Two-node Model Research Articles

Internal temperature estimation for lithium-ion batteries through distributed equivalent circuit network model

Lithium-ion cells experience significant internal thermal gradients during operation, with a direct impact on their safety, performance, cost and lifetime. The estimation of the internal temperature of cells is therefore particularly important. In this work, a 3D distributed electro-thermal model for internal temperature estimation is developed for a cylindrical cell (LG M50T, NMC811). The model is parameterized and comprehensively validated against experimental data for 21700 cells, including direct core temperature measurements. Multiple types of electrical load are considered, including constant current discharge, pulse discharge, drive cycle and instant discharge/charge switching. The developed model is used to estimate core temperature based on surface temperature measurement. The predictions are shown to have good accuracy at relatively low computational cost. We show that the widely adopted two-node lumped thermal estimation model is increasingly inaccurate for more aggressive discharges, when thermal gradients become higher. Compared to the standard two-node model, the distributed equivalent circuit network model predicts the effects of detailed internal cell structure (electrode, current collector, metal can and tab) and distributed internal heat generation. The results are of immediate interest to cell manufacturers and battery pack designers, while the modelling and parameterization framework is a useful tool for energy storage systems design.

Neuronal activity induces symmetry breaking in neurodegenerative disease spreading

Dynamical systems on networks typically involve several dynamical processes evolving at different timescales. For instance, in Alzheimer’s disease, the spread of toxic protein throughout the brain not only disrupts neuronal activity but is also influenced by neuronal activity itself, establishing a feedback loop between the fast neuronal activity and the slow protein spreading. Motivated by the case of Alzheimer’s disease, we study the multiple-timescale dynamics of a heterodimer spreading process on an adaptive network of Kuramoto oscillators. Using a minimal two-node model, we establish that heterogeneous oscillatory activity facilitates toxic outbreaks and induces symmetry breaking in the spreading patterns. We then extend the model formulation to larger networks and perform numerical simulations of the slow-fast dynamics on common network motifs and on the brain connectome. The simulations corroborate the findings from the minimal model, underscoring the significance of multiple-timescale dynamics in the modeling of neurodegenerative diseases.

Chiral filtration and Faraday rotation in multi-Weyl semimetals

The Maxwell equations in Weyl semimetals (WSMs) with broken inversion and time-reversal symmetries are modified by the presence of the axion terms b and b0 where, for a simple two-node model, 2ℏb is the vector that connects the two nodes in momentum space and 2ℏb0 is energy separation between the two Dirac points. As is well known, this modification leads to some unique optical properties such as non-reciprocal propagation, dichroism, birefringence and Faraday rotation. In this paper, we study numerically how these properties depend on the various parameters that characterize the WSM such as doping, axion terms, width, scattering time τ for intraband processes and background dielectric constant. More specifically, we study how the wave propagation, transmission coefficient and Faraday rotation depend on these parameters. For example, the threshold frequency ωthr=2eF/ℏ for interband transitions (with eF the Fermi level) can be split in two when b0 is finite. When intraband transitions are considered and b=0, the left (LCP) and right (RCP) circularly polarized lights are evanescent below the intraband plasmon frequency ωp<ωthr but can propagate with almost no attenuation in the frequency range ω∈ωp,ωth. Attenuation becomes really important when τ<1 ps. A finite b leads to different refractive indices for the RCP and LCP wave and controls the frequency ranges ω∈ω+,ωth (for RCP) and ω∈ω−,ωth (for LCP) where they can propagate without dissipation. Below ω+, both waves are evanescent since ω+<ω−. For light propagating along b, we find that ω+ω− decreases (increases) with b. In the thin-film limit, the Faraday rotation angle due to b is directly proportional to the width d of the WSM and to the Chern number n of the Weyl nodes. This linear behavior breaks down for d≳500μm. When d becomes larger than the wavelength λ+λ− of the RCP(LCP) wave inside the WSM, oscillations in the transmission coefficient appear whose shape and amplitude depends on the frequency range considered. Perfect transmission is possible when the quantization condition d=mλ±/2 is satisfied. One can control these oscillations by inserting the WSM between two dielectrics.

Research on dynamic evaluation method of individual scientific impact under multiple key nodes

Introduction. The purpose of this paper is to research an evaluation method for the development trend of the scientific impact of individual scientists before and after different key nodes in scientific careers. Method. This paper focuses on scientists at universities in Shanghai who obtained their first key programmes from the National Natural Science Foundation of China (NSFC) from 2011 to 2015. A two-node piecewise linear regression is used to divide the scientists’ individual academic trajectories. The Boston Consulting Group matrix (BCG-M) model is used to propose four types of talent. Analysis. The pr(y)-index is applied to evaluate the scientists’ impact. Several characteristics of the trajectory of the impact of individual scientists are defined by the change in the pr(y)-index growth rate. Results. The scientific impact of most scientists (66% and 62%) increased after they first obtained NSFC funding or their first key programme, respectively. The pr(y)-index of a 5-year time window is more sensitive to judge the of influence on scientific career. Conclusion. The two-node piecewise linear regression model successfully divided the academic trajectories of individual scientists into three stages。NSFC funding promotes academic influence. The talents are divided into star talent, focus talent, question talent and taurus talent.

Quantifying Invasive Pest Dynamics through Inference of a Two-Node Epidemic Network Model

Invasive woodland pests have substantial ecological, economic, and social impacts, harming biodiversity and ecosystem services. Mathematical modelling informed by Bayesian inference can deepen our understanding of the fundamental behaviours of invasive pests and provide predictive tools for forecasting future spread. A key invasive pest of concern in the UK is the oak processionary moth (OPM). OPM was established in the UK in 2006; it is harmful to both oak trees and humans, and its infestation area is continually expanding. Here, we use a computational inference scheme to estimate the parameters for a two-node network epidemic model to describe the temporal dynamics of OPM in two geographically neighbouring parks (Bushy Park and Richmond Park, London). We show the applicability of such a network model to describing invasive pest dynamics and our results suggest that the infestation within Richmond Park has largely driven the infestation within Bushy Park.

A modified method of the standard effective temperature (SET) based on the extended mean skin temperature index (EMSTI)

Among the existing thermal environment evaluation indexes, the standard effective temperature (SET) is based on the two-node model and performs better than the predicted mean vote (PMV) in non-neutral environments. However, previous studies show that the mean skin temperature and skin wettedness of the SET standard environment do not equal to the actual value, which violates the premise of SET. Moreover, it is found that the mean skin temperature of the standard environment differs from the actual value significantly under high temperature and humidity. Therefore, the applicability of SET in hot and humid environments deserves further study. The mean skin temperature is a superior evaluation index of thermal sensation in steady-state thermal environments with moderate temperature and humidity, and has been widely used in thermal sensation prediction. However, there also lacks in-depth research on the relationship between thermal sensation and mean skin temperature under high temperature and humidity. In this study, an extended mean skin temperature index (EMSTI) based on mean skin temperature combined with the maximum latent heat loss from skin surface is proposed through theoretical derivation. By verifying the index using the experimental data from different laboratories, it is shown that the proposed EMSTI can well evaluate the thermal sensation of hot and humid environments in different areas. The EMSTI is further used to represent thermal sensation to establish the equivalent relationship between the standard and actual environment, and the SET in hot-humid areas is modified.

Geographic Information System-Based Model of Outdoor Thermal Comfort: Case Study for Zurich

The importance of walking, the most basic form of transportation, is growing. Climate change and the associated warmer temperatures could reduce comfortable walking distances drastically. There is a clear need to better understand how outdoor thermal comfort (OTC) and walking interact. In this work, thermoregulation of the human body is modeled with the two-node model to determine the influence of the microclimate on pedestrians’ OTC. First, the impact of the current microclimate in Zurich on the route choice of pedestrians is analyzed. No significant correlation is found between simulated OTC of walking a particular route and route choices for all trips, but results for longer trips indicate a possible influence of OTC. It is pointed out that the same assessment could be done for other regions, and the results could contribute to more accurate pedestrian modeling. Second, a tool is developed that can estimate OTC-corrected walking distances from any location. The tool is applied to the current climate and future climate scenarios. The results show that, in the future, OTC of pedestrians in Zurich will be severely decreased. Further, the tool can detect where there is potential for and, through its accessibility approach, quantify improvements to the built environment citywide. Future work should focus on enhancing physiological input parameters to the model. This work provides a novel use of the two-node model for walking subjects in a citywide assessment.

Adapting the two-node model to evaluate sleeping thermal environments

While it is evident that thermal environment plays a significant role in human sleep quality, currently there remains a paucity of literature on the assessment of sleeping thermal environment. In this study, the two-node model has been adapted to evaluate sleeping thermal environments through two phases of work - modifications to the model's inputs and coefficients, and the conversion to a transient model. A calculation method for the model's key input intrinsic bedding insulation, Icl,bed, was proposed. The default heat transfer coefficients in the two-node model were replaced with the values corresponding to a supine human body. The two-node model's algorithm was adapted from its default, steady-state solution to a transient, time-series approach, to accommodate transients in both thermal environmental and physiological parameters through the course of the night. The modified two-node model was used to identify the optimum summer SET*sleep in a Sydney sleep survey database. Nocturnal mean skin temperatures predicted by the modified two-node model agree with the published physiological data in the literature. The upper limit of the Sydney summer bedroom SET*sleep for sleeping persons was 31 °C. In addition, the upper limit of summer operative temperatures was also determined for typical bedding systems. For instance, for the combination of short-sleeved sleepwear and Quilt1 (Warmth level 1), the upper limit of bedroom temperature was recommended to be 26.5 °C. Finally, the bedroom temperature control strategy for optimal sleep thermal comfort was predicted.

High Precision Velocity Estimation of AUV in an Underwater Distributed Sensor Network

Accurate estimating the velocity of a mobile object like AUV has received much attention in ocean exploration. The positioning-velocity estimation method is commonly used, which relies on observation information from multiple sensors (as nodes) over a time interval in underwater acoustics. However, its estimation accuracy heavily depends on the measurement accuracy of the positions. Also, there is a contradiction between estimation accuracy and the update rate. Thus, we propose a high-precision velocity estimation method in this paper. Firstly, we establish a two-node velocity estimation model based on the propagation delay and the Doppler shift and analyze the solution under different conditions. Then, we deduce the error transfer formula of velocity estimation theoretically and analyze the error spatial distribution characteristics. Besides, we introduce the estimation method in an underwater distributed sensor network with two steps to further improve the resolution of the velocity estimation using the redundant information generated by the pairwise combinations of multiple nodes. Meanwhile, we also give the idea of the post-processing method using the Kalman filter combined with the proposed method. Both simulation analysis and the lake test corroborate the feasibility and effectiveness of this method and higher precision than the pve method.

A neural-network based variable universe fuzzy control method for power and axial power distribution control of large pressurized water reactors

This paper proposes a neural network-based variable universe fuzzy controller (NN-VUFC) for power and axial power distribution control of large pressurized water reactors (PWRs). First, a two-node reactor kinetics model is introduced, and the fuzzy inference rules are formulated for the reactor power and axial power distribution control according to their deviations from corresponding setpoint values. Then, based on the idea of variable universe, the scaling factor of the input fuzzy universe is designed to maximize the utilization of fuzzy rules. Finally, a neural network is designed to optimize the proportionality coefficient of the scaling factor online to further improve the fuzzy control performance. Simulation results of the CPR1000 reactor under typical transient conditions show that the NN-VUFC can realize good control of both the reactor power and axial power distribution, and its control performance is effectively improved compared to traditional fuzzy controllers.

Theory of phonon instabilities in Weyl semimetals at high magnetic fields

The behavior of three-dimensional (3D) semimetals under strong magnetic fields is a topic of recurring interest in condensed matter physics. Recently, the advent of Weyl and Dirac semimetals has brought about an interesting platform for potentially uncovering phases of matter that combine nontrivial band topology and interactions. While electronic instabilities of such semimetals at strong magnetic fields have been explored theoretically and experimentally, the role of electron-phonon interactions therein has been largely neglected. In this paper, we study the interplay of electron-electron and electron-phonon interactions in a minimal two-node model of Weyl semimetal. Using a Kadanoff-Wilson renormalization group approach, we analyze lattice (Peierls) instabilities emerging from chiral and nonchiral Landau levels as a function of the magnetic field. We consider both the adiabatic and the nonadiabatic phonon regimes, in the presence or in the absence of improper symmetries that relate Weyl nodes of opposite chirality. We find that (i) the Cooper channel, often neglected in recent studies, can prevent purely electronic instabilities while enabling lattice instabilities that are not Bardeen-Cooper-Schrieffer-like; (ii) breaking the improper symmetry that relates the two Weyl nodes suppresses the Cooper channel, thereby increasing the critical temperature for the lattice instability; (iii) in the adiabatic phonon regime, lattice instabilities can preempt purely electronic instabilities; (iv) pseudoscalar phonons are more prone to undergo a Peierls instability than scalar phonons. In short, our study emphasizes the importance of taking electron-phonon interactions into account for a complete understanding of interacting phases of matter in Dirac and Weyl semimetals at high magnetic fields.

A new dynamic zOnal model with air-diffuser (DOMA) - Application to thermal comfort prediction

A new Dynamic zOnal Model with Air-diffuser (DOMA) was developed. Several case studies were investigated and tested to evaluate and validate this program using measurement data. This new model was integrated into a TRaNsient SYstems Simulation program library and coupled with the multi-zone thermal model. The DOMA/TRNSYS coupled model was then used to predict room temperature distribution over an entire day of a single-zone building. The results show that increasing the heating outputs of the electric floor system, for example, from 75 to 200 W/m2, would not effectively improve the indoor thermal comfort, since the thermostat will reach the set point first and then turn off the system before the room gets enough heat and reach a comfortable level. This indicates the importance of selecting an appropriate location and set point for the thermostat when using a floor heating system. This potential thermal comfort issue can only be identified through the two-node model with a dynamic zonal model rather than the conventional PMV model, which thus suggests that for optimizing indoor thermal comfort of a building equipped with a time-sensitive control strategy and/or HVAC system, the TSENS results obtained from the two-node model integrated with DOMA are more appropriate than PMVs.

Fatal pediatric hyperthermia: A forensic review.

This paper examines a pediatric hyperthermia homicide in which the decedent was placed into a room with only a diaper on and left unattended overnight. There were no furnishings in the room except for a 1500-W space heater and a stroller. The following morning, emergency personnel were summoned to the residence. A caretaker said the decedent was playing normally 5min before making the 911 call. The decedent's initial rectal temperature was 42.2°C. Law enforcement asked how long the child had to be exposed to a high temperature in order to induce fatal hyperthermia in an empty bedroom. The scene was reconstructed using the child's residence and the same heater. Environmental data were gathered over a 16-h period. The thermal parameters of the room and environment were analyzed using a lumped-element thermal model. These parameters were then fed into an adapted Gagge's two-node model of human thermal regulation, which provided a time-window of exposure necessary to elicit hyperthermia, which in this case, depending on certain variables, ranged from 45min to 4h.

Data-model alliance network for the online multi-step thermal warning of energy storage system based on surface temperature diffusion

SummaryAs an important type of energy storage, battery energy storage systems have been widely used. However, there are frequent cases of battery explosion due to high temperature. To address this issue, researches have been carried out either in the model-driven or the data-driven aspects to predict the temperature of the battery. In this paper, a two-node electrothermal model and a multi-scale long short-term memory network are established formulating a data-model alliance network (DMAN) for surface temperature diffusion. An improved adaptive boosting algorithm is then employed to enhance the bridge of the two models. Integrating a data-model alliance module (DMAM) and multi-step-ahead thermal warning network (MATWN), this DMAN provides an advanced online multi-step-ahead thermal warning structure to achieve early warning of temperature crossing. Experimental results verify the progressiveness of the proposed technique.

Validation of improved Two-node model for prediction of core temperature during bathing

Validation of improved Two-node model for prediction of core temperature during bathing

Interpretation of standard effective temperature (SET) and explorations on its modification and development

Standard effective temperature (SET) is a commonly used index in thermal comfort evaluation. It was established based on two-node model which could reflect thermal regulation process of human body. The misunderstanding and confusion of SET are always existed as its definition and calculation method are relatively complex and have been revised several times since proposed. It is necessary to analyse and unify the application of SET index thoroughly. This study reviewed the development process of the SET, and interpreted its definition and calculation based on Gagge's 1986 paper. As the results, the correct definition and equivalent conditions of SET standard environment were proposed, and the modifications on calculation methods were conducted. It's pointed out that the clothing insulation and the air velocity of the standard environment were not of the fixed values but the functions of the actual metabolic rate. Explorations on calculation time length and adaptive items values of SET were carried out. And the advantages, problems and future development directions of SET index were discussed. A more reasonable understanding and application of the SET could support better thermal environment construction and prediction.

Human Body Exergy Analysis Model in Building Thermal Comfort Evaluation

To explore the application of the human body exergy analysis method in assessing the indoor thermal environment, strictly according to the definition of metabolic exergy, based on the two existing exergy analysis models, a more reasonable calculation method of metabolic exergy was first proposed and established, which is a new two-node exergy analysis model. Then, the experimental data in the ASHRAE database were used to verify the reliability of the established model. Finally, the human body exergy exchange rate and exergy loss rate with indoor and outdoor environmental parameters were revealed. The research results show that the new metabolic calculation method can more accurately analyze the human body’s exergy; the exergy loss rate is larger than the exergy exchange rate in the metabolic exergy rate; when the operating temperature is 25∘C, the exergy exchange rate mainly includes the radiation exergy rate and the convective exergy rate; operation at a temperature of 32∘C, the evaporation rate and respiration rate are the main components of the exergy exchange rate; the human body’s exergy loss rate has extreme values at low or high operating temperatures, and it is used separately for the evaluation of human thermal comfort. Combining the exergy loss rate and the exergy exchange rate can better evaluate the indoor thermal environment, the minimum exergy loss rate and the minimum exergy exchange rate under the given indoor conditions, both occur under outdoor high-temperature and low humidity conditions; outdoor temperature affects the human body exergy loss rate and human body exergy exchange rate more strongly than outdoor relative humidity.

A two-node mechanistic thermophysiological model for pigs reared in hot climates – Part 2: Model performance assessments

The performance of the mechanistic two-node thermophysiological model was assessed using the experimental data with respect to gestating sows and fattening pigs. The relation between the convective heat transfer coefficient and local airspeed was derived from CFD simulation. The improvement brought by the newly proposed active module over the selected available models was analysed and discussed. Generally, the proposed two-node model with novel active modules for pulmonary ventilation rate (related to panting) and vasodilatation could predict rectal and skin temperatures for fattening pigs and gestating sows with an error of 0.88% and 3.96%, and 0.42% and 1.27% respectively. Employing existing relationships for pulmonary ventilation rate and vasodilatation resulted overestimations on the skin and rectal temperature. Additionally, the convective heat transfer coefficient should be developed based on the field conditions when the flow pattern is not similar to that under which the existing models were developed. The mean radiant temperature should be input with a decent level of accuracy when a high level of accuracy of prediction was necessary. The proposed model is reliable and robust when predicting the pig thermal status under various climate conditions and it is expected to be applied when operating the technical approaches to mitigate the heat stress. • Experimental measurements conducted under various test conditions. • Thermophysiological model for pigs validated using experimental data. • Influence of the active modules on the model performance investigated. • Convective heat transfer coefficient determined by CFD simulations.

A two-node mechanistic thermophysiological model for pigs reared in hot climates – Part 1: Physiological responses and model development

Due to the climate change and the increasing heat production of modern pigs (e.g. larger size sows having a larger number of piglets nowadays), pigs are more frequently suffering heat stress. In order to prevent the occurrence of heat stress, there is a need to develop a model which can effectively and efficiently predict the effect of ambient thermal environments on pigs. This study developed a two-node mechanistic model to simulate processes of pig thermoregulation and heat release to an ambient hot environment based on biophysical laws. The two-node model consists of a passive system, which can simulate the heat transfer processes occurring in the body core and at the skin surface, and an active system, which controls the thermoregulatory system based on a positive deviation of core temperature from its reference value under thermal neutral conditions. Vasodilatation and panting in relation to the ambient environment were specifically investigated and mathematically described based on the experimental data from previously published studies. The functions to predict vasodilatation and panting provided a relatively more detailed modelling of the thermo-physiological processes of the pigs compared to the available mechanistic models. The proposed two-node model was expected to effectively predict the thermal status of pigs under various combinations of environmental conditions without further tuning. • A mathematical model simulating pig thermoregulatory processes in hot climates. • Correlation between skin blood flow rate and ambient air temperature. • Correlation between pulmonary ventilation rate and ambient air temperature. • A novel active system developed with emphases on vasodilatation and panting.

Evaluation and improvement of the thermoregulatory system for the two-node bioheat model

The two-node bioheat model is widely used in thermal comfort standards and design tools. In recent years, there have been many new experimental studies and thermoregulatory models developed under stressful heat or cold conditions, but those have not been tested under the two-node model structure. Furthermore, limited validation studies of the two-node model revealed significant discrepancies in the prediction of skin temperature. This study collects relevant thermoregulatory models (six for sweating, three for skin blood flow and shivering, and four for sweat evaporation efficiency) and devises a methodology to compare the accuracy of various model combinations against experimental data. An improved model is developed and validated under heat and cold exposure conditions. The RMSE method is used to compare the accuracy of various model combinations and to optimize the proposed thermoregulatory model constants. The results reveal that only several model combinations can be considered as accurate for the core and skin temperature predictions, amongst which are the proposed models at the first rank.