Several questions have emerged in relation to deep cover bleeder entry performance and support loading:how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understan...Several questions have emerged in relation to deep cover bleeder entry performance and support loading:how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented,observed, and numerically modeled.This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel—specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction.The primary focus was on the extent and magnitude of the abutment loading experienced by the standing support.As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports—less than 23 Mg load and 2.54 cm convergence.The Flac3D program was used to evaluate these four bleeder entries using previously defined modeling and input parameter estimation procedures.The results indicated only a minor increase in load during the extraction of the longwall panel.The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction.The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies.The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal.The farther away from the startup room, the lower the applied load and smaller the convergence in the entry if all else is held constant.Finally, the numerical modeling method used in this study was capable of replicating the expected and measured results near seam.展开更多
A metal rubber（MR） dry friction damper was designed based on the load supported by the rotor. An experimental apparatus for obtaining hysteresis loops of support under the precession load was designed. The elastic-d...A metal rubber（MR） dry friction damper was designed based on the load supported by the rotor. An experimental apparatus for obtaining hysteresis loops of support under the precession load was designed. The elastic-damping characteristics of the ring-shaped MR damper used as a rotor support under variable loads were presented by studying the hysteresis loops of the damper. The vibration rigidity and the energy dissipation coefficient were calculated from the hysteresis loops, based on the description of the deformation process of the MR element with simple structure in a dimensionless coordinating system. The calculation results showed that the energy dissipation coefficient in the inner of MR element and on the boundary between the damper and the frame of the rotor support were approximately equal. The comparison of the hysteresis loops for a precession load and a one-axial load indicated a large difference when the coefficient of the energy dissipation and the stiffness of the MR damper were concerned.展开更多
Despite the increasing popularity of mechanized coal mining, there are no convenient and accurate means available to measure the loads of powered supports. The measurement of such loads is important for monitoring min...Despite the increasing popularity of mechanized coal mining, there are no convenient and accurate means available to measure the loads of powered supports. The measurement of such loads is important for monitoring mine pressure and ensuring production safety. The load-carrying features of a powered support were used to develop a method for load measurement using the mag-netoelastic principle. A cross bridge-type magnetoelastic stress sensor was designed for the support structures to measure the different parts of the supports. Tests on single-body hydraulic cylinders and simulated linkages showed that an approximately linear relationship between the values of the sensor output signal and the loads borne by the hydraulic cylinders or linkages. The results were used to analyze the load-carrying measurements of powered supports with the cross bridge-type magnetoelastic stress sensor.展开更多
Based on the Duhamel integral, a couple of analytical solutions are derived to predict the strain rates of concrete and steel reinforcement in reinforced concrete slabs under blast loads and to estimate their variatio...Based on the Duhamel integral, a couple of analytical solutions are derived to predict the strain rates of concrete and steel reinforcement in reinforced concrete slabs under blast loads and to estimate their variation over depth of a cross-section along the entire length of the member. The analytical approach utilizes the single-degree-of-freedom mode for the analysis of reinforced concrete simply supported one-way panels subjected to blast loads. These analytical solutions can give the strain rate profile for any cross-section at any time and permit variations of strain rate in each time step of numerical iteration method, thus making it possible to directly incorporate strain rate effects into non-linear dynamic response analysis of structural members subjected to blast loads.展开更多
Based on the application of the four-oil-pad radial hydrostatic bearing in heavy equipments, the deformation of the four-oil-pad radial hydrostatic bearing was calculated by using the finite element method. The formul...Based on the application of the four-oil-pad radial hydrostatic bearing in heavy equipments, the deformation of the four-oil-pad radial hydrostatic bearing was calculated by using the finite element method. The formula of film stiffness, film thickness and carrying capacity were established; the influence of the main parameters, such as load, load area and deformation on the supportability was analyzed; and the capacity of the two kinds of bearings was compared. The result shows that the carrying capacity of typeⅠ is prior to that of type Ⅱ . Calculations provide a theoretical basis for the bearing choosing and structure designing in the actual project.展开更多
Long-term load forecasting (LTLF) is a challenging task because of the complex relationships between load and factors affecting load. However, it is crucial for the economic growth of fast developing countries like Ch...Long-term load forecasting (LTLF) is a challenging task because of the complex relationships between load and factors affecting load. However, it is crucial for the economic growth of fast developing countries like China as the growth rate of gross domestic product (GDP) is expected to be 7.5%, according to China’s 11th Five-Year Plan (2006-2010). In this paper, LTLF with an economic factor, GDP, is implemented. A support vector regression (SVR) is applied as the training algorithm to obtain the nonlinear relationship between load and the economic factor GDP to improve the accuracy of forecasting.展开更多
Taking the chock shield supports as the object of study, methods formeasuring and calculating the external load of powered supports were discussed. Selecting the angleparameters as variables, the simple formulae of in...Taking the chock shield supports as the object of study, methods formeasuring and calculating the external load of powered supports were discussed. Selecting the angleparameters as variables, the simple formulae of interactive computation with respect to the workangles of a powered support were deduced and verified by an example. Furthermore, the formulaedetermining the magnitude, direction and action point of the external load were put forward. Theinvestigation results have provided a sound basis for the software design of the intelligentinstrument for load measuring of powered supports.展开更多
As the existing heating load forecasting methods are almostly point forecasting,an interval forecasting approach based on Support Vector Regression (SVR) and interval estimation of relative error is proposed in this p...As the existing heating load forecasting methods are almostly point forecasting,an interval forecasting approach based on Support Vector Regression (SVR) and interval estimation of relative error is proposed in this paper.The forecasting output can be defined as energy saving control setting value of heating supply substation;meanwhile,it can also provide a practical basis for heating dispatching and peak load regulating operation.By means of the proposed approach,SVR model is used to point forecasting and the error interval can be gained by using nonparametric kernel estimation to the forecast error,which avoid the distributional assumptions.Combining the point forecasting results and error interval,the forecast confidence interval is obtained.Finally,the proposed model is performed through simulations by applying it to the data from a heating supply network in Harbin,and the results show that the method can meet the demands of energy saving control and heating dispatching.展开更多
Background: Globally, HIV viral load suppression rate, which is an indirect measure of the efficacy of antiretroviral (ART) medication, is 47% and 52% in Africa. In Cameroon, the viral load (VL) suppression rate is 44...Background: Globally, HIV viral load suppression rate, which is an indirect measure of the efficacy of antiretroviral (ART) medication, is 47% and 52% in Africa. In Cameroon, the viral load (VL) suppression rate is 44.7% and poor adherence is widely documented as being responsible for the large gap in VL Suppression. Enhanced adherence counselling (EAC) sessions, and enrolment and participation in support groups are specific interventions to improve ART adherence and improve viral load suppression. Purpose: This study assesses the uptake and contribution of support groups and EAC sessions in the management of adolescents with unsuppressed VL results at Centre Hospitalier d’Essos, Yaounde. Methods: A retrospective correlational quantitative patient files review was conducted for 138 files of HIV positive adolescents aged between 10 - 19 years with HIV VL above 1000 copies/ml enrolled in care between January 2009 and December 2019. Data from the questionnaire was entered into CSPRO version 7.4. and analyzed by using SPSS version 25.0. Results: A total of 138 participants (75 females and 63 males) with a mean age of 15 ± 3 years were included in our study. Sixty-nine (50%) participants were in World Health Organization (WHO) stage I;32.6% were in Stage II;13.0% and 4.3% were in stages III and IV, respectively. Thirty (21.7%) had a history of tuberculosis and 76% of the adolescents were being cared for primarily by their parents. The charts of the adolescents revealed that there was an association between completion of EAC sessions in adolescents with unsuppressed VL and eventual VL suppression (R.R = 2.5;CI 0.848 - 6.162;p = 0.033). However, there was no significant association between support group enrolment and active participation, and eventual VL Suppression. Furthermore, combining EAC and support group interventions was strongly associated with eventual VL Suppression in this group of initially unsuppressed adolescents (R.R = 7.5;C.I 2.544 - 22.360;p Conclusion: Suppression rates were good after completion of EAC sessions and participation in support group enrolment for adolescents with a high VL. As we move towards having 95% of ART-treated adolescents achieve and maintain viral suppression, there is a need to reinforce EAC sessions and support group enrolment in ART clinics targeting this priority group.展开更多
文摘Several questions have emerged in relation to deep cover bleeder entry performance and support loading:how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented,observed, and numerically modeled.This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel—specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction.The primary focus was on the extent and magnitude of the abutment loading experienced by the standing support.As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports—less than 23 Mg load and 2.54 cm convergence.The Flac3D program was used to evaluate these four bleeder entries using previously defined modeling and input parameter estimation procedures.The results indicated only a minor increase in load during the extraction of the longwall panel.The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction.The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies.The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal.The farther away from the startup room, the lower the applied load and smaller the convergence in the entry if all else is held constant.Finally, the numerical modeling method used in this study was capable of replicating the expected and measured results near seam.
基金This project is supported by National Natural Science Foundation of China (No.50675042).
文摘A metal rubber（MR） dry friction damper was designed based on the load supported by the rotor. An experimental apparatus for obtaining hysteresis loops of support under the precession load was designed. The elastic-damping characteristics of the ring-shaped MR damper used as a rotor support under variable loads were presented by studying the hysteresis loops of the damper. The vibration rigidity and the energy dissipation coefficient were calculated from the hysteresis loops, based on the description of the deformation process of the MR element with simple structure in a dimensionless coordinating system. The calculation results showed that the energy dissipation coefficient in the inner of MR element and on the boundary between the damper and the frame of the rotor support were approximately equal. The comparison of the hysteresis loops for a precession load and a one-axial load indicated a large difference when the coefficient of the energy dissipation and the stiffness of the MR damper were concerned.
文摘Despite the increasing popularity of mechanized coal mining, there are no convenient and accurate means available to measure the loads of powered supports. The measurement of such loads is important for monitoring mine pressure and ensuring production safety. The load-carrying features of a powered support were used to develop a method for load measurement using the mag-netoelastic principle. A cross bridge-type magnetoelastic stress sensor was designed for the support structures to measure the different parts of the supports. Tests on single-body hydraulic cylinders and simulated linkages showed that an approximately linear relationship between the values of the sensor output signal and the loads borne by the hydraulic cylinders or linkages. The results were used to analyze the load-carrying measurements of powered supports with the cross bridge-type magnetoelastic stress sensor.
文摘Based on the Duhamel integral, a couple of analytical solutions are derived to predict the strain rates of concrete and steel reinforcement in reinforced concrete slabs under blast loads and to estimate their variation over depth of a cross-section along the entire length of the member. The analytical approach utilizes the single-degree-of-freedom mode for the analysis of reinforced concrete simply supported one-way panels subjected to blast loads. These analytical solutions can give the strain rate profile for any cross-section at any time and permit variations of strain rate in each time step of numerical iteration method, thus making it possible to directly incorporate strain rate effects into non-linear dynamic response analysis of structural members subjected to blast loads.
基金Project(zjg0702-01) supported by the Key Program of Natural Science Foundation of Heilongjiang Province, ChinaProject(20050214001) supported by the Doctoral Fund of Ministry of Education of China+1 种基金Project(11531051) supported by the Science and Technology Foundation of Heilongjiang Provincial Education Department, ChinaProject(QC08c88) supported by Heilongjiang Province Foundation for Youths, China.
文摘Based on the application of the four-oil-pad radial hydrostatic bearing in heavy equipments, the deformation of the four-oil-pad radial hydrostatic bearing was calculated by using the finite element method. The formula of film stiffness, film thickness and carrying capacity were established; the influence of the main parameters, such as load, load area and deformation on the supportability was analyzed; and the capacity of the two kinds of bearings was compared. The result shows that the carrying capacity of typeⅠ is prior to that of type Ⅱ . Calculations provide a theoretical basis for the bearing choosing and structure designing in the actual project.
文摘Long-term load forecasting (LTLF) is a challenging task because of the complex relationships between load and factors affecting load. However, it is crucial for the economic growth of fast developing countries like China as the growth rate of gross domestic product (GDP) is expected to be 7.5%, according to China’s 11th Five-Year Plan (2006-2010). In this paper, LTLF with an economic factor, GDP, is implemented. A support vector regression (SVR) is applied as the training algorithm to obtain the nonlinear relationship between load and the economic factor GDP to improve the accuracy of forecasting.
文摘Taking the chock shield supports as the object of study, methods formeasuring and calculating the external load of powered supports were discussed. Selecting the angleparameters as variables, the simple formulae of interactive computation with respect to the workangles of a powered support were deduced and verified by an example. Furthermore, the formulaedetermining the magnitude, direction and action point of the external load were put forward. Theinvestigation results have provided a sound basis for the software design of the intelligentinstrument for load measuring of powered supports.
基金Sponsored by the National 11th 5-year Plan Key Project of Ministry of Science and Technology of China (Grant No.2006BAJ01A04)
文摘As the existing heating load forecasting methods are almostly point forecasting,an interval forecasting approach based on Support Vector Regression (SVR) and interval estimation of relative error is proposed in this paper.The forecasting output can be defined as energy saving control setting value of heating supply substation;meanwhile,it can also provide a practical basis for heating dispatching and peak load regulating operation.By means of the proposed approach,SVR model is used to point forecasting and the error interval can be gained by using nonparametric kernel estimation to the forecast error,which avoid the distributional assumptions.Combining the point forecasting results and error interval,the forecast confidence interval is obtained.Finally,the proposed model is performed through simulations by applying it to the data from a heating supply network in Harbin,and the results show that the method can meet the demands of energy saving control and heating dispatching.
文摘Background: Globally, HIV viral load suppression rate, which is an indirect measure of the efficacy of antiretroviral (ART) medication, is 47% and 52% in Africa. In Cameroon, the viral load (VL) suppression rate is 44.7% and poor adherence is widely documented as being responsible for the large gap in VL Suppression. Enhanced adherence counselling (EAC) sessions, and enrolment and participation in support groups are specific interventions to improve ART adherence and improve viral load suppression. Purpose: This study assesses the uptake and contribution of support groups and EAC sessions in the management of adolescents with unsuppressed VL results at Centre Hospitalier d’Essos, Yaounde. Methods: A retrospective correlational quantitative patient files review was conducted for 138 files of HIV positive adolescents aged between 10 - 19 years with HIV VL above 1000 copies/ml enrolled in care between January 2009 and December 2019. Data from the questionnaire was entered into CSPRO version 7.4. and analyzed by using SPSS version 25.0. Results: A total of 138 participants (75 females and 63 males) with a mean age of 15 ± 3 years were included in our study. Sixty-nine (50%) participants were in World Health Organization (WHO) stage I;32.6% were in Stage II;13.0% and 4.3% were in stages III and IV, respectively. Thirty (21.7%) had a history of tuberculosis and 76% of the adolescents were being cared for primarily by their parents. The charts of the adolescents revealed that there was an association between completion of EAC sessions in adolescents with unsuppressed VL and eventual VL suppression (R.R = 2.5;CI 0.848 - 6.162;p = 0.033). However, there was no significant association between support group enrolment and active participation, and eventual VL Suppression. Furthermore, combining EAC and support group interventions was strongly associated with eventual VL Suppression in this group of initially unsuppressed adolescents (R.R = 7.5;C.I 2.544 - 22.360;p Conclusion: Suppression rates were good after completion of EAC sessions and participation in support group enrolment for adolescents with a high VL. As we move towards having 95% of ART-treated adolescents achieve and maintain viral suppression, there is a need to reinforce EAC sessions and support group enrolment in ART clinics targeting this priority group.
