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This thesis analyses the relationship between month-ahead natural gas prices and imports into Europe against the backdrop of the 2022 Russian gas curtailment and gas price spike. Employing an ARCH model, the analysis focuses on the consortium of five major European consumers of natural gas: Italy, Germany, the Netherlands, the United Kingdom, and France. To gain a comprehensive understanding of the factors influencing natural gas prices in the European market, we include key variables such as natural gas consumption, production, storage levels, oil prices and temperature. The study finds that the European natural gas market is sensitive to decreased imports which exert a positive effect on prices and volatility. Therefore, we can infer that the proposed market factors influence gas prices in Europe. This research provides insights into the dynamics of natural gas pricing, presenting the implications of disruptions and uncertainties in the contemporary natural gas market.

Dams are relatively simple hydraulic structures that provide vital services to communities in the United States (U.S.). However, many of the dams in the (U.S.) have surpassed their design life. Dams experience changes from external threats that result in deformation of the structure. Traditional surveying techniques provide limited information on deformation in pre-determined areas of a structure, but the collection effort can often be lengthy. In this research, different instruments used for change detection were reviewed and Terrestrial Laser Scanning (TLS), also known as ground-based Light Detection and Ranging (LiDAR), was selected as the most probable method to accurately evaluate deformation in dams. TLS is a remote sensing instrument that uses light to form a pulsed laser to measure ranges to variable targets, and it provides the ability to measure displacement with high accuracy using dense point clouds collected in a short amount of time. Deformation is identified by measuring changes in point clouds generated by TLS. The accuracy of TLS to identify deformation was tested on a thin arch dam at the Big Black Test site in Vicksburg, Mississippi, using the TLS system, Terrestrial Laser Scanner RIEGL VZ-400, for data collection and for registering scan positons between a pre-test condition and a post-test condition. Final data analysis was performed using Microstation TopoDOTTM Wall Monitoring Tool.

This thesis aims to fit and compare different time series models namely the ARIMA-model, conditional heteroscedastic models and lastly a dynamic regression model with ARIMA error to Bitcoin closing price data that spans over 5 consecutive years. The purpose is to evaluate if the sanction on Russia had any effect on the cryptocurrency Bitcoin. After giving a very brief introduction to time series models and the nature of the error term, we describe the models that we want to compare. Quite early in on, autocorrelation was detected and that the time series were nonstationary. Additionally, as we are dealing with financial data, we found that the best alternative was to transform the data into logarithmic return and we then took the first difference. As we then detected a very large outlier, we decided to replace the extreme value with the mean of the two adjacent observations as we suspected it would affect the forecast interval. The dataset with first differenced log-returns was used in the ARIMA model but it turned out that there was no autocorrelation which indicated that returns in financial assets are uncorrelated across time and therefore unpredictable. The conditional heteroscedastic models, the ARCH and the GARCH models turned out to be best suitable for our data, as there was an ARCH-effect present. We could conclude that the GARCH(1,1) model using student t-distribution had the best fit, which had the lowest AIC and the highest log likelihood. In order to study the effect of the sanctions on Bitcoin volatility a dynamic regression model was used by allowing the error term to contain autocorrelation and include an independent dummy variable. The model showed that the Russian invasion of Ukraine did not, surprisingly, have any effect on the Bitcoin closing price.

The present study examined the application of modern, computer-based analysis methods to two existing historic bridges in Massachusetts. The first bridge featured in this study is the Woronoco Bridge, a reinforced concrete open spandrel arch bridge that was constructed in 1923. It was hoped that a computer-based, parametric study of this bridge would prove it to be deck-stiffened, similar to select bridges of Swiss engineer Robert Maillart. However, the results do not support that there was any intent to reduce bending in the arch as a result of increasing the stiffness of the bridge deck. Instead, the Woronoco Bridge appears to optimize column stiffness in order to reduce bending stresses in the arch. The second bridge featured in this study is the Bardwell’s Ferry Bridge, a wrought iron lenticular truss that was constructed in 1882. A finite element model was created to identify the magnitude and location of maximum stresses within a critical lower truss chord (eye bar) connection in order to aid future rehabilitation and monitoring efforts. In addition, this model was used in combination with currently available material data in order to evaluate the fatigue life expectancy of the structure given the current 10 ton posted capacity. It was determined to be below the endurance limit and therefore is safe indefinitely, however, more specific material data is required.

In order to predict hydraulic jump characteristics for channel design, the jump height may be determined by calculating the subcritical sequent depth from momentum theory. In closed conduits, however, outlet submergence may fill the conduit entirely before the expected sequent depth is reached. This is called an incomplete or pressure jump (as opposed to a complete or free-surface jump), because pressure flow conditions prevail downstream. Since the momentum equation involves terms for the top width, area, and centroid of flow, the subcritical sequent depth is a function of the conduit shape in addition to the upstream depth and Froude number. This paper reviews momentum theory as applicable to closed-conduit hydraulic jumps and presents general solutions to the sequent depth problem for four commonly-shaped conduits: rectangular, circular, elliptical, and pipe arch. It also provides a numerical solution for conduits of any shape, as defined by the user. The solutions conservatively assume that the conduits are prismatic, horizontal, and frictionless within the jump length; that the pressure is hydrostatic and the velocity is uniform at each end of the jump; and that the effects of air entrainment and viscosity are negligible. The implications of these assumptions are briefly discussed. It was found that these solutions may be applied successfully to determine the subcritical sequent depth for hydraulic jumps in closed conduits of any shape or size. In practice, this may be used to quantify jump size, location, and energy dissipation.

OBJECTIVES: The purpose of this in vitro study is to measure and compare the accuracy of the conventional impression, the intraoral scanner, and the photogrammetry techniques for full-arch implant-supported dental prostheses at the abutment level. METHODS: An edentulous maxillary master model containing 6 implant abutment replicas (RP analog for screw-retained abutment straight from NobelReplace® Multi-unit Abutment Plus Replica) was fabricated. A reference STL of the master model was obtained using a desktop scanner (inEos X5, Dentsply Sirona) with high trueness and precision and served as the control STL. Three impression techniques were performed: the intraoral scanning (IOS) group (TRIOS 3 Battery Cart, 3Shape A/S), the photogrammetry (PTG) group (ICam 4D Generation 3, Imetric), and the conventional (CNV) group. Ten impressions from each group were tested. Scan bodies in each STL file acquired from the different impression techniques were converted to implant abutment replicas using a digital library. Three tests were completed to compare the different registration techniques. A 3D deviation test between the experimental group and the reference was done on an inspection software (IScan4D Dental Version 9.1.104; Imetric) using a “best fit” algorithm to obtain the root mean square values, and on another inspection software (IScan3D Dental Version 9.1.104; Imetric) using spatial similarity transformation. The second test was meant to assess the angular deviations of the implant abutment replicas using a reverse engineering software (Geomagic Control X 2020.1; 3D Systems). The final test for cross-arch distances was done on an inspection software (IScan3D Dental Version 9.1.104; Imetric) which allows to determine the 3-dimensional coordinates for each implant by using the origin point and compare the cross-arch distance deviations as well as deviations at the x-, y-, and z- coordination. Trueness and precision were the two parameters used to define the accuracy of a system. The term "trueness" was used to see how close the measurements from the experimental files of each group were to those of the reference file. The term "precision" was defined as to see how close the measurements of each experimental files were to each other within the same group. The 3D discrepancies were then calculated and the trueness and precision of the three impression techniques were assessed and compared statistically (α = 0.05). RESULTS: The root mean square of 3D deviation values through the ICP “best-fit” method showed statistically significant differences between the PTG and CNV group (p < .0001), and the PTG and IOS group (p < .0001). The CNV and IOS group did not show statistically significant differences (p = 0.8626) through the “best-fit” method, but significant differences were observed via the “spatial similarity” method (p = 0.0041). Both methods however showed the best results in terms of trueness for the PTG group, followed by the CNV group and least the IOS group. In terms of precision, PTG showed the best results, followed by the IOS group and least the CNV group. The angular deviation test using the “best-fit” alignment method showed that the PTG and CNV had no statistically significant difference (p = 0.7955) and were equivalent. However, both showed a statistically significant difference to the IOS group (p < .0001), which had the highest angular deviation. Finally, in terms of cross-arch distances, the photogrammetry group showed optimal results followed by the IOS group and then the CNV group. In general, the shorter the inter-arch distance, the lower the deviation was. A larger deviation was observed on longer inter-arch distances. Considering the deviations on the 3 axes of each implant, the CNV technique had the highest deviation in the X-axis (longitudinal) and the IOS technique showed the highest deviation on the Y-axis (lateral) and Z-axis (vertical). The PTG technique experienced significantly less deviation on the X-axis, Y-axis, and the Z-axis. CONCLUSION: Within the scope of this study, the photogrammetry technique reported the best accuracy in terms of trueness and precision of implant positions for complete-arch implant rehabilitation. Conventional impressions showed better accuracy results than intraoral scanning in the 3D deviations test and global angular deviation test, however the latter exhibited better results in terms of accuracy in terms of cross-arch distances test. / 2023-08-11T00:00:00Z

Many tropical aquatic environments worldwide are characterized by intermittent or prolonged hypoxia (low dissolved oxygen). Nevertheless, many tropical freshwater fishes are able to inhabit these challenging environments via a range of morphological, physiological and behavioral adaptations. Brachyhypopomus is a diverse genus of weakly electric fishes represented by 28 known species distributed from Panama to Argentina. 17 species are restricted to permanently normoxic habitats (blackwater rivers and terra firme streams), eight species are restricted to seasonally or perennially hypoxic habitats (whitewater floodplains of large tropical rivers or permanent swampy habitats), and three species are eurytopic (occur in both seasonally hypoxic and normoxic habitats). These habitat distributions offer the opportunity to explore both species- and population-level variation in adaptive responses to hypoxia. Across 25 of the 28 known species in the genus (for which specimens were available), one- and two-way ANOVA was used to correlate total gill filament length (a metric of gill surface area) with lifestyle-divided into four categories: 1) stenotopic species (i.e. species occurring in a narrow range of habitats) restricted to hypoxic habitats; 2) stenotopic species restricted to normoxic habitats; 3) populations of eurytopic species from hypoxic habitats, and; 4) populations of eurytopic species from normoxic habitats. One-way ANOVA revealed that populations of eurytopic species from hypoxic habitats had significantly larger total gill filament lengths than stenotopic species from the same habitat (P = 0.0169). Likewise, populations of eurytopic from normoxic habitats had significantly larger total gill filament lengths than stenotopic species from normoxic habitats (P[less than] 0.005). Two-way ANOVA showed that eurytopic species had significantly larger total gill filament lengths than stenotopic species, independent of the disparity in total gill filament length associated with either hypoxic or normoxic habitats. Results indicate a strong correlation between gill surface area and oxygen-habitat among species and populations, which supports the hypothesis that an enlarged gill surface area increases oxygen uptake and serves as an adaptive response to seasonal hypoxia.

Physical bench top experiments are performed to validate and complement ongoing computational fluid dynamics (CFD) analyses of ventricular assist device (VAD) circulation. VADs are used in patients whose hearts do not function to their maximum potential due advanced stages of heart disease and, consequently, are unable to adequately supply blood to the systemic circulation. VADs are commonly utilized as a bridge-to-transplantation, meaning that they are implanted in patients while waiting for a heart transplant. In such cases of long term utilization of VADs, it has been reported in the literatures that thrombo-embolic cerebral events occur in 14-47% of patients over the period of 6 to 12 months. This is a result of thrombus forming despite the use of anticoagulants and advances in VAD design. Accepting current rates of thrombo-embolisms, the main objective of the project is to identify and propose an optimal surgical cannula implantation orientation aimed at reducing the rate of thrombi reaching the carotid and vertebral arteries and thus reduce the morbidity and mortality rate associated with the long term use of VADs to patients suffering from advanced heart failure. The main focus of the experiment is on the physical aspect using a synthetic anatomically correct model constructed by rapid prototyping of the human aortic arch and surrounding vessels. Three VAD cannula implantation configurations are studied with and without bypass to the left carotid artery or to the Innominate artery with ligation of the branch vessel at its root. A mixture of water and glycerin serves to match blood viscosity measured with a rotating cone-plate viscometer. The Reynolds number in the ascending aorta is matched in the flow model. A closed loop mock circulatory system is then realized. In order to match the Reynolds number in the ascending aorta and LVAD cannula with that of the CFD model, a volumetric flow rate of 2.7 liters per minute is supplied through the synthetic VAD cannula and 0.9 liter per minute is supplied to the ascending aorta. Flow rates are measured using rotary flow meters and a pressure sensor is used to ensure a mean operating pressure of 100 mmHg is maintained. Synthetic acrylic blood iv clots are injected at the inlet of the VAD cannula and they are captured and counted at the vertebral and carotid arteries. The sizes of the thrombi simulated are 2, 3.5 and 5 mm which are typical of the range of diameters encountered in practice. Nearly 300 particles are released over 5 separate runs for each diameter, and overall embolization rates as well as individual embolization rates are evaluated along with associated confidence levels. The experimental results show consistency between CFD and experiment. Means comparison of thromboembolization rates predicted by CFD and bench-top results using a Z-score statistic with a 95% confidence level results in 22 of 24 cases being statistically equal. This study provides confidence in the predictive capabilities of the bench-top model as a methodology that can be utilized in upcoming studies utilizing patient-specific aortic bed model.

The objective of this research project involves determining a seismic response modification factor for three-hinge glulam Tudor arches. In an attempt to meet this objective, the methods and procedures outlined in FEMA technical document P-695 were implemented on the provided arch designs. Computational models were created using finite elements within OpenSees to accurately depict the behavior of the arch. Incremental dynamic analyses were conducted on each of the provided designs and collapse margin ratios were determined allowing performance groups to be evaluated for each of seven design R-values within two gravity load cases. With the performance groups evaluated, it was determined that only groups within the low gravity load level designs were successfully able to pass, none of the groups designed for high gravity loads passed the evaluations. Within P-695, all performance groups associated with a given design R-value must pass the evaluations for that R-value to be deemed acceptable for use in designs. Because of the implications of this requirement, a seismic response modification factor could not be determined for this type of structural system within the scope of this project. / Master of Science