Values Of Quantities Research Articles

Influence of temperature and plastic deformation on AA2024 T3 friction stir welded joint microstructure

This paper deals with analysis and comparison of the equivalent plastic strain and temperature fields in the aluminium alloy 2024 T3 (AA2024 T3) joint, with macro/microstructure appearance and hardness profile. In the alloys hardened by heat treatment, grain size and particle size of the precipitate are functions of equivalent plastic strain, strain rate and temperature. By analysing the equivalent plastic strain fields and temperature fields it is possible, to some extent, to capture the effect of welding parameters and thermo-mechanical conditions on grain structure, and therefore hardness and strength in the welded joint. A coupled thermo-mechanical model is applied to study the material behaviour during the linear welding stage of friction stir welding. The 3-D finite element model has been created in ABAQUS/EXPLICIT software using the Johnson-Cook material law. The values of thermo-mechanical quantities during the welding stage are obtained from the numerical model and shown as distributions across the joint. The obtained values of these quantities are related to the microstructure of the joint zones and hardness distribution, and this relation is discussed.

Research algorithm and dynamic characteristics of three-phase electromagnetic current transducers in filter-compensation devices

The article presents a three-phase current transducer for filter-compensation devices, representing the value of the stator current of an asynchronous motor. An algorithm for determining the values of the output electric quantities in them was developed based on the methods of interconnecting the loops of the sensitive element of the three-phase electromagnetic current transducer arranged in accordance with the stator slots of the asynchronous motor. In addition, based on this algorithm, the time-dependent dynamic characteristics of the output signal of the sensitive element loops are determined according to the connection method. Based on the dynamic description, it is possible to see the time for the output voltage signal of the three-phase current transducer to reach stability and the effect of high harmonic currents affecting it. Theoretical studies were carried out in Matlab program, and practical studies were carried out using CassyLab device. The theoretical and practical results determined because of research are compared with each other.

VARIABLE THERMAL CONDUCTIVITY AND VISCOSITY EFFECTS ON THIN FILM FLOW OVER AN UNSTEADY POROUS STRETCHING SHEET

The aim of our current investigation is to examine, heat and mass transfer rates of thin liquid film, considering a permeable stretching sheet. In this study, we assume that the medium is porous, the sheet is unstable, and the flow is two-dimensional with nonlinear radiation, variable viscosity, and variable thermal conductivity. Similarity variables are used to convert partial differential equations (PDEs) into dimensionless ordinary differential equations (ODEs), which are solved numerically by Runge-Kutta-Fehlberg (RKF45) method along with shooting technique. MATLAB R2017a is used to illustrate the effects of unsteady, magnetic field, permeability, radiation, suction, temperature ratio, and chemical reaction parameter on velocity, temperature, and concentration profiles. Numerical values of physical quantities are provided in tabular form. The velocity profile tends to diminish as the permeability parameter increases. Our current results show great agreement with the previously reported investigations.

Sustainability and perspectives of the North Macedonian dairy industry

The subject of this review is the dairy industry in the Republic of North Macedonia. This industry can bring many economic and social benefits to society and the economy. The paper provides a description and analysis of the current situation within the dairy industry in our country. Milk production rates in our country are analyzed, with a comparative approach to production rates at global and European levels. In the Republic of North Macedonia, milk production is characterized by many traditional small farmers (80% of the total) with 1-3 cows and low annual milk productivity (2-3 thousand liters per cow). The number of large specialized farms with more than 15 cows (about 3% of the total) with annual milk production of about 5 thousand liters per cow is minimal. Only 1% of all farms have more than 50 cows. The Republic of North Macedonia is an absolute importer of milk and its products. The quantity and monetary value of imported milk and its products are many times higher than the quantity and value of exported milk. Today, the dairy industry faces various challenges in the three main pillars of sustainability: economic, social and environmental including fluctuating market prices, high labor costs, and demographic characteristics of the population in terms of age. In conclusion, for the dairy industry to be sustainable, all activities should be carried out in partnership with the industry (along the value chain), policymakers and a wide range of stakeholders, including consumers.

Robust Path Tracking Control of Distributed Driving Six-Wheel Steering Commercial Vehicle Based on Coupled Active Disturbance Rejection

With the advancement of chassis technology, a distributed driving six-wheel steering commercial vehicle chassis (DD-6WS CVC) became useful for enhancing traffic efficiency and facilitating rapid emergency rescue. In the face of harsh, complex working conditions and multiple unknown disturbances, the difficulty of research is determining how to comprehensively integrate the benefits of various subsystems to improve the stability of dynamics. Based on the dynamic model of the DD-6WS CVC, a coupled active disturbance rejection controller (ADRC) is designed to improve the robustness of path tracking in emergency obstacle avoidance. First, the preview path information is optimized by the tracking differentiator (TD), and then the six-wheel steering control quantity is computed using model predictive control (MPC). Using the extended state observer (ESO), the total lateral disturbance is estimated and compensated. Second, the heading state quantity and disturbance estimation value are incorporated into the nonsingular fast terminal sliding mode control (NFT-SMC) so that the direct yaw moment control (DYC) can achieve yaw stability in real time. Finally, the optimal distribution of six-wheel drive torque is completed. Experiments validate the algorithm's effectiveness and high robustness under multiple coupling disturbance. The results demonstrate that, in comparison to MPC and the linear quadratic regulator (LQR), the proposed algorithm has superior control characteristics and effectively enhances the robustness of the DD-6WS CVC in-phase steering path tracking.

Global path planning method for smart driving cars based on extension neural network

Current global path planning algorithms for smart driving cars are capable of effective path type output, but some of them are expensive to develop and are not conducive to maintenance and iteration. In this paper, based on an extension neural network (ENN), the basic-elements model in Extenics is used to construct the information-elements involved in global path planning for smart driving cars as the input of the neurons; the maximum and minimum values of the quantity values of the input information-elements are used as the double weight values, and the midpoint of the interval formed by them is used as the midpoint of weight value interval, and the initial output function of the extension neurons is constructed based on the midpoint extension distance; The input and output layers are connected by double weight values to build the overall structure of the ENN for global path planning of smart driving cars. The ENN model is trained by collecting relevant data, adjusting the weight values and midpoints of weight value intervals of the ENN for incorrect predictions, and replacing the initial weight values and midpoints of weight value intervals to form a new output function. The trained model can predict path types quickly and accurately, showing that ENN can be used to optimize the efficiency and accuracy of the global path planning algorithm for smart driving cars in terms of output path types.

Rapid identification of components in Wuzhuyu Decoction using UHPLC Q-Exactive Orbitrap MS~n and molecular network technology

Wuzhuyu Decoction, the classical formula recorded in the Treatise on Febrile Diseases(Shang Han Lun), has been included in the Catalogue of Ancient Classic Prescriptions(the First Batch). Consisting of Euodiae Fructus, Ginseng Radix et Rhizoma, Zingiberis Rhizoma Recens, and Jujubae Fructus, it is effective in warming the middle, tonifying deficiency, dispelling cold, and descending adverse Qi, and is widely applied clinically with remarkable efficacies. For a classical formula, the chemical composition is the material basis and an important premise for quantity value transfer. This study aimed to establish a rapid identification method of chemical components in Wuzhuyu Decoction by high-resolution mass spectrometry(HR-MS) and molecular network. AQUITY UPLC BEH C_(18) column(2.1 mm×100 mm, 1.7 μm) was used for sample separation, and acetonitrile-0.1% formic acid in water was used as mobile phases for gradient elution. Q-Exactive Orbitrap MS data were collected in positive and negative ion modes, and GNPS molecular network was plotted according to the similarity of MS/MS fragmentation modes. Cytoscape 3.6.1 was used to screen molecular clusters with similar structures. Finally, the chemical components of Wuzhuyu Decoction were rapidly identified according to the controls, as well as the information of retention time, accurate relative molecular weight of HR-MS, and MS/MS multistage fragments. A total of 105 chemical components were identified in Wuzhuyu Decoction. This study can provide data for the follow-up quality control, standard substance research, and pharmacodynamic material research on Wuzhuyu Decoction, as well as references for the rapid qualitative analysis of the chemical components of Chinese medicine.

A statistical approach for the assessment of the saturated hydraulic conductivity applied to an Austrian region

Study regionThis study refers to the Hydrological Open Air Laboratory (HOAL) watershed, located in South-West Austria. Study focusThe spatial variability of saturated hydraulic conductivity, Ks, is sometimes synthetized by geometric mean, K̃s, and coefficient of variation, while areal-average infiltration models rely upon the arithmetic mean, K¯sl, associated to log-transformed Ks, and relative coefficient of variation, CVal. Robust estimation of K¯sl and CVal, as well as of K̃s and associated coefficient of variation, CVg,would require a large number of Ks observations. The determination of the minimum number of Ks measurements, n*, for obtaining sufficiently accurate values of each aforementioned quantity over an area is an open issue addressed here. A statistical approach has been applied to Ks datasets on three grassy plots for an uncertainty analysis based on the non-parametric bootstrap method with replacement. The uncertainty of each quantity has been derived for different observation numbers and areas. New hydrological insights for the regionConsidering different sub-regions in the largest plot the uncertainty is almost invariant with increasing the sub-region area beyond a threshold. Furthermore, for a given n*, the uncertainty of K¯sl and CVal is much smaller than that of K̃s and CVg. Our approach defines a methodology for determining over an area the n* associated to a fixed uncertainty level in the joint estimation of the selected quantities. Guidelines for investigations over different plots are also proposed.

Rotary 3D Magnetic Field Scanner for the Research and Minimization of the Magnetic Field of UUV

Research on the value and nature of physical quantities allows for a detailed understanding of the conditions in the studied area, and the quality and precision of the final conclusions depend on the accuracy of the measurements. In order to increase the accuracy of measurements, the measurement infrastructure and unmanned vehicles used during the observation should introduce the lowest possible disturbance-they should be minimized in terms of the magnetic field. This article presents a solution based on the infrastructure model and the development of a method using polynomial regression to study the magnetic field in three dimensions (3D-longitudinal X, transverse Y, and vertical Z components). The test stand consists of an Arduino Mega microcontroller, a rotary table driven and controlled by a stepper motor, a touch display whose task is to control the magnetic field measurement parameters and display 3D data, and proprietary software made in the Python programming language. The structural elements of the stand model were produced by an additive method using a 3D printer. The presented solution belongs to the group of modern technological solutions known as the technology of low object detection (stealth technology or low observable technology).

Investigation of MHD natural convective flow of optically thick medium-radiating CNT Casson nanofluid over an infinite flat plate with reference to Caputo fractional derivative: As an application to water purification

In this article, the application of Caputo fractional operators of order α, α∈ (0,1) has been studied. Heat transmission near the surface of a vertical plate in the flow of optically thick radiating Casson nanofluid along with mass diffusion in the presence of heat source/sink and constant magnetic flux is investigated. In the fluid problem, an H2O-based Casson nanofluid with carbon nanotube (CNTs) suspensions is investigated. The non-dimensionalized governing PDEs have been solved analytically via the combination of Fourier-sine and Laplace transform techniques and closed form of solutions are attained for the velocity, temperature, and concentration fields in terms of the Mittag-Leffler function. The physical behavior of the significant parameters has been scrutinized graphically. As a result, it is identified that the concentration, temperature, and velocity curves escalate drastically with the raising values of the fractional quantity α due to the alteration in mass, thermal, and momentum boundary layers with higher values of time t. When t>1, the species level in the fluid along with the fluid temperature and velocity rises with the fractional quantity α and decelerates when 0<t<1. Further analysis reveals that as the magnetic field is strengthened, the flow curves decelerate rapidly. Also, tables have been presented to show the influence of the controlling physical quantities on the friction drag and heat transmission rate.

ANALYSIS AND EVALUATION OF THE ACCURACY OF METHODS FOR CALCULATING THE DENSITY OF CHANNELS AND THE COMBINED AREA OF THE CONTACT SURFACE OF LUBRICATION-FREE PISTON SEALS

On the basis of the theory of stochastic fields, methods of calculating the tightness of the deadly piston seals were developed to perform the engineering methods of calculations intended for the field of mechanical engineering. The dependence of the channel probability density on the set of contact conditions was investigated based on the theory of stochastic fields. Analysis of research shows that the dependence of the channel probability density on the complex of contact conditions is extreme. This result is explained by the influence of the process of merging the contact spots during the loading process. To determine the density of the channels, an exact formula is derived that depends on the spectral moments and the effective level of deformation. On the basis of the exact formula, the calculation formula of the probability density of the channels was obtained for carrying out engineering calculations of the tightness of lubrication-free piston seals. The values calculated by the exact and estimated channel density formulas differ by no more than 0.0045. The exact formula of the specific surface area of the joint washed by the working medium is derived and investigated. The dependence of the combined surface area of the joint washed by the medium on the set of contact conditions was investigated. Values of quantities calculated according to exact and calculation formulas of the specific surface area of the joint washed by the medium differ by no more than 6.1%.

CONTROL OF ASYNCHRONOUS AC ELECTRIC MOTOR ACCORDING TO THE PRINCIPLE OF CONSTANT V/F AND CONVENTIONAL PWM CONTROL

The principle of operation of any automatic control system is to detect deviations of regulated values from set values and to form influences on the control process to eliminate these deviations. Often, a variable value whose value must be maintained constantly or changed according to the desired law is called a controlled value (coordinate). It is customary to call the required value of the regulated value (coordinate) set, and the actual value - current. The difference between the setpoint and the actual value is a deviation or error signal. A set of devices that affect the object of control, maintaining the current value of the controlled quantity (coordinate) equal to the given one, is called an automatic regulator or a dynamic system. The influence of the regulator on the object with the aim of bringing the current value of the controlled value closer to the set value (or adding the desired properties to the closed system) is called the control influence, and the set of devices and physical environments through which the control influence acts on the controlled value is called the control channel. The control process carried out by the regulator manifests itself in a change in the set value of the regulated quantity or a deviation of at least one of the unregulated quantities that affect the regulated one through feedback circuits. A change in the set value of an adjustable quantity is called a controlling or internal setting influence, and a change in unregulated quantities is called an external disturbance. The principle of deviation control is to compare the set value of the regulated value (setting) with its current value. In this case, the error signal Δ is used to create such a regulatory influence on the control object that this error, regardless of the reasons that caused it, does not go beyond the permissible values. In order to protect the environment and reduce the effect of greenhouse gas emissions, regulations are being introduced all over the world that require manufacturers of household electrical equipment and industrial enterprises to produce products that use electricity more economically. Most often, this can be achieved by effectively controlling the speed of the electric motor. This is the reason why consumer appliance developers and semiconductor suppliers are now interested in developing low-cost and economical adjustable actuators.

A numerical analysis of the performance of linear interpolation schemes coupled with finite volume method in determining velocity distribution for confined convection-diffusion turbulent flow field

Numerical methods are widely used to obtain solutions of fluid flow problems because they well compliment experimental methods. The numerical results obtained are however never exact due to errors emanating from the scheme used in discretizing the governing equations and the flow domain. For convection-diffusion flow, the magnitudes of these errors vary depending on the scheme used to interpolate the nodal values of the flow quantities to the interfaces. The precision level of an interpolation scheme is determined by its ability to minimize these errors hence generating results that are consistent with experimental results. This paper documents the performance of three linear interpolation schemes; upwind differencing, central differencing scheme and the hybrid scheme in obtaining velocity profiles for a convection-diffusion turbulent flow field. The field variables present in the governing equations are decomposed into a mean and a fluctuating component and averaged so as to reduce the enormous scales inherent in a turbulent flow regime. The closure problem was solved using the turbulence model. The turbulence equations have been converted into discrete form using the robust finite volume discretization technique. The discretized equations are solved using a segregated pressure-based algorithm. The numerical results were validated using the benchmark results of Ampofo and Karayiannis, (2003). The results revealed that linear interpolation schemes are not appropriate in analyzing velocity distribution for confined convection-diffusion turbulent flows because the results obtained using all the three linear schemes were inconsistent with experimental results.

Application of the Methodology of Multi-Valued Logic Trees with Weighting Factors in the Optimization of a Proportional Valve

Hydraulic valves are used to determine the set values of hydraulic quantities (flow rate, pressure, or pressure difference) in a hydraulic system or its part. This is achieved through the appropriate throttling of the stream flowing through the valve, which is automatically set by the operator (e.g., opening the throttle valve). The procedures for determining its static and dynamic properties were described using the example of modeling a two-stage proportional relief valve. Subsequently, the importance of the design and operational parameters was determined using multi-valued logic trees. Modeling began with the determination of equations describing the flow and movement of moving parts in a valve. Based on the equations, a numerical model was then created, e.g., in the Matlab/Simulink environment (R2020b). The static characteristics were obtained as the result of a model analysis of slow changes in the flow rate through the valve. Various coefficients of logical products have not been taken into account in the separable and common minimization processes of multi-valued logic equation systems in any available literature. The results of the model tests can be used to optimize several types of hydraulic valve constructions.

Accurate recognition of the reproductive development status and prediction of oviposition fecundity in Spodoptera frugiperda (Lepidoptera: Noctuidae) based on computer vision

Spodoptera frugiperda (Lepidoptera: Noctuidae) is an important migratory agricultural pest worldwide, which has invaded many countries in the Old World since 2016 and now poses a serious threat to world food security. The present monitoring and early warning strategies for the fall army worm (FAW) mainly focus on adult population density, but lack an information technology platform for precisely forecasting the reproductive dynamics of the adults. In this study, to identify the developmental status of the adults, we first utilized female ovarian images to extract and screen five features combined with the support vector machine (SVM) classifier and employed male testes images to obtain the testis circular features. Then, we established models for the relationship between oviposition dynamics and the developmental time of adult reproductive organs using laboratory tests. The results show that the accuracy of female ovary development stage determination reached 91%. The mean standard error (MSE) between the actual and predicted values of the ovarian developmental time was 0.2431, and the mean error rate between the actual and predicted values of the daily oviposition quantity was 12.38%. The error rate for the recognition of testis diameter was 3.25%, and the predicted and actual values of the testis developmental time in males had an MSE of 0.7734. A WeChat applet for identifying the reproductive developmental state and predicting reproduction of S. frugiperda was developed by integrating the above research results, and it is now available for use by anyone involved in plant protection. This study developed an automated method for accurately forecasting the reproductive dynamics of S. frugiperda populations, which can be helpful for the construction of a population monitoring and early warning system for use by both professional experts and local people at the county level.

Use of critical response spectrum for design of multi-story steel buildings under multi-component seismic excitation

During an earthquake, buildings are simultaneously excited by three-components of ground motion (two horizontal and one vertical) orientations of which are not known apriori. To take account for the uncertainty in the direction of incidence of earthquake waves, a structure is required to be designed such that it is safe for all directions of incidence. For this purpose, the combined effects of two horizontal components of motion are commonly determined using simplified methods such as the percentage rules (e.g. 100%+30%, 100%+40%), square root of the sum of squares (SRSS) and Complete Quadratic Combination (CQC-3) rules. The modern building codes recommend to estimate the orthogonal response quantities for the individual horizontal component of motion using response spectrum superposition methods with design spectrum in the principal direction of motion. In the present paper, a new method is proposed to evaluate the maximum response of multi-story buildings under the simultaneous action of two horizontal components of ground motion using the concept of critical response spectrum. The critical response spectrum is computed using the resultant response of a bidirectional single degree of freedom system at each time step under the simultaneous action of the two horizontal components of motion. For an illustration of the proposed method, steel building asymmetric in the plan is analysed using critical response spectra of the three different pairs of recorded ground motion and the results obtained are validated by comparison with the exact time-history solutions. The exact response is taken as the maximum of the responses estimated by applying the two horizontal time-histories of ground acceleration at different angles from 0 to 180 degree with respect to the structural x-axis. On the other hand, in the response spectrum method, two values of the desired response quantity are obtained by applying the critical response spectrum along the x- and y-directions of the structure and are combined using SRSS method. It has been found that the use of the critical spectrum provides a very convenient method for estimating the maximum response under multi-component excitation without the need for computation of critical incident angle of incidence.

A case study on an innovative seismic performance evaluation procedure for irregular RC buildings

Assessing the structural capacity of an irregular structure requires an appropriate and robust representation of the analytical model. Conventional procedures are flawed because they lack the reversal effects of higher modes. Therefore, more robust procedures have been tested to accurately capture the capacity of irregular building-type structures. Some of these may be classified as adaptive pushover techniques in which the lateral load vector is revised instantaneously. These adaptive techniques generally refer to SRSS as a modal combination rule to superpose the maximum values of the modal quantities. However, this results in an overestimated capacity value. Furthermore, the reversal effects of the modes are not included in the evaluation process. Hence, in this research, a force-based adaptive multimode pushover method was tested on a plan-irregular building using a code developed and implemented into ZEUS-NL. First, an eigenvalue analysis was used to obtain the modal quantities of the considered building, and subsequently, the modal story shear forces were obtained using the modal story forces. Furthermore, the lateral load patterns were calculated at each iterative step. Finally, the structure was pushed using this calculated lateral load pattern up to a previously calculated target displacement value using a three-step adaptive pushover analysis. The first step is to run an adaptive single-mode pushover analysis considering the first mode. After comparing the fundamental period with a constant threshold limit, it is then decided whether to run an adaptive multimode pushover analysis considering the first two modes or to run two adaptive multimode pushover analyses considering the contribution of both the second and third modes. Neither SRSS nor CQC was used to obtain the maximum response quantities; instead, the use of the envelope response is suggested. After evaluating the capacity diagram of the considered building, the story drifts were determined. The outcomes of the adaptive pushover analyses were later checked with the nonlinear dynamic results. It can be concluded that the result of the tested procedure is in good correlation with the dynamic results. Furthermore, the top displacement–time traces were plotted to check which ground motion record reveals the maximum values. Using the ground motion record, interstory drift ratio–time graphs were developed for each story level and compared with the code limit. Base shear–time history traces were then obtained and compared with the tested FAP. Lastly, story shear–interstory drift relations were plotted to investigate the absorbed energy level as an indicator of damage. As a result, for irregular RC structures, the tested procedure was found to be more accurate. However, in its current form, the procedure reflects the seismic behavior of irregular midrise buildings.

18F]FAPI-42 PET/CT in differentiated thyroid cancer: diagnostic performance, uptake values, and comparison with 2-[18F]FDG PET/CT

PurposeThis study aimed to assess the diagnostic performance of [18F]FAPI-42 PET/CT and compare it with that of 2-[18F]FDG PET/CT in patients with differentiated thyroid cancer (DTC) with biochemical elevations in Tg or anti-Tg antibodies.MethodsA total of 42 patients with DTC with biochemical elevations in Tg or anti-Tg antibodies underwent [18F]FAPI-42 PET/CT as part of this study; of which, 11 additionally underwent 2-[18F]FDG PET/CT within 7 days. Images were semi-quantitatively and visually interpreted, and the quantity, location, and uptake values of lesions were noted. The diagnostic capacity of [18F]FAPI-42 PET/CT and biomarkers affecting the uptake of [18F]FAPI-42 were evaluated. In addition, the diagnostic performance and uptake of [18F]FAPI-42 and 2-[18F]FDG were compared, and the correlation between lesion diameter and quantitative parameters was investigated.ResultsA total of 161 lesions were detected in 27 (64%) patients on [18F]FAPI-42 PET/CT. FAPI-positive local recurrence showed the highest uptake intensity, followed by lymphatic, other site-associated (bone and pleura), and pulmonary lesions (mean SUVmax, 4.7 versus 3.7 versus 3.0 versus 2.2, respectively; P < 0.0001). The levels of TSH, Tg, and Tg-Ab did not affect the uptake value of lesions (median SUVmax: 2.4 versus 3.2, P = 0.56; 2.9 versus 2.4, P = 0.0935; 2.8 versus 2.6, P = 0.0525, respectively). A total of 90 positive lesions were detected in 7 patients using both modalities. All positive lesions showed statistically higher uptake of 2-[18F]FDG than that of [18F]FAPI-42 (SUVmax, 2.6 versus 2.1; P = 0.026). However, the SUVmax of [18F]FAPI-42 was higher than that of 2-[18F]FDG in local recurrences and lymphatic lesions (SUVmax, 4.2 versus 2.9 and 3.9 versus 3.4, respectively; P > 0.05).Conclusion[18F]FAPI-42 can be used for detecting lesions and reflecting FAP expression during local recurrence and metastasis in patients with DTC with biochemical elevations in Tg or anti-Tg antibodies. The diagnostic performance of [18F]FAPI-42 PET/CT is comparable with that of 2-[18F]FDG PET/CT in such patients.

Occurrence and Source Identification of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans and Polychlorinated Biphenyls in Surface Sediments from Liangshui River in Beijing, China

Polychlorinated dibenzo-p-dioxins and dibenzofurans and polychlorinated biphenyls were measured in the surface sediments of Liangshui River, the second largest drainage river in Beijing, China. The sum concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans and polychlorinated biphenyls ranged from 3.5 to 3019 (mean value: 184) pg g-1 dry weight and from 319 to 5949 (mean value: 1958) pg g-1 dry weight, and the corresponding World Health Organization toxic equivalent quantity values were 0.0011-5.1 pg TEQ g-1 dry weight and 0.0074-1.4 pg TEQ g-1 dry weight, respectively. The spatial distributions of polychlorinated dibenzo-p-dioxins and dibenzofurans and polychlorinated biphenyls showed increasing trends from urban area and development area to suburb. Principal component analysis revealed that polychlorinated dibenzo-p-dioxins and dibenzofurans contamination in the sediments may originate from pentachlorophenol and sodium pentachlorophenate and municipal solid waste incineration. Regarding polychlorinated biphenyls, the steel industry, combustion processes and usage of some commercial polychlorinated biphenyl products were identified as the major sources. The emission from a former steel plant could be the main contributor to polychlorinated biphenyls in urban areas. The mean value of the total toxic equivalent quantities in the sediment samples exceeded the Canadian interim sediment quality guidelines. Long-term wastewater irrigation increases the load of sediment-bound pollutants in agricultural soil and may pose potential ecological risks to crops and human health.

Research on crowd dynamic risk management based on the psychological stress perception function

Number of people, density and so on are often used as a risk indicator in crowd dynamic risk management, but crowd size cannot truly reflect the change process of psychological stress perception that leads to crowd behavior disorder. Therefore, this research calculates risk index thresholds from the perspective of psychological stress perception to help managers assess crowd-gathering risks. On the one hand, the behavior model and psychological stress perception model are constructed based on corresponding experiments at the micro layer. On the other hand, risk decision models, including the average density and phubbers ratio, are built at the macro level. Finally, a long subway transfer channel was used as a simulation scenario, and the critical value of the decision quantity was determined by taking the psychological stress perception of the crowd as the objective function. The simulation shows that the perceived pressure of the crowd changes nonlinearly with time. The simulation result of the critical threshold can be divided into four zones, namely, the safety area, warning area, disposal area and dangerous area, so that managers can take targeted measures. The results are validated by applying psychological stress perception to practical population risk management.