The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical ...The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical aluminum alloy 7050-T7451. Combined high-speed orthogonal cutting experiments with the cutting process simulations, the data relationship of high temperature, high strain rate and large strain in high-speed cutting is modified. The Johnson-Cook empirical model considering the effects of strain hardening, strain rate hardening and thermal softening is selected to describe the data relationship in high-speed cutting, and the material constants of flow stress constitutive model for aluminum alloy 7050-T7451 are determined. Finally, the constitutive model of aluminum alloy 7050-T7451 is established through experiment and simulation verification in high-speed cutting. The model is proved to be reasonable by matching the measured values of the cutting force with the estimated results from FEM simulations.展开更多
The hot working behaviors of Mg-9Y-1MM-0.6Zr （WE91） magnesium alloy were researched in a temperature range of 653 773 K and strain rate range of 0.001 1 s 1 on Gleeble 1500D hot simulator under the maximum deformati...The hot working behaviors of Mg-9Y-1MM-0.6Zr （WE91） magnesium alloy were researched in a temperature range of 653 773 K and strain rate range of 0.001 1 s 1 on Gleeble 1500D hot simulator under the maximum deformation degree of 60%. A mathematical model was established to predict the stress—strain curves of this alloy during deformation. The experimental results show that the relationship between stress and strain is obviously affected by the strain rates and deformation temperatures. The flow stress of WE91 magnesium alloy during high temperature deformation can be represented by Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation, and the stress—strain curves obtained by the established model are in good agreement with the experimental results,which prove that the model reflects the real deformation characteristics of the WE91 alloy. The average deformation activation energy is 220 kJ/mol at strain of 0.1. The microstructures of WE91 during deformation processing are influenced by temperature and strain rates.展开更多
In accordance to the anisotropic feature of turbulent flow, ananisotropic algebraic stress model is adopted to predict theturbulent flow field and turbulent characteristics generated by aRushton disc turbine with the ...In accordance to the anisotropic feature of turbulent flow, ananisotropic algebraic stress model is adopted to predict theturbulent flow field and turbulent characteristics generated by aRushton disc turbine with the improved inner-outer iterativeprocedure. The predicted turbulent flow is compared with experimentaldata and the simulation by the standard k-ε turbulence model. Theanisotropic algebraic stress model is found to give better predictionthan the standard k-ε turbulence model. The predicted turbulent flowfield is in accordance to experimental data and the trend of theturbulence intensity can be effectively reflected in the simulation.展开更多
The flow stress behaviors of AZ61 alloy has been investigated at temperature rangefrom 523 to 673K with the strain rates of 0.001-1s^(-1). It is found that the averageactivation energy, strain rate sensitive exponent ...The flow stress behaviors of AZ61 alloy has been investigated at temperature rangefrom 523 to 673K with the strain rates of 0.001-1s^(-1). It is found that the averageactivation energy, strain rate sensitive exponent and stress exponent are different atvarious deformation conditions changing from 143.6 to 176.3kJ/mol, 0.125 to 0.167and 6 to 8 respectively. A flow stress model for AZ61 alloy is derived by analyzingthe stress data based on hot compression test. It is demonstrated that the flow stressmodel including strain hardening exponent and strain softening exponent is suitableto predicate the flow stress. The prediction of the flow stress of AZ61 alloy has shownto be good agreement with the test data. The maximum differences of the peak stressescalculated by the model and obtained by experiment is less than 8%.展开更多
A second-order dynamic model based on the general relation between the subgrid-scale stress and the velocity gradient tensors was proposed. A priori test of the second-order model was made using moderate resolution di...A second-order dynamic model based on the general relation between the subgrid-scale stress and the velocity gradient tensors was proposed. A priori test of the second-order model was made using moderate resolution direct numerical simulation date at high Reynolds number ( Taylor microscale Reynolds number R-lambda = 102 similar to 216) for homogeneous, isotropic forced flow, decaying flow, and homogeneous rotating flow. Numerical testing shows that the second-order dynamic model significantly improves the correlation coefficient when compared to the first-order dynamic models.展开更多
An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 wor...An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.展开更多
OBJECTIVE To explore the pathogenesis of depression according to the LC-MS/MS-based metabolomics in the mouse model which exhibits social avoidance state induced by the chronic social defeat stress model(CSDS).METHODS...OBJECTIVE To explore the pathogenesis of depression according to the LC-MS/MS-based metabolomics in the mouse model which exhibits social avoidance state induced by the chronic social defeat stress model(CSDS).METHODS Twenty male C57BL/6N mice were randomly divided into control group and model group suffering CSDS,and the ICR retired breeder mice were used to attack the model group for 14 d of chronic social defeated stress.The open field test and source preference test were both used to observe depression-like behavior.Besides,the social interaction test is used to observe the social interaction state,especially.After the stress,the serum samples of mice were collected,and the changes of endogenous metabolites were analyzed by LC-MS metabolomics technology,and the pathway analysis of the differential metabolites was performed to explore the pathogenesis of the CSDS induced depressive-like mouse model.RESULTS After the stress of CSDS was completed,the mice in the model group showed a significant slowdown in body weight growth,a reduction in the source preference rate,and a significant reduction in the total distance and the number of rearing in the open field test.Distinctively,the social interaction rate is remarkably decreasing.There are 24 differential metabolites found in the serum of CSDS model mice.CONCLUSION The mouse who suffered CSDS stress would show depressive-like behavior.Based on the LC-MS/MS metabolomics,24 differential metabolites were found in the serum of CSDS model mice.The amino acid metabolism might be significant to the pathogenesis of the CSDS induced depressive-like mouse model.展开更多
[Objectives]To explore the antidepressant effect of Shenwei Ningyu Tablet,a new antidepressant traditional Chinese medicine,on rat chronic stress depression model and mouse tail suspension models.[Methods]Rat chronic ...[Objectives]To explore the antidepressant effect of Shenwei Ningyu Tablet,a new antidepressant traditional Chinese medicine,on rat chronic stress depression model and mouse tail suspension models.[Methods]Rat chronic stress model:except for the normal group,the rats in other groups were given corresponding chronic stress,and administered by gavage 1 h before modeling,for a total of 21 d.The changes of each indicator before and after the experiment were observed through the body weight change,the sugar water test,and open field test.The relevant hormone levels were detected by radioimmunoassay.Mouse tail suspension depression model:after continuous administration for 7 d,the activity times was recorded with the mouse automatic recorder,and the mouse immobility time was recorded after tail suspension,to explore the effects of each administration group on the tail suspension immobility time of mice.[Results]Chronic stress depression model:21 d after modeling,compared with the normal group,rats in the model group exhibited significantly reduced body weight,sucrose preference index,and horizontal and vertical movement scores(P<0.05).Compared with the model group,the low-dose Shenwei Ningyu Tablets group had significant differences in the sugar water test,horizontal and vertical movement scores(P<0.05).In addition,all three dose groups of Shenwei Ningyu Tablets could effectively reduce the content of CRF in chronic stress model rats,and the low dose group could significantly reduce the ACTH level in model rats(P<0.05).Mouse tail suspension depression model:the immobility time after tail suspension in each administration group was significantly different from that in the model group(P<0.05).[Conclusions]Shenwei Ningyu Tablets has a certain anti-depression effect on both the rat chronic stress depression model and the mouse tail suspension depression model.展开更多
An explicit algebraic stress model (EASM) has been formulated for two-dimensional turbulent buoyant flows using a five-term tensor representation in a prior study. The derivation was based on partitioning the buoyant ...An explicit algebraic stress model (EASM) has been formulated for two-dimensional turbulent buoyant flows using a five-term tensor representation in a prior study. The derivation was based on partitioning the buoyant flux tensor into a two-dimensional and a three-dimensional component. The five-term basis was formed with the two-dimensional component of the buoyant flux tensor. As such, the derived EASM is limited to two-dimensional flows only. In this paper, a more general approach using a seven-term representation without partitioning the buoyant flux tensor is used to derive an EASM valid for two- and three-dimensional turbulent buoyant flows. Consequently, the basis tensors are formed with the fully three-dimensional buoyant flux tensor. The derived EASM has the two-dimensional flow as a special case. The matrices and the representation coefficients are further simplified using a four-term representation. When this four-term representation model is applied to calculate two-dimensional homogeneous buoyant flows, the results are essentially identical with those obtained previously using the two-dimensional component of the buoyant flux tensor. Therefore, the present approach leads to a more general EASM formulation that is equally valid for two- and three-dimensional turbulent buoyant flows.展开更多
Large-strain deformations introduce several confounding factors that affect the application of the Mechanical Threshold Stress model. These include the decrease with the increasing stress of the normalized activation ...Large-strain deformations introduce several confounding factors that affect the application of the Mechanical Threshold Stress model. These include the decrease with the increasing stress of the normalized activation energy characterizing deformation kinetics, the tendency toward Stage IV hardening at high strains, and the influence of crystallographic texture. Minor additions to the Mechanical Threshold Stress model are introduced to account for variations of the activation energy and the addition of Stage IV hardening. Crystallographic texture cannot be modeled using an isotropic formulation, but some common trends when analyzing predominantly shear deformation followed by uniaxial deformation are described. Comparisons of model predictions with measurements in copper processed using Equal Channel Angular Pressing are described.展开更多
In order to quantify the understanding of crack formation in Horizontal Continuous Casting billet.the two-dimensional unsteady state mathematical model for heat transfer and elas-toplastic stress model have been estab...In order to quantify the understanding of crack formation in Horizontal Continuous Casting billet.the two-dimensional unsteady state mathematical model for heat transfer and elas-toplastic stress model have been established.Using these models to calculate the thermal stress which occurred both during surface reheating of 150× 150 mm billet which is just taken out of mold and during temperature drop in billet centre near the end of solidification,the reasonable crack formation criteria for about 0.45%carbon steel have been proposed as follows:In high temperature brittle zone higher than 1300℃,the critical tensile strength is about 170-390 N/cm^2,the critical strain to fracture is about 0.10%- 0.24%.展开更多
Environmental stress model is proposed as an effective tool to the analysis and evaluation of navigational safety in ports and waterways. Marine traffic simulations are carried out in a virtual port area with various ...Environmental stress model is proposed as an effective tool to the analysis and evaluation of navigational safety in ports and waterways. Marine traffic simulations are carried out in a virtual port area with various arrangements and conditions. Calculations of stress values and traffic volume criteria are illustrated. The simulation results provide a valuable hint for safety management of vessel traffic. The model provides quantitative information and helps administrators in decision making to achieve desired safety level and improve the efficiency of vessel traffic in ports and waterways.展开更多
The residual stress generated in the laser cladding could lead to undesirable distortions or even crack formation. In order to better understand the evolution/yielding process of stress field,a 3 D finite-element ther...The residual stress generated in the laser cladding could lead to undesirable distortions or even crack formation. In order to better understand the evolution/yielding process of stress field,a 3 D finite-element thermo-mechanical model was established for the laser cladding formation of thin wall with the 17-4 PH powder on the FV520( B) steel. The temperature field was firstly analyzed,based on which the stress field and strain field of the laser cladding forming process were analyzed.In order to validate the prediction,the final residual stress field in the obtained thin wall was tested by X-ray diffraction in comparison with the predicted results.展开更多
Clarifying the relationship between stress sensitivities of permeability and porosity is of great significance in guiding underground resource mining.More and more studies focus on how to construct stress sensitivity ...Clarifying the relationship between stress sensitivities of permeability and porosity is of great significance in guiding underground resource mining.More and more studies focus on how to construct stress sensitivity models to describe the relationship and obtain a comprehensive stress sensitivity of porous rock.However,the limitations of elastic deformation calculation and incompleteness of considered tortuosity sensitivity lead to the fact that the existing stress sensitivity models are still unsatisfactory in terms of accuracy and generalization.Therefore,a more accurate and generic stress sensitivity model considering elastic-structural deformation of capillary cross-section and tortuosity sensitivity is proposed in this paper.The elastic deformation is derived from the fractal scaling model and Hooke's law.Considering the effects of elastic-structural deformation on tortuosity sensitivity,an empirical formula is proposed,and the conditions for its applicability are clarified.The predictive performance of the proposed model for the permeability-porosity relationships is validated in several sets of publicly available experimental data.These experimental data are from different rocks under different pressure cycles.The mean and standard deviation of relative errors of predicted stress sensitivity with respect to experimental data are 2.63%and 1.91%.Compared with other models,the proposed model has higher accuracy and better predictive generalization performance.It is also found that the porosity sensitivity exponent a,which can describe permeability-porosity relationships,is 2 when only elastic deformation is considered.a decreases from 2 when structural deformation is also considered.In addition,a may be greater than 3 due to the increase in tortuosity sensitivity when tortuosity sensitivity is considered even if the rock is not fractured.展开更多
Context/Objective: High blood pressure (HBP) currently represents the most widespread chronic non-communicable disease in Cameroon. The increase in its prevalence in the country is the result of multiple factors inclu...Context/Objective: High blood pressure (HBP) currently represents the most widespread chronic non-communicable disease in Cameroon. The increase in its prevalence in the country is the result of multiple factors including economic stress imposed by precariousness, poor living conditions, sources of anxiety, anguish, depression and other behavioral disorders. Economic stress is a globalizing concept that integrates into a purely hermeneutic approach, a particular functioning of the nervous system of an individual who faces employment problems and precarious remuneration conditions. The non-satisfaction by an individual of his basic needs due to insufficient financial means can cause him to become irritable, aggressive, and socially and symbolically isolated, thereby increasing the desire to resort to morbid life models such as excessive consumption of narcotics and other psychoactive substances often associated with high blood pressure. The fight against the emergence of BPH is a complex, multifaceted and multifactorial reality that requires taking into account economic stress. The main objective of this survey is to describe the situation of economic stress within the Cameroonian population, which imposes precariousness and life models at risk of high blood pressure. Specifically, we determined the level of household income and the sources of income. Methods: A cross-sectional survey with a descriptive aim among five hundred households in the Central Region of Cameroon was conducted. A probabilistic technique called simple randomness was used. The number of households to be surveyed was determined indirectly using the Cochrane formula. Data collection in face-to-face mode using a physical questionnaire took place from July 1 to August 31, 2023, after obtaining ethical clearance from the Regional Health Research Ethics Committee, Human from the Center and an administrative authorization for data collection. Regarding their processing, the data was grouped during processing in Excel sheets. Normality and reliability tests of the collected data were carried out. For this, the Chi-square test was used for data with a qualitative value and that of Kolmogorov-Sminorf for data with a quantitative value. Descriptive analysis was possible using R software version 3.2, SPSS version 25.0, XLSTAT 2016, PAST and EXCEL programs from Microsoft Office 2013. Results: The main results highlight economic stress, with 45.60% of households surveyed earning less than US$154 per month;55% of household heads were women in single-parent families;14% of household heads were unemployed, 22% worked in the private sector and 19% were self-employed. This general economic situation leads to precarious living conditions, thereby increasing the risk of high blood pressure among the Cameroonian population.展开更多
Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response.Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice ...Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response.Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region–specific,particularly involving the corticolimbic system,including the ventral tegmental area,nucleus accumbens,prefrontal cortex,amygdala,and hippocampus.Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology.In this review,we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression.We focused on associated molecular pathways and neural circuits,with special attention to the brain-derived neurotrophic factor–tropomyosin receptor kinase B signaling pathway and the ventral tegmental area–nucleus accumbens dopamine circuit.We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature,severity,and duration of stress,especially in the above-mentioned brain regions of the corticolimbic system.Therefore,BDNF might be a biological indicator regulating stress-related processes in various brain regions.展开更多
The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model b...The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model based on Arrhenius equation was proposed for TC4,which is composed of peak flow stress(PFS) prediction and strain compensation. The predicted PFS is set as a reference to derive the flow stress model at any strain ranging from approximately 0 to 0.7. The predictability and efficiency among the proposed model, conventional model,and an existing physical-based model of TC4 were comparatively evaluated. It is found that the newly proposed model can simultaneously track the hardening and softening behaviors of TC4 through a single expression while the other existing models are only valid in the softening region.Besides, the wider application range and acceptable accuracy of the new model have been achieved by fewer material constants with much-simplified modeling procedure than the other models.展开更多
The Speziale,Sarkar and Gatski Reynolds Stress Model(SSG RSM)is utilized to simulate the fluid dynamics in a full baffled stirred tank with a Rushton turbine impeller.Four levels of grid resolutions are chosen to dete...The Speziale,Sarkar and Gatski Reynolds Stress Model(SSG RSM)is utilized to simulate the fluid dynamics in a full baffled stirred tank with a Rushton turbine impeller.Four levels of grid resolutions are chosen to determine an optimised number of grids for further simulations.CFD model data in terms of the flow field,trailing vortex,and the power number are compared with published experimental results.The comparison shows that the global fluid dynamics throughout the stirred tank and the local characteristics of trailing vortices near the blade tips can be captured by the SSG RSM.The predicted mean velocity components in axial,radial and tangential direction are also in good agreement with experiment data.The power number predicted is quite close to the designed value,which demonstrates that this model can accurately calculate the power number in the stirred tank.Therefore,the simulation by using a combination of SSG RSM and MRF impeller rotational model can accurately model turbulent fluid flow in the stirred tank,and it offers an alternative method for design and optimisation of stirred tanks.展开更多
This paper is set in the high-order finite-difference discretization of the Reynolds-averaged Navier-Stokes(RANS)equations,which are coupled with the turbulence model equations.Three alternative scale-providing variab...This paper is set in the high-order finite-difference discretization of the Reynolds-averaged Navier-Stokes(RANS)equations,which are coupled with the turbulence model equations.Three alternative scale-providing variables for the specific dissipation rate(o)are implemented in the framework of the Reynolds stress model(RSM)for improving its robustness.Specifically,g(=1/√ω)has natural boundary conditions and reduced spatial gradients,and a new numerical constraint is imposed on itω(=lnω)can preserve positivity and also has reduced spatial gradients;the eddy viscosity v,also has natural boundary conditions and its equation is improved in this work.The solution polynomials of the mean-flow and turbulence-model equations are both reconstructed by the weighted compact nonlinear scheme(WCNS).Moreover,several numerical techniques are introduced to improve the numerical stability of the equation system.A range of canonical as well as industrial turbulent flows are simulated to assess the accuracy and robustness of the scale-transformed models.Numerical results show that the scale-transformed models have significantly improved robustness compared to the w model and still keep the characteristics of RSM.Therefore,the high-order discretization of the RANS and RSM equations,which number 12 in total,can be successfully achieved.展开更多
The Reynolds stress model(RSM)outperforms the eddy viscosity model(EVM)when simulating complex flows and has increased demand for high-order discretization.However,the complexity of the RSM equations results in poor n...The Reynolds stress model(RSM)outperforms the eddy viscosity model(EVM)when simulating complex flows and has increased demand for high-order discretization.However,the complexity of the RSM equations results in poor numerical stability and weak convergence performance.One of the reasons is that the properties of Reynolds stresses are not fully considered in the design of the numerical scheme.In response to this issue,this study develops an adaptive algorithm to adjustε_(β)values(an empirical parameter in nonlinear weights)according to the magnitude and smoothness of the Reynolds stresses.This algorithm is introduced into the fifth-order weighted compact nonlinear scheme(WCNS)and is applied to the high-order discretization of the RSM.Three aeronautic test cases are simulated to investigate the performance of the algorithm.The numerical results show that,the adaptive algorithm can reduce the residual by up to 3 orders of magnitude and predict the correct weights for gradient reversals.These results confirm that the application of theε_(β)-adaptive algorithm to the high-order discretization of the RSM is beneficial both for enhancing convergence and improving resolution.展开更多
文摘The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical aluminum alloy 7050-T7451. Combined high-speed orthogonal cutting experiments with the cutting process simulations, the data relationship of high temperature, high strain rate and large strain in high-speed cutting is modified. The Johnson-Cook empirical model considering the effects of strain hardening, strain rate hardening and thermal softening is selected to describe the data relationship in high-speed cutting, and the material constants of flow stress constitutive model for aluminum alloy 7050-T7451 are determined. Finally, the constitutive model of aluminum alloy 7050-T7451 is established through experiment and simulation verification in high-speed cutting. The model is proved to be reasonable by matching the measured values of the cutting force with the estimated results from FEM simulations.
基金Projects(2007CB613704,2007CB613705)supported by the National Basic Research Program of China
文摘The hot working behaviors of Mg-9Y-1MM-0.6Zr （WE91） magnesium alloy were researched in a temperature range of 653 773 K and strain rate range of 0.001 1 s 1 on Gleeble 1500D hot simulator under the maximum deformation degree of 60%. A mathematical model was established to predict the stress—strain curves of this alloy during deformation. The experimental results show that the relationship between stress and strain is obviously affected by the strain rates and deformation temperatures. The flow stress of WE91 magnesium alloy during high temperature deformation can be represented by Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation, and the stress—strain curves obtained by the established model are in good agreement with the experimental results,which prove that the model reflects the real deformation characteristics of the WE91 alloy. The average deformation activation energy is 220 kJ/mol at strain of 0.1. The microstructures of WE91 during deformation processing are influenced by temperature and strain rates.
基金the National Natural Science Foundation of China (No. 29792074).
文摘In accordance to the anisotropic feature of turbulent flow, ananisotropic algebraic stress model is adopted to predict theturbulent flow field and turbulent characteristics generated by aRushton disc turbine with the improved inner-outer iterativeprocedure. The predicted turbulent flow is compared with experimentaldata and the simulation by the standard k-ε turbulence model. Theanisotropic algebraic stress model is found to give better predictionthan the standard k-ε turbulence model. The predicted turbulent flowfield is in accordance to experimental data and the trend of theturbulence intensity can be effectively reflected in the simulation.
文摘The flow stress behaviors of AZ61 alloy has been investigated at temperature rangefrom 523 to 673K with the strain rates of 0.001-1s^(-1). It is found that the averageactivation energy, strain rate sensitive exponent and stress exponent are different atvarious deformation conditions changing from 143.6 to 176.3kJ/mol, 0.125 to 0.167and 6 to 8 respectively. A flow stress model for AZ61 alloy is derived by analyzingthe stress data based on hot compression test. It is demonstrated that the flow stressmodel including strain hardening exponent and strain softening exponent is suitableto predicate the flow stress. The prediction of the flow stress of AZ61 alloy has shownto be good agreement with the test data. The maximum differences of the peak stressescalculated by the model and obtained by experiment is less than 8%.
文摘A second-order dynamic model based on the general relation between the subgrid-scale stress and the velocity gradient tensors was proposed. A priori test of the second-order model was made using moderate resolution direct numerical simulation date at high Reynolds number ( Taylor microscale Reynolds number R-lambda = 102 similar to 216) for homogeneous, isotropic forced flow, decaying flow, and homogeneous rotating flow. Numerical testing shows that the second-order dynamic model significantly improves the correlation coefficient when compared to the first-order dynamic models.
基金supported by the Jiangxi Provincial Natural Science Foundation of China(No.550067)Jiangxi Provincial Education Commission Foundation(No.2005-26).
文摘An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.
文摘OBJECTIVE To explore the pathogenesis of depression according to the LC-MS/MS-based metabolomics in the mouse model which exhibits social avoidance state induced by the chronic social defeat stress model(CSDS).METHODS Twenty male C57BL/6N mice were randomly divided into control group and model group suffering CSDS,and the ICR retired breeder mice were used to attack the model group for 14 d of chronic social defeated stress.The open field test and source preference test were both used to observe depression-like behavior.Besides,the social interaction test is used to observe the social interaction state,especially.After the stress,the serum samples of mice were collected,and the changes of endogenous metabolites were analyzed by LC-MS metabolomics technology,and the pathway analysis of the differential metabolites was performed to explore the pathogenesis of the CSDS induced depressive-like mouse model.RESULTS After the stress of CSDS was completed,the mice in the model group showed a significant slowdown in body weight growth,a reduction in the source preference rate,and a significant reduction in the total distance and the number of rearing in the open field test.Distinctively,the social interaction rate is remarkably decreasing.There are 24 differential metabolites found in the serum of CSDS model mice.CONCLUSION The mouse who suffered CSDS stress would show depressive-like behavior.Based on the LC-MS/MS metabolomics,24 differential metabolites were found in the serum of CSDS model mice.The amino acid metabolism might be significant to the pathogenesis of the CSDS induced depressive-like mouse model.
基金National Major Scientific and Technological Special Project for"Significant New Drugs Development"(2019ZX09301-005).
文摘[Objectives]To explore the antidepressant effect of Shenwei Ningyu Tablet,a new antidepressant traditional Chinese medicine,on rat chronic stress depression model and mouse tail suspension models.[Methods]Rat chronic stress model:except for the normal group,the rats in other groups were given corresponding chronic stress,and administered by gavage 1 h before modeling,for a total of 21 d.The changes of each indicator before and after the experiment were observed through the body weight change,the sugar water test,and open field test.The relevant hormone levels were detected by radioimmunoassay.Mouse tail suspension depression model:after continuous administration for 7 d,the activity times was recorded with the mouse automatic recorder,and the mouse immobility time was recorded after tail suspension,to explore the effects of each administration group on the tail suspension immobility time of mice.[Results]Chronic stress depression model:21 d after modeling,compared with the normal group,rats in the model group exhibited significantly reduced body weight,sucrose preference index,and horizontal and vertical movement scores(P<0.05).Compared with the model group,the low-dose Shenwei Ningyu Tablets group had significant differences in the sugar water test,horizontal and vertical movement scores(P<0.05).In addition,all three dose groups of Shenwei Ningyu Tablets could effectively reduce the content of CRF in chronic stress model rats,and the low dose group could significantly reduce the ACTH level in model rats(P<0.05).Mouse tail suspension depression model:the immobility time after tail suspension in each administration group was significantly different from that in the model group(P<0.05).[Conclusions]Shenwei Ningyu Tablets has a certain anti-depression effect on both the rat chronic stress depression model and the mouse tail suspension depression model.
文摘An explicit algebraic stress model (EASM) has been formulated for two-dimensional turbulent buoyant flows using a five-term tensor representation in a prior study. The derivation was based on partitioning the buoyant flux tensor into a two-dimensional and a three-dimensional component. The five-term basis was formed with the two-dimensional component of the buoyant flux tensor. As such, the derived EASM is limited to two-dimensional flows only. In this paper, a more general approach using a seven-term representation without partitioning the buoyant flux tensor is used to derive an EASM valid for two- and three-dimensional turbulent buoyant flows. Consequently, the basis tensors are formed with the fully three-dimensional buoyant flux tensor. The derived EASM has the two-dimensional flow as a special case. The matrices and the representation coefficients are further simplified using a four-term representation. When this four-term representation model is applied to calculate two-dimensional homogeneous buoyant flows, the results are essentially identical with those obtained previously using the two-dimensional component of the buoyant flux tensor. Therefore, the present approach leads to a more general EASM formulation that is equally valid for two- and three-dimensional turbulent buoyant flows.
文摘Large-strain deformations introduce several confounding factors that affect the application of the Mechanical Threshold Stress model. These include the decrease with the increasing stress of the normalized activation energy characterizing deformation kinetics, the tendency toward Stage IV hardening at high strains, and the influence of crystallographic texture. Minor additions to the Mechanical Threshold Stress model are introduced to account for variations of the activation energy and the addition of Stage IV hardening. Crystallographic texture cannot be modeled using an isotropic formulation, but some common trends when analyzing predominantly shear deformation followed by uniaxial deformation are described. Comparisons of model predictions with measurements in copper processed using Equal Channel Angular Pressing are described.
文摘In order to quantify the understanding of crack formation in Horizontal Continuous Casting billet.the two-dimensional unsteady state mathematical model for heat transfer and elas-toplastic stress model have been established.Using these models to calculate the thermal stress which occurred both during surface reheating of 150× 150 mm billet which is just taken out of mold and during temperature drop in billet centre near the end of solidification,the reasonable crack formation criteria for about 0.45%carbon steel have been proposed as follows:In high temperature brittle zone higher than 1300℃,the critical tensile strength is about 170-390 N/cm^2,the critical strain to fracture is about 0.10%- 0.24%.
文摘Environmental stress model is proposed as an effective tool to the analysis and evaluation of navigational safety in ports and waterways. Marine traffic simulations are carried out in a virtual port area with various arrangements and conditions. Calculations of stress values and traffic volume criteria are illustrated. The simulation results provide a valuable hint for safety management of vessel traffic. The model provides quantitative information and helps administrators in decision making to achieve desired safety level and improve the efficiency of vessel traffic in ports and waterways.
基金supported by a great from the Major State Basic Research Development Program of China(No.2011CB013403)the Scientific Research Foundation for Talent,Guizhou University(No.201665)
文摘The residual stress generated in the laser cladding could lead to undesirable distortions or even crack formation. In order to better understand the evolution/yielding process of stress field,a 3 D finite-element thermo-mechanical model was established for the laser cladding formation of thin wall with the 17-4 PH powder on the FV520( B) steel. The temperature field was firstly analyzed,based on which the stress field and strain field of the laser cladding forming process were analyzed.In order to validate the prediction,the final residual stress field in the obtained thin wall was tested by X-ray diffraction in comparison with the predicted results.
基金funding support from the State Key Program of National Natural Science Foundation of China(Grant No.U1637206)Shanghai Sailing Program(Grant No.20YF1417200).
文摘Clarifying the relationship between stress sensitivities of permeability and porosity is of great significance in guiding underground resource mining.More and more studies focus on how to construct stress sensitivity models to describe the relationship and obtain a comprehensive stress sensitivity of porous rock.However,the limitations of elastic deformation calculation and incompleteness of considered tortuosity sensitivity lead to the fact that the existing stress sensitivity models are still unsatisfactory in terms of accuracy and generalization.Therefore,a more accurate and generic stress sensitivity model considering elastic-structural deformation of capillary cross-section and tortuosity sensitivity is proposed in this paper.The elastic deformation is derived from the fractal scaling model and Hooke's law.Considering the effects of elastic-structural deformation on tortuosity sensitivity,an empirical formula is proposed,and the conditions for its applicability are clarified.The predictive performance of the proposed model for the permeability-porosity relationships is validated in several sets of publicly available experimental data.These experimental data are from different rocks under different pressure cycles.The mean and standard deviation of relative errors of predicted stress sensitivity with respect to experimental data are 2.63%and 1.91%.Compared with other models,the proposed model has higher accuracy and better predictive generalization performance.It is also found that the porosity sensitivity exponent a,which can describe permeability-porosity relationships,is 2 when only elastic deformation is considered.a decreases from 2 when structural deformation is also considered.In addition,a may be greater than 3 due to the increase in tortuosity sensitivity when tortuosity sensitivity is considered even if the rock is not fractured.
文摘Context/Objective: High blood pressure (HBP) currently represents the most widespread chronic non-communicable disease in Cameroon. The increase in its prevalence in the country is the result of multiple factors including economic stress imposed by precariousness, poor living conditions, sources of anxiety, anguish, depression and other behavioral disorders. Economic stress is a globalizing concept that integrates into a purely hermeneutic approach, a particular functioning of the nervous system of an individual who faces employment problems and precarious remuneration conditions. The non-satisfaction by an individual of his basic needs due to insufficient financial means can cause him to become irritable, aggressive, and socially and symbolically isolated, thereby increasing the desire to resort to morbid life models such as excessive consumption of narcotics and other psychoactive substances often associated with high blood pressure. The fight against the emergence of BPH is a complex, multifaceted and multifactorial reality that requires taking into account economic stress. The main objective of this survey is to describe the situation of economic stress within the Cameroonian population, which imposes precariousness and life models at risk of high blood pressure. Specifically, we determined the level of household income and the sources of income. Methods: A cross-sectional survey with a descriptive aim among five hundred households in the Central Region of Cameroon was conducted. A probabilistic technique called simple randomness was used. The number of households to be surveyed was determined indirectly using the Cochrane formula. Data collection in face-to-face mode using a physical questionnaire took place from July 1 to August 31, 2023, after obtaining ethical clearance from the Regional Health Research Ethics Committee, Human from the Center and an administrative authorization for data collection. Regarding their processing, the data was grouped during processing in Excel sheets. Normality and reliability tests of the collected data were carried out. For this, the Chi-square test was used for data with a qualitative value and that of Kolmogorov-Sminorf for data with a quantitative value. Descriptive analysis was possible using R software version 3.2, SPSS version 25.0, XLSTAT 2016, PAST and EXCEL programs from Microsoft Office 2013. Results: The main results highlight economic stress, with 45.60% of households surveyed earning less than US$154 per month;55% of household heads were women in single-parent families;14% of household heads were unemployed, 22% worked in the private sector and 19% were self-employed. This general economic situation leads to precarious living conditions, thereby increasing the risk of high blood pressure among the Cameroonian population.
基金supported financially by the National Natural Science Foundation of China,No.82071272(to YZ).
文摘Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response.Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region–specific,particularly involving the corticolimbic system,including the ventral tegmental area,nucleus accumbens,prefrontal cortex,amygdala,and hippocampus.Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology.In this review,we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression.We focused on associated molecular pathways and neural circuits,with special attention to the brain-derived neurotrophic factor–tropomyosin receptor kinase B signaling pathway and the ventral tegmental area–nucleus accumbens dopamine circuit.We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature,severity,and duration of stress,especially in the above-mentioned brain regions of the corticolimbic system.Therefore,BDNF might be a biological indicator regulating stress-related processes in various brain regions.
基金financially supported by the National Natural Science Foundation of China (No. 51475295)
文摘The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model based on Arrhenius equation was proposed for TC4,which is composed of peak flow stress(PFS) prediction and strain compensation. The predicted PFS is set as a reference to derive the flow stress model at any strain ranging from approximately 0 to 0.7. The predictability and efficiency among the proposed model, conventional model,and an existing physical-based model of TC4 were comparatively evaluated. It is found that the newly proposed model can simultaneously track the hardening and softening behaviors of TC4 through a single expression while the other existing models are only valid in the softening region.Besides, the wider application range and acceptable accuracy of the new model have been achieved by fewer material constants with much-simplified modeling procedure than the other models.
基金support from the Major State Basic Research Development Program of China(973 Program,Grant No.2005CB221205)。
文摘The Speziale,Sarkar and Gatski Reynolds Stress Model(SSG RSM)is utilized to simulate the fluid dynamics in a full baffled stirred tank with a Rushton turbine impeller.Four levels of grid resolutions are chosen to determine an optimised number of grids for further simulations.CFD model data in terms of the flow field,trailing vortex,and the power number are compared with published experimental results.The comparison shows that the global fluid dynamics throughout the stirred tank and the local characteristics of trailing vortices near the blade tips can be captured by the SSG RSM.The predicted mean velocity components in axial,radial and tangential direction are also in good agreement with experiment data.The power number predicted is quite close to the designed value,which demonstrates that this model can accurately calculate the power number in the stirred tank.Therefore,the simulation by using a combination of SSG RSM and MRF impeller rotational model can accurately model turbulent fluid flow in the stirred tank,and it offers an alternative method for design and optimisation of stirred tanks.
基金supported by the National Natural Science Foundation of China(Grant No.12002379)the Natural Science Foundation of Hunan Province in China(Grant No.2020JJ5648)+1 种基金the Scientific Research Project of National University of Defense Technology(Grant No.ZK20-43)the National Key Project(Grant No.GJXM92579).
文摘This paper is set in the high-order finite-difference discretization of the Reynolds-averaged Navier-Stokes(RANS)equations,which are coupled with the turbulence model equations.Three alternative scale-providing variables for the specific dissipation rate(o)are implemented in the framework of the Reynolds stress model(RSM)for improving its robustness.Specifically,g(=1/√ω)has natural boundary conditions and reduced spatial gradients,and a new numerical constraint is imposed on itω(=lnω)can preserve positivity and also has reduced spatial gradients;the eddy viscosity v,also has natural boundary conditions and its equation is improved in this work.The solution polynomials of the mean-flow and turbulence-model equations are both reconstructed by the weighted compact nonlinear scheme(WCNS).Moreover,several numerical techniques are introduced to improve the numerical stability of the equation system.A range of canonical as well as industrial turbulent flows are simulated to assess the accuracy and robustness of the scale-transformed models.Numerical results show that the scale-transformed models have significantly improved robustness compared to the w model and still keep the characteristics of RSM.Therefore,the high-order discretization of the RANS and RSM equations,which number 12 in total,can be successfully achieved.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.12002379 and 11972370)the National Key Project(Grant No.GJXM92579).
文摘The Reynolds stress model(RSM)outperforms the eddy viscosity model(EVM)when simulating complex flows and has increased demand for high-order discretization.However,the complexity of the RSM equations results in poor numerical stability and weak convergence performance.One of the reasons is that the properties of Reynolds stresses are not fully considered in the design of the numerical scheme.In response to this issue,this study develops an adaptive algorithm to adjustε_(β)values(an empirical parameter in nonlinear weights)according to the magnitude and smoothness of the Reynolds stresses.This algorithm is introduced into the fifth-order weighted compact nonlinear scheme(WCNS)and is applied to the high-order discretization of the RSM.Three aeronautic test cases are simulated to investigate the performance of the algorithm.The numerical results show that,the adaptive algorithm can reduce the residual by up to 3 orders of magnitude and predict the correct weights for gradient reversals.These results confirm that the application of theε_(β)-adaptive algorithm to the high-order discretization of the RSM is beneficial both for enhancing convergence and improving resolution.
