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Cement needs to be designed to prevent short-term and long-term gas migration scenarios. In the short term, the cement must prevent gas flow immediately following cement placement. In the long term, the cement must resist pressure and temperature cycling during drilling and production. Wells are subjected to substantial stresses from pressure and well testing, injection and stimulation treatments, thermal effects, production cycling, and changes in the surrounding formation over years. Due to these stresses, the cement sheath damage can occur during drilling, perforation and stimulation, and subsequent production. Polymer latex has been used to help reduce the fluid loss to minimize gas migration and aid in the mixing ability of cement slurries. However, there are some engineers who believe that polymer latex will improve cement mechanical properties.The objective of this study is to evaluate the effect of polymer latex on cement mechanical properties after curing at elevated temperature and pressures. Experimental work in this study includes formulations at different polymer latex concentrations, densities measurements, rheology measurement, fluid loss testing, thickening time tests, curing for 30 days at elevated temperature and pressure, and finally mechanical properties measurements (Young's modulus, Poisson's ratio and compressive strength). The study shows that polymer latex will improve mechanical properties of cementing which will lead to improved wellbore integrity.

The objective of this dissertation is to investigate several dynamical approaches aiming to improve the sensitivity and performance of microelectromechanical systems (MEMS) resonant sensors. Resonant sensors rely on tracking shifts in the dynamic features of microstructures during sensing, such as their resonance frequency. We aim here to demonstrate analytically and experimentally several new concepts aiming to sharpen their response, enhance the signal to noise ratio, and demonstrate smart functionalities combined into a single resonator. The dissertation starts with enhancing the excitations of the higher order modes of vibrations of clamped-clamped microbeam resonators. The concept is based on using partial electrodes with shapes that induce strong excitation of the mode of interest. Using a half electrode, the second mode is excited with a high amplitude of vibration. Also, using a two-third electrode configuration is shown to amplify the third mode resonance amplitude compared with the full electrode under the same electrical loading conditions. Then, we demonstrate the effectiveness of higher order mode excitation and metal organic frameworks (MOFs) functionalization for improving the sensitivity and selectivity of resonant gas sensors. Also, using a single mode only, we show the possibility of realizing a smart switch triggered upon exceeding a threshold mass when operating the resonator near the dynamic pull-in instability. The second part of the dissertation deals with the dynamics of the microbeam under a two-source harmonic excitation. We experimentally demonstrate resonances of an additive and subtractive type. It is shown that by properly tuning the frequency and amplitude of the excitation force, the frequency bandwidth of the resonator is controlled. Finally, we employ the multimode excitation of a single resonator to demonstrate smart functionalities. By monitoring the frequency shifts of two modes, we experimentally demonstrate the effectiveness of this technique to measure the environmental temperature and gas concentration. Also, we present a hybrid sensor and switch device, which is capable of accurately measuring gas concentration and perform switching when the concentration exceeds a specific (safe) threshold. In contrast to the single mode operation, we show that monitoring the third mode enhances sensitivity, improves accuracy, and lowers the sensor sensitivity to noise.

Using biogas to partially replace diesel fuel in agriculture tractors seems a good solution to reduce greenhouse gases and other pollutants. For this reason, a research project to convert a tractor to dual-fuel operation was initiated; this paper's specific aim was to develop a control algorithm feeding biogas to the engine's intake manifold. The effect of biogas addition on engine performance, focusing on brake specific heat consumption and fuel replacement rates, was first studied. Then several load estimation methods were assessed and the Manifold Absolute Pressure (MAP) sensor was chosen as a main load detector. Finally, a prototype algorithm was built upon an engine control unit and was tested. The algorithm was able to change biogas flow with engine speed and load, without knock and misfire.

The research on biogas tractor was started as a possible solution to reduce tractor's fuel consumption and increase farmer's benefit out of a biogas plant. The tractor was equipped with a fontal gas unit containing 4 cylinders of purified biogas (more than 95% methane) with a volume of 26.5 L each at 19.6 MPa. A pressure regulating system was used to insure constant pressure potential across the biogas injectors. Based on previous study regarding biogas effects on the diesel engine, two possible algorithms were developed and tested. In the field tests, the first one was successful at replacing the high amounts of fuel (about 80%) while the other was able to run the engine at its best efficiency point.

In this study, we present analytical and experimental investigation of electrically actuated micro cantilever based resonators. These devices are fabricated using polyimide and coated with chrome and gold layers from both sides. The cantilevers are highly curled up due to stress gradient, which is a common imperfection in surface micro machining. Using a laser Doppler vibrometer, we applied a noise signal to experimentally find the first four resonance frequencies. Then, using a data acquisition card, we swept the excitation frequency around the first four natural modes of vibrations. Theoretically, we derived a reduced order model using the Galerkin method to simulate the dynamics of the system. Extensive numerical analysis and computations were performed. The numerical analysis was able to provide good matching with experimental values of the resonance frequencies. Also, we proved the ability to excite higher order modes using partial electrodes with shapes that resemble the shape of the mode of interest. Such micro-resonators are shown to be promising for applications in mass and gas sensing.

Ancient off-shore lighthouses have a phenomenal cultural significance. They were built as physical aid for navigation to guide mariners and to warn them from dangerous shallow rocky reefs. Understanding their structural response under waves loading is a challenging task. La Jument lighthouse, off the coast of Brittany, has sustained extreme environmental loading for more than 110 years. The main motivation of the present study is to characterize its structural response under extreme waves loading by 3D Finite Element Modeling using the commercial software DIANA. The model is calibrated based on the data collected from accelerometers and photographical documentations during a measurement campaign in winter 2018 in which the highest wave recorded with 19 meters height is considered for this study. The effect on the lighthouse’s structural response of slamming pressure magnitude, tide level, and slamming area is investigated in a parametric study. The predictions of the FE model were comparable to the actual measurements confirming the main hypothesis in this study. The tide level was proven to be an important factor contributing to the structural response parameters. The FE model suggested 230 kPa as the most likely pressure of the wave under consideration. Moreover, intervention methods using UHPFRC combined with a measurement campaign are proposed to preserve the outstanding cultural significance of La Jument lighthouse. Extending the life of off-shore lighthouses is essential to understand non-linear characteristics of extreme waves in future field measurements which helps validating numerical computations and removing uncertainties about their dynamic behavior.

The Fertile Crescent, its hilly flanks and surrounding drylands has been a critical region for studying how climate has influenced societal change, and this review focuses on the region over the last 20,000 years. The complex social, economic, and environmental landscapes in the region today are not new phenomena and understanding their interactions requires a nuanced, multidisciplinary understanding of the past. This review builds on a history of collaboration between the social and natural palaeoscience disciplines. We provide a multidisciplinary, multiscalar perspective on the relevance of past climate, environmental, and archaeological research in assessing present day vulnerabilities and risks for the populations of southwest Asia. We discuss the complexity of palaeoclimatic data interpretation, particularly in relation to hydrology, and provide an overview of key time periods of palaeoclimatic interest. We discuss the critical role that vegetation plays in the human-climate-environment nexus and discuss the implications of the available palaeoclimate and archaeological data, and their interpretation, for palaeonarratives of the region, both climatically and socially. We also provide an overview of how modelling can improve our understanding of past climate impacts and associated change in risk to societies. We conclude by looking to future work, and identify themes of "scale" and "seasonality" as still requiring further focus. We suggest that by appreciating a given locale's place in the regional hydroscape, be it an archaeological site or palaeoenvironmental archive, more robust links to climate can be made where appropriate and interpretations drawn will demand the resolution of factors acting across multiple scales. This article is categorized under:Human Water > Water as Imagined and RepresentedScience of Water > Water and Environmental ChangeWater and Life > Nature of Freshwater Ecosystems.

Künstliche Terrassen sind künstlich konstruierte Trockenmauern, die Hänge in Ebenen unterteilen. Petra im Süden Jordaniens gehört zu einer trockenen Klimazone, die sich durch unwegsames Gelände und eine mit Terrassen durchsetzte Landschaft auszeichnet. Die vorliegenden Ergebnisse wurden vom Autor im Rahmen einer multidisziplinären Studie gesammelt, die aus Vermessungen, Erkundungsgrabungen, geophysikalischen Prospektionen, Untersuchungen der Bodentextur sowie chemischen Analysen, optisch stimulierender Lumineszenzdatierung (OSL), Radiokohlenstoffdatierung (14C), Phytolithanalysen und geografischen Analysen zur Untersuchung der Terrassen in einem Gebiet von etwa 391 km2 bestand. Die vorliegende Studie zeigt, dass die künstlichen Terrassen in Trockengebieten für eine Vielzahl von Funktionen konzipiert und genutzt wurden. Die Terrassen dienten somit der Rückhaltung, Sammlung und Verteilung von Boden und Wasser und verhinderten, dass Wasser unkontrolliert abfließt und Erde weggespült wird. Das trockene Klima, das raue Gelände und die für dieses Gebiet charakteristischen Überschwemmungen machten diese Eingriffe in die Natur notwendig. Neben diesen beiden Hauptaufgaben konnten die Terrassen der Nabatäer noch andere Funktionen erfüllen. Neben der landwirtschaftlichen Nutzung der Terrassen nutzten die Nabatäer sie auch zum Schutz ihrer Infrastruktur wie Straßen und hydrologische Einrichtungen. Ein Aspekt, der in der Forschung noch nicht diskutiert wurde. All dies deutet darauf hin, dass die Nabatäer die Gegend sehr gut kannten und gezielt den Bau einer bestimmten Art von Terrasse nutzten. Basierend auf verschiedenen Datierungstechniken begann der Bau der Terrassen in Petra um 350-320 v. Chr. Drei zeitliche Höhepunkte in der Bauausweitung lassen sich unterscheiden: um das 1. Jahrhundert n. Chr., um das 6. bis 7. Jahrhundert n. Chr. und um das 12. Jahrhundert n. Chr., Man-made terraces are often-overlooked feature in the landscapes of southern Jordan, especially around Petra. These features are artificial constructions dry walls that create flat surfaces on slopes (Spencer, J. and Hale, G. 1961: 3; Treacy, J. and Denevan, W. 1994: 93; Kvapil, L. 2013: 6612). These terraces are usually attributed to have agricultural functions, which is only partially true. This study shows that terraces constructed in arid areas have been designed and used for a wide set of functions that go beyond their agrarian aspects. Petra, located in the south of Jordan, falls within an arid climatic zone, is of rough terrain, and has a landscape dotted with terraces. A multidisciplinary study was conducted by the author which included survey, sounding excavations, geophysical prospecting, soil texture and chemical analysis, Optical Stimulating Luminescence (OSL), radiocarbon dating (14C), phytolith analysis and spatial analysis for studying the terraces. Two major functions were assigned to the constructed terraces: hydrological (water) and pedogenic (soil). Applied to prevent, retain, collect and distribute soil and water. Nabataeans managed to apply terraces to a wide range of fields such as: agriculture, infrastructure such as roads and hydrological installations, an aspect never discussed before. The study concluded, based on OSL, pottery sherds and 14C dates, terrace construction in Petra started around 350-320 B.C.E. at the upper catchment areas, probably for flood water mitigation. Three peaks in the construction expansion can be grouped: around the 1st century A.D, around 6th -7th century and around 12th century, which correspond to more humid climatic conditions and stability in the political situation.