The case–cohort design has been widely used to reduce the cost of covariate measurements in large cohort studies.In this paper,we study the high-dimensional accelerated failure time(AFT)model under the case–cohort d...The case–cohort design has been widely used to reduce the cost of covariate measurements in large cohort studies.In this paper,we study the high-dimensional accelerated failure time(AFT)model under the case–cohort design.Based on?0-regularization and a newly defined weight function,we propose a weighted least squares procedure for variable selection and parameter estimation.Computationally,we develop a support detection and root finding(SDAR)algorithm,where the support is first determined based on the primal and dual information,then the estimator is obtained by solving the weighted least squares problem restricted to the estimated support.We show the proposed algorithm is essentially one Newton-type algorithm,thus it is more efficient and stable compared with other regularized methods.Theoretically,we establish a sharp error bound for the solution sequences generated from the proposed method.Furthermore,we propose an adaptive version of the proposed SDAR algorithm,which determines the support size of the estimated coefficient in a data-driven manner.Extensive simulation studies demonstrate the superior performance of the proposed procedures,especially for the computational efficiency.As an illustration,we apply the proposed method to a malignant breast tumor gene expression data.展开更多
The optimum design of equivalent accelerated life testing plan based on proportional hazards-proportional odds model using D-optimality is presented. The defined equivalent test plan is the test plan that has the same...The optimum design of equivalent accelerated life testing plan based on proportional hazards-proportional odds model using D-optimality is presented. The defined equivalent test plan is the test plan that has the same value of the determinant of Fisher information matrix. The equivalent test plan of step stress accelerated life testing （SSALT） to a baseline optimum constant stress accelerated life testing （CSALT） plan is obtained by adjusting the censoring time of SSALT and solving the optimization problem for each case to achieve the same value of the determinant of Fisher information matrix as in the baseline optimum CSALT plan. Numer- ical examples are given finally which demonstrate the equivalent SSALT plan to the baseline optimum CSALT plan reduces almost half of the test time while achieving approximately the same estimation errors of model parameters.展开更多
In this paper, the generalized Oldroyd-B with fractional calculus approach is used. An exact solution in terms of Fox-H function for flow past an accelerated horizontal plate in a rotating fluid is obtained by using d...In this paper, the generalized Oldroyd-B with fractional calculus approach is used. An exact solution in terms of Fox-H function for flow past an accelerated horizontal plate in a rotating fluid is obtained by using discrete Laplace transform method. A comparison among the influence of various parameters in the Oldroyd-B model and the angular velocity of the fluid on the velocity profiles is made through numerical method in graphic form.展开更多
Microarc oxidation（MAO） has become a promising technique for the surface modification of implants. Therefore, the aims of this study were to further quantitatively and qualitatively evaluate the osteointegration abi...Microarc oxidation（MAO） has become a promising technique for the surface modification of implants. Therefore, the aims of this study were to further quantitatively and qualitatively evaluate the osteointegration abilities of MAO-treated and smooth surface（SF） implants in vivo and to investigate the areas in which the superiority of MAO-treated implants are displayed. In a rabbit model,a comprehensive histomorphological, osteogenic, mineralizational, and integrative assessment was performed using light microscopy, fluorescence microscopy, confocal laser scanning microscopy, and radiographic analyses. Compared with the SF groups, the MAO-treated groups exhibited more active contact osteogenesis, as well as distant osteogenesis, under fluorescence examination, the mineral apposition rate was found to be greater for all of the MAO-treated implants, and the osteointegration index（OI） value was greater in the MAO-treated groups at different times. In conclusion, the calcium-rich amorphous layer created by MAO provided a better environment for osteointegration, with more active contact osteogenesis, a more rapid mineral apposition rate and greater OI values.展开更多
Objective:To compare the prognostic factors of mortality among melioidosis patients between lognormal accelerated failure time(AFT),Cox proportional hazards(PH),and Cox PH with time-varying coefficient(TVC)models.Meth...Objective:To compare the prognostic factors of mortality among melioidosis patients between lognormal accelerated failure time(AFT),Cox proportional hazards(PH),and Cox PH with time-varying coefficient(TVC)models.Methods:A retrospective study was conducted from 2014 to 2019 among 453 patients who were admitted to Hospital Sultanah Bahiyah,Kedah and Hospital Tuanku Fauziah,Perlis in Northern Malaysia due to confirmed-cultured melioidosis.The prognostic factors of mortality from melioidosis were obtained from AFT survival analysis,and Cox’s models and the findings were compared by using the goodness of fit methods.The analyses were done by using Stata SE version 14.0.Results:A total of 242 patients(53.4%)survived.In this study,the median survival time of melioidosis patients was 30.0 days(95%CI 0.0-60.9).Six significant prognostic factors were identified in the Cox PH model and Cox PH-TVC model.In AFT survival analysis,a total of seven significant prognostic factors were identified.The results were found to be only a slight difference between the identified prognostic factors among the models.AFT survival showed better results compared to Cox's models,with the lowest Akaike information criteria and best fitted Cox-snell residuals.Conclusions:AFT survival analysis provides more reliable results and can be used as an alternative statistical analysis for determining the prognostic factors of mortality in melioidosis patients in certain situations.展开更多
In order to study the cross-linking density and aging constitutive relationship of HTPB coating during storage,the thermal accelerated aging tests at 0%,3%,6%and 9%prestrains were carried out.The crosslinking density ...In order to study the cross-linking density and aging constitutive relationship of HTPB coating during storage,the thermal accelerated aging tests at 0%,3%,6%and 9%prestrains were carried out.The crosslinking density of HTPB coating at different aging stages were tested using low-field^1 H NMR and the variation of cross-linking density was analyzed.The aging model of cross-linking density considering the chemical aging and the physical stretching factors was established.The uniaxial tensile tests were carried out on HTPB coating at different aging stages and the cross-linking density was introduced into Ogden hyperelastic constitutive model as a characterization parameter of correction coefficient.Combined with uniaxial tensile test results,a prestrain aging constitutive model of HTPB coating was established.The results show that the cross-linking density of HTPB coating increases rapidly at first and then slowly with the increase of thermal accelerated aging time without prestrain.Under prestrain conditions,the crosslinking density of HTPB coating decreases at the early stage,and increases rapidly at first and then slowly at the middle and late stages of thermal accelerated aging.The correlation coefficients of aging model of cross-linking density and aging constitutive model with test results are R>0.9500 and R>0.9900 respectively,which can be used to accurately describe the cross-linking density and aging constitutive relationship of HTPB coating under prestrain accelerated thermal aging conditions.展开更多
We report the results of protein folding （219M, C34, N36, 2KES, 2KHK） by the method of accelerated molecular dynamics （aMD） at room temperature with the implicit solvent model. Starting from the linear structures,...We report the results of protein folding （219M, C34, N36, 2KES, 2KHK） by the method of accelerated molecular dynamics （aMD） at room temperature with the implicit solvent model. Starting from the linear structures, these proteins successfully fold to the native structure in a lO0-ns aMD simulation. In contrast, they are failed under the traditional MD simulation in the same simulation time. Then we find that the lowest root mean square deviations of helix structures from the native structures are 0.36 A, 0.63 A, 0.52 A, 1.1 A and 0.78 A. What is more, native contacts, cluster and free energy analyses show that the results of the aMD method are in accordance with the experiment very well. All analyses show that the aMD can accelerate the simulation process, thus we may apply it to the field of computer aided drug designs.展开更多
Survival of HIV/AIDS patients is crucially dependent on comprehensive and targeted medical interventions such as supply of antiretroviral therapy and monitoring disease progression with CD4 T-cell counts. Statistical ...Survival of HIV/AIDS patients is crucially dependent on comprehensive and targeted medical interventions such as supply of antiretroviral therapy and monitoring disease progression with CD4 T-cell counts. Statistical modelling approaches are helpful towards this goal. This study aims at developing Bayesian joint models with assumed generalized error distribution (GED) for the longitudinal CD4 data and two accelerated failure time distributions, Lognormal and loglogistic, for the survival time of HIV/AIDS patients. Data are obtained from patients under antiretroviral therapy follow-up at Shashemene referral hospital during January 2006-January 2012 and at Bale Robe general hospital during January 2008-March 2015. The Bayesian joint models are defined through latent variables and association parameters and with specified non-informative prior distributions for the model parameters. Simulations are conducted using Gibbs sampler algorithm implemented in the WinBUGS software. The results of the analyses of the two different data sets show that distributions of measurement errors of the longitudinal CD4 variable follow the generalized error distribution with fatter tails than the normal distribution. The Bayesian joint GED loglogistic models fit better to the data sets compared to the lognormal cases. Findings reveal that patients’ health can be improved over time. Compared to the males, female patients gain more CD4 counts. Survival time of a patient is negatively affected by TB infection. Moreover, increase in number of opportunistic infection implies decline of CD4 counts. Patients’ age negatively affects the disease marker with no effects on survival time. Improving weight may improve survival time of patients. Bayesian joint models with GED and AFT distributions are found to be useful in modelling the longitudinal and survival processes. Thus we recommend the generalized error distributions for measurement errors of the longitudinal data under the Bayesian joint modelling. Further studies may investigate the models with various types of shared random effects and more covariates with predictions.展开更多
Alcohol oxidation is a widely used green chemical reaction.The reaction process produces flammable and explosive hydrogen,so the design of the reactor must meet stringent safety requirements.Based on the limited exper...Alcohol oxidation is a widely used green chemical reaction.The reaction process produces flammable and explosive hydrogen,so the design of the reactor must meet stringent safety requirements.Based on the limited experimental data,utilizing the traditional numerical method of computational fluid dynamics(CFD)to simulate the gas-liquid two-phase flow reactor can mitigate the risk of danger under varying working conditions.However,the calculation process is highly time-consuming.Therefore,by integrating process simulation,computational fluid dynamics,and deep learning technologies,an intelligent hybrid chemical model based on machine learning was proposed to expedite CFD calculations,enhance the prediction of flow fields,conversion rates,and concentrations inside the reactor,and offer insights for designing and optimizing the reactor for the alcohol oxidation system.The results show that the hybrid model based on the long and short-term memory neural network achieves 99.8%accuracy in conversion rate prediction and 99.9%accuracy in product concentration prediction.Through validation,the hybrid model is accelerated by about 360 times compared with instrumental analysis in conversion rate prediction and about 45 times compared with CFD calculation in concentration distribution prediction.This hybrid model can quickly predict the conversion rate and product concentration distribution in the gas-liquid two-phase flow reactor and provide a model reference for fast prediction and accurate control in the actual chemical production process.展开更多
We present a new nonparametric predictive inference(NPI)method using a power-normal model for accelerated life testing(ALT).Combined with the accelerating link function and imprecise probability theory,the proposed me...We present a new nonparametric predictive inference(NPI)method using a power-normal model for accelerated life testing(ALT).Combined with the accelerating link function and imprecise probability theory,the proposed method is a feasible way to predict the life of the product using ALT failure data.To validate the method,we run a series of simulations and conduct accelerated life tests with real products.The NPI lower and upper survival functions show the robustness of our method for life prediction.This is a continuous research,and some progresses have been made by updating the link function between different stress levels.We also explain how to renew and apply our model.Moreover,discussions have been made about the performance.展开更多
The main objective of accelerated life tests in this setting is the recovery of the distribution of the random variable representing lifetime which is difficult to observe at a certain level of a given stress factor. ...The main objective of accelerated life tests in this setting is the recovery of the distribution of the random variable representing lifetime which is difficult to observe at a certain level of a given stress factor. A general model for accelerated life test is proposed that utilizes the inverse problem approach, that is, the variable is observe at different level/s and the transfer function is used to recover the elusive random variable (life time). The problem then is reduced to finding the transfer function. We derive some properties of the proposed general model. The Lognormal distribution and the Arrhenius model for lifetime are used as examples. Its relationship with the Cox proportional hazards model is also discussed.展开更多
Dependent competing risks model is a practical model in the analysis of lifetime and failure modes.The dependence can be captured using a statistical tool to explore the re-lationship among failure causes.In this pape...Dependent competing risks model is a practical model in the analysis of lifetime and failure modes.The dependence can be captured using a statistical tool to explore the re-lationship among failure causes.In this paper,an Archimedean copula is chosen to describe the dependence in a constant-stress accelerated life test.We study the Archimedean copula based dependent competing risks model using parametric and nonparametric methods.The parametric likelihood inference is presented by deriving the general expression of likelihood function based on assumed survival Archimedean copula associated with the model parameter estimation.Combining the nonparametric estimation with progressive censoring and the non-parametric copula estimation,we introduce a nonparametric reliability estimation method given competing risks data.A simulation study and a real data analysis are conducted to show the performance of the estimation methods.展开更多
In this paper, we have studied the nonparameter accelerated failure time (AFT) additive regression model, whose covariates have a nonparametric effect on high-dimensional censored data. We give the asymptotic property...In this paper, we have studied the nonparameter accelerated failure time (AFT) additive regression model, whose covariates have a nonparametric effect on high-dimensional censored data. We give the asymptotic property of the penalty estimator based on GMCP in the nonparameter AFT model.展开更多
Modern highly reliable products may have two or more quality characteristics(QCs) because of their complex structures and abundant functions. Relations between the QCs should be considered when assessing the reliabili...Modern highly reliable products may have two or more quality characteristics(QCs) because of their complex structures and abundant functions. Relations between the QCs should be considered when assessing the reliability of these products. This paper conducts a Bayesian analysis for a bivariate constant-stress accelerated degradation model based on the inverse Gaussian(IG) process. We assume that the product considered has two QCs and each of the QCs is governed by an IG process. The relationship between the QCs is described by a Frank copula function. We also assume that the stress on the products affects not only the parameters of the IG processes, but also the parameter of the Frank copula function. The Bayesian MCMC method is developed to calculate the maximum likelihood estimators(MLE) of the model parameters. The reliability function and the mean-time-to-failure(MTTF) are estimated through the calculation of the posterior samples. Finally, a simulation example is presented to illustrate the proposed bivariate constant-stress accelerated degradation model.展开更多
Aim Using animals as object of experiment to acquire various patterns of low cerebral blood pressure and reduced blood capacity in cerebral tissues of astronauts due to the load of acceleration. Methods The isotope ...Aim Using animals as object of experiment to acquire various patterns of low cerebral blood pressure and reduced blood capacity in cerebral tissues of astronauts due to the load of acceleration. Methods The isotope tracking technique was applied to mark the blood and record the dynamic curves of cerebral blood flow changes under various accelerations, and the relevant mathematical model was set up using the method of system recognition. Also the method of factor analyzing was used to select two out of the data collected by eight sensors as two factors. Results One of the two factors reflects the various patterns in the astronaut's upper body, the other for the lower body. Parameters of rise time, delay time and steady value reflect the results under different acceleration. Conclusion Whether for the upper body or the lower body, blood flow changes can be considered as a second order system model. This method provides a new technique and method of doing research on astronaut's endurance of acceleration and selecting astronauts.展开更多
A current statistical model for maneuvering acceleration using an adaptive extended Kalman filter（CS-MAEKF） algorithm is proposed to solve problems existing in conventional extended Kalman filters such as large esti...A current statistical model for maneuvering acceleration using an adaptive extended Kalman filter（CS-MAEKF） algorithm is proposed to solve problems existing in conventional extended Kalman filters such as large estimation error and divergent tendencies in the presence of continuous maneuvering acceleration. A membership function is introduced in this algorithm to adaptively modify the upper and lower limits of loitering vehicles＇ maneuvering acceleration and for realtime adjustment of maneuvering acceleration variance. This allows the algorithm to have superior static and dynamic performance for loitering vehicles undergoing different maneuvers. Digital simulations and dynamic flight testing show that the yaw angle accuracy of the algorithm is 30% better than conventional algorithms, and pitch and roll angle calculation precision is improved by 60%.The mean square deviation of heading and attitude angle error during dynamic flight is less than3.05°. Experimental results show that CS-MAEKF meets the application requirements of miniature loitering vehicles.展开更多
To satisfy the need of high speed NC (numerical control) machining, an acceleration and deceleration (acc/dec) control model is proposed, and the speed curve is also constructed by the cubic polynomial. The proposed c...To satisfy the need of high speed NC (numerical control) machining, an acceleration and deceleration (acc/dec) control model is proposed, and the speed curve is also constructed by the cubic polynomial. The proposed control model provides continuity of acceleration, which avoids the intense vibration in high speed NC machining. Based on the discrete characteristic of the data sampling interpolation, the acc/dec control discrete mathematical model is also set up and the discrete expression of the theoretical deceleration length is obtained furthermore. Aiming at the question of hardly predetermining the deceleration point in acc/dec control before interpolation, the adaptive acc/dec control algorithm is deduced from the expressions of the theoretical deceleration length. The experimental result proves that the acc/dec control model has the characteristic of easy implementation, stable movement and low impact. The model has been applied in multi-axes high speed micro fabrication machining successfully.展开更多
With the theory of subcritical crack growth, we can deduce the fundamental equation of regional seismicity acceleration model. Applying this model to intraplate earthquake regions, we select three earthquake subplates...With the theory of subcritical crack growth, we can deduce the fundamental equation of regional seismicity acceleration model. Applying this model to intraplate earthquake regions, we select three earthquake subplates: North China Subplate, Chuan Dian Block and Xinjiang Subplate, and divide the three subplates into seven researched regions by the difference of seismicity and tectonic conditions. With the modified equation given by Sornette and Sammis (1995), we analysis the seismicity of each region. To those strong earthquakes already occurred in these region, the model can give close fitting of magnitude and occurrence time, and the result in this article indicates that the seismicity acceleration model can also be used for describing the seismicity of intraplate. In the article, we give the magnitude and occurrence time of possible strong earthquakes in Shanxi, Ordos, Bole Tuokexun, Ayinke Wuqia earthquake regions. In the same subplate or block, the earthquake periods for each earthquake region are similar in time interval. The constant α in model can be used to describe the intensity of regional seismicity, and for the Chinese Mainland, α is 0.4 generally. To the seismicity in Taiwan and other regions with complex tectonic conditions, the model does not fit well at present.展开更多
The performance degradation rates of the missile tank are generally time-varying functions uneasily evaluated by general classical evaluation methods. This paper develops a segmented nonlinear accelerated degradation ...The performance degradation rates of the missile tank are generally time-varying functions uneasily evaluated by general classical evaluation methods. This paper develops a segmented nonlinear accelerated degradation model （SNADM） based on the equivalent method of accumulative damage theory, which tackles the problem that product life is difficult to be determined with degradation rate being a function of the variable of time. A segmented expression of the function of population accumulative degradation is derived. And combined with nonlinear function, an accelerated degradation function, i.e., SNADM is obtained. The parameters of the SNADM are identified by numerical iteration, and the statistical function of degradation track is extrapolated. The reliability function is determined through the type of random process of the degradation distribution. Then an evaluation of product storage life is undertaken by combining the statistical function of degradation track, reliability function and threshold. An example of a missile tank undergoes a step-down stress accelerated degradation test （SDSADT）, in which the results with the SNADM and the classical method are evaluated and compared. The technology introduced is validated with the resultant coincidence of both evaluated and field storage lives.展开更多
The correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials was investigated according to the variation of the functional group of exposure models aged. Environment aging ...The correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials was investigated according to the variation of the functional group of exposure models aged. Environment aging intensities at different zones （ Wuhan and Lasa with the same latitude ） and the influences of indoor accelerating factors including water and ultraviolet on weathering performant.e of high polymer materials were also studied by comparing different indoor accelerated corrosion testing results. The experimental results show that ： by testing variations of carbonyl exponent of polythene （ which represented the degradation behavior of high polymer materials due to ultraviolet oxidation of douIole bond） and ultraviolet absorbance of polycarbonate （which represented the degradation behavior of high polymer materials due to abevacuation of branched chain ）, the degradation behavior of high polymer materials could be studied. Carbonyl exponent of polythene exposed in Wuhan and Lasa for 1 year was equal to that exposed in indoor cycle ultraviolet for 128 h anti 170 It, respectively, the ultraviolet absorbance of polycarbonate exposed in Wuhan for 1 year was equal to that exposed in indoor cycle ultraviolet for 240 h. The ratio of environment aging intensity of Lasa to Wuhan was around 1.2. With the prolongation of cycle accelerated ultraviolet exposure time, the variations of carbonyl exponent of polythene and the ultraviolet absorbance of polycarbonate were in the same shape of first order exponential decay curiae. Accompanied with ultraviolet, the effect of water condensated on the sample on weathering performance of polythene was more .significant than that of polycarbonate.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.12371274,12271459)National Social Science Foundation of China(Grant No.24CTJ036)+1 种基金Natural Science Foundation of Hubei Province(Grant No.2021CFB502)the Fundamental Research Funds for the Central Universities,Zhongnan University of Economics and Law(Grant No.2722024BY024)。
文摘The case–cohort design has been widely used to reduce the cost of covariate measurements in large cohort studies.In this paper,we study the high-dimensional accelerated failure time(AFT)model under the case–cohort design.Based on?0-regularization and a newly defined weight function,we propose a weighted least squares procedure for variable selection and parameter estimation.Computationally,we develop a support detection and root finding(SDAR)algorithm,where the support is first determined based on the primal and dual information,then the estimator is obtained by solving the weighted least squares problem restricted to the estimated support.We show the proposed algorithm is essentially one Newton-type algorithm,thus it is more efficient and stable compared with other regularized methods.Theoretically,we establish a sharp error bound for the solution sequences generated from the proposed method.Furthermore,we propose an adaptive version of the proposed SDAR algorithm,which determines the support size of the estimated coefficient in a data-driven manner.Extensive simulation studies demonstrate the superior performance of the proposed procedures,especially for the computational efficiency.As an illustration,we apply the proposed method to a malignant breast tumor gene expression data.
文摘The optimum design of equivalent accelerated life testing plan based on proportional hazards-proportional odds model using D-optimality is presented. The defined equivalent test plan is the test plan that has the same value of the determinant of Fisher information matrix. The equivalent test plan of step stress accelerated life testing （SSALT） to a baseline optimum constant stress accelerated life testing （CSALT） plan is obtained by adjusting the censoring time of SSALT and solving the optimization problem for each case to achieve the same value of the determinant of Fisher information matrix as in the baseline optimum CSALT plan. Numer- ical examples are given finally which demonstrate the equivalent SSALT plan to the baseline optimum CSALT plan reduces almost half of the test time while achieving approximately the same estimation errors of model parameters.
基金supported by The project supported by the Natural Science Foundation of Shandong Province of China (Y2007A06)
文摘In this paper, the generalized Oldroyd-B with fractional calculus approach is used. An exact solution in terms of Fox-H function for flow past an accelerated horizontal plate in a rotating fluid is obtained by using discrete Laplace transform method. A comparison among the influence of various parameters in the Oldroyd-B model and the angular velocity of the fluid on the velocity profiles is made through numerical method in graphic form.
文摘Microarc oxidation（MAO） has become a promising technique for the surface modification of implants. Therefore, the aims of this study were to further quantitatively and qualitatively evaluate the osteointegration abilities of MAO-treated and smooth surface（SF） implants in vivo and to investigate the areas in which the superiority of MAO-treated implants are displayed. In a rabbit model,a comprehensive histomorphological, osteogenic, mineralizational, and integrative assessment was performed using light microscopy, fluorescence microscopy, confocal laser scanning microscopy, and radiographic analyses. Compared with the SF groups, the MAO-treated groups exhibited more active contact osteogenesis, as well as distant osteogenesis, under fluorescence examination, the mineral apposition rate was found to be greater for all of the MAO-treated implants, and the osteointegration index（OI） value was greater in the MAO-treated groups at different times. In conclusion, the calcium-rich amorphous layer created by MAO provided a better environment for osteointegration, with more active contact osteogenesis, a more rapid mineral apposition rate and greater OI values.
文摘Objective:To compare the prognostic factors of mortality among melioidosis patients between lognormal accelerated failure time(AFT),Cox proportional hazards(PH),and Cox PH with time-varying coefficient(TVC)models.Methods:A retrospective study was conducted from 2014 to 2019 among 453 patients who were admitted to Hospital Sultanah Bahiyah,Kedah and Hospital Tuanku Fauziah,Perlis in Northern Malaysia due to confirmed-cultured melioidosis.The prognostic factors of mortality from melioidosis were obtained from AFT survival analysis,and Cox’s models and the findings were compared by using the goodness of fit methods.The analyses were done by using Stata SE version 14.0.Results:A total of 242 patients(53.4%)survived.In this study,the median survival time of melioidosis patients was 30.0 days(95%CI 0.0-60.9).Six significant prognostic factors were identified in the Cox PH model and Cox PH-TVC model.In AFT survival analysis,a total of seven significant prognostic factors were identified.The results were found to be only a slight difference between the identified prognostic factors among the models.AFT survival showed better results compared to Cox's models,with the lowest Akaike information criteria and best fitted Cox-snell residuals.Conclusions:AFT survival analysis provides more reliable results and can be used as an alternative statistical analysis for determining the prognostic factors of mortality in melioidosis patients in certain situations.
基金supported by the National Defense Pre-Research Foundation of China[grant number ZS2015070132A12002]。
文摘In order to study the cross-linking density and aging constitutive relationship of HTPB coating during storage,the thermal accelerated aging tests at 0%,3%,6%and 9%prestrains were carried out.The crosslinking density of HTPB coating at different aging stages were tested using low-field^1 H NMR and the variation of cross-linking density was analyzed.The aging model of cross-linking density considering the chemical aging and the physical stretching factors was established.The uniaxial tensile tests were carried out on HTPB coating at different aging stages and the cross-linking density was introduced into Ogden hyperelastic constitutive model as a characterization parameter of correction coefficient.Combined with uniaxial tensile test results,a prestrain aging constitutive model of HTPB coating was established.The results show that the cross-linking density of HTPB coating increases rapidly at first and then slowly with the increase of thermal accelerated aging time without prestrain.Under prestrain conditions,the crosslinking density of HTPB coating decreases at the early stage,and increases rapidly at first and then slowly at the middle and late stages of thermal accelerated aging.The correlation coefficients of aging model of cross-linking density and aging constitutive model with test results are R>0.9500 and R>0.9900 respectively,which can be used to accurately describe the cross-linking density and aging constitutive relationship of HTPB coating under prestrain accelerated thermal aging conditions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 31200545,11274206 and 11574184
文摘We report the results of protein folding （219M, C34, N36, 2KES, 2KHK） by the method of accelerated molecular dynamics （aMD） at room temperature with the implicit solvent model. Starting from the linear structures, these proteins successfully fold to the native structure in a lO0-ns aMD simulation. In contrast, they are failed under the traditional MD simulation in the same simulation time. Then we find that the lowest root mean square deviations of helix structures from the native structures are 0.36 A, 0.63 A, 0.52 A, 1.1 A and 0.78 A. What is more, native contacts, cluster and free energy analyses show that the results of the aMD method are in accordance with the experiment very well. All analyses show that the aMD can accelerate the simulation process, thus we may apply it to the field of computer aided drug designs.
文摘Survival of HIV/AIDS patients is crucially dependent on comprehensive and targeted medical interventions such as supply of antiretroviral therapy and monitoring disease progression with CD4 T-cell counts. Statistical modelling approaches are helpful towards this goal. This study aims at developing Bayesian joint models with assumed generalized error distribution (GED) for the longitudinal CD4 data and two accelerated failure time distributions, Lognormal and loglogistic, for the survival time of HIV/AIDS patients. Data are obtained from patients under antiretroviral therapy follow-up at Shashemene referral hospital during January 2006-January 2012 and at Bale Robe general hospital during January 2008-March 2015. The Bayesian joint models are defined through latent variables and association parameters and with specified non-informative prior distributions for the model parameters. Simulations are conducted using Gibbs sampler algorithm implemented in the WinBUGS software. The results of the analyses of the two different data sets show that distributions of measurement errors of the longitudinal CD4 variable follow the generalized error distribution with fatter tails than the normal distribution. The Bayesian joint GED loglogistic models fit better to the data sets compared to the lognormal cases. Findings reveal that patients’ health can be improved over time. Compared to the males, female patients gain more CD4 counts. Survival time of a patient is negatively affected by TB infection. Moreover, increase in number of opportunistic infection implies decline of CD4 counts. Patients’ age negatively affects the disease marker with no effects on survival time. Improving weight may improve survival time of patients. Bayesian joint models with GED and AFT distributions are found to be useful in modelling the longitudinal and survival processes. Thus we recommend the generalized error distributions for measurement errors of the longitudinal data under the Bayesian joint modelling. Further studies may investigate the models with various types of shared random effects and more covariates with predictions.
基金the support from the National Natural Science Foundation of China(22478429)the Special Project Fund of Taishan-Scholars(tsqn202408101)+3 种基金the Natural Science Foundation of Shandong Province(ZR2023YQ009)CNPC Innovation Found(2024DQ02-0504)Fundamental Research Funds for the Central Universities,Ocean University of China(202364004)the State Key Laboratory of Heavy Oil Processing(SKLHOP202403003)。
文摘Alcohol oxidation is a widely used green chemical reaction.The reaction process produces flammable and explosive hydrogen,so the design of the reactor must meet stringent safety requirements.Based on the limited experimental data,utilizing the traditional numerical method of computational fluid dynamics(CFD)to simulate the gas-liquid two-phase flow reactor can mitigate the risk of danger under varying working conditions.However,the calculation process is highly time-consuming.Therefore,by integrating process simulation,computational fluid dynamics,and deep learning technologies,an intelligent hybrid chemical model based on machine learning was proposed to expedite CFD calculations,enhance the prediction of flow fields,conversion rates,and concentrations inside the reactor,and offer insights for designing and optimizing the reactor for the alcohol oxidation system.The results show that the hybrid model based on the long and short-term memory neural network achieves 99.8%accuracy in conversion rate prediction and 99.9%accuracy in product concentration prediction.Through validation,the hybrid model is accelerated by about 360 times compared with instrumental analysis in conversion rate prediction and about 45 times compared with CFD calculation in concentration distribution prediction.This hybrid model can quickly predict the conversion rate and product concentration distribution in the gas-liquid two-phase flow reactor and provide a model reference for fast prediction and accurate control in the actual chemical production process.
基金the National Natural Science Foundation of China(No.11272082)the China Scholarship Council State Scholarship Fund(No.201506070017)
文摘We present a new nonparametric predictive inference(NPI)method using a power-normal model for accelerated life testing(ALT).Combined with the accelerating link function and imprecise probability theory,the proposed method is a feasible way to predict the life of the product using ALT failure data.To validate the method,we run a series of simulations and conduct accelerated life tests with real products.The NPI lower and upper survival functions show the robustness of our method for life prediction.This is a continuous research,and some progresses have been made by updating the link function between different stress levels.We also explain how to renew and apply our model.Moreover,discussions have been made about the performance.
文摘The main objective of accelerated life tests in this setting is the recovery of the distribution of the random variable representing lifetime which is difficult to observe at a certain level of a given stress factor. A general model for accelerated life test is proposed that utilizes the inverse problem approach, that is, the variable is observe at different level/s and the transfer function is used to recover the elusive random variable (life time). The problem then is reduced to finding the transfer function. We derive some properties of the proposed general model. The Lognormal distribution and the Arrhenius model for lifetime are used as examples. Its relationship with the Cox proportional hazards model is also discussed.
基金Supported by the National Natural Science Foundation of China(12101476,12061091,11901134)the Fundamental Research Funds for the Central Universities(ZYTS23054,QTZX22054)+1 种基金the Yunnan Funda-mental Research Projects(202101AT070103)the Natural Science Basic Research Program of Shaanxi Province(2020JQ-285).
文摘Dependent competing risks model is a practical model in the analysis of lifetime and failure modes.The dependence can be captured using a statistical tool to explore the re-lationship among failure causes.In this paper,an Archimedean copula is chosen to describe the dependence in a constant-stress accelerated life test.We study the Archimedean copula based dependent competing risks model using parametric and nonparametric methods.The parametric likelihood inference is presented by deriving the general expression of likelihood function based on assumed survival Archimedean copula associated with the model parameter estimation.Combining the nonparametric estimation with progressive censoring and the non-parametric copula estimation,we introduce a nonparametric reliability estimation method given competing risks data.A simulation study and a real data analysis are conducted to show the performance of the estimation methods.
文摘In this paper, we have studied the nonparameter accelerated failure time (AFT) additive regression model, whose covariates have a nonparametric effect on high-dimensional censored data. We give the asymptotic property of the penalty estimator based on GMCP in the nonparameter AFT model.
基金the National Natural Science Foundation of China(No.11671080)the Jiangsu Provincial Key Laboratory of Networked Collective Intelligence(No.BM2017002)
文摘Modern highly reliable products may have two or more quality characteristics(QCs) because of their complex structures and abundant functions. Relations between the QCs should be considered when assessing the reliability of these products. This paper conducts a Bayesian analysis for a bivariate constant-stress accelerated degradation model based on the inverse Gaussian(IG) process. We assume that the product considered has two QCs and each of the QCs is governed by an IG process. The relationship between the QCs is described by a Frank copula function. We also assume that the stress on the products affects not only the parameters of the IG processes, but also the parameter of the Frank copula function. The Bayesian MCMC method is developed to calculate the maximum likelihood estimators(MLE) of the model parameters. The reliability function and the mean-time-to-failure(MTTF) are estimated through the calculation of the posterior samples. Finally, a simulation example is presented to illustrate the proposed bivariate constant-stress accelerated degradation model.
文摘Aim Using animals as object of experiment to acquire various patterns of low cerebral blood pressure and reduced blood capacity in cerebral tissues of astronauts due to the load of acceleration. Methods The isotope tracking technique was applied to mark the blood and record the dynamic curves of cerebral blood flow changes under various accelerations, and the relevant mathematical model was set up using the method of system recognition. Also the method of factor analyzing was used to select two out of the data collected by eight sensors as two factors. Results One of the two factors reflects the various patterns in the astronaut's upper body, the other for the lower body. Parameters of rise time, delay time and steady value reflect the results under different acceleration. Conclusion Whether for the upper body or the lower body, blood flow changes can be considered as a second order system model. This method provides a new technique and method of doing research on astronaut's endurance of acceleration and selecting astronauts.
文摘A current statistical model for maneuvering acceleration using an adaptive extended Kalman filter（CS-MAEKF） algorithm is proposed to solve problems existing in conventional extended Kalman filters such as large estimation error and divergent tendencies in the presence of continuous maneuvering acceleration. A membership function is introduced in this algorithm to adaptively modify the upper and lower limits of loitering vehicles＇ maneuvering acceleration and for realtime adjustment of maneuvering acceleration variance. This allows the algorithm to have superior static and dynamic performance for loitering vehicles undergoing different maneuvers. Digital simulations and dynamic flight testing show that the yaw angle accuracy of the algorithm is 30% better than conventional algorithms, and pitch and roll angle calculation precision is improved by 60%.The mean square deviation of heading and attitude angle error during dynamic flight is less than3.05°. Experimental results show that CS-MAEKF meets the application requirements of miniature loitering vehicles.
基金the Hi-Tech Research and Development Pro-gram (863) of China (No. 2006AA04Z233)the National NaturalScience Foundation of China (No. 50575205)the Natural ScienceFoundation of Zhejiang Province (Nos. Y104243 and Y105686),China
文摘To satisfy the need of high speed NC (numerical control) machining, an acceleration and deceleration (acc/dec) control model is proposed, and the speed curve is also constructed by the cubic polynomial. The proposed control model provides continuity of acceleration, which avoids the intense vibration in high speed NC machining. Based on the discrete characteristic of the data sampling interpolation, the acc/dec control discrete mathematical model is also set up and the discrete expression of the theoretical deceleration length is obtained furthermore. Aiming at the question of hardly predetermining the deceleration point in acc/dec control before interpolation, the adaptive acc/dec control algorithm is deduced from the expressions of the theoretical deceleration length. The experimental result proves that the acc/dec control model has the characteristic of easy implementation, stable movement and low impact. The model has been applied in multi-axes high speed micro fabrication machining successfully.
文摘With the theory of subcritical crack growth, we can deduce the fundamental equation of regional seismicity acceleration model. Applying this model to intraplate earthquake regions, we select three earthquake subplates: North China Subplate, Chuan Dian Block and Xinjiang Subplate, and divide the three subplates into seven researched regions by the difference of seismicity and tectonic conditions. With the modified equation given by Sornette and Sammis (1995), we analysis the seismicity of each region. To those strong earthquakes already occurred in these region, the model can give close fitting of magnitude and occurrence time, and the result in this article indicates that the seismicity acceleration model can also be used for describing the seismicity of intraplate. In the article, we give the magnitude and occurrence time of possible strong earthquakes in Shanxi, Ordos, Bole Tuokexun, Ayinke Wuqia earthquake regions. In the same subplate or block, the earthquake periods for each earthquake region are similar in time interval. The constant α in model can be used to describe the intensity of regional seismicity, and for the Chinese Mainland, α is 0.4 generally. To the seismicity in Taiwan and other regions with complex tectonic conditions, the model does not fit well at present.
文摘The performance degradation rates of the missile tank are generally time-varying functions uneasily evaluated by general classical evaluation methods. This paper develops a segmented nonlinear accelerated degradation model （SNADM） based on the equivalent method of accumulative damage theory, which tackles the problem that product life is difficult to be determined with degradation rate being a function of the variable of time. A segmented expression of the function of population accumulative degradation is derived. And combined with nonlinear function, an accelerated degradation function, i.e., SNADM is obtained. The parameters of the SNADM are identified by numerical iteration, and the statistical function of degradation track is extrapolated. The reliability function is determined through the type of random process of the degradation distribution. Then an evaluation of product storage life is undertaken by combining the statistical function of degradation track, reliability function and threshold. An example of a missile tank undergoes a step-down stress accelerated degradation test （SDSADT）, in which the results with the SNADM and the classical method are evaluated and compared. The technology introduced is validated with the resultant coincidence of both evaluated and field storage lives.
基金Funded by Ministry of Science and Technology of China (No.50499331)
文摘The correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials was investigated according to the variation of the functional group of exposure models aged. Environment aging intensities at different zones （ Wuhan and Lasa with the same latitude ） and the influences of indoor accelerating factors including water and ultraviolet on weathering performant.e of high polymer materials were also studied by comparing different indoor accelerated corrosion testing results. The experimental results show that ： by testing variations of carbonyl exponent of polythene （ which represented the degradation behavior of high polymer materials due to ultraviolet oxidation of douIole bond） and ultraviolet absorbance of polycarbonate （which represented the degradation behavior of high polymer materials due to abevacuation of branched chain ）, the degradation behavior of high polymer materials could be studied. Carbonyl exponent of polythene exposed in Wuhan and Lasa for 1 year was equal to that exposed in indoor cycle ultraviolet for 128 h anti 170 It, respectively, the ultraviolet absorbance of polycarbonate exposed in Wuhan for 1 year was equal to that exposed in indoor cycle ultraviolet for 240 h. The ratio of environment aging intensity of Lasa to Wuhan was around 1.2. With the prolongation of cycle accelerated ultraviolet exposure time, the variations of carbonyl exponent of polythene and the ultraviolet absorbance of polycarbonate were in the same shape of first order exponential decay curiae. Accompanied with ultraviolet, the effect of water condensated on the sample on weathering performance of polythene was more .significant than that of polycarbonate.
