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Why Seismicity in Ireland Is Low: A Possible Geometric Explanation
Get PDFFor each geographic location, its seismicity level is usually determined by how close this location is to the boundaries of tectonic plates. However, there is one notable exception: while Ireland and Britain are at approximately the same distance from such boundaries, the seismicity level in Ireland is much lower than in Britain. A recent paper provided a partial explanation for this phenomenon: namely, it turns out that the lithosphere under Ireland is unusually thick, and this can potentially lead to lower seismicity. However, the current explanation of the relation between the lithosphere thickness and seismicity level strongly depends on the specific details of the corresponding hypothetical mechanism. In this paper, we provide a general geometric explanation of this relation, an explanation that does not depend on the specific geophysical details
Experimental And Computational Investigation Of Green Laser Propagation Through Turbulent Medium In A Water Tank
No full textTurbulence medium poses significant challenges to the propagation of laser beams, impacting applications such as free-space optical communication, remote sensing, and laser weapons systems. Therefore, comprehending and mitigating turbulence effects are vital for enhancing the performance of these systems. Analysis of a strong turbulence impact on electromagnetic wave propagation requires extensive knowledge of the Earth\u27s atmospheric and Oceanic phenomena and Maxwell\u27s electromagnetic theory of light as a propagating wave of electric and magnetic fields. Optical systems\u27 propagation often encounters Strong Turbulence, causing interference and diffraction. Nonetheless, light propagation through randomly fluctuating media has been an exciting and active area of extensive research over many decades. This research holistically examined Maxwell\u27s electromagnetic theory of light propagation through unstable medium and its effects (diffraction/interference) on optical systems. Generally, Turbulence causes scintillations, beam spreading, phase fluctuations, beam-wander, and jitter that can degrade and limit the performance of imaging and laser systems. However, the need for further investigation into the adequate characterization of strong turbulent waves and their effects on electromagnetic wave propagation is urgent to improve the existing mitigation measures. The Directed Energy (DE) Directorate of the Air Force Research Laboratory (AFRL), the U.S. Air Force, and the U.S. Space Force need to consider the impact of strong and substantial Turbulence on optical systems. Our holistic approach examined the problem and evaluated existing mitigation measures for gaps. We focused on refractive index fluctuation (scintillation), a primary cause of Turbulence in optical systems and light propagation. Our investigation into Refractive Index Structure Function, Dn(r), Power Spectral Density (PSD), and associated atmospheric and oceanic parameters was thorough and meticulous. We explored multiple concepts leading to the Refractive Index Structure Function, Dn(r), and different Power Spectral Density (PSD) mathematical formulations. Additionally, we formulated an analytical approach to solving the wave equation using the multiple integrals technique, which involves complex integrands. We investigated and implemented various mathematical and computational algorithms governing strong Turbulence and spatial-temporal imaging. We proposed developing a mathematical framework to simulate optical propagation through Turbulence. Our research continued with a meticulous design and setup of an apparatus for controlled simulated experiments using a 76.2cm (about 30inches) by 31cm (about 12.21inches) acrylic tank. We carefully varied temperature and salinity to observe the behavior of light under different turbulence levels. The results of these significant experiments, conducted with utmost precision, revealed how turbulence affects light propagation. They demonstrated the intricate relationship between turbulence levels and the resulting patterns of light intensity in laser beam propagation. These results offer valuable visual insights into how turbulence impacts how laser beams travel through a medium and provide valuable information about the physics of turbulent flow dynamics. In turbulent conditions, the movement of fluid particles becomes irregular and chaotic, making light propagation through the medium complex. As the laser beam moves through the turbulent medium, it encounters fluctuations in refractive index due to temperature, density, and velocity variations in the flow field. These fluctuations cause spatial and temporal changes in the laser beam\u27s intensity, resulting in the intricate patterns of intensity observed in the distribution. Higher salt concentrations result in reduced turbulence intensity. This reduction is evident in the decreased amplitude of fluctuations, indicating that saline water, which is denser, creates a stabilizing effect in the convection cell. As the salt concentration increases, the fluid becomes more stratified, suppressing vertical motions and leading to less pronounced turbulence. The use of SVD in analyzing signal amplitude versus frame number and amplitude versus frequency plots offers valuable insights into the temporal and spectral characteristics of turbulence. The amplitude versus frequency plots reveal that higher salt concentrations are associated with lower amplitudes across various frequency bands. This indicates a decrease in turbulent energy and a reduction in the strength of turbulent fluctuations. The normalized amplitude versus mode number plots show that higher salt concentrations lead to fewer distinct oscillatory patterns, indicating simpler and less varied convective motions. This analysis reveals that increasing salinity reduces both the intensity and complexity of turbulent structures within the convection cell. These findings have practical implications for understanding fluid dynamics under varying salinity conditions, potentially informing engineering and environmental applications where turbulence control is critical. This significant level is a defining feature of seawater. At a salinity of 3.5%, seawater presents a set of physical properties that differ from freshwater. These include higher density, a lower freezing point, and unique buoyancy characteristics. Understanding these practical implications is crucial for our research, as they directly apply to various fields. Controlled laboratory experiments provide valuable knowledge and insights
Preparing Educators to Effectively Engage with Postsecondary STEM Students with Autism
Get PDFAutism spectrum disorder (ASD) is a lifetime mental disability (Boucher, 2009). Because the brains of people with autism work differently than their non-neurodiverse peers (Kuzminskaite et al., 2020), they tend to respond to external stimuli in a hypo- or hyper-sensory fashion. One of the primary considerations that must be accounted for when working with individuals with autism is that the brains of these persons are each neurologically distinct. In other words, there is no one-size-fits-all means by which individuals with ASD learn and develop and, consequently, no single way to therefore engage with said individuals (Anderson & Butt, 2017; Kuzminski et al., 2019). Students with ASD present with strengths that position them to be successful in STEM fields, including attention to and focus on details, persistence, and recognizing and using patterns (Hassenfeldt et al., 2019). However, even though students with ASD demonstrate cognitive and academic capabilities that contribute to the STEM fields, they also experience barriers in other areas (sensorial, social, emotional, communication, routine changes, time management) that pose difficulties in college (Wick, 2022). Therefore, students with ASD need continuous accommodation, support, and/or interventions or treatments as their unique needs change and evolve. Consequently, those educators working alongside students with ASD require a comprehensive understanding of the studentsâ?? extraordinary and efficient neurological distinctness, as the brain of ASD just â??works differentâ?? (Wick, 2022). The work presented herein seeks to address these considerations and to promote conversation around best practices for supporting and engaging with postsecondary STEM students with ASD
The Additive Effect of Neuromuscular Electrical Stimulation on Resistance Training Induced Adaptations in Glycemic Control, Muscle Mass and Muscular Strength
Get PDFBackground: Most adults do not reach the physical activity guidelines set by ACSM (\u3e75%). Resistance training is well known to improve muscle mass, strength, and glycemic control. Neuromuscular electrical stimulation (NMES) is a mode of inducing involuntary muscle contractions. Previously, we have shown neuromuscular electrical stimulation is able to improve glycemic control. However, the effects of superimposing NMES while resistance training on glycemic control, substrate utilization and resting energy expenditure (REE) is unknown. Purpose: To investigate the effects of 8 weeks of superimposed NMES on resistance training compared to resistance training for glycemic control, substrate utilization, REE, muscle mass and strength. Methods: Sedentary, untrained participants with overweight to obesity (n=24; age-32.12±2.64 years; BMI-34.24±1.45 kg/m²) were randomized into a superimposed NMES on resistance training or resistance training group. All participants performed resistance training (24 sessions, 3x/week for 8 weeks) while also receiving bilateral quadricep stimulation using low intensity (minimum setting on device) or high intensity (maximum tolerable) NMES (50 Hz, 300µs pulse width). Insulin sensitivity was assessed by homeostatic model assessment of insulin resistance (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI-IS), oral glucose tolerance test, and continuous glucose monitoring. REE and substrate utilization was measured by indirect calorimetry, with body composition measured by dual energy X-ray absorptiometry and strength by 1 repetition maximum. Results: Both groups had comparable fasting glucose, glucose tolerance, substrate utilization, muscle mass, and strength at baseline (p \u3e 0.05). 8 weeks of superimposed NMES on resistance training improved insulin sensitivity measured by HOMA-IR and QUICKI and trended to improve glucose tolerance (p\u3c0.05). REE increased in the resistance training group (p\u3c0.05) while substrate utilization did not change in either group (p\u3e0.05). Both groups similarly improved lower body strength (p\u3c0.05) and body composition (p\u3c0.05). Conclusion: Superimposing NMES during resistance training results in greater improvement in insulin sensitivity compared to resistance training alone. Improvement in muscle mass and strength was comparable between the two groups
Method Development for the Quantification of Critically Valuable Elements in Permian Basin Produced Waters
Get PDFProduced waters (PW) are a major byproduct of the oil and gas industrial hydraulic fracturing processes that create a major waste disposal issue with a need for disposal, treatment, and reuse method developments. The current primary disposal method is subsurface injection, which can lead to high pressures in the subsurface. PWs are often highly saline from mineral leaching due to long residence in subsurface reservoirs. According to the USGS National Minerals Information Center, bromine, calcium chloride, iodine, lithium, magnesium, and sodium chloride have been found in and extracted from these domestic subsurface brines, suggesting that there may be other economically valuable elements present in these brines. The quantification of critically valuable elements (CVEs) in high total dissolved solids (TDS) brines is an underdeveloped area of analysis. Chelex-100 resin is well documented to work with high concentration brines. In this study, high TDS brines are pre-treated and diluted to ~50 g/L prior to preconcentration in Chelex-100 resins to combat the effects of low Na/(Ca+Mg) ratios. This study utilized vertical columns that employ gravity elution. In addition, water samples were analyzed via Inductively Coupled Plasma â?? Optical Emission Spectra (ICP-OES), for their sodium, calcium, and magnesium masses, which are used to determine salt ratios and compared to the TDS concentration and recoveries.This study finds that Chelex-100 resin is effective for recovering lanthanides and improves recovery of high field strength elements and industrial elements compared to the previous study. Alkaline and Alkali Earth elements were also analyzed, but performed poorly, as expected, by nature of the resinâ??s preference to sorb multivalent cations. Precious metals, similarly, performed poorly, as expected. The Na/(Ca+Mg) ratios indicated that the drop in recovery is likely associated with resin degradation, rather than salt interference with the resin
Ecological, Climatic, And Geomorphic Controls Of The Transport And Fate Of Co2 In Coastal Arctic Aquatic Ecosystems
No full textDue to the ecological and physical responses of arctic tundra to warming, organic carbon (C) stored in frozen permafrost soils is increasingly at risk of mineralization and export to aquatic systems, the coast, and atmosphere. Although many coastal aquatic systems in the Arctic are likely net sources of CO2 to the atmosphere, little is known about the drivers of inorganic C flux and how these systems contribute to regional C budgets. This dissertation addresses several lapses in our understanding of coastal inorganic C dynamics in arctic Alaska via three data chapters. In chapter 2, I examine seasonal and regional variability in carbon cycling and CO2 flux in five shallow arctic estuaries with varying connectivity to the adjacent shelf sea and terrestrial inputs. We found that heterotrophic conditions during the ice covered season led to CO2 accumulation in bottom waters. In contrast, all of the estuaries were atmospheric CO2 sinks during spring breakup and open water periods, however, the degree of terrestrial influence determined the overall strength of CO2 uptake. Chapter 3 is a spatially and temporally integrative study of CO2 fluxes in one arctic estuary during the open water season. We found that wind-driven currents controlled where water from rivers or incoming oceanic influence was distributed in the lagoon, which created a mosaic of CO2 release and uptake events across the estuary. Chapter 4 examines how organic C and lateral connectivity of Alaskan Coastal Plain tundra streams influence metabolism and CO2 efflux. We especially highlight the impact of varying stream geomorphologies and hydrological regimes, including extreme rainfall events, in controlling soil C movement and processing. Overall, this dissertation will contribute to better understanding of the movement of terrestrially derived C across the stream-ocean shelf continuum in critically understudied small, coastal arctic watersheds
Training Neural Networks on Interval Data: Unexpected Results and Their Explanation
No full textIn many practically useful numerical computations, training-and-then-using a neural network turned out to be a much faster alternative than running the original computations. When we applied a similar idea to take into account interval uncertainty, we encountered two unexpected results: (1) that while for numerical computations, it is usually better to represent an interval by its midpoint and half-width, for neural networks, it is more efficient to represent an interval by its endpoints, and (2) that while usually, it is better to train a neural network on the whole data processing algorithm, in our problems, it turned out to be more efficient to train several subnetworks on subtasks and then combine their results. In this paper, we provide a theoretical explanation for these unexpected results
Warmth of the Welcome: Immigration and Local Housing Returns
Get PDFWe study the effect of immigration on home values in the U.S. Applying a county-level instrument for immigration, we find that immigration increases local house price appreciation and decreases its within-county spatial dispersion. Our estimates suggest that, on average, a one percentage point in- crease in the immigrant share of the local population raises house price appreciation by approximately 7 percent and reduces the dispersion of housing return within a county by about 1.5 percentage points. We also show that such effects are strikingly heterogeneous across counties and appear to be deter- mined by local culture. Using several proxies for attitudes toward immigration at the county level, we find that immigration boosts housing returns and limits its spatial dispersion only in counties with residents who are younger, more educated, and less racially biased. Our findings highlight that the effect of immigration on home values (or the lack thereof) is highly contingent on natives’ attitudes toward immigrants
How Technology Affordances of Sharing Economy Platforms Influence Cultural Distance and the Affective Commitment of Immigrants at the Base of the Pyramid
Get PDFWithin the immigrant population, there is a sub-group at the Base of the Pyramid (BoP). Compared to others, BoP immigrants receive lower incomes, have weaker informal networks, and face greater resource constraints. As more and more BoP immigrants participate in the sharing economy, we suggest that the use of sharing economy platforms by BoP immigrants would have a significant impact on their integration into a new country because it would influence cultural distance and affective commitment in multiple ways. Hence, in the present study, we seek to explore the relationships among the technology affordance of sharing economy platforms, the cultural distance, and the affective commitment of BoP immigrants. Unlike prior research suggesting a nonlinear relationship between cultural distance and affective commitment, our results support cultural distance as a full mediator of the relationship between technology affordance and the affective commitment of BoP immigrants. Our study makes several theoretical and practical contributions related to technology affordance theory, the sharing economy literature, and BoP immigrant populations