The dynamic photoelastic technique is employed to visualize and quantify the propagation properties of backward Lamb waves in a plate. Higher energy leakage of second-order symmetric backward wave mode S2b in contrast...The dynamic photoelastic technique is employed to visualize and quantify the propagation properties of backward Lamb waves in a plate. Higher energy leakage of second-order symmetric backward wave mode S2b in contrast to third-order anti-symmetric backward mode A3b is shown by the dispersion curve of a plate immersed in water, and then verified by experiments. To avoid the considerable high leakage, the plate is placed in air, both group and phase velocities of modes S2b and A3b in the glass plate are experimentally measured. In comparison with the theoretical values, less than 5% errors are found in experiments.展开更多
Chemical solvents instead of pure water being as hydraulic fracturing fluid could effectively increase permeability and improve clean methane extraction efficiency.However,pore-fracture variation features of lean coal...Chemical solvents instead of pure water being as hydraulic fracturing fluid could effectively increase permeability and improve clean methane extraction efficiency.However,pore-fracture variation features of lean coal synergistically affected by solvents have not been fully understood.Ultrasonic testing,nuclear magnetic resonance analysis,liquid phase mass spectrometry was adopted to comprehensively analyze pore-fracture change characteristics of lean coal treated by combined solvent(NMP and CS_(2)).Meanwhile,quantitative characterization of above changing properties was conducted using geometric fractal theory.Relationship model between permeability,fractal dimension and porosity were established.Results indicate that the end face fractures of coal are well developed after CS2and combined solvent treatments,of which,end face box-counting fractal dimensions range from 1.1227 to 1.4767.Maximum decreases in ultrasonic longitudinal wave velocity of coal affected by NMP,CS_(2)and combined solvent are 2.700%,20.521%,22.454%,respectively.Solvent treatments could lead to increasing amount of both mesopores and macropores.Decrease ratio of fractal dimension Dsis 0.259%–2.159%,while permeability increases ratio of NMR ranges from 0.1904 to 6.4486.Meanwhile,combined solvent could dissolve coal polar and non-polar small molecules and expand flow space.Results could provide reference for solvent selection and parameter optimization of permeability-enhancement technology.展开更多
Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well ...Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well water solution mining with oil as a cushion,engineering challenges arise with the leaching tubing,leading to issues like damage and instability.These problems significantly hinder the progress of cavern construction and the control of cavern shape.The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space,which results in severe bending or damage to the tubing.This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus.The experiment utilizes a silicone-rubber pipe(SRP)and a polycarbonate pipe(PCP)to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid.These factors include external space constraint,flexural rigidity,medium outside the pipe,overhanging length,and end conditions.The experiments reveal four dynamic response phenomena:water hammer,static buckling,chaotic motion,and flutter instability.The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid.Additionally,the flutter critical flow velocity is influenced by the end conditions and different external media.展开更多
Crime scene investigation(CSI)image is key evidence carrier during criminal investiga-tion,in which CSI image retrieval can assist the public police to obtain criminal clues.Moreover,with the rapid development of deep...Crime scene investigation(CSI)image is key evidence carrier during criminal investiga-tion,in which CSI image retrieval can assist the public police to obtain criminal clues.Moreover,with the rapid development of deep learning,data-driven paradigm has become the mainstreammethod of CSI image feature extraction and representation,and in this process,datasets provideeffective support for CSI retrieval performance.However,there is a lack of systematic research onCSI image retrieval methods and datasets.Therefore,we present an overview of the existing worksabout one-class and multi-class CSI image retrieval based on deep learning.According to theresearch,based on their technical functionalities and implementation methods,CSI image retrievalis roughly classified into five categories:feature representation,metric learning,generative adversar-ial networks,autoencoder networks and attention networks.Furthermore,We analyzed the remain-ing challenges and discussed future work directions in this field.展开更多
The combined microwave-convective drying is a novel drying method and has many advantages, such as swift drying, equable drying and sterilization. This paper studies the drying characteristic of medical pill in microw...The combined microwave-convective drying is a novel drying method and has many advantages, such as swift drying, equable drying and sterilization. This paper studies the drying characteristic of medical pill in microwave-convective drying process. The influential parameters of pill drying characteristics including pill size, quality, air velocity, temperature and the input power of microwave, are experimentally investigated. Results show that the drying process is influenced by the intrinsic heat of microwave power, and the environment and the resistance of mass transfer. It has the advantage of the microwave-convective drying in saving energy, reducing labor intensity and sterilizing. The method with the high efficiency is suitable for pharmacy industry.展开更多
Electrolytic Copper used in the shaped charge liner manufacturing can be produced from acid solution using electro-deposition technique. The intensity of the applied electric current controls the quality of the produc...Electrolytic Copper used in the shaped charge liner manufacturing can be produced from acid solution using electro-deposition technique. The intensity of the applied electric current controls the quality of the produced copper grade. The electric current intensity within the electrolytic acidic solution cell with the minimum oxygen and sulfur elements in the produced copper was optimized and found to be 30-40 A/Ft^2. The elemental composition of the obtained electrolytic copper was determined using highend stationary vacuum spectrometer, while the oxygen was determined precisely using ELTRA ONH-2000 apparatus. Besides, SEM was used to investigate the shape of the copper texture inside the deposited layers and to determine the average grain size. New relations have been obtained between the applied current intensity and both the oxygen and sulfur contents and the average grain size of the produced copper. Experimental result showed that when the applied current density increases to a certain limit, the oxygen and sulfur content in the electrolytic copper decreases. Performance of the produced copper liner was investigated by the static firing of a small caliber shaped charge containing an electro-formed copper liners, where the penetration depth of the optimized electrolytic liner was enhanced by 22.7% compared to that of baseline non-optimized liner.展开更多
This study investigates the avoidance of relative clauses by high vocational college students and also explores the differences in the avoidance of the RCs by high-level students and low-level students in their Englis...This study investigates the avoidance of relative clauses by high vocational college students and also explores the differences in the avoidance of the RCs by high-level students and low-level students in their English writings. The data used in this study have been collected from English writing tasks and analyzed by Statistical Package for Social Sciences(SPSS17.0). The major findings of this study are stated as follows: 1) There are significant differences in the production of the relative clauses in their English writings by Chinese higher vocational college students and English native speakers. Avoidance of relative clauses exists in the English writings of higher vocational college students. 2) High-level Chinese higher vocational college students display less of the avoidance phenomenon in their English writings than low-level students.展开更多
This study investigated the application and the effect of Group Investigation(GI) in the College English Program in a Chinese University. A qualitative case study method was used to understand the GI system used by Ch...This study investigated the application and the effect of Group Investigation(GI) in the College English Program in a Chinese University. A qualitative case study method was used to understand the GI system used by Chinese instructors as well as the achievements acquired and challenges met by the participants. Three instructors and fifteen second-year-undergraduates taking a course titled Sources of European Culture participated. Interviews, observations, and documents were used to collect the data. Data analysis showed Chinese instructors applied a GI technique similar to that discussed by Johnson and Johnson(1999); however, GI in the Chinese context demanded more effort from the teacher for designing tasks and provided help in modeling uses of English and in preparing visual, especially Power Point, presentations. Although participants used their mother tongue at some stages, their autonomy over English learning was activated, and horizons in the course content were broadened.展开更多
Business English Major is the key specialty in Jiangsu Maritime Institute.Grasping and understanding the situation of graduates is of very important meaning to the major construction and the personnel cultivating prog...Business English Major is the key specialty in Jiangsu Maritime Institute.Grasping and understanding the situation of graduates is of very important meaning to the major construction and the personnel cultivating program.This article is mainly about the investigation and survey of graduate of 2011,and rational suggestions will be put forward on improving the quality of graduate and the major construction and the personnel cultivating program.展开更多
Based on laboratory results of time-dependent mechanical behavior tests,we investigated short-term and mechanical creep behavior of sandstone,observed in conventional triaxial compression experiments at room temperatu...Based on laboratory results of time-dependent mechanical behavior tests,we investigated short-term and mechanical creep behavior of sandstone,observed in conventional triaxial compression experiments at room temperature,using a servo-controlled rheology testing machine.Given our short-term experimental test results,we confirmed deviatoric creep stress levels of sandstone.Multiple deviatoric stress levels were applied in steps to each sample.Each deviatoric stress level before the final failed deviatoric stress was maintained for 48 h or longer.Time-dependent variations of axial strains of sandstone samples are discussed and evaluated.During the creep tests,complete tertiary creep curves of sandstone were observed under failed deviatoric stress levels with different confining pressures.Slices of coal in sandstone samples can lead to distinct tertiary creep deformation failure.展开更多
Objectives To investigate the overall prevalence of cardiovascular disease （CVD） in subjects hospitalized for chronic obstructive pulmonary disease （COPD）,and explore the prevalence of the major CVD complications ...Objectives To investigate the overall prevalence of cardiovascular disease （CVD） in subjects hospitalized for chronic obstructive pulmonary disease （COPD）,and explore the prevalence of the major CVD complications and trends in patients with COPD over a 10-year period.Methods Medical records in the PLA General Hospital,Beijing Union Medical College Hospital,and Beijing Hospital from 2000/01/01 to 2010/03/03 were retrospectively reviewed.A total of 4960 patients with COPD were reviewed in the study （3570 males,mean age,72.2 ± 10.5 years; 1390 females,mean age,72.0 ± 10.4 years）.Results The prevalence of CVD in COPD patients was 51.7％.The three most prevalent CVDs were ischemic heart disease （28.9％）,heart failure （19.6％）,and arrhythmia （12.6％）.During the 10-year study period,the prevalence of various CVDs in COPD patients showed a gradual increasing trend with increasing age.There was higher morbidity due to ischemic heart disease （P ＜ 0.01） in male COPD patients than in the female counterparts.However,heart failure （P ＜ 0.01）and hypertension （P ＜ 0.01） occurred less frequently in male COPD patients than in female COPD patients.Furthermore,the prevalence of ischemic heart disease decreased year by year.In addition to heart failure,various types of CVD complications in COPD patients tended to occur in younger subjects.The prevalence of all major types of CVD in women tended to increase year by year.Conclusions The prevalence of CVD in patients hospitalized for COPD in Beijing was high.Age,sex and CVD trends,as well as life style changes,should be considered when prevention and control strategies are formulated.展开更多
Based on the particularities of gas outbursts,i.e.,low gas bearing capacity and low gas pressure in the "Three Soft" coal seam in western Henan,we applied the theories of plate tectonics and regional structu...Based on the particularities of gas outbursts,i.e.,low gas bearing capacity and low gas pressure in the "Three Soft" coal seam in western Henan,we applied the theories of plate tectonics and regional structural evolution to investigate the mechanism of this seam and its impact on the coal seam gas formation.Our investigation revealed that coal and gas outbursts are distributed in a strip in a NW direction,with a number of high-penetration mines scattered towards the south side and low-gas mines largely located on the north side.We analyzed the statistics of 38 gas explosions and the rock-coal sturdiness number coefficient f of 167 sampling sites in the region and found the gas outburst mechanism that features a "low indicator outburst phenomenon".The mechanism is characterized by structural coal as its core,a low gas bearing capacity,low gas pressure and sturdiness coefficient f mostly less than 0.3.Our research results provide a theoretical foundation for effective control of gas disasters.展开更多
Experimental studies are carried out with slender bodies vertically exiting out of the water using a high-speed camera. The mechanisms for the formation, development, and collapse of the cavity around the slender body...Experimental studies are carried out with slender bodies vertically exiting out of the water using a high-speed camera. The mechanisms for the formation, development, and collapse of the cavity around the slender body are explored. The dynamic characteristics of the shoulder cavity and the trail cavity during the water-exit of low-speed bodies are analyzed for various water depths and initial velocities. The results show that the initial velocity has a great influence on the formation, development, and collapse of the cavity. The length and the thickness of the shoulder cavity vary non-linearly with the depth.展开更多
According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We presen...According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We present theoretical and experimental investigations into the flexural vibration transfer properties of a high-pressure periodic pipe with the force on the inner pipe wall by oii pressure taken into consideration. The results show that the vibration attenuation of periodic pipe decreases along with the elevation of working pressure for the hydraulic system, and the band gaps in low frequency ranges move towards high frequency ranges. The periodic pipe has good vibration attenuation performance in the frequency range below 1000 Hz and the vibration of the hydraulic system is effectively suppressed. A11 the results are validated by experiment. The experimental results show a good agreement with the numerical calculations, thus the flexural vibration transfer properties of the high- pressure periodic pipe can be precisely calculated by taking the fluid structure interaction between the pipe and oil into consideration. This study provides an effective way for the vibration control of the hydraulic system.展开更多
Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out i...Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out in a plane sand bed with two circular piers of same diameter arranged in tandem manner under no seepage, 10% seepage and 20% seepage conditions. Downward seepage minimizes the scour depth around piers and restrains the development of scour depth with time. Strong reversal flow is found near the bed at upstream of piers and near free surface at downstream of piers where velocity and Reynolds shear stress are found to be negative which reduce in magnitude with downward seepage. The flow is more critical within the gap between two piers where velocity is lesser near free surface and gradually increasing towards bed. Quadrant analysis shows that contribution of each event to the total Reynolds shear stress increases with downward seepage. Sedimentation effect prevails within the scour hole whereas outside the scour hole erosive forces become more dominant. Reduced reversal flow at upstream of pier because of downward seepage results in decreasing higher order moments and turbulent kinetic energy. At downstream of piers, secondary currents are dominant due to wake vortices. Strouhal number decreases in case of seepage runs than no seepage condition.展开更多
The dynamic characteristics of a belt conveyor are determined to a large extent by the properties of the belt. This paper describes experiments designed to establish the dynamic properties of belting material. The dyn...The dynamic characteristics of a belt conveyor are determined to a large extent by the properties of the belt. This paper describes experiments designed to establish the dynamic properties of belting material. The dynamic elastic modulus, viscous damping and rheologicat constants of the belt were measured. Several properties were studied as a function of the tensile loading on the belt. These included longitudinal vibration, the natural vibration frequency in the transverse direction and the response to an impulse excitation. Vibration response was observed under several different excitation frequencies. Most of these properties have not been tested previously under conditions appropriate for the ISO/DP9856 standard. Two types of belt were tested, a steel reinforced belt and a fabric reinforced belt. The test equipment was built to provide data appropriate for designing belt conveyors. It was observed that the stress wave propagation speed increased with tensile load and that tensile load was the main factor influencing longitudinal vibrations.展开更多
The transient performance and optimization of a passive residual heat removal heat exchanger(PRHR HX)were investigated.First,a calculation method was developed for predicting the heat transfer of the PRHR HX.The calcu...The transient performance and optimization of a passive residual heat removal heat exchanger(PRHR HX)were investigated.First,a calculation method was developed for predicting the heat transfer of the PRHR HX.The calculation results were validated through comparisons with ROSA experimental data.The heat-transfer performance of the AP1000 PRHR HX in the initial period was predicted,and it satisfied the design requirements.Second,the distributions of the heat flux,tube-inside/outside heattransfer coefficients,and heat load for the AP1000 PRHR HX over 2000 s were examined.Third,an optimization study was conducted by adjusting the horizontal length and tube diameter.Their effects on the four main heat-transfer parameters and the heat-transfer area were analyzed.Furthermore,the influence of the initial in-containment refueling water storage tank(IRWST)temperature was investigated using an established simulation procedure.The results indicated that it significantly affected the trends of the IRWST temperature and reactor outlet temperature.Finally,the minimum required flow rates over time to maintain the reactor outlet temperature at the safety line were determined for different start-up times.The trends of the minimum required flow rate and the peak flow rate were analyzed.展开更多
Careful and thorough incident investigations and pre-job safety analyses completed by knowledgeable and competent individuals can significantly reduce workplace incidents. Working parties must act together to make the...Careful and thorough incident investigations and pre-job safety analyses completed by knowledgeable and competent individuals can significantly reduce workplace incidents. Working parties must act together to make these safety tools effective. To get the staff units to work together in a co-ordinated manner, they must be shown the value of their work in preventing accidents. Examples of actual accidents investigated during the author's 18 years as a mine inspector in Saskatchewan are discussed within the context of pre-job safety analyses. The causes of the accidents are explored with close reference to how pre-job safety analyses could have prevented their occurrence.展开更多
The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel r...The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11374325 and 11427809
文摘The dynamic photoelastic technique is employed to visualize and quantify the propagation properties of backward Lamb waves in a plate. Higher energy leakage of second-order symmetric backward wave mode S2b in contrast to third-order anti-symmetric backward mode A3b is shown by the dispersion curve of a plate immersed in water, and then verified by experiments. To avoid the considerable high leakage, the plate is placed in air, both group and phase velocities of modes S2b and A3b in the glass plate are experimentally measured. In comparison with the theoretical values, less than 5% errors are found in experiments.
基金financially supported by National Natural Science Foundation of China(No.52274171)Joint National-Local Engineering Research Centre for Safe and Precise Coal Mining Fund(No.EC2023015)+1 种基金Excellent Youth Project of Universities in Anhui Province(No.2023AH030042)Unveiled List of Bidding Projects of Shanxi Province(No.20201101001)。
文摘Chemical solvents instead of pure water being as hydraulic fracturing fluid could effectively increase permeability and improve clean methane extraction efficiency.However,pore-fracture variation features of lean coal synergistically affected by solvents have not been fully understood.Ultrasonic testing,nuclear magnetic resonance analysis,liquid phase mass spectrometry was adopted to comprehensively analyze pore-fracture change characteristics of lean coal treated by combined solvent(NMP and CS_(2)).Meanwhile,quantitative characterization of above changing properties was conducted using geometric fractal theory.Relationship model between permeability,fractal dimension and porosity were established.Results indicate that the end face fractures of coal are well developed after CS2and combined solvent treatments,of which,end face box-counting fractal dimensions range from 1.1227 to 1.4767.Maximum decreases in ultrasonic longitudinal wave velocity of coal affected by NMP,CS_(2)and combined solvent are 2.700%,20.521%,22.454%,respectively.Solvent treatments could lead to increasing amount of both mesopores and macropores.Decrease ratio of fractal dimension Dsis 0.259%–2.159%,while permeability increases ratio of NMR ranges from 0.1904 to 6.4486.Meanwhile,combined solvent could dissolve coal polar and non-polar small molecules and expand flow space.Results could provide reference for solvent selection and parameter optimization of permeability-enhancement technology.
基金financial support received from the Open Research Fund of the State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences (Grant No.Z019011)the Shandong Provincial Natural Science Foundation (Grant No.ZR2020QE112)+1 种基金the National Natural Science Foundation of China (No.51874273)the Excellent Young Scientists Fund Program of National Natural Science Foundation of China (No.52122403)。
文摘Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well water solution mining with oil as a cushion,engineering challenges arise with the leaching tubing,leading to issues like damage and instability.These problems significantly hinder the progress of cavern construction and the control of cavern shape.The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space,which results in severe bending or damage to the tubing.This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus.The experiment utilizes a silicone-rubber pipe(SRP)and a polycarbonate pipe(PCP)to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid.These factors include external space constraint,flexural rigidity,medium outside the pipe,overhanging length,and end conditions.The experiments reveal four dynamic response phenomena:water hammer,static buckling,chaotic motion,and flutter instability.The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid.Additionally,the flutter critical flow velocity is influenced by the end conditions and different external media.
文摘Crime scene investigation(CSI)image is key evidence carrier during criminal investiga-tion,in which CSI image retrieval can assist the public police to obtain criminal clues.Moreover,with the rapid development of deep learning,data-driven paradigm has become the mainstreammethod of CSI image feature extraction and representation,and in this process,datasets provideeffective support for CSI retrieval performance.However,there is a lack of systematic research onCSI image retrieval methods and datasets.Therefore,we present an overview of the existing worksabout one-class and multi-class CSI image retrieval based on deep learning.According to theresearch,based on their technical functionalities and implementation methods,CSI image retrievalis roughly classified into five categories:feature representation,metric learning,generative adversar-ial networks,autoencoder networks and attention networks.Furthermore,We analyzed the remain-ing challenges and discussed future work directions in this field.
文摘The combined microwave-convective drying is a novel drying method and has many advantages, such as swift drying, equable drying and sterilization. This paper studies the drying characteristic of medical pill in microwave-convective drying process. The influential parameters of pill drying characteristics including pill size, quality, air velocity, temperature and the input power of microwave, are experimentally investigated. Results show that the drying process is influenced by the intrinsic heat of microwave power, and the environment and the resistance of mass transfer. It has the advantage of the microwave-convective drying in saving energy, reducing labor intensity and sterilizing. The method with the high efficiency is suitable for pharmacy industry.
文摘Electrolytic Copper used in the shaped charge liner manufacturing can be produced from acid solution using electro-deposition technique. The intensity of the applied electric current controls the quality of the produced copper grade. The electric current intensity within the electrolytic acidic solution cell with the minimum oxygen and sulfur elements in the produced copper was optimized and found to be 30-40 A/Ft^2. The elemental composition of the obtained electrolytic copper was determined using highend stationary vacuum spectrometer, while the oxygen was determined precisely using ELTRA ONH-2000 apparatus. Besides, SEM was used to investigate the shape of the copper texture inside the deposited layers and to determine the average grain size. New relations have been obtained between the applied current intensity and both the oxygen and sulfur contents and the average grain size of the produced copper. Experimental result showed that when the applied current density increases to a certain limit, the oxygen and sulfur content in the electrolytic copper decreases. Performance of the produced copper liner was investigated by the static firing of a small caliber shaped charge containing an electro-formed copper liners, where the penetration depth of the optimized electrolytic liner was enhanced by 22.7% compared to that of baseline non-optimized liner.
文摘This study investigates the avoidance of relative clauses by high vocational college students and also explores the differences in the avoidance of the RCs by high-level students and low-level students in their English writings. The data used in this study have been collected from English writing tasks and analyzed by Statistical Package for Social Sciences(SPSS17.0). The major findings of this study are stated as follows: 1) There are significant differences in the production of the relative clauses in their English writings by Chinese higher vocational college students and English native speakers. Avoidance of relative clauses exists in the English writings of higher vocational college students. 2) High-level Chinese higher vocational college students display less of the avoidance phenomenon in their English writings than low-level students.
基金supported by the 2013 Fundamental Re-search Funds for the Central Universities of Xi’an Jiaotong UniversityThe Subject of Shaanxi Province Educational Science Twelveth-Five-Year Plan
文摘This study investigated the application and the effect of Group Investigation(GI) in the College English Program in a Chinese University. A qualitative case study method was used to understand the GI system used by Chinese instructors as well as the achievements acquired and challenges met by the participants. Three instructors and fifteen second-year-undergraduates taking a course titled Sources of European Culture participated. Interviews, observations, and documents were used to collect the data. Data analysis showed Chinese instructors applied a GI technique similar to that discussed by Johnson and Johnson(1999); however, GI in the Chinese context demanded more effort from the teacher for designing tasks and provided help in modeling uses of English and in preparing visual, especially Power Point, presentations. Although participants used their mother tongue at some stages, their autonomy over English learning was activated, and horizons in the course content were broadened.
文摘Business English Major is the key specialty in Jiangsu Maritime Institute.Grasping and understanding the situation of graduates is of very important meaning to the major construction and the personnel cultivating program.This article is mainly about the investigation and survey of graduate of 2011,and rational suggestions will be put forward on improving the quality of graduate and the major construction and the personnel cultivating program.
基金Projects 50709008 and 50539110 are supported by the National Natural Science Foundation of China.
文摘Based on laboratory results of time-dependent mechanical behavior tests,we investigated short-term and mechanical creep behavior of sandstone,observed in conventional triaxial compression experiments at room temperature,using a servo-controlled rheology testing machine.Given our short-term experimental test results,we confirmed deviatoric creep stress levels of sandstone.Multiple deviatoric stress levels were applied in steps to each sample.Each deviatoric stress level before the final failed deviatoric stress was maintained for 48 h or longer.Time-dependent variations of axial strains of sandstone samples are discussed and evaluated.During the creep tests,complete tertiary creep curves of sandstone were observed under failed deviatoric stress levels with different confining pressures.Slices of coal in sandstone samples can lead to distinct tertiary creep deformation failure.
文摘Objectives To investigate the overall prevalence of cardiovascular disease （CVD） in subjects hospitalized for chronic obstructive pulmonary disease （COPD）,and explore the prevalence of the major CVD complications and trends in patients with COPD over a 10-year period.Methods Medical records in the PLA General Hospital,Beijing Union Medical College Hospital,and Beijing Hospital from 2000/01/01 to 2010/03/03 were retrospectively reviewed.A total of 4960 patients with COPD were reviewed in the study （3570 males,mean age,72.2 ± 10.5 years; 1390 females,mean age,72.0 ± 10.4 years）.Results The prevalence of CVD in COPD patients was 51.7％.The three most prevalent CVDs were ischemic heart disease （28.9％）,heart failure （19.6％）,and arrhythmia （12.6％）.During the 10-year study period,the prevalence of various CVDs in COPD patients showed a gradual increasing trend with increasing age.There was higher morbidity due to ischemic heart disease （P ＜ 0.01） in male COPD patients than in the female counterparts.However,heart failure （P ＜ 0.01）and hypertension （P ＜ 0.01） occurred less frequently in male COPD patients than in female COPD patients.Furthermore,the prevalence of ischemic heart disease decreased year by year.In addition to heart failure,various types of CVD complications in COPD patients tended to occur in younger subjects.The prevalence of all major types of CVD in women tended to increase year by year.Conclusions The prevalence of CVD in patients hospitalized for COPD in Beijing was high.Age,sex and CVD trends,as well as life style changes,should be considered when prevention and control strategies are formulated.
基金support for this work,provided by the National Natural Science Foundation of China (No.50834005)
文摘Based on the particularities of gas outbursts,i.e.,low gas bearing capacity and low gas pressure in the "Three Soft" coal seam in western Henan,we applied the theories of plate tectonics and regional structural evolution to investigate the mechanism of this seam and its impact on the coal seam gas formation.Our investigation revealed that coal and gas outbursts are distributed in a strip in a NW direction,with a number of high-penetration mines scattered towards the south side and low-gas mines largely located on the north side.We analyzed the statistics of 38 gas explosions and the rock-coal sturdiness number coefficient f of 167 sampling sites in the region and found the gas outburst mechanism that features a "low indicator outburst phenomenon".The mechanism is characterized by structural coal as its core,a low gas bearing capacity,low gas pressure and sturdiness coefficient f mostly less than 0.3.Our research results provide a theoretical foundation for effective control of gas disasters.
文摘Experimental studies are carried out with slender bodies vertically exiting out of the water using a high-speed camera. The mechanisms for the formation, development, and collapse of the cavity around the slender body are explored. The dynamic characteristics of the shoulder cavity and the trail cavity during the water-exit of low-speed bodies are analyzed for various water depths and initial velocities. The results show that the initial velocity has a great influence on the formation, development, and collapse of the cavity. The length and the thickness of the shoulder cavity vary non-linearly with the depth.
文摘According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We present theoretical and experimental investigations into the flexural vibration transfer properties of a high-pressure periodic pipe with the force on the inner pipe wall by oii pressure taken into consideration. The results show that the vibration attenuation of periodic pipe decreases along with the elevation of working pressure for the hydraulic system, and the band gaps in low frequency ranges move towards high frequency ranges. The periodic pipe has good vibration attenuation performance in the frequency range below 1000 Hz and the vibration of the hydraulic system is effectively suppressed. A11 the results are validated by experiment. The experimental results show a good agreement with the numerical calculations, thus the flexural vibration transfer properties of the high- pressure periodic pipe can be precisely calculated by taking the fluid structure interaction between the pipe and oil into consideration. This study provides an effective way for the vibration control of the hydraulic system.
文摘Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out in a plane sand bed with two circular piers of same diameter arranged in tandem manner under no seepage, 10% seepage and 20% seepage conditions. Downward seepage minimizes the scour depth around piers and restrains the development of scour depth with time. Strong reversal flow is found near the bed at upstream of piers and near free surface at downstream of piers where velocity and Reynolds shear stress are found to be negative which reduce in magnitude with downward seepage. The flow is more critical within the gap between two piers where velocity is lesser near free surface and gradually increasing towards bed. Quadrant analysis shows that contribution of each event to the total Reynolds shear stress increases with downward seepage. Sedimentation effect prevails within the scour hole whereas outside the scour hole erosive forces become more dominant. Reduced reversal flow at upstream of pier because of downward seepage results in decreasing higher order moments and turbulent kinetic energy. At downstream of piers, secondary currents are dominant due to wake vortices. Strouhal number decreases in case of seepage runs than no seepage condition.
文摘The dynamic characteristics of a belt conveyor are determined to a large extent by the properties of the belt. This paper describes experiments designed to establish the dynamic properties of belting material. The dynamic elastic modulus, viscous damping and rheologicat constants of the belt were measured. Several properties were studied as a function of the tensile loading on the belt. These included longitudinal vibration, the natural vibration frequency in the transverse direction and the response to an impulse excitation. Vibration response was observed under several different excitation frequencies. Most of these properties have not been tested previously under conditions appropriate for the ISO/DP9856 standard. Two types of belt were tested, a steel reinforced belt and a fabric reinforced belt. The test equipment was built to provide data appropriate for designing belt conveyors. It was observed that the stress wave propagation speed increased with tensile load and that tensile load was the main factor influencing longitudinal vibrations.
基金supported by the Shanghai Nuclear Engineering Research and Design Institute,State Power Investment Corporation
文摘The transient performance and optimization of a passive residual heat removal heat exchanger(PRHR HX)were investigated.First,a calculation method was developed for predicting the heat transfer of the PRHR HX.The calculation results were validated through comparisons with ROSA experimental data.The heat-transfer performance of the AP1000 PRHR HX in the initial period was predicted,and it satisfied the design requirements.Second,the distributions of the heat flux,tube-inside/outside heattransfer coefficients,and heat load for the AP1000 PRHR HX over 2000 s were examined.Third,an optimization study was conducted by adjusting the horizontal length and tube diameter.Their effects on the four main heat-transfer parameters and the heat-transfer area were analyzed.Furthermore,the influence of the initial in-containment refueling water storage tank(IRWST)temperature was investigated using an established simulation procedure.The results indicated that it significantly affected the trends of the IRWST temperature and reactor outlet temperature.Finally,the minimum required flow rates over time to maintain the reactor outlet temperature at the safety line were determined for different start-up times.The trends of the minimum required flow rate and the peak flow rate were analyzed.
文摘Careful and thorough incident investigations and pre-job safety analyses completed by knowledgeable and competent individuals can significantly reduce workplace incidents. Working parties must act together to make these safety tools effective. To get the staff units to work together in a co-ordinated manner, they must be shown the value of their work in preventing accidents. Examples of actual accidents investigated during the author's 18 years as a mine inspector in Saskatchewan are discussed within the context of pre-job safety analyses. The causes of the accidents are explored with close reference to how pre-job safety analyses could have prevented their occurrence.
基金supported by the National Natural Science Foundation of China(No.51276088)
文摘The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.
