Does Globalization Affect the Performance of Secondary Education Systems? A Coevolution Model of Multiplex Transnational Networks and Educational Performance

In Chap. 10.1007/978-3-030-78885-8_4, Helen Seitzer and Michael Windzio address PISA scores, student exchange, service sector trade flows, and migration. PISA, a study on education system effectiveness, is used to compare, name, and shame the ‘best’ and ‘worst’ of state education. Better education in connection to job prospects is one reason for migration but might also influence students’ choice of the destination for an exchange. But, both these networks might also follow existing paths of interconnectedness, similar to service trade relations. Applying a network coevolution model, the authors ask if a country’s change in PISA scores coincides with student exchange flows and migration patterns, or if other factors such as cultural, geographical, or economic aspects influence the choice of destination.

Tidally modified western boundary current drives interbasin exchange between the Sea of Okhotsk and the North Pacific

The interbasin exchange between the Sea of Okhotsk and the North Pacific governs the intermediate water ventilation and fertilization of the nutrient-rich subpolar Pacific, and thus has an enormous influence on the North Pacific. However, the mechanism of this exchange is puzzling; current studies have not explained how the western boundary current (WBC) of the subarctic North Pacific intrudes only partially into the Sea of Okhotsk. High-resolution models often exhibit unrealistically small exchanges, as the WBC overshoots passing by deep straits and does not induce exchange flows. Therefore, partial intrusion cannot be solely explained by large-scale, wind-driven circulation. Here, we demonstrate that tidal forcing is the missing mechanism that drives the exchange by steering the WBC pathway. Upstream of the deep straits, tidally-generated topographically trapped waves over a bank lead to cross-slope upwelling. This upwelling enhances bottom pressure, thereby steering the WBC pathway toward the deep straits. The upwelling is identified as the source of joint-effect-of-baroclinicity-and-relief (JEBAR) in the potential vorticity equation, which is caused by tidal oscillation instead of tidally-enhanced vertical mixing. The WBC then hits the island chain and induces exchange flows. This tidal control of WBC pathways is applicable on subpolar and polar regions globally.

Machine Learning Analysis of Hydrologic Exchange Flows and Transit Time Distributions in a Large Regulated River

Hydrologic exchange between river channels and adjacent subsurface environments is a key process that influences water quality and ecosystem function in river corridors. High-resolution numerical models were often used to resolve the spatial and temporal variations of exchange flows, which are computationally expensive. In this study, we adopt Random Forest (RF) and Extreme Gradient Boosting (XGB) approaches for deriving reduced order models of hydrologic exchange flows and associated transit time distributions, with integrated field observations (e.g., bathymetry) and hydrodynamic simulation data (e.g., river velocity, depth). The setup allows an improved understanding of the influences of various physical, spatial, and temporal factors on the hydrologic exchange flows and transit times. The predictors also contain those derived using hybrid clustering, leveraging our previous work on river corridor system hydromorphic classification. The machine learning-based predictive models are developed and validated along the Columbia River Corridor, and the results show that the top parameters are the thickness of the top geological formation layer, the flow regime, river velocity, and river depth; the RF and XGB models can achieve 70% to 80% accuracy and therefore are effective alternatives to the computational demanding numerical models of exchange flows and transit time distributions. Each machine learning model with its favorable configuration and setup have been evaluated. The transferability of the models to other river reaches and larger scales, which mostly depends on data availability, is also discussed.

Effects of natural streambed sediment on the riverbed exchange flows and microbial respiration

<p>Exchange flows at the water-sediment interface control river water quality and carbon cycling through microbial respiration. However, accurate quantification of these exchange flows and microbial respiration is still challenging in field surveys due in part to the dynamic turbulence generated by streambed topography. Using a framework that combines Structure-from-Motion (SfM) photogrammetry with a fully-coupled surface-subsurface computational fluid dynamics (CFD) model, this work studies the effects of streambed sediment structure on riverbed turbulence and its impact on exchange flows and microbial respiration. Specifically, the SfM photogrammetry is first applied to obtain mm- to cm-scale resolution riverbed topography over a meter scale domain at four sites; these high-resolution riverbed topography data are then used to generate meshes for use in hyporheicFoam, a fully coupled surface-subsurface model developed in OpenFOAM. Simulated time series of water depth and average flow velocity from a previously-developed 30-kilometer scale CFD model will be used to set the water depth and mean flow velocity conditions for high-resolution CFD models of the SfM-characterized locations. The modeling results will be used to investigate the dependence of riverbed exchange flows, concentration gradients, and the concentration profile from the water surface to riverbed on water depth, mean velocity, roughness size, sediment distribution, bed porosity, and subsurface permeability. The relative importance of flow advection, turbulence dispersion, and microbial reaction in both streambed and surface water will also be evaluated.</p>

Rotational effects on exchange flows across a submerged sill

This paper presents new laboratory-scale numerical simulations of density-driven exchange flows generated across an idealised, submerged sill obstruction under both non-rotating and rotating frames of reference using the Bergen Ocean Model (BOM), a three-dimensional general ocean circulation model. Initial non-rotating BOM simulations are compared directly with previous laboratory data obtained in a large-scale channel facility incorporating an idealised trapezoidal sill. These laboratory experiments demonstrate that the saline intrusion flux across the sill is initially reduced and then eventually fully blocked under increasing net-barotropic flow conditions imposed in the counterflowing upper freshwater layer, with the saline blockage also more evident for reduced sill submergence depths. These parametric dependences are also demonstrated in the equivalent BOM simulations of the non-rotating sill exchange flows, although the numerical model results tend to overpredict both the interfacial velocity and density gradients across the sill (as indicative of suppressed interfacial mixing), as well as the fresh-saline source flux ratio at which full blockage of the saline intrusion occurs. The BOM simulations are then extended to consider rotating sill exchange flow dynamics. In particular, these additional runs demonstrate that Coriolis forces increase the overall blockage of the saline intrusion layer compared to equivalent non-rotating exchange flows, especially when the Rossby number associated with the saline intrusion flow across the sill is considerably less than unity. This effect is largely attributed to the development of Ekman boundary layer dynamics and associated secondary circulations within the bi-directional exchange flows. These are shown to impose strong control on the transverse distribution and extent of the lower saline intrusion flow across the sill and, hence, the parametric conditions under which full saline intrusion blockage is achieved in rotating sill exchange flows.