A Modernized View of Coherence Pathways Applied to Magnetic Resonance Experiments in Unstable, Inhomogeneous Fields

Over recent decades, the value of conducting experiments at lower frequencies and in inhomogeneous and/or time-variable fields has grown. For example, an interest in the nanoscale heterogeneities of hydration dynamics demands increasingly sophisticated and automated measurements deploying Overhauser Dynamic Nuclear Polarization (ODNP) at low field. The development of these methods poses various challenges that drove us to develop a standardized alternative to the traditional schema for acquiring and analyzing coherence pathway information employed by the overwhelming majority of contemporary Nuclear Magnetic Resonance (NMR) research. Specifically, on well-tested, stable NMR systems running well-tested pulse sequences in highly optimized, homogeneous magnetic fields, traditional hardware and software quickly isolate a meaningful subset of data by averaging and discarding between 3/4 and 127/128 of the digitized data. In contrast, spurred by recent advances in the capabilities of open-source libraries, the domain colored coherence transfer (DCCT) schema implemented here builds on the long-extant concept of Fourier transformation along the pulse phase cycle domain to enable data visualization that more fully reflects the rich physics underlying these NMR experiments. In addition to discussing the outline and implementation of the general DCCT schema and associated plotting methods, this manuscript presents a collection of algorithms that provide robust phasing, avoidance of baseline distortion, and the ability to realize relatively weak signals amidst background noise through signal-averaged correlation alignment. The methods for visualizing the raw data, together with the processing routines whose development they guide should apply directly to or extend easily to other techniques facing similar challenges.Comment: 32 pages, 18 figure

Diamonds On The Inside: Imaging Nanodiamonds With Hyperpolarized MRI

Nontoxic nanodiamonds (NDs) have proven useful as a vector for therapeutic drug delivery to cancers and as optical bioprobes of subcellular processes. Despite their potential clinical relevance, an effective means of noninvasively imaging NDs in vivo is still lacking. Recent developments in hyperpolarized MRI leverage an over 10 000 times increase in the nuclear polarization of biomolecules, enabling new molecular imaging applications. This work explores hyperpolarization via intrinsic paramagnetic defects in nanodiamond. We present the results of MRI experiments that enable direct imaging of nanodiamond via hyperpolarized 13C MRI and indirect imaging of nanodiamonds via Overhauser-enhanced MRI. The construction of custom hardware for these experiments is detailed and the path to future in vivo experiments outlined. As nanodiamond has been established as a biocompatible platform for drug delivery, our results will motivate further research into hyperpolarized MRI for tracking nanoparticles in vivo

Resonant nonlinear magneto-optical effects in atoms

In this article, we review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. We begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances, and contrast these effects with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultra-narrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity- and time-reversal-invariance violation in atoms.Comment: 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002, Figure added, typos corrected, text edited for clarit

58th Annual Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 58th annual meeting of the Rocky Mountain Conference on Magnetic Resonance, co-endorsed by the Colorado Section of the American Chemical Society and the Society for Applied Spectroscopy. Held in Breckenridge, Colorado, July 17-21, 2016

A short & sweet story of CHO

The solid state nuclear magnetic resonance (SSNMR) study of nearly intact plant cell walls along with the computational study of glucose and malonic acid are presented. Previously unassigned 13C chemical shifts are presented for the various carbohydrates in the primary plant cell wall of Arabidopsis thaliana. A continuation of the SSNMR study involved the computational determination of glucose chemical shifts, a model compound for the study of larger carbohydrates. Additional computational studies determined the energy relationship between hydrated tautomers of malonic acid, a commonly occurring atmospheric dicarboxylic acid. In the malonic acid study, agreement between experiment and calculated frequencies verified the presence of the enol form of malonic acid. The development and analysis of a chemical education tool, a quantum chemistry concept inventory, whose aim is to understand misconceptions is also included in this dissertation

MEMS SENSOR PLATFORMS FOR IN SITU CHARACTERIZATION OF LI-ION BATTERY ELECTRODES

Lithium-ion batteries provide high energy density while being compact and light-weight and are the most pervasive energy storage technology powering portable electronic devices such as smartphones, laptops, and tablet PCs. Considerable efforts have been made to develop new electrode materials with ever higher capacity, while being able to maintain long cycle life. A key challenge in those efforts has been characterizing and understanding these materials during battery operation. While it is generally accepted that the repeated strain/stress cycles play a role in long-term battery degradation, the detailed mechanisms creating these mechanical effects and the damage they create still remain unclear. Therefore, development of techniques which are capable of capturing in real time the microstructural changes and the associated stress during operation are crucial for unravelling lithium-ion battery degradation mechanisms and further improving lithium-ion battery performance. This dissertation presents the development of two microelectromechanical systems sensor platforms for in situ characterization of stress and microstructural changes in thin film lithium-ion battery electrodes, which can be leveraged as a characterization platform for advancing battery performance. First, a Fabry-Perot microelectromechanical systems sensor based in situ characterization platform is developed which allows simultaneous measurement of microstructural changes using Raman spectroscopy in parallel with qualitative stress changes via optical interferometry. Evolutions in the microstructure creating a Raman shift from 145 cm−1 to 154 cm−1 and stress in the various crystal phases in the LixV2O5 system are observed, including both reversible and irreversible phase transitions. Also, a unique way of controlling electrochemically-driven stress and stress gradient in lithium-ion battery electrodes is demonstrated using the Fabry-Perot microelectromechanical systems sensor integrated with an optical measurement setup. By stacking alternately stressed layers, the average stress in the stacked electrode is greatly reduced by 75% compared to an unmodified electrode. After 2,000 discharge-charge cycles, the stacked electrodes retain only 83% of their maximum capacity while unmodified electrodes retain 91%, illuminating the importance of the stress gradient within the electrode. Second, a buckled membrane microelectromechanical systems sensor is developed to enable in situ characterization of quantitative stress and microstructure evolutions in a V2O5 lithium-ion battery cathode by integrating atomic force microscopy and Raman spectroscopy. Using dual-mode measurements in the voltage range of the voltage range of 2.8V – 3.5V, both the induced stress (~ 40 MPa) and Raman intensity changes due to lithium cycling are observed. Upon lithium insertion, tensile stress in the V2O5 increases gradually until the α- to ε-phase and ε- to δ-phase transitions occur. The Raman intensity change at 148 cm−1 shows that the level of disorder increases during lithium insertion and progressively recovers the V2O5 lattice during lithium extraction. Results are in good agreement with the expected mechanical behavior and disorder change in V2O5, highlighting the potential of microelectromechanical systems as enabling tools for advanced scientific investigations. The work presented here will be eventually utilized for optimization of thin film battery electrode performance by achieving fundamental understanding of how stress and microstructural changes are correlated, which will also provide valuable insight into a battery performance degradation mechanism

In situ studies of surface reactions affecting Li-ion battery failure

Li-ion batteries dominate commercial use in economically important applications such as portable electronic devices and electric vehicles. Tremendous effort has been dedicated to improving the safety and cycle life of Li-ion batteries. Unfortunately, many of the mechanisms and fundamental atomistic processes governing the degradation and failure of Li-ion batteries remain poorly understood. Capacity fade in commercially relevant systems can broadly be traced back to the interfaces between the cell components and electrolyte where so-called side reactions occur; such as Li trapping in non-active regions, loss of active electrode material, gas evolution, electrolyte decomposition, and chemical reactions with packaging and current collectors. Particular side reactions dominating capacity fade vary with electrode and electrolyte chemistry. Many of the general trends and associated design principles have not been established and are not generally agreed upon. Investigating battery evolution is challenging as many structural and analytical characterization techniques are best suited for ex situ study. This can be problematic due to the sensitivity of such systems, particularly their surface chemistry, to the ambient environment, particularly H2O and O2. Since the surface reactions are also dynamic and can exhibit time dependent relaxations in situ study is better suited to elucidating surface reaction mechanisms. The work in this dissertation develops a novel cross-platform in situ open cell approach to carry out studies with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The cell was first utilized to study the mechanism of lithium dendrite growth, which imposed a safety concern for the current Li-ion battery. This study elucidated the underlying mechanism for lithium dendrite growth on carbon, which presents a significant safety risk in Li-ion systems. Second, the open cell configuration was used to study the conversion anode material CuO, demonstrating the first advanced in situ XPS/AES cell in the field of Li-ion battery research. This work shed lights on the inconsistencies in the published literature with respect to the reaction pathway of CuO during Li-ion cycling. Furthermore, the cell was applied to study the surface evolution of LiMn2O4 cathode material. A series of systematic experiments suggest that its poor cycle life results in part from the cyclic formation and decomposition of Li2CO3 that occurs upon cycling which in turn leads to CO/CO2 evolution. Finally, related experiments were performed on several cathode materials including LiCoO2, LiNiO2, LiMn2O4, LiFePO4 and LiNi1/3Mn1/3Co1/3O2. A relationship between carbon surface stability and cycle life was identified. This instability is hypothesized to be associated with CO2 evolution commonly observed in measurements of gas evolution from cathodes. To further investigate the role of these gases in affecting full cell cycle life, cycling experiments were carried out in flowing mixed gases of Ar, CO, and CO2. This dissertation deals with the detailed observation and description of the mechanism controlling the surface evolution of several cathode and anode electrodes, demonstrating the importance of surface reactions affecting the battery failure. The results provide new visions into the surface modification or functionalization for improved cycle life in the commercial Li-ion battery

Approaches Toward Combining Positron Emission Tomography with Magnetic Resonance Imaging

Positron emission tomography (PET) and magnetic resonance imaging (MRI) provide complementary information, and there has been a great deal of research effort to combine these two modalities. A major engineering hurdle is that photomultiplier tubes (PMT), used in conventional PET detectors, are sensitive to magnetic field. This thesis explores the design considerations of different ways of combining small animal PMT-based PET systems with MRI through experimentation, modelling and Monte Carlo simulation. A proof-of-principle hybrid PET and field-cycled MRI system was built and the first multimodality images are shown. A Siemens Inveon PET was exposed to magnetic fields of different strengths and the performance is characterized as a function of field magnitude. The results of this experiment established external magnetic field limits and design studies are shown for wide range of approaches to combining the PET system with various configurations of field-cycled MRI and superconducting MRI systems. A sophisticated Monte Carlo PET simulation workflow based on the GATE toolkit was developed to model the Siemens Inveon PET. Simulated PET data were converted to the raw Siemens list-mode format and were processed and reconstructed using the same processing chain as the data measured on the actual scanner. A general GATE add-on was developed to rapidly generate attenuation correction sinograms using the precise detector geometry and attenuation coefficients built into the emission simulation. Emission simulations and the attenuation correction add-on were validated against measured data. Simulations were performed to study the impact of radiofrequency coil components on PET image quality and to test the suitability of various MR-compatible materials for a dual-modality animal bed