Search

The Navy is interested in comparing multi-thermocouple probes, tested in the field, with scanned laser absorption thermometry. This comparison aims to understand the effects of excess Carbon Monoxide (CO) and carbon (soot) resulting from rich nitromethane (CH3NO2) combustion events interacting with the outside air, as well as aluminum catalysts, on the temperature of the ensuing fireball. These interactions create mixing zones with varying gas temperature and composition. Currently, research at the UCF shock tube involves taking preliminary CO-scanned thermometry data with the goal of comparing thermocouple insert results in the future. The thermocouple insert is securely positioned within a specially designed end wall and protected by a heat shield. By comparing the temperature measurements obtained by one-dimensional shock relations with those obtained through scanned laser thermometry, based on CO characterization experiments conducted previously on the same shock tube, we aim to analyze temperature measurements and evaluate how the presence of the thermocouple insert affects the incident shockwave geometry, as well as the resulting reflected wave and temperature conditions. The goal is to observe any discrepancies in temperature measurements between the one-dimensional shock relations and the scanned laser method. This will enable researchers to assess the impact of the thermocouple insert in testing environments. Experiments were conducted using a mixture of 3% carbon monoxide (CO), 20% helium (He), and 77% argon (Ar), with an expected temperature range of 950 – 1950K, at pressures of 0.7 – 1 atmosphere (atm).

In this work, Resonantly Ionized Photoemission Thermometry (RIPT) is established and validated as a novel, non-intrusive, non-seeded, One-Dimensional (1D) line thermometry technique. The RIPT technique resonantly ionizes a target molecule via REMPI (Resonant Enhanced Multi-Photon Ionization) of selectively chosen rotational peaks within a resonant absorption band. Thus, efficiently ionizing and subsequently exciting local nitrogen molecules either by direct or indirect schemes. The excited nitrogen deexcites through photoemissions of the first negative band of N2+[molecular nitrogen], specifically near 390, 425, and 430nm [nanometers], that is then acquired as a 1D line signal. The signal strength at all transitions shares a direct relationship with the line strength of the selectively excited rotational peak, which are temperature sensitive. The thermal distribution of the REMPI rotational levels is given by a statistically weighted (i.e., quantum degenerated) Boltzmann factor, thus with knowledge of the rotational spectrum, a statistical fit can be applied that relates the slope of the Boltzmann plots to a gas temperature. The RIPT technique bypasses the need for a fully rotational-resolved spectrum of the ionized region, instead directly probing up to four rotational lines within the spectrum. By relation, the acquired photoemissions strength directly represents the line strengths at each of the probed rotational wavelengths enabling a rotational state distribution analysis to be applied via the photoemission intensities and generating Boltzmann plots at each probed peak. The slope of a statistical fit to the Boltzmann plots allows a gas temperature assignment. The groundwork is laid for both oxygen and nitrogen-based RIPT techniques through detailed calibration studies that will allow ease-of-use in future applications by scientists and researchers. Furthermore, the potential for 1D thermometry applications is realize for oxygen-based RIPT by implementation in various high-speed, low enthalpy flow environments.

Simultaneous velocity and temperature measurements are critical for understanding the heat and momentum transfer in thermal fluid flow applications. PIV measures the displacement of a constellation of tracer particles using cross-correlation to obtain the velocity field, while LIF uses temperature-dependent fluorescence emission to map the intensity to temperature using a suitable calibration. In this thesis, we present a non-toxic 2c/2d ratiometric LIF technique to obtain single-shot temperature fields for use in large-scale water tunnel facilities. The implementation of LIF temperature measurements in large-scale water tunnels is challenging since the commonly used fluorescent dyes are toxic and their use in large water volumes can lead to environmental problems. In this work, we evaluate the applicability of two non-toxic dyes: uranine and chlorophyll. Uranine is used as a temperature-dependent dye and chlorophyll is used as a weak temperature-dependent reference that provides the excitation intensity information. We show that the intensity ratio of the dyes is strictly increasing and the dynamic temperature sensitivity is high (5 %/◦C) when excited with a pulsed laser (λe = 532 nm). We find that the added advantages of using the two dyes was that they can be disposed of easily and the required concentrations remained relatively low, and hence, in terms of costs, they were quite cheap even when used in large-scale water tunnel facilities. We demonstrate the importance of simultaneous velocity and temperature measurements and the role of buoyancy in understanding heat removal with an array of heated cubes immersed in a turbulent boundary layer using non-toxic dyes in a large water tunnel. Further, we present a simplified, integrated PIV-LIF system to simultaneously measure velocity and temperature fields in aqueous flows using a single color camera, a low-cost CW laser (λe = 465 nm), and a novel dye, RuPhen. The technique can also be extended to 3D LIF/PIV using a scanning light sheet. We find that the RuPhen dye is well-suited due to its peak absorption in the blue, emission in the red, and a strong temperature-dependent emission with a sensitivity coefficient of 4% ◦C−1. We also propose a method to use the red and green channels to correct for any laser power fluctuations. In the end, we present a challenging case study of flow past a heated hollow hemisphere in a refractive index matching water tunnel. We find the flow inside the heated hemisphere is similar to a Rayleigh-Bénard convection cell, with the characteristic thermal plume structure and large-scale circulation. We also document the influence of cross-flow and the symmetric-asymmetric-symmetric transition of the mean flow pattern inside the heated hemisphere and the 3D flow structure by scanning LIF/PIV measurements.

In recent decades we assisted to the evolution of many technological and scientific fields towards miniaturization. Size reduction provides advantages to improve the performance of existing devices or to exploit special physical regimes of the microscopic world. For instance, miniaturization in microfluidics, on one hand allows to reduce the sample volume and speed-up the experiments, and on the other hand gives perfect laminar flow due to the predominance of viscous over inertial forces at small fluid volumes. Heat generation and control of temperature in miniaturised systems represents a promising resource for the development of novel applications and for the study of fundamental questions related to heat. Yet, to fully express these potentials, we need a method to induce microscale thermal perturbations, measure the resulting temperature, and characterise their effects on the system under study. In this doctoral thesis, after presenting the main strategy found in literature to control and measure the temperature on the microscale, we introduce a platform for the systematic study of the effects of thermal perturbations, that integrates microscale characterization, heat generation and thermometry. This platform is based on optical microscopy and allows sample characterization through microscope imaging. It uses thermoplasmonics effect for remote heat generation, that is the conversion of light to heat by noble metal nanoparticles when illuminated at their plasmonic resonance frequency, at which they possess enhanced light absorption properties. Combining transmission microscopy with digital holography, it also provides optical phase sensitivity, allowing to measure the distortions in the wavefront of the light propagating through the sample caused by its refractive index changes with temperature. In turn, this information can be converted to a 3D temperature map of the sample using a well-established retrieval algorithm based on analytical solutions of heat equation. In the subsequent chapters, we show the application of this platform to the field of microfluidics, immunology and thermoplasmonics. First, we use it to induce and characterise fluid and particle transport caused by local thermal perturbations in the microfluidic environment. With this study we identify and quantify the different transport mechanisms involved, show how the fluid dynamics depend on the geometry of the microfluidics system, and demonstrate that a localised thermal perturbation with micrometric size can be used to induce laminar flow on the millimetres scale. To validate its potentials, we showcase full optical control of long-range fluid transport in a proof-of-concept microfluidic device. Next, we use our platform to investigate the molecular mechanism behind the immune response during fever, conducting an in vitro study of the effects of a local thermal perturbation on neutrophils. Our experiments show that the exposure to fever-like temperatures induces an adaptation mechanism on the cells that is characterised by enhanced motility, a crucial factor of their natural behaviour, that can justify an improved immune response. Moreover, measuring a quick and reversible adaptation, our experiments demonstrate that this mechanism does not depend on the production of new protein by the cell in response to the thermal stimulus, but rather from those normally present in the cytoplasm. These observations, suggest a key role of myosin II to regulate immune systems response during fever. Finally, we use our platform to characterise the heating and cooling dynamics of the water body surrounding a thermoplasmonic heat source and measure the characteristic thermalization times of our model samples. To overcome the limitations of phase-based thermometry, extending the applicability of our platform to those samples characterised by dynamic and non-planar heat sources, we introduce and validate a novel approach that combines digital holography and optical tomography, and that is capable of 3D thermometry without prior assumptions on the sample temperature field. By measuring the heating dynamics of a cell with internalised thermoplasmonic particles, we demonstrate the suitability of this optical platform for photothermal therapy studies. In conclusion, discussing the relevance of this approach for further applications in thermoplasmonics, we present the outlooks of this thesis work.

Personalized medicine is the science for developing remedies tailored to the individual necessities of each and every patient. The regulatory approval of the first engineered mammalian cell therapies enhanced the anticipation that these are to become the next pillar of medical care for complex and chronic disease. Although such cells are biological entities, they are modified using engineering principles in what is now established as the field of synthetic biology, and could thus be better described as biocomputing units. The foundations of these systems lie in the integrated therapeutic circuitry, which may provide an open or closed-loop control over the beneficial cellular functions. Open-loops would allow for more flexibility as the input strength and processes can be varied, while closed-loops are rigid and closely emulate the natural physiology. A common feature of every cellular circuit are the input converters, which may also be transcription factors activated by specialized cues. In this work we engineered the first mammalian transcription factor directly sensing temperatures in the physiological range from 38 to 40 °C. This enabled its use as a fever sensor in pyrexia animal models as well as for precise thermoelectrical control over therapeutic implants of engineered cells for controlling glycemia in a type-1-diabetes model. Capitalizing on this work, we envisioned natural energy sources such as sunlight as facilitators for temperature-based cellular control. In particular, we engineered endocrine cells to accumulate diverse therapeutic proteins in their storage granules and release them within minutes upon thermal stimulation in physiological saline. This generated injection ready solutions in an emergency biopharmaceutical process for production of therapeutics in remote areas. Finally, we engineered a closed-loop circuit capable of sensing cardiac troponin I, a protein considered as a gold standard biomarker for myocardial infarction, and responding to it with the secretion of a half-life optimized cardioprotective peptide.

Plasma is the state of matter produced when molecules and atoms are energized to a point where their electrons escape and the constituent material becomes ionized. It is described as the fourth state of matter making up the vast majority of the observable universe, and over the past century has been studied and developed into usable human-scale applications. As a category, plasma exists in a thermal spectrum as ionization and unbound electrons are the defining characteristics. Thus, non-thermal plasmas made up of near room temperature ionized gasses formed through strong alternating electromagnetic fields make up one side of the spectrum and thermal plasmas that have heated materials to the point of ionizing constitute the other. This dissertation focuses on the application of non-thermal plasmas for reactive gas generation and nanomaterial synthesis, in addition to more fundamental studies of how the plasma interacts with solid interfaces or forms nanomaterials. The studies that this work is composed of are broken down into sections, the first of which is fundamental investigations of non-thermal plasma properties, such as in-situ monitoring of plasma-induced surface-heating via Raman-thermometry and investigations into nanomaterial growth mechanics when exposed to discontinuous (pulsing) plasma conditions. The second section puts the silicon nanomaterials produced via plasma to use in quantum dots, where the silicon nanocrystal is combined with non-toxic organic molecules to achieve record setting photon upconversion and investigates the fundamental mechanisms impacting this method of light conversion. Next, plasma-grown and commercial silicon nanomaterials are applied as a next generation lithium-ion battery anode material, where unanswered questions about carbon shell structure and solid electrolyte interphase growth are investigated with novel techniques of material production and analysis. Finally, the reactive gas output of a plasma is put to work as a cheap and efficient method of pathogen decontamination for face-piece-respirators, demonstrating the wide breadth of applications for non-thermal plasmas and the materials it can produce.

Induction heating causes the release of enormous amounts of heat from dispersed magnetic nanoparticles. While the rate of heat transfer can be easily quantified calorimetrically, measuring the temperature of the nanoparticles on the nanoscale presents experimental challenges. Fully characterizing the temperature and thermal output of these magnetic particles is necessary to gauge overall heating efficiency and to provide a more holistic understanding of heat transfer on the nanoscale. Herein, this dissertation seeks to develop a novel nanoparticle thermometry technique, which correlates diffusion behavior in core-shell nanoparticles to local temperature. Initial measurements suggested that heating silica capped ferrous nanoparticles (SCNPs) via induction in a saline environment encouraged the diffusion of dissolved sodium ions into the silica shell. The concentration gradient of sodium ions within the shell underwent an observable transition after only a few seconds of heating, thus implying that the increased core temperature was the driving force behind the diffusion event. Calculating nanoscale temperature required a three-prong approach, which combined experimental and theoretical analyses. First, a computational model of the core-shell system was developed to accurately depict diffusion into the core-shell structure. Experimental X-ray methods then analyzed the relationship between diffusivity and temperature for the material system and also measured nanoscale concentration gradients within physical SCNPs. By comparing the experimental diffusion data to the theoretical model, the estimated nanoscale temperature was able to be extracted. Understanding nanoscale temperature provides insight into more encompassing thermal models for nanoparticle induction heating, which will ultimately lead to advancements in numerous applications.

Spontaneous Raman scattering from nitrogen is studied in high pressure gases. Collision frequency increases with increasing gas density, causing spectral lines to broaden due to pressure broadening and mix when the lines are strongly overlapped. Because spontaneous Raman thermometry is accomplished by fitting a simulated spectrum to an experimental spectrum, spectral models that neglect these collision-induced effects will lead to erroneous temperature inference. This work investigates the influence of high density on ro-vibrational spontaneous Raman scattering, which must be understood to obtain accurate thermometry in high pressure gases. The temperature profile through a flame front was measured at 1 atm, 3 atm, and 5 atm using spontaneous Raman scattering from nitrogen. The pressure broadening was measured for the anisotropic tensor component of spontaneous Raman scattering from room temperature nitrogen over the pressure range of 10 atm to 70 atm for three gas compositions: pure nitrogen, air, and nitrogen in argon. The unmixed line model was found to give good fits to the O and S branches for all pressures, which indicates that line mixing effects are not significant in the O and S branches over this pressure range. Using indirect experimental evidence, line mixing effects in the anisotropic component of the Q branch were inferred to be below the threshold set by the experimental spectral resolution at pressures up to 70 atm at room temperature. Assuming that the anisotropic Q branch lines mix like the isotropic lines was found to result in a small systematic error in the inferred temperature at flame temperatures, with the error increasing slowly with pressure. The bias can be removed by modeling the anisotropic spectrum separately from the isotropic spectrum. Line mixing effects should be included in the modeling of the isotropic component of the Raman spectrum, but can probably be neglected in the anisotropic component of the ro-vibrational spontaneous Raman spectrum of nitrogen.

Probing energy dissipation and transport at the micro- and nanoscale has become increasingly important across various disciplines including solid-state electronics and optoelectronics, thermoelectrics, plasmonics, catalysis, hydrogen storage, and electrochemical energy storage. This thesis describes the development of high-resolution calorimetry, thermometry, and thermal microscopy tools, and next how these techniques can be utilized for investigating nanoscale systems with applications in energy conversion, energy storage, and thermal management of electronics. First, I present a high-temperature and high-pressure calorimetric micro-reactor with microwatt heat flow resolution for studying heterogeneous reactions and phase transformations of nanomaterials. This instrument enables measurements of enthalpy of reaction and reactant consumption with milligram scale (

Basalts are windows into the mantle from which they were derived, and their eruption at the surface provides an opportunity to probe the conditions in the mantle that lead to their formation including temperature, water content, and oxidation state. In this thesis, Quaternary basalts from three localities in the Basin and Range (western Basin and Range, the Mojave Desert, Yellowstone/Snake River Plain) are examined to evaluate how temperature and dissolved water content vary as a function of mantle source (i.e., subduction-modified lithosphere, asthenosphere, mantle plume). In Chapters 2 and 3, basalts that contain mantle xenoliths were, which requires rapid transit through the crust and precludes prolonged storage in crustal magma chambers. Instead, the hypothesis of rapid phenocryst growth of olivine during ascent along fractures was evaluated. A second hypothesis that was tested is whether the most Mg-rich olivine analyzed in each sample matches the expected liquidus composition for a basalt with the whole-rock composition. For all samples that passed olivine-melt liquidus tests, olivine-melt thermometry and hygrometry were applied at the liquidus. This gives the temperature and melt water content at the onset of phenocryst growth. In Chapter 2, the hypothesis of rapid phenocryst growth during ascent was tested for a suite of 10 basalts from the Big Pine volcanic field, CA, one of which contains mantle xenoliths. Olivine and clinopyroxene phenocrysts display diffusion-limited growth textures, which is consistent with rapid phenocryst growth during ascent. When the most Mg-rich olivine composition in each sample is paired with the whole-rock composition, all olivine-melt equilibrium tests are passed. Application of olivine-melt thermometry and hygrometry at the liquidus gives temperatures (~1250-1100 °C) that vary with MgO content (~13-7 wt%), and water contents that range from ~1.5-3.0, which matches those analyzed in olivine-hosted melt inclusions from the literature. In Chapter 3, alkaline lavas from the Mojave Desert (Cima volcanic field and Dish Hill, CA) were targeted due to their mantle xenoliths. Several of the xenolith-bearing samples are notable for their low MgO content (as low as 5 wt%) and are not direct partial melts of mantle. Thus, an outstanding question is how they were able to carry mantle xenoliths to the surface, if they first underwent fractional crystallization. Although evidence of rapid phenocryst growth is present in all samples, the most Mg-rich olivine in each sample fails olivine-melt equilibrium tests. The only hypothesis that could not be disproven is that magma mixing between two (or more) melts occurred rapidly during ascent along fractures, one of which is a high-MgO melt with entrained mantle xenoliths. In Chapter 4, Quaternary basalts adjacent to the active Yellowstone volcanic field and along the Snake River Plain were examined. Despite the absence of any mantle xenoliths, the most Mg-rich olivine analyzed in 15 of 16 basalts pass olivine-melt equilibrium tests. Application of olivine-melt thermometry and hygrometry give temperatures of ~1200-1130°C and water contents ≤ 1.8 wt% (which match H2O analyses in olivine-hosted melt inclusions from the literature). The YS/SRP basalts are not anomalously hot, have modest melt water contents, and relatively low Mg# values, which is consistent a larger volume of melt. In Chapter 5 olivine-melt equilibrium experiments were performed to evaluate chemical equilibrium in an undercooled Big Pine basalt that experienced a kinetic delay to nucleation. All experiments indicate chemical equilibrium is preserved despite textural disequilibrium in undercooled experiments.

Multi-turn Energy Recovery Linacs (ERLs) powered by Superconducting Radio Frequency (SRF) cavities enable the production of continuous bright high-current beams while being very efficient. The low energy consumption can be attributed to diminishing refrigeration costs from increasingly advanced SRF materials and the efficient use of rf power in maintaining the accelerating gradient. Operating the main linac cavities of SRF ERLs with large QL reduces average rf power consumption but increases its sensitivity to resonance detuning. We discuss passive measures as well as develop a novel Active Noise Control algorithm to reduce microphonics detuning and ensure stable field. This dissertation describes the complete rf commissioning process of a SRF main linac in detail including the use of automation in various steps. These techniques were utilized in the Cornell BNL ERL Test Accelerator (CBETA), the first multi-turn SRF ERL, which achieved an energy recovery efficiency of 99.4 % during high-current operations in the single turn mode. We further analyze the effect of transient beam loading using a novel linear model which predicts the existence of reactive beam loading arising from relativistic effects in the presence of low energy beam. Finally, we discuss a novel thermometry system to image local heating and thermal runaway on the surface of SRF cavities, thus aiding the development of more efficient SRF materials for future ERLs.

High-silica rhyolites (> 75 wt% SiO2) are the most differentiated magmas on Earth and are known for explosively erupting in large (100-1000s km3) quantities. Understanding the formation of these magmas is crucial, as the processes involved fundamentally reconstitute continental crust, and the western U.S. has been the site of two super-volcano eruptions of high-silica rhyolite in the past 800,000 years. This thesis focuses on the extensively studied—yet controversial—origin of the Bishop Tuff in California, formed when > 600 km3 of zoned high-silica rhyolite was erupted in less than a week, forming the Long Valley caldera. Key to understanding the origin of this voluminous magma are tight constraints on its temperature and volatile content. Various phenocryst phases in the Bishop Tuff can be used for thermometry and hygrometry, and requires accurate analyses of mineral phases, as well as valid tests of mineral-mineral (and mineral-melt) equilibrium. Chapter 2 addresses a long-standing controversy in the literature over the application of Fe–Ti oxide thermometry to the Bishop Tuff. Analyses of ilmenite and titanomagnetite in each single pumice clast span a wide compositional range, which had been interpreted as evidence of disequilibrium. In this study, quantification of analytical error allows: (1) accurate identification of disequilibrium phases (rare); and (2) determination of the minimum number of analyses required for high-precision thermometry (< ±10 °C). The resulting Fe–Ti oxide temperatures (~700–800 °C) show excellent agreement with two-feldspar temperatures. Application of plagioclase-liquid hygrometry provides a high-resolution record of decreasing H2O content (~7.2–4.1 wt%) in the Bishop rhyolite with increasing temperature. Documentation of linear compositional variations in phenocrysts with temperature confirm that their growth occurred after thermal and compositional gradients in the Bishop rhyolite melt were developed. Chapter 3 examines the origin of the strong variations in different trace element concentrations with temperature in the high-silica rhyolite portion (> 400 km3) of the Bishop Tuff. It is hypothesized these gradients arose from the segregation of variable melt fractions from a granitic crystalline mush. This hypothesis is tested by constraining the stoichiometry of the crystallization/melting reaction in the crystalline mush by determining the relative compatibility value of each trace element and combining it with their respective partition coefficients (between all mineral phases in the granitic mush and high-SiO2 rhyolite). Constraints are placed on the pressure (350–500 MPa) and average activity of H2O (~0.5) during melt segregation. Several unresolved paradoxes in the literature are now explained, including: why fO2 increases with temperature across the Bishop magma; why H2O decreases with temperature; and why plagioclase phenocrysts are subordinate to quartz and sanidine. In Chapter 4, focus shifts to the source of heat and H2O required to form the Bishop rhyolite, namely the Long Valley basalts, which erupted in close spatial and temporally proximity. It is established that phenocryst growth in the basalts was rapid, and that the most Mg-rich olivine analyzed in most samples passes the liquidus test when paired with a liquid composition that matches that of the whole rock. When olivine–melt thermometry/hygrometry is applied to this pairing, resulting temperatures range from 1170–1060 ˚C and the average minimum water content is ≥ 2.9 wt% H2O. These new data are necessary to accurately model how the influx of basalt into the crust beneath Long Valley caldera led to the formation of the Bishop rhyolite through the transfer of their heat and water.

Particles at the nanoscale have emerged as promising tools for a broad range of applications in medicine. Tailored nanostructures enable novel possibilities in disease therapy and diagnostics (summarized as theranostics), complementing and improving the state of the art techniques. Their unique performance can be attributed to their extremely small size, that not only enables crossing certain biological barriers or higher targeting efficiencies compared to molecular drugs, but also evokes novel effects that only occur at small scales. A highly attractive subgroup among these nanostructures is light-activated theranostics due to their versatility and absence of harmful radiation such as X-rays. As such, they can, for example, be used to localize and image cancerous tissue, selectively destroy cancer cells and simultaneously act as control units during therapy. Owing to the possibility of combining multiple functionalities into one nanostructure, such systems have the potential to address an imminent need in today’s society for advanced, specific and controlled theranostics. In Chapter 1, the interaction of light with biological tissue is discussed in detail. The focus lies on the wavelength-dependent phenomena governing imaging and therapy, specifically absorption, scattering, and autofluorescence. When visible light hits biological tissue, most of the photons are absorbed and scattered, limiting applications to very superficial layers such as during in vitro cell-monolayer experiments. However, based on the spectral properties of selected representative tissues, two most promising spectral regions in the near-infrared (NIR) are identified for light-activated theranostics, namely the NIR-I (650 – 900 nm) and NIR-II (1000 – 1350 nm). Within these regions, light absorption, scattering, and autofluorescence are minimized, enabling light to penetrate much deeper into biological tissue. By tuning the operational range of a theranostic modality into these regions, its working depth in tissue is extended to the centimeter range. In the following, three examples of light-activated theranostics - photothermal therapy, fluorescence imaging, and nanothermometry - are introduced and their underlying principles are elucidated. To enhance the performance or selectivity in light-activated theranostics, exogenous agents such as nanoparticles are often introduced. Therefore, a short overview of currently available classes of nanoparticles is given. Special attention is paid to identify potential drawbacks and shortcomings of different material groups, as well as remaining challenges in terms of material design. Photothermal therapy relies on the conversion of incoming light to heat, thereby locally heating up the surrounding tissue. When targeted to a tumor, this therapy allows to selectively kill diseased cells. To increase specificity, photothermal agents with strong light-absorption such as plasmonic nanoparticles are employed. However, the most commonly used gold particles require sophisticated geometries (i.e. rods, stars, cages) to shift their absorption into the near-infrared. Besides increasing the already high costs of gold-particles, such complex geometries also impair their stability. To overcome these drawbacks, chapters 2 and 3 describe the synthesis of titanium nitride (TiN) nanoparticles as alternative photothermal agents. Titanium nitride represents a low-cost material that exhibits strong NIR-I absorption, even for spherical particles. The synthesis involves first the preparation of TiO2 nanoparticles by flame-spray pyrolysis (FSP), and second the nitridation under ammonia atmosphere into TiN. The influence of the nitridation parameters (holding time, temperature) on the product characteristics are investigated with commercially available, bare TiO2 nanoparticles (P25) as a model system. Longer nitridation at higher temperatures gradually decreases the remaining oxygen in the particles, thereby improving their absorption. However, too high temperatures (> 850 °C) result in strong aggregation and decreased performance. To overcome this problem, an amorphous SiO2-coating is introduced as a spacer layer around the particles. Specifically, TiO2 particles are produced by FSP and in-situ coated with a SiO2 layer. Through close control over process parameters, both the thickness of the SiO2-coating and the TiO2 core particles can be independently controlled. Despite the SiO2-coating, these particles can still be nitrided to form SiO2-coated TiN, whereby the core-shell structure is maintained. These SiO2-coated TiN particles exhibit improved optical absorption and photothermal efficiency, as well as better dispersibility and thermal stability against reoxidation. This makes them superior to well-established materials such as gold nanoshells or other alternative photothermal agents. The interaction of these particles with HeLa cells is investigated in detail in chapter 3. They are taken up by the cells and localized in membrane-enclosed vesicles within the cytoplasm. The particles themselves are well-tolerated by cells. In contrast, when combined with laser irradiation, they can effectively kill HeLa cancer cells through the increase in temperature, making SiO2-coated TiN most appealing as a photothermal agent. The treatment of tumors is typically preceded by a detailed diagnosis based on an imaging modality. Fluorescence imaging is known for its inexpensive real-time imaging possibilities with high spatial and temporal resolution. However, the currently available fluorescent contrast agents operating in the NIR-regions exhibit major limitations, such as poor photostability and quick degradation. To tackle this problem, novel inorganic nanoparticles with NIR-II emission are developed based on Mn5+ (chapter 4). These are doped into a Ba3(VO4)2 host matrix, leading to strong emission at around 1180 nm following 750 nm excitation. However, these particles exhibited substantial dissolution. This, in turn, led to relatively high cytotoxicity, which was traced back to released vanadium ions. To overcome this problem, a bismuth-containing mixed oxide with the composition Ba3(VO4)2:Mn5+ - Bi2O3 (called BaVOMn – BiO) was prepared. The addition of bismuth resulted in higher particle stability, and therefore negligible cytotoxicity. Furthermore, also the brightness of these particles was increased by almost an order of magnitude through the addition of Bi2O3. The particles also exhibited excellent colloidal, chemical and photostability, in contrast to commercial ICG or PbS-CdS quantum dots. Finally, BaVOMn-BiO particles were incubated together with HeLa cells and imaged by fluorescence microscopy, revealing their uptake by cells and accumulation around the nucleus. Finally, their performance for ex vivo deep-tissue imaging was assessed, placing their performance on par with PbS-CdS quantum dots. Interestingly, the emitted fluorescence signal carries more information: The luminescence is typically also affected by the surrounding temperature. Therefore, some luminescent contrast agents can also act as local temperature sensors to allow for non-contact nanothermometry. This enables the local determination of temperature within tissues, which is crucial to control the heating during photothermal therapy (chapters 2 and 3). The most important performance parameter for such thermometers is its sensitivity. In a first approach (chapter 5), the sensitivity is optimized based on the selection of emission lines for a ratiometric read-out of a previously developed NIR-emitting material (BiVO4:Nd3+). Founded on a detailed understanding of the rich variety of involved Nd3+-energy states, the sensitivity can be increased by an order of magnitude, enabling the accurate temperature sensing even within deeper tissues up to 6 mm. In chapter 5, the focus lies on the optimization of thermometric performance. However, other parameters crucial to their use in biomedical imaging are just as important and need to be carefully considered. These include suitable particle sizes, brightness, (chemical, colloidal and photo-)stability, and biocompatibility. As it was suggested to retain from using toxic metals in the formulations at all, regardless of the product stability, we investigate in chapter 6 a promising material composition based on phosphates. For the first time, Ba3(PO4)2 nanoparticles doped with Mn5+ are produced with sizes below 100 nm, suitable for intravascular applications. Besides the optimization of particle emission intensity (λ = 1190 nm), close attention is paid to their stability and biocompatibility. The response of three cell lines (cancer cells (HeLa), fibroblasts (NHDF), monocytes (THP-1)) to particle exposure is analyzed in detail, showing no signs of adverse reaction. Finally, the suitability of these particles for temperature sensing is evaluated, considering different read-out strategies. The result is a bright NIR-II emitting, stable, and biocompatible nanoprobe capable of temperature sensing in deep-tissue.

Abstract: In the current state-of-the-art, a wide variety of devices, from computer clocks to smartphone accelerometers and from pressure gauges to atomic force microscope sensors, rely on mechanical resonators, either in microscale or nanoscale. Nanoscale mechanical resonators have even more potential than microscale by offering unprecedented sensitivity through weighing a single proton (10^(-24) g) or by measuring aN (10^(-18) N) force or µK temperature. The smaller size of nanometric mechanical resonators allows high sensitivity to their environment; ensuring excellent frequency stability, through high resonance frequency with a higher quality factor, Q, takes the best advantage of this sensitivity. At the same time, their smaller dimension makes these more susceptible to environmental fluctuations, such as thermomechanical (TM) noise, and to energy dissipation, which degrades the Q at atmospheric pressure. The amplitude of TM noise sets a limit to the frequency stability via limiting the signal to noise ratio (SNR). This limit on SNR happens to improve (decrease) as Q is lowered at a rate of Q^(1/2). Meanwhile, nonlinearity practically limits the maximum signal and also causes SNR to improve as Q is lowered with signal proportional to Q^(-1/2). By definition, SNR is the ratio of amplitude at the onset of nonlinearity to the TM noise peak. As a consequence, in widely accepted Robins' picture, frequency stability improves inversely with Q×SNR and motivates nanomechanical sensor operations mostly at high vacuum to get better performance via high-Q by resolving TM noise. The negative effect on the stability of early appearance of nonlinearity in high-Q mechanical resonators is underappreciated by researchers and the mantra that the better the Q, the better the frequency stability is well known. Interestingly, if the SNR can be improved at the same rate that Q is degraded, then mass sensitivity can be maintained despite lower Q conditions. Amongst excellent demonstrations of high-Q NEMS sensors to date, such interplay between Q and SNR is not well studied, despite importance not only for fundamental studies but also for practical applications. This thesis shows that the high displacement sensitivity of a nano-optomechanical (NOMS) transduction scheme ensures that mass sensing is generally occurring with only fundamental limitations to the stability. Put another way, NOMS transduction tends to resolve thermomechanical noise at orders of magnitude above the instrumentation noise background. Frequency stability measurements by phase-locked loop and open loop method validate Robins' picture by attaining the same level of stability at different Q. We test experimental results, both in the analytical and numerical frameworks, and provide a full model to unfold different fundamental noise sources existing in the system and noise suppression effects in phase-locked loop Allan-deviation experiments. Phase-locked loop experiments show increasing noise signal suppression with damping due to loop bandwidth artifacts. Surprisingly, open-loop experiments also show some improvement of mechanical sensor performance with increasing damping, which is attributed to reduced frequency-fluctuation noise in resonance through improved temperature fluctuation noise level via heat conduction by air molecules at atmospheric pressure. We confirm these findings by demonstrating better temperature resolution in atmosphere than in vacuum. For temperature sensing experiments, we study the temperature dependent properties of the optical ring and NEMS to develop NOMS thermometry. Our thermometry results reveal the existence of nanoscale heat transfer issue for the NEMS that results in very high 0.7 MWm-2K-1 heat transfer coefficient in atmosphere for the doubly clamped beam resonator and agrees well with COMSOL multiphysics simulations. We further apply the obtained frequency stability at atmospheric pressure by integrating the NOMS system with a commercial gas-chromatography. The designed, integrated GC-NOMS gas sensor demonstrates 1 ag (10^(-18) g) mass resolution, even at truncated SNR of the mechanical resonator, by detecting GC separated toluene and xylene in a mixture. The retention time of toluene and xylene are identical both in NEMS and FID and asserts the success of GC-NOMS integration in ambient condition. The obtained ambient ag mass resolution is comparable to that predicted by Robins' formula at 100 µTorr even though the Q of 29 at 760 Torr is ≈300× lower than that at 100 µTorr. Such an intriguing mass resolving capacity by the GC-NOMS in atmosphere is a baby step for future generations of portable GC-MS in ambient air.

Calorimetry, a heat measuring process, has opened a way to quantify generated heat, both in physical and in biological systems. The resolution of a typical calorimeter (Q ̇=G_Th× ∆T) can be improved in three ways, either by improving temperature resolution (∆T) or by reducing thermal conductance (G_Th) or both. With intensive efforts to improve thermal resolution, microcalorimeters can now be widely used for measuring minute heat generation and transport in the micro/nanoscale. Still, there are several topics that remain insufficiently explored due to sensitivity limitations. One unanswered question in nanoscale thermal science is of thermal transport in single-atomic or single-molecular junctions. Similar to electrical conductance, many theoretical studies suggest that thermal conductance is also quantized. While quantized electric conductance (2e2/h or 1/12.9 kΩ-1) was measured in the late 20th century, quantized thermal conductance measurements at room temperature (π2 kB2T/3h or 300 pW/K) have been challenging due to insufficient calorimeter resolution and technical obstacles in creating stable atomic junctions. A second elusive measurement is metabolic rates in small model organisms. This research is fueled by accrued evidence that human diseases, such as cancer and obesity, and aging are correlated to abnormal metabolic states. Recent advances in calorimetry have benefitted from both operations in a vacuum where parasitic heat conduction can be attenuated and the use of microfabrication tools which significantly decrease thermal conductance and increase temperature resolution. However, such approaches cannot be simply adopted for biological systems so that none of the currently available bio-calorimetric tools are capable of the sub-nW resolution that is necessary for resolving C. elegans metabolic heat output. Biocalorimetery has to be performed in a liquid environment to keep organisms alive, and the size of calorimeters cannot be smaller than that of the micro-sized biological organisms. Moreover, integration of optical imaging is challenging as this naturally couples environmental temperature fluctuations into the system. This dissertation presents two types of calorimeters. The first calorimeter is to measure thermal conductance at atomic scale, especially in single atomic or single-molecular junctions. It features a high stiffness (10 N/m) for stably holding atomic and molecular junctions at room temperature. Further, we achieved both a high temperature resolution (0.6 mK in a 10 Hz bandwidth) and a low thermal conductance (800 nW/K) of thermal bridge to resolve quantized thermal conductance (300 pW/K) in atomic junctions and length independent thermal conductance (25 pW/K) in molecular junctions. The second calorimeter is employed to measure metabolic heat outputs from C. elegans. Specifically, we achieved unprecedented heat resolution of 270 pW for biological systems, which represents a 500-fold improvement over calorimeters employed for past C. elegans studies and a 10-fold improvement compared to the state-of-the-art bio-calorimeters. This advance was realized by 1) achieving a low thermal conductance of 27 µW/K by operating in a high vacuum environment and attenuating the radiative conductance via gold coating, 2) achieving temperature stability of ±5 µK over a day using three nested shields with independent temperature control for each shield. Using this calorimeter, we demonstrate for the first time, time-resolved metabolic measurements of single C. elegans from ~4 nW for the L1 stage to ~100 nW for the adult stage. These demonstrations clearly highlight the broad potential of this tool for studying the role of metabolism in disease, development and aging of small model organisms and single cells.

Thermal measurements are an important tool for experimental condensed matter physics. They are the most general methods available: any excitation in a solid will carry energy, and thus heat. Such measurements require accurate and precise temperature readings at multiple points on a crystal, often only a few millimeters apart. This is especially important when making thermal Hall effect measurements, which require precision in intense magnetic fields that can interfere with resistive thermometers. We have exploited the strongly temperature dependent dielectric permittivity of strontium titanate to make capacitive thermometers which are not subject to this interference. To test these thermometers, thermal Hall effect measurements were carried out on crystalline bismuth. Bismuth is one of the best known semimetals, a material which hosts both electrons and holes with high mobility. With the strontium titante microthermometers, we were able to conduct measurements up to 10 T and at temperatures down to 40 K. A large thermal Hall coefficient is measured, indicative of high mobility carriers. Another application of these techniques is thermal measurements of frustrated magnets. These systems often have itinerant excitations which do not carry charge, making thermal measurements all the more important. We discuss our measurements on strontium copper borate, in which pairs of spin-1/2 sites are paired up in strongly coupled dimers. The magnetic excitations of this system are mobile triplet states, called triplons. It has been predicted that these triplet bands could have non-trivial topology, making strontium copper borate a bosonic topological insulator, and resulting in a specific thermal Hall effect signal. Experimental measurements in this system fail to find this signal, casting doubt on this theory. However, we observe magnetic field dependent thermal conductivity at temperatures below 1 K, where the triplet excitations should be frozen out. This may be related to another phenomena found in this material: the formation of spin superlattices.

Augustine Volcano, located in southern Alaska, has erupted a wide compositional variety of volcanic rocks over its ~26,000 year lifespan. We performed an investigation of the mineralogy and petrology of the low-K dacite (LKD), the oldest yet-unstudied unit in the Augustine tephrostratigraphic succession, with the goal of creating a hypothesis of how the unit formed, as well as finding the unit's relationship to other ancient Augustine tephras. Our work was based on examination of hand samples, grain mounts, and thin sections of the LKD, the latter examined with both petrographic microscopes and with the electron microprobe at the American Museum of Natural History. We found a mineral assemblage in the LKD including plagioclase, calcic amphiboles, cummingtonite, magnetite, and ilmenite. Modeled values for the temperature, pressure, oxygen fugacity, and water content of the LKD's parent melt led us to the conclusion that the unit was derived from mixing of a rhyolitic parent magma similar to that of the ~30 m thick rhyolite erupted by Augustine in the Pleistocene, together with deeply-sourced mafic material of a similar geochemical character to the mafic component of the high-P dacite hypothesized by other research. Further work is needed to fully characterize this unit, as well as those above it in the Augustine tephrostratigraphic column, in order to arrive at a complete understanding of the relationship between ancient and modern Augustine tephras.

Cotopaxi is a stratovolcano in the Northern Andes Volcanic Zone, and has a history of bimodal volcanism, alternating between rhyolite and andesite. With Cotopaxi reawakening in 2015 after 138 years of quiescence, the question of what is occurring beneath the surface becomes especially poignant. To contribute to this question, it is productive to look to the volcano's recent past. This work characterizes the mineralogy and geochemistry of the recent eruptive products of Cotopaxi, with emphasis on the two pulses of the 1877 eruption. Additionally, pressures and temperatures are estimated for magmas prior to all eruptions. This will allow a better understanding of the magma plumbing system and its evolution over time. Over the past 500 years Cotopaxi has had five major eruptive events (VEI 3-4), which occurred in 1532, 1742, 1744, 1768, and 1877, and included pyroclastic surges, scoria flows, and lahars. After the initial pulse of the 1877 eruption and the subsequent lahars, a second pulse of magma produced a pyroclastic density current, containing scoria clasts up to 1 meter in diameter. All samples collected from these eruptions are basaltic-andesite to andesite (56-59 wt. % SiO2), with a mineral assemblage of pl + opx + cpx + mag ± ol. Plagioclase from all samples range from An47 to An78 and show both normal and reverse zoning. Normally zoned crystals exhibit greater compositional variation between cores and rims than reversely zoned crystals (median Ancore-Anrim 8% vs 4%, respectively). The presence of disequilibrium textures such as zoned plagioclase and mingled magma indicate that magma mixing plays a role in magma genesis in addition to crystal fractionation. Pyroxenes occur as augite and enstatite and do not exhibit significant zoning. The very similar petrologic character of these deposits suggests that they were sourced from a relatively long-lived magma system that underwent differentiation and replenishment between eruptions. Thermobarometric data indicate that magma storage occurred at temperatures of 1000-1150°C and pressures ranging from 0.20 GPa (during the 1877 eruption) to 0.43 GPa (during the 1532 eruption), which is equivalent to depths of 7 and 15 km (± 9 km), respectively. Data from geodetic and seismic studies indicate that magma was injected at a depth of 4 to 5 km which caused the ground deformation and seismic unrest from 2001 to 2002. While thermobarometry is poorly constrained, these results suggest that magma storage has become progressively shallower over time.

Mantle plumes are anomalously hot, narrow upwellings of mantle material that originate at the core-mantle boundary. As plumes rise they may form volumetrically large "heads" (~1000 km in diameter) with narrower (~100 km) "tails." Plume head melting is thought to form Large Igneous Provinces (LIPs), vast outpourings of basaltic lava (~106 km3), while plume tail melting forms linear chains of ocean island basalts (OIBs) similar the Emperor-Hawaii Seamount chain. Mantle plume derived melts indicate that these structures sample deep Earth geochemical and lithological heterogeneities. Studying plume-derived lavas can clarify important planetary-scale questions relating to the accretion of the Earth, primordial geochemical reservoirs, the fate of subducted materials, planetary differentiation, and convective mixing.

Nitric oxide (NO) rotational temperatures have been measured around a tick mark shaped body in a hypersonic flow with total enthalpy of 11:3 MJ=kg and freestream density of 2:1 g=m3, and around a 30° wedge in a hypersonic flow with total enthalpy of 3:1 MJ=kg and freestream density of 6:4 g=m3. The temperature was measured with multi-line planar laser induced fluorescence (PLIF) thermometry, and the hypersonic flow generated by a free-piston shock tunnel. The temperature measurements at the high-enthalpy condition are the highest total enthalpy NO-PLIF thermometry measurements made to date in a hypersonic flow. Additionally, this is the first experimental investigation of the flow around a tick mark shaped body. The tick mark body flow was visualised using time-resolved near-resonantly enhanced shearing interferometry (RESI), with lithium seeded into the flow as a refractivity enhancing species. Several improvements to the RESI visualisation method were also investigated. The time-resolved visualisations of the tick mark shaped body were analysed to provide quantitative measurements of the flow structure. Additionally, the flow structures in lithium seeded and unseeded flows, visualised with both the RESI and NO-PLIF techniques, were compared. This comparison showed that lithium seeding was not completely non-intrusive, as had been previously supposed. The wedge thermometry experiments at the low-enthalpy condition were conducted to validate the NO-PLIF system performance. The freestream temperature measured here showed good agreement with prediction, and with previous NO-PLIF thermometry experiments conducted at this flow condition. Near the fluorescence discontinuity produced by the oblique shock wave, a fluorescence bleeding effect was found, which caused the freestream temperature to increase and post-shock temperature to decrease near the shock wave. Analysis of previous NO-PLIF thermometry studies in free-piston shock tunnels shows this effect was present in previous experiments, but had not been previously identified. At the high-enthalpy condition, the freestream temperature was significantly lower than the predicted value, yet Boltzmann plots for various regions of the tick mark model flow showed that a single rotational temperature is appropriate for this condition. This indicated that there is an as yet unidentified systematic error that becomes significant for NO-PLIF measurements in high-enthalpy flows.

PurposeTo determine under-sampled k-space gradient echo trajectories for MR thermometry with PRF shift to increase acquisition speed while maintaining temperature accuracy.MethodsA computer simulation was built and used to study the behaviour of temperature measurement errors as different lines of k-space were acquired. A fully acquired k-space was constructed from the information in the Bioheat Transfer Equation (BHTE), various k-space under-sampling schemes were employed and temperature maps were reconstructed using the PRF shift method as a basis. Temperature errors were calculated as the difference in the maximum temperature predicted by the BHTE and the maximum temperature measured by the under-sampled scheme. ResultsUnder-sampled gradient echo keyhole trajectories showed promising results for making temperature measurements. Using 5 interleaves with a 63 keyhole size estimates temperature with only a 0.4% error while providing a 1.68x faster frame rate.ConclusionGradient echo keyhole trajectories can be used to make temperature measurements for MR thermometry with PRF shift. This method can also be applied for shorter sonications and making temperature estimates for multiple slices.

Heat transfer at the nanoscale has been one of the primary concerns in the design of nanoelectronics and nanostructured materials for applications such as thermal management and thermoelectric energy conversion. This thesis examines the thermal transport in nanoscale thin films and two-dimensional (2D) materials using an optical pump-probe technique based on frequency domain thermoreflectance (FDTR). The design and implementation of a continuous-wave laser based FDTR system is described in detail. The system is extended to an imaging microscope capable of producing micrometer scale maps of several thermophysical properties simultaneously. An analytical formula, which accounts for experimental noise and uncertainty in the controlled model parameters, is derived to calculate the precision of thermoreflectance measurements. The FDTR system is used to study the anisotropic heat conduction in periodic nanoscale Mo/Si superlattices and a 2D material, graphene. The measured in-plane thermal conductivity values of the superlattices are in good agreement with calculations taking into account both electron and phonon thermal transport, using a phonon mean free path which depends on the Mo layer thickness. The measurement procedure of graphene is described in detail, including the sample preparation, sensitivity analysis, and parameter fitting. Various graphene flakes supported on SiO2 surfaces and atomically flat Muscovite mica surfaces are measured. The results show that the thermal conductivity of single-layer graphene can be improved by ~3 times by using a mica substrate compared to commonly used SiO2 substrates. In addition, comparison with the reported values of suspended graphene suggest that the out-of-plane flexural phonon modes may contribute at least 70% to the thermal conductivity of graphene. Finally, the thermal model is modified to include volumetric heating for the measurement of materials without a transducer layer. An amorphous silicon film deposited on fused silica and silicon substrates is measured to validate the model.

Ultracold atomic gas systems provide a remarkably versatile platform for studying a wide range of physical phenomena, from analogue particle physics and gravity, to the emergence of subtle and profound order in many body and condensed matter systems. In addition, ultracold atomic gas systems can be used to perform a range of precision measurements, from time keeping to variations in the fine structure constant. In this dissertation, I describe our efforts to build a new apparatus capable testing a range of techniques for performing precision measurements in a magnetic storage ring for cold, possibly Bose-condensed, lithium and rubidium atoms. Next, I briefly touch upon our explorations of spin vortices in a ferromagnetic rubidium Bose-Einstein condensate before presenting an exhaustive account of our work using free-particle-like magnon excitations of the ferromagnetic gas to cool it and measure its temperature in a never-before-seen regime of low entropy. Using magnons as a thermometer, we measure temperatures as low as one nanokelvin in gases with an entropy per particle of about one thousandth of the Boltzmann constant, 0.001 k_B. I conclude by presenting the details of our procedure for calculating the entropy of our coldest, lowest entropy gases in the regime where the local density approximation does not apply.

The overall goal of this work is to provide an alternative approach to the thermographic phosphor (TP) time constant calibration method for temperature recovery. In this work two techniques are proposed that retain the pulsed source input used in the standard TP time constant calibration approach but reinterpret the phosphor response taken a fixed distance such that the single-exponential decay assumption is removed. The methods do not require knowledge of key parameters prior to data processing, nor do they involve complicated numerical schemes that attempt to fit data in the low signal-to-noise region of the phosphor response. The approaches do involve integrating the full phosphor response signal to arrive at a single value related to the integrated intensity trajectory. This value can be calibrated to temperature. One method uses the slope of the integrated intensity in the rise portion of the phosphor emission as the calibration parameter, while the second technique uses the total integral of the emission as the calibration parameter. Both techniques are validated as an effective means of TP calibration by experimental data. First, the phosphor emission response is recorded at different steady-state temperatures in order to form a calibration curve. Different regression models are investigated to determine the functional relationship that best fits the observed calibration data. Second, the phosphor is heated under transient conditions and both calibration techniques are applied to resolve the temporal temperature history of the test sample. From the experimental results, it is found that a bi-exponential based calibration curve or a rational function based calibration curve accurately predict the temperature measurements of the transient tests for both calibration procedures. However, it is suggested that the total integrated intensity method is more reliable compared to the slope calibration method since smaller error estimates are observed using the total integral in the transient sense. Another attractive feature of the integral method is that the only numerical manipulation of the raw physical experimental data to resolve the calibration parameter involves integrating the signal. The outcome of this work is highly encouraging and indicates that these techniques could be found useful in certain applications.

The purpose of this dissertation was to investigate the temporal limit on the ability to measure temperature changes using magnetic resonance imaging (MRI). The limit was examined in experiments using a variety of imaging techniques for MRI-based temperature measurements. We applied these methods for monitoring temperature changes in focused ultrasound (FUS) heating experiments. FUS is an attractive alternative to surgical resection due to its noninvasive character. FUS treatments have been successfully conducted in several clinical applications. MRI and MR thermometry is a natural choice for the guidance of FUS surgeries, given its ability to visualize, monitor, and evaluate the success of treatments. MR thermometry, however, can be a very challenging application, as good resolution is often needed along spatial, temporal as well as temperature axes. These three quantities are strictly related to each other, and normally it is theoretically impossible to simultaneously achieve high resolutions for all axes. In this dissertation, techniques were developed to achieve this at cost of some reduction in spatial coverage. Given that the heated foci produced during thermal therapies are typically much smaller than the anatomy being imaged, much of the imaged field-of-view is not actually being heated and may not require temperature monitoring. By sacrificing some of the in-plane spatial coverage outside the region-of-interest (ROI), significant gains can be obtained in terms of temporal resolution. In the extreme, an ROI can be chosen to be a narrow pencil-like column, and a sampling time for temperature imaging is possible with a temporal resolution of a few milliseconds. MRI-based thermal imaging, which maps temperature-induced changes in the proton resonance frequency, was implemented in two projects. In the first project, three previously described, fast MR imaging techniques were combined in a hybrid method to significantly speed up acquisition compared to the conventional thermometry. Acceleration factors up to 24-fold were obtained, and a temporal resolution as high as 320 milliseconds was achieved. The method was tested in a gel phantom and in bovine muscle samples in FUS heating experiments. The robustness of the hybrid method with respect to the cancellation of the fat signal, which causes temperature errors, and the incorporation of the method into an ultrafast, three dimensional sequence were also investigated. In the second project, a novel MR spectroscopic sequence was investigated for ultrafast one-dimension thermometry. Temperature monitoring was examined during FUS sonications in a gel phantom, SNR performance was evaluated in vivo in a rabbit brain, and feasibility was tested in a human heart. It was shown capable in a FUS heating experiment in a gel phantom of increasing temporal resolution to as high as 53 milliseconds in a three Tesla MRI. The temporal resolution achieved is an order of magnitude faster than any other rapid MR thermometry sequences reported. With this one-dimensional approach, a short sampling time as low as 3.6 milliseconds was theoretically achievable. However, given the SNR that could be achieved and the limited heating induced by FUS in the gel phantom in a few milliseconds, any temperature changes in such a short period were obscured by noise. We have analyzed the conditions whereby a temporal resolution of a few-milliseconds could be obtained.

Pure rotational CARS thermometry is used to study low-temperature plasma assisted oxidation kinetics in ethylene-air and hydrogen-air mixtures at stoichiometric and fuel lean conditions at 40 Torr pressure. Air and fuel-air mixtures are excited by a burst of high voltage nanosecond pulses at a pulse repetition rate of 40 kHz and a burst repetition rate of 10 Hz. The number of pulses in the burst is varied from a few pulses to a few hundred pulses and the results are compared with a fuel-air plasma chemistry model developed at The Ohio State University. Air and all fuel-air mixtures are found to agree well with the model. In ethylene-air mixtures, it is found that the heating rate is much faster than in air plasmas, primarily due to energy release in exothermic reactions of fuel with O atoms generated by the plasma. It is also found that the initial heating rate in ethylene-air mixtures is independent of equivalence ratio and is mainly controlled by the rate of radical production, specifically O atoms. At long burst durations, the heating rate in the lean mixture is significantly reduced when all of the ethylene is oxidized.In hydrogen-air mixtures, it is found that the heating rate is much faster than in air plasmas, primarily due to the heat release from reactions hydrogen with H and O atoms generated by the plasma. The pure rotational CARS temperature measurements also show a maximum in temperature after approximately 17 ms in the φ =1.0 and φ =0.5 mixtures, which is indicative of ignition. Sensitivity analysis shows that radicals generated by the plasma are important for low temperature plasma chemical fuel oxidation and associated heat release. It also shows that ignition is primarily controlled by the chain branching sequence O + H2 yields OH + H and H + O2 yields OH + O.Pure rotational CARS thermometry is also used to study a dielectric barrier discharge. It is found that in the plane to plane configuration, there is no detectable temperature rise, most likely due to the filaments moving from pulse to pulse, making it impossible to get the CARS beams into the filament. This issue is solved by using a floating electrode on the ground electrode to stabilize a filament. To ensure that the CARS beams are in a filament, for every spectrum a corresponding image is taken. Temperature measurements are taken at varying times after a 50 pulse burst and at short times after the burst (100 ns to 1 microsecond) there is approximately a 35 K increase from room temperature, while at longer times (10 – 100 microseconds) a 25 K increase is seen.

TD-22

3He films adsorbed on graphite were studied down to temperatures below 1 mK using nuclear magnetic resonance (NMR) and heat capacity as probes. This is the first work that combined heat capacity and NMR in the same cell. The substrate used was Grafoil, a form of exfoliated graphite. Continuous wave NMR was measured using conventional Q-meter circuits, whereas heat capacity was measured using the standard adiabatic method. Thermometry was based on a melting curve thermometer, which served as the primary thermometer. A platinum pulsed NMR and a lanthanum diluted cerium magnesium nitrate (LCMN) thermometers, both calibrated against the melting curve thermometer were also employed. The work focused mainly in the study of the nuclear magnetism when the film is in a solid phase. For pure 3He films, submonolayer and second layer films were investigated. Here, it was observed that the Heisenberg model is appropriate to describe both nuclear magnetic susceptibility and heat capacity of this system. However, the discrepancies in the exchange constants inferred from the different experimental probes are attributed to multiple spin exchange effects, in line with what has been observed in bulk solid 3He. Another system studied in this work was 3He adsorbed on two layers of deuterium hydride (HD) preplated graphite. In this case, a cusp in the susceptibility at a temperature of 1 mK, interpreted as indicative of a magnetic phase transition, was a particularly intriguing observation