Dissertations / Theses on the topic 'Dynamic thermography'

The ability to measure ocular surface temperature (OST) with thermal imaging offers potential insight into ocular physiology that has been acknowledged in the literature. The TH7102MX thermo-camera (NEC San-ei, Japan) continuously records dynamic information about OST without sacrificing spatial resolution. Using purpose-designed image analysis software, it was possible to select and quantify the principal components of absolute temperature values and the magnitude plus rate of temperature change that followed blinking. The techniques was examined for repeatability, reproducibility and the effects of extrinsic factors: a suitable experimental protocol was thus developed. The precise source of the measured thermal radiation has previously been subject toe dispute: in this thesis, the results of a study examining the relationships between physical parameters of the anterior eye and OST, confirmed a principal role for the tear film in OST. The dynamic changes in OST were studied in a large group of young subjects: quantifying the post-blink changes in temperature with time also established a role for tear flow dynamics in OST. Using dynamic thermography, the effects of hydrogel contact lens wear on OST were investigated: a model eye for in vivo work, and both neophyte and adapted contact lens wearers for in vivo studies. Significantly greater OST was observed in contact lens wearers, particularly with silicone hydrogel lenses compared to etafilcon A, and tended to be greatest when lenses had been worn continuously. This finding is important to understanding the ocular response to contact lens wear. In a group of normal subjects, dynamic thermography appeared to measure the ocular response to the application of artificial tear drops: this may prove to be a significant research and clinical tool.

Neurosurgery is a demanding medical discipline that requires a complex interplay of several neuroimaging techniques. This allows structural as well as functional information to be recovered and then visualized to the surgeon. In the case of tumor resections this approach allows more fine-grained differentiation of healthy and pathological tissue which positively influences the postoperative outcome as well as the patient's quality of life. In this work, we will discuss several approaches to establish thermal imaging as a novel neuroimaging technique to primarily visualize neural activity and perfusion state in case of ischaemic stroke. Both applications require novel methods for data-preprocessing, visualization, pattern recognition as well as regression analysis of intraoperative thermal imaging. Online multimodal integration of preoperative and intraoperative data is accomplished by a 2D-3D image registration and image fusion framework with an average accuracy of 2.46 mm. In navigated surgeries, the proposed framework generally provides all necessary tools to project intraoperative 2D imaging data onto preoperative 3D volumetric datasets like 3D MR or CT imaging. Additionally, a fast machine learning framework for the recognition of cortical NaCl rinsings will be discussed throughout this thesis. Hereby, the standardized quantification of tissue perfusion by means of an approximated heating model can be achieved. Classifying the parameters of these models yields a map of connected areas, for which we have shown that these areas correlate with the demarcation caused by an ischaemic stroke segmented in postoperative CT datasets. Finally, a semiparametric regression model has been developed for intraoperative neural activity monitoring of the somatosensory cortex by somatosensory evoked potentials. These results were correlated with neural activity of optical imaging. We found that thermal imaging yields comparable results, yet doesn't share the limitations of optical imaging. In this thesis we would like to emphasize that thermal imaging depicts a novel and valid tool for both intraoperative functional and structural neuroimaging.

Abstract Since ancient times, warm or cold skin on the human body has been used as a parameter in evaluating health. Changes in body temperature are attributed to diseases or disorders. The assessment of body temperature is often performed to measure fever by detecting an elevated core temperature. With techniques such as infrared thermography, it is possible to perform a non-contact temperature measurement on a large surface area. The overall aim of this thesis was to contribute to a better understanding of the hand skin temperature variability in healthy persons and in persons experiencing whitening fingers (WF). The enclosed four papers discuss issues such as thermal variability response to cold stress test (CST) in repeated investigations; the specific rewarming pattern after CST; the difference between the hand’s palmar and dorsal temperatures; and evaluating skin temperatures and response to CST in participants with WF and healthy participants. All four papers used an experimental approach involving healthy males (I-III) and females (III) as well as individuals with (IV) and without WF (I-IV). Data were generated using dynamic infrared imaging before and after a CST. The radiometric images were analyzed using image analysis and statistics. The study showed that: (I) there is variability in hand skin temperature; (II) there are cold and warm hand skin temperature response patterns; (III) the skin temperatures on the palmar and dorsal sides of the hand are closely related; and (IV) a baseline hand skin temperature measurement can distinguish between whitening fingers and controls. The conclusion of this thesis is that it is necessary to engage in thorough planning before an investigation in order to choose the most adequate method for evaluating peripheral skin temperature response depending on the question asked.

L’économie d’énergie dans le bâtiment est devenue une question préoccupante d’envergure internationale. Le secteur du bâtiment en effet, est l’un des plus énergétivores avec par exemple plus de 43% du total d’énergie produite en France, mais aussi l’un des plus polluants avec environs, 23% des émissions de gaz à effet de serre. Avec l’accroissement des ménages, et la demande par conséquent d’énergie, les problèmes ci-dessus évoqués vont décupler et devenir rapidement ingérables les années à venir, si aucune mesure n’est prise. Ainsi, pour faire face à la situation, plusieurs stratégies sont mises en œuvre aux fins de réaliser l’économie d’énergie dans le bâtiment. Il y a le volet prédiction d’énergie qui oeuvre pour l’énergie juste heure après heure ; le volet recherche et élimination de ponts thermiques, afin de réduire au minimum les déperditions d’énergie représentant environ 30% de la consommation d’énergie ; et le volet conservation d’énergie dans les parois de bâtiment pour sa réutilisation future. Notre thèse s’est penchée sur les deux derniers volets en proposant différentes méthodes de CND et des traitements appropriés permettant la mise en évidence de défauts dans les structures de bâtiment. Des approches d’estimation de matrice de transfert ont été aussi abordées, pour permettre de prévoir le comportement thermique du bâtiment soumis à une sollicitation quelconque. La grande contribution de cette thèse concerne la mise au point d’une technique de mesure de capacité de stockage in-situ. Elle est importante, car il existe quantité de logiciels proposant la composition des structures d’un bâtiment pour une capacité de stockage d’énergie donnée. Mais il n’existe aucune méthode permettant de confirmer ou d’infirmer les résultats issus de calculs artificiels. Cette thèse apporte une solution à cette situation en proposant une méthode simple, sans encombrement, facile à mettre en œuvre et offrant un résultat satisfaisant<br>Energy saving in buildings has become a major international issue. Indeed, the building sector is one the most energy consuming sectors, for instance in France it consumes more than 43% of the total produced energy, and also it is one of the most polluter with around 23% of the green house gas emissions. As more and more households appear, the energy demand will increase and the above mentioned problems will be ten times more sever making them unmanageable in the upcoming years if no measure is taken. Thus, to face this situation, many strategies have been setup in order to achieve some energy saving in buildings. Among these strategies we find the energy prediction part which deals with hour by hour right energy; the research and elimination part of thermal bridges which its main objective is to reduce as much as possible the energy losses representing around 30% of the energy consumption; and the energy conservation part in wall buildings for future recycling. Our thesis focuses on the last two parts by proposing different methods of CND as well as appropriate survey treatments which allow to highlight structural failure in buildings. Transfer matrix estimation approaches have been used to predict the thermal behavior for a building that is being put under any kind of stress.The main contribution of this thesis concerns the developing of an in-situ storage capacity measuring technique. This is important since there are many softwares proposing the structural composition of a building for a given amount of energy. Nevertheless, there isn’t any method available for confirming or invalidating the results coming from artificial calculations. This thesis brings a solution to this situation by proposing a simple method, with no obstacles, easy to setup and with satisfactory results

Heat dissipation during sport exercise is an important physiological mechanism that may influence athletic performance. Therefore, monitoring skin temperature during exercise provides important physiological information about thermoregulatory processes. Skin temperature measurements through infrared thermography have the advantages to be non-invasive and to record temperature data simultaneously from different points on a wide area of the body. The aim of the present investigation were: first, to compare three methods of thermal images analysis in skin temperature evaluation, and second to study the skin temperature dynamics during two types of physical exercise. In the present thesis three studies will be presented and discussed. The analysis of thermographic images, with the goal of obtaining a temperature value representative of a specific area, is usually performed by different methods of averaging temperature values inside a selected Region of Interest (Troi and Tot). A comparison between the methods mainly used in literature in the specific case of a muscular group of calves on a population of 33 healthy subjects is presented. Here, it is presented an alternative method (Tmax) to obtain a temperature value of a specific area based on maximal temperature detection instead of considering the average temperature on the selected area. No meaningful difference in mean temperature between Troi and Ttot was found (p = 0.9), while temperature values calculated using Tmax were higher than the above methods (p < 0.001). The high correlation among the compared methods prove that they can equally represent temperature trends in cutaneous thermographic analyses. The second and the third study presented here are applicative study investigating the skin temperature response during physical exercise. The aim of the second study was to test the hypothesis that differences exist in the dynamics of exercise-associated skin temperature changes between trained and untrained subjects. Thermoregulation of a local muscle area (muscle–tendon unit) involved in a localized steady-load exercise (standing heels raise) using infrared thermography was investigated. Seven trained female subjects and seven untrained female controls were studied. Each subject performed standing heels raise exercise for 2 min. Thermal images were recorded prior to exercise (1 min), during exercise (2 min), and after exercise (7 min). The analysis of thermal images provided the skin temperature time course, which was characterized by a set of descriptive parameters. Two-way ANOVA for repeated measures detected a significant interaction (p = 0.03) between group and time, thus indicating that athletic subjects increased their skin temperature differently with respect to untrained subjects. This was confirmed by comparing the parameters describing the speed of rise of skin temperature. It was found that trained subjects responded to exercise more quickly than untrained controls (p<0.05). In conclusion, physical training improves the ability to rapidly elevate skin temperature in response to a localized exercise in female subjects. The third study presented here is a preliminary report, since the data analysis is still in progress. It aimed to investigate the skin temperature response by using infrared thermography during slow speed low intensity exercise as compared to normal speed low intensity exercise in squat trial. We hypothesized that low intensity resistance exercise with slow movement would result in a skin temperature response slower than the one of the normal speed exercise with the same intensity. 13 active males performed 2 sessions of deep squat exercise until exhaustion, with 50% of 1 RM. The pace of movement was set in 1s eccentric / 1s concentric and 5s eccentric / 5s concentric phase in the 1st and in the 2nd session respectively. Thermal images were recorded every 20s before exercise (2min), during exercise (until exhaustion), and after exercise (10min). Surprisingly, a different behaviour of skin temperature during and after exercise was observed among subjects: a decrease in skin temperature in 9 subjects (down group) and an increase in the other 4 (up group). Thus, statistics will be performed in each group separately. It was shown that the response of cutaneous circulation to dynamic exercise is characterized by a initial vasoconstriction to dissipate heat from the core through the skin followed by vasodilation driving the blood flow from inactive tissue (including the skin) to active muscles involved in exercise. We speculate that the unexpected different behaviour of the skin temperature response in the 2 sub-groups was probably due to a time-dependent predominance of vasoconstriction over vasodilation or viceversa.

Ce travail tente de mieux comprendre les dommages par fatigue dans les aciers à ferrite-perlite dans la fatigue à très grand nombre de cycles (VHCF). Les influences de deux paramètres, le pourcentage de phase perlite et le pourcentage d'atomes interstitiels libres dans une solution solide, sont étudiées pour comprendre les mécanismes de dissipation en fatigue à 20 kHz. Une thermographie infrarouge in situ est réalisée pour enregistrer les changements de température, tandis que des observations au microscope sont menées pour étudier le mécanisme de dissipation. Pour les matériaux de BCC, sous fortes amplitudes de contrainte, une augmentation soudaine de la température se produit sans initiation de fissure ni fracture. L’augmentation inévitable de la température jusqu’à des centaines de degrés aux fortes amplitudes de contrainte est principalement due à la mobilité des dislocations vis, qui est l’une des clés permettant d’expliquer le comportement en fatigue observée de la structure du BCC sous un chargement haute fréquence. Par conséquent, les PSB en surface et les micro-vides dans la matrice émergent en masse, accompagnant cette élévation abrupte de la température. Ces phénomènes sont considérés comme une transition du mécanisme de déformation du régime thermique au régime athermique. À faible amplitude, peu de PSB ou de rugosité de surface sont encore observés. Il a été constaté que les PSB sur le fer armco étaient susceptibles d’apparaître avant 1x107 cycles et que le seuil de PSB était inférieur à la limite de fatigue conventionnelle. La présence d'atomes interstitiels libres dans les aciers entraîne l'apparition d'une augmentation secondaire de la température dans la domain de la température stabilisée à 100-200 °C. Ce comportement semble être lié à l'interaction des dislocations coins avec des atomes interstitiels libres. De plus, on pense que le phénomène remarquable de durcissement-adoucissement-durcissement après l'élévation soudaine de la température jusqu'à plus de 300 °C est l'interaction de dislocations à vis multipliées et d'atomes interstitiels libres<br>This work attempts to a better understanding of the fatigue damage in ferrite-pearlite steels in the Very High Cycle Fatigue (VHCF) domain. The influences of two parameters, pearlite phase percentage and free interstitial atoms percentage in solid solution, are investigated to understand dissipative mechanisms under 20 kHz high frequency fatigue loading. In-situ infrared thermography is carried out to record the temperature changes, while fractography studies and microscope observations are conducted to investigate the dissipative mechanism on the surface of specimens.For body centered cubic (BCC) materials, under high stress amplitudes, a sudden increase of the temperature occurs without a crack initiation and fracture. The inevitable temperature increase up to hundreds of degrees at high stress amplitudes, is caused mainly by the screw dislocations mobility, which is the key to explaining the observed fatigue behavior and thermal response of BCC structure under high frequency loading. Therefore, PSBs on surface and micro-voids in matrix emerge massively, accompanying with this abrupt temperature increase. These phenomena are considered as transition of deformation mechanism from thermal regime to athermal regime. At low amplitudes, few PSBs or surface roughness are still observed on the specimen surface. Through the cycles of PSB appearance on armco-iron, it’s found that PSBs are inclined to appear before 1x10(7)cycles, and PSB threshold lies below the conventional fatigue limit. The increase of pearlite phase content weakens the temperature elevation, and strengthens the fatigue properties. The presence of free interstitial atoms in steels results in appearence of a secondary temperature increase in the stabilized temperature part (100-200 degree). This behavior seems to be related to the interaction of edge dislocations with free interstitial atoms. Moreover, the remarkable hardening-softening-hardening phenomenon after the sudden temperature elevation to above 300 degree is thought as the interaction of multiplicated screw dislocations and free interstitial atoms

L'objectif de cette thèse est d'étudier expérimentalement les phénomènes de vieillissement dus à la diffusion des atomes en solution dans les alliages d'aluminium et les instabilités qui leur sont associées comme le phénomène Portevin-Le Châtelier ou les bandes de Lüders et de proposer une modélisation de ces phénomènes dans le cadre de la thermodynamique des processus irréversibles. Une étude expérimentale détaillée est alors entreprise sur les alliages d'aluminium AA5083-H116 et AA5182-O. Le comportement du premier présente l'effet PLC de façon prononcée et les deux types d'instabilités sont observées simultanément pour le second. La corrélation d'images numériques et la thermographie infrarouge sont essentiellement employées pour détecter et caractériser les aspects spatiotemporels des instabilités observées. La déformation non homogène due à l'apparition et la propagation de bandes de localisation est mise en évidence. Ces bandes de déformation sont visualisées, permettant à leurs diverses caractéristiques (vitesse, orientation, largeur, vitesse de déformation à l'intérieur des bandes, augmentation de la température à l'intérieur des bandes) d'être mesurées sur des éprouvettes lisses (plates, cylindriques ou prismatiques). Dans le cas des éprouvettes plates, l'effet des épaisseurs de l'éprouvette a aussi été examiné. Les caractéristiques des bandes sont aussi analysées sur d'autres géométries d'éprouvette (entaillées avec divers types d'entailles) à des vitesses de déformation différentes pour exhiber leur morphologie en présence de chargements multiaxiaux. Des simulations non linéaires et tridimensionnelles ont été effectuées en utilisant le modèle de McCormick pour montrer comment la prise en compte des phénomènes de vieillissement, même partielle, permet de décrire les hétérogénéités et le mouvement des bandes de déformation ainsi que de prévoir leurs différentes caractéristiques. Enfin, en se basant sur les mécanismes physiques à la base des phénomènes de vieillissement et en soulignant les limites du modèle de McCormick, un modèle élasto-viscoplastique prenant en considération les phénomènes de vieillissement est proposé dans le cadre de la thermodynamique des processus irréversibles.

L'objectif de la thèse est d'analyser le comportement mécanique de matériaux granulaires composites bidimensionels en terme de textures granulaires en utilisant deux approches : étude expérimentale par "thermoelastic stress analysis" et étude numérique par dynamique moléculaire. Les systèmes granulaires composites sont préparés à l'aide de cylindres en polyoxyméthylène (POM) et polyéthylène haute densité (PEHD), présentant un rapport de rigidité de 4 entre eux. Différents rapports de diamètres et de nombres de particules sont considérés. Les résultats expérimentaux et numériques sont en bon accord à l'échelle macroscopique. En particulier, le réseau fort (qui est ici caractérisé par des contraintes hydrostatiques supérieures à la valeur moyenne) contient moins de 50% des particules, et présente une distribution décroissance exponentielle quel que soit le type de particules considéré pour l'analyse (particules souples, particules rigides, toutes les particules). De plus, la distribution des contacts entre particules rigides (contacts POM-POM) est anisotrope et tend à s'organiser dans le sens de la direction du chargement extérieur appliqué, tandis que les autres types de contact agissent principalement pour maintenir le système en équilibre<br>The main objective of our dissertation is to analyze the mechanical behavior of two-dimensional composite granular materials through the granular textures. Thermoelatic stress analysis experiments and molecular dynamics simulations are used for this purpose. The composite granular systems are prepared from polyoxymethylene (POM) and high-density polyethylene (HDPE) cylinders with a stiffness ratio of about 4 between them. Different configurations in terms of ratios of diameter size and ratio of particle numbers are systematically investigated. Experimental and numerical results are good correlated at the macroscopic scale. In particular the strong network, which is here characterized by hydrostatic stresses higher than the mean value, consists of less than 50% of all particles, and exhibits an exponential decay whatever the type of particles considered for the analysis (soft, stiff, or both types). In addition, the contact distributions between stiff particles (POM-POM contacts) is anisotropic with an effort to arrange parallel to the direction of the external applied load, whereas the other types of contacts just act to sustain the granular system in equilibrium

This thesis experimentally investigates the phenomenon of ingress through gas turbine rim seals. The work focuses on developing experimental and numerical techniques for measuring the required sealing flow levels to purge the wheel-space against ingress and the effect of externally-induced ingress on the surface temperature as well as heat transfer to the rotor. Ingress is driven by a pressure difference between the mainstream annulus and wheel-space cavity resulting from the asymmetric external pressure profile in the annulus and/or the rotation of fluid in the rotor-stator wheel-space cavity. It can be prevented by pressurising the wheel-space through the supply of sealant flow. The University of Bath had measured and shown, for the first time, the thermal effects of ingress on the rotor in the wheel-space for a datum seal (axial-clearance seal) using thermo-chromic liquid crystal. However, as the previously used experimental technique with thermo-chromic liquid crystal was prone to large uncertainties, a non-intrusive temperature measurement technique using an infrared (IR) temperature sensor was developed. The new technique was successfully applied to the Bath one-stage gas turbine test facility and provided a full temperature history of the rotor surface in a transient heat transfer experiment. Moreover, a data analysis method appropriate for transient experiments using the IR temperature measurement technique was developed. The method was used to accurately calculate the heat transfer coefficient and the adiabatic surface temperature based on the full temperature history. A series of numerical experiments was carried out to develop the analysis method and the results from the numerical experiments were used to design new heat transfer experiments for both the 1 and 1.5-stage ingestion rigs of the University of Bath. Gas concentration measurements were made on the stator of the Bath one-stage gas turbine test rig to determine the variation of sealing effectiveness with sealant flow rate for four different seal geometries at design operational conditions. The IR temperature measurement technique was used to determine the effect of ingress on the heat transfer coefficient and the adiabatic wall temperature on the rotor of the ingestion test facility. Concurrent gas concentration measurements were made on the stator to compare the effects of ingress on the two discs (stator and rotor). Comparison between the adiabatic effectiveness on the rotor and the concentration effectiveness on the stator showed that the rotor was protected against the effects of ingress relative to the stator. The sealing air, which was drawn into the rotor boundary layer from the source region, thermally buffered the rotor against the ingested fluid in the core. Subsequently, a thermal buffer ratio hypothesis was developed and shown to be in good agreement with the experimental data. A previously published orifice model was modified so that the sealing effectiveness determined from the concentration measurements in a rig could be used to determine the effectiveness based on pressure measurements in an engine. There was good agreement between the effectiveness acquired from pressure measurement determined using the theoretical model and the sealing effectiveness determined from concentration measurements. It was also shown how parameters obtained from measurements of pressure and concentration in a rig could be used to calculate the sealing effectiveness in an engine.

博士<br>國立臺灣大學<br>流行病學與預防醫學研究所<br>99<br>Background and Objective: Breast thermography is an examination which delineates physiological response of the tumor. The purpose of our study is to evaluate the diagnostic performance of the two types of breast thermography- steady-state and dynamic thermography, and investigate the association of thermographic signs with breast cancer prognostic indicators, including ER (estrogen receptor), PR (progesterone receptor), HER2 (human epidermal growth factor receptor 2) statuses, clinical staging, and histologic grade. Methods: We conducted a cross-sectional study, and enrolled women who had suspicious findings on mammography or breast ultrasound. We interpreted steady-state thermography using five thermographic signs and evaluated the diagnostic performance by ROC analysis (Receiver operating characteristics) from age-adjusted multiple logistic regression model For the subpopulation of women receiving both steady-state and dynamic thermography, the interpretation was determined by the two steady-state signs and two dynamic signs. The age-adjusted logistic regression models with only steady-state signs (model A) and with both steady-state and dynamic signs (model B), and the resulting AUC (Area under the ROC curve) can be derived. The association of thermographic signs and the prognostic indicators of the cancerous lesions were estimated for steady-state thermography and dynamic thermography. Results: A total of 298 breast lesions were included for steady-state thermographic study. The AUC was 0.781 for the fitted model (95% CI: 0.683-0.855). The specificity was 30.4% when the sensitivity was 94.3%. Of the 171 cancerous lesions, two thermographic signs were inversely associated with ER (P=0.010 and 0.037), and three signs were inversely associated with PR (P=0.039, 0.020, and 0.022). Triple-negative (ER, PR, and HER2 negative) cancers tended to show higher thermographic scores than other types of cancers (P =0.029). One thermographic sign was positively associated with clinical staging (P=0.008). One thermographic sign was positively associated with histologic grade of invasive ductal carcinoma (n=128; P=0.037). There were 56 lesions with both steady-state and dynamic images available. The AUC was both 0.744 for the models A and B (95% CI: model A, 0.512-0.978; B, 0.514-0.975), and the specificity was 33.3% when the sensitivity was 100% for both models. Of the 26 malignant lesions, one of the dynamic signs was inversely associated with ER (P=0.021). The two dynamic signs were positively associated with HER2 status (P=0.015 and 0.033). One steady-state sign was positively related with the histologic grade of invasive ductal carcinoma (P=0.006; n=22). Conclusion: The specificity of breast thermography was low when the sensitivity >90%. Dynamic thermography did not show additional diagnostic yield than steady-state thermography. The thermographic signs may be predictive of breast cancer prognosis.

Neurosurgery is a demanding medical discipline that requires a complex interplay of several neuroimaging techniques. This allows structural as well as functional information to be recovered and then visualized to the surgeon. In the case of tumor resections this approach allows more fine-grained differentiation of healthy and pathological tissue which positively influences the postoperative outcome as well as the patient's quality of life. In this work, we will discuss several approaches to establish thermal imaging as a novel neuroimaging technique to primarily visualize neural activity and perfusion state in case of ischaemic stroke. Both applications require novel methods for data-preprocessing, visualization, pattern recognition as well as regression analysis of intraoperative thermal imaging. Online multimodal integration of preoperative and intraoperative data is accomplished by a 2D-3D image registration and image fusion framework with an average accuracy of 2.46 mm. In navigated surgeries, the proposed framework generally provides all necessary tools to project intraoperative 2D imaging data onto preoperative 3D volumetric datasets like 3D MR or CT imaging. Additionally, a fast machine learning framework for the recognition of cortical NaCl rinsings will be discussed throughout this thesis. Hereby, the standardized quantification of tissue perfusion by means of an approximated heating model can be achieved. Classifying the parameters of these models yields a map of connected areas, for which we have shown that these areas correlate with the demarcation caused by an ischaemic stroke segmented in postoperative CT datasets. Finally, a semiparametric regression model has been developed for intraoperative neural activity monitoring of the somatosensory cortex by somatosensory evoked potentials. These results were correlated with neural activity of optical imaging. We found that thermal imaging yields comparable results, yet doesn't share the limitations of optical imaging. In this thesis we would like to emphasize that thermal imaging depicts a novel and valid tool for both intraoperative functional and structural neuroimaging.

An infrared (IR) imaging system has been developed recently at Caltech for measuring the temperature increase during the dynamic deformation of materials. The system consists of an 8x8 HgCdTe focal plane array, with 64 parallel preamplifiers. Outputs from the 64 detector/preamplifiers are digitized using a row-parallel scheme. In this approach, all 64 signals are simultaneously acquired and held using a bank of track and hold amplifiers. An array of eight 8:1 multiplexers then routes the signals to eight 10MHz digitizers, acquiring data from each row of detectors in parallel. The maximum rate is one million frames per second. Crack tip temperature rise during dynamic deformation is known to alter the fracture mechanisms and consequently the fracture toughness of a material. However, no direct experimental measurements have ever been made to determine the same because of limited diagnostic tools. Further, the temperature rise in the vicinity of the crack tip could potentially be used as a direct measure of loading and could serve as a diagnostic tool in order to extract appropriate fracture parameters. By transcending the existing experimental limitations, this investigation presents detailed, real time evolution of the transient crack tip temperature fields in two different steels (C300 and HY100 steels), using the 2-D high speed IR camera. The crack tip temperature rise at initiation in C300 steel was found to be about 55K. In case of HY100, the crack tip temperature rise was above 90K and was seen to be a strong function of loading rate. HRR elastic-plastic singular field has been used to extract J integral evolution from the measured temperature field. Critical value of J integral at initiation was seen to increase with loading rate. An experimental investigation has been conducted to study the initiation and propagation characteristics of dynamic shear bands in C300 maraging steel. Pre-fatigued single edge notched specimens were impacted on the edge under the notch to produce shear dominated mixed mode stress fields. The optical technique of coherent gradient sensing (CGS) was employed to study the evolution of the mixed mode stress intensity factors. Simultaneously, the newly developed 2-D high speed infrared (IR) camera was employed to obtain the temperature field evolution during the initiation and propagation of the shear bands. A criterion for shear band initiation is proposed in terms of a critical mode II stress intensity factor. The IR images, for the first time, revealed the transition of crack tip plastic zone into a shear band and also captured the structure of the tip of a propagating shear band. These thermographs support the notion of a diffuse shear band tip and reveal "hot spots" distributed along the length of a well developed shear band.

Boiling is used in a wide variety of industries, including electronics cooling, distillation, and power generation. Fundamental studies on the boiling process are needed for effective implementation. Key performance characteristics of boiling are the heat transfer coefficient, which determines the amount of heat flux that can be dissipated for a given superheat, and critical heat flux(CHF), the failure point that occurs when vapor blankets the surface. The wettability of a surface is one of the key parameters that affects boiling behavior. Wetting surfaces(e.g., hydrophilic surfaces), typically characterized by a static contact angle below 90°,have better critical heat flux due to effective rewetting, but compromised heat transfer coefficients due to increased waiting times between nucleation of each bubble. Meanwhile, nonwetting surfaces (e.g., hydrophobic surfaces), characterized by static contact angles greater than 90°, have better heat transfer coefficients due to improved nucleation characteristic, but reach critical heat flux early due to surface dry out. However, recent studies have shown that the static contact angle alone offers and incomplete, and sometimes inaccurate, description of this behavior, which is instead governed entirely by the dynamic wettability. Specifically, the receding contact angle impacts the size and contact area of bubbles forming on a surface during boiling, while the advancing contact angle determines how the bubble departs. With this more complete set of wettability descriptors, three characteristic wetting regimes define the boiling behavior: hygrophilic surfaces having advancing and receding contact angles both under 90°; hygrophobic surfaces having both these dynamic contact angles over 90°;and ambiphilic surfaces having a receding contact angle less than 90°, but an advancing contact angle greater than 90°.The goal of this thesis is to experimentally characterize and compare the behavior of boiling surfaces in each of these regimes, observe the contact line behavior, and explain the mechanisms for their differences in performance.

Measurements of process variations and particle morphology are widely employed in the pulp and paper industry. Two techniques with high potential, infrared thermography and microparticle characterisation, are mainly used qualitatively. Quantitative thermography requires knowledge of the emittance, a material property which has not been measured under many process-relevant conditions. Quantitative characterisation of microparticles, e.g. pulp fines and mineral fillers, requires the analysis of a large number of particles, which can be accomplished using flow microscopes. Flow microscopes for pulp analysis have had insufficient spatial resolution to resolve fines and fillers. Additionally, there has been a lack of methods which can differentiate between fines and fillers in a mixed suspension. State-of-the-art instruments for particle image analysis were evaluated and compared to laser diffractometry, a measurement method based on scattering by diffraction. Laser diffractometry was found to be highly sensitive to the complex refractive index of the particles, and especially to its change due to moisture absorption. A high-resolution imaging flow cytometer and a high-resolution fibre analyser were found to be complementary for characterisation of pure fines and fines/filler mixtures, and superior to laser diffractometry. A method for differentiating between fines and fillers in a suspension based on their autofluorescence and side-scattering was proposed and qualitatively evaluated. Furthermore, a method for measuring the directional and integrated emittance of paper was developed and its accuracy was determined. Measurements on a wide range of samples showed that the emittance of fibre-based materials vary significantly with wavelength, pulp type, observation angle, and moisture content. By applying measured quantitative values of the emittance, the thermal energy emitted by sack paper samples during mechanical deformation could be quantitatively calculated. The increase in thermal energy at the time of rupture was found to correlate well with the elastic share of the mechanical energy that was stored in the sample during its elongation. In summary, the results of this work have facilitated the use of quantitative microparticle analysis and infrared thermography for pulp and paper applications.<br>Mätningar av processvariationer och partiklars form och storlek utförs i stor skala inom massa- och pappersindustrin. Två mättekniker med stor potential, infraröd termografi och mikropartikel-karaktärisering, används mest kvalitativt idag. Kvantitativ termografi kräver att provets emittans är känd. Emittansen är en materialegenskap som inte har mätts för många förhållanden som är relevanta inom papperstillverkning. Kvantitativ karaktärisering av partiklar kräver att ett tillräckligt stort antal partiklar analyseras, något som kan göras med flödesmikroskop. Flödesmikroskop för mäldanalys har haft otillräcklig upplösning för att karaktärisera mikrometerstora partiklar, t.ex. fines och fyllmedel. Det har heller inte funnits någon metod som kan särskilja mellan fines och fyllmedel i en blandning. Högupplösta mätinstrument för bildbaserad mikropartikelkaraktärisering utvärderades och jämfördes med en laserdiffraktometer, en mätmetod baserad på ljusspridning genom diffraktion. Laserdiffraktometerns mätresultat påverkades starkt av det brytningsindex som antogs för provet, och hur brytningsindexet ändrades med fukthalt. En högupplöst bildbaserad flödescytometer och en högupplöst fibermätare konstaterades komplettera varandra vid mätningar av mäldens finmaterial. De var även pålitligare än laserdiffraktometern vid mätningar av organiskt finmaterial. En metod för att skilja mellan organiskt och oorganiskt finmaterial i en mäld baserat på deras autofluorescens och ljusspridning presenterades och utvärderades kvalitativt. En metod för att mäta den vinkelberoende och våglängdsintegrerade emittansen hos fiberbaserade material utvecklades och dess mätnoggrannhet utvärderades. Mätningar på ett stort antal prover visade att emittansen varierade betydligt med våglängd, mäldtyp, observationsvinkel, och fukthalt. Genom att använda den uppmätta emittansen kunde den termiska energin som frigjordes av ett säckpappersprov vid brottögonblicket beräknas. Denna energi korrelerade väl med den elastiska energi som lagrades i provet medan det töjdes, fram till tidpunkten för brottet. Sammanfattningsvis har resultaten av detta arbete möjliggjort kvantitativ användning av mikropartikel-karaktärisering och infraröd termografi i massa- och papperstillämpningar.<br><p>QC 20160122</p>

<p>Microscale environments provide significant resolution and distortion challenges with respect to measurement techniques; however, with improvements to existing techniques, it is possible to gather relevant data to better understand the thermal and fluidic mechanisms at such small scales in evaporating droplets.</p> <p> </p> <p>Infrared thermography provides several unique challenges at small scales. A primary issue is that the low native resolution of traditional infrared cameras significantly hamper the collection of details of microscale features. Furthermore, surfaces exhibiting vastly different emissivities, results in inaccurate temperature measurements that can only be corrected with irradiance-based emissivity maps of the surface; however, due to the resolution limitations of infrared thermography, these emissivity maps can also display significant errors. These issues are overcome through the use of multi-frame super-resolution. The enhanced resolution allows for better capture of microscale features, therefore, enhancing the emissivity map. A quantitative error analysis of the system is conducted to quantify the feature size resolution improvement as well as the smoothing effect of super-resolution reconstruction. Furthermore, a sensitivity analysis is conducted to quantify the impact of registration uncertainty on the accuracy of the reconstruction. Finally, the improved emissivity map from super-resolution is demonstrated to show the increased accuracy over low-resolution mapping.</p> <p> </p> <p>When applied to water droplets, particularly on nonwetting surfaces, infrared thermography is confounded by the presence of nonuniform reflectivities due to the spherical curvature of the liquid-air interface. Thus, when measuring the temperature along the vertical axis of a water droplet, it is necessary to correct the reflection. Using a controlled background environment, in conjunction with the Fresnel equations, it is possible to correct the reflective effects on the interface and calculate the actual temperature profile. This allows for a better understanding of the governing mechanisms that determine the thermal transport within the droplet. While thermal conduction is the primary transport mechanism along the vertical axis of the droplet, it is determined that the temperature drop is partially dampened by the convective transport from the ambient air to the liquid interface. From this understanding revealed by the measurements, the vapor-diffusion-based model for evaporation was enhanced to better predict evaporation rates.</p> <p> </p> <p>Further exploration into the mechanisms behind droplet evaporation on nonwetting surfaces requires accurate knowledge of the internal flow behavior. In addition, the influence of the working fluid can have a significant impact on the governing mechanisms driving the flow and the magnitude of the flowrate. While water droplet evaporation has been shown to be governed by buoyancy-driven convection on nonwetting substrates, similar studies on organic liquid droplets are lacking. Particle image velocimetry is effective at generating a velocity flow field, but droplets introduce distortion due to the refraction from the spherical interface of the droplet. As such, velocity correction using a ray-tracing approach was conducted to correct the velocity magnitudes and direction. With the velocity measurements, the flow was determined to be surface-tension-driven and showed speeds that are an order of magnitude higher than those seen in buoyancy-driven flow in water droplets. This resulted in the discovery that advection plays a significant role in the transport within the droplet. As such, the vapor-diffusion-governed evaporation model was adjusted to show a dramatic improvement at predicting the temperature gradient along the vertical axis of the droplet.</p> <p> </p> <p>Armed with the knowledge of flow behavior inside droplets, it is expected that droplets with aqueous solutions should exhibit buoyancy-driven convection. The final part of this work, therefore, leverages this phenomenon to enhance mixing during reactions. Colorimetry is a technique that is widely utilized to measure the concentration of a desired sample within some liquid; the sample reacts with a reagent dye the color change is measured, usually through absorbance measurements. In particular, the Bradford assay is used to measure protein concentration by reacting the protein to a Coomassie^TM Brilliant Blue G-250. The absorbance of the dye increases, most significantly at the 590 nm wavelength, allowing for precise quantitation of the amount of protein in the solution. A droplet-based reaction chamber with buoyancy-enhanced mixing has the potential to speed up the measurement process by removing the need for a separate pre-mixing step. Furthermore, the reduced volume makes the process more efficient in terms of reactant usage. Experimental results of premixed solutions of protein sample and reagent dye show that the absorbance measurement through a droplet tracks strongly with the protein concentration. When the protein sample and dye reagent are mixed <i>in situ</i>, the complex interaction between the reactants, the mixing, and the adsorption of protein onto the substrate creates a unique temporal evolution in the measured absorbance of the droplet. The characteristic peaks and valleys of this evolution track strongly with concentration and provide the framework for measurement of concentration in a droplet-based system.</p> <p> </p> <p>This thesis extends knowledge about droplet thermal and fluidic behavior through enhanced measurement techniques. This knowledge is then leveraged in a novel application to create a simple, buoyancy-driven colorimetric reaction setup. Overall, this study contributes to the field of miniaturized, efficient reaction and measurement devices.</p>

Characterization of local boiling trends, in addition to the typically reported area-averaged trends, is essential for the robust design and implementation of phase change technologies to sensitive heat transfer applications such as electronics cooling. Obtaining the values of heat fluxes corresponding to locally varying surface temperatures has been a challenge limiting most investigations to area-averaged results. This thesis illustrates the importance of a spatially local heat transfer analysis during boiling. Pool and submerged jet impingement boiling scenarios on a silicon surface are considered at the macroscale (27.5 mm heater with multiple nucleation sites) and microscale (1000 ��m heater for isolated bubble generation), by the use of two thin film serpentine heater geometries. The macroscale heater highlights the effect of spatial variations in imposed heat flux on boiling heat transfer with a circumferentially uniform but radially non-uniform heat flux distribution. The microscale heater simulates a local hot-spot for spot cooling on an electronic device. Spatial variation in boiling heat transfer and bubble dynamics with and without a jet flow are documented using thin film voltage sensors along with qualitative and quantitative high speed imaging and infra-red thermography. Unique to this study is the documentation of local boiling curves for different radial locations on the heat transfer surface and their comparison with the corresponding area-averaged representations. It is shown here that sectionally averaged representations of boiling curves over regions of like-imposed heat flux can substantially simplify the interpretation of data while retaining important information of the local variations in heat transfer. The radial influence of the convective jet flow on the bubble dynamics and boiling heat transfer is assessed for a single circular submerged jet configuration. Varied parameters include jet exit Reynolds numbers, nozzle geometry, test fluid (deionized water and FC-72), fluid subcooling and the supplied heat flux. Distinct modifications of the surface temperature distribution imposed by the impinging jet flow are highlighted by comparing radial temperature profiles during pool and jet impingement boiling. It is demonstrated that in contrast with pool boiling, thermal overshoots during jet impingement boiling for a highly wetting fluid like FC-72 are highest in regions farthest from the impingement point. The effect of jet inertia on bubble departure characteristics are compared with pool boiling under subcooled conditions for FC-72. Qualitative high speed visualization indicates the presence of two modes of bubble generation during jet impingement boiling (a) bubble departure from the surface and (b) bubble separation from the source resulting in sliding bubbles over the surface. The effect of jet flow on bubble entrainment is depicted. Quantitative results indicate that in general departure diameters for pool and jet impingement boiling increase and plateau at a maximum value with increasing power input while no notable trends were observed in the corresponding departure frequencies. The largest departure diameters for jet impingement boiling at fixed fluid subcoolings of 10��C and 20��C were found to be smaller than that for the corresponding pool boiling test by a factor of 1.6 and 2.3, respectively.<br>Graduation date: 2013