Two nonlinear systems from mathematical physics

The dissertation is divided into two chapters. In the first one, we consider the 2-Vortex problem for two point vortices in a complex domain. The Hamiltonian of the system contains the regular part of a hydrodynamic Green’s function, the Robin function h and two coefficinets which are the strengths of the point vortices. We prove the existence of infinitely many periodic solutions with minimal period T which are a superposition of a slow motion of the center of vorticity along a level line of h and of a fast rotation of the two vortices around their center of vorticity. These vortices move in a prescribed subset of the domain that has to satisfy a geometric condition. The minimal period can be any T in a certain interval. Subsets to which our results apply can be found in any generic bounded domain. The proofs are based on a recent higher dimensional version of the Poincaré-Birkhoff theorem due to Fonda and Ureña. In the second part, we study bifurcations of a multi-component Schrödinger system. We construct a solution branch synchronized to a positive solution of a simpler system. From this branch, we find a sequence of local bifurcation values in the one dimensional case and also in the general case provided that the positive solution is nondegenerate

The Effects Of Students Predispositions Toward Communication, Learning Styles, And Sex On Academic Achievement

Females are more apprehensive when talking in class, but more nonverbally immediate, and prefer a collaborative learning style.  Males prefer independent and avoidant learning styles, and report learning less than females

The Optimal Taxation of Asset Income when Government Consumption is Endogenous: Theory, Estimation and Welfare

This paper derives the Ramsey optimal policy for taxing asset income in a model where government expenditure is a function of net output or the inputs that produce it. Extending Judd (1999), I demonstrate that the canonical result that the optimal tax on capital income is zero in the medium to long term is a special case of a more general model. Employing a vector error correction model to estimate the relationship between government consumption and net output or the factor inputs that generate it for the United States between 1948Q1 to 2015Q4, I demonstrate that this special case is empirically implausible, and show how a cointegrating vector can be used to determine the optimal tax schedule. I simulate a version of the model using the empirical estimates to measure the welfare implications of changing the tax rate on asset income, and contrast these results with those generated in a version of the model where government consumption is purely exogenous. The shifting pattern of welfare measurements con rms the theoretical results. I calculate that the prevailing effective tax rate on net asset income in the US between 1970 and 2014 averaged 0.449. Hence abolishing the tax completely does generate welfare improvements, though only by the equivalent of between 1.103 and 1.616% percent permanent increase in consumption - well under half the implied welfare benefit when the endogeneity of the government consumption is ignored. The maximum welfare improvement from shifting part of the burden of tax from capital to labor is the equivalent of a permanent increase in consumption of between only 1.491 and 1.858%, and is attained when the tax rate on asset income is lowered to between 0.148 and 0.186. Allowing the tax rate to vary over time raises the maximum welfare bene t to 1.865%. All the results are very robust to a wide range of elasticities of labor supply

Barriers and facilitators to physical activity: a comparative analysis of transplant athletes competing in high intensity sporting events with other transplant recipients

Background: There is widespread recognition that many transplant recipients struggle to become and remain physically active. However, some transplant recipients do undertake strenuous training and significant physical activity (PA) and participate in intensive sports.Aim: This study sought to understand facilitators and barriers to be physically active for Transplant Athletes (TXA) compared to a group of Dutch transplantees. This explorative mixed methods study analysed race performance and interview data from TxA who participated in cycling and/or the sprint triathlon at the World Transplant Games 2023, and compared their lived experiences in terms of barriers and facilitators of PA with those of 16 transplantees in a study from the Netherlands previously published in this journal.Methods: Using Patient and Public Involvement and engagement (PPI), race data from World Transplant Games 2023 and subsequent in-depth interviews were used from 27 TxA. A visual artefact of barriers and facilitators from the previous Dutch study was used to prompt identification and discussion of barriers and facilitators of PA. Interview data were coded by three coders.Results: Many of the barriers to PA previously reported by Dutch transplant recipients were not shared by the majority of TxA in this study. The TxA in this study reported significantly lower physical limitations, lower fear to undertake exercise, and no comorbidity issues for TxA. Furthermore, TxA perceived they received substantial social support, had the strength to do PA, and were in control of their weight.Conclusion: Several TxA reported a lack of understanding from medical and other professionals about the appropriate intensity of PA. An evidence-based framework of PA for transplant recipients and transplant athletes is needed for safe and appropriate PA

Capital-skill complementarity and the immigration surplus

We build a neoclassical growth model with overlapping dynasties and capital–skill complementarities to evaluate changes in immigration policy. Calibrating the model using US data, we quantify the differential effects of skilled and unskilled immigration on factor returns and on the welfare of different sectors of the population. An influx of high-skilled immigrants lowers the wages of skilled workers, raises the wages of unskilled workers, and because of the relative complementarity between capital and skilled labor, substantially raises the rate of return to native-owned capital. By contrast, an influx of unskilled immigrants produces an opposite effect on wages, and has only a negligible effect on the return to capital. Because of capital–skill complementarity, an increase in the number of skilled immigrants generates an immigration surplus—the overall welfare benefit accruing to the native population—that is approximately ten times larger than the immigration surplus generated by an identical increase in the number of unskilled immigrants. This differential welfare effect is far higher than can be accounted for by the disparity between the productivities of each type of worker

Using social media in health literacy research: A promising example involving Facebook with young Aboriginal and Torres Strait Islander males from the top end of the Northern Territory

This brief report describes three key lessons learned during a health literacy research project with young Aboriginal and Torres Strait Islander males from the Top End of the Northern Territory (NT), Australia. More specifically, it is a methodologically focused paper that discusses processes associated with using a combination of yarning sessions and social media content as tools to unpack conceptualisations of health and well‐being among this marginalised population. The lessons discussed include (a) the utility of using social media in providing an authentic window into the lives of a hard‐to‐reach populations; (b) the need to carefully consider ethical implications; and (c) the benefits of using social media content to triangulate data and enhance methodological rigour. To understand the methodological contribution social media can make to equity‐focused health literacy research, it is first useful to understand what is meant by health literacy

Barriers and facilitators to physical activity: a comparative analysis of transplant athletes competing in high intensity sporting events with other transplant recipients

Background There is widespread recognition that many transplant recipients struggle to become and remain physically active. However, some transplant recipients do undertake strenuous training and significant physical activity (PA) and participate in intensive sports. Aim This study sought to understand facilitators and barriers to be physically active for Transplant Athletes (TXA) compared to a group of Dutch transplantees. This explorative mixed methods study analysed race performance and interview data from TxA who participated in cycling and/or the sprint triathlon at the World Transplant Games 2023, and compared their lived experiences in terms of barriers and facilitators of PA with those of 16 transplantees in a study from the Netherlands previously published in this journal. Methods Using Patient and Public Involvement and engagement (PPI), race data from World Transplant Games 2023 and subsequent in-depth interviews were used from 27 TxA. A visual artefact of barriers and facilitators from the previous Dutch study was used to prompt identification and discussion of barriers and facilitators of PA. Interview data were coded by three coders. Results Many of the barriers to PA previously reported by Dutch transplant recipients were not shared by the majority of TxA in this study. The TxA in this study reported significantly lower physical limitations, lower fear to undertake exercise, and no comorbidity issues for TxA. Furthermore, TxA perceived they received substantial social support, had the strength to do PA, and were in control of their weight. Conclusion Several TxA reported a lack of understanding from medical and other professionals about the appropriate intensity of PA. An evidence-based framework of PA for transplant recipients and transplant athletes is needed for safe and appropriate PA

Derivation and external validation of a clinical prognostic model identifying children at risk of death following presentation for diarrheal care

Diarrhea continues to be a leading cause of death for children under-five. Amongst children treated for acute diarrhea, mortality risk remains elevated during and after acute medical management. Identification of those at highest risk would enable better targeting of interventions, but available prognostic tools lack validation. We used clinical and demographic data from the Global Enteric Multicenter Study (GEMS) to build clinical prognostic models (CPMs) to predict death (in-treatment, after discharge, or either) in children aged ≤59 months presenting with moderate-to-severe diarrhea (MSD), in Africa and Asia. We screened variables using random forests, and assessed predictive performance with random forest regression and logistic regression using repeated cross-validation. We used data from the Kilifi Health and Demographic Surveillance System (KHDSS) and Kilifi County Hospital (KCH) in Kenya to externally validate our GEMS-derived CPM. Of 8060 MSD cases, 43 (0.5%) children died in treatment and 122 (1.5% of remaining) died after discharge. MUAC at presentation, respiratory rate, age, temperature, number of days with diarrhea at presentation, number of people living in household, number of children <60 months old living in household, and how much the child had been offered to drink since diarrhea started were predictive of death both in treatment and after discharge. Using a parsimonious 2-variable prediction model, we achieved an area under the ROC curve (AUC) of 0.84 (95% CI: 0.82, 0.86) in the derivation dataset, and an AUC = 0.74 (95% CI 0.71, 0.77) in the external dataset. Our findings suggest it is possible to identify children most likely to die after presenting to care for acute diarrhea. This could represent a novel and cost-effective way to target resources for the prevention of childhood mortality

Trycycler: consensus long-read assemblies for bacterial genomes

While long-read sequencing allows for the complete assembly of bacterial genomes, long-read assemblies contain a variety of errors. Here, we present Trycycler, a tool which produces a consensus assembly from multiple input assemblies of the same genome. Benchmarking showed that Trycycler assemblies contained fewer errors than assemblies constructed with a single tool. Post-assembly polishing further reduced errors and Trycycler+polishing assemblies were the most accurate genomes in our study. As Trycycler requires manual intervention, its output is not deterministic. However, we demonstrated that multiple users converge on similar assemblies that are consistently more accurate than those produced by automated assembly tools

On the Political Economy of Deficit Bias and Immigration

How much can governments shift the cost of their expenditure from today’s voters to tomorrow’s generations of immigrants, without resorting to taxation that is explicitly discriminatory? I demonstrate that if their societies are absorbing continuous flows of new immigrants, we should expect governments that represent the interests of today’s population to choose policies that shift some portion of the tax burden to the future, even if that population is altruistically linked to future generations. To measure the deficit bias, I analyse the dynamic behaviour of an optimal growth model with overlapping dynasties and factor taxation, calibrated for the US economy, and consider the welfare implications for today’s population and their descendants of intertemporal shifts in the tax rates on labour and asset income as well as transfer payments. Models with overlapping infinite-lived dynasties allow for a very clear distinction between natural population growth (an increase in the size of existing dynasties) and immigration (the addition of new dynasties). They also provide an alternative to the strict dichotomy between models with overlapping generations, where agents disregard the impact of their choices on future generations, and the quasi-Ricardian world of infinite-lived dynasties with representative agents that fully participate in both the economy and the political system in every period. The trajectory of the debt burden predicted by the model is a good match for the rise in US Federal Government debt since the early 1980’s, as well as the increases in debt projected by the Congressional Budget Office over the next few decades