Marine ranching has been widely considered as a new mode of marine fishery production. Marine ranching ecological security (MRES) is the basis and premise to ensure the sustainable utilization of ...marine ranching functions. In this study, an MRES early warning system was constructed based on comprehensive marine ranching ecological security index (CMRESI) and system dynamic model to reveal the main factors affecting the development of marine ranching and explore the changes in MRES under different future development scenarios in China's coastal areas from 2011 to 2035. The results showed that (1) the mean CMRESI of China was only 0.3265 and spatial heterogeneity was significant, showing a general security state; (2) coupling and coordination degree of MRES subsystems was high in Jiangsu, Fujian, Shandong, and Guangdong, and resources was a major constraint on the coordinated development of MRES in the study area (63.6%); (3) Under the ecological priority development scenario, the CMRESI will be the highest in 2035; however, 27% of MRES (in Jiangsu, Fujian, and Hainan) will continue to issue serious early warnings. This study could provide a reference for construction planning, management maintenance, and decision-making of marine ranching.
•We built a MRES early warning system based on comprehensive evaluation and system dynamic models.•MRES in China's coastal areas increased between 2011 and 2018.•Resources are the major constraint to coordinated development of China's MRES.•The scenario of ecological priority development for the MRES was best.
Vacuum packaging is known to be an effective way to limit the growth of food spoilage and food-poisoning bacteria. However, Listeria monocytogenes (LM) can survive under low-oxygen conditions and as ...well as refrigeration temperatures. This study was conducted to model the fate of LM-inoculated meatballs and Sundae, a Korean black pudding, and assess the effect of packaging (aerobic packaging, AP; vacuum packaging, VP) on risk. Meatballs and Sundae were spiked with LM and stored at temperatures ranging from 5 to 37 °C. Primary models were developed using the Baranyi model, and secondary models for the maximum growth rate (μmax) of meatballs and Sundae were developed using a square root model. The developed primary and secondary models were fitted well with a high goodness-of-fit (R2 ≥ 0.98). The bias factor (Bf) was 1.002–1.015, and the root mean square error (RMSE) was 0.002–0.051 1/h. Furthermore, dynamic models were developed and validated, with corresponding RMSE values < 0.851 ln CFU/g (<0.370 log CFU/g) and acceptable simulation zone (ASZ) values > 82%. Comparing the growth of LM according to the packaging, the lag phase duration of both samples was significantly shorter in VP than in AP; however, μmax of meatball at 10 °C was significantly faster in VP than in AP (p < 0.05). The probability of infection (Pinf) from the consumption of meatballs or Sundae with different packaging types was estimated using Monte Carlo simulations and scenario analysis. Simulation results showed that Pinf from the consumption of meat-based ready-to-eat foods with VP was not always lower than that with AP. There is a need to control the contamination of LM before packaging by placing efforts on implementing control measures during processing.
•A predictive model of Listeria monocytogenes in meatball and Sundae was developed.•Developed model performed well under isothermal and fluctuating temperatures.•Vacuum packaging cannot guarantee the prevention of the Listeria growth.•Vacuum packaging should not be considered much safer than aerobic packaging.
•A novel excitation method is proposed to produce the torsional vibration.•A novel torsional vibration transfer matrix model is created for the square torsional piezoelectric element.•Two novel ...sandwiched piezoelectric actuators are designed to stimulate torsional vibration modes.•Electromechanical coupling dynamic models of the proposed actuators are developed using the transfer matrix method.
The sandwiched type torsional piezoelectric actuators have widely been employed in the fields of ultrasonic cutting, ultrasonic drilling, ultrasonic welding, ultrasonic wire drawing, ultrasonic spraying, and microdroplet generation, due to their unique vibration form. However, the circular piezoelectric ceramic plate polarized in the circumferential direction holds a complicated manufacturing process, a long processing period, and a high price. It can only be used for the excitation of the torsional vibration of circular rods, and cannot be used for square cross-section beams, severely restricting its applications. In order to solve the above problems, a novel excitation method is proposed for generating torsional vibration in the square cross-section beam in this study, which uses the d15 vibration mode of rectangular piezoelectric ceramic plates to produce the torsional vibration, and a novel transfer matrix model of square torsional piezoelectric element is created. Then a case study is conducted in this paper to confirm the proposed excitation method and the developed model, in which two novel sandwiched type torsional piezoelectric actuators are designed. Moreover, electromechanical coupling models of these two torsional piezoelectric actuators are developed using the transfer matrix method, in order to reveal their dynamics behaviors. Finally, the finite element method and the experimental investigations are adopted to analyze and test the frequency response characteristics and vibration shapes of the proposed piezoelectric actuators. Both simulation analysis and experimental tests verify the effectiveness of the proposed excitation method and the correctness of the developed electromechanical coupling dynamic models. The proposed excitation method provides a new idea for the design of sandwiched type torsional piezoelectric actuators, and the developed theoretical model lays a theoretical foundation for the further research of torsional piezoelectric actuators.
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In practical applications, the main beam direction of massive multi-input multi-output (mMIMO) transmitters varies with the user's location. However, different directions will result in different ...distortions in mMIMO transmitters, and this poses a big challenge to digital pre-distortion (DPD). This paper first analyzes the relationship between direction configuration and main beam distortion in the fully-connected hybrid beamforming (FC-HBF) transmitters. In order to transmit the signal correctly under dynamic directions, two DPD models using heterogeneous neural networks (HNNs) based on vector decomposition (VD) and block-oriented (BO) structure, called HNN-VD and HNN-BO, respectively, have been proposed. The direction information is used directly as the input of HNNs. Then, a gating-based neural network model is proposed called direction adaptive neural network (DANN), which is composed of a gating network and a backbone network, and its core idea is to dynamically adjust the hidden layer features of the backbone network by utilizing direction information through the gating network. The simulation indicates that all of the proposed models exhibit good performance, but DANN has the best performance and low complexity among models, which provides a good digital pre-distortion scheme for FC-HBF transmitters under dynamic directions.
Rather than being sold several months before a program is aired, more than 20% of TV advertising slots are retained for sale weekly near the program’s broadcast time. Distinct from the literature ...that mainly focuses on the forecasting of program ratings for advanced sales of advertising slots, we explore approaches that can provide more accurate forecasts for near real-time ratings. We propose two dynamic models that mainly employ individual viewing records for past episodes to forecast viewers’ decisions on episodes in the coming week, and therefore the ratings for these episodes. One is a reduced-form dynamic model that measures the influence of past watching experience by the weighted average of the viewers’ choices of past episodes. The other is a structural dynamic model that goes deeper in its use of previous viewing information by modeling the underlying process of this influence based on the Bayesian updating theory. Using data from the Hong Kong TV industry, we test and compare the two models. Results show that the reduced-form model generally performs better when the variance of ratings across episodes is small, while the structural model generates more accurate forecasts in other cases.
•A lumped parameter nonlinear dynamic model for UTSG is developed.•UTSG is modeled by being divided into seven regions.•The model is verified with the published models.•The comparison results support ...the reliability of the model.
A lumped parameter nonlinear dynamic model for U-tube recirculation steam generator (UTSG) transient analysis is developed based on the conservation laws of mass, momentum and energy. UTSG is modeled by being divided into seven regions (control volumes), namely, primary-side region, steam region, water-downcomer region, subcooled region of heated rising channel, boiling region of heated rising channel, unheated rising section and water-steam separator region, and heat transfer tube region. The model is verified with the published models. The comparison results show that the accuracy of the steady-state simulation, the trend and most amplitudes of the transient response of this model are consistent with those of the published models, which supports the reliability of this model. This model can be used for the development of the steam dump and bypass control system and as a simulation module for coupling with the primary loop system.
This study constructs a nonlinear dynamic model of articulated vehicles and a model of hydraulic steering system. The equations of state required for nonlinear vehicle dynamics models, stability ...analysis models, and corresponding eigenvalue analysis are obtained by constructing Newtonian mechanical equilibrium equations. The objective and subjective causes of the snake oscillation and relevant indicators for evaluating snake instability are analysed using several vehicle state parameters. The influencing factors of vehicle stability and specific action mechanism of the corresponding factors are analysed by combining the eigenvalue method with multiple vehicle state parameters. The centre of mass position and hydraulic system have a more substantial influence on the stability of vehicles than the other parameters. Vehicles can be in a complex state of snaking and deviating. Different eigenvalues have varying effects on different forms of instability. The critical velocity of the linear stability analysis model obtained through the eigenvalue method is relatively lower than the critical velocity of the nonlinear model.
•Paper studies behavior of PMSG-WT assisted with diode rectifier and boost converter.•Paper develops theoretical analyses for the control design and stability analysis.•Linearized average dynamic ...model of the combined system is extracted.•The relation between PMSG torque and boost converter current is extracted.•Impact of PMSG speed controller on the stability of the system is evaluated.
Permanent magnet synchronous generator (PMSG) based wind turbines (WTs) are widely used as grid connected energy sources. Usually, a PMSG based wind energy system is connected to the grid via machine side and grid side converters. From the machine side converter point of view, there are two types of PMSG-based WTs: PMSG with back-to-back voltage source converters, and PMSG assisted with diode rectifier and boost converter. Since most of the research works regarding the PMSG-based WTs are devoted to the former type, this paper deals with the elaborated controller design and stability analysis of the grid connected PMSG based WT assisted with diode bridge rectifier and boost converter. Hence, the linearized average dynamic model of the combined system comprising PMSG, diode rectifier and boost converter is presented. Based on the linearized model, the relation between the PMSG electromagnetic torque and boost converter current is extracted, and then system’s control-loops are developed. Next, small signal stability of the full system comprising PMSG, boost-diode rectifier, dc-link capacitor, GSC, and corresponding controllers is presented and then impact of PMSG speed controller on the stability of the system is examined theoretically and by time domain simulations.
The load wheel is the main power transmission and bearing component of a tracked vehicle. In this paper, a simplified structural dynamic model of load wheel is proposed. By developing a non-contact ...rubber tread rolling dynamics test rig, the rolling deformation characteristics of load wheel are captured. Digital image correlation method is used to calculate the transient and continuous variation of strain rate of rubber tread under the influence of load, speed and different carbon black components. The feasibility of simplified structural dynamic model is evaluated by analyzing the fitting accuracy of strain rate of marker obtained from the non-contact measurement and the structural model simulation. The accuracy and validity of simplified structural dynamic model of load wheel are demonstrated based on the comparison results of tread mechanical model and full-field strain distribution. The developed simplified structural dynamic model of load wheel could describe and predict full-field strain and full-field stress distribution within the contact patch.
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