Geólogo / En el rubro de la minería siempre están muy presentes dos factores, la rentabilidad del negocio y la seguridad de los trabajadores. Para cumplir con ambas es necesario tener un acabado conocimiento sobre el comportamiento local de la roca. Entre las pruebas más básicas e importantes dentro de la caracterización física de la roca está el de compresión uniaxial no confinado (UCS), que como bien dice su nombre, es una prueba donde se aplica compresión en un solo sentido (vertical) a una muestra de roca cilíndrica, hasta que esta falle. Externamente se usa un dispositivo para medir la deformación, como los strain gauges y LVDT. Si bien estos son métodos confiables y ampliamente usados, en este trabajo, el objetivo es validar una técnica relativamente nueva en esta área, la medición de deformación usando correlación de imágenes digitales (DIC). El concepto básico de esta consiste en tomar una gran cantidad de fotos de un objeto en una ventana de tiempo en la que presente algún tipo de movimiento o deformación. Estas imágenes son luego procesadas en un software especializado que identifica los desplazamientos a través de la comparación de imágenes. Lo que se hace en este trabajo es realizar y grabar 15 ensayos UCS de carga fija en probetas de roca, con los que se busca determinar hasta donde llegan las capacidades del DIC en estudios de roca. En las pruebas realizadas se encuentra que los gráficos de deformación versus estrés son parecidos a los que se hacen con otros métodos. La cantidad de deformación es similar, mientras que la forma y eventos capturados en la curva dependen mucho del criterio de posicionamiento de las mediciones por DIC. Se confeccionan representaciones visuales de la deformación, donde se muestra, usando mapas de colores, las zonas que sufren desplazamiento durante el proceso de falla. Por último, en el análisis estructural de la secuencia se hace un detalle de cómo va apareciendo cada fractura durante la carga, dando la posibilidad de encontrar relaciones entre cada falla. A partir de los resultados obtenidos se concluye que el DIC es un método muy flexible en cuanto que puede hacer infinitas mediciones de la cara estudiada, de alta precisión y que entrega mucha más información que otros métodos. Todo esto hace que sea muy útil en tres escenarios: cuando se quieren hacer mediciones de deformación sobre una muestra, cuando se quiere mostrar visualmente la deformación ocurrida en la muestra y para hacer análisis estructurales muy enfocados.

Monolayer molybdenum disulfide (MoS2) is a three-atom-thick direct band gap semiconductor, which has received considerable attention for use as a channel material in atomically thin transistors, photodetectors, excitonic LED’s, and many other potential applications. It is also a mechanically exceptional material with a large stiffness and flexibility, and can withstand very large strains (11%) before rupture. In this dissertation we investigated the mechanics of the stiffness and adhesion forces in atomically thin MoS2 membranes, and how biaxial strains can be used to induce large modulations in the band structure of the material. First, we used chemical vapor deposition (CVD) to grow MoS2 crystals that are highly impermeable to gas, and used a pressure difference across suspended membranes to induce large biaxial strains. We demonstrated the continuous and reversible tuning of the optical band gap of suspended monolayer membranes by as much as 500 meV, and induced strains of as much as 5.6% before rupture. We observed the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) and Raman spectra and found their linear strain tuning rates, then report evidence for the strain tuning of higher level optical transitions. Second, we determined the Young’s modulus and works of separation and adhesion of MoS2 membranes, and found that adhesion hysteresis is an important effect in determining the behavior of our systems. Finally, we investigated the use of atomically thin materials as nanofiltration membranes, by perforating the material with nanopores which selectively permit the transport of smaller molecules while rejecting larger ones. We studied ion transport through nanopores in graphene membranes and demonstrate that in-situ atomic force microscope measurements in liquid are a powerful way to reveal occlusions and contaminants around the pores - work which will aid future researchers in further unveiling the properties of these fascinating systems.

Operationally, marine components and structures such as boiler in a Ship, are exposed to varying mechanically and thermally induced forces. High-frequency mechanical loading arises from the cyclic pressure, temperature transients, and six directional Rapid Amplitude Operator (RAOs). These types of loadings are mainly in the elastic region usually denoted as high cycle fatigue (HCF), most pronounced during the start-up, and the shut-down sequence of operation, which are responsible for an astronomically  reduction in Marine Boiler’s lifetime as compared to land boiler with same designed operating condition. Therefore, there is a need to determine the limitations of the engineering variables of the boiler with respect to Pressure, temperature, RAOs, and best locational point for the optimization of its designed lifetime during Operation. Detailed knowledge of this interaction between varying temperatures, RAOs and load cases is of considerable importance for precise lifetime calculations.  In order to understand and analyze the material behavior under contentious stress exposure, a general-purpose linear Finite Element (FE) code, LS-DYNA software is used as a pre-processor and solver during the simulation and data are post-processed using stress-based analysis method.

L’objectif de cette thèse est d'étudier le ventricule droit (VD) dans différentes conditions de charge en utilisant imagerie et modélisation. Le premier axe de ce travail est une étude prospective qui analyse la déformation VD chez des patients sains et avec hypertension pulmonaire (HTP) en utilisant l’échocardiographie trans-thoracique 3D. Les maillages VD ont été obtenus par tracking myocardique et post-traités afin d’extraire le strain de surface. Les correspondances spatiotemporelles ont été vérifiées avant de réaliser les statistiques des maillages. La forme et déformation globale VD sont associées à la sévérité de l'HTP et donnent des informations pronostiques. Le deuxième axe de ce travail présente le rôle d'une évaluation longitudinale par rapport à celui d’une évaluation instantanée, en utilisant la même méthodologie. Nous avons démontré la valeur ajoutée pronostique des modifications dans le temps de déformation VD et l'importance du septum. Dans le troisième axe, les aspects complémentaires de la forme (définie par la courbure) et déformation VD ont été évalués dans des populations de surcharge en volume VD. Alors que forme et déformation sont altérés chez les patients avec tétralogie de Fallot, seule la forme a permis de différencier les patients avec CIA des témoins. Enfin, dans le dernier axe, nous avons étudié la valeur ajoutée de la personnalisation d'un modèle circulatoire 0D pour caractériser la pathologie et prédire la réponse au traitement dans l’hypertension artérielle pulmonaire. Le modèle a été personnalisé pour 11 patients avant et après traitement spécifique de l’HTP. Les paramètres du modèle reflètent bien les changements attendus avec la thérapie. / The aim of this thesis is to study the right ventricle (RV) in different loading conditions using imaging and modelling. The first axis of this work was a prospective study in which we studied RV deformation in healthy controls and pulmonary hypertension (PH) patients (pressure overload) using 3D transthoracic RV echocardiographic sequences. Output RV meshes; obtained after myocardial tracking; were post-processed to extract area strain and spatiotemporal correspondences were checked before computing statistics on these meshes. RV shape and strain patterns were gradually deteriorated with the severity of PH and provided independent prognostic information. The second axis of this work focused on the role of a longitudinal evaluation in comparison with a single assessment at baseline, using the same methodology. We demonstrated the additional prognostic value of changes in RV area strain and the importance of septal segments. In the third axis, we assessed the complementary aspects of RV deformation and shape (using curvature index) in RV volume overload patients. While shape and strain are both altered in tetralogy of Fallot patients, only RV shape allows to differentiate atrial septal defects from normal controls. Finally, in the last axis, we focused on the added value of the personalisation of a 0D circulation model to characterize the pathology and predict the response to therapy in pulmonary arterial hypertension. The model was personalised to 11 PH patient data before and after advanced specific PH therapy. The model parameters reflected accurately the expected changes with therapy.

Recently, the railway pavement structure system, as an integral part of the transport infrastructure, has been under fast development in some countries such as China, Turkey, and some European Union countries, particularly for the use of high-speed trains. In designing and constructing the railway pavement structure, it is necessary to take into account the infrastructure demand of the High-Speed Railway Lines (HSRL). Compared to traditional railway trains, HSRL can cause more significant problems to the ballast or base layer of commonly used ballasted railway pavements. The deteriorated ballast or base layer may further result in substructure degradation that may cause safety issues and catastrophic accidents. As a consequence, heavy goods or high-speed trains will affect railway efficiency. As a countermeasure, a railway pavement structure may be reinforced by geosynthetic materials in the ballast or base layer. In the literature, however, there is still a need to quantify the effect of geosynthetic materials, geogrid in particular, on the mechanical responses of railway pavement structures to HSRL loads, which is necessary knowledge in supporting the selection of appropriate material and placement location of geogrid. Therefore, the goal of this study is to investigate how a geogrid reinforcement layer can change the essential characteristics of a ballasted railway pavement structure, with focus on the material type and placement location of geogrid that can help minimize the rate of deterioration of the railway pavement structure system. This research attempts to validate the advantage of geogrid reinforcement through numerical simulation in a realistic railway setting. All technical literature on the use of geogrids in the railway system has been studied. A three-dimensional (3D) finite element model was constructed for the numerical simulation, in which three different types of geogrid placed at two different locations (i.e., within the ballast layer, between the ballast and the sub-ballast layer) within a railway pavement structure were analyzed under a range of vertical wheel loads. Therefore, four possible applications of geogrid reinforcement systems (G0: no-reinforcement; G1: reinforced with geogrid having the lowest density and Young’s modulus; G2: reinforced with geogrid having the intermediate Young’s modulus and density; G3: reinforced with geogrid having the highest density and Young’s modulus) were modeled to represent different situations in ballasted railway systems. Railway mechanical responses, such as vertical surface deflection, maximum principal stress and strain, and maximum shear stress were analyzed and compared among the four geogrid reinforcement scenarios and under four vertical wheel load levels (i.e., 75, 100, 150 and 200 kN). The advantages of such geosynthetics in ballast are indicated by result difference in the mechanical responses of railway pavement structures due to the use of different geogrid materials. The results also show that the reinforced structures have lower vertical surface deflection, lower maximum shear stress at the interface of sleeper and ballast, and maximum principal stress at the bottom of the ballast layer than a non-reinforced railway pavement structure. Consequently, the addition of geogrid into the ballast layer, and between the ballast and sub-ballast layer has been shown to reduce critical shear and principal stresses and vertical surface deflection in a ballasted railway pavement structure. Besides that, the results of the analysis confirm that geogrid reinforced layers exhibit higher resistance to deformation than the non-reinforced layers.

With the development of modern industrial engineering technology, increasing demands of multifunctional materials drive the exploration of new applications of electrical conductive polymer nanocomposites (CPNCs). Toward applications of smart materials, sensing performance of CPNCs has gained immense attention in the last decade. Among them, strain sensors, based on piezoresistive behavior of CPNCs, are of high potential to carry out structural health monitoring (SHM) tasks. Poly(vinylidene fluoride) (PVDF) is highly thought to be potential for SHM applications in civil infrastructures like bridges and railway systems, mechanical systems, automobiles, windgenetors and airplanes, etc. because of its combination of flexibility, low weight, low thermal conductivity, high chemical corrosion resistance, and heat resistance, etc. This work aimed to achieve high piezoresistive sensitivity and wide measurable strain ranges in carbon nanotube based poly(vinylidene fluoride) (PVDF) nanocomposites. Four strategies were introduced to tune the sensitivity of the relative electrical resistance change (ΔR/R0) versus the applied tensile strain for such nanocomposites. Issues like the influence of dispersion of multi-walled carbon nanotubes (MWCNTs) on initial resistivity of PVDF nanocomposites and conductive network structure of MWCNTs, as well as piezoresistive properties of the nanocomposites, were addressed when using differently functionalized MWCNTs (strategy 1). In addition, the effects of crystalline phases of PVDF, mechanical ductility of its nanocomposites and interfacial interactions between PVDF and fillers on piezoresistive properties of PVDF nanocomposites were studied. Using hybrid fillers, to combine MWCNTs with conductive carbon black (strategy 2) or isolating organoclay (strategy 3), piezoresistive sensitivity and sensing strain ranges of PVDF nanocomposites could be tuned. Besides, both higher sensitivity and larger measurable strain ranges are achieved simultaneously in PVDF/MWCNT nanocomposites when using the ionic liquid (IL) BMIM+PF6- as interface linker/modifier (strategy 4). The detailed results and highlights are summarized as following: 1. The surface functionalization of MWCNTs influences their dispersion in the PVDF matrix, the PVDF-nanotube interactions and crystalline phases of PVDF, which finally results in different ΔR/R0 and the strain at the yield point (possibly the upper limit of sensing strain ranges). As a whole, regarding to the fabrication of strain sensors based on PVDF/MWCNT nanocomposite, in contrast to pristine CNTs, CNTs-COOH and CNTs-OH, CNT-NH2 filled PVDF nanocomposites possess not only high piezoresistive sensitivity but also wide measurable strain ranges. Gauge factor, i.e. GF, is ca.14 at 10% strain (strain at the yield point) for the nanocomposites containing 0.75% CNTs-NH2. 2. Using hybrid fillers of CNTs and CB to construct strain-susceptible network structure (conductive pathway consisting of string-like array of CNTs and CB particles) enhances the piezoresistive sensitivity of PVDF nanocomposites, which is tightly associated with the CNT content in hybrid fillers and mCNTs/mCB. The best piezoresistive effect is achieved in PVDF nanocomposites with fixed CNT content lower than the ΦC (0.53 wt. %) of PVDF/CNT nanocomposites. 3. ΔR/R0 and possible sensing strain ranges of PVDF nanocomposites were tailored by changing crystalline phases of PVDF and PVDF-MWCNT interactions. Besides, the increase of the strain at yield point in PVDF nanocomposites filled by CNTs-OH is more obvious than that in the nanocomposites containing the same amount of clay and CNTs. The nanocomposite consisting of 0.25% clay and 0.75% CNTs-OH have ca. 70% increase of the strain at the yield point (17%) and the GF at this strain is ca. 14, while GF for the nanocomposite filled by only 0.75% CNTs-OH is ca. 5 at 10% strain. 4. IL BMIM+PF6- served as interface linker for PVDF and MWCNTs, which significantly increased the values of ΔR/R0 and strain at the yield point of PVDF nanocomposites simultaneously. Besides, this increases with increasing IL content. With the aid of IL, the dispersion of nanotube and toughness of the nanocomposites are greatly improved, but the electrical conductivity of the nanocomposites is decreased with the incorporation of IL, which is related to the IL modified PVDF-MWCNT interface connection or bonding. GF reaches ca. 60 at 21% strain (the strain at the yield point) for PVDF nanocomposites filled by 10% IL premixed 2%CNTs-COOH.

<p>Measurement of physiological deformations in specific tissues can provide significant information for the diagnosis, monitoring, and treatment of medical conditions. Yet these deformation measurements can be hard to obtain, especially when the targeted tissue is inside the body where optical access is denied. Current medical imaging technologies, including ultrasound, magnetic resonance imaging (MRI) and X-ray, can image soft tissues and bones with decent spatial resolution. However, they are not feasible for chronic tissue monitoring or cases in which rapid tissue deformation/vibration measurements are required. Wireless magnetic sensing is a favorable option for implantable pressure, strain, or deformation sensing systems due to its compact size, passiveness, high sampling rate and minimal interference from biological materials. Polymeric magnets, made from polymer carrier and embedded magnetic micro/nano-particles, possess the traits of flexibility, stretchability and biocompatibility that are preferred for biomedical applications. Nonetheless, their magnetic field is much weaker comparing to that of traditional ferrous/rare earth magnets. Emergence of highly sensitive magnetic sensors based on various principles (Hall effect, anisotropic magneto-resistance (AMR), giant magneto-resistance (GMR), giant magneto-impedance (GMI), tunneling magneto-resistance (TMR)) has enabled precise magnetic sensing of such polymeric magnets. To this end, we developed wireless magnetic sensing systems capable of measuring tissue deformations through implantable polymeric magnets for biomedical applications. This thesis work details the end-to-end development (magnetic sensor selection, magnetic transducer design & fabrication, measurement algorithm development) and the collaborative, interdisciplinary experiment result of a wireless brain deformation sensing system for blast induced traumatic brain injury (bTBI) featuring a polymeric magnetic disk, and a wireless strain sensing system for bladder dysfunction or heart failure (HF) featuring a stretchable polymeric magnetic band. Both systems comprise of one or more polymeric magnetic transducers, an external magnetic sensor / sensor array, and a signal processing unit. Upon tissue deformation, the magnetic transducers attached to the tissue deform jointly, inducing a change in the magnetic field that can be measured wirelessly by the external magnetic sensor / sensor array. Tissue deformation is then recovered from the measured magnetic field signal via the signal processing unit.</p>

In this work, the effect of reversible elastic lattice strain on the electronic properties of a) (Pr1−y Lay )0.7 Ca0.3 MnO3 (PLCMO) thin films and b) the interface layer of La0.7 Sr0.3 MnO3 (LSMO) with SrTiO3 (STO) has been determined using piezoelectric substrates. Lattice strain is known to effectively alter the electronic structure of compounds from the manganite family, since it shifts the balance of competing electronic interactions by changing bond angles and bond lengths.The PLCMO films have been repared by pulsed laser deposition (PLD) from a La0.7 Ca0.3 MnO3 (LCMO) and a Pr0.7 Ca0.3 MnO3 (PCMO) target. The metal- insulator phase boundary has been established to lie around y = 0.6. In films with y = 0.6, the piezoelectric release of tensile strain in the film plane induces a drastic reduction of the resistance, or a “colossal” elastoresistance. Resistive gauge factors as high as Γ = 1000 have been found. Consistent with the transport results, the release of tensile strain leads to an increase in both the Curie temperature and the magnetisation. The coexistence of the ferromagnetic metallic (FMM) and charge ordered insulating (COI) phases in PLCMO has been found to be strongly affected by the reversible substrate strain. Both the magnetisation and the resistance data in controlled strain states demonstrate a strong suppression of the ferromagnetic double exchange interaction by tensile strain. [La0.7 Sr0.3 MnO/SrTiO3 ] superlattices have been deposited on STO and piezoelectric PMN-PT (001) (PbMg1/3 Nb2/3 O3 )0.72 (PbTiO3 )0.28 substrates by PLD. X-ray reflectivity (XRR) measurements show clear Kiessig fringes as well as the larger interference maxima caused by the superlattice, giving qualitative proof of a well defined superlattice structure with sharp interfaces on both substrates. With decreasing LSMO layer thickness d, the samples show a sharp decrease of the Curie temperature, accompanied by a decrease of the saturation magnetisation and an increase of the coercive field around d = 5 nm. Reversible strain measurements on thicker superlattices (d = 16.7 nm) reveal a behaviour of the magnetisation similar to that of single thick films of LSMO. When d is decreased, the strain induced relative change in magnetisation ∆M/M0 shows a behaviour comparable to PLCMO thin films. This has been attributed to the increased volume fraction of the LSMO inter- face layer with STO, which displays a reduced magnetic order and phase-separated tendencies. From the absolute change in magnetisation per interface, the thickness of the so-called magnetically “dead” layer of the LSMO has been estimated to lie between 1.3 nm and 1.7 nm in the superlattices grown on PMN-PT.

Victims of child sex trafficking in prostitution in the United States are often overlooked, misidentified, and among the most underserved type of child victim of crime. The majority of previous research on child sex trafficking has been conducted without a theoretical framework or reliable sampling methods. In this study, a schematic composed of a series of stepping-stones from childhood abuse to prostitution, which has been described by gendered pathways researchers, served as a sensitizing template for the study's development of a strain-reactive pathway into child sex trafficking. Agnew's general strain theory provided the primary theoretical basis for the proposed pathway, supplying both explanations of the generative factors of the pathway and the mechanisms operating within the life trajectory terminating in child sex trafficking in prostitution. Based on this theoretical framework, this study utilized structural equation modeling to examine the pathway by investigating the effects of caregiver strain, child maltreatment, and risk-inflating responses to strain on vulnerability to victimization in child sex trafficking in prostitution. Four structural equation models, incorporating different forms of child maltreatment, were assessed using data from a matched sample of 174 minority females who were residents of one U.S. city and participated in a longitudinal study on the effects of child sexual abuse. Findings show that the occurrence of child maltreatment including child neglect, child physical abuse, and juvenile sexual victimization increased with caregiver strain. Consequentially, neglected and abused children were more likely to have engaged in the risk-inflating responses of running away and earlier initiation of drug or alcohol use, and they also reported higher levels of relational shame. Both running away and early initiation of substance use impacted vulnerability to victimization in child sex trafficking in prostitution. Lastly, implications of the findings related to protection and intervention strategies that are projected to obstruct the progression of minors along the analytically identified pathway into child sex trafficking in prostitution are presented for criminal justice professionals, child protection investigators, and social service providers.

Past literature suggests that working mothers are at an increased risk for experiencing role strain compared to other employed adults. The current study investigated attitudes and beliefs of 783 working mothers of 15-month-old children using data from the National Institute of Child Health and Human Development's Study of Early Child Care and Youth Development. Working mothers' levels of role strain was associated with perceived social support, attitudes toward maternal employment, job and parental role quality, financial stress, and depression. Negative attitudes toward maternal employment predicted maternal separation anxiety, while positive attitudes toward employment did not affect separation anxiety. These findings have implications for the importance of decreasing role strain in working mothers.