<p dir="ltr">The chemical industry faces unprecedented pressure to reduce its carbon footprint while meeting growing global demand. As a major contributor to greenhouse gas emissions, accounting for approximately 7% of global carbon release, the sector plays a crucial role in achieving net-zero goals. This challenge is further compounded by projections suggesting that demand for chemicals could increase up to four-fold by 2050, and by the sector's role in producing several raw materials for other industries.</p><p dir="ltr">Within this context, endothermic reactors are of particular concern. The production of ethylene, propylene, and hydrogen alone accounts for around 3.6% of global CO2 emissions, representing over half of the chemical industry's total release. This situation underscores the need for alternatives in reactor design and operation.</p><p dir="ltr">To address these challenges, we introduce novel decarbonized process schemes and unit operations. The research centers around the development of Electric Reaction Towers (ERTs), a novel reactor configuration designed to ensure consistent product composition despite intense process fluctuations, such as those associated with Variable Renewable Energy (VRE). This is achieved by creating Custom Non-linear Heat Profiles (CNHPs) that maintain the key dimensionless groups of the system under dynamic conditions.</p><p dir="ltr">We present the concept of ERTs, explore their key principles, and the intuition behind their design. Additionally, we introduce Modular Reaction Towers (MRTs), which retain the benefits of handling fluctuations while addressing the investment and logistical challenges of adopting electric reactors.</p><p dir="ltr">The research employs a combination of Dimensional Analysis, Process Simulations, and Computational Fluid Dynamics (CFD) to evaluate these novel designs. Using ethylene production as a case study, we demonstrate that ERTs can enhance output by up to 4.2 times compared to state-of-the-art industrial designs.</p><p dir="ltr">The study further explores several additional concepts: Intermediate Cooling Zones (ICZs) and their potential to optimize complex reaction systems; the application of MRTs in the decentralized production of liquid hydrocarbons from shale gas to reduce flaring; and TurboQuenching, a novel approach to rapidly cool reaction products without a cooling agent while co-producing power. Finally, we discuss the broader implications of these innovations for the chemical industry's transition to more sustainable and efficient production methods.</p><p dir="ltr">By fundamentally re-thinking reactor design, this research contributes to the development of more efficient and sustainable production methods in the chemical industry, supporting the transition to a Net-Zero future.</p><p><br></p>

Células transformadas de E.coli DH5-&#945; expressando a proteína verde fluorescente (GFPuv, pico de excitação e emissão de 394nm e 509nm) foram submetidas a extração pelo método de partição de três fases (TPP) e o extrato obtido purificado por cromatografia de interação hidrofóbica (HIC). O objetivo principal deste trabalho foi estudar a termoestabilidade da GFPuv extraída, para avaliar a sua possível utilização como indicador biológico econômico, de resposta rápida e precisa para processos térmicos de esterilização utilizando o calor úmido. A estabilidade térmica da proteína foi estudada em diferentes soluções-tampão (acetato, fosfato e tris-HCI 10mM) no intervalo de valor de pH de 5,O a 9,0 e, em temperaturas entre 75&#176; e 95&#176;C. Os parâmetros de resistência térmica determinados foram: o tempo de redução decimal (Valor D - min), valor z (&#176;C), coeficiente Q10 e valor de energia de ativação (kcal/mol). A termoestabilidade da GFPuv, expressa em valor D, mostrou correlação linear para valores de pH &#8805; 5,50, em tampão acetato. Em tampão fosfato, para valores de pH &#8805; 7,50 a estabilidade térmica da proteína foi independente do valor de pH da solução. Em tampão tris-HCI, o valor D mostrou-se inconstante ao aumento do valor de pH da solução. No intervalo de temperatura estudada, em tampão acetato a GFPuv apresentou melhor termoestabilidade (Ea de 19,27 kcal/mol) do que em tampão fosfato (Ea de 26,18 kcal/mol ao valor de pH 6,S) e em tampão tris-HCI (Ea 28,19 kcallmol ao valor de pH 7,0). Em tampão acetato e tris-HCI ao valor de pH 7,0, a termoestabilidade da proteína mostrou-se equivalente. Entretanto, em tampão fosfato aos valores de pH 7,5 e 8,0 e em tampão tris-HCI aos valores de pH 8,0 e 8,5 a GFPuv apresentou menor estabilidade térmica A GFPuv apresenta potencialidade para ser utilizada como indicador biológico em processos térmicos que utilizam calor úmido às temperaturas inferiores a 100°C. / Transformed cells of Escheríchía coli DH5-&#945; expressing recombinant green fluorescent protein (GFPuv, excitation and emission peaks at 394nm and 509nm), were subjected to the three-phase partitioning (TPP) method and the release extracts were eluted through methyl HIC column with a buffer solution (10 mM Tris-HCI, 10mM EDTA, pH=8.0). The purpose of this work was to study the thermal stability of the TPP-extracted recombinant protein, GFPuv, to determine its utility as a quick, accurate and economical biological indicator for moist heat-treatments. The thermal stability of the extracted GFPuv was studied in different buffer solutions (acetate, phosphate and tris-HCI 10mM) in the range of pH between 5.0 and 9.0 and at temperature between 75-95°C. The thermal resistance parameters determinated were: decimal reduction times (D-values, min), z-value (&#1776C), Q<sub<10 coefficient and Activation Energy (Ea, Kcal/mol). The thermal stability of GFPuv, expressed in D-values, showed linear correlation for pH &#8805; 5.50 in acetate buffer. In phosphate buffer, for pH &#8805; 7.50 the thermal stability was independent of pH value. In tris-HCI buffer the D-value was shown variable with the increase of pH value. In the studied temperature range, the acetate buffer at pH 6.0 presented better thermal stability for GFPuv (Ea 19.27kcal/mol) than phosphate (Ea 26.18 kcal/mol at pH 6.5) and tris-HCI buffer (Ea 28.19 kcal/mol at pH 7.0). In acetate and tris-HCI buffers at pH 7.0, GFPuv showed equivalent thermal stability. However, GFPuv showed lower thermal stability in phosphate buffer at pH 7.5 and 8.0 and in tris-HCI buffer at pH 8.0 and 8.5. The TPP-extracted GFPuv has great potential to be applied as a biological indicator in moist heat processes at temperatures below 100°C.

Células transformadas de E.coli DH5-&#945; expressando a proteína verde fluorescente (GFPuv, pico de excitação e emissão de 394nm e 509nm) foram submetidas a extração pelo método de partição de três fases (TPP) e o extrato obtido purificado por cromatografia de interação hidrofóbica (HIC). O objetivo principal deste trabalho foi estudar a termoestabilidade da GFPuv extraída, para avaliar a sua possível utilização como indicador biológico econômico, de resposta rápida e precisa para processos térmicos de esterilização utilizando o calor úmido. A estabilidade térmica da proteína foi estudada em diferentes soluções-tampão (acetato, fosfato e tris-HCI 10mM) no intervalo de valor de pH de 5,O a 9,0 e, em temperaturas entre 75&#176; e 95&#176;C. Os parâmetros de resistência térmica determinados foram: o tempo de redução decimal (Valor D - min), valor z (&#176;C), coeficiente Q10 e valor de energia de ativação (kcal/mol). A termoestabilidade da GFPuv, expressa em valor D, mostrou correlação linear para valores de pH &#8805; 5,50, em tampão acetato. Em tampão fosfato, para valores de pH &#8805; 7,50 a estabilidade térmica da proteína foi independente do valor de pH da solução. Em tampão tris-HCI, o valor D mostrou-se inconstante ao aumento do valor de pH da solução. No intervalo de temperatura estudada, em tampão acetato a GFPuv apresentou melhor termoestabilidade (Ea de 19,27 kcal/mol) do que em tampão fosfato (Ea de 26,18 kcal/mol ao valor de pH 6,S) e em tampão tris-HCI (Ea 28,19 kcallmol ao valor de pH 7,0). Em tampão acetato e tris-HCI ao valor de pH 7,0, a termoestabilidade da proteína mostrou-se equivalente. Entretanto, em tampão fosfato aos valores de pH 7,5 e 8,0 e em tampão tris-HCI aos valores de pH 8,0 e 8,5 a GFPuv apresentou menor estabilidade térmica A GFPuv apresenta potencialidade para ser utilizada como indicador biológico em processos térmicos que utilizam calor úmido às temperaturas inferiores a 100°C. / Transformed cells of Escheríchía coli DH5-&#945; expressing recombinant green fluorescent protein (GFPuv, excitation and emission peaks at 394nm and 509nm), were subjected to the three-phase partitioning (TPP) method and the release extracts were eluted through methyl HIC column with a buffer solution (10 mM Tris-HCI, 10mM EDTA, pH=8.0). The purpose of this work was to study the thermal stability of the TPP-extracted recombinant protein, GFPuv, to determine its utility as a quick, accurate and economical biological indicator for moist heat-treatments. The thermal stability of the extracted GFPuv was studied in different buffer solutions (acetate, phosphate and tris-HCI 10mM) in the range of pH between 5.0 and 9.0 and at temperature between 75-95°C. The thermal resistance parameters determinated were: decimal reduction times (D-values, min), z-value (&#1776C), Q<sub<10 coefficient and Activation Energy (Ea, Kcal/mol). The thermal stability of GFPuv, expressed in D-values, showed linear correlation for pH &#8805; 5.50 in acetate buffer. In phosphate buffer, for pH &#8805; 7.50 the thermal stability was independent of pH value. In tris-HCI buffer the D-value was shown variable with the increase of pH value. In the studied temperature range, the acetate buffer at pH 6.0 presented better thermal stability for GFPuv (Ea 19.27kcal/mol) than phosphate (Ea 26.18 kcal/mol at pH 6.5) and tris-HCI buffer (Ea 28.19 kcal/mol at pH 7.0). In acetate and tris-HCI buffers at pH 7.0, GFPuv showed equivalent thermal stability. However, GFPuv showed lower thermal stability in phosphate buffer at pH 7.5 and 8.0 and in tris-HCI buffer at pH 8.0 and 8.5. The TPP-extracted GFPuv has great potential to be applied as a biological indicator in moist heat processes at temperatures below 100°C.

This thesis deals with the problem of waste heat, namely, the exhaust gas which are not frequently used. Specifically, it is a design of thermoelectric generators set, power electronics for fan and heat exchanger proposal. The entire system uses the energy of the waste heat to increase the heating efficiency.

The lithium-ion battery (LIB) recycling industry is currently under development to improve the yields for critical metals. However, the organic components of LIBs must also be handled, which may result in harmful chemical emissions as by-products. Of particular concern are highly persistent and mobile per- and polyfluoroalkyl substances (PFAS) that could be released during LIB recycling since some of these compounds have been linked with adverse health effects. In this work, an extensive literature review was conducted to determine the presence of fluorinated materials in state-of-the-art LIBs and the recycling conditions which could lead to the release of problematic PFAS. This information was used to develop a new analytical approach to capture the broadest range of organic and inorganic fluorine species in samples taken in different stages of the recycling process. This new method is based on a sequential extraction procedure using different solvents, followed by combustion ion chromatography (CIC) to quantify the potential emission of fluorine-containing chemicals of different polarities. The results show that organofluorine compounds are formed during recycling, particularly for the cathodes, indicating that PFAS might be present. For other samples, such as the NiMnCo salt product of recycling, only low fluorine levels were detected which implies almost complete removal. Future work should further outline the emission paths of these processes. This study highlights the necessity to further investigate the emissions related to fluorinated materials during LIB recycling and indicates that post-treatments or changes in conditions might be necessary to avoid the formation and emission of PFAS.

<p dir="ltr">The objective of this research is to advance the development and application of laser diagnostics in gas phase medium, which ranges from atmospheric non-reacting flows to turbulent reacting flows in high-pressure, high-temperature environments. Laser diagnostic techniques are powerful tools for non-intrusive and in-situ measurements of important chemical parameters, such as temperature, pressure, and species mole fractions, in harsh environments. These measurements significantly advance the knowledge across various research disciplines, such as combustion dynamics, chemical kinetics, and molecular spectroscopy. In this thesis, detailed theoretical models and experimental analysis are presented for three different techniques: 1. Chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs CARS); 2. Two-color polarization spectroscopy (TCPS); 3. Ultrafast-laser-absorption-spectroscopy (ULAS). The first chapter provides a brief survey of laser diagnostics, including both linear and nonlinear methods. The motivations behind the three studies covered in this dissertation are also discussed. </p><p dir="ltr">In the second chapter, single-shot CPP fs CARS thermometry is developed for the hydrogen molecule at 5 kHz. The results are divided into two parts. The first part concentrates on the development of H₂ CPP fs CARS thermometry for high-pressure and high-temperature conditions. The second part demonstrates the application of H₂ CPP fs CARS in a model rocket combustor at pressures up to 70 bar. In the first part, H₂ fs CARS thermometry was performed in Hencken burner flames up to 2300 K, as well as in a heated gas-cell at temperatures up to 1000 K. It was observed that the H₂ fs CARS spectra are highly sensitive to the pump and Stokes chirp. Chirp typically originates from optical components such as windows and polarizers. As a result, the pump delay is modeled to provide a shift to the Raman excitation efficiency curve. With the updated theoretical model, excellent agreement was found between the simulated and experimental spectra. The averaged error and precision are 2.8% and 2.3%, respectively. In addition, the spectral phase and pump delay determined from the experimental spectra closely align with the theoretical predictions. It is also found that pressure does not have significant effects on the H₂ fs CARS spectra up to 50 bar at 1000 K. The collision model provides excellent agreement with the experiment. This allows the use of low-pressure laser parameters for high-pressure thermometry measurements. In the second part, spatially resolved H₂ temperature was measured in a rocket chamber at pressures up to 70 bar. This is the first demonstration of fs CARS thermometry inside a high-pressure rocket combustor. These results highlight the potential of using H₂ CPP fs CARS thermometry to provide quantitative data in high-pressure experiments for the study of combustion dynamics and model validation efforts at application relevant operating conditions.</p><p dir="ltr">The third chapter presents the development of a TCPS system for the study of the NO (<i>A</i>²Σ⁺-<i>X</i>²Π) state-to-state collision dynamics with He, Ar, and N₂. Two sets of TCPS spectra for 1% NO, diluted in different buffer gases at 295 K and 1 atm, were obtained with the pump beam tuned to the R₁₁(11.5) and ^OP₁₂(1.5) transitions. The probe was scanned while the pump beam was tuned to the line center. Collision induced transitions were observed in the spectra as the probe scanned over transitions that were not coupled with the pump frequency. The strength and structure of the collision induced transitions in the TCPS spectra were compared between the three colliding partners. Theoretical TCPS spectra, calculated by solving the density matrix formulation of the time-dependent Schrödinger wave equation, were compared with the experimental spectra. A collision model based on the modified exponential-gap law was used to model the rotational level-to-rotational level collision dynamics. An unique aspect of this work is that the collisional transfer from an initial to a final Zeeman state was modeled based on the difference in the cosine of the rotational quantum number <i>J</i> projection angle with the z-axis for the two Zeeman states. Rotational energy transfer rates and Zeeman state collisional dynamics were varied to obtain good agreement between theory and experiment for the two different TCPS pump transitions and for the three different buffer gases. One key finding, in agreement with quasi-classical trajectory calculations, is that the spin-rotation changing transition rate in the <i>A</i>²Σ⁺ level of NO is almost zero for rotational quantum numbers ≥ 8. It was necessary to set this rate to near zero to obtain agreement with the TCPS spectra. </p><p dir="ltr">The fourth chapter presents the development and application of a broadband ULAS technique operating in the mid-infrared for simultaneous measurements of temperature, methane (CH₄), and propane (C₃H₈) mole fractions. Single-shot measurements targeting the C-H stretch fundamental vibration bands of CH₄ and C₃H₈ near 3.3 μm were acquired in both a heated gas cell up to ~650 K and laminar diffusion flames at 5 kHz. The average temperature error is 0.6%. The average species mole fraction error are 5.4% for CH₄, and 9.9% for C₃H₈. This demonstrates that ULAS is capable of providing high-fidelity hydrocarbon-based thermometry and simultaneous measurements of both large and small hydrocarbons in combustion gases. </p>

<p>      </p> <p>Full exploitation of shale resources requires new catalytic techniques to efficiently convert the methane, ethane, and propane found in shale gas to value-added fuels and chemicals. A promising process of converting ethane and propane involves catalytic light alkane dehydrogenation and the subsequent oligomerization of light alkenes. The first part of this work focuses on the examination of the mechanistic details of propane dehydrogenation on Pt-based alloy catalysts, where first principles-based free energy, microkinetic, and degrees of rate control analyses are performed to understand and rationalize the selective propane dehydrogenation using a Pt3Mn alloy. We show that only the under-coordinated, Mn-decorated Pt sites, represented by a Pt3Mn(211) surface, are selective to propylene formation, which can be attributed to several key mechanistic details: (1) facile propylene desorption and (2) hindered pathways that are inherently non-selective to propylene and lead to the formation of isomers. These kinetic details can, in turn, be interpreted using the free energy landscapes of propane dehydrogenation on the Pt3Mn(211) surface, which features a reasonably stronger binding of propylene than those of its isomers. From this study, we extract two selectivity descriptors for propane dehydrogenation: The energetics of propylene desorption versus deep-dehydrogenation, as well as the energetics of the formation of propylene versus its isomers. The properties can be used for designing further improved light alkane dehydrogenation catalysts.</p>

<p dir="ltr">Soot is a byproduct formed during incomplete combustion of hydrocarbon fuels. Atmospheric soot from aircraft emissions increases local air temperatures, drives cloud formation, and decreases albedo on snow and ice: three factors that promote global warming. It is also potentially harmful to humans and has been associated with negative effects on heart and lung health. Operationally, soot formation indicates an inefficiency in combustion and can cause deterioration in aircraft engines. Modeling soot formation in complex flow fields is difficult and has been largely unsuccessful. In-situ soot measurements at relevant conditions can inform the design and operation of aircraft engines with reduced soot emissions. Laser-induced incandescence (LII) is a diagnostic that allows for non-intrusive measurements of soot volume fraction and primarily particle size in combustion environments. It involves laser-heating soot particles to temperatures at which they incandescence and measuring the radiated signal. The strong absorption capabilities and high sublimation temperature of soot make this diagnostic highly selective against the detection of other species. A coupled set of differential equations can be used to model the change in temperature and mass of a soot particle over time. Methods for modeling the fundamental processes in LII were reviewed in this work and comparisons were made between several different models.</p><p dir="ltr">International Sooting Flame target conditions were used to form a laminar diffusion flame in a Yale burner with a range of soot levels. Soot volume fraction measurements were conducted and compared with other experimental values to validate the accuracy of the experimental setup and techniques used. A calibration was performed using a laser extinction measurement from a previous study. Results showed an overall increase in soot volume fraction with increasing percentages of ethylene, as well as a transition in the peak location. Time-resolved LII was conducted at 10 MHz to determine the primary particle size of soot particles. Larger primary particles were observed with increasing height for flames with higher ethylene content. Changes in the soot formation and surface growth rates are suspected factors in the observed trends in the data. </p><p dir="ltr">The overall objective of this study was to validate an experimental setup for Laser-Induced Incandescence using a laminar diffusion flame. LII measurements were successfully demonstrated using the same diagnostic setup in a liquid-fueled swirl-stabilized flame at aircraft engine-relevant conditions. This study sets the groundwork for further investigation into aircraft soot generation using LII. </p>

<p dir="ltr">Laser absorption spectroscopy (LAS) is a widely used technique to acquire path-integrated measurements of gas properties such as temperature and mole fraction. Although extremely useful, the application of LAS to study heterogeneous combustion environments can be challenging. For example, beam steering can be one such challenge that arises during measurements in heterogeneous combustion environments such as metallized propellant flames or measurements at high-pressure conditions. The ability to only obtain path integrated measurements has been a major challenge of conventional LAS techniques, especially in characterizing combustion environments with a non-uniform thermo-chemical distribution along the line of sight (LOS). Additionally, simultaneous measurements of multiple species using LAS with narrow-bandwidth lasers often necessitates employing multiple light sources. Aerospace applications, such as characterizing hypersonic flows may require ultrashort time resolution to study fast-evolving chemistry. Similarly, atmospheric entry most often requires measurements of atoms and molecules that absorb at wavelengths ranging from ultraviolet to mid-infrared. The availability of appropriate light sources for such measurements has been limited. In the past, several researchers have come up with diagnostic techniques to overcome the above-mentioned challenges to a certain extent. Most often, these solutions have been need-based while compromising on other diagnostic capabilities. Therefore, LAS diagnostics capable of acquiring broadband measurements with ultrafast time resolution and the ability to acquire measurements at wavelengths in ultraviolet through mid-infrared is required to study advanced combustion systems and for the development of advanced aerospace systems for future space missions. Ultrafast laser absorption spectroscopy is one such technique that provides broadband measurements, enabling simultaneous multi-species and high-pressure measurements. The light source utilized for ULAS provides the ultrafast time resolution necessary for resolving fast-occurring chemistry and more importantly the ability to acquire measurements at a wide range of wavelengths ranging from ultraviolet to far-infrared. The development and application of ULAS for characterizing propellant flames and hypersonic flows under non-equilibrium conditions by overcoming the above-mentioned challenges is presented here. </p><p>This work describes the development of a single-shot ultrafast laser absorption spectroscopy (ULAS) diagnostic for simultaneous measurements of temperature and concentrations of CO, NO, and H₂O in flames and aluminized fireballs of HMX (C₄H₈N₈O₈). Ultrashort (55 fs) pulses from a Ti:Sapphire oscillator emitting near 800 nm were amplified and converted into the mid-infrared through optical parametric amplification (OPA) at a repetition rate of 5 kHz. Ultimately, pulses with a spectral bandwidth of ≈600 cm^-1 centered near 4.9 µm were utilized in combination with a mid-infrared spectrograph to measure absorbance spectra of CO, NO, and H₂O across a 30 nm bandwidth with a spectral resolution of 0.3 nm. The gas temperature and species concentrations were determined by least-squares fitting simulated absorbance spectra to measured absorbance spectra. Measurements of temperature, CO, NO, and H₂O were acquired in an HMX flame burning in air at atmospheric pressure and the measurements agree well with previously published results. Measurements were also acquired in fireballs of HMX with and without 16.7 wt% H-5 micro-aluminum. Time histories of temperature and column densities are reported with a 1-σ precision of 0.4% for temperature and 0.3% (CO), 0.6% (NO), and 0.5% (H₂O), and 95% confidence intervals (C.I.) of 2.5% for temperature and 2.5% (CO), 11% (NO), and 7% (H₂O), thereby demonstrating the ability of ULAS to provide high-fidelity, multi-parameter measurements in harsh combustion environments. The results indicate that the addition of the micron-aluminum increases the fireball peak temperature by ≈100 K and leads to larger concentrations of CO. The addition of aluminum also increases the duration fireballs remain at elevated temperatures above 2000 K.</p><p dir="ltr">Next, the application of ULAS for dual-zone temperature and multi-species (CO, NO, H₂O, CO₂, HCl, and HF) measurements in solid-propellant flames is presented. ULAS measurements were acquired at three different central wavelengths (5.121 µm, 4.18 µm, and 3.044 µm) for simultaneous measurements of temperature and: 1) CO, NO, and H₂O, 2) CO₂ and HCl, and 3) HF and H₂O. Absorption measurements with a spectral resolution of 0.35 nm and bandwidth of 7 cm^-1, 18 cm^-1, and 35 cm^-1, respectively were acquired. In some cases, a dual-zone absorption spectroscopy model was implemented to accurately determine the gas temperature in the hot flame core and cold flame boundary layer via broadband absorption measurements of CO₂, thereby overcoming the impact of line-of-sight non-uniformities. Results illustrate that the hot-zone temperature of CO₂ agrees well with the equilibrium flame temperature and single-zone thermometry of CO, the latter of which is insensitive to the cold boundary layer due to the corresponding oxidation of CO to CO₂.</p><p dir="ltr">The initial development and implementation of an ultraviolet and broadband ultrafast-laser-absorption-imaging (UV-ULAI) diagnostic for one dimensional (1D) imaging of temperature and CN via its <i>B</i>²Σ⁺←<i>X</i>²Σ⁺absorption bands near 385 nm. The diagnostic was demonstrated by acquiring single-shot measurements of 1D temperature and CN profiles in HMX flames at a repetition rate of 25 Hz. Ultrashort pulses (55 fs) at 800 nm were generated using a Ti:Sapphire oscillator and then amplification and wavelength conversion to the ultraviolet was carried out utilizing an optical parametric amplifier and frequency doubling crystals. The broadband pulses were spectrally resolved using a 1200 l/mm grating and imaged on an EMCCD camera to obtain CN absorbance spectra with a resolution of ≈0.065 nm and a bandwidth of ≈4 nm (i.e. 260 cm^-1). Simulated absorbance spectra of CN were fit to the measured absorbance spectra using non-linear curve fitting to determine the gas properties. The spatial evolution of gas temperature and CN concentration near the burning surface of an HMX flame was measured with a spatial resolution of ≈10 µm. 1D profiles of temperature and CN concentration were obtained with a 1-σ spatial precision of 49.3 K and 4 ppm. This work demonstrates the ability of UV-ULAI to acquire high-precision, spatially resolved absorption measurements with unprecedented temporal and spatial resolution. Further, this work lays the foundation for ultraviolet imaging of numerous atomic and molecular species with ultrafast time resolution.</p><p dir="ltr">Ultraviolet ULAS was applied to characterize the temporal evolution of non-Boltzmann CN (<i>X</i>²Σ⁺) formed behind strong shock waves in N₂-CH₄ mixtures at conditions relevant to entry into Titan's atmosphere. An ultrafast (femtosecond) light source was utilized to produce 55 fs pulses near 385 nm at a repetition rate of 5 kHz and a spectrometer with a 2400 lines/mm grating was utilized to spectrally resolve the pulses after passing through the Purdue High-Pressure Shock Tube. This enabled broadband single-shot absorption measurements of CN to be acquired with a spectral resolution and bandwidth of ≈0.02 nm and ≈6 nm (≈402 cm^-1 at these wavelengths), respectively. A line-by-line absorption spectroscopy model for the <i>B</i>²Σ⁺←<i>X</i>²Σ⁺ system of CN was developed and utilized to determine six internal temperatures (two vibrational temperatures, four rotational) of CN from the (0,0), (1,1), (2,2) and (3,3) absorption bands. Measurements were acquired behind reflected shock waves in 5.65% CH₄ and 94.35% N₂ with an initial pressure of 1.56 mbar and incident shock speed of ≈2.1 km/s. For this test condition, the chemically and vibrationally frozen temperature of the mixture behind the reflected shock was 5000 K and the pressure was 0.6 atm. The high repeatability of the shock-tube experiments (0.3% variation in shock speed across tests) enabled multi-shock time histories of CN mole fraction and six internal temperatures to be acquired with a single-shot time resolution of less than 1 ns. The measurements revealed that CN <i>X</i>²Σ⁺ is non-Boltzmann rotationally and vibrationally for greater than 200 µs, thereby strongly suggesting that chemical reactions are responsible for the non-Boltzmann population distributions. </p><p><br></p>

Les infrastructures de transport est essentielle au maintien et à l'expansion des activités sociales et économiques dans les régions circumpolaires. À mesure que le climat se réchauffe, la dégradation du pergélisol sous les remblais a entraîné de graves dommages structuraux à la route, entraînant une augmentation importante des coûts d'entretien et une réduction de la durée de vie des infrastructures. Pendant ce temps, l'advection de chaleur déclenchée par les écoulements d’eau souterrains peut altérer le bilan énergétique du remblai et du pergélisol sous-jacent et modifier le régime thermique des remblais routiers. Cependant, peu de recherches ont été effectuées pour comprendre la synergie entre les processus thermiques de surface et souterrains des remblais routiers des régions froides. L'objectif de cette recherche était de comprendre les interactions thermiques entre l'atmosphère, le remblai routier, les écoulements d’eau et le pergélisol dans le contexte du changement climatique. Cette base, de connaissances est nécessaire pour la conception technique, l'entretien des routes et l'évaluation de la vulnérabilité des infrastructures. Les travaux de recherche ont permis de développer de nouvelles méthodes d'analyse thermique pour caractériser et identifier le rôle de l'advection thermique sur le changement de température d'un remblai routier expérimental au Yukon (Canada) en termes d’intensité, de vitesse et de profondeur de l'impact thermique. Les résultats montrent que l'augmentation de la température due aux flux de chaleur advectifs déclenchés par l’écoulement d'eau peut être jusqu'à deux ordres de grandeur plus rapide qu'en raison du seul réchauffement atmosphérique. La recherche a ensuite présenté un bilan énergétique de surface pour quantifier la quantité d'énergie entrant dans le centre et la pente du remblai avec des épaisseurs et des propriétés de neige variables. Le tout a été appuyé par des observations géothermique de plusieurs années et une grande quantité de données météorologiques. Les résultats illustrent que le bilan énergétique de surface est principalement contrôlé par le rayonnement net et moins par le flux de chaleur sensible. Le flux de chaleur transmis à la pente du remblai diminue de façon exponentielle avec l'augmentation de l'épaisseur de la neige et diminue de façon linéaire avec l’installation du couvert de neige et la longueur de la période d’enneigement. De plus, un modèle de bilan énergétique de surface et un modèle cryohydrologique entièrement couplé ont été développés pour étudier l'impact thermique de l'advection de chaleur associée à l'écoulement de l'eau souterraine sur le dégel du pergélisol et le développement de taliks (c.-à-d. zone perpétuellement non gelée dans les zones de pergélisol). Le modèle couplé a réussi à reproduire la tendance à la hausse du plafond du pergélisol (erreur absolue moyenne <0,2 m) au cours de la période 1997-2018. Les résultats montrent que l'advection de chaleur a fourni une source d'énergie supplémentaire pour accélérer le dégel du pergélisol et a doublé le taux d’augmentation de l’épaisseur de la couche active 0,1 m·a-1 à 0,19 m·a-1, par rapport au scénario où aucun écoulement d'eau ne se produit. Le talik s'est initialement formé et développé en fonction du temps sous l’effet combiné des écoulement d’eau, de l'isolation de la neige, de la construction de la route et du réchauffement climatique. Le débit d'eau souterraine a relié des corps isolés de talik et a amené le remblai de la route dans un état thermique irréversible, en raison de la rétroaction de l'eau liquide (effet de chaleur latente) piégée dans le talik. Ces résultats montrent l'importance de l'advection de chaleur induite par l'écoulement d'eau sur le régime thermique de la sous-couche (c.-à-d. la couche de matériau de remblai) et du sous-sol (c.-à-d. le matériau natif sous un remblai) du remblai lorsque le remblai routier intercepte le drainage local. De plus, les résultats obtenus soulignent la nécessité de coupler les processus thermiques de surface et souterrains dans le but d'évaluer la stabilité thermique des routes subarctiques. / Transportation infrastructure is crucial to maintaining and expanding the social and economic activities in circumpolar regions. As the climate warms, degradation of the permafrost causes severe structural damages to the road embankment, leading to large increases in maintenance costs and reductions in its lifespan. Meanwhile, heat advection triggered by mobile water flow can alter energy balance of the embankment and underlying permafrost and modify the thermal regime of road embankments. However, little research has been done to understand the synergy between surface and subsurface thermal processes of cold region road embankments. The overall goal of this research was to elucidate thermal interactions between the atmosphere, the road embankment, mobile water flow, and permafrost within the context of climate change. This knowledge is needed for engineered design, road maintenance, and infrastructure vulnerability assessment. The research first used new thermal analysis to characterize and identify the role of heat advection on temperature change of an experimental road embankment, Yukon, Canada in terms of magnitude, rate and thermal impact depth. It shows that soil temperature increase due to advective heat fluxes triggered by mobile water flow can be up to two orders of magnitude faster than due to atmospheric warming only. The research then presented a novel surface energy balance to quantify the amount of ground heat flux entering the embankment center and slope with varying snow depth and properties, supported by multi-year thermal and meteorological observations. My results illustrate that the surface energy budget is mainly controlled by net radiation, and less by the sensible heat flux. The ground heat flux released at embankment slope exponentially decreased with the increase of snow depth, and was linearly reduced with earlier snow cover and longer snow-covered period. A fully integrated surface energy balance and cryohydrogeological model was implemented to investigate the thermal impact of heat advection associated with subsurface water flow on permafrost thaw and talik (i.e., perennially unfrozen zone in permafrost areas) development. The integrated model successfully reproduced the observed increasing trend of the active layer depth (mean absolute error < 0.2 m) over the 1997-2018 period. The results show that heat advection provided an additional energy source to expedite permafrost thaw, doubling the increasing rate of permafrost table depth from 0.1 m·a-1 to 0.19 m·a-1, compared with the scenario where no water flow occurs. Talik formation and development occurred over time under the combined effect of subsurface water flow, snow insulation, road construction and climate warming. Subsurface water flow connected isolated talik bodies and triggered an irreversible thermal state for the road embankment, due to a local feedback mechanism (latent heat effect) of trapped, unfrozen water in talik. These findings elucidate the importance of heat advection induced by mobile water flow on the thermal regime of embankment subbase (i.e., a layer of fill material) and subgrade (i.e., the native material under an embankment) when the road embankment intercepts the local drainage. Furthermore, the obtained results emphasize the need to couple surface and subsurface thermal processes to evaluate the thermal stability of sub-Arctic roads.