Viscoelastic fluids, or Non-Newtonian fluids, are those that do not have a linear algebraic relation between the velocity field and the stresses arising in the media. Such fluids exhibit properties of both solids and liquids, and therefore cannot be modeled with methods of elasticity or Newtonian fluid mechanics. The popular models of viscoelasticity differ from each other only by the differential equation that describes the constitutive law for the fluid. Also, the media can have several relaxation modes, such as fluid mixes. This means that the stresses are determined as the sum of the stresses for each individual relaxation mode, which are described by corresponding differential equations evolving independently. The question of controllability of the equations that describe the evolution of viscoelastic fluids is largely open. The presence of the non-algebraic constitutive relation makes the analysis unfeasible in general setup. The presence of several relaxation modes makes the problem even more complicated. Another issue is the necessity of controlling the stresses, since they are not determined by the momentary velocity field, thus they need to be included as the controlled states. In this work we are concentrating on the controllability of the stresses arising in the viscoelastic fluid that has its motion constrained to be of the shearing type. This restriction allows us to concentrate on the stresses only and assign the shearing rate to be the control. We consider only the Upper Convected Maxwell fluid which has several relaxation modes present. The results demonstrate that contrary to the one relaxation mode case the normal stresses cannot be driven arbitrary close to the exponentially decaying regime, unless the shearing stresses satisfy certain requirements, while the shear stresses remain exactly controllable. / Ph. D.

Measuring V02peak is an important health assessment used to indicate cardiorespiratory fitness, prescribe exercise, and diagnose heart abnormalities (2,12). Utilizing the muscles of the upper body, the new StairMaster kayak ergometer is ideal for measuring V02peak on people with lower extremity disorders and those whose occupational or recreational activities rely primarily on the muscles of the upper body (16). Twenty-four healthy college-aged (17-31 years) males and females were screened, gave informed consent, and received orientation to experimental procedures prior to participation in the study. Subjects performed two maximal exercise bouts on the kayak incremental protocol and one on the treadmill incremental protocol. Pearson's r correlation estimated the stability-reliability coefficient of the kayak protocol to be 0.84. Pearson's r correlation estimated the relationship of the kayak protocol to the treadmill protocol to be 0.69. Given performance on the kayak ergometer, the predictive equation for treadmill performance was Y = 11.2605 + 1.02748X (r = 0.48). Body mass index and forearm circumference were found to be adequate predictors of kayak performance using the equation 45.2 - 1.60 BMI + 1.03 Forearm (~ 0.49). Although the kayak incremental protocol demonstrates adequate test-retest reliability for measuring V02peak, it has only a fair relationship to the gold standard of uphill treadmill running. The kayak incremental protocol, therefore, is generally best suited for those who, due to lower extremity complications, are unable to perform traditional modes of testing, or for those whose occupational or recreational activity is dominated by the upper body. / Master of Science

This thesis presents the design, simulation, and evaluation of a passive, wearable, and human-scale actuator that includes pulleys and uses polymers for energy storage. Repetitive tasks such as packing boxes on an assembly line may require high strength movements of the shoulder, arm, and hand and may result in musculoskeletal disorders. With the objective to offset the weight of the arm and thereby lower the forces on the muscles in the shoulder and arm, this actuator is able to provide gravity compensation for the upper extremities of workers, if used in conjunction with an arm exoskeleton. The actuator is passive, meaning that it does not use motors or sensors, but instead creates a force on a cable that is a function of the displacement of the cable. This thesis details the design of the actuator and the selection of an appropriate polymer for use with the actuator. To determine the best polymer for this application, tests were conducted on nine polymers to ind their average Young's modulus and their hysteresis. A 90A abrasion-resistant polyurethane rubber belt was used in the final design due to its high modulus and low hysteresis. The final actuator design was tested in an Instron machine to validate its performance. During testing, the actuator provided 720N in extension and 530N in retraction, which are roughly 112% and 83% of the torque required to lift a human arm, respectively. / Master of Science

Previous studies have identified longitudinal structures associated with non-migrating tides in observations of the upper neutral atmosphere of Mars. MAVEN’s Imaging Ultraviolet Spectrometer (IUVS) observations of the upper atmosphere reveal variations in density with longitude at altitudes of 130 – 200 km, and can be used to identify non-migrating tides. These observations cover higher latitudes and allow for studying the local time variations of tides. The analysis presented here shows that the longitudinal structure attributed to non-migrating tides is dominated by wavenumber 2 and wavenumber 3 harmonics during the periods studied. Comparison with the Neutral Ion and Gas Mass spectrometer (NGIMS) shows a good agreement in wave amplitudes observed for the first two cases studied. The temperatures and 𝑂/𝐶𝑂# ratios from the IUVS L2 data files revealed an anti-correlation with the densities which confirms the theoretical interpretation from the linear wave theory. / Master of Science / There are waves internal to all fluids in our surroundings and daily lives, such as sound waves. Waves in the atmosphere are also fluid in nature. In planetary atmospheres, the scale sizes of some of these waves become comparable to the size of the planet itself. The waves interact with the structure of the surface of Mars to form a certain type of wave called “Non-migrating tides”. These waves have been observed in multiple previous studies in the upper atmosphere of Mars (~130 km and above). These waves cause the atomic and molecular content of the upper atmosphere to be displaced in a particular manner to form a unique structure. The structures formed are observed on a scale that covers the entire planet. It is by studying these structures in the upper atmosphere that it is possible to characterize the waves that control them and thereby understand their nature and impact. Understanding how these waves vary helps spacecraft to gain better control over mechanisms required to swing them into the desired orbit (location). This study uses the observations from an instrument aboard the MAVEN mission and compares it to the observations from another instrument aboard the same mission. The results of this study demonstrate that these “Non-migrating” tides play a vital role in controlling the behavior of the upper atmosphere.

Framväxten av artificiell intelligens (AI) och generativ AI har lett till lanseringen av AI-baserade chatbottar som OpenAI:s ChatGPT. Det är i stort sett fortfarande oklart vilken effekt användningen av dessa verktyg har på undervisning i engelska som främmande språk. Den empiriska undersökningen som presenteras i detta examensarbete har därför syftet att undersöka vilken effekt ChatGPT-feedback har i jämförelse med lärarfeedback på svenska gymnasieelevers komplexitet, korrekthet och flyt i skriftlig produktion på engelska. Ett ytterligare mål med denna studie var att undersöka om elevernas språkliga kompetens påverkar dessa effekter. Studien genomfördes genom att undersöka 56 gymnasielevers argumenterande texter före och efter feedback. Studiens resultat pekar på att båda feedbackmodaliteter har liknande effekt på elevernas komplexitet, korrekthet och flyt. Statistiskt signifikanta ökningar går att se i dimensionerna för korrekthet, lexikal komplexitet och flyt för båda feedbackmodliteter. För dimensionen syntaktisk komplexitet har endast ChatGPT gruppen nått en statistiskt signifikant ökning, och för korrekthet har Lärarfeedback haft en större effekt med statistiskt signifikanta ökningar inom alla fyra analytiska mått för dimensionen. Vidare visar studien att elever med lägre språklig kompetens gynnas mer av feedbacken än elever med högre språkliga kompetens. Studien belyser även behovet av att framtida forskning fokuserar på ChatGPT-feedbacks effekter på texters generella kommunikativa funktion för att bättre förstå vilka effekter AI-genererad feedback har på skriftlig produktion i engelska som främmande språk.

The goal of this study was to determine the impact of land use activities on the subsurface flow regime in the Upper Roanoke River Watershed in Virginia to determine the impacts of land use change on the subsurface flow system, and to provide a tool for future management decisions. Land use activities can impact the groundwater system in two ways. The volume of water recharging the groundwater system can be reduced due to an increase in low permeable areas. It is assumed in this investigation that the input recharge values reflect the increase of low permeability zones that may occur due to land use activities. Increased water withdrawal associated with an increase in population can be another impact of land use change. This possible increase in water withdrawal is explicitly simulated in this investigation. MODFLOW, the USGS, three-dimensional, finite-difference, groundwater flow model was used to develop a regional conceptualization of the flow system. The fractured bedrock aquifer system consists of three sloping geohydrologic units: the Ordovician to Mississippian clastics, the Cambrian and Ordovician carbonates, and the Precambrian and Cambrian metamorphics and clastics. The 575 mi² study area was divided into cells with dimensions of 0.25 miles by 0.25 miles and containing four layers. The upper model layer was used to simulate the saturated unconsolidated deposits that lie on top of the fractured bedrock and serve primarily as a recharge reservoir. The second layer simulated shallow flow driven by recharge and the withdrawal of water by pumping wells. The bottom two layers were used to simulate deep regional flow within the system and account for possible vertical flow that may be occurring through deep fractures. Several simplifying assumptions were made during the conceptualization of groundwater flow in the study area: (1) Flow through fractures is approximately equivalent to flow through a porous medium; (2) Darcy's Law is applicable from a regional perspective; (3) Hydraulic properties are homogeneous and isotropic for an area that is represented by a model cell; and (4) Groundwater flow divides correspond to surface-water flow divides. Although these assumptions are probably valid for parts of the study area, the validity of each assumption is mostly unknown. Therefore, the model results are considered to be conceptual and should be interpreted carefully. The groundwater flow model was calibrated using UCODE, a USGS code for universal inverse modeling. Parameter estimation was conducted using UCODE for a total of 18 parameters, including hydraulic conductivities, river bottom conductance values, and recharge rates. The model was calibrated to observed hydraulic head information from 1969-1970. Due to the limited data availability, however, the calibrated values are at best, approximate. Nonetheless, several inferences can be made regarding flow in the province. The calibrated recharge values indicate that approximately 28% of the total precipitation recharges the aquifer system. This is consistent with previous estimates performed in the study area (Rutledge, Mesko, 1996). The Cambrian and Ordovician carbonates were found generally to have the highest hydraulic conductivity in each layer which reflects the notion that due to dissolution, this geohydrologic unit contains more fractures than the other two units. The calibrated values of hydraulic conductivity for the Cambrian and Ordovician carbonates ranged from 0.89m/d in layer 2 to 0.0011m/d in layer 4. The calibrated values of hydraulic conductivity for the Precambrian and Cambrian metamorphics and clastics ranged from 0.013m/d in layer 2 to 0.708E-3m/d in layer 4, and for the Ordovician to Mississippian clastics followed a similar trend in layers 2 and 3, with values of 0.390m/d in layer 2 and 0.242E-4m/d in layer 3. The streambed conductance values reflected both the variation in streambed thickness, which ranges from nonexistent in some areas to several feet thick in others, and streambed material, which ranges from sandy material with relatively high conductivity values to silty material with lower hydraulic conductivity values. The streambed conductance values range from 4.79 m²/d in the upland reaches to 234.13 m²/d in reaches closer to the outlet. Present pumping conditions were simulated with the groundwater flow model to establish a "baseline simulation" to which all future scenarios could be compared. Three future scenarios were developed based on the projected increase in population for Roanoke County through the year 2010. Each scenario represented a distinct settlement pattern within the watershed. Development scenario 1 simulated the impacts of the increased population if settled in the same areas as present development. Development scenario 2 simulated the impacts of the increased population if half settled in areas of present development and the other half in the western half of the watershed. Development scenario 3 simulated the impacts of the increased population if half of the population increase settled in areas of present development and the other half settled in the Tinker Creek sub-watershed. Development scenario 2 resulted in a drastic change in hydraulic head values, and the volume of water discharged from the streams was, on average, reduced by 56%, whereas, for both scenarios 1 and 2, these reductions were less than 1%. Results indicate that flow in the system is predominantly horizontal. There is no deep vertical flow from possible deep fractures. There may be shallow vertical flow occurring that is driven by recharge, however due to the resolution of the model, this flow is not simulated. In general, the simulation of horizontal flow follows the overall trend of the hydraulic gradient from west to east, which also follows the overall topographic trend. Therefore, upland regions in the province are recharging down-gradient areas. However, simulations indicate that the hydraulic head values in the eastern part of the study area are relatively insensitive to this horizontal recharge contribution from the west. The most sensitive areas in the basin to increased water withdrawal are the upland areas in the west side of the study area that are receiving no horizontal flow contribution from other places in the watershed. These areas are only being recharged by precipitation, and are the first to react to regional flow changes. Since the resolution of the model is such that local variations in the flow system are not simulated and the model represents regional trends, inferences can only be made about regional impacts. Therefore, if increased withdrawals are so great as to impact the regional system, the west- side of the study area will be affected before all other areas in the watershed. The study results include estimates of hydraulic properties, direction of regional flow, possible impacts from land use change, and a discussion of the results with respect to gaining a more complete understanding of the subsurface flow system. Perhaps this work will be the first step in learning more about the subsurface flow system of the Upper Roanoke River Watershed, and provide a useful tool to manage and properly plan future land use changes to minimize the impacts on the groundwater resources of the basin. / Master of Science

As humanity continues its expansion into space, the understanding of the near-Earth space environment has never been more critical. As the ionosphere and thermosphere form the boundary between Earth's atmosphere and outer space, characterization of these regions is critical to understanding geospace. The Ionospheric Connection Explorer (ICON), launched in 2019, sought to establish the effects of forcing on the ionosphere and thermosphere from below and above, in part by using observations of ultraviolet airglow, which have long been used as a tool for making remote sensing observations of the upper atmosphere. The Extreme Ultraviolet Spectrometer (EUV) instrument was included on ICON to measure atmospheric airglow between 54 and 88 nm in order to estimate the density and structure of the ionosphere. In this work, we analyze the EUV observations throughout the ICON mission, characterizing the signal observed at various wavelengths during normal operations and during nadir and lunar calibrations. We use the ICON EUV data to develop the first algorithm for retrieval of neutral densities from EUV airglow. / Doctor of Philosophy / As humanity continues its expansion into space, the understanding of the near-Earth space environment has never been more critical. The neutral (thermosphere) and charged (ionosphere) particles in the upper atmosphere, around the altitude where satellite orbit, play a key role as the boundary between Earth and space. The Ionospheric Connection Explorer (ICON), launched in 2019, sought to establish how the ionosphere and thermosphere change over time. It measured the density of particles using light emitted from the atmosphere by chemical reactions (airglow). Extreme Ultraviolet (EUV) light is highly energetic, almost as much as X-rays, and the EUV airglow emitted by the atmosphere at certain can be used to detect O^+. In this work, we examine the measurements from the ICON EUV detector at various wavelengths to determine what other particles can be seen. Notably, we find that the measurements contain information about neutral atomic oxygen and molecular nitrogen. We develop a technique for using the EUV airglow brightness to measure the amount of O and N_2, the first of its kind.

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COMPARATIVE STUDY OF FLUVIAL LAKES IN FLOODPLAINS OF THE ELBE, LUŽNICE AND SVRATKA RIVERS Petra Havlíková ABSTRACT The aim of the thesis was to specify key differences in chemistry and biota (zooplankton communities) among fluvial lakes in three regions of Czech Republic: "střední Polabí" (central part of the Elbe River on the territory of Bohemia), "Horní Lužnice" (the upper part of the Lužnice River on the territory of Bohemia), and the Svratka River near Milovy (upper part of the Svratka River). The 10 studied lakes of the three regions differ in size, geology, shading, the influence of the river, and the level of anthropogenic impact. The following hypotheses were tested: 1) The chemical composition of the water in fluvial lakes is significantly different in different areas (floodplains). In the central Elbe River floodplain, there are the highest values of conductivity and concentrations of organic matter and nutrients. Fluvial lakes of the Svratka River floodplain near Milovy show the lowest level of these parameters, and fluvial lakes of the upper Lužnice River occur between the two previous regions. 2) The chemistry of fluvial lakes that have contact with the river through surface connection is significantly influenced by the river, and differs from the chemistry in fluvial lakes without any direct...

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