkably high-temperature ferromagnetic ordering was found for RFe 20Zn20 (R = Gd - Tm). Furthermore, pseudo-ternary compounds GdxY1-xFe2Zn20 manifest ferromagnetic ordering above 1.8 K for Gd concentrations x>0.02. In contrast, for the isostructural RCo2Zn20 series, only Gd and Tb compounds manifest antiferromagnetic ordering above 2 K, correspondent a 'normal metal' behavior of YCo2Zn 20. Six Yb compounds (YbT2Zn20, T = Fe, Co, Ru. Rh ...


A Study Of Jet Energy Loss In Heavy-Ion Collisions At Phenix-Rhic, Via 2-Particle And "2+1" Correlations, And Future Upgrade, Hua Pei Jan 2008

A Study Of Jet Energy Loss In Heavy-Ion Collisions At Phenix-Rhic, Via 2-Particle And "2+1" Correlations, And Future Upgrade, Hua Pei

Retrospective Theses and Dissertations

No abstract provided.


Applications Of Effective Field Theories Within And Beyond The Standard Model, Oleg Antipin Jan 2008

Applications Of Effective Field Theories Within And Beyond The Standard Model, Oleg Antipin

Retrospective Theses and Dissertations

We review the role of the effective field theories in modern physics, especially modern elementary particle physics. We provide field-theoretical description of the three effective field theories: chiral perturbation theory, heavy-quark effective theory and Randall-Sundrum (RS) Model. Applications of these formalisms in the particle physics research are discussed, ranging from B-physics and baryon physics to search for the first RS Kaluza-Klein graviton mode via gluon-fusion process at the LHC.


Investigations Of The R5(Si(Subscript X)Ge(Subscript 1-X)4 Intermetallic Compounds By X-Ray Resonant Magnetic Scattering, Lizhi Tan Jan 2008

Investigations Of The R5(Si(Subscript X)Ge(Subscript 1-X)4 Intermetallic Compounds By X-Ray Resonant Magnetic Scattering, Lizhi Tan

Retrospective Theses and Dissertations

No abstract provided.


Quantum Phases In Frustrated Strongly Correlated 2-D Systems, Jun Liu Jan 2007

Quantum Phases In Frustrated Strongly Correlated 2-D Systems, Jun Liu

Retrospective Theses and Dissertations

The strong Coulomb repulsion between charge carriers in a system with one electron per site can lead to a full localization of the electrons. The resulting state is called a Mott insulating state. The interplay between the physics of Mott insulators and of unconventional superconductors has been a focus in condensed matter physics for a long time. Although it has frequently been argued that the proximity to a Mott insulating phase is responsible for the emergence of unconventional superconductivity, little progress has been made in obtaining a convincing microscopic theory. Due to the strong electron-electron (e-e) interaction involved in Mott ...


Combinatorial Fabrication & Studies Of Small Molecular Organic Light Emitting Devices (Oleds) And Structurally Integrated Oled-Based Chemical And Biological Sensors, Zhaoqun Zhou Jan 2007

Combinatorial Fabrication & Studies Of Small Molecular Organic Light Emitting Devices (Oleds) And Structurally Integrated Oled-Based Chemical And Biological Sensors, Zhaoqun Zhou

Retrospective Theses and Dissertations

No abstract provided.


An Investigation Of Student Thinking Regarding Calorimetry, Entropy, And The Second Law Of Thermodynamics, Warren Michael Christensen Jan 2007

An Investigation Of Student Thinking Regarding Calorimetry, Entropy, And The Second Law Of Thermodynamics, Warren Michael Christensen

Retrospective Theses and Dissertations

This thesis constitutes an investigation into student understanding of concepts in thermal physics in an introductory calculus-based university physics course. Nearly 90% of students enrolled in the course had previous exposure to thermodynamics concepts in chemistry and/or high-school physics courses. The two major thrusts of this work are (1) an exploration of student approaches to solving calorimetry problems involving two substances with differing specific heats, and (2) a careful probing of student ideas regarding certain aspects of entropy and the second law of thermodynamics. We present extensive free-response, interview, and multiple-choice data regarding students' ideas, collected both before and ...


Nmr Studies Of The Vanadium Spin Dynamics And Spin Structure In Liv2o4, Cav2o4, And (Lixv1-X)3bo5 (X ≈ 0.33, 0.40), Xiaopeng Zong Jan 2007

Nmr Studies Of The Vanadium Spin Dynamics And Spin Structure In Liv2o4, Cav2o4, And (Lixv1-X)3bo5 (X ≈ 0.33, 0.40), Xiaopeng Zong

Retrospective Theses and Dissertations

No abstract provided.


The Study Of Electromagnetic Wave Propagation In Photonic Crystals Via Planewave Based Transfer (Scattering) Matrix Method With Active Gain Material Applications, Ming Li Jan 2007

The Study Of Electromagnetic Wave Propagation In Photonic Crystals Via Planewave Based Transfer (Scattering) Matrix Method With Active Gain Material Applications, Ming Li

Retrospective Theses and Dissertations

In this dissertation, a set of numerical simulation tools are developed under previous work to efficiently and accurately study one-dimensional (1D), two-dimensional (2D), 2D slab and three-dimensional (3D) photonic crystal structures and their defects effects by means of spectrum (transmission, reflection, absorption), band structure (dispersion relation), and electric and/or magnetic fields distribution (mode profiles). Further more, the lasing property and spontaneous emission behaviors are studied when active gain materials are presented in the photonic crystal structures.;First, the planewave based transfer (scattering) matrix method (TMM) is described in every detail along with a brief review of photonic crystal history ...


Phase Transitions In Sn-Modified Lead Zirconate Titanate Antiferroelectric Ceramics, Hui He Jan 2007

Phase Transitions In Sn-Modified Lead Zirconate Titanate Antiferroelectric Ceramics, Hui He

Retrospective Theses and Dissertations

Electric field-induced antiferroelectric-to-ferroelectric phase transformation forms the physics basis for the applications of the PbZrO3-based antiferroelectric ceramics. The primary objective was to gain a better understanding of the phase transitions in between ferroelectric and antiferroelectric states. A secondary goal was to verify certain feasible applications by taking advantage of the phase transitions. In-situ techniques were extensively used including in-situ TEM and in-situ Raman microscopy.;Electric field in situ TEM technique was used in the study of the electric field induced antiferroelectric to ferroelectric phase transformation in PbZrO3-PbTiO3-PbSnO3 (PZST) ceramics. Our TEM study indicates that the incommensurate modulation in the modified ...


Qcd Resummation For The Fully Differential Drell-Yan Cross Section, Ricardo A. Rodriguez-Pedraza Jan 2007

Qcd Resummation For The Fully Differential Drell-Yan Cross Section, Ricardo A. Rodriguez-Pedraza

Retrospective Theses and Dissertations

We study an extension of resummation to the fully differential cross section in the Drell-Yan process. This new method extends the Collins-Soper-Sterman formalism to the longitudinal WL and double delta helicity structure function WDeltaDelta, recovering the next-to-leading-order predictions. The new extension also modifies the transverse structure function WT obtained in previous extensions.;The angular coefficients, lambda and nu, used for parametrization of the angular distribution, were studied with the new structure functions. No violation of the Lam-Tung relation was found. A possible solution to explain the difference between theoretical and experimental results is proposed. This solution may also explain the ...


Coherent Multiple Scattering Effect In Dis, Jun Li Jan 2007

Coherent Multiple Scattering Effect In Dis, Jun Li

Retrospective Theses and Dissertations

In nuclear medium, the parton can lose its energy by gluon radiation and collisional energy loss. In order to understand heavy quark energy loss, the collisional energy loss could be an important source for the observed suppression of hadron production.;We calculate the multiple scattering effect on single hadron production in semi-inclusive lepton-nucleus deeply inelastic scattering. We show that the quantum interference of multiple scattering amplitudes leads to suppression in hadron productions. At the leading power in medium length, the suppression can be approximately expressed in terms of a shift in zh of the fragmentation function, and could be therefore ...


Electromagnetic Materials Characterization Of Ferromagnetic Composites At Microwave Frequencies, Eric Ryan Abram Jan 2007

Electromagnetic Materials Characterization Of Ferromagnetic Composites At Microwave Frequencies, Eric Ryan Abram

Retrospective Theses and Dissertations

No abstract provided.


Absorption And Emission Properties Of Photonic Crystals And Metamaterials, Lili Peng Jan 2007

Absorption And Emission Properties Of Photonic Crystals And Metamaterials, Lili Peng

Retrospective Theses and Dissertations

We study the emission and absorption properties of photonic crystals and metamaterials using Comsol Multiphysics and Ansoft HFSS as simulation tools.;We calculate the emission properties of metallic designs using drude model and the results illustrate that an appropriate termination of the surface of the metallic structure can significantly increase the absorption and therefore the thermal emissivity.;We investigate the spontaneous emission rate modifications that occur for emitters inside two-dimensional photonic crystals and find the isotropic and directional emissions with respect to different frequencies as we have expected.


Self Assembled Nano-Structures Of Pb On Si(111) Studied By Spa-Leed: Quantum Size Effect Driven Pb Islands And The "Devil's Staircase" , Michael Keith Yakes Jan 2006

Self Assembled Nano-Structures Of Pb On Si(111) Studied By Spa-Leed: Quantum Size Effect Driven Pb Islands And The "Devil's Staircase" , Michael Keith Yakes

Retrospective Theses and Dissertations

An important goal in present day surface science is to grow uniform sized self-assembled nanostructures. One system which has displayed a number of interesting surface structures is Pb grown on a Si(111) substrate. The first part of the thesis discusses the "Devil's Staircase" (DS) of linear phases studied with Scanning Tunneling Microscopy (STM) and Spot-Profile Analysis Low Energy Electron Diffraction (SPA-LEED). The DS is one of the outstanding predictions in theoretical physics and is expected to exist in systems with two competing interactions. It was found that at low temperatures (<120>K) over 15 different DS phases can be ...


Coupled Magnetic And Structural Transitions In High-Purity Dy And Gd[Subscript 5]Sb[Subscript X]Ge[Subscript 4-X] , Alexander S. Chernyshov Jan 2006

Coupled Magnetic And Structural Transitions In High-Purity Dy And Gd[Subscript 5]Sb[Subscript X]Ge[Subscript 4-X] , Alexander S. Chernyshov

Retrospective Theses and Dissertations

We undertook a detailed study of a single crystal of dysprosium metal, which is a classical example of a system where magnetic and crystallographic sublattices can be either coupled or decoupled from one another. Magnetocaloric effect, magnetization, ac magnetic susceptibility, and heat capacity of high purity single crystals of dysprosium have been investigated over broad temperature and magnetic field intervals with the magnetic field vector parallel to either the a- or c-axes of the crystal. Notable differences in the behavior of the physical properties when compared to Dy samples studied in the past have been observed between 110 K and ...


Search For Multi-Photon Signatures Of A Higgs Boson In Ppbar Collisions At Sqrt(S) = 1.96 Tev , Oleksiy Vladimirovich Atramentov Jan 2006

Search For Multi-Photon Signatures Of A Higgs Boson In Ppbar Collisions At Sqrt(S) = 1.96 Tev , Oleksiy Vladimirovich Atramentov

Retrospective Theses and Dissertations

We have performed a search for a fermiophobic Higgs boson in tri-photon events. The study has been performed on 0.83 fb-1 of data collected with the DZero detector at the Tevatron collider, the world's highest energy accelerator. The study was motivated by the recent phenomenological study that suggests that at presently attained energies and statistics new Higgs production mechanisms become experimentally accessible. All backgrounds were estimated from the data in a self consistent manner. We observed zero tri-photon events and expected 0.5 +/- 0.2 from the Standard Model processes. Therefore, we set 95% CL upper limit on ...


Designing Of Metallic Photonic Structures And Applications , Yong-Sung Kim Jan 2006

Designing Of Metallic Photonic Structures And Applications , Yong-Sung Kim

Retrospective Theses and Dissertations

In this thesis our main interest has been to investigate metallic photonic crystal and its applications. We explained how to solve a periodic photonic structure with transfer matrix method and when and how to use modal expansion method. Two different coating methods were introduced, modifying a photonic structure's intrinsic optical properties and rigorous calculation results are presented;Two applications of metallic photonic structures are introduced. For thermal emitter, we showed how to design and find optimal structure. For conversion efficiency increasing filter, we calculated its efficiency and the way to design it.


Quantum Monte Carlo Calculations Applied To Magnetic Molecules , Larry Paul Engelhardt Jan 2006

Quantum Monte Carlo Calculations Applied To Magnetic Molecules , Larry Paul Engelhardt

Retrospective Theses and Dissertations

In this dissertation, we have implemented a quantum Monte Carlo (QMC) algorithm, and have used it to perform calculations for a variety of finite Heisenberg spin systems. A detailed description of the QMC method has been provided, which is followed by applications of the method to various systems. These applications begin with a detailed analysis of the (calculated) equilibrium magnetization and magnetic susceptibility for a number of Heisenberg Hamiltonians. In particular, we have studied the dependence of these quantities on intrinsic spin s, and have quantified the approach to the classical (s → infinity) limit. These results are not specific to ...


Soft-Lithographical Fabrication Of Three-Dimensional Photonic Crystals In The Optical Regime , Jae-Hwang Lee Jan 2006

Soft-Lithographical Fabrication Of Three-Dimensional Photonic Crystals In The Optical Regime , Jae-Hwang Lee

Retrospective Theses and Dissertations

This dissertation describes several projects to realize low-cost and high-quality three-dimensional (3D) microfabrication using non-photolithographic techniques for layer-by-layer photonic crystals. Low-cost, efficient 3D microfabrication is a demanding technique not only for 3D photonic crystals but also for all other scientific areas, since it may create new functionalities beyond the limit of planar structures. We have developed an advanced microtransfer molding technique, called two-polymer microtransfer molding (2P-[mu]TM) that shows an extremely high yield in layer-by-layer microfabrication sufficient to produce highly layered microstructures. The use of two different photo-curable prepolymers, a filler and an adhesive, allows for fabrication of layered ...


Investigations Of The Rni2ge2 Intermetallic Compounds By X-Ray Resonant Magnetic Scattering , Jong-Woo Kim Jan 2005

Investigations Of The Rni2ge2 Intermetallic Compounds By X-Ray Resonant Magnetic Scattering , Jong-Woo Kim

Retrospective Theses and Dissertations

The x-ray magnetic scattering (XRMS) intensities of the Gd, Tb, Dy, Ho, Er, and Tm L2,3 edges were investigated using two isostructural samples [Gd1/4Tb1/4Dy1/4Ho 1/4]Ni2Ge2 and [Gd1/3Er1/3Tm 1/3]Ni2Ge2 in order to elucidate systematics in the underlying resonance process. Taken together with theoretical linearized augmented planewave (LAPW) calculations employing LDA + U, we found that the XRMS intensity at the heavy rare-earth L edges is strongly related to the 4f-5d exchange interaction and that the branching ratio arises from the effects of spin orbit coupling in the 5d band. For Gd, the ...


Field-Induced Magnetic Phase Transitions And Correlated Electronic States In The Hexagonal Ragge And Rptin Series , Emilia Morosan Jan 2005

Field-Induced Magnetic Phase Transitions And Correlated Electronic States In The Hexagonal Ragge And Rptin Series , Emilia Morosan

Retrospective Theses and Dissertations

Rare earth intermetallic compounds provide rich grounds for investigating the properties of both local moment and strongly correlated, hybridized moment systems. These areas have been intensively explored mostly on cubic and tetragonal intermetallic compounds, and very little work existed on materials with lower symmetry. Moreover, a large number of Ce-based heavy fermion compounds have been studied, whereas the analogous Yb-based ones are much rarer. We thus wanted to study local moment metamagnetism and Yb-based heavy fermion physics in hexagonal systems.;The RAgGe and RPtIn series belonging to the Fe2P family of hexagonal compounds allowed us to perform such studies on ...


Spin Models For The Single Molecular Magnet Mn12-Ac , Mohamad A. Al-Saqer Jan 2005

Spin Models For The Single Molecular Magnet Mn12-Ac , Mohamad A. Al-Saqer

Retrospective Theses and Dissertations

The single molecular magnet (SMM) Mn12-AC attracted the attention of scientists since the discovery of its magnetic hystereses which are accompanied by sudden jumps in magnetic moments at low temperature. Unlike conventional bulk magnets, hysteresis in SMMs is of molecular origin. This qualifies them as candidates for next generation of high density storage media where a molecule which is at most few nanometers in size can be used to store a bit of information. However, the jumps in these hystereses, due to spin tunneling, can lead to undesired loss of information.;Mn12-AC molecule contains twelve magnetic ions antiferromagnetically coupled by ...


Tuning The Superconducting Properties Of Magnesium Diboride , Rudeger Heinrich Theoderich Wilke Jan 2005

Tuning The Superconducting Properties Of Magnesium Diboride , Rudeger Heinrich Theoderich Wilke

Retrospective Theses and Dissertations

The changes in normal state and superconducting properties of MgB 2 as a result of various perturbations have been investigated. Carbon doping was achieved using a two step reaction process wherein boron filaments were doped with carbon via a chemical vapor deposition technique. The subsequent filaments were then exposed to magnesium vapor to form the superconducting phase. Studies on the effects of defects introduced by neutron irradiation were performed on both pure and carbon doped MgB2 wires that were exposed to thermal neutron fluences in the range 1018-10 19 n/cm2;Different techniques for synthesizing carbon doped MgB2 powders were ...


Modeling Of Deposition And Reaction Processes On Si(100) , Marvin Argulla Albao Jan 2005

Modeling Of Deposition And Reaction Processes On Si(100) , Marvin Argulla Albao

Retrospective Theses and Dissertations

In this dissertation, we analyzed selected deposition and reaction processes on Si(100) using Kinetic Monte Carlo (KMC) simulation of suitable atomistic lattice-gas models. For the first project on the room-temperature deposition of Ga on Si(100), analysis of the island size distribution reveals that it is monotonically decreasing rather than monomodal, a clear departure from classical nucleation theory. KMC simulations of a realistic model recover this behavior, and simulations of refined models show that aggregation is responsible for the unexpected shape of the island size distribution. From these simulations, we were also able to extract reasonable values for the ...


Theoretical Studies Of Pb On Si(111) And Si(100), Global Search For H-Passivated Si Nanowires, And Construction Of Highly Localized Quasiatomic Minimal Basis Orbitals For Mo , Tzu-Liang Chan Jan 2005

Theoretical Studies Of Pb On Si(111) And Si(100), Global Search For H-Passivated Si Nanowires, And Construction Of Highly Localized Quasiatomic Minimal Basis Orbitals For Mo , Tzu-Liang Chan

Retrospective Theses and Dissertations

By first-principles calculations, we have performed extensive studies for the structures of Pb on Si(111) at low coverage. Relative stabilities between these low coverage phases were compared and comparison with scanning tunneling microscopy (STM) experiments were made. By tight-binding molecular dynamics simulations, we discovered that there are significant atomic rearrangements at the Pb/Si interface of the Pb islands on Si(111), which can lead to a change in the electronic structures of ultra-thin Pb films predicted by quantum size effect. In particular, the electronic behavior of nano-scale Moire pattern observed in STM for ultra-thin Pb films on Si ...


Systematic Study Of High-Pt Di-Jet Correlations In Nuclear Collisions With The Phenix Experiment At Rhic , Nathan Conrad Grau Jan 2005

Systematic Study Of High-Pt Di-Jet Correlations In Nuclear Collisions With The Phenix Experiment At Rhic , Nathan Conrad Grau

Retrospective Theses and Dissertations

One major goal of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory on Long Island, New York, is to create and study the quark-gluon plasma (QGP). This state of matter results from the phase transition of Quantum Chromodynamics (QCD) at extremely high temperature (1012 K) and densities (100 times normal nuclear matter). Au ions are collided in an attempt to increase the temperature necessary to cross the phase boundary. To study the properties of this new matter, high energy jets are used as a probe. Jets are a collimated spray of hadrons resulting from the fragmentation of high-energy ...


Optically Detected Magnetic Resonance (Odmr) Measurements On Conjugated Polymers And Studies Of Poly-(N-Vinyl Carbazole) (Pvk) Based Leds, Moon-Ky Lee Jan 2005

Optically Detected Magnetic Resonance (Odmr) Measurements On Conjugated Polymers And Studies Of Poly-(N-Vinyl Carbazole) (Pvk) Based Leds, Moon-Ky Lee

Retrospective Theses and Dissertations

The Origin of the PLDMR enhancing signal and various aspects of the device physics of small molecular doped PLEDs were described and discussed. The difference between the delay model and the quenching model was explained. The microwave- and laser-modulation-frequency dependence of the PLDMR and DM-PLDMR, respectively, in MEH-PPV, invalidated the delay models, questioning reports of SE yields exceeding 25% in fluorescent OLEDs. Rather, the results were consistent with the quenching model where SEs are annihilated by TEs and polarons. For the device, the proper procedure for the treatment of the PEDOT/PSS layer with EG was suggested and a 10 ...