In Bahawalpur,a cross-sectional study assessed depression prevalence across age and gender groups,involving 442 participants from diverse socioeconomic backgrounds and settings.Utilizing the PHQ9 questionnaire,84%were...In Bahawalpur,a cross-sectional study assessed depression prevalence across age and gender groups,involving 442 participants from diverse socioeconomic backgrounds and settings.Utilizing the PHQ9 questionnaire,84%were found to meet depression levels.The findings revealed a higher incidence in females(88%)than males(79%),with the greatest disparity among young adults,particularly young women,due to factors like academic pressure and financial stress.School children had the lowest depression rates(68%),possibly due to better immunity.Elderly individuals exhibited more severe depression,likely related to aging and domestic challenges.The study’s findings highlight a significant variation in depression severity across different demographic groups,with an overall higher incidence in women.The research underscores the necessity for targeted mental health resources and interventions tailored to the specific needs of each demographic group.It also points to the importance of addressing academic and socioeconomic stressors to mitigate depression,particularly among young women.While the study provides valuable insights,it relies on self-reported data,which may introduce bias.Therefore,future research should include clinical assessments to validate these findings and ensure a more accurate representation of depression within the community.展开更多
Field and laboratory observations indicate that the variation of drag coefficient with wind speed at high winds is different from that under low-to-moderate winds.By taking the effects of wave development and sea spra...Field and laboratory observations indicate that the variation of drag coefficient with wind speed at high winds is different from that under low-to-moderate winds.By taking the effects of wave development and sea spray into account,a new parameterization of drag coefficient applicable from low to extreme winds is proposed.It is shown that,under low-to-moderate wind conditions so that the sea spray effects could be neglected,the nondimensional aerodynamic roughness first increases and then decreases with the increasing wave age;whereas under high wind conditions,the drag coefficient decreases with the increasing wind speed due to the modification of the logarithmic wind profile by the effect of sea spray droplets produced by bursting bubbles or wind tearing breaking wave crests.The drag coefficients and sea surface aerodynamic roughnesses reach their maximum values vary under different wave developments.Correspondingly,the reduction of drag coefficient under high winds reduces the increasing rate of friction velocity with increasing wind speed.展开更多
This article lists all possible conversion equations of influence coefficients(ICs)with different formats when some of these are known to handle two-plane balancing tasks with no or less trial weight runs.There are tw...This article lists all possible conversion equations of influence coefficients(ICs)with different formats when some of these are known to handle two-plane balancing tasks with no or less trial weight runs.There are two approaches for two-plane balancing.One can treat it as a multi-plane balance problem involving a 2×2 matrix of complex ICs where two direct ICs along with two cross-effect ICs are generated so that correction weights at one or two balance planes can be determined.One can also apply a static pare(in-phase)and/or couple pair(180 degrees out-of-phase)weights for balancing.The latter approach has been used quite often in the field,especially on steam turbine and generator rotors.Dependent on vibration mode shapes and combinations as well as balance plane accessibility,sometimes applying static or couple pair weights can be a wise choice;other times weights at one or two end planes are needed.There are totally 4 possible sets of IC data due to weights at plane 1,plane 2,static pair,and couple pair.IC data would typically be obtained by applying trial weights followed by trial weight runs.It is found,however,that all these IC data can be converted easily without trial weight runs once any two of 4 sets are known.The above findings and conversion equations have been obtained analytically and verified by experimental results.Real cases are given to demonstratetheirapplications.展开更多
Measurement error of unbalance's vibration response plays a crucial role in calibration and on-line updating of influence coefficient(IC). Focusing on the two problems that the moment estimator of data used in cali...Measurement error of unbalance's vibration response plays a crucial role in calibration and on-line updating of influence coefficient(IC). Focusing on the two problems that the moment estimator of data used in calibration process cannot fulfill the accuracy requirement under small sample and the disturbance of measurement error cannot be effectively suppressed in updating process, an IC calibration and on-line updating method based on hierarchical Bayesian method for automatic dynamic balancing machine was proposed. During calibration process, for the repeatedly-measured data obtained from experiments with different trial weights, according to the fact that measurement error of each sensor had the same statistical characteristics, the joint posterior distribution model for the true values of the vibration response under all trial weights and measurement error was established. During the updating process, information obtained from calibration was regarded as prior information, which was utilized to update the posterior distribution of IC combined with the real-time reference information to implement online updating. Moreover, Gibbs sampling method of Markov Chain Monte Carlo(MCMC) was adopted to obtain the maximum posterior estimation of parameters to be estimated. On the independent developed dynamic balancing testbed, prediction was carried out for multiple groups of data through the proposed method and the traditional method respectively, the result indicated that estimator of influence coefficient obtained through the proposed method had higher accuracy; the proposed updating method more effectively guaranteed the measurement accuracy during the whole producing process, and meantime more reasonably compromised between the sensitivity of IC change and suppression of randomness of vibration response.展开更多
In order to develop a general calculating rotor’s torsional stiffness based on stiffness influence coefficient for different rotor assembling, the calculation method of the torsional stiffness influence coefficient o...In order to develop a general calculating rotor’s torsional stiffness based on stiffness influence coefficient for different rotor assembling, the calculation method of the torsional stiffness influence coefficient of equal thickness disc is researched in this paper at first. Then the torsional stiffness influence coefficient λ of equal thickness disc is fit to a binary curved face and a calculation equation is obtained based on a large quantity of calculating data, which lays the foundation for research on a general calculating method of rotor torsional stiffness. Thirdly a simplified calculation method for equivalent stiffness diameter of stepped equal thickness disc and cone disc in the steam turbine generators is suggested. Finally a general calculating program for calculating rotor’s torsional vibration features is developed, and the torsional vibration features of a verity of steam turbine rotors are calculated for verification. The calculating results show that stiffness influence coefficient λ of equal-thickness disc depends on parameters of B and H, as well as the stiffness influence coefficient λ;and discs with complex structure can be simplified to equal-thickness discs with little error by using the method suggested in this paper;error can be controlled within 1% when equivalent diameter of stiffness is calculated by this method.展开更多
In this paper, we study local influence analysis for Zhang's generalized correlation coefficients and Hotelling's generalized correlation coefficient by using approach. of local influence analysis suggested by...In this paper, we study local influence analysis for Zhang's generalized correlation coefficients and Hotelling's generalized correlation coefficient by using approach. of local influence analysis suggested by Shi (1991), i.e., generalized influence function (GIF) and generalized Cook distance (GCD). An example is given to illustrate our results.展开更多
In order to execute geometric analysis for planar deployable mechanism of scissors unit,the dynamic analysis model of scissor planar deployable structure is created based on the Cartesian coordinate system,the influen...In order to execute geometric analysis for planar deployable mechanism of scissors unit,the dynamic analysis model of scissor planar deployable structure is created based on the Cartesian coordinate system,the influence coefficient is acquired by means of the coordinate transformation,combining the D 'Alembert 's principle with Dynamic-Static method,the dynamic characteristic analysis is completed finally. Moreover,specific calculating examples are adopted to verify the effectiveness of proposed method,and the result shows that the movement of each component of scissors unit mechanism is more smooth during initial deployment stage,however,when the configuration angle θ of unit mechanism is approaching π,some comparative large variations would appear on movement parameters and hinge constraint force.展开更多
Based on the model structure of the influence coefficient method analyzed in depth by matrix theory ,it is explained the reason why the unreasonable and instable correction masses with bigger MSE are obtained by LS in...Based on the model structure of the influence coefficient method analyzed in depth by matrix theory ,it is explained the reason why the unreasonable and instable correction masses with bigger MSE are obtained by LS influence coefficient method when there are correlation planes in the dynamic balancing. It also presencd the new ridge regression method for solving correction masses according to the Tikhonov regularization theory, and described the reason why the ridge regression can eliminate the disadvantage of the LS method. Applying this new method to dynamic balancing of gas turbine, it is found that this method is superior to the LS method when influence coefficient matrix is ill-conditioned,the minimal correction masses and residual vibration are obtained in the dynamic balancing of rotors.展开更多
According to the concept of virtual bending force,a rational explanation for SHOHET's model was presented. Considering the deformation characters of the work rolls in four-high mill,the deformation model of the wo...According to the concept of virtual bending force,a rational explanation for SHOHET's model was presented. Considering the deformation characters of the work rolls in four-high mill,the deformation model of the work roll was regarded as a cantilever beam and new influence coefficients were deduced.The effect of the bending force was taken into account independently. Therefore,the contribution to work roll deflection caused by rolling load,rolling pressure between rolls and bending force can be got from the new formulas.To validate the accuracy of the formulas,the results obtained from the new formulas were compared with those from SHOHET's formulas.It is found that they highly coincide,which illustrates that the formulas are reliable.展开更多
The influence of the pressure transmission medium(PTM)on the excitonic interband transitions in monolayer tungsten diselenide(WSe2)is investigated using photoluminescence(PL)spectra under hydrostatic pressure up...The influence of the pressure transmission medium(PTM)on the excitonic interband transitions in monolayer tungsten diselenide(WSe2)is investigated using photoluminescence(PL)spectra under hydrostatic pressure up to 5GPa.Three kinds of PTMs,condensed argon(Ar),1:1 n-pentane and isopentane mixture(PM),and4:1 methanol and ethanol mixture(MEM,a PTM with polarity),are used.It is found that when either Ar or PM is used as the PTM,the PL peak of exciton related to the direct K-K interband transition shows a pressure-induced blue-shift at a rate of 32±4 or 32±1 meV/GPa,while it turns to be 50±9meV/GPa when MEM is used as the PTM.The indirect A-K interband transition presents almost no shift with increasing pressure up to approximatel.y 5 GPa when Ar and PM are used as the PTM,while it shows a red-shift at the rate of-17±7meV/GPa by using MEM as the PTM.These results reveal that the optical interband transitions of monolayer WSe2 are very sensitive to the polarity of the PTM.The anomalous pressure coefficient obtained using the polar PTM of MEM is ascribed to the existence of hydrogen-like bonds between hydroxyl in MEM and Se atoms under hydrostatic pressure.展开更多
Typical rotors such as those on steam turbine or generator are often supported by two bearings with two balance planes at both ends.Vibrations are monitored by a pair of proximity probes at each bearing.There are two ...Typical rotors such as those on steam turbine or generator are often supported by two bearings with two balance planes at both ends.Vibrations are monitored by a pair of proximity probes at each bearing.There are two approaches to reduce 1X vibration due to unbalance at both ends via balancing with influence coefficient method.The first approach is to treat it as a multiple-plane balancing problem involving 2x2 matrix of complex influence coefficients.The second approach is to treat it as two single-plane balance problems using static(in-phase)and couple(180 degree out-of-phase)components,respectively.Conversion equations of influence coefficients between these two approaches have been found previously by the author.The corresponding spreadsheets that convert influence coefficients between these two formats are presented in the current paper.The paper shows effectiveness of these conversion equations in dealing with real balancing problems in the field.A detailed balance case is presented to demonstrate how the conversion equations are used to reduce vibration effectively.展开更多
The usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefficient (ADC...The usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefficient (ADC) values and their variations with age is necessary when interpreting normal testicular anatomy and pathology. We evaluated 147 normal testes using DWI, including 71 testes from 53 men aged 20-39years (group 1), 67 testes from 42 men aged 40-69 years (group 2) and nine testes from six men older than 70years (group 3). DWI was performed along the axial plane, using a single shot, multislice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm-2. The mean and standard deviation of the ADC values of normal testicular parenchyma were calculated for each age group separately. Analysis of variance (ANOVA) followed by post hoc analysis (Dunnett T3) was used for statistical purposes. The ADC values (x 10-3 mm2s-1) of normal testicular tissue were different among age groups (group 1:1.08 ± 0.13; group 2:1.15 ±0.15 and group 3:1.31± 0.22). ANOVA revealed differences in mean ADC among age groups (F= 11.391, P〈 0.001). Post hoc analysis showed differences between groups 1 and 2 (P= 0.008) and between groups 1 and 3 (P= 0.043), but not between groups 2 and 3 (P= 0.197). Our findings suggest that ADC values of normal testicular tissue increase with advancing age.展开更多
The steel slag (SS) permeable concrete was prepared by SS. The influences of the aggregate-cement rate, the aggregate particle size, the water-cement rate, the admixture dosage and other factors on the permeability ...The steel slag (SS) permeable concrete was prepared by SS. The influences of the aggregate-cement rate, the aggregate particle size, the water-cement rate, the admixture dosage and other factors on the permeability coefficient of SS permeable concrete were analyzed. The law of influence was also investigated. The study serves as a technological reference for the construction and design of SS permeable concrete.展开更多
The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The c...The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The chloride diffusion coefficients of recycled aggregate concrete under compressive stresses were measured by the rapid chloride ion migration(RCM)method.The experimental results show that the chloride diffusion coefficients of recycled aggregate concrete(RAC)under different compressive stress ratios generally decrease with the increase of curing age.For RAC subjected to the same compressive stress ratios,the chloride diffusion coefficients approximately have power functions with curing ages and the relationship models are proposed.Moreover,the influence of curing age on chloride diffusion coefficient firstly decreases and then increases as the compressive stress ratio increases.展开更多
Due to the diversity of work requirements and environment,the number of degrees of freedom(DOFs)and the complexity of structure of industrial robots are constantly increasing.It is difficult to establish the accurate ...Due to the diversity of work requirements and environment,the number of degrees of freedom(DOFs)and the complexity of structure of industrial robots are constantly increasing.It is difficult to establish the accurate dynamical model of industrial robots,which greatly hinders the realization of a stable,fast and accurate trajectory tracking control.Therefore,the general expression of the constraint relation in the explicit dynamic equation of the multi-DOF industrial robot is derived on the basis of solving the Jacobian matrix and Hessian matrix by using the kinematic influence coefficients method.Moreover,an explicit dynamic equation with general constraint relation expression is established based on the Udwadia-Kalaba theory.The problem of increasing the time of establishing constraint relationship when the multi-DOF industrial robots complete complex task constraints is solved.With the SCARA robot as the research object,the simulation results show that the proposed method can provide a new idea for industrial robot system modeling with complex constraints.展开更多
Objective:To investigate the economic burden of patients with acute kidney injury(AKI)by analyzing the distribution of hospitalization expenses and its influencing factors in the Affiliated Hospital of Hebei Universit...Objective:To investigate the economic burden of patients with acute kidney injury(AKI)by analyzing the distribution of hospitalization expenses and its influencing factors in the Affiliated Hospital of Hebei University.Methods:The hospitalization information of patients with AKI from January 2020 to January 2023 was collected and sorted through the hospital charging system and the factors affecting the total hospitalization cost were analyzed by multiple linear regression.Results:Univariate analysis showed that age,occupation,marriage,length of hospitalization,recovery of renal function,and stage of AKI had significant effects on hospitalization cost(P<0.05).The result of the multiple linear regression analysis model showed that age(t=4.11,P<0.0001),length of hospitalization(t=16.10,P<0.0001),recovery of renal function(t=3.26,P<0.0001),AKI stage(t=5.23,P=0.002)are factors affecting the economic burden of patients with AKI.Conclusion:AKI patients should be managed according to age stratification to effectively control the progression of the disease and improve the quality of the medical services provided.This will reduce the economic burden of patients.展开更多
Various characteristics play very important role in the process of students' second language acquisition and language development,including age,gender,personality,cognitive ability,motivation,learning strategies a...Various characteristics play very important role in the process of students' second language acquisition and language development,including age,gender,personality,cognitive ability,motivation,learning strategies and so on.Among all these factors mentioned,age factor received much attention in second language research.In this essay,two opposing views on age factor are discussed.In the last part,on the basis of the theory,some strategies on the real classroom teaching are provided after the discussion.展开更多
<p align="justify"> <span style="font-family:Verdana;"></span>The results were analyzed by unconditional logistic regression. The analysis results showed that the positions entere...<p align="justify"> <span style="font-family:Verdana;"></span>The results were analyzed by unconditional logistic regression. The analysis results showed that the positions entered into the regression model (OR = 2.339);the expected retirement age (OR = 3.280);and delayed retirement can better solve the pension problem (OR = 0.553). Retirement can relieve child financial pressure (OR = 0.217), emotional exhaustion (OR = 0.913) and social opportunities (OR = 1.132). The OR of job title, expected retirement age, and social opportunities is greater than 1, and the others are less than 1. <strong>Conclusion:</strong> The most expected retirement age for nurses is 50 to 55 years old, and they are more inclined to retire early. Factors affecting the willingness to postpone retirement include position and expected retirement age. Postponement of retirement can better solve pension problems. Postponement of retirement can alleviate child financial pressure, social opportunities and emotional exhaustion. </p>展开更多
Left-behind children comprise a special population inChinese rural areas. According to the 2007 China Census,the number ofleft-behind children aged≤14 years was estimated at 58 million which suggested that these chil...Left-behind children comprise a special population inChinese rural areas. According to the 2007 China Census,the number ofleft-behind children aged≤14 years was estimated at 58 million which suggested that these childrencon stituted a展开更多
Plantations of Rupprecht's larch(Larix principis-rupprechtii)have been widely established in the drylands of northwest and north China under traditional fastgrowing plantation management strategies.These strategie...Plantations of Rupprecht's larch(Larix principis-rupprechtii)have been widely established in the drylands of northwest and north China under traditional fastgrowing plantation management strategies.These strategies and the long-term logging ban have led to over-populated stands with lower structural and functional stability,less economic benefit and higher water consumption.To guide the sustainable management of larch plantations,field surveys and historical data compilation were undertaken in the Liupan Mountains of northwest China.The main influencing factors(stand structure and site condition)and their effects on mean tree height,mean DBH and timber volumes were determined based on up-boundary line analysis.Tree growth models coupling the effects of tree age,stand density,and elevation were established.Both height and DBH markedly increased initially and then slowly with tree age,decreased with stand density,and showed unimodal change with elevation.The coupled growth models accounted for72-78%of the variations in tree height,DBH and timber growth.Recommendations for future plantation management are:(1)prolong the rotation to at least 60 years to produce large-diameter,high-quality timber and maintain greater carbon stocks;(2)zone the target functions of stands by elevation;and,(3)reduce stand density for balanced supply of multiple ecosystem services.The growth models developed can predict growth response of larch plantations to density alteration under given ages and elevations,and assist the transformation from traditional management for maximum timber production to site-specific and multifunctional management with longer rotations and moderate tree density.展开更多
文摘In Bahawalpur,a cross-sectional study assessed depression prevalence across age and gender groups,involving 442 participants from diverse socioeconomic backgrounds and settings.Utilizing the PHQ9 questionnaire,84%were found to meet depression levels.The findings revealed a higher incidence in females(88%)than males(79%),with the greatest disparity among young adults,particularly young women,due to factors like academic pressure and financial stress.School children had the lowest depression rates(68%),possibly due to better immunity.Elderly individuals exhibited more severe depression,likely related to aging and domestic challenges.The study’s findings highlight a significant variation in depression severity across different demographic groups,with an overall higher incidence in women.The research underscores the necessity for targeted mental health resources and interventions tailored to the specific needs of each demographic group.It also points to the importance of addressing academic and socioeconomic stressors to mitigate depression,particularly among young women.While the study provides valuable insights,it relies on self-reported data,which may introduce bias.Therefore,future research should include clinical assessments to validate these findings and ensure a more accurate representation of depression within the community.
基金supported by the National Key R&D Program of China(No.2018YFB1501901)the National Natural Science Foundation of China(Nos.51909114,U1806227 and U1906231)the Guangxi Key Laboratory of Marine Environmental Science,Guangxi Academy of Sciences(No.GXKLHY21-04).
文摘Field and laboratory observations indicate that the variation of drag coefficient with wind speed at high winds is different from that under low-to-moderate winds.By taking the effects of wave development and sea spray into account,a new parameterization of drag coefficient applicable from low to extreme winds is proposed.It is shown that,under low-to-moderate wind conditions so that the sea spray effects could be neglected,the nondimensional aerodynamic roughness first increases and then decreases with the increasing wave age;whereas under high wind conditions,the drag coefficient decreases with the increasing wind speed due to the modification of the logarithmic wind profile by the effect of sea spray droplets produced by bursting bubbles or wind tearing breaking wave crests.The drag coefficients and sea surface aerodynamic roughnesses reach their maximum values vary under different wave developments.Correspondingly,the reduction of drag coefficient under high winds reduces the increasing rate of friction velocity with increasing wind speed.
文摘This article lists all possible conversion equations of influence coefficients(ICs)with different formats when some of these are known to handle two-plane balancing tasks with no or less trial weight runs.There are two approaches for two-plane balancing.One can treat it as a multi-plane balance problem involving a 2×2 matrix of complex ICs where two direct ICs along with two cross-effect ICs are generated so that correction weights at one or two balance planes can be determined.One can also apply a static pare(in-phase)and/or couple pair(180 degrees out-of-phase)weights for balancing.The latter approach has been used quite often in the field,especially on steam turbine and generator rotors.Dependent on vibration mode shapes and combinations as well as balance plane accessibility,sometimes applying static or couple pair weights can be a wise choice;other times weights at one or two end planes are needed.There are totally 4 possible sets of IC data due to weights at plane 1,plane 2,static pair,and couple pair.IC data would typically be obtained by applying trial weights followed by trial weight runs.It is found,however,that all these IC data can be converted easily without trial weight runs once any two of 4 sets are known.The above findings and conversion equations have been obtained analytically and verified by experimental results.Real cases are given to demonstratetheirapplications.
基金supported by National Hi-tech Research and Development Program of China (863 Program, Grant No. 2008 AA04Z114)
文摘Measurement error of unbalance's vibration response plays a crucial role in calibration and on-line updating of influence coefficient(IC). Focusing on the two problems that the moment estimator of data used in calibration process cannot fulfill the accuracy requirement under small sample and the disturbance of measurement error cannot be effectively suppressed in updating process, an IC calibration and on-line updating method based on hierarchical Bayesian method for automatic dynamic balancing machine was proposed. During calibration process, for the repeatedly-measured data obtained from experiments with different trial weights, according to the fact that measurement error of each sensor had the same statistical characteristics, the joint posterior distribution model for the true values of the vibration response under all trial weights and measurement error was established. During the updating process, information obtained from calibration was regarded as prior information, which was utilized to update the posterior distribution of IC combined with the real-time reference information to implement online updating. Moreover, Gibbs sampling method of Markov Chain Monte Carlo(MCMC) was adopted to obtain the maximum posterior estimation of parameters to be estimated. On the independent developed dynamic balancing testbed, prediction was carried out for multiple groups of data through the proposed method and the traditional method respectively, the result indicated that estimator of influence coefficient obtained through the proposed method had higher accuracy; the proposed updating method more effectively guaranteed the measurement accuracy during the whole producing process, and meantime more reasonably compromised between the sensitivity of IC change and suppression of randomness of vibration response.
文摘In order to develop a general calculating rotor’s torsional stiffness based on stiffness influence coefficient for different rotor assembling, the calculation method of the torsional stiffness influence coefficient of equal thickness disc is researched in this paper at first. Then the torsional stiffness influence coefficient λ of equal thickness disc is fit to a binary curved face and a calculation equation is obtained based on a large quantity of calculating data, which lays the foundation for research on a general calculating method of rotor torsional stiffness. Thirdly a simplified calculation method for equivalent stiffness diameter of stepped equal thickness disc and cone disc in the steam turbine generators is suggested. Finally a general calculating program for calculating rotor’s torsional vibration features is developed, and the torsional vibration features of a verity of steam turbine rotors are calculated for verification. The calculating results show that stiffness influence coefficient λ of equal-thickness disc depends on parameters of B and H, as well as the stiffness influence coefficient λ;and discs with complex structure can be simplified to equal-thickness discs with little error by using the method suggested in this paper;error can be controlled within 1% when equivalent diameter of stiffness is calculated by this method.
文摘In this paper, we study local influence analysis for Zhang's generalized correlation coefficients and Hotelling's generalized correlation coefficient by using approach. of local influence analysis suggested by Shi (1991), i.e., generalized influence function (GIF) and generalized Cook distance (GCD). An example is given to illustrate our results.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51175422)
文摘In order to execute geometric analysis for planar deployable mechanism of scissors unit,the dynamic analysis model of scissor planar deployable structure is created based on the Cartesian coordinate system,the influence coefficient is acquired by means of the coordinate transformation,combining the D 'Alembert 's principle with Dynamic-Static method,the dynamic characteristic analysis is completed finally. Moreover,specific calculating examples are adopted to verify the effectiveness of proposed method,and the result shows that the movement of each component of scissors unit mechanism is more smooth during initial deployment stage,however,when the configuration angle θ of unit mechanism is approaching π,some comparative large variations would appear on movement parameters and hinge constraint force.
文摘Based on the model structure of the influence coefficient method analyzed in depth by matrix theory ,it is explained the reason why the unreasonable and instable correction masses with bigger MSE are obtained by LS influence coefficient method when there are correlation planes in the dynamic balancing. It also presencd the new ridge regression method for solving correction masses according to the Tikhonov regularization theory, and described the reason why the ridge regression can eliminate the disadvantage of the LS method. Applying this new method to dynamic balancing of gas turbine, it is found that this method is superior to the LS method when influence coefficient matrix is ill-conditioned,the minimal correction masses and residual vibration are obtained in the dynamic balancing of rotors.
基金Project(20050216007) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘According to the concept of virtual bending force,a rational explanation for SHOHET's model was presented. Considering the deformation characters of the work rolls in four-high mill,the deformation model of the work roll was regarded as a cantilever beam and new influence coefficients were deduced.The effect of the bending force was taken into account independently. Therefore,the contribution to work roll deflection caused by rolling load,rolling pressure between rolls and bending force can be got from the new formulas.To validate the accuracy of the formulas,the results obtained from the new formulas were compared with those from SHOHET's formulas.It is found that they highly coincide,which illustrates that the formulas are reliable.
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFA0301202the National Natural Science Foundation of China under Grant Nos 11474275,61674135 and 91536101+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDPB0603the China Postdoctoral Science Foundation under Grant No 2017M622400
文摘The influence of the pressure transmission medium(PTM)on the excitonic interband transitions in monolayer tungsten diselenide(WSe2)is investigated using photoluminescence(PL)spectra under hydrostatic pressure up to 5GPa.Three kinds of PTMs,condensed argon(Ar),1:1 n-pentane and isopentane mixture(PM),and4:1 methanol and ethanol mixture(MEM,a PTM with polarity),are used.It is found that when either Ar or PM is used as the PTM,the PL peak of exciton related to the direct K-K interband transition shows a pressure-induced blue-shift at a rate of 32±4 or 32±1 meV/GPa,while it turns to be 50±9meV/GPa when MEM is used as the PTM.The indirect A-K interband transition presents almost no shift with increasing pressure up to approximatel.y 5 GPa when Ar and PM are used as the PTM,while it shows a red-shift at the rate of-17±7meV/GPa by using MEM as the PTM.These results reveal that the optical interband transitions of monolayer WSe2 are very sensitive to the polarity of the PTM.The anomalous pressure coefficient obtained using the polar PTM of MEM is ascribed to the existence of hydrogen-like bonds between hydroxyl in MEM and Se atoms under hydrostatic pressure.
文摘Typical rotors such as those on steam turbine or generator are often supported by two bearings with two balance planes at both ends.Vibrations are monitored by a pair of proximity probes at each bearing.There are two approaches to reduce 1X vibration due to unbalance at both ends via balancing with influence coefficient method.The first approach is to treat it as a multiple-plane balancing problem involving 2x2 matrix of complex influence coefficients.The second approach is to treat it as two single-plane balance problems using static(in-phase)and couple(180 degree out-of-phase)components,respectively.Conversion equations of influence coefficients between these two approaches have been found previously by the author.The corresponding spreadsheets that convert influence coefficients between these two formats are presented in the current paper.The paper shows effectiveness of these conversion equations in dealing with real balancing problems in the field.A detailed balance case is presented to demonstrate how the conversion equations are used to reduce vibration effectively.
文摘The usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefficient (ADC) values and their variations with age is necessary when interpreting normal testicular anatomy and pathology. We evaluated 147 normal testes using DWI, including 71 testes from 53 men aged 20-39years (group 1), 67 testes from 42 men aged 40-69 years (group 2) and nine testes from six men older than 70years (group 3). DWI was performed along the axial plane, using a single shot, multislice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm-2. The mean and standard deviation of the ADC values of normal testicular parenchyma were calculated for each age group separately. Analysis of variance (ANOVA) followed by post hoc analysis (Dunnett T3) was used for statistical purposes. The ADC values (x 10-3 mm2s-1) of normal testicular tissue were different among age groups (group 1:1.08 ± 0.13; group 2:1.15 ±0.15 and group 3:1.31± 0.22). ANOVA revealed differences in mean ADC among age groups (F= 11.391, P〈 0.001). Post hoc analysis showed differences between groups 1 and 2 (P= 0.008) and between groups 1 and 3 (P= 0.043), but not between groups 2 and 3 (P= 0.197). Our findings suggest that ADC values of normal testicular tissue increase with advancing age.
文摘The steel slag (SS) permeable concrete was prepared by SS. The influences of the aggregate-cement rate, the aggregate particle size, the water-cement rate, the admixture dosage and other factors on the permeability coefficient of SS permeable concrete were analyzed. The law of influence was also investigated. The study serves as a technological reference for the construction and design of SS permeable concrete.
基金supported by the Fundamental Research Funds for the Central UniversitiesFoundation of Graduate Innovation Center in Nanjing University of Aeronautics and Astronautics (No.kfjj20150105)the National Natural Science Foundation of China (No. 51279074)
文摘The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The chloride diffusion coefficients of recycled aggregate concrete under compressive stresses were measured by the rapid chloride ion migration(RCM)method.The experimental results show that the chloride diffusion coefficients of recycled aggregate concrete(RAC)under different compressive stress ratios generally decrease with the increase of curing age.For RAC subjected to the same compressive stress ratios,the chloride diffusion coefficients approximately have power functions with curing ages and the relationship models are proposed.Moreover,the influence of curing age on chloride diffusion coefficient firstly decreases and then increases as the compressive stress ratio increases.
基金the Beijing Municipal Scienceand Technology Project (No.KM202111417006)the Academic Research Projects of Beijing Union University (Nos.ZK10202305 and ZK80202004)the Beijing Municipal Science and Technology Project (No.KM202111417005)。
文摘Due to the diversity of work requirements and environment,the number of degrees of freedom(DOFs)and the complexity of structure of industrial robots are constantly increasing.It is difficult to establish the accurate dynamical model of industrial robots,which greatly hinders the realization of a stable,fast and accurate trajectory tracking control.Therefore,the general expression of the constraint relation in the explicit dynamic equation of the multi-DOF industrial robot is derived on the basis of solving the Jacobian matrix and Hessian matrix by using the kinematic influence coefficients method.Moreover,an explicit dynamic equation with general constraint relation expression is established based on the Udwadia-Kalaba theory.The problem of increasing the time of establishing constraint relationship when the multi-DOF industrial robots complete complex task constraints is solved.With the SCARA robot as the research object,the simulation results show that the proposed method can provide a new idea for industrial robot system modeling with complex constraints.
文摘Objective:To investigate the economic burden of patients with acute kidney injury(AKI)by analyzing the distribution of hospitalization expenses and its influencing factors in the Affiliated Hospital of Hebei University.Methods:The hospitalization information of patients with AKI from January 2020 to January 2023 was collected and sorted through the hospital charging system and the factors affecting the total hospitalization cost were analyzed by multiple linear regression.Results:Univariate analysis showed that age,occupation,marriage,length of hospitalization,recovery of renal function,and stage of AKI had significant effects on hospitalization cost(P<0.05).The result of the multiple linear regression analysis model showed that age(t=4.11,P<0.0001),length of hospitalization(t=16.10,P<0.0001),recovery of renal function(t=3.26,P<0.0001),AKI stage(t=5.23,P=0.002)are factors affecting the economic burden of patients with AKI.Conclusion:AKI patients should be managed according to age stratification to effectively control the progression of the disease and improve the quality of the medical services provided.This will reduce the economic burden of patients.
文摘Various characteristics play very important role in the process of students' second language acquisition and language development,including age,gender,personality,cognitive ability,motivation,learning strategies and so on.Among all these factors mentioned,age factor received much attention in second language research.In this essay,two opposing views on age factor are discussed.In the last part,on the basis of the theory,some strategies on the real classroom teaching are provided after the discussion.
文摘<p align="justify"> <span style="font-family:Verdana;"></span>The results were analyzed by unconditional logistic regression. The analysis results showed that the positions entered into the regression model (OR = 2.339);the expected retirement age (OR = 3.280);and delayed retirement can better solve the pension problem (OR = 0.553). Retirement can relieve child financial pressure (OR = 0.217), emotional exhaustion (OR = 0.913) and social opportunities (OR = 1.132). The OR of job title, expected retirement age, and social opportunities is greater than 1, and the others are less than 1. <strong>Conclusion:</strong> The most expected retirement age for nurses is 50 to 55 years old, and they are more inclined to retire early. Factors affecting the willingness to postpone retirement include position and expected retirement age. Postponement of retirement can better solve pension problems. Postponement of retirement can alleviate child financial pressure, social opportunities and emotional exhaustion. </p>
基金supported by grants from the National Natural Science Foundation of China [81172680]
文摘Left-behind children comprise a special population inChinese rural areas. According to the 2007 China Census,the number ofleft-behind children aged≤14 years was estimated at 58 million which suggested that these childrencon stituted a
基金funded by the National Natural Science Foundation of China (U20A2085,U21A2005,41971038)the Central Public-Interest Scientifi c Institution Basal Research Fund of Chinese Academy of Forestry (CAFYBB2021ZW002,CAFYBB2020QB004)。
文摘Plantations of Rupprecht's larch(Larix principis-rupprechtii)have been widely established in the drylands of northwest and north China under traditional fastgrowing plantation management strategies.These strategies and the long-term logging ban have led to over-populated stands with lower structural and functional stability,less economic benefit and higher water consumption.To guide the sustainable management of larch plantations,field surveys and historical data compilation were undertaken in the Liupan Mountains of northwest China.The main influencing factors(stand structure and site condition)and their effects on mean tree height,mean DBH and timber volumes were determined based on up-boundary line analysis.Tree growth models coupling the effects of tree age,stand density,and elevation were established.Both height and DBH markedly increased initially and then slowly with tree age,decreased with stand density,and showed unimodal change with elevation.The coupled growth models accounted for72-78%of the variations in tree height,DBH and timber growth.Recommendations for future plantation management are:(1)prolong the rotation to at least 60 years to produce large-diameter,high-quality timber and maintain greater carbon stocks;(2)zone the target functions of stands by elevation;and,(3)reduce stand density for balanced supply of multiple ecosystem services.The growth models developed can predict growth response of larch plantations to density alteration under given ages and elevations,and assist the transformation from traditional management for maximum timber production to site-specific and multifunctional management with longer rotations and moderate tree density.