The center cutter of a hard rock tunnel boring machine(TBM) is installed on the cutterhead at a small radius and thus bears complex side force.Given this fact,the formation mechanism and change law of the side force s...The center cutter of a hard rock tunnel boring machine(TBM) is installed on the cutterhead at a small radius and thus bears complex side force.Given this fact,the formation mechanism and change law of the side force suffered by the center cutter were studied.Based on the rock shear failure criterion in combination with the lateral rolling width,a model for predicting the average side force was set up.Besides,a numerical analysis model of the rock fragmentation of the center cutter was established,and the instantaneous load changing features were investigated.Results shows that the inner side of the center cutter can form lateral rolling annulus in rock during the rotary cutting process.The smaller the installation radius is,the greater the cutter side force will be.In a working condition,the side force of the innermost center cutter is 11.66 k N,while it decreases sharply when installation radius increases.Variation tends to be gentle when installation radius is larger than 500 mm,and the side force of the outermost center cutter is reduced to 0.74 k N.展开更多
Beneficiation of coal of -4.76 mm + 3 mm size fraction was investigated in a laboratory model Denver jig.Process variables were studied to analyze their effect on the performance of jig in terms of yield and ash conte...Beneficiation of coal of -4.76 mm + 3 mm size fraction was investigated in a laboratory model Denver jig.Process variables were studied to analyze their effect on the performance of jig in terms of yield and ash content of clean coal. Three-factor three-level Box-Behnken design of experiments with response surface methodology(RSM) was employed to understand the performance behavior of jig. From the study, the bed height was found to be the most significant parameter affecting the yield and ash content of clean coal. It was possible to reduce the ash content from 24.32% in feed to an ash content of 16.55% in clean coal at 2 L/min water flow rate and 10 min jigging time. Influence of operating variables of the jig on responses was presented and discussed in 3D surface plots. The developed model was found to be significant within the range of parameters under investigation with correlation of co-efficient values as 0.99(yield) and 0.98(ash).展开更多
This study is focused on service quality assessment in the Nigerian ports with Westem and Eastern port zones as study areas. It discovered the level of satisfaction derived by port users by evaluating expectations and...This study is focused on service quality assessment in the Nigerian ports with Westem and Eastern port zones as study areas. It discovered the level of satisfaction derived by port users by evaluating expectations and perceptions at the ports using some selected analysis tools to test raised hypothesis. This evaluation was based on the service quality model as developed by Parasuraman within the core dimensions of Empathy, Responsiveness, Tangibles, Reliability and Assurance. The attributes of expectations and perceptions raised within these dimensions were addressed with two hypotheses. H1 （Hypothesis one） and H2 （Hypothesis two） were addressed with the results of Factor Analysis which identified the significance port users attach to service quality dimensions and their respective attributes.展开更多
This paper falls into two parts. In the first part, the widely used analytical-empirical method of pavement design and evaluation is discussed and in the second part two simulation models are presented to predict the ...This paper falls into two parts. In the first part, the widely used analytical-empirical method of pavement design and evaluation is discussed and in the second part two simulation models are presented to predict the design of flexible pavement. Analytical results are compared with simulation models.展开更多
The paper investigates the determinants of capital structure in Nigerian listed insurance firms using data obtained from annual report of the sampled firms for the period of 2001-2010. It used five explanatory variabl...The paper investigates the determinants of capital structure in Nigerian listed insurance firms using data obtained from annual report of the sampled firms for the period of 2001-2010. It used five explanatory variables to measure their effects on debt ratio. Multiple regression is employed as a tool of analysis. The result reveals that all the explanatory variables have statistically and significantly influenced the explained variable. The results approve the prediction of pecking order theory in the case of profitability and trade-off theory in case of tangibility variables. The growth variable supports the agency theory hypothesis whereas size variable confirms to the asymmetry of information theory. It is therefore recommended that the management of listed insurance firms in Nigeria should always consider their positions using these capital structure determinants as important inputs before embarking on debt financing decision.展开更多
The objective of this paper is to implement ＂Soil and Water Assessment Tool （SWAT）＂ model to assess the possible impact of land-use changes on nutrient yields from Song Cau watershed located in Northern Viet Nam. ...The objective of this paper is to implement ＂Soil and Water Assessment Tool （SWAT）＂ model to assess the possible impact of land-use changes on nutrient yields from Song Cau watershed located in Northern Viet Nam. Organic nitrogen （N） as well as phosphorus （P） output due to nonpoint source erosion was estimated through SWAT. Parameters governing the mechanics of streamflow discharge, sediment yield, nitrogen, and phosphorus output in SWAT were calibrated in a distributed fashion. A five-year period of record for nutrient was used for model calibration, while a four-year period was used for model validation. Comparing measured versus simulated average monthly total N, and P loads for the calibration and validation periods; respectively, we found that SWAT model performed reasonably well for Song Cau watershed. Simulation results showed that monthly Nash-Sutcliffe coefficient of Efficiency （NSE） ranged from 0.65 to 0.83, observation＇s standard deviation ratio （RSR） and percent bias （PBIAS） ranged from 0.41 to 0.58 and -36.12 to 2.78, respectively. Additionally, SWAT simulation results also showed that land-use changes caused significant percentage of changes in sediment yield, total N, and P loads within Song Cau watershed.展开更多
基金Project (2013CB035401) supported by the National Basic Research Program of ChinaProject (51475478) supported by the National Natural Science Foundation of ChinaProject (2012AA041803) supported by the High-Tech Research and Development Program of China
文摘The center cutter of a hard rock tunnel boring machine(TBM) is installed on the cutterhead at a small radius and thus bears complex side force.Given this fact,the formation mechanism and change law of the side force suffered by the center cutter were studied.Based on the rock shear failure criterion in combination with the lateral rolling width,a model for predicting the average side force was set up.Besides,a numerical analysis model of the rock fragmentation of the center cutter was established,and the instantaneous load changing features were investigated.Results shows that the inner side of the center cutter can form lateral rolling annulus in rock during the rotary cutting process.The smaller the installation radius is,the greater the cutter side force will be.In a working condition,the side force of the innermost center cutter is 11.66 k N,while it decreases sharply when installation radius increases.Variation tends to be gentle when installation radius is larger than 500 mm,and the side force of the outermost center cutter is reduced to 0.74 k N.
文摘Beneficiation of coal of -4.76 mm + 3 mm size fraction was investigated in a laboratory model Denver jig.Process variables were studied to analyze their effect on the performance of jig in terms of yield and ash content of clean coal. Three-factor three-level Box-Behnken design of experiments with response surface methodology(RSM) was employed to understand the performance behavior of jig. From the study, the bed height was found to be the most significant parameter affecting the yield and ash content of clean coal. It was possible to reduce the ash content from 24.32% in feed to an ash content of 16.55% in clean coal at 2 L/min water flow rate and 10 min jigging time. Influence of operating variables of the jig on responses was presented and discussed in 3D surface plots. The developed model was found to be significant within the range of parameters under investigation with correlation of co-efficient values as 0.99(yield) and 0.98(ash).
文摘This study is focused on service quality assessment in the Nigerian ports with Westem and Eastern port zones as study areas. It discovered the level of satisfaction derived by port users by evaluating expectations and perceptions at the ports using some selected analysis tools to test raised hypothesis. This evaluation was based on the service quality model as developed by Parasuraman within the core dimensions of Empathy, Responsiveness, Tangibles, Reliability and Assurance. The attributes of expectations and perceptions raised within these dimensions were addressed with two hypotheses. H1 （Hypothesis one） and H2 （Hypothesis two） were addressed with the results of Factor Analysis which identified the significance port users attach to service quality dimensions and their respective attributes.
文摘This paper falls into two parts. In the first part, the widely used analytical-empirical method of pavement design and evaluation is discussed and in the second part two simulation models are presented to predict the design of flexible pavement. Analytical results are compared with simulation models.
文摘The paper investigates the determinants of capital structure in Nigerian listed insurance firms using data obtained from annual report of the sampled firms for the period of 2001-2010. It used five explanatory variables to measure their effects on debt ratio. Multiple regression is employed as a tool of analysis. The result reveals that all the explanatory variables have statistically and significantly influenced the explained variable. The results approve the prediction of pecking order theory in the case of profitability and trade-off theory in case of tangibility variables. The growth variable supports the agency theory hypothesis whereas size variable confirms to the asymmetry of information theory. It is therefore recommended that the management of listed insurance firms in Nigeria should always consider their positions using these capital structure determinants as important inputs before embarking on debt financing decision.
文摘The objective of this paper is to implement ＂Soil and Water Assessment Tool （SWAT）＂ model to assess the possible impact of land-use changes on nutrient yields from Song Cau watershed located in Northern Viet Nam. Organic nitrogen （N） as well as phosphorus （P） output due to nonpoint source erosion was estimated through SWAT. Parameters governing the mechanics of streamflow discharge, sediment yield, nitrogen, and phosphorus output in SWAT were calibrated in a distributed fashion. A five-year period of record for nutrient was used for model calibration, while a four-year period was used for model validation. Comparing measured versus simulated average monthly total N, and P loads for the calibration and validation periods; respectively, we found that SWAT model performed reasonably well for Song Cau watershed. Simulation results showed that monthly Nash-Sutcliffe coefficient of Efficiency （NSE） ranged from 0.65 to 0.83, observation＇s standard deviation ratio （RSR） and percent bias （PBIAS） ranged from 0.41 to 0.58 and -36.12 to 2.78, respectively. Additionally, SWAT simulation results also showed that land-use changes caused significant percentage of changes in sediment yield, total N, and P loads within Song Cau watershed.
