Master of Science, The Ohio State University, 1924, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy, Case Western Reserve University, 2024, Physics

In this work we study magnetization dynamics and pinning in thin film permalloy (Py) microdisks. Thin, micron-scale Py disks magnetize into a vortex state in which the magnetization curls around a central core. To study pinning, we raster scan a vortex core within a thin Py disk using in-plane magnetic fields, and monitor the displacement using the magneto-optical Kerr effect. The resulting measurements yield a map of how defects and inhomogeneities in the material serve to trap high energy-density magnetization configurations such as vortex cores or domain walls. Next, we study magnetic vortex magnetization dynamics as a function of applied in-plane static field and AC driving frequency by optically monitoring a nearby nitrogen vacancy (NV) defect center spin. Despite driving the AC field at frequencies far detuned from an NV spin transition, we observe off-resonant NV spin relaxation in ODMR spectra, due to two different dynamic vortex modes. First, the low frequency gyrotropic mode of the vortex core couples to the NV spin non-linearly due to higher frequencies in the spectrum of the magnetic fringe field arising from the soliton-like nature of the gyrotropic mode. And second, when an in-plane magnetic bias field is applied to the Py disk we observe off-resonant NV spin relaxation due to coupling of a confined magnon mode to an NV spin transition through a parallel pumping effect. Each of these findings is supported through micromagnetic simulations. The results of this research help make progress towards magnetic and spintronic technology that rely on nanoscale control of magnetization dynamics in magnetic spin textures.

Committee: Jesse Berezovsky (Advisor); Anna Samia (Committee Member); Shulei Zhang (Committee Member); Xuan Gao (Committee Member) Subjects: Condensed Matter Physics

Doctor of Philosophy, The Ohio State University, 2022, Physics

Quantum information science and engineering requires novel low-loss magnetic materials for magnon-based quantum-coherent operations. The search for low-loss magnetic materials, traditionally driven by applications in microwave electronics near room-temperature, has gained additional constraints from the need to operate at cryogenic temperatures for many applications in quantum information science and technology. Whereas yttrium iron garnet (YIG) has been the material of choice for decades, the emergence of molecule-based materials with robust magnetism and ultra-low damping has opened new avenues for exploration. Specifically, thin-films of vanadium tetracyanoethylene (V[TCNE]x) can be patterned into the multiple, connected structures needed for hybrid quantum elements and have shown room-temperature Gilbert damping (α = 4 x 10^(-5)) that rivals the intrinsic (bulk) damping otherwise seen only in highly-polished YIG spheres (far more challenging to integrate into arrays). However, while these properties clearly establish the potential of V[TCNE]x for new applications in traditional microwave electronics, very little is known about its low-temperature magnetization dynamics and therefore its potential for applications in quantum information science and technology. Presented in this thesis a comprehensive and systematic study of the low-temperature magnetization dynamics for V[TCNE]x thin films, with implications for their application in quantum systems. These studies reveal a temperature-driven, strain-dependent magnetic anisotropy that compensates the thin-film shape anisotropy, and the recovery of a magnetic resonance linewidth at 5 K that is comparable to room-temperature values (roughly 2 G at 9.4 GHz). We can account for these variations of the V[TCNE]x linewidth within the context of scattering from very dilute paramagnetic impurities, and anticipate additional linewidth narrowing as the temperature is further reduced. Additionally, ongoing work investigati (open full item for complete abstract)

Committee: Ezekiel Johnston-Halperin Professor (Advisor); Marc Bockrath Professor (Committee Member); Ciriyam Jayaprakash Professor (Committee Member); Christopher Hirata Professor (Committee Member) Subjects: Physics

Doctor of Philosophy in Engineering, Cleveland State University, 2022, Washkewicz College of Engineering

Iron-based magnetic alloys possess very good magnetic and mechanical properties. Among these alloys Fe-Si-B-based alloys show outstanding saturation magnetization and coercivity which makes them great candidates for many industrial applications. Addition of certain elements to the Fe-Si-B base is proven to improve the homogeneity and fineness of microstructure as well as enhance the magnetic behavior of these alloys. In this research work, we have studied the effect of adding copper and niobium to the Fe-Si-B base alloy. Previous studies have shown that magnetic alloys show better magnetic properties when their microstructure consists of nanocrystals embedded in an amorphous matrix. In order to reach amorphization, magnetic alloys are traditionally melted and then cooled down very fast to prevent crystallization and grain growth in their microstructure. However, there are several disadvantages associated with this method of fabrication, such as the limitation in thickness of the products. To solve this issue, we proposed a new method of fabrication for magnetic alloys where amorphization occurs through mechanical alloying, and the amorphous powder alloy that is produced by this process is then consolidated using a technique called spark plasma sintering finding appropriate mechanical alloying processing parameters to get an amorphous structure. Many different processing parameters were investigated, and the mechanical properties, microstructure, and magnetic properties of all samples were examined. The effect of spark plasma sintering processing parameters on samples sintered from the amorphous powders was then studied. Finally, the amount of energy introduced to the powder from the milling balls during the mechanical alloying process was calculated. We were able to find a trend between the energy introduced to the powder during the milling process and the amorphous structure of the milled powders. From our data, we draw an energy map that shows the window (open full item for complete abstract)

Committee: Tushar Borkar (Advisor); Majid Rashidi (Committee Member); Somnath Chattopadhyay (Committee Member); Maryam Younessi Sinaki (Committee Member); Petru Fodor (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2021, Materials Engineering

Additive Manufacturing (AM) is a rapidly developing field that offers new possibilities for manufacturing with materials that are difficult to process with traditional manufacturing methods. This report will examine the application of selective laser melting in making magnetic cores out of Hiperco 50. The iron-cobalt family of alloys is known to offer the best magnetic properties of all soft magnetic materials but is extremely brittle. Additive manufacturing offers the opportunity to make high quality magnetic cores in unique geometries that traditional manufacturing is unable to replicate. To test the viability of this process three types of test specimens were built out of Hiperco 50 powder to examine key material properties. First 1 cm3 cube specimens were built to measure the density of the final parts, and they were also used to examine the porosity and microstructure. The second type of specimens were tensile bars, built in both vertical and horizontal orientations with respect to the build plate, to examine the mechanical properties of the final parts as well as the impact of build orientation. The final test specimens were magnetic toroids, comprised of cores to be wound with copper magnet wire and tested for magnetic permeability and remanence. Half of these specimens were also subjected to a final magnetic heat treatment cycle, which was the same as the cycle used for traditionally manufactured Hiperco 50 components, in order to determine the change in performance. These AM fabricated specimens showed a 1-5% decrease in density from traditionally manufactured Hiperco 50 parts, with the build parameters being the largest deciding factor of final density and porosity. These parts also had a poorly defined grain structure until subjected to a magnetic heat treatment. After undergoing the recommended heat-treatment, niobium precipitates were observed along the newly defined grain boundaries. However, there was a severe drop in mechanical performance, (open full item for complete abstract)

Committee: Donald Klosterman (Committee Chair); Zafer Turgut (Committee Member); Li Cao (Committee Member) Subjects: Electromagnetics; Electromagnetism; Materials Science

Doctor of Philosophy, The Ohio State University, 2018, Physics

The origin of magnetism can be found in the purely quantum mechanical property of spin, an intrinsic form of angular momentum. Investigations into understanding and controlling the spin degree of freedom have driven condensed matter research for the better part of a century. Real-world applications of the spin-degree of freedom depend on a microscopic understanding of the underlying mechanisms that define the dynamic and static interactions of the magnetization with the material's environment. Investigating new tools and techniques to probe the dynamics and statics of a magnetic material is thus a vital part in the design of new spin-based applications, and in developing an understanding of magnetization dynamics on a fundamental time scale. This dissertation discusses three topics of research that focus on the development of techniques to study fundamental static and dynamic magnetic degrees of freedom. First, an unexpected sign flip in the Kerr response of a thin film manganite perovskite La2/3Sr1/3MnO3 is investigated through the magneto-optical Kerr effect. By applying an external tensile strain to another La2/3Sr1/3MnO3 thin film, the origin of the sign flip is linked to a strain modification of the electro-optic response. This section examines the strong link between the magnetic structure, electronic structure, and lattice in the La2/3Sr1/3MnO3 system. The second topic of research examines the role of magnetic interparticle interactions of superparamagnetic iron oxide nanoparticles (SPION) in the dynamics of DNA-origami hinges. Numerically calculated magnetic dipole interactions are added to the measured free energy distribution of DNA-origami hinges to determine the potential for hinge dynamics driven by the magnetic interaction. The results predict a potential for hinge latching due to an attractive magnetic dipole-dipole interaction between the attached SPIONs. The final research topic of this dissertation details progress towards a material generi (open full item for complete abstract)

Committee: Ezekiel Johnston-Halperin (Advisor); Jay Gupta (Committee Member); Mohit Randeria (Committee Member); Lou DiMauro (Committee Member) Subjects: Condensed Matter Physics; Optics; Physics

Doctor of Philosophy, Case Western Reserve University, 2018, Biomedical Engineering

Adenosine Triphosphate (ATP) serves as the universal currency of energy in cellular systems. Hydrolysis of ATP thermodynamically drives the majority of cellular processes fundamental to life. The existence of a fast and robust method to observe ATP and its reactions in vivo would have profound applications both in the clinical diagnosis of metabolic abnormalities, and in the evaluation of therapies. Phosphorus-31 (31P) spectroscopy is the only modality capable of non-invasive non-destructive in vivo detection of ATP and its reactions. However, 31P spectroscopy methods are often challenging to perform due to two reasons. First, the instruments have an inherently low sensitivity to the biological signal. Second, conventional 31P spectroscopy methods have emphasized mathematical tractability rather than optimal signal detection. Consequently, 31P spectroscopy methods require long experiment times, and this has precluded their use in many applications. In this thesis, a new acquisition paradigm, the Magnetic Resonance Fingerprinting (MRF) framework, was applied to 31P spectroscopy method design in order to shorten experiment times. By prioritizing signal detection over mathematical tractability, the methods designed in this thesis sought to overcome the limitations imposed by instrument sensitivity and shorten experiment times. Success in this goal may enable new applications. Three main projects are described in this thesis. First, the MRF framework based 31P-MRF method was used to obtain efficient and simultaneous quantification of T1 relaxation time and concentration of multiple metabolites. This method was tested in simulation and validated ex-vivo. Second, sensitivity to magnetization transfer (MT) effects between phosphocreatine (PCr) and ATP was added to the 31P-MRF method to measure the in vivo chemical exchange rate of creatine kinase enzyme. This new method, the CK-MRF method, was assessed in vivo rat hindlimb. Finally, the 31P-MRF method was (open full item for complete abstract)

Committee: Dominique Durand PhD (Committee Chair); Chris Flask PhD (Committee Member); Mark Griswold PhD (Committee Member); Charles Hoppel MD (Committee Member); Nicole Seiberlich PhD (Committee Member); Xin Yu ScD (Advisor) Subjects: Biomedical Engineering; Medical Imaging

Doctor of Philosophy, The Ohio State University, 2017, Physics

Central to the advancement of many biomedical and nanotechnology capabilities is the capacity to precisely control the motion of micro and nanostructures. These applications range from single molecule experiments to cell isolation and separation, to drug delivery and nanomachine manipulation. This dissertation focuses on actuation of biological micro- and nano-entities through the use of weak external magnetic fields, superparamagnetic beads, and ferromagnetic thin films. The magnetic platform presents an excellent method for actuation of biological systems due to its ability to directly control the motion of an array of micro and nanostructures in real-time with calibrated picoNewton forces. The energy landscape of two ferromagnetic thin film patterns (disks and zigzag wires) is experimentally explored and compared to corresponding theoretical models to quantify the applied forces and trajectories of superparamagnetic beads due to the magnetic traps. A magnetic method to directly actuate DNA nanomachines in real-time with nanometer resolution and sub-second response times using micromagnetic control was implemented through the use of stiff DNA micro-levers which bridged the large length scale mismatch between the micro-actuator and the nanomachine. Compared to current alternative methods which are limited in the actuation speeds and the number of reconfiguration states of DNA constructs, this magnetic approach enables fast actuation (~ milliseconds) and reconfigurable conformations achieved through a continuous range of finely tuned steps. The system was initially tested through actuation of the stiff arm tethered to the surface, and two prototype DNA nanomachines (rotor and hinge) were successfully actuated using the stiff mechanical lever. These results open new possibilities in the development of functional robotic systems at the molecular scale. In exploiting the use of DNA stiff levers, a new technique was also developed to investigate the emergence of the mag (open full item for complete abstract)

Committee: Ratnasingham Sooryakumar (Advisor) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2016, Physics

In this dissertation, I explore the interactions that occur between transported spins and magnetization dynamics using spatially resolved imaging and magnetic resonance. The integration of spin transport and dynamics will be a crucial aspect of realizing spintronic devices, which seek to improve upon current charge based electronics. Rather than focusing on the charge degree of freedom as in traditional electronics, spintronics seeks to utilize the properties of the electron spin degree of freedom to revolutionize the fundamental operating principles of data processing and storage devices. Spintronics promises greater functionality and energy efficiency in devices based on electron spin. However, improved understanding and control of the spin degree of freedom is required for spintronics to reach its full potential. The work in this dissertation represents efforts towards addressing these requirements. I discuss my work relating to the development of a custom scanned probe microscope allowing simultaneous spatially resolved imaging while imposing transport in electrically active spintronic devices. Using this microscope, I correlate the switching of magnetic electrodes in a graphene spin valve to the resistance states by directly imaging the electrode magnetization configuration while simultaneously measuring the non-local magnetoresistance. I investigate interactions between a ferromagnet driven into resonance and proximal nitrogen vacancy centers in diamond. Spinwaves generated during the decay of the uniform mode driven to ferromagnetic resonance relax the diamond nitrogen vacancy center spins resulting in a change in the fluorescence intensity. This technique allows the study of transport of angular momentum between two separated spin systems, as well as the possibility for the nanoscale imaging of magnetization dynamics. I demonstrate Heusler alloy ferromagnetic materials as high spin polarization spin injectors for device applications by studying t (open full item for complete abstract)

Committee: P. Chris Hammel Professor (Advisor); Jay Gupta Professor (Committee Member); Richard Hughes Professor (Committee Member); Ciriyam Jayaprakash Professor (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2016, Materials Science and Engineering

Magnesium diboride (MgB2) is a material with a superconducting transition temperature of 39 K. Discovered in 2001, the relatively large coherence length (and associated lack of weak links) together with its simple binary composition (making phase pure formation relatively easy) have made it a material of substantial interest. However, its inadequate in-field performance limits the high field applications. Chemical doping is the key to increasing the Bc2 of MgB2. Chemical doping aiming at Mg site or B site substitution is of interest and both routes are explored in this thesis. Structure-property correlations are developed for dopants that either do or do not, incorporate themselves into the MgB2 matrix. First, the effects of C doping in the state of art MgB2 wires were investigated. In order to do so, a series of state of the art C doped MgB2 wires, in both mono-filamentary and multi-filamentary forms, were fabricated by a local company. Their transport and magnetic performance in various magnetic fields, and mechanical induced degradation, were examined. The C doping influence on the critical current density and the n-values were discussed. Secondly, the effects of rare earth oxide (REO) doping in MgB2 were studied. Two sets of samples including both bulk samples and wires were fabricated. Microstructural evidence obtained by SEM and TEM proved that nano-size inclusions formed after REO doping acted as grain growth inhibitors, as evidenced a reduction of MgB2 grain size in REO doped bulk samples. The results of XRD and magnetic measurements on the bulk samples demonstrated that Dy2O3 and Nd2O3 do not alloy with MgB2, no changes being observed in the lattice parameters, Tc and Bc2 of doped MgB2. Enhancements in flux pinning and Jc were obtained in both bulk samples and wires by REO doping, consistent with the microstructural evidence of notable grain refinements and the presence of nano-size inclusions as new pinning sites in MgB2 grains. Lastly, a set of metal d (open full item for complete abstract)

Committee: Michael Sumption (Advisor); Patricia Morris (Committee Member); Roberto Myers (Committee Member) Subjects: Electromagnetics; Electromagnetism; Engineering; Materials Science; Metallurgy; Physics

Doctor of Philosophy, The Ohio State University, 2015, Biomedical Engineering

Osteoarthritis (OA) is a huge disease burden in United States, affecting almost 30 million Americans, and is the leading cause of disability in the elderly. Knee and hip replacements cost over $40 billion annually, but may be avoided through early detection of at risk cartilage and early intervention. There are abundant MRI tools for non-invasive, quantitative imaging that reveal characteristics of cartilage structure and physiology such as collagen alignment, molecular content, and health of subchondral bone vasculature. However, no quantitative MRI technique has been added to clinical standard of care for cartilage imaging because of lack of specificity and technical difficulty. Chemical exchange saturation transfer (CEST) MRI is a promising technique to detect small metabolites such as glutamate, creatine and glucose, as well as large soluble molecules such as protein, proteoglycans, and glycogen. It has been demonstrated that CEST MRI can detect glycosaminoglycan (GAG), a proteoglycan crucial to the functioning of healthy articular cartilage, however only with high-field non-clinical scanners (> 3 Tesla). In osteoarthritis development, reduction in GAG content is a preliminary step before gross changes in cartilage thickness and joint space, and therefore clinical methods to detect GAG may have a tremendous impact on OA prevention. In this dissertation, we discuss multiple quantitative MRI techniques used to characterize articular cartilage, but then focus on CEST MRI. A miniature horse model of cartilage injury is used to evaluate several MRI techniques through serial imaging of the healing process over the course of one year. While promising, the techniques lack specificity and are technically challenging to perform, especially delayed gadolinium enchance MRI of cartilage (dGEMRIC), a technique used to detect GAG content. To meet the challenge of GAG detection at 3 Tesla, we hypothesized that a variant of CEST, using a novel variable saturation power (vCES (open full item for complete abstract)

Committee: Michael Knopp MD, PhD (Advisor); Seth Smith PhD (Committee Member); Orlando Simonetti PhD (Committee Member); Jun Liu PhD (Committee Member) Subjects: Biomedical Engineering; Medical Imaging

PhD, University of Cincinnati, 2006, Arts and Sciences : Physics

We study the magnetic and optical properties of diluted magnetic semiconductor CdMnTe quantum dots (QDs) using various photoluminescence (PL) techniques. We use spatially resolved photoluminescence imaging to study single magnetic QDs. A solid immersion lens is combined with the confocal microscopy to achieve a high spatial resolution (~ 200nm) for PL imaging. We observe formation of exciton magnetic polarons (EMPs) in magnetic QDs for non-resonant excitation at B = 0T and T = 7K. However, the spin alignments of individual EMPs are distributed randomly resulting in zero global magnetization. Moreover, the spin alignment in the magnetic QD persists as long as the excitation is continued. This persistent magnetization is because of a long spin relaxation time of Mn ions. We estimate the relaxation time to be of the order of 1ms in CdMnTe QDs. For resonant excitations, CdMnTe QDs exhibit a strong PL polarization (40%) at B = 0T and T = 7K. The measurements show predominant &sigma +(&sigma -) –polarized PL emission for &sigma +(&sigma -) –polarized excitations that create spin polarized excitons. This suggests that one can control the spin alignment of magnetic impurities in magnetic CdMnTe QDs optically by using selectively polarized excitations. The magnetization created by such spin polarized excitons persists up to 170K. We attribute this robust persistent magnetization to strong three dimensional confinements of excitons in smaller CdMnTe QDs. In a low Manganese density QD sample, we observe a mixture of PL emission lines of magnetic and non-magnetic QDs. The results demonstrate that the Zeeman splitting of such non-magnetic QDs depends on the polarization of excitation. We believe that this excitation dependent Zeeman splitting is due to coupling between magnetic and non-magnetic QDs through the exchange interaction.

Committee: Dr. Leigh Smith (Advisor) Subjects: Physics, Condensed Matter

Doctor of Philosophy, The Ohio State University, 2006, Physics

In this thesis, the physics underlying the magnetic behavior of metallic microstructures, including their responses to magnetic fields and electric currents is explored. The dynamic and static components of the magnetization are respectively probed through Brillouin light scattering and Kerr imaging method. The design, growth and fabrication of various structures are presented, while the experimental findings are analyzed by theoretical modeling and calculations. The highlights include (a) Brillouin light scattering studies of spin precession under tunable magnetic field imbalance, (b) Kerr imaging of layer-by-layer magnetic reversal in cobalt-platinum multilayer, (c) Observation of spin-polarized current induced domain wall motion in magnetic microwires. All of these results demonstrate that light scattering as an excellent tool for probing novel functionality of metallic magnetic microstructures. Future prospects along the direction of research involved in this thesis are also presented.

Committee: Ratnasingham Sooryakumar (Advisor) Subjects:

Master of Science, The Ohio State University, 1977, Geological Sciences

Committee: Hallan Noltimier (Advisor) Subjects:

PHD, Kent State University, 2009, College of Arts and Sciences / Department of Physics

This dissertation is a study of praseodymium (Pr) doped YBCO single crystals in the underdoped regime starting from very close to the critical doping. The normalized critical current density varies non monotonically with the decrease in carrier concentration, which is found to be maximum for the 34% of Pr doping. Magnetic relaxation measurements on a series of Y(1-x)Pr(x)Ba(2)Cu(3)O(7-delta)(x = 0.13, 0.34, 0.47) single crystals were performed over a large field and temperature range in order to investigate the characteristics of the vortex matter across the second magnetization peak (SMP). The magnitude of the SMP varies non-monotonically with Pr concentration; i.e., the irreversible magnetization normalized by its value at the onset field Hon displays a maximum for the x = 0.34 single crystal. The two characteristic fields, Hon and Hsp, follow different temperature T dependences: Hon proportional to T^(nu on) and Hsp proportional to [1-(T/Tc)^2]^(nu sp) . The extracted values of the apparent activation energy U^(star) and the creep exponent mu display a maximum at a field Hon < H^(star) < Hsp. Their field dependencies point toward the coexistence of both elastic and plastic creep for H > Hon. The degree of participation of each creep mechanism is determined by the charge carrier density, which controls both the elastic properties of the vortex matter and the pinning potential. The magnetic response of the strongly underdoped Y(0.47)Pr(0.53)Ba(2)Cu(3)O(7-delta) was investigated. We found the presence of superconducting order and magnetic order deep into the paramagnetic state, up to 200 K, which manifest as diamagnetic like response and hysteresis, respectively. We propose that the main source of irreversibility in this T range is the softening and melting of the glassy state into a viscous liquid of entities that behave like superparamagnetic particles with antiferromagnetic cores.

Committee: Carmen Almasan Dr. (Committee Chair); David Allender Dr. (Committee Member); Almut Schroeder Dr. (Committee Member); Songping Huang Dr. (Committee Member); Anatoly Khitrin Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy in Clinical-Bioanalytical Chemistry, Cleveland State University, 2008, College of Science

In the last few decades, the development and use of nanotechnology has become of increasing importance. Magnetic nanoparticles, because of their unique properties, have been employed in many different areas of application. They are generally made of a core of magnetic material coated with some other material to stabilize them and to help disperse them in suspension. The unique feature of magnetic nanoparticles is their response to a magnetic field. They are generally superparamagnetic, in which case they become magnetized only in a magnetic field and lose their magnetization when the field is removed. It is this feature that makes them so useful for drug targeting, hyperthermia and bioseparation. For many of these applications, the synthesis of uniformly sized magnetic nanoparticles is of key importance because their magnetic properties depend strongly on their dimensions. Because of the difficulty of synthesizing monodisperse particulate materials, a technique capable of characterizing the magnetic properties of polydisperse samples is of great importance. Quadrupole magnetic field-flow fractionation (MgFFF) is a technique capable of fractionating magnetic particles based on their content of magnetite or other magnetic material. In MgFFF, the interplay of hydrodynamic and magnetic forces separates the particles as they are carried along a separation channel. Since the magnetic field and the gradient in magnetic field acting on the particles during their migration are known, it is possible to calculate the quantity of magnetic material in the particles according to their time of emergence at the channel outlet. Knowing the magnetic properties of the core material, MgFFF can be used to determine both the size distribution and the mean size of the magnetic cores of polydisperse samples. When magnetic material is distributed throughout the volume of the particles, the derived data corresponds to a distribution in equivalent spherical diameters of magnetic material in (open full item for complete abstract)

Committee: Dr. P.Stephen Williams (Committee Chair); Dr. Aaron Fleischman (Committee Member); Dr. John Turner (Advisor); Dr. Yan Xu (Committee Member); Dr. Maciej Zborowski (Committee Member) Subjects: Chemistry

Doctor of Philosophy, Case Western Reserve University, 2009, Biomedical Engineering

The advent of the genomic age is revolutionizing the experimental cardiovascular research irreversibly. Dissecting molecular switches that control the changes of cardiac physiology with transgenic mouse models has proven to offer important insights into the control of cardiac function. The integration of novel MR tissue tracking techqniques with these genetically manipulated mice may allow comprehensive characterization of contractile dysfunction non-invasively at the earliest diseased stages, thus facilitate our understanding of the pathogenesis of human cardiac diseases. In the current thesis, we aimed at developing fast and accurate MR tissue tracking techniques and applying them for the assessment of ventricular function in transgenic mouse models of cardiac diseases. First, spatial modulation of magnetization (SPAMM) tagging was implemented in the mouse heart; and a 3D SPAMM tagging analysis method was developed based on harmonic phase (HARP) and homogeneous strain analysis. Using this 3D tagging analysis method, longitudinal strain and circumferential-longitudinal shear was quantified in addition to the 2D ventricular wall strain. Second, to improve the limited tagging resolution of existing SPAMM techniques, a HARP-based high-resolution tagging analysis method was proposed in mouse. The utility of such method was demostrated by quantifying the transmural heterogeneity of the left ventricle. Third, a 2D multi-phase displacement encoding with stimulated echoes (DENSE) imaging and analysis method was developed which allows direct and automatic Lagrangian strain quantification with high spatial and temporal resolution. Additionally, the utility of this multi-phase DENSE method was demonstrated in mouse both at baseline and with high workload. Functional enhancement was identified upon dobutamine stimulation both at the global and the regional levels. Fourth, for the evaluation of longitudinal wall motion within the short axis (SA) plane, 2D multi-phase DENSE ima (open full item for complete abstract)

Committee: XIN YU (Committee Chair); DAVID WILSON (Committee Member); MARK GRISWOLD (Committee Member); CHRIS FLASK (Committee Member); BRIAN HOIT (Committee Member) Subjects: Biomedical Research; Engineering

Doctor of Philosophy, The Ohio State University, 2013, Physics

Ultrafast laser optics is becoming a powerful tool in materials research. The interaction between femtosecond laser pulses with electrons and the subsequent relaxation process is an active research topic in recent years. In the time scale of femtoseconds to nanoseconds, several interesting physics take place. The laser pulses are short that they can be used to probe these very short time scale interactions, for example, the spin precession in GHz range. The laser can be easily focused using an objective lens, thus providing a micron-scale spatial resolution. In this dissertation, I will start by discussing the dynamics of electron, lattice and spin after a sample absorbs focused femtosecond laser pulses and the information can be used for measurement of elastic constants and saturation magnetization. The micron-scale spatial resolution and picosecond temporal resolution of our ultrafast laser pump-probe system allows us to measure elastic, magnetic and thermal properties of materials locally. By performing such measurements on diffusion couple/multiple samples with composition gradients, we can more effectively establish composition dependent property databases than conventional ways of making single uniform alloys and measuring them one at a time. Absorption of low power focused femtosecond laser pulses by sample surface leads to localized thermal expansion, which launches Surface Acoustic Waves (SAW) that can be used to measure elastic modulus. Such measurements must be supplemented by theoretical calculations since there are complications related to pseudo-SAWs and skimming longitudinal waves in addition to regular SAWs. It is a bit surprising that a mathematical solution to the surface response induced by a thermally expansion source on an arbitrary bulk surface (half space) of an isotropic crystal/solid is not available in the literature. By convolving the strain Green's function with the thermal stress field created by an ultrafast Gaussian laser illuminat (open full item for complete abstract)

Committee: Peter Hammel (Committee Chair); Zhao Ji-Cheng (Advisor); John Wilkins (Committee Member); Yuri Kovchegov (Committee Member) Subjects: Physics