The aim of this research is to calibrate conductive polymer nanocomposite materials for large strain sensing and develop a structural health monitoring algorithm for gossamer structures by using nanocomposites as strain sensors. Any health monitoring system works on the principle of sensing the response (strain, acceleration etc.) of the structure to an external excitation and analyzing the response to find out the location and the extent of the damage in the structure. A sensor network, a mathematical model of the structure, and a damage detection algorithm are necessary components of a structural health monitoring system. In normal operating conditions, a gossamer structure can experience normal strain as high as 50%. But presently available sensors can measure strain up to 10% only, as traditional strain sensor materials do not show low elastic modulus and high electrical conductivity simultaneously. Conductive polymer nanocomposite which can be stretched like rubber (up to 200%) and has high electrical conductivity (sheet resistance 100 Ohm/sq.) can be a possible large strain sensor material. But these materials show hysteresis and relaxation in the variation of electrical properties with mechanical strain. It makes the calibration of these materials difficult. We have carried out experiments on conductive polymer nanocomposite sensors to study the variation of electrical resistance with time dependent strain. Two mathematical models, based on the modified fractional calculus and the Preisach approaches, have been developed to model the variation of electrical resistance with strain in a conductive polymer. After that, a compensator based on a modified Preisach model has been developed. The compensator removes the effect of hysteresis and relaxation from the output (electrical resistance) obtained from the conductive polymer nanocomposite sensor. This helps in calibrating the material for its use in large strain sensing. Efficiency of both the mathematical models and the compensator has been shown by comparison of their results with the experimental data. A prestressed square membrane has been considered as an example structure for structural health monitoring. Finite element analysis using ABAQUS has been carried out to determine the response of the membrane to an uniform transverse dynamic pressure for different damage conditions. A neuro-fuzzy system has been designed to solve the inverse problem of detecting damages in the structure from the strain history sensed at different points of the structure by a sensor that may have a significant hysteresis. Damage feature index vector determined by wavelet analysis of the strain history at different points of the structure are taken by the neuro-fuzzy system as input. The neuro-fuzzy system detects the location and extent of the damage from the damage feature index vector by using some fuzzy rules. Rules associated with the fuzzy system are determined by a neural network training algorithm using a training dataset, containing a set of known input and output (damage feature index vectors, location and extent of damage for different damage conditions). This model is validated by using the sets of input-output other than those which were used to train the neural network. / Ph. D.

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第25293号 / 工博第5252号 / 新制||工||1999(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 松尾 哲司, 教授 引原 隆士, 教授 土居 伸二 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

This thesis examines the magnetic field and magnetic flow at the end of the stator synchronous machine. This problem is solid using nonlinear magnetic resistive network, which is simulating by PSpice software. A simple model of stator, consisting of stator plates, air gaps and the two-thumbs, which hold the stator together. All of this is replace magnetic nonlinear resistive network, which is then divided into elements. According to these element is a simplified model solid and analyzed.

In dieser Arbeit wird eine einheitliche physikalische Beschreibung des Feuchtespeicherverhaltens poröser Materialien gegeben, und ein anwendungsorientiertes Modell daraus abgeleitet. Insbesondere wird die Hysteresis der Feuchtespeicherung berücksichtigt. Die thermodynamischen Grundlagen der Feuchtespeicherung werden vollständig abgeleitet. Die Energie des kondensierten Wassers wird durch die Energie der freien Flüssigphase zuzüglich einer Porenwechselwirkungsenergie dargestellt. Um das Kondensationsverhalten zu beschreiben, wird ein thermodynamisches Kondensationspotential eingeführt; dabei werden ein Ungleichgewicht zwischen Kondensatphase und Wasserdampf sowie mehrere unabhängige Wassergehalte im Porensystem zur Darstellung der Hysteresis berücksichtigt. Für verschiedene in der Literatur beschriebene Sorptionsprozesse wird mit einheitlichen Zustandsgrössen das Kondensationspotential berechnet. Die Hysteresis wird als verzögerte Bewegung des Systemzustandes in der Berg- und Tallandschaft des Kondensationspotentials interpretiert. Es wurden an 11 Materialien Sorptionsmessungen im hygroskopischen Luftfeuchtebereich (0-92% RH) durchgeführt: Eine Adsorptionskurve und mehrere Desorptionskurven, sowie eine Langzeitmessung der Feuchteaufnahme bei 92% RH. Aus dem Adsorptions-Desorptionsverhältnis entnimmt man, dass der Hysteresis-Effekt typischerweise etwa 20% ausmacht. Mit den Messungen werden für alle Materialien das Modell der unabhängigen Domänen, das hysteretische thermodynamische Kondensationspotential und das Sorptionskurvensystem parametrisiert. Die Feuchteaufnahme bei dem Langzeitexperiment lässt sich durch eine bimodale Exponentialfunktion beschreiben. Die Kurven von hygroskopischer Adsorption und Desorption werden durch analytische Funktionen angenähert. Die Steigungen der Zwischenkurven werden aus den Steigungen der Hauptkurven berechnet. In gleicher Weise wird auch der überhygroskopische Bereich dargestellt, unter Zuhilfenahme externer Messdaten. Schliesslich ergeben sich zwei getrennt parametrisierte, aneinander angrenzende Sorptionsschleifen für den hygroskopischen und den überhygroskopischen Bereich. Alle Parameter werden so angepasst, dass eine grösstmögliche Übereinstimmung mit dem Domänenmodell erzielt wird.:1. Einleitung 2. Allgemeine Thermodynamik der Feuchtesorption 3. Sorptionsmodelle in einheitlicher Beschreibung 4. Experimentell untersuchte Materialien 5. Parametrisierung von Modell und Sorptionskurven 6. Zusammenfassung A.1. Details zur Theorie A.2. Details zum Experiment A.3. Details zur Parametrisierung / This work gives a unified physical description of moisture storage in very different porous materials and derives an application-oriented model, especially the hysteresis of moisture storage has been investigated extensively. A full derivation of the thermodynamics of moisture sorption is given. The energy of condensed water is described by the energy of the free liquid plus a pore interaction energy. To describe the condensation behaviour, a thermodynamic condensation potential is introduced. It takes into account a non-equilibrium between condensed water and water vapour as well as several independent moisture contents in the liquid phase to describe the hysteresis. For many different sorption processes described in literature the condensation potential is derived, using always the same state variables. Hysteresis is interpreted as a delayed movement of the system in the hill-and-valley-landscape of the condensation potential. Sorption measurements have been performed for 11 different materials in the hygroscopic region (0-92% RH). One adsorption curve and several desorption curves and also the time dependent moisture sorption at 92% RH in a long-time experiment have been measured. From the adsorption-desorption ratio it can be concluded that the influence of hygroscopic hysteresis is typically about 20%. From the measurement results, for all materials the model of independent domains, the hysteretic condensation potential and the sorption curve system are parameterised. The moisture uptake of the long-time experiment can be described by a bimodal exponential function. The curves of hygroscopic adsorption and desorption are approximated by analytical functions. The slopes of the intermediate curves are calculated from the slopes of the main curves. In the same way the overhygroscopic region is approximated, using external measurement results. Finally a model is presented with two neighbouring sorption loops, one for the hygroscopic, one for the overhygroscopic region. All parameters are fitted to the predictions of the domain model.:1. Einleitung 2. Allgemeine Thermodynamik der Feuchtesorption 3. Sorptionsmodelle in einheitlicher Beschreibung 4. Experimentell untersuchte Materialien 5. Parametrisierung von Modell und Sorptionskurven 6. Zusammenfassung A.1. Details zur Theorie A.2. Details zum Experiment A.3. Details zur Parametrisierung

Icing severely affects society, especially in the Nordic countries. Iceaccumulation can result in critical performance problems and safetyconcerns for instance in road, air and sea transportation, transmissionlines, marine and offshore structures, wind turbines and heat exchangers.Present active ice-combating approaches possess environmental,efficiency and cost drawbacks. Thus, fabricating icephobic surfaces orcoatings impeding ice formation (anti-icing), but facilitating ice removal(de-icing) is desired. However, different conditions in the environmentduring ice formation and growth add to the complexity of the problem.An icephobic surface that works for a certain application might not be agood candidate for another. These surfaces and the challenges are infocus in this thesis.Wetting properties are important for ice formation on surfaces fromthe liquid phase (often supercooled water), where the water repellency ofthe surfaces could enhance their anti-icing effect. Considering this,different hydrophobic and superhydrophobic surfaces with differentchemistry, morphology and roughness scale were prepared. Since anyinduced wetting state hysteresis on hydrophobic surfaces could influencetheir performance, the wetting stability was investigated. In particulardynamic wetting studies of the hydrophobic surfaces revealed whatsurface characteristics benefit a stable wetting performance. Further, theeffect of temperature, particularly sub-zero temperatures, on the wettingstate of flat and nanostructured hydrophobic surfaces was investigated.This was complemented with studies of the wetting stability of sessilewater droplets on flat to micro- and multi-scale (micro-nano) roughhydrophobic samples in a freeze-thaw cycle. To be consistent with mostapplications, all temperature-controlled experiments were performed inan environmental condition facilitating frost formation. Further, antiicingproperties of hydrophobic surfaces with different topography butsimilar chemistry were studied by freezing delay measurements.A dynamic wetting study using hydrophobic samples with similarchemistry but different topography revealed that multi-scale roughnesscould benefit the wetting stability. However, when these surfaces areutilized at low temperatures the wetting hysteresis observed during acooling/heating cycle is significant. Such a temperature-inducedhysteresis is also significant on superhydrophobic surfaces. I attributethis to condensation followed by frost formation facilitating spreading of  the supercooled water droplet. The freezing delay measurementsdemonstrate no significant effect of surface topography on anti-icingproperties of hydrophobic surfaces, however the flat surfaces showed thelongest delay. These findings are in agreement with heterogeneous icenucleation theory, suggesting preferential ice nucleation in concave sites,provided they are wetted.In the second part of this thesis, I consider the findings from theprevious part illustrating the limitations of (super)hydrophobic surfaces.The de-icing properties of hydrophilic surfaces with a hydration waterlayer, hypothesized to lubricate the interface with ice, were studied. Heretemperature-controlled shear ice adhesion measurements, down to -25oC, were performed on an adsorbed layer of a polymer, either bottle-brushstructured poly(ethylene oxide) or linear poly(ethylene oxide). The iceadhesion strength was reduced significantly on the bottle-brushstructured polymer layer, specifically at temperatures above -15 oC,whereas less adhesion reduction was observed on the layer formed by thelinear polymer. These findings are consistent with differential scanningcalorimetry (DSC) data, demonstrating that the hydration water, boundto the bottle-brush structured polymer, is in the liquid state at thetemperatures where de-icing benefit is observed. Further, continuingwith the hypothesis of the advantage of surfaces with a natural lubricantlayer for de-icing targets, I studied shear ice adhesion on the molecularlyflat basal plane of hydrophilic mica down to -35 oC. Interestingly, ultralowice adhesion strength was measured on this surface. I relate this to theproposed distinct structure of the first ice-like but fluid water layer onmica, with no free OH groups, followed by more bulk liquid-like layers.This combined with the molecularly smooth nature of mica results in aperfect plane for ice sliding. / Isbildning har en stark inverkan på samhället, speciellt i de nordiskaländerna. Isuppbyggnad kan resultera i kritiska prestandaproblem ochsäkerhetsrisker inom t.ex. väg-, luft-, och sjötransport, kraftledningar,marina- och offshorestrukturer, vindkraftverk och värmeväxlare.Nuvarande aktiva isbekämpningsmetoder uppvisar brister i avseende påmiljö, effektivitet och kostnad. Det finns därmed ett behov av attframställa ytor eller ytbeläggningar som förhindrar isbildning (antiisning)eller underlättar borttagandet av redan bildad is (avisning). Dockkompliceras problemet av de många olika förhållanden under vilka is kanbildas. En beläggning som fungerar för en viss tillämpning behöver intenödvändigtvis vara en bra kandidat för en annan. Dessa ytor ochutmaningar relaterade till dem är i fokus i denna avhandling.Vätningsegenskaper är viktiga för isbildning på ytor från vätskefas(ofta underkylt vatten), och det har visats att vattenavstötande ytor i vissasammanhang kan motverka isbildning. Med detta i åtanke framställdesolika hydrofoba och superhydrofoba ytor, med varierande kemi,morfologi och ytråhet. Eftersom en förändring i de hydrofoba ytornasvätningsegenskaper kan påverka deras funktion studerades vätningsstabilitetenför dessa ytor. I synnerhet dynamiska vätningsstudier av dehydrofoba ytorna avslöjade vilka ytegenskaper som är fördelaktiga förvätningsstabiliteten. Vidare studerades hur temperaturen, särskilt undernoll grader, påverkar vätningstillståndet på släta och nanostruktureradehydrofoba ytor. Arbetet kompletterades med studier av vätningsstabilitetenför vattendroppar på släta samt mikro- och multistrukturerade(mikro-nano) hydrofoba ytor under flera frysningsupptiningscykler.För att vara i linje med de flesta tillämpningar, utfördesalla temperaturkontrollerade mätningar i en miljö där frost kunde bildaspå ytorna. Anti-isegenskaperna hos de hydrofoba ytorna med varierandetopografi men samma kemi studerades vidare genom att studera hur långtid det dröjde innan en vattendroppe på ytan fryste vid en visstemperatur.De dynamiska vätningsstudierna på hydrofoba ytor med samma kemimen olika topografi avslöjade att en ytråhet på flera längdskalor kan haen positiv inverkan på vätningsstabiliteten. När dessa ytor är exponeradeför låga temperaturer är dock vätningshysteresen under en nedkylnings-/uppvärmnings-cykel significant. Den temperatur-inducerade hysteresenär också betydande för superhydrofoba ytor. Detta tillskriver jag  kondensation på ytan som följs av frostbildning, vilket i sin tur möjliggörspridning av den underkylda vattendroppen på ytan. Mätning avfördröjningen i frysningsförloppet påvisade ingen betydande effekt avyttopografin för hydrofoba ytor, men släta hydrofoba ytor uppvisade denlängsta fördröjningen. Dessa resultat är i överensstämmelse med rådandeheterogen iskärnbildningsteori, som visar på fördelaktig iskärnbildningpå konkava delar av ytan, förutsatt att dessa väts.I den andra delen av avhandlingen utnyttjar jag observationerna frånden första delen vilka illustrerade begränsningarna för superhydrofobaytor, och söker en annan lösning. Avisningsegenskaper för hydrofilastarkt hydratiserade ytor studerades, med hypotesen att hydratiseringkan smörja gränsskiktet med is. Temperatur-kontrolleradeisadhesionsmätningar ned till -25 °C utfördes på adsorberade skikt av enpolymer med många sidokedjor av polyetylenoxid (”bottle-brush”), såvälsom på ett skikt av linjär polyetylenoxid. Isadhesionen blev kraftigtreducerad på ”bottle-brush”-polymeren, speciellt vid temperaturer högreän -15°C. Däremot kunde knappast ingen minskad isadhesion observerasför den linjära polymeren. Dessa observationer överensstämmer meddifferentialskanningskalorimetri (DSC) data, som visar att dethydratiserade vattenskiktet, vilket är bundet till ”bottle-brush”-polymeren, är i vätskeform vid de temperaturer där avisningsfördelar ärobserverade. För att vidare undersöka hypotesen att det vore fördelaktigtmed ett naturligt smörjande skikt på ytan för att uppnå godaavisningsegenskaper, utförde jag isadhesionsmätningar på molekylärtsläta glimmerytor ner till -35 °C. Intressant nog uppmättes extremt lågisadhesion på denna yta. Detta relaterar jag till den föreslagna utprägladehydratiseringsstrukturen, bestående av ett första is-liknande vattenskiktutan fria OH-grupper, följt av ett mer bulkliknande skikt. Detta ikombination med den molekylärt släta naturen hos glimmer resulterar iett perfekt plan för isen att glida på. / <p>QC 20160504</p> / TopNano

Lubricated friction issues are central to all hydraulic actuation systems undergoing motion and any in-depth understanding of the nature of lubricated friction will advance future component design. The classic friction models of hydraulic actuation systems under steady state conditions and their dependency on velocity and temperature have been studied extensively over the past years. A model which is commonly employed to represent the characteristics of friction is that of Stribeck in which the dependency of the friction force is based on velocity alone. However, experimentally, it has been found that lubricated friction is dependent on acceleration. Thus, the Stribeck model can be considered as a subset of a dynamic friction model in which acceleration is zero. Thus, it can be concluded that the Stribeck model is best applied to cases when the change rate of the velocities is very small. This thesis considers the dependency of lubricated friction on acceleration when pressure and temperature changes are relatively constant. As such, the basic hypothesis for this study was proposed as follows: “Lubricated friction in hydraulic actuation systems is not only a function of velocity, but is also a function of both velocity and acceleration”. In this thesis several terms are defined which facilitate the description under which friction models are developed. For example, the term non-steady state friction is used to account for the effect of acceleration on lubricated friction force while in motion. Further, the lubricated friction models are divided into two groups: steady state friction models and non-steady state friction models. Nonlinear friction modeling and measuring methods are reviewed in this dissertation. This review also includes nonlinear lubricated friction modeling in hydraulic actuation systems. A conclusion from this review was that limited research has been done in documenting and explicitly demonstrating the role of acceleration on lubricated friction. The research first introduced a methodology to experimentally measure friction as a function of acceleration and to demonstrate this dependency in the form of a three dimensional graph. A novel technique to experimentally obtain data for the lubricated friction model was introduced. This allowed the lubricated friction forces to be measured as a function of velocity in a continuous manner, but with acceleration being held constant as a family parameter. Two different valve controlled hydraulic actuation systems (VCHAS) were studied under a wide variety of accelerations at constant temperature and pressure. To enable repeatable data collection for the different friction conditions and to accommodate for the effect of hysteresis, a periodic parabolic displacement waveform was chosen which enabled the acceleration to be a family parameter. The second phase of the research introduced a method of representing the data (lubricated friction model) in a lookup table form. The relationship of lubricated friction (in this work, pressure differential, ΔP across the actuator) as a function of velocity and acceleration was presented in a unique semi-empirical 2D lookup table (2D LUT). Limitations of this experimental approach were identified, but the dependency on acceleration was clearly established. The last phase of the study implemented this 2D LUT model into a practical software model of an actuator and demonstrated its accuracy when compared to its experimental counterpart. The semi-empirical model (2D LUT) was experimentally verified by implementing the semi-empirical and Stribeck models into a real time simulation of an actuator and by comparing the experimental outputs against simulated outputs for a common sinusoidal input. A sinusoidal actuator displacement input was chosen to test the simulations as it was not used in the collection of the original data. The output of the simulation was compared to the experimental results and it was evident that for the range in which data could be collected in developing the model, the proposed 2D LUT model predicted an output that was superior to a model which used a standard Stribeck model. It was concluded that the semi-empirical model could be integrated into a simulation environment and predict outputs in a superior fashion when compared to the Stribeck friction model. Thus it was concluded that the stated hypothesis is consistent with the experimental evidence shown by all hydraulic actuators considered. Further, it was also observed that the traditional Stribeck form (steady state dynamic friction) does change with increasing acceleration to the point that the standard breakaway friction almost disappears. It is evident that the 2D LUT is a viable tool for modeling the non-steady state friction of hydraulic actuation systems. The semi-empirical 2D LUT model so developed is a more global representation of hydraulic actuator lubricated friction. In this research, only linear hydraulic actuators were considered; however, the novel nonlinear semi-empirical 2D LUT lubricated friction model can be applied to any actuator (linear and rotary) and provides a new way in which the dynamic friction can be viewed and modeled.

Phan (2003)等人的研究首先採用網路結構的觀點，來進行在獨占市場下的消費行為分析。本文延伸Phan等人的研究，採用多樣性的不同網路結構，特別是以「無標度網路」(scale-free)作為市場背後的網路結構，藉此來探討網路對於市場需求行為的影響。同時，為了有效地進行量化分析，我們建立了一些數學公式，以便能夠精準地比較不同網路對於需求面的影響程度，其中包含了消費者剩餘、雪崩效果和磁滯效果等。在實驗結果中，我們發現網路結構的確會影響到消費行為的表現，並且當市場規模變大時，仍存在著一些因網路不同而有的差異性。 / The economic implications of network topologies are studied via a monopolist's model of market networks originally proposed by Phan, et al. (2003). By embedding the market into a larger collection of network topologies, in particular, a class of scale-free networks, we extend the early analysis built upon a class of ring networks. To facilitate the study of the impacts of network topologies upon market demand, various measures concerning social welfare (the consumer's surplus), the avalanche effect, and the hysteresis effect, are formally established. Comparisons based on these measures show that network topologies matter, and their implied differences will remain even when the network size becomes large.

External post-tensioning is an attractive technique for strengthening reinforced concrete structures because of its ability to actively control stresses and deflections, speed of installation, minimum interruption for the existing structure, and ease of inspection under service conditions. However, external prestressing implies exposing the tendons to the environment outside the concrete section, which may lead to corrosion in steel tendons. Therefore, the interest in using fiber reinforced polymer (FRP) tendons, which are corrosion resistant, has increased. The present work investigated, experimentally and analytically, the flexural performance of reinforced concrete beams strengthened with externally post-tensioned Carbon FRP (CFRP) tendons, under monotonic and fatigue loadings. Initially, tensile fatigue tests were carried out on CFRP tendon-anchor assemblies to assess their response under repeated cyclic loads, before implementing them in the beam tests. New wedge-type anchors (Waterloo anchors) were used in gripping the CFRP specimens. The assemblies exhibited excellent fatigue performance with no premature failure occurring at the anchorage zone. The fatigue tests suggested a fatigue limit of a stress range of 10% of the tendon ultimate capacity (approximately 216 MPa). Monotonic and fatigue experiments on twenty-eight beams (152x254x3500 mm) were then undertaken. Test parameters included the tendon profile (straight and double draped), the initial loading condition of the beam prior to post-tensioning (in-service and overloading), the partial prestressing ratio (0.36 and 0.46), and the load ranges applied to the beam during the fatigue life (39% to 76% of the yield load). The CFRP tendons were post-tensioned at 40% of their ultimate capacity. The monotonic tests of the post-tensioned beams suggested that overloading the beam prior to post-tensioning increased the beam deflections and the strains developed in the steel reinforcing bars at any stage of loading. However, overloading had no significant effect on the yield load of the strengthened beam and the mode of failure at ultimate. It also had no discernable effect on the increase in the tendon stress at yielding. The maximum increase in the CFRP stress at yield load was approximately 20% of the initial post-tensioning stress, for the in-service and overloaded beams. A very good performance of the strengthened beams was observed under fatigue loading. The fatigue life of the beams was mainly governed by the fatigue fracture of the internal steel reinforcing bars at a flexural crack location. Fracture of the bars occurred at the root of a rib where high stress concentration was likely to occur. No evidence of wear or stress concentration were observed at the deviated points of the CFRP tendons due to fatigue. The enhancement in the fatigue life of the strengthened beams was noticeable at all load ranges applied. Post-tensioning considerably decreased the stresses in the steel reinforcing bars and, consequently, increased the fatigue life of the beams. The increase in the fatigue life was slightly affected by the loading history of the beams. At the same load range applied to the beam, increasing the amount of the steel reinforcing bars for the same post-tensioning level decreased the stress range in the bars and significantly increased the fatigue life of the strengthened beams. In the analytical study, a monotonic model that predicts the non-linear flexural response of the CFRP post-tensioned beams was developed and implemented into a computer program. The model takes into account the loading history of the strengthened beams prior to post-tensioning (in-service and overloading). Good agreement was obtained between the measured and the predicted monotonic results. A strain-life based fatigue model was proposed to predict the fatigue life of the CFRP post-tensioned beams. The model takes into consideration the stress-strain history at the stress raisers in the steel bars. It accounts for the inelastic deformation occurring at the ribs during cycling and the resulting changes in the local mean stresses induced. Good agreement between the experimental and predicted fatigue results was observed. A step-by-step fatigue design approach is proposed for the CFRP externally post-tensioned beams. General conclusions of the study and recommendations of future work are given.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Justification: Le glaucome entraîne une perte progressive de la vision causée par la détérioration du nerf optique. Le glaucome est répandu dans le monde et cause la cécité dans environ sept millions de personnes. Le glaucome touche plus de 400 000 Canadiens et sa prévalence augmente avec le vieillissement de la population.1,2 Il s'agit d'une maladie chronique surnoise dont les symptômes se manifestent uniquement lors des stades avancés et qui peuvent mener à la cécité. Présentement, le seul moyen possible d’arrêter la progression du glaucome au stade initial est de diminuer la pression intra-oculaire (PIO). Les analogues de prostaglandines (APG) topiques sont fréquemment utilisées comme traitement de première ligne. Cependant, la recherche démontre que cette classe de médicaments peut changer certaines propriétés de la cornée, et possiblement influencer la mesure de la PIO.3 Objectif: À déterminer si l'utilisation d'APG affecte les propriétés biomécaniques de la cornée. La conclusion sera basée sur l'analyse intégrée des résultats obtenus de l'analyseur Reichert oculaire Réponse (ORA), la tonométrie par applanation de Goldmann (TAG) et la pachymétrie ultrasonographique. Le deuxième objectif potentiel de cette étude est de déterminer la corrélation, le cas échéant, entre les propriétés biomécaniques de la cornée, l'épaisseur de la cornée centrale (ECC) et la PIO chez les patients subissant un traitement d’APG topique. L'hypothèse principale de cette étude est que l’APG influence les propriétés de la cornée telles que l'épaisseur centrale, l'élasticité et la résistance. Patients et méthodes : Soixante-dix yeux de 35 patients, âgés de 50-85 ans, atteints de glaucome à angle ouvert (GAO) et traités avec APG topique ont été examinés. Seulement les sujets avec une réfraction manifeste entre -6,00 D et +4,25 D ont été inclus. Les critères d'exclusion sont: patients avec n'importe quelle autre maladie de la cornée de l’œil, telles que la dystrophie endothéliale de Fuch’s et kératocône, ou tout antécédent de traumatisme ou d'une chirurgie de la cornée, ainsi que le port de lentilles de contact. Nous avons demandé aux patients atteints du glaucome qui ont des paramètres stables et qui utilisent l’APG dans les deux yeux de cesser l’APG dans l'œil moins affecté par la PIO, et de continuer l’utilisation d’APG dans l'œil contralatéral. Le meilleur œil est défini comme celui avec moins de dommage sur le champ visuel (CV) (déviation moyenne (DM), le moins négatif) ou une PIO maximale historique plus basse si la DM est égale ou encore celui avec plus de dommage sur la tomographie par cohérence optique (TCO, Cirrus, CA) ou la tomographie confocale par balayage laser (HRT, Heidelberg, Allemagne). Toutes les mesures ont été prises avant la cessation d’APG et répétées 6 semaines après l’arrêt. Les patients ont ensuite recommencé l’utilisation d’APG et toutes les mesures ont été répétées encore une fois après une période supplémentaire de 6 semaines. Après commencer ou de changer le traitement du glaucome, le patient doit être vu environ 4-6 semaines plus tard pour évaluer l'efficacité de la goutte.4 Pour cette raison, on été décidé d'utiliser 6 semaines d'intervalle. Toutes les mesures ont été effectuées à l’institut du glaucome de Montréal par le même technicien, avec le même équipement et à la même heure de la journée. L'œil contralatéral a servi comme œil contrôle pour les analyses statistiques. La tonométrie par applanation de Goldmann a été utilisée pour mesurer la PIO, la pachymétrie ultrasonographique pour mesurer l'ECC, et l’ORA pour mesurer les propriétés biomécaniques de la cornée, incluant l'hystérèse cornéenne (HC). L’hypothèse de l'absence d'effet de l'arrêt de l’APG sur les propriétés biomécaniques a été examiné par un modèle linéaire à effets mixtes en utilisant le logiciel statistique R. Les effets aléatoires ont été définies à deux niveaux: le patient (niveau 1) et l'œil de chaque patient (niveau 2). Les effets aléatoires ont été ajoutés au modèle pour tenir compte de la variance intra-individuelle. L’âge a également été inclus dans le modèle comme variable. Les contrastes entre les yeux et les temps ont été estimés en utilisant les valeurs p ajustées pour contrôler les taux d'erreur internes de la famille en utilisant multcomp paquet dans R. Résultats: Une augmentation statistiquement significative due l 'HC a été trouvée entre les visites 1 (sur APG) et 2 (aucun APG) dans les yeux de l'étude, avec une moyenne (±erreur standard) des valeurs de 8,98 ± 0,29 mmHg et 10,35 ± 0,29 mmHg, respectivement, correspondant à une augmentation moyenne de 1,37 ± 0,18 mmHg (p <0,001). Une réduction significative de 1,25 ± 0,18 mmHg (p <0,001) a été observée entre les visites 2 et 3, avec une valeur moyenne HC finale de 9,09 ± 0,29 mmHg. En outre, une différence statistiquement significative entre l’oeil d’étude et le contrôle n'a été observée que lors de la visite 2 (1,01 ± 0,23 mmHg, p <0,001) et non lors des visites 1 et 3. Une augmentation statistiquement significative du facteur de résistance conréen (FRC) a été trouvée entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 10,23 ± 0,34 mmHg et 11,71 ± 0,34 mmHg, respectivement. Le FRC a ensuite été réduit de 1,90 ± 0,21 mmHg (p <0,001) entre les visites 2 et 3, avec une valeur moyenne FRC finale de 9,81 ± 0,34 mmHg. Une différence statistiquement significative entre l’oeil d’étude et le contrôle n'a été observée que lors de la visite 2 (1,46 ± 0,23 mmHg, p <0,001). Une augmentation statistiquement significative de l'ECC a été trouvée entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 541,83 ± 7,27 µm et 551,91 ± 7,27 µm, respectivement, ce qui correspond à une augmentation moyenne de 10,09 ± 0,94 µm (p <0,001). L'ECC a ensuite diminué de 9,40 ± 0,94 µm (p <0,001) entre les visites 2 et 3, avec une valeur moyenne finale de 542,51 ± 7,27 µm. Une différence entre l’étude et le contrôle des yeux n'a été enregistré que lors de la visite 2 (11,26 ± 1,79 µm, p <0,001). De même, on a observé une augmentation significative de la PIO entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 15,37 ± 0,54 mmHg et 18,37 ± 0,54 mmHg, respectivement, ce qui correspond à une augmentation moyenne de 3,0 ± 0,49 mmHg (p <0,001). Une réduction significative de 2,83 ± 0,49 mmHg (p <0,001) a été observée entre les visites 2 et 3, avec une valeur moyenne de la PIO finale de 15,54 ± 0,54 mmHg. L’oeil de contrôle et d’étude ne différaient que lors de la visite 2 (1,91 ± 0,49 mmHg, p <0,001), ce qui confirme l'efficacité du traitement de l’APG. Lors de la visite 1, le biais de la PIO (PIOcc - PIO Goldmann) était similaire dans les deux groupes avec des valeurs moyennes de 4,1 ± 0,54 mmHg dans les yeux de contrôles et de 4,8 ± 0,54 mmHg dans les yeux d’études. Lors de la visite 2, après un lavage de 6 semaines d’APG, le biais de la PIO dans l'œil testé a été réduit à 1,6 ± 0,54 mmHg (p <0,001), ce qui signifie que la sous-estimation de la PIO par TAG était significativement moins dans la visite 2 que de la visite 1. La différence en biais PIO moyenne entre l'étude et le contrôle des yeux lors de la visite 2, en revanche, n'a pas atteint la signification statistique (p = 0,124). On a observé une augmentation peu significative de 1,53 ± 0,60 mmHg (p = 0,055) entre les visites 2 et 3 dans les yeux de l'étude, avec une valeur de polarisation finale de la PIO moyenne de 3,10 ± 0,54 mmHg dans les yeux d'études et de 2,8 ± 0,54 mmHg dans les yeux de contrôles. Nous avons ensuite cherché à déterminer si une faible HC a été associée à un stade de glaucome plus avancé chez nos patients atteints du glaucome à angle ouvert traités avec l’APG. Lorsque l'on considère tous les yeux sur l’APG au moment de la première visite, aucune association n'a été trouvée entre les dommages sur le CV et l'HC. Cependant, si l'on considère seulement les yeux avec un glaucome plus avancé, une corrélation positive significative a été observée entre la DM et l'HC (B = 0,65, p = 0,003). Une HC inférieure a été associé à une valeur de DM de champ visuelle plus négative et donc plus de dommages liés au glaucome. Conclusions : Les prostaglandines topiques affectent les propriétés biomécaniques de la cornée. Ils réduisent l'hystérèse cornéenne, le facteur de résistance cornéen et l'épaisseur centrale de la cornée. On doit tenir compte de ces changements lors de l'évaluation des effets d’APG sur la PIO. Plus de recherche devrait être menées pour confirmer nos résultats. De plus, d’autres études pourraient être réalisées en utilisant des médicaments qui diminuent la PIO sans influencer les propriétés biomécaniques de la cornée ou à l'aide de tonomètre dynamique de Pascal ou similaire qui ne dépend pas des propriétés biomécaniques de la cornée. En ce qui concerne l'interaction entre les dommages de glaucome et l'hystérésis de la cornée, nous pouvons conclure qu' une HC inférieure a été associé à une valeur de DM de CV plus négative. Mots Clés glaucome - analogues de prostaglandines - hystérèse cornéenne – l’épaisseur de la cornée centrale - la pression intraoculaire - propriétés biomécaniques de la cornée. / Rationale: Glaucoma is a chronic disease that causes a gradual loss of vision due to progressive damage to the optic nerve. It is widespread in the world and causes blindness in about seven million people. In addition, it affects more than 400,000 Canadians and its prevalence is increasing with the aging of the population.1, 2 Glaucoma becomes symptomatic only in the more advanced stages of the disease, and currently, the goal of treatment is to halt the progression of the disease by lowering the intra-ocular pressure (IOP). Topical prostaglandin analogs (PGA) are currently the first line treatment, however research has shown that this class of medications may change certain properties of the cornea, and hence the measurement of IOP.3 Aim: To determine whether the use of topical prostaglandin analogs (PGA) affects the biomechanical properties of the cornea. The conclusion will be based on the integrated analysis of the data collected from the Reichert Ocular Response Analyzer (ORA), Goldmann tonometry and ultrasound pachymetry. The second potential aim of this study is to determine the correlations, if any, between the biomechanical properties of cornea, the Central Corneal Thickness (CCT) and IOP in patients undergoing topical PGA treatment. The main hypothesis of this study is that the PGA drops influence the properties of the cornea such as central thickness, elasticity and resistance. Patients and Methods: In this study, seventy eyes of 35 patients, aged 50 - 85 years, with open angle glaucoma (OAG) and treated with topical PGA were examined. Only subjects with a manifest refraction between -6.00 D and +4.25 D were included. Exclusion criteria included patients with any other corneal eye disease, such as Fuch’s endothelial dystrophy or keratoconus, or any past history of corneal trauma or surgery. Contact lens wearers were also excluded. Patients with stable glaucoma parameters who were using topical PGA in both eyes prior to the start of the study were asked to discontinue the PGA in the best eye and to continue the application of PGA to the contralateral eye. The "best" eye, representing the eye with the least amount of glaucoma-related damage, was selected based on the results of the Humphrey Visual Field (HFA, Carl Zeiss Meditec, Inc., Dublin, CA), Heidelberg Retinal Tomography (HRT II, Heidelberg Engineering GmbH, Heidelberg, Germany), Optical Coherence Tomography (CIRRUS HD-OCT, Carl Zeiss Meditec, Inc., Dublin, CA) and maximum IOP. The contralateral eye served as a control for statistical analyses. Corneal measurements were taken before PGA cessation and repeated 6 weeks after cessation. Patients then restarted the use of PGA and all measurements were repeated once more after an additional 6 weeks. After starting or changing glaucoma treatment the patient should be seen approximately 4-6 weeks later to assess efficacy of the drop.4 For this reason it was decided to use 6 weeks interval. All measurements were performed at The Montreal Glaucoma Institute by the same trained technician, with the same equipment and at the same time of day. Goldmann applanation tonometry was used to measure the patient’s intraocular pressure (IOP), ultrasound pachymetry was used to measure central corneal thickness (CCT) and the ORA provided the measurements of the corneal biomechanical properties, including corneal hysteresis (CH). The hypothesis of no effect regarding the discontinuation of PGA on the biomechanical properties was examined by a linear mixed-effect model using the nlme package in R. Random-effects was defined on two levels: the patient (level-1) and the eye within each patient (level-2). Those random-effects were added to the model to account for the intra-individual variance due to the repeated-measure design. Age was also included in the model as a covariate. Contrasts between the eyes and times were estimated using adjusted p-values to control for familywise error rate using multcomp package in R. Results: A statistically significant increase in CH was found between Visit 1 (on PGA) and Visit 2 (no PGA) in the study eyes, with mean (±Standard Error) values of 8.98 ± 0.29 mmHg and 10.35 ± 0.29 mmHg, respectively, corresponding to a mean increase of 1.37 ± 0.18 mmHg (p < 0.001). A significant reduction of 1.25 ± 0.18 mmHg (p < 0.001) was also observed between Visits 2 and 3, with a final mean CH value of 9.09 ± 0.29 mmHg. In addition, a statistically significant difference between the study and control eyes was only observed at Visit 2 (1.01 ± 0.23 mmHg; p < 0.001) and not at Visits 1 and 3. A statistically significant increase in Corneal Resistance Factor (CRF) was found between Visits 1 and 2 in the study eyes, with mean values of 10.23 ± 0.34 mmHg and 11.71 ± 0.34 mmHg, respectively. CRF was then reduced by 1.90 ± 0.21 mmHg (p < 0.001) between Visits 2 and 3, with a final mean CRF value of 9.81 ± 0.34 mmHg. A statistically significant difference between the study and control eyes was only observed at Visit 2 (1.46 ± 0.23 mmHg; p < 0.001). A statistically significant increase in CCT was found between Visits 1 and 2 in the study eyes, with mean values of 541.83 ± 7.27 µm and 551.91 ± 7.27 µm respectively, corresponding to a mean increase of 10.09 ± 0.94 µm (p < 0.001). CCT then decreased by 9.40 ± 0.94 µm (p < 0.001) between Visits 2 and 3, with a final mean value of 542.51 ± 7.27 µm. A difference between the study and control eyes was only recorded at Visit 2 (11.26 ± 1.79 µm; p < 0.001). Similarly, a significant increase in IOP was observed between Visits 1 and 2 in the study eyes, with mean values of 15.37 ± 0.54 mmHg and 18.37 ± 0.54 mmHg respectively, corresponding to a mean increase of 3.0 ± 0.49 mmHg (p < 0.001). A significant reduction of 2.83 ± 0.49 mmHg (p < 0.001) was observed between Visits 2 and 3, with a final mean IOP value of 15.54 ± 0.54 mmHg. The control and study eyes only differed at Visit 2 (1.91 ± 0.49 mmHg; p < 0.001), confirming the effectiveness of PGA treatment. At Visit 1, the IOP bias (IOPcc – Goldmann IOP) was similar in both groups, all eyes at that time being on long term PGA medication, with mean values of 4.1 ± 0.54 mmHg in the control eyes and 4.8 ± 0.54 mmHg in the study eyes. At Visit 2, after a 6 week washout of PGAs, the IOP bias in the tested eye was reduced to 1.6 ± 0.54 mmHg (p<0.001), meaning that underestimation of IOP by Goldmann tonometry was significantly less than at Visit 1. The difference in mean IOP bias between the study and control eyes at Visit 2, however, did not reach statistical significance (p= 0.124). A marginally significant increase of 1.53 ± 0.60 mmHg (p = 0.055) was observed between Visits 2 and 3 in the study eyes, with a final mean IOP bias value of 3.10 ± 0.54 mmHg in the study eyes and 2.8 ± 0.54 mmHg in the control eyes. We then tried to determine if a low CH was associated with signs of more severe glaucoma progression among our open-angle glaucoma patients treated with PGA. When considering all eyes on PGA at the time of the first Visit, no association was found between VF damage and CH. However, when considering only eyes with more advanced glaucoma, a significant positive correlation was observed between VF MD and CH (B = 0.65; p = 0.003). A lower CH was associated with a more negative visual field MD value and thus greater glaucoma-related damage. Conclusions: Topical prostaglandin analogs reduce CH, CRF, CCT and IOP in glaucomatous eyes. The changes in CH and CCT influence the measurement of IOP, and therefore, these changes should be taken into account when evaluating IOP lowering response to PGA medications. To discern an interaction between IOP and corneal hysteresis, further research should be conducted with intraocular pressure control. It can be achieved by using systemic medications that decrease IOP and do not influence biomechanical properties. It can also be achieved by using Pascal dynamic contour tonometry or a similar tonometer that does not depend on the biomechanical properties of the cornea. Regarding the interaction between severity of glaucoma damage and corneal hysteresis, it was demonstrated that a lower CH was associated with a more negative visual field MD value. Key Words glaucoma – prostaglandin analogs – corneal hysteresis – central corneal thickness – intraocular pressure – biomechanical properties of the cornea.