The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research...The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research and analysis of remolding deep soil described herein indicate that the static earth pressure of thick overburden has a notable non lin-ear characteristic. It also appears larger than that of superficial soils. It is necessary for deep coal mine design and con-struction to consider this particularity of soil pressure so as to avoid engineering accidents and heavy loss of life and property.展开更多
In order to improve the cutting stiffness,the paper studies the vertical hydrostatic bearing in the slide when a ram is in feed process.The change of the oil film thickness on hydrostatic guide rail and the curve of t...In order to improve the cutting stiffness,the paper studies the vertical hydrostatic bearing in the slide when a ram is in feed process.The change of the oil film thickness on hydrostatic guide rail and the curve of the oil film thickness in various cutting forces are calculated and a relation model through theoretical analysis method is derived.The pressure field of the guide rail recess is simulated based on the finite volume method and demonstrated through experiments.The study is of vital theoretical significance for the improvement of machining accuracy of numerical control machines and the entire computer numerical control(CNC) equipment and provides valuable theoretical basis for the design of hydrostatic guide rail in engineering practice.展开更多
AIM: To investigate the oxidative-stress-related changes in rats with portal hypertension with particular emphasis on nitric oxide (NO) and trace metals. METHODS: Cirrhosis was induced by partial portal vein ligation ...AIM: To investigate the oxidative-stress-related changes in rats with portal hypertension with particular emphasis on nitric oxide (NO) and trace metals. METHODS: Cirrhosis was induced by partial portal vein ligation (PVL) in Wistar rats. The lipid peroxidation marker (malondialdehyde, MDA), antioxidant defense enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and agents known to have antioxidant features including nitric oxide (NO), zinc (Zn), copper (Cu) were determined both in serum and in liver tissue at 4 wk after surgery in PVL and sham-operated rats. Portal pressure of all experimental animals was measured. MDA was detected by thiobarbituric acid reactivity assay.SOD activity was determined by inhibition of nitroblue tetrazolium reduction with xanthine/xanthine oxidase used asa superoxide generator. CAT activity was determined by the breakdown of hydrogen peroxide. GSH concentrations were measured by using metaphosphoric acid for protein precipitation and 5'-5'-dithio-bis-2-nitrobenzoic acid for color development. NO was detected by the Griess method after reduction of nitrate to nitrite with nitrate reductase, and the concentrations of Zn and Cu were measured by a Shimadzu 680 AA atomic absorption spectrometer. Histopathological confirmation was done under light microscope. Statistical analyses were done by Student's t-test, and significance of the difference was tested by the unpaired Mann-Whitney test. P＜0.05 was considered statistically significant.RESULTS: Histopathological studies confirmed PVL induced cirrhotic changes. There was a statistically significant difference in portal pressure between PVL and control groups (P＜0.001). The results showed significant increases in the levels of MDA and NO in both tissue and serum (P＜0.05 and P＜0.001, respectively in tissue; P＜0.001 for each in serum), and Zn only in tissue (P＜0.001)in rats with PVL compared with sham-operated rats. Besides, PVL rats exhibited reduced plasma and tissue GSH, CAT, SOD (P＜0.001 for each). Serum and tissue Cu concentration did not change.CONCLUSION: Our findings suggest that PVL in rats induces important biochemical and molecular changes related to oxidative stress in the liver.展开更多
A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program o...A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing. The effects of key lubrication parameters of the hydrostatic bearing are evaluated and analyzed under various working conditions,i.e. under no-load,a load of 40 t,a full load of 160 t,and the rotation speed of 1r/min,2r/min,4r/min,8r/min,16r/min,32r/min. The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing. It allows the effective prediction of dynamic performance of large size hydrostatic bearing. Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model. The results showed that the oil film thickness became thinner with the increase of the operating time of the hydrostatic bearing,both the oil film rigidity and the oil cavity pressure increased significantly,and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness. Meanwhile,the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition. The error between the simulation value and the experimental value was 4.25%.展开更多
The volute of a centrifugal compressor causes a non-uniform pressure distribution which leads to a radial force on the impeller. This force was measured using magnetic bearings. In addition, the radial force was estim...The volute of a centrifugal compressor causes a non-uniform pressure distribution which leads to a radial force on the impeller. This force was measured using magnetic bearings. In addition, the radial force was estimated using the static pressure distribution measured at the impeller outlet. The impeller force was found to be the highest at choke, the lowest at the design flow and moderate at stall. The radial force determined from the pressure measurements was only slightly different from the force obtained from the bearing measurements. The rotational speed was seen to affect the force to some extent.展开更多
基金Project 50534040 supported by the National Natrual Science Foundation of China
文摘The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research and analysis of remolding deep soil described herein indicate that the static earth pressure of thick overburden has a notable non lin-ear characteristic. It also appears larger than that of superficial soils. It is necessary for deep coal mine design and con-struction to consider this particularity of soil pressure so as to avoid engineering accidents and heavy loss of life and property.
基金Supported by the National Natural Science Funds for Young Scholar of China(No.51005063)the Science and Technology Innovation People of Harbin(No.2013RFQXJ086)+1 种基金Heilongjiang Postdoctoral Foundation(No.LBH-Q12062)the National Natural Science Foundation of China(No.51075106)
文摘In order to improve the cutting stiffness,the paper studies the vertical hydrostatic bearing in the slide when a ram is in feed process.The change of the oil film thickness on hydrostatic guide rail and the curve of the oil film thickness in various cutting forces are calculated and a relation model through theoretical analysis method is derived.The pressure field of the guide rail recess is simulated based on the finite volume method and demonstrated through experiments.The study is of vital theoretical significance for the improvement of machining accuracy of numerical control machines and the entire computer numerical control(CNC) equipment and provides valuable theoretical basis for the design of hydrostatic guide rail in engineering practice.
文摘AIM: To investigate the oxidative-stress-related changes in rats with portal hypertension with particular emphasis on nitric oxide (NO) and trace metals. METHODS: Cirrhosis was induced by partial portal vein ligation (PVL) in Wistar rats. The lipid peroxidation marker (malondialdehyde, MDA), antioxidant defense enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and agents known to have antioxidant features including nitric oxide (NO), zinc (Zn), copper (Cu) were determined both in serum and in liver tissue at 4 wk after surgery in PVL and sham-operated rats. Portal pressure of all experimental animals was measured. MDA was detected by thiobarbituric acid reactivity assay.SOD activity was determined by inhibition of nitroblue tetrazolium reduction with xanthine/xanthine oxidase used asa superoxide generator. CAT activity was determined by the breakdown of hydrogen peroxide. GSH concentrations were measured by using metaphosphoric acid for protein precipitation and 5'-5'-dithio-bis-2-nitrobenzoic acid for color development. NO was detected by the Griess method after reduction of nitrate to nitrite with nitrate reductase, and the concentrations of Zn and Cu were measured by a Shimadzu 680 AA atomic absorption spectrometer. Histopathological confirmation was done under light microscope. Statistical analyses were done by Student's t-test, and significance of the difference was tested by the unpaired Mann-Whitney test. P＜0.05 was considered statistically significant.RESULTS: Histopathological studies confirmed PVL induced cirrhotic changes. There was a statistically significant difference in portal pressure between PVL and control groups (P＜0.001). The results showed significant increases in the levels of MDA and NO in both tissue and serum (P＜0.05 and P＜0.001, respectively in tissue; P＜0.001 for each in serum), and Zn only in tissue (P＜0.001)in rats with PVL compared with sham-operated rats. Besides, PVL rats exhibited reduced plasma and tissue GSH, CAT, SOD (P＜0.001 for each). Serum and tissue Cu concentration did not change.CONCLUSION: Our findings suggest that PVL in rats induces important biochemical and molecular changes related to oxidative stress in the liver.
基金Supported by the National Natural Science Foundation of China(No.51005063,51375123)National Science and Technology Cooperation Projects of China(No.2012DFR70840)
文摘A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing. The effects of key lubrication parameters of the hydrostatic bearing are evaluated and analyzed under various working conditions,i.e. under no-load,a load of 40 t,a full load of 160 t,and the rotation speed of 1r/min,2r/min,4r/min,8r/min,16r/min,32r/min. The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing. It allows the effective prediction of dynamic performance of large size hydrostatic bearing. Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model. The results showed that the oil film thickness became thinner with the increase of the operating time of the hydrostatic bearing,both the oil film rigidity and the oil cavity pressure increased significantly,and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness. Meanwhile,the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition. The error between the simulation value and the experimental value was 4.25%.
文摘The volute of a centrifugal compressor causes a non-uniform pressure distribution which leads to a radial force on the impeller. This force was measured using magnetic bearings. In addition, the radial force was estimated using the static pressure distribution measured at the impeller outlet. The impeller force was found to be the highest at choke, the lowest at the design flow and moderate at stall. The radial force determined from the pressure measurements was only slightly different from the force obtained from the bearing measurements. The rotational speed was seen to affect the force to some extent.
