Modification of streamer-to-leader transition model based on radial thermal expansion in the sphere-plane gap discharge at high altitude

Historically,streamer-to-leader transition studies mainly focused on the rod-plane gap and low altitude analysis,with limited attention paid to the sphere-plane gap at high altitude analysis.In this work,sphere-plane gap discharge tests were carried out under the gap distance of 5 m at the Qinghai Ultra High Voltage(UHV)test base at an altitude of 2200 m.The experiments measured the physical parameters such as the discharge current,electric field intensity and instantaneous optical power.The duration of the dark period and the critical charge of streamer-toleader transition were obtained at high altitude.Based on radial thermal expansion of the streamer stem,we established a modified streamer-to-leader transition model of the sphere-plane gap discharge at high altitude,and calculated the stem temperature,stem radii and the duration of streamer-to-leader transition.Compared with the measured duration of sphere-plane electrode discharge at an altitude of 2200 m,the error rate of the modified model was 0.94%,while the classical model was 6.97%,demonstrating the effectiveness of the modified model.From the comparisons and analysis,several suggestions are proposed to improve the numerical model for further quantitative investigations of the leader inception.

Development of the Transitional Care Model for nursing care in China's Mainland:A literature review

Background:The Transitional Care Model(TCM)for nursing care has yet to be implemented in China despite its success in Western countries.However,rapid social changes have demanded an upgrade in the quality of nursing care;in 2010,the Chinese government has acknowledged the need to implement the TCM in China.Objective:This study has the following objectives:(1)perform a thorough review of the literature regarding the development and implementation of the TCM in China's Mainland within the past 5 years;(2)provide a comprehensive discussion of the current status,problems,and strategies related to the implementation of the TCM in China's Mainland;and(3)suggest strategies pertaining to the future of the TCM in China.Design:The current pertinent literature is systematically reviewed.Data sources:Systematic and manual searches in computerized databases for relevant studies regarding the TCM led to the inclusion of 26 papers in this review.Review methods:Abstracts that satisfied the inclusion criteria were reviewed independently by the two authors of this manuscript,and discrepancies were resolved through discussion.The same reviewers independently assessed the paper in its entirety for selected abstracts.Results:The present English literature reviewrevealed a paucity of updated information about the development and implementation of the TCM in China's Mainland.Nevertheless,the dramatic growth of the TCM in the past 5 years has had a vital impact within the society and in nursing development.This review also revealed numerous issues regarding the focus of the TCM.Overall implications for practiceandrecommendations for future researchare discussed.Conclusion:Despite the potential of this nursing model to have a successful and beneficial impact in China's Mainland,it remains an under-researched topic.Further research on education and training as well as premium policies for nurses under the TCM are needed.

Heat transfer simulation of annular elliptical fin-and-tube heat exchanger by transition SST model

In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,horizontal to vertical fin diameter ratios,and fin densities were examined in detail.The simulations indicate superior performance of elliptical fin layout.It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance.The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin.Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin.The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6%and 3.2%,respectively.For further elaboration of the superiority of the elliptical layout from the second law perspective,normalized entropy generation was also studied.In all cases,the entropy generation rate in circular fin was higher than that of an elliptical fin.

Phase Transitions of Majority-Vote Model on Modular Networks

We investigate the phase transitions behavior of the majority-vote model with noise on a topology that consists of two coupled random networks. A parameter p is used to measure the degree of modularity, defined as the ratio of intermodular to intramodular connectivity. For the networks of strong modularity （small p）, as the level of noise f increases, the system undergoes successively two transitions at two distinct critical noises, fc1 and fc2. The first transition is a discontinuous jump from a coexistence state of parallel and antiparallel order to a state that only parallel order survives, and the second one is continuous that separates the ordered state from a disordered state. As the network modularity worsens, fc1 becomes smaller and fc1 does not change, such that the antiparallel ordered state will vanish if p is larger than a critical value of pc. We propose a mean-field theory to explain the simulation results.

Deconfinement Phase Transition with External Magnetic Field in the Friedberg-Lee Model

The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. We expand the potentiM around the two locM minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.

Four Types of Percolation Transitions in the Cluster Aggregation Network Model

We study the percolation transition in a one-species cluster aggregation network model, in which the parameter α describes the suppression on the cluster sizes. It is found that the model can exhibit four types of percolation transitions, two continuous percolation transitions and two discontinuous ones. Continuous and discontinuous percolation transitions can be distinguished from each other by the largest single jump. Two types of continuous percolation transitions show different behaviors in the time gap. Two types of discontinuous percolation transitions are different in the time evolution of the cluster size distribution. Moreover, we also find that the time gap may also be a measure to distinguish different discontinuous percolations in this model.

Ecosystem service multifunctionality of mixed conifer-broad-leaved forests under climate change and forest management based on matrix growth modelling

Climate change and forest management are recognized as pivotal factors influencing forest ecosystem services and thus multifunctionality.However,the magnitude and the relative importance of climate change and forest management effects on the multifunctionality remain unclear,especially for natural mixed forests.In this study,our objective is to address this gap by utilizing simulations of climate-sensitive transition matrix growth models based on national forest inventory plot data.We evaluated the effects of seven management scenarios(combinations of various cutting methods and intensities)on the future provision of ecosystem services and multifunctionality in mixed conifer-broad-leaved forests in northeastern China,under four climate scenarios(SSP1-2.6,SSP2-4.5,SSP5-8.5,and constant climate).Provisioning,regulating,cultural,and supporting services were described by timber production,carbon storage,carbon sequestration,tree species diversity,deadwood volume,and the number of large living trees.Our findings indicated that timber production was significantly influenced by management scenarios,while tree species diversity,deadwood volume,and large living trees were impacted by both climate and management separately.Carbon storage and sequestration were notably influenced by both management and the interaction of climate and management.These findings emphasized the profound impact of forest management on ecosystem services,outweighing that of climate scenarios alone.We found no single management scenario maximized all six ecosystem service indicators.The upper story thinning by 5%intensity with 5-year interval(UST5)management strategy emerged with the highest multifunctionality,surpassing the lowest values by more than 20%across all climate scenarios.In conclusion,our results underlined the potential of climate-sensitive transition matrix growth models as a decision support tool and provided recommendations for long-term strategies for multifunctional forest management under future climate change context.Ecosystem services and multifunctionality of forests could be enhanced by implementing appropriate management measures amidst a changing climate.

Critical Behavior of the Energy Gap and Its Relation with the Berry Phase Close to the Excited State Quantum Phase Transition in the Lipkin Model

In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition （ESQPT） in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.

STRESS-STRAIN HYSTERESIS OF POLYCRYSTALLINE SMAs─Ⅰ:A MODEL

In this paper, a theoretical model was presented to simulate the stress-strain hysteresis and the inner hysteretic behaviors, which were observed for polycrystalline Ni-Ti and Cu-based shape memory alloys (SMAs) at various temperatures. It was assumed that the stress-strum hysteresis of the grains of a polycrystalline sample of SMAs was relatively simple and easy to be calculated. The texture of the sample was characterized by a distribution function, which could be obtained from the experiments. Thercfore,the model provided a means to simulate and, for the first time, to predict the stressstrain hysteresis at different loading temperatures for polycrystalline SMAs.

Transition Logic Regression Method to Identify Interactions in Binary Longitudinal Data

Logic regression is an adaptive regression method which searches for Boolean (logic) combinations of binary variables that best explain the variability in the outcome, and thus, it reveals interaction effects which are associated with the response. In this study, we extended logic regression to longitudinal data with binary response and proposed “Transition Logic Regression Method” to find interactions related to response. In this method, interaction effects over time were found by Annealing Algorithm with AIC (Akaike Information Criterion) as the score function of the model. Also, first and second orders Markov dependence were allowed to capture the correlation among successive observations of the same individual in longitudinal binary response. Performance of the method was evaluated with simulation study in various conditions. Proposed method was used to find interactions of SNPs and other risk factors related to low HDL over time in data of 329 participants of longitudinal TLGS study.

Extension of the KDO turbulence/transition model to account for roughness

Wall roughness significantly influences both laminar-turbulent transition process and fully developed turbulence.A wall roughness extension for the KDO turbulence/transition model is developed.The roughness effect is introduced via the modification of the k andνt boundary conditions.The wall is considered to be lifted to a higher position.The difference between the original position and the higher position,named as equivalent roughness height,is linked to the actual roughness height.The ratio between the two heights is determined by reasoning.With such a roughness extension,the predictions of the KDO RANS model agree well with the measurements of turbulent boundary layer with a sand grain surface,while the KDO transition model yields accurate cross-flow transition predictions of flow past a 6:1 spheroid.

A symmetry-based length model for characterizing the hypersonic boundary layer transition on a slender cone at moderate incidence

The hypersonic boundary layer(HBL)transition on a slender cone at moderate incidence is studied via a symmetry-based length model:the SED-SL model.The SED-SL specifies an analytic stress length function(which defines the eddy viscosity)describing a physically sound two-dimensional multi-regime structure of transitional boundary layer.Previous studies showed accurate predictions,especially on the drag coefficient,by the SED-SL for airfoil flows at different subsonic Mach numbers,Reynolds numbers and angles of attack.Here,the SED-SL is extended to compute the hypersonic heat transfer on a 7∘half-angle straight cone at Mach numbers 6 and 7 and angles of attack from 0∘to 6∘.It is shown that a proper setting of the multi-regime structure with three parameters(i.e.a transition center,an after-transition near-wall eddy length,and a transition width quantifying transition overshoot)yields an accurate description of the surface heat fluxes measured in wind tunnels.Uniformly good agreements between simulations and measurements are obtained from windward to leeward side of the cone,implying the validity of the multi-regime description of the transition independent of instability mechanisms.It is concluded that a unified description for the HBL transition of cone is found,and might offer a basis for developing a new transition model that is simultaneously of computational simplicity,sound physics and greater accuracy.

A phenomenological memristor model for synaptic memory and learning behaviors

Properties that are similar to the memory and learning functions in biological systems have been observed and reported in the experimental studies of memristors fabricated by different materials. These properties include the forgetting effect, the transition from short-term memory（STM） to long-term memory（LTM）, learning-experience behavior, etc. The mathematical model of this kind of memristor would be very important for its theoretical analysis and application design.In our analysis of the existing memristor model with these properties, we find that some behaviors of the model are inconsistent with the reported experimental observations. A phenomenological memristor model is proposed for this kind of memristor. The model design is based on the forgetting effect and STM-to-LTM transition since these behaviors are two typical properties of these memristors. Further analyses of this model show that this model can also be used directly or modified to describe other experimentally observed behaviors. Simulations show that the proposed model can give a better description of the reported memory and learning behaviors of this kind of memristor than the existing model.

A Numerical Research on a Compressibility-correlated Langtry＇s Transition Model for Double Wedge Boundary Layer Flows

A new compressibility correlation is introduced in the Langtry＇s local variable-based transition model to investigate the phe- nomenon on double wedge shock/boundary layer interactions. The cmnputational analysis compared with experimental data has been made to assess the influence of the wall temperature and the leading edge nose radius on a hypersonic double wedge boundary layer. It has been found that the laminar boundary layer separation occurs on the first ramp. Furthermore, the wall temperature and the leading edge nose radius have remarkable influence on the separation characteristics in the kink. Comparison of the calculated pressure coefficient distribution and the boundary layer profile with the experimental data shows that better results can be achieved when using the modified transition model.

Boundary-layer transition prediction using a simplified correlation-based model

This paper describes a simplified transition model based on the recently developed correlation-based γ - Reot transition model. The transport equation of transition momentum thick- ness Reynolds number is eliminated for simplicity, and new transition length function and critical Reynolds number correlation are proposed. The new model is implemented into an in-house com- putational fluid dynamics （CFD） code and validated for low and high-speed flow cases, including the zero pressure flat plate, airfoils, hypersonic flat plate and double wedge. Comparisons between the simulation results and experimental data show that the boundary-layer transition phenomena can be reasonably illustrated by the new model, which gives rise to significant improvements over the fully laminar and fully turbulent results. Moreover, the new model has comparable features of accuracy and applicability when compared with the original 3＇ - Reot model. In the meantime, the newly proposed model takes only one transport equation of intermittency factor and requires fewer correlations, which simplifies the original model greatly. Further studies, especially on separation- induced transition flows, are required for the improvement of the new model.

Validation of a RANS transition model using a high-order weighted compact nonlinear scheme

A modified transition model is given based on the shear stress transport (SST) turbulence model and an intermittency transport equation. The energy gradient term in the original model is replaced by flow strain rate to saving computational costs. The model employs local variables only, and then it can be conveniently implemented in modern computational fluid dynamics codes. The fifth-order weighted compact nonlinear scheme and the fourth-order staggered scheme are applied to discrete the governing equations for the purpose of minimizing discretization errors, so as to mitigate the confusion between numerical errors and transition model errors. The high-order package is compared with a second-order TVD method on simulating the transitional flow of a flat plate. Numerical results indicate that the high-order package give better grid convergence property than that of the second-order method. Validation of the transition model is performed for transitional flows ranging from low speed to hypersonic speed.

Accuracy assessment and error analysis for diameter at breast height measurement of trees obtained using a novel backpack LiDAR system

Background: The LiBackpack is a recently developed backpack light detection and ranging(LiDAR) system that combines the flexibility of human walking with the nearby measurement in all directions to provide a novel and efficient approach to LiDAR remote sensing, especially useful for forest structure inventory. However, the measurement accuracy and error sources have not been systematically explored for this system.Method: In this study, we used the LiBackpack D-50 system to measure the diameter at breast height(DBH) for a Pinus sylvestris tree population in the Saihanba National Forest Park of China, and estimated the accuracy of LiBackpack measurements of DBH based on comparisons with manually measured DBH values in the field. We determined the optimal vertical slice thickness of the point cloud sample for achieving the most stable and accurate LiBackpack measurements of DBH for this tree species, and explored the effects of different factors on the measurement error.Result: 1) A vertical thickness of 30 cm for the point cloud sample slice provided the highest fitting accuracy(adjusted R2= 0.89, Root Mean Squared Error(RMSE) = 20.85 mm);2) the point cloud density had a significant negative, logarithmic relationship with measurement error of DBH and it explained 35.1% of the measurement error;3) the LiBackpack measurements of DBH were generally smaller than the manually measured values, and the corresponding measurement errors increased for larger trees;and 4) by considering the effect of the point cloud density correction, a transitional model can be fitted to approximate field measured DBH using LiBackpackscanned value with satisfactory accuracy(adjusted R2= 0.920;RMSE = 14.77 mm), and decrease the predicting error by 29.2%. Our study confirmed the reliability of the novel LiBackpack system in accurate forestry inventory, set up a useful transitional model between scanning data and the traditional manual-measured data specifically for P.sylvestris, and implied the applicable substitution of this new approach for more species, with necessary parameter calibration.

Assessment and improvement of k-ω-γ model for separation-induced transition prediction

The purpose of this work is to improve the k-ω-γtransition model for separationinduced transition prediction.The fundamental cause of the excessively small separation bubble predicted by k-ω-γmodel is scrutinized from the perspective of model construction.On the basis,three rectifications are conducted to improve the k-ω-γmodel for separation-induced transition.Firstly,a damping function is established via comparing the molecular diffusion timescale with the rapid pressure-strain timescale.The damping function is applied to prevent the effective length scale from incorrect distribution near the leading edge of the separation bubble.Secondly,the pressure gradient parameterλζ,is proposed as an indicator for local susceptibility to the separation instability.Additionally,λζ,-based separation intermittencyγsep is constructed to accelerate the substantial growth of turbulent kinetic energy after flow separation.The improved model appropriate for both low-and high-speed flow has been calibrated against a variety of diverse and challenging experiments,including the subsonic T3L plate,Aerospatial A airfoil,transonic NLR-7301 airfoil and deformed hypersonic inflatable aerodynamic decelerator aeroshell.The improved model is strictly based on local variables and Galilean invariance.Besides,the proposed improvement for k-ω-γmodel can be fairly convenient to incorporate into other existing intermittency-based transition models.

Robust design of natural laminar flow supercritical airfoil by multi-objective evolution method

Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.