Steady Distribution Research Articles

Evaluation of Air Pollutants in Extra-Long Road Tunnel with the Combination of Pollutants Nonlinear Evolution and Machine Learning Method

The extra-long expressway tunnel has a high socio-economic effect on inter-regional development, with high traffic and strong traffic winds. Nevertheless, the impacts of the tunnel traffic volume on pollutant evolution are rarely considered. This study conducted a field measurement in a real-world extra-long highway tunnel for 578 days. For the first time, the nonlinear dynamics of traffic pollutants (CO, VOCs, NO2, PM2.5, PM10) were analyzed using the Multifractal Detrended Fluctuation Analysis approach. Using the Random Forest model, the impacts of traffic and environmental parameters on air quality were quantified. The findings indicated that COVID-19 had a considerable impact on tunnel traffic, although the variance in pollutant concentration was not very noteworthy. The bidirectional effect of traffic was the main reason for this phenomenon. The Canonical Correlation Analysis was unable to quantify the correlation between pollutants and environmental parameters. The pollutant concentration evolution has a steady power-law distribution structure. Further, an inverse Random Forest model was proposed to predict air pollutants. Compared with other prediction models (baseline and machine learning), the proposed model provided higher goodness of fit and lower prediction error, and the prediction accuracy was higher under the semi-enclosed structure of the tunnel. The relative deviations between the predictions and measured data are less than 5%. These findings ascertain the nonlinear evolutionary mechanisms of pollutants inside the expressway tunnel, thus eventually improving tunnel environmental sustainability. The data in this paper can be used to clarify the changes in the traffic environment under the COVID-19 lockdown.

Steady-state thermal model based on new dedicated boundary conditions – application in the simulation of laser powder bed fusion process

Analytical and numerical methods have been widely used to predict the melt pool morphology and temperature distribution of thermomechanical processes involving a moving heat source, such as welding or additive manufacturing. Compared to analytical methods (based on the Rosenthal equation), the finite element method (FEM) provides more realistic results because it allows the consideration of more physical phenomena involved in the laser powder bed fusion (LPBF) process. However, its computation time is significantly longer than that of the analytical methods. In this context, this study proposes a new FE thermal model based on a steady-state simulation and analytically inspired boundary conditions to predict the melt pool morphology and temperature distribution. This proposed model possibly considers temperature-dependent material properties, Gaussian distribution of heat source, convective and radiative heat losses, powder-compact transition, enthalpy due to solid-liquid transition, and effect of heat convection in the melt pool, while allowing fast and accurate predictions of the melt pool size and steady-state temperature distribution. Single-track LPBF simulations were carried out for two most used materials (AlSi10Mg and Inconel 718). The melt pool sizes simulated by the proposed model are compared to those of a transient model and experimental results (melt pool morphology), and a relative error of less than 5% was observed for all the numerical and experimental validation tests. Furthermore, it is shown that the proposed boundary conditions allow accurate prediction of the steady temperature distribution, even with a short geometry in the source moving direction, which drastically reduces the computational cost and greatly facilitate the utilization of steady-state model.

Preclinical Pharmacokinetics and In Vitro Properties of GS-441524, a Potential Oral Drug Candidate for COVID-19 Treatment.

Preclinical pharmacokinetics (PK) and In Vitro ADME properties of GS-441524, a potential oral agent for the treatment of Covid-19, were studied. GS-441524 was stable in vitro in liver microsomes, cytosols, and hepatocytes of mice, rats, monkeys, dogs, and humans. The plasma free fractions of GS-441524 were 62–78% across all studied species. The in vitro transporter study results showed that GS-441524 was a substrate of MDR1, BCRP, CNT3, ENT1, and ENT2; but not a substrate of CNT1, CNT2, and ENT4. GS-441524 had a low to moderate plasma clearance (CLp), ranging from 4.1 mL/min/kg in dogs to 26 mL/min/kg in mice; the steady state volume distribution (Vdss) ranged from 0.9 L/kg in dogs to 2.4 L/kg in mice after IV administration. Urinary excretion appeared to be the major elimination process for GS-441524. Following oral administration, the oral bioavailability was 8.3% in monkeys, 33% in rats, 39% in mice, and 85% in dogs. The PK and ADME properties of GS-441524 support its further development as an oral drug candidate.

Electric-field-dependent bimodal distribution functions for electrons in argon, xenon, and krypton owing to the Ramsauer-Townsend minima in the electron-atom momentum-transfer cross sections

This paper considers solutions of the linear Fokker-Planck equation for the steady velocity distribution functions of electrons dilutely dispersed in an excess of either argon, xenon, or krypton. Owing to the large Ramsauer-Townsend minima in the electron-atom momentum-transfer cross sections for these atoms, the steady electron distribution, often referred to as the Davydov distribution, exhibits a bimodal distribution which varies dramatically with the strength of the external electric field. This effect provides a unique verification of the location and shape of the Ramsauer-Townsend minima in the cross sections. It is anticipated that current experimental techniques that probe the details of nonequilibrium electron distributions will verify the results reported in this paper. In addition, these nonequilibrium, non-Maxwellian distributions cannot be rationalized in terms of either the Gibbs-Boltzmann entropy nor the Tsallis nonextensive entropy.

Early Earthquake Detection Using Batch Normalization Graph Convolutional Neural Network (BNGCNN)

Earthquake is a major hazard to humans, buildings, and infrastructure. Early warning systems should detect an earthquake and issue a warning with earthquake information such as location, magnitude, and depth. Earthquake detection from raw waveform data using deep learning models such as graph neural networks (GNN) is becoming an important research area. The multilayered structure of the GNN with a number of epochs takes more training time. It is also hard to train the model with saturating nonlinearities. The batch normalization technique is applied to each mini-batch to reduce epochs in training and obtain a steady distribution of activation values. It improves model training and prediction accuracy. This study proposes a deep learning model batch normalization graph convolutional neural network (BNGCNN) for early earthquake detection. It consists of two main components: CNN and GNN. Input to the CNN model is multi-station and three-component waveform data with magnitude ≥3.0 were collected from January 2000 to January 2015 for Southern California. The extracted features of CNN are appended with location information and input to GNN model for earthquake detection. After hyperparameter tuning of the BNGCNN, when testing and evaluating the model on the Southern California dataset, our method shows promising results to the baseline model GNN by obtaining a low error rate to predict the magnitude, depth, and location of an earthquake.

Gene-influx-driven evolution.

Here we analyze the evolutionary process in the presence of continuous influx of genotypes with submaximum fitness from the outside to the given habitat with finite resources. We show that strong influx from the outside allows the low-fitness genotype to win the competition with the higher fitness genotype, and in a finite population, drive the latter to extinction. We analyze a mathematical model of this phenomenon and obtain the conditions for the transition from the high-fitness to the low-fitness genotype caused by the influx of the latter. We calculate the time to extinction of the high-fitness genotype in a finite population with two alleles and find the exact analytical dynamics of extinction for the case of many genes with epistasis. We solve a related quasispecies model for a single peak (random) fitness landscape as well as for a symmetric fitness landscape. In the symmetric landscape, a nonperturbative effect is observed such that even an extremely low influx of the low-fitness genotype drastically changes the steady state fitness distribution. A similar nonperturbative phenomenon is observed for the allele fixation time as well. The identified regime of influx-driven evolution appears to be relevant for a broad class of biological systems and could be central to the evolution of prokaryotes and viruses.

Energy landscape decomposition for cell differentiation with proliferation effect.

Complex interactions between genes determine the development and differentiation of cells. We establish a landscape theory for cell differentiation with proliferation effect, in which the developmental process is modeled as a stochastic dynamical system with a birth-death term. We find that two different energy landscapes, denoted U and V, collectively contribute to the establishment of non-equilibrium steady differentiation. The potential U is known as the energy landscape leading to the steady distribution, whose metastable states stand for cell types, while V indicates the differentiation direction from pluripotent to differentiated cells. This interpretation of cell differentiation is different from the previous landscape theory without the proliferation effect. We propose feasible numerical methods and a mean-field approximation for constructing landscapes U and V. Successful applications to typical biological models demonstrate the energy landscape decomposition's validity and reveal biological insights into the considered processes.

On Solutions to a Class of Functional Differential Equations with Time-Dependent Coefficients

In this paper, we study initial boundary value problems that involve functional (nonlocal) partial differential equations with variable coefficients. These problems arise in cell growth models with symmetric and asymmetric modes of division. We determine the general solution to the symmetric cell division problem for a certain class of coefficients and establish the convergence of solutions to a large time asymptotic solution. The existence of a steady size distribution (SSD) solution for an asymmetric cell division problem is established and is shown to be the large time-attracting solution for a certain class of coefficients. The rate of convergence of solutions towards the SSD solution is affected by the choice of coefficients and remains unaffected by the asymmetry in cell division. The uniqueness of solutions to the initial boundary value problem is also established.

Particle Nonresolved DNS‐DEM Study of Flocculation Dynamics of Cohesive Sediment in Homogeneous Isotropic Turbulence

AbstractA two‐phase Euler‐Lagrangian framework was implemented to investigate the flocculation dynamics of cohesive sediment in isotropic turbulence. The primary particles are modeled as sticky soft spheres using the discrete element method (DEM). The attractive van der Waals forces are modeled by the DLVO theory and the JKR adhesive contact theory. The near steady state equilibrium floc size distribution (FSD) strongly depends on the ratio of the turbulent shear to the floc strength (or particle stickiness). When turbulence is strong, a single peak around the Kolmogorov length scale appears in the FSD, and the distribution fits the Weibull distribution well. A power‐law floc size distribution develops when the floc strength is greater than the destabilizing effect of turbulent shear. Sediment concentration does not significantly affect the shape of FSD or the average floc size. The average apparent floc settling velocity Ws increases with the average floc size. Fractal dimension of flocs decreases with the floc size following a power‐law relation for large flocs. Settling velocity of flocs as a function of floc size also follows a power‐law relation. Deviation from the power‐law relationship is found for large flocs because of their porous nature. At equilibrium stage, the construction by aggregation is balanced with the destruction by breakup, and the construction by breakup is balanced with the destruction by aggregation. The aggregation kernel by turbulent shear and power‐law breakup kernel can describe the dynamics reasonably well for the flocculation of cohesive sediment in homogeneous isotropic turbulence.

Effect of a recirculated air curtain with incomplete coverage of room width on the protection zone in ventilated room

An air curtain is an aerodynamic barrier for contaminants and is frequently installed in the doorway to separate indoor and outdoor spaces. There are few studies on the isolation of areas within a room. In this study, the effect of a recirculated air curtain, which did not completely cover the width of the room, i.e., an incomplete air curtain, was investigated when used inside a ventilated room. The steady contaminant distributions were analyzed numerically. The impacts of air curtain length, air extract position in the air curtain, and position of the contaminant source were studied. The results for the incomplete air curtain were compared with those for complete air curtain and traditional ventilation dilution. The results showed that installing an additional incomplete and recirculated air curtain could reduce the pollution in the protection zone compared with traditional ventilation. The concentrations of contaminant could be reduced by 30.8 and 43.9% in the subzone covered by the air curtain and that not completely covered by the air curtain, respectively. When the curtain length exceeded the source position, the direct invasion of high pollution could be prevented. A relative concentration deviation of up to 26.1% was caused by different air extract positions. Under the coupled airflow field resulting from air supply jets, recirculated curtain airflow, and airflow surrounding exhaust air outlets, a complete air curtain was not necessarily a better choice. This study provides guidance for the flexible use of incomplete and recirculated air curtains for the maintenance of protection zones.

Topological phase transition induced by gain and loss in a photonic Chern insulator

We present a design of a non-Hermitian photonic Chern insulator whose band topology can be tuned via gain and loss. It is found that, by continuously varying the gain and loss parameter, a topological phase transition can take place in the photonic crystal, accompanied by the closing and reopening of a Dirac cone. We demonstrate this phenomenon through numerical simulations of the bulk and the edge dispersions, and steady field distributions excited by a point source. Our results show the possibility of non-Hermitian control over band topology in a Chern insulator setting and may find applications in active topological photonic devices.

Cloud-Model-Based Feature Engineering to Analyze the Energy–Water Nexus of a Full-Scale Wastewater Treatment Plant

Wastewater treatment plants (WWTPs) are important and energy-intensive municipal infrastructures. High energy consumption and relatively low operating performance are major challenges from the perspective of carbon neutrality. However, water–energy nexus analysis and models for WWTPs have rarely been reported to date. In this study, a cloud-model-based energy consumption analysis (CMECA) of a WWTP was conducted to explore the relationship between influent and energy consumption by clustering its influent’s parameters. The principal component analysis (PCA) and K-means clustering were applied to classify the influent condition using water quality and volume data. The energy consumption of the WWTP is divided into five standard evaluation levels, and its cloud digital characteristics (CDCs) were extracted according to bilateral constraints and golden ratio methods. Our results showed that the energy consumption distribution gradually dispersed and deviated from the Gaussian distribution with decreased water concentration and quantity. The days with high energy efficiency were extracted via the clustering method from the influent category of excessive energy consumption, represented by a compact-type energy consumption distribution curve to identify the influent conditions that affect the steady distribution of energy consumption. The local WWTP has high energy consumption with 0.3613 kW·h·m−3 despite low influent concentration and volumes, across four consumption levels from low (I) to relatively high (IV), showing an unsatisfactory operation and management level. The average oxygenation capacity, internal reflux ratio, and external reflux ratio during high energy efficiency days recognized by further clustering were obtained (0.2924–0.3703 kg O2·m−3, 1.9576–2.4787, and 0.6603–0.8361, respectively), which could be used as a guide for the days with low energy efficiency. Consequently, this study offers a water–energy nexus analysis method to identify influent conditions with operational management anomalies and can be used as an empirical reference for the optimized operation of WWTPs.

Solute Dispersion From a Continuous Release Source in a Vegetated Flow: An Analytical Study

AbstractSteady dispersion of solute in flows with submerged vegetation due to a continuous release source is a focus in water resources research. This paper presents a fully analytical effort for a complete description of the steady‐state concentration field. The analytically predicted vertical concentration profiles agree well with both experimental measurements and numerical simulation results. Relations between the steady dispersion for a continuous release source and the transient dispersion due to an instantaneous release source are also discussed. Results show that the mean concentration in the canopy layer is higher than that in the upper water layer and the steady concentration distribution approaches relative uniformity at a dimensionless downstream distance x = 0.5. The solute release position is shown highly remarkably affecting the way in which the downstream state is approached. Moreover, the vertical concentration profiles predicted by a spatially dependent four‐zone turbulent diffusivity model are better than those predicted by a constant single‐zone model. The obtained analytical results contribute essentially to our understanding of solute transport in water flows with submerged vegetation.

Sealing Contact Transient Thermal-Structural Coupling Analysis of the Subsea Connector

Taking the subsea collect connector as an example, the sealing characteristics of the sealing structure of the subsea connector under transient thermal–structural coupling were studied. Based on Airy’s thermal stress function, the mathematical model was established, the complex stress function was used to solve the problem, and a three-dimensional transient thermal stress model of the core sealing parts was obtained. The transient thermal–structural coupling stress model of the core seal was obtained by linear superposition principle. The transient temperature field of the subsea collet connector under different working conditions was analyzed. It was found that the larger the temperature difference between the components was, the greater the difference of expansion rate was, and the greater the impact on the sealing performance of LSG was in the process of temperature variation from transient to steady distribution. Numerical simulations of various working conditions under the transient temperature field were carried out. The results showed that sudden change of the temperature and oil–gas pressure will bring about large fluctuations of the maximum contact stress and equivalent stress of the seal, which was easy to fatigue wear, and thus affect the reliability of the sealing performance. Finally, the experiment proves that the sealing ring can maintain sealing performance under the conditions of temperature-cyclic loading. The coupled mathematical model proposed in this paper could be used for the transient thermal–structural coupling theoretical analysis of similar subsea equipment.

Flow of evaporating fluid in multiple parallel pipes-vertical downwards flow

Evaporation of liquid in parallel heated pipes with common inlet and outlet manifolds was investigated mainly for co-current horizontal and upward flow. Almost no work was published on parallel heated pipes with an upper inlet header where sub cooled liquid is injected. In the present work such a system has been investigated. It seems that the Ledinegg excursion instability and the transient simulations used for co- current horizontal flow (Hayat et al. [1]) are not fully sufficient to predict the behavior of parallel heated pipes with vertical downward flow. In the present case the flow rate distribution between the parallel pipes include also solutions for counter current flow, where the flow in one of the pipe is directed upwards.Experimental results of the characteristics pressure drop curve, the steady state flow rate distribution as well as the transient response of the system to changes in the operational conditions are presented. At certain regions of inlet flow rates a cyclic process, similar to a geysering phenomenon, was observed where pressure drop and flow rate oscillations take place in both pipes. It occurs when upward flow is observed in one of the pipes.A theoretical model based on the local instantaneous flow pattern was used for calculating the characteristic pressure drop curve for both downward and upward flows. The theoretical pressure drop curve compares quite well with the experimental results. The characteristic pressure drop, a linear stability analysis and transient simulations were used to predict the flow rate distribution between the pipes at steady state and under transient conditions. The model predicts correctly the experimental results as long as there is no upward flow in one of the pipes.

Thermoreflectance Imaging of Semiconductor Lasers With a Numerical Thermal Model

High resolution surface temperature maps of a slotted surface grating laser operating at approx. 1550 nm are obtained by means of CCD-thermoreflectance imaging. The resolution is such that the temperature of the 2 µm wide ridge can be determined. Experimental temperature profiles along the ridge and in the lateral direction are provided. A 2D numerical model is developed to simulate the steady state thermal distributions in the laser. There is good agreement between the experiment and simulation. This technique allows for high-resolution imaging and will be useful where hot spots occur on laser devices.

A population-based study of TyG index distribution and its relationship to cardiometabolic risk factors in children and adolescents

The purpose of this study was to present age- and sex-specific distributions of the triglyceride-glucose (TyG) index and to evaluate their relationship with cardiometabolic risk factors in children and adolescents. A total of 7404 participants aged 10–18 years from the Korean National Health and Nutrition Survey were included as the reference population. The TyG index was calculated as ln(fasting triglyceride [mg/dL] × fasting glucose [mg/dL]/2). The percentile of the TyG index exhibited a steady linear relationship with age for both sexes. TyG index significantly correlated with waist circumference (WC) standard deviation score (SDS; r = 0.110, p < 0.001), systolic blood pressure (SBP; r = 0.104, p < 0.001), diastolic blood pressure (DBP; r = 0.083, p < 0.001), glucose (r = 0.220, p < 0.001), high-density lipoprotein cholesterol (HDL-C; r = − 0.325, p < 0.001), and triglycerides (TG; r = 0.926, p < 0.001). Multiple linear regression analysis revealed that the TyG index was significantly associated with WC SDS (β = 0.116, p < 0.001), SBP (β = 2.009, p < 0.001), DBP (β = 1.464, p < 0.001), glucose (β = 3.376, p < 0.001), HDL-C (β = − 6.431, p < 0.001), and TG (β = 85.518, p < 0.001). Our results suggest that the TyG index has a steady linear distribution for sex and age in children and adolescents and constitutes an indicator for predicting metabolic disorders that could lead to cardiovascular disease later in life.

Cellular automata modeling for rotary friction welding of Inconel 718

ABSTRACT This work investigates the microstructure evolution during the rotary friction welding (RFW) of Inconel 718 alloy. A cellular automata (CA) approach is implemented to evaluate a cylindrical component (at weld center and edge wall), predicting dynamic recrystallization (DRX) and grain size of friction welds. The input variables for RFW were rotational speed (500, 1000, and 1200 rpm), feed rate (2 mm/s), and feed distance (3.6 mm). The CA model is based on the Laasraoui-Jonas model and explains intricate grain transformation in terms of microstructure, temperature, strain, and strain rate. Calculated grain consists of very fine grain structure at the stir zone followed by the thermo-mechanical affected zone, where partial recrystallized microstructure was present. The average grain size was 2.5 µm, which is comparable to reported experimental values. The grain analysis revealed that temperature and strain are most affecting factors to attain a refined microstructure. The strain rates predicted for both center and edge locations of the weld were found to be higher as rotational speed increased. A steady strain distribution is noted at greater temperature for all the rotational speeds. The results of this work contribute toward the understanding of microstructure and mechanical response for RFW of Inconel 718.

Modelling vertical water distribution and separation in the unsaturated coal and iron ores during oscillation

The effect of oscillation on the water distribution in unsaturated coal and iron ores plays a significant role in the material processing but has not been analysed quantitatively. This paper developed a model based on the Richards equation to describe the transient residual water distribution in the unsaturated coal and iron ores, and predicted the separated water with time. In this model, the effect of oscillation was quantised as a dynamic potential of the unsaturated water. The model was experimentally verified and applied to characterise the separated and residual water. The effects of initial water content, hydraulic conductivity, dynamic potential and bottom boundary were quantitatively analysed. The results showed that the dynamic potential affects the transient and steady water distribution for the overall height of the coal and iron ores. These findings can be applied to the minimisation of water distribution in wet coal or iron ores and optimisation of their processing.

One-dimensional thermal equation modeled on a two-dimensional heat exchanger with variable solid-fluid interface

In this study, we are to present that a one-dimensional equation for vertically averaged temperature, modeled on a vertically thin, two-dimensional heat exchanger with variable top solid-fluid interface, recovers the two-dimensional thermal information, i.e. steady temperature and flux distribution on the top and temperature-fixed bottom faces. The relative error of these quantities is less than 5% with the maximum gradient of the height kept approximately below 0.5, while the computational time is reduced to 0.1–5%, when compared with direct two-dimensional computations, depending on the shape of the top face. The model equation, derived by the vertical averaging of the two-dimensional thermal conduction equation, is closed by an approximation that the heat exchanger is sufficiently thin in the sense that the second derivative of temperature with respect to the horizontal coordinate depends only on the coordinate. In this model equation, the fluid equation above the exchanger is decoupled by a conventional equation for the normal heat flux on the top surface. In principle, however, the coupling of the model and the fluid equation is possible through the temperature and heat flux on the top interface, recovered by the model equation. The type of mathematical modeling can be applicable to a wide variety of bodies with extremely small dimensions in some (coordinate-transformed) directions.