Exchange Model Research Articles

An improved model for air–sea exchange of elemental mercury in MITgcm-ECCOv4-Hg: the role of surfactants and waves

Abstract. The air–sea exchange of elemental mercury (Hg0) plays an important role in the global Hg cycle. Existing air–sea exchange models for Hg0 have not considered the impact of sea surfactants and wave breaking on the exchange velocity, leading to insufficient constraints on the flux of Hg0. In this study, we have improved the air–sea exchange model of Hg0 in the three-dimensional ocean transport model MITgcm (MIT General Circulation Model) by incorporating sea surfactants and wave-breaking processes through parameterization, utilizing the total organic carbon concentration and significant wave height data. The inclusion of these factors results in an increase of 62 %–225 % in the global transfer velocity of Hg0 relative to the baseline model. Air–sea exchange flux is increased in mid-latitude to high-latitude regions with high wind and wave-breaking efficiency, while it is reduced by surfactant and concentration change at low latitudes with low wind speeds and in nearshore areas with low wave heights. Compared with previous parameterizations, the updated model demonstrates a stronger dependence of Hg0 air–sea exchange velocity on wind speed. Our results also provide a theoretical explanation for the large variances in estimated transfer velocity between different schemes.

Development of heat exchanger modelling capability for a finite volume aeroelasticity solver

Abstract Heat exchangers are frequently used in aero engines and are known to significantly affect the surrounding steady and unsteady flow. In certain applications, they may thereby also influence the aeroelastic stability of upstream or downstream components but there is limited research on this in the public domain. This paper aims to demonstrate the influence of heat exchangers on unsteady flows relevant to aeroelastic problems. This is achieved by developing heat exchanger modelling capability for an in-house finite volume aeroelasticity solver, for which heat exchanger is represented as a porous medium, as this is the established approach in existing aerodynamic studies using commercial CFD software. The governing equations for a Darcy-Forchheimer porous media model suitable for unsteady and compressible flows are presented, which are derived by the application of volume averaging theory to the Navier-Stokes equations. The implementation of this model within the time integration method used for the solver is then described and verified by comparison of results for steady flows against an established commercial CFD solver, where close agreement between both in-house and commercial solvers has been observed. Lastly a preliminary demonstration of the capability to model unsteady heat exchanger flows is presented by application to an aeroacoustic problem, where the interaction of the pressure waves and the heat exchanger is investigated.

Magnetic ground state and excitations in the mixed 3d−4d quasi-one-dimensional spin-chain oxide Sr3NiRhO6

Entanglement of spin and orbital degrees of freedom, via relativistic spin-orbit coupling, in 4d transition metal oxides can give rise to a variety of unique quantum phases. A previous study of mixed 3d−4d quasi-1D spin-chain oxide Sr3NiRhO6 using the magnetization measurements by Mohapatra [] revealed a partially disordered antiferromagnetic structure below 50 K. We here report the magnetic ground state and spin-wave excitations in Sr3NiRhO6 using muon spin rotation and relaxation (μSR), and neutron (elastic and inelastic) scattering techniques. Our neutron diffraction study reveals that in the magnetic structure of Sr3NiRhO6 Rh4+ and Ni2+ spins are aligned ferromagnetically in a spin chain, with moments along the crystallographic c axis. However, spin chains are coupled antiferromanetically in the ab plane. μSR reveals the presence of oscillations in the asymmetry-time spectra below 50 K, supporting the long-range magnetically ordered ground state. Our inelastic neutron scattering study reveals gapped quasi-1D magnetic excitations with a large ratio of gap to exchange interaction. The observed spin-wave spectrum could be well fitted with a ferromagnetic isotropic exchange model (with J=3.7 meV) and single ion anisotropy (D=10 meV) on the Ni2+ site. The magnetic excitations survive up to 85 K, well above the magnetic ordering temperature of ∼50 K, also indicating a quasi-1D nature of the magnetic interactions in Sr3NiRhO6. Published by the American Physical Society 2024

Performance Analysis of a Brazed Plate Heat Exchanger during Condensation of R1233zd(E)

Abstract This paper focuses on the validation of a brazed plate heat exchanger (BPHE) model that acts as the condenser of a novel in-rack cooling loop. In the proposed system, the primary fluid enters as a saturated vapor, while the secondary fluid enters as a sub-cooled liquid flowing in a counterflow configuration. The model augments an existing general technique for simplicity and computational efficiency and is applied to the condensation of a low-pressure, environmentally friendly refrigerant i.e., R1233zd(E). The model analyzes the heat transfer and pressure drop values of both fluids in the heat exchanger and uses these results to predict the heat exchanger duty and exit temperature and pressure of both fluids. The model predicts the values of fluid output properties along with heat exchanger duty to within 20% of experimental measurements. The validated model is then used to assess the magnitude of the heat transfer coefficient and friction factor attained on both fluid sides of the heat exchanger, including relatively uniform water-side heat transfer coefficient, a substantial (30%-80% of overall flow length) region of two-phase condensation, and a minimum refrigerant-side friction factor in the sub-cooled regime.

Data-Model Fusion-Driven Method for Fault Quantitative Diagnosis of Heat Exchanger

Heat exchangers play essential roles in the oil and gas production process for convective heat transfer and heat conduction. The health management of heat exchangers stays in the direct monitoring of performance parameters. Aiming at the difficulty of precise fault identification and quantification for heat exchangers in multiple unknown failure modes, a data-model fusion-driven fault quantitative diagnosis method is proposed. Firstly, based on the monitoring data such as temperature, pressure and flow rate, the secondary parameters characterizing the heat exchanger running state are constructed combined with structural physical parameters. Then, by analyzing the correlation among parameter variation, failure modes and deterioration degree, a qualitative inference model of heat exchanger is formed for fault identification, where weights of parameters are introduced based on their sensitivity for different failure modes. After the fault mode is identified, to achieve quantitative analysis of the failure degree, an index-integrated mechanism equation is constructed using monitoring data and secondary parameters, where the index is dynamically modified by online data. Finally, a heat exchanger experiment is carried out to demonstrate the robustness and accuracy of the proposed method.

Secure Supply Chain Information Interchange using Distributed Trust Backbone

International trade requires transparent visibility of the goods transportation. High-quality data related to containers is essential for container movement across the border speed. However, customs and port authorities face information incorrectness and inconsistency, which are significant determinants that decrease the performance of container clearance in supply chain activities. The Seamless Integrated Data Pipeline principle has been proposed to overcome the mentioned data quality shortcomings and enhance supply chain visibility. Based on the Data Pipeline idea, we proposed the Distributed Trust Backbone (DTB) as a model of secure information exchange between parties within the supply chain activity. However, the supply chain data is highly dynamic. Access control on dynamic resources is the key to enabling secure data exchange and clear visibility. We take this challenge up in this paper. We propose an access control mechanism based on the supply chain Data Pipeline concept and apply it to the DTB model. The elaboration on the concrete detail of the system is presented in this paper. The prototype has been developed and performed in the simulation tests. It reduces 58% of requesting data for supply chain activities. The results of the experiments show that our proposed method performs 100% access control to data with BigO(1) accessing the Access Control List. It can ensure that the information for decision-making in the supply chain is of high quality. The supply chain visibility is clearer and speeds up a modern information exchange system of supply chains.

A novel mechanism and model of hydrogen isotope exchange in vacancy considering nuclear quantum effects

Abstract Tritium (T) retention in plasma-facing materials (PFMs) raises significant radiological safety concerns and adversely affects the self-sustained burning of T in fusion reactors. Therefore, the removal of retained T from PFMs has become an urgent task. Hydrogen isotope (HI) exchange has proven to be an effective method for T removal. However, the microscopic mechanisms, particularly the role of isotope effects, remain insufficiently understood. For the first time, this work employs path integral molecular dynamics (PIMD) to account for the nuclear quantum effects of HIs and explore the microscopic mechanisms of HI exchange in tungsten (W) vacancies. Atomic-scale simulations reveal that the fundamental principle of HI exchange is the reduction in binding energy between HIs and vacancies as the defect filling level increases, involving two key processes: de-trapping and trapping. These processes are influenced by isotope effects, with pronounced differences observed at low temperatures. Notably, T exhibits a higher probability of de-trapping from vacancies compared to hydrogen (H), while vacancies demonstrate a stronger affinity for trapping H. In contrast, the isotope effect is less pronounced between deuterium (D) and H, leading to different exchange efficiencies between H and T, as well as between D and T. Based on these isotope effects, we proposed a detailed microscopic mechanism for HI exchange in vacancies and developed a T evolution model that accounts for variations in HI concentrations. This work advances our understanding of HI exchange for T removal applications and offers a more accurate assessment of T retention in future D-T environments.

Relaxation-exchange magnetic resonance imaging (REXI): a non-invasive imaging method for evaluating trans-barrier water exchange in the choroid plexus.

The choroid plexus (CP) plays a crucial role in cerebrospinal fluid (CSF) production and brain homeostasis. However, non-invasive imaging techniques to assess its function remain limited. This study was conducted to develop a novel, contrast-agent-free MRI technique, termed relaxation-exchange magnetic resonance imaging (REXI), for evaluating CP-CSF water transport, a potential biomarker of CP function. REXI utilizes the inherent and large difference in magnetic resonance transverse relaxation times (T2s) between CP tissue (e.g., blood vessels and epithelial cells) and CSF. It uses a filter block to remove most CP tissue magnetization (shorter T2), a mixing block for CP-CSF water exchange with mixing time tm, and a detection block with multi-echo acquisition to determine the CP/CSF component fraction after exchange. The REXI pulse sequence was implemented on a 9.4 T preclinical MRI scanner. For validation of REXI's ability to measure exchange, we conducted preliminary tests on urea-water proton-exchange phantoms with various pH levels. We measured the steady-state water efflux rate from CP to CSF in rats and tested the sensitivity of REXI in detecting CP dysfunction induced by the carbonic anhydrase inhibitor acetazolamide. REXI pulse sequence successfully captured changes in the proton exchange rate (from short-T2 component to long-T2 component [i.e., ksl]) of urea-water phantoms at varying pH, demonstrating its sensitivity to exchange processes. In rat CP, REXI significantly suppressed the CP tissue signal, reducing the short-T2 fraction (fshort) from 0.44 to 0.23 (p < 0.0001), with significant recovery to 0.28 after a mixing time of 400 ms (p = 0.014). The changes in fshort at various mixing times can be accurately described by a two-site exchange model, yielding a steady-state water efflux rate from CP to CSF (i.e., kbc) of 0.49 s-1. A scan-rescan experiment demonstrated that REXI had excellent reproducibility in measuring kbc (intraclass correlation coefficient = 0.90). Notably, acetazolamide-induced CSF reduction resulted in a 66% decrease in kbc within rat CP. This proof-of-concept study demonstrates the feasibility of REXI for measuring trans-barrier water exchange in the CP, offering a promising biomarker for future assessments of CP function.

Adaptive Bounded Bilinear Control of a Parallel‐Flow Heat Exchanger

ABSTRACTThis work investigates the adaptive constrained control design for a parallel‐flow heat exchanger represented by a system of two coupled linear first‐order hyperbolic partial differential equations (PDEs). This system incorporates structured uncertainty involving unknown in‐domain parameters that characterize neglected dynamics in the heat exchanger model. These parameters may encompass unmodeled heat transfer phenomena, variations in fluid properties, and modeling simplifications. The objective is to regulate the internal fluid outlet temperature to track a desired reference trajectory by adjusting the external fluid velocity. Due to inherent physical constraints, this manipulated variable is upper and lower‐bounded. Accordingly, the control problem is bounded and bilinear. Using the set‐invariance principle and an energy‐like framework, we first develop a bounded state‐feedback controller. Then, since the measurements are considered only at the boundaries, we propose an adaptive boundary observer using a swapping scheme and a recursive least squares identifier. The proposed adaptive observer provides online estimates of the distributed state and the unknown parameters. Next, the state‐feedback controller is associated with the boundary observer and parameter identifier, and the exponential stability of the closed‐loop system is guaranteed using Lyapunov's stability theory. Finally, we provide numerical simulations to demonstrate the efficiency of the proposed control scheme.

Heat transfer characteristics of buried pipes under groundwater seepage in Karst regions

Utilising geothermal energy through ground-source heat pump (GSHP) systems is a viable option. Karst regions, renowned for their abundant geothermal resources and complex geological structures, present a unique challenge owing to the presence and fluctuations of groundwater, which significantly alter the operational environment of GSHPs. Therefore, it is crucial to explore the mechanisms and performance of GSHPs in such areas. Based on actual Karst geological structures and using similarity theory, a multi-layer experimental model of a ground heat exchanger (GHE) was established in a laboratory. To enhance the GSHP performance, a forced seepage plan for shallow soil layers was proposed. Then, a controlled variable method was employed to investigate the impact of aquifer-related groundwater seepage factors on the heat transfer performance of buried pipes. Thresholds for groundwater velocity and temperature that enhanced thermal performance were identified. Groundwater seepage shortens the recovery time of the temperature field in geotechnical materials and influences the heat exchange intensity based on the flow temperature. This study focuses on a layered heat transfer model and proposes a relationship between aquifer thickness and geotechnical heat transfer, providing theoretical support for the application and optimisation of GSHP systems in Karst regions.

Reinforced Borrowing Framework: Leveraging Auxiliary Data for Individualized Inference.

Increasingly during the past decade, researchers have sought to leverage auxiliary data for enhancing individualized inference. Many existing methods, such as multisource exchangeability models (MEM), have been developed to borrow information from multiple supplemental sources to support parameter inference in a primary source. MEM and its alternatives decide how much information to borrow based on the exchangeability of the primary and supplemental sources, where exchangeability is defined as equality of the target parameter. Other information that may also help determine the exchangeability of sources is ignored. In this article, we propose a generalized reinforced borrowing framework (RBF) leveraging auxiliary data for enhancing individualized inference using a distance-embedded prior which uses data not only about the target parameter but also uses different types of auxiliary information sources to "reinforce" inference on the target parameter. RBF improves inference with minimal additional computational burden. We demonstrate the application of RBF to a study investigating the impact of the COVID-19 pandemic on individual activity and transportation behaviors, where RBF achieves 20%-40% lower MSE compared with existing methods.

Optimisation of a converging-diverging nozzle for the wet-to-dry expansion of the siloxane MM

Wet-to-dry expansion within the nozzle guide vane of an ORC turbine has been proposed as a means to improve the power output of ORC systems for waste-heat recovery (<250 °C). However, given the rapid fluid acceleration in the stator, the phases can develop significant velocity and temperature disparity due to density difference and finite rate of interphase heat transfer. Since these factors can significantly affect the phase-change process, wet-to-dry nozzle design techniques must account for non-equilibrium effects. The first part of this paper aims to further verify a previously developed quasi-1D inviscid non-equilibrium nozzle design tool by comparing it to non-equilibrium CFD simulations, which, unlike the design model, account for lateral flow variations, viscous and turbulence effects, along with secondary momentum forces. Within the CFD model, the interphase mass, momentum, and energy exchange models have been updated using correlations better tailored to evaporating droplet flows and a corrected drag equation. Moreover, the definition of the vapour mass fraction has been modified, while a simplified droplet breakup model has been used to predict the droplet size. The results from the CFD simulations indicate that the outlet vapour mass fraction is approximately 10 to 15% lower than that predicted by the quasi-1D tool. However, the overall flow behaviour and phase-change pattern were in satisfactory agreement, justifying the use of the design tool for 1D optimisation. As such, the quasi-1D tool is coupled to a gradient-based optimiser to optimise the nozzle pressure profile and enhance evaporation of siloxane MM for expansions with an inlet pressure ranging from 450 to 650 kPa, and inlet vapour quality of 0.3. CFD simulations of the optimised geometries indicate an increase of 3.3 to 5.7% in the outlet vapour mass fraction, which was raised from 84.9, 87.7 and 90.5% to 88.2, 93.4 and 95.7% for 450, 550 and 650 kPa inlet pressures respectively. However, a more abrupt expansion in the optimised nozzles resulted in the development of a shock and led to deterioration in nozzle efficiency compared to the baseline nozzles. Finally, a CFD-based shape optimisation was conducted, which demonstrated that it may be difficult to further enhance the vapourisation rate. However, the optimised geometry did mitigate the effect of the oblique shock that appears in the diverging section of the nozzle, raising the expansion efficiency by around 3%.

The Effectiveness of Teacher-Student Interaction in the English as a Foreign Language Classroom

The aim of the present study is to evaluate the effectiveness of teacher-student interaction in promoting authentic L2 classroom discourse. Classroom discourse is a major part of instruction that promotes speaking and develops students and teachers’ conversational skills. It constitutes a significant factor in the English as a Foreign Language (EFL) classroom, as it promotes communicative activities (reception, production, interaction, mediation) fundamental to L2 learning. A common exchange pattern used extensively in classroom discourse is the Initiation, Response, Feedback (IRF) model, by Sinclair and Coulthard, (1975, 1992), in which the teacher initiates (I) an exchange through questioning the whole class or one single student, the student responds (R) to the question, and then the teacher gives feedback (F). A qualitative case study approach was adopted. Twenty-seven EFL high school classrooms in Israel were observed. Research instruments were: classroom observation forms, filled by the researcher, where instances of IRF exchanges were marked; and semi-structured interviews with seven of the teachers observed to obtain information regarding their use of L1 in IRF exchanges. Findings show that teachers use the IRF exchange model to organize talk and follow basic turn taking rules. However, deviations from common IRF exchanges result in (1) imbalance of dominance between teacher and student talk time; (2) excessive use of L1 in exchanges, minimizing students’ exposure to L2; and (3) limited flow of teacher-student spoken communication and lack of student willingness to participate in the lesson. Practical implications for teacher educators will be discussed.

Internationalization of Higher Education: Critical Examination of Virtual Intercultural Exchange Models at Moroccan Universities

This article explores an intercultural and international teaching approach for higher education through the implementation of Collaborative Online Intercultural Learning (COIL) models to bolster cross-cultural communication competence among Moroccan EFL students. In particular, the integration of virtual exchange models aims to internationalize teaching practices and simultaneously equipping undergraduate students with critical skills such as intercultural awareness, intercultural competence, empathy, and global citizenship. These skills are essential for effective communication in diverse cultural contexts. The article underscores the importance of developing students&amp;apos; ability to critically engage with cultural differences, reflect on their own cultural assumptions, and navigate the complexities of intercultural interactions in a globalized world. The COIL approach fosters not only language proficiency but also an ethical understanding of the cultural &amp;apos;other,&amp;apos; thus preparing students to become active participants in a multicultural and interconnected world. To pursue this endeavor, the study adopted a qualitative research method in order to investigate the role of tele-collaborative projects in Moroccan higher education. The article presents a case study of involving students and teachers from Morocco and the United States, highlighting how the COIL model enhances cross-cultural awareness, promotes dialogue, and deepens understanding of diverse cultures. The findings reveal that incorporating COIL was key to both internationalizing teaching methods and fostering students&amp;apos; intercultural competence, making it a valuable tool in preparing students for global engagement.

DEVELOPMENT AND SIMULATION OF SPIKE NEURAL NETWORK ARCHITECTURE

A review of different models of spike neural networks has been conducted. A spike type neural network is developed in the article. The mathematical model of exchange of neurotransmitters between neurons is proposed. An algorithm for network operation and neuron interaction is proposed, as well as an approach to training the network based on the formation of new connections from dendrites and increasing the signal transmission coefficient. The model of neural network was created in Python using the developed algorithm and mathematical model. To speed up the calculations, they were paralleled using the Numba library. The library Matplotlib was used for visual modelling and plotting the number of neurotransmitters on neurons. Experimental studies of the developed model of biological type network were carried out. It was shown that the developed network after training responds faster to the signals that were applied to it in the process of training.

Comparative Analysis of Heat Exchanger Models for Phase Change Material Melting Process: Experimental and Numerical Investigation

ABSTRACTThermal energy storage systems using PCM offer promising solutions for efficient thermal applications. This study aims to provide valuable insights into the PCM melting process and compare the thermal performance of different heat exchanger models. The experimental rig is carefully designed to simulate a shell and tube heat exchanger with five longitudinal copper fins at specific conditions. Three distinct models of the heat exchanger, labeled Models A, B, and C, were examined for their heat transfer efficiency during the melting process. Numerical simulations were conducted for the three models and compared with experimental results. Model A represented the benchmark model. It had uniform fin length, location, and angle. Model B was the modified design aimed at enhancing melting progress. These modifications included a longer lower fin, a shorter side fin compared to the reference, and a lower fin angle to optimize heat transfer performance. Model C incorporates further design modifications, with a longer lower fin, a shorter top fin, and different lower fin location. Numerical simulations and experimental observations revealed significant differences in heat transfer performance among the three models. The average heat transfer rates, measured up to the critical decline point, are crucial parameters for practical applications. A comparison among the three models showed that Model B surpassed the average heat transfer rate up to the critical point of Models A and C by 10% and 4%, respectively, demonstrating its superior practical applicability.

From interacting agents to Boltzmann-Gibbs distribution of money

Abstract We investigate the unbiased model for money exchanges: agents give at random time a dollar to one another (if they have one). Surprisingly, this dynamics eventually leads to a geometric distribution of wealth (shown empirically by Dragulescu and Yakovenko, and rigorously by several follow-up papers). We prove a uniform-in-time propagation of chaos result as the number of agents goes to infinity, which links the stochastic dynamics to a deterministic infinite system of ordinary differential equations. This deterministic description is then analyzed by taking advantage of several entropy–entropy dissipation inequalities and we provide a quantitative almost-exponential rate of convergence toward the equilibrium (geometric distribution) in relative entropy.

Modeling pulmonary perfusion and gas exchange in alveolar microstructures

Pulmonary capillary perfusion and gas exchange are physiological processes that take place at the alveolar level and that are fundamental to sustaining life. Present-day computational simulations of these phenomena are based on low-dimensional mathematical models solved in idealized alveolar geometries, where the chemical reactions between O2-CO2 and hemoglobin are simplified. While providing general insights, current modeling efforts fail to capture the complex chemical reactions that take place in pulmonary capillary blood flow on arbitrary geometries and ignore the crucial impact of microstructural morphology on pulmonary function. Here, we propose a coupled continuum perfusion and gas exchange model that captures complex gas and hemoglobin dynamics in realistic geometries of alveolar tissue. To this end, we derive appropriate governing equations incorporating a two-way Hill-like relationship between gas partial pressures and hemoglobin saturations. We numerically solve the resulting boundary-value problem using a non-linear finite-element approach to simulate and validate velocity, partial pressure, and hemoglobin saturation fields in simple geometries. We further perform sensitivity studies to understand the impact of blood speed and acidity variability on key physiological fields. Notably, we simulate perfusion and gas exchange on anatomical alveolar domains constructed from 3D μ-computed-tomography images of murine lungs. Based on these models, we show that morphological variations decrease O2 and CO2 diffusing capacity, predicting trends and values that are consistent with current medical knowledge. We envision that our model will provide an effective in silico framework to study how exercise and pathological conditions affect perfusion dynamics and the overall gas exchange function of the respiratory system. Source code is available at https://github.com/comp-medicine-uc/alveolar-perfusion-transport-modeling.

Testing a biexponential kinetic model for the heterogeneous isotopic exchange of phosphate ions on several types of soil

In this study, a new kinetic equation was applied for the heterogeneous isotopic exchange of phosphate ions on soil. Phosphate sorption on chernozem, marshy meadow and meadow soil was studied by P-32 heterogeneous isotopic exchange in steady-state. The soil samples were incubated with 5 different amounts of KH2PO4 for 1, 3, 13, 10, 12 and 22 weeks. Then they were equilibrated with destilled water, and after the equilibrium was reached, H332PO4 radiotracer was added to the soil solution. At different times samples were taken from the soil solution, and radioactivities were determined by liquid scintillation (LSC) technique. The concentration of phosphate ions was determined by photometry. The relative radioactivity of soil vs time could be fitted well by the biexponential kinetic equation, which assumes two types of weakly bonded phosphate. From the fitting parameters of the biexponential equation and the phosphate concentration determined by photometry the amounts of the two types of weakly bonded phosphate and their steady-state rates were determined. The amounts of weakly bonded phosphate were plotted vs phosphate concentration – data points could be fitted by a Langmuir-like representation or the S-shape sorption isotherms. The rate orders of the desorption proved to be 1 or 2; rate constants were determined. It can be concluded that in some cases cooperative sorption can occure, which can be due to hydrogen bonding between the hydrogenphosphate ions on the surface.

The influence of applying skin temperature corrections to gas exchange models on air-sea oxygen flux estimates

The influence of applying skin temperature corrections to gas exchange models on air-sea oxygen flux estimates