Mg-6 Al-1 Zn-xFe（x = 0,1,3,5 and 7 wt%）alloys were prepared by powder metallurgy and followed by hot extrusion.Majority of Fe element exists as insoluble particles in the alloys.The as-extruded alloys showed higher ...Mg-6 Al-1 Zn-xFe（x = 0,1,3,5 and 7 wt%）alloys were prepared by powder metallurgy and followed by hot extrusion.Majority of Fe element exists as insoluble particles in the alloys.The as-extruded alloys showed higher degradable rates but less stable mechanical properties than as-annealed alloys.Corrosion rate of all the alloys increased with increasing Fe concentration,reaching 2.4 mL cm-2h-1.0.2% yield strength of all the alloys was higher than 150 MPa.In short,Mg-6 Al-1 Zn-xFe alloys have an attractive combination of corrosion and mechanical properties,which holds a bright future for fracturing balls applications.展开更多
The effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron （CADI） grinding balls were systematically investigated in this work. The microstructures we...The effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron （CADI） grinding balls were systematically investigated in this work. The microstructures were oberserved by optical metallography and analyized by X-ray diffraction. The surface residual stress measured by the cutting method is mainly composed of thermal stress and phase transformation stress.The thermal stress in grinding balls was determined by ANSYS simulation technique, and the surface phase transformation stress was obtained by subtracting the simulated surface thermal stress from the measured surface residual stress. Results show that all microstructures consist of ausferrite, white-bright zones （mixture of martensite and austenite）, nodular graphite, and carbides. The distribution of ausferrite shows uniform. With the increase of austempering temperature, the volume fraction and carbon content of austenite increase, whereas the amount of white-bright zone decreases. In addition, the surface residual stress increases with the increase of austempering temperature. Only the tension exists at the austempering temperature of 200 ℃, and the pressure exists at the austempering temperature of 220-260 °C. The thermal stress changes from the tension on the inside with the radius of 0-35 mm to the pressure on the outside with the radius of 35-62.5 mm, and the stress balance state presents at the radius of 35 mm. It is also found that the transformation stress is related to the content of carbon-rich austenite, and will reduce by 5.03 MPa accompanied with 1vol.% increase of the austenite.The thermal compressive stress and the transformation tensile stress on the surface both decrease with the increase of the austempering temperature.展开更多
Ordered mesoporous aluminosilicate Al-SBA-15 materials with cage-like macropores have been synthesized by using micrometer-sized aluminum balls as an Al source,tetraethyl orthosilicate(TEOS) as a silica source,and tri...Ordered mesoporous aluminosilicate Al-SBA-15 materials with cage-like macropores have been synthesized by using micrometer-sized aluminum balls as an Al source,tetraethyl orthosilicate(TEOS) as a silica source,and triblock copolymer Pluronic P123 as a template.The resulting materials were fully characterized by XRD,N2 adsorption,SEM,TEM,ICP-AES,and 27Al MAS-NMR.The products(Al-SBA-15) have ordered two-dimensional(2-D) hexagonal mesostructures(space group p6mm).The calcined Al-SBA-15 materials exhibit disordered macropores with diameters of about 70―80 nm and ordered mesopores with a diameter of ～5 nm,a BET surface area of about 500 m2/g,Si/Al ratio of 40―80,and a ratio of tetrahedral Al to octahedral Al sites of about 2:1.This combination of properties gives these materials potential applications in areas such as adsorption,catalysis and separation.展开更多
For the process of point cloud registration,and the problem of inaccurate registration due to errors in correspondence between keypoints.In this paper,a registration method based on calibration balls was proposed,the ...For the process of point cloud registration,and the problem of inaccurate registration due to errors in correspondence between keypoints.In this paper,a registration method based on calibration balls was proposed,the trunk,branch,and crown were selected as experimental objects,and three calibration balls were randomly placed around the experimental objects to ensure different distances between two ball centers.Using the Kinect V2 depth camera to collect the point cloud of the experimental scene from four different viewpoints,the PassThrough filter algorithm was used for point cloud filtering in each view of the experimental scenes.The Euclidean cluster extraction algorithm was employed for point cloud clustering and segmentation to extract the experimental object and the calibration ball.The random sample consensus(RANSAC)algorithm was applied to fit the point cloud of a ball and calculate the coordinates of the ball center so that the distance between two ball centers under different viewpoints can be obtained by using the coordinates of the ball center.Comparing the distance between the ball centers from different viewpoints to determine the corresponding relationship between the ball centers from different viewpoints,and then using the singular value decomposition(SVD)method,the initial registration matrix was obtained.Finally,Iterative Closest Point(ICP)and its improved algorithm were used for accurate registration.The experimental results showed that the method of point cloud registration based on calibration balls can solve the problem of corresponding error of keypoints,and can register point clouds from different viewpoints of the same object.The registration method was evaluated by using the registration running time and the fitness score.The final registration running time of different experimental objects was not more than 6.5 s.The minimum fitness score of the trunk was approximately 0.0001,the minimum fitness score of the branch was approximately 0.0001,and the minimum fitness score of the crown was 展开更多
For domains composed by balls in C^n, this paper studies the boundary behaviour of Cauchy type integrals with discrete holomorphic kernels and the corresponding linear singular integral equation on each piece of smoot...For domains composed by balls in C^n, this paper studies the boundary behaviour of Cauchy type integrals with discrete holomorphic kernels and the corresponding linear singular integral equation on each piece of smooth lower dimensional edges on the boundary of the domain.展开更多
Rational proper holomorphic maps from the unit ball in C2 into the unit ball CN with degree 2 are studied. Any such map must be equivalent to one of the four types of maps.
<正> The distributions of the sojourn time of a ball and hitting time for a sphere for Brownian motion starting at any point in space, as well as the joint distributions of the maximum excursion before last exit...<正> The distributions of the sojourn time of a ball and hitting time for a sphere for Brownian motion starting at any point in space, as well as the joint distributions of the maximum excursion before last exit sphere and first instance of attaining such a maximum for Brownian motion starting at the inside of a ball are given.展开更多
Ordered macroporous titania photonic crystals （PCs） and photonic balls were fabricated by functional modified polymer colloidal crystals. The TiO2 PCs and balls formed through this method exhibit no cracks and lacun...Ordered macroporous titania photonic crystals （PCs） and photonic balls were fabricated by functional modified polymer colloidal crystals. The TiO2 PCs and balls formed through this method exhibit no cracks and lacunae in large areas on their surface and their inner structures.展开更多
BACKGROUND The incidence of ingestion of magnetic foreign bodies in the gastrointestinal tract has been increasing year by year.Due to their strong magnetic attraction,if multiple gastrointestinal foreign bodies enter...BACKGROUND The incidence of ingestion of magnetic foreign bodies in the gastrointestinal tract has been increasing year by year.Due to their strong magnetic attraction,if multiple gastrointestinal foreign bodies enter the small intestine,it can lead to serious complications such as intestinal perforation,necrosis,torsion,and bleeding.Severe cases require surgical intervention.CASE SUMMARY We report a 6-year-old child who accidentally swallowed multiple magnetic balls.Under timely and safe anesthesia,the magnetic balls were quickly removed through gastroscopy before entering the small intestine.CONCLUSION General anesthesia with endotracheal intubation can ensure full anesthesia under the condition of fasting for less than 6 h.In order to prevent magnetic foreign bodies from entering the small intestine,timely and effective measures must be taken to remove the foreign bodies.展开更多
In Euclidean geometry, for a real submanifold M in E n+a , M is a piece of E n if and only if its second fundamental form is identically zero. In projective geometry, for a complex submanifold M in CP n+a , M is a pie...In Euclidean geometry, for a real submanifold M in E n+a , M is a piece of E n if and only if its second fundamental form is identically zero. In projective geometry, for a complex submanifold M in CP n+a , M is a piece of CP n if and only if its projective second fundamental form is identically zero. In CR geometry, we prove the CR analogue of this fact in this paper.展开更多
Biliary obstructions can lead to infections of the biliary system, particularly in patients with occluded biliary stents. Fungal organisms are frequently found in bili-ary aspirates of patients who have been on antibi...Biliary obstructions can lead to infections of the biliary system, particularly in patients with occluded biliary stents. Fungal organisms are frequently found in bili-ary aspirates of patients who have been on antibiotics and have stents; however, fungal masses, or "balls", that fully obstruct the biliary system are uncommon and exceedingly diff icult to eradicate. We present 4 cases of obstructing fungal cholangitis in patients who had metal biliary stents placed for pancreatic malignancies, and subsequently required aggressive antifungal administration along with endoscopic and radiologic interventions. This report also reviews approaches previously undertaken to manage severe obstructing fungal cholangitis.展开更多
The shaping quality of green ceramic balls is directly related to the efficiency and cost of later machining for the ceramic balls. Until now the shaping for green ceramic balls is still conducted by handwork. In this...The shaping quality of green ceramic balls is directly related to the efficiency and cost of later machining for the ceramic balls. Until now the shaping for green ceramic balls is still conducted by handwork. In this paper, a new shaping model for green ceramic balls was designed. In the new model, two grinding wheels with the same generator line as circular arc are mounted on symmetry, and their axes are parallel. The green ball can be put in the enveloping space formed by the two grinding wheels. The radius of generator line must be equal to or slightly greater than the final radius of the green balls, which can ensure that an ideal sphere can be enveloped by the generator of grinding wheel as grinding the green body surface with the wheels. One of the two wheels rotates in upward direction at high speed v 1, conversely, the other wheel rotates in downward direction at low speed v 2, and a cluster of compressed air is exerted on the green ball above for canceling out the force acting upon the green ball created by the action of the grinding wheel revolving at high speed and avoiding that the green ball jumps off its station. Because of the randomness of the distributions of abrasive grains on the surface of grinding wheels, the size and shape of the abrasive grains, and the posture of green body when falling into the grinding space, the values and directions of the resultant forces and torques exerted on the body, caused by the tow wheels, are random, the rotation of green body is irregular under the actions of the compressed air and the wheels. The irregularity of rotation can ensure an ideal sphere in theory. Experiment researches indicate that the new shaping model can improve the spherical deviations and the size distribution of the green ceramic balls, raise the production, and reduce the costs. The spherical deviations can be improved to 0.04 mm easily. It can be observed by SEM that there is no crack in the surface of sintered ceramic balls shaped with the new model in green blank.展开更多
基金supported by project of the National Natural Science Foundation of China (51671041, 51701029 and 51531002)the National Key Research and Development Program of China (2016YFB0301100)+2 种基金the Fundamental Research Funds for the Central Universities (106112016CDJXZ138811 and 2018CDGFCL005)the China Postdoctoral Science Foundation Funded Project (2017M620410 and 2018T110942)the Chongqing Postdoctoral Scientific Research Foundation (Xm2017010)
文摘Mg-6 Al-1 Zn-xFe（x = 0,1,3,5 and 7 wt%）alloys were prepared by powder metallurgy and followed by hot extrusion.Majority of Fe element exists as insoluble particles in the alloys.The as-extruded alloys showed higher degradable rates but less stable mechanical properties than as-annealed alloys.Corrosion rate of all the alloys increased with increasing Fe concentration,reaching 2.4 mL cm-2h-1.0.2% yield strength of all the alloys was higher than 150 MPa.In short,Mg-6 Al-1 Zn-xFe alloys have an attractive combination of corrosion and mechanical properties,which holds a bright future for fracturing balls applications.
基金financially supported by the National Natural Science Foundation of China(NSFC)(Grant No.51601054)the Natural Science Foundation of Hebei Province of China(Grant Nos.E2017202095 and E2016202100)+1 种基金the Plan Program for International S&T Cooperation Projects of Hebei Province of China(Grant No.17391004D)the Tianjin Science and Technology Support Program(Grant No.16YFZCGX00140)
文摘The effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron （CADI） grinding balls were systematically investigated in this work. The microstructures were oberserved by optical metallography and analyized by X-ray diffraction. The surface residual stress measured by the cutting method is mainly composed of thermal stress and phase transformation stress.The thermal stress in grinding balls was determined by ANSYS simulation technique, and the surface phase transformation stress was obtained by subtracting the simulated surface thermal stress from the measured surface residual stress. Results show that all microstructures consist of ausferrite, white-bright zones （mixture of martensite and austenite）, nodular graphite, and carbides. The distribution of ausferrite shows uniform. With the increase of austempering temperature, the volume fraction and carbon content of austenite increase, whereas the amount of white-bright zone decreases. In addition, the surface residual stress increases with the increase of austempering temperature. Only the tension exists at the austempering temperature of 200 ℃, and the pressure exists at the austempering temperature of 220-260 °C. The thermal stress changes from the tension on the inside with the radius of 0-35 mm to the pressure on the outside with the radius of 35-62.5 mm, and the stress balance state presents at the radius of 35 mm. It is also found that the transformation stress is related to the content of carbon-rich austenite, and will reduce by 5.03 MPa accompanied with 1vol.% increase of the austenite.The thermal compressive stress and the transformation tensile stress on the surface both decrease with the increase of the austempering temperature.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 20890123 & 20721063)Shanghai Science & Technology Committee (08DZ2270500)Shanghai Leading Academic Discipline Project (No.B108)
文摘Ordered mesoporous aluminosilicate Al-SBA-15 materials with cage-like macropores have been synthesized by using micrometer-sized aluminum balls as an Al source,tetraethyl orthosilicate(TEOS) as a silica source,and triblock copolymer Pluronic P123 as a template.The resulting materials were fully characterized by XRD,N2 adsorption,SEM,TEM,ICP-AES,and 27Al MAS-NMR.The products(Al-SBA-15) have ordered two-dimensional(2-D) hexagonal mesostructures(space group p6mm).The calcined Al-SBA-15 materials exhibit disordered macropores with diameters of about 70―80 nm and ordered mesopores with a diameter of ～5 nm,a BET surface area of about 500 m2/g,Si/Al ratio of 40―80,and a ratio of tetrahedral Al to octahedral Al sites of about 2:1.This combination of properties gives these materials potential applications in areas such as adsorption,catalysis and separation.
基金This research was funded by the National Key R&D Program of China(Grant No.2018YFD0700601)and the National Natural Science Foundation of China(Grant No.31600588).
文摘For the process of point cloud registration,and the problem of inaccurate registration due to errors in correspondence between keypoints.In this paper,a registration method based on calibration balls was proposed,the trunk,branch,and crown were selected as experimental objects,and three calibration balls were randomly placed around the experimental objects to ensure different distances between two ball centers.Using the Kinect V2 depth camera to collect the point cloud of the experimental scene from four different viewpoints,the PassThrough filter algorithm was used for point cloud filtering in each view of the experimental scenes.The Euclidean cluster extraction algorithm was employed for point cloud clustering and segmentation to extract the experimental object and the calibration ball.The random sample consensus(RANSAC)algorithm was applied to fit the point cloud of a ball and calculate the coordinates of the ball center so that the distance between two ball centers under different viewpoints can be obtained by using the coordinates of the ball center.Comparing the distance between the ball centers from different viewpoints to determine the corresponding relationship between the ball centers from different viewpoints,and then using the singular value decomposition(SVD)method,the initial registration matrix was obtained.Finally,Iterative Closest Point(ICP)and its improved algorithm were used for accurate registration.The experimental results showed that the method of point cloud registration based on calibration balls can solve the problem of corresponding error of keypoints,and can register point clouds from different viewpoints of the same object.The registration method was evaluated by using the registration running time and the fitness score.The final registration running time of different experimental objects was not more than 6.5 s.The minimum fitness score of the trunk was approximately 0.0001,the minimum fitness score of the branch was approximately 0.0001,and the minimum fitness score of the crown was
基金Project supported by the National Science Foundation of China (10271097)
文摘For domains composed by balls in C^n, this paper studies the boundary behaviour of Cauchy type integrals with discrete holomorphic kernels and the corresponding linear singular integral equation on each piece of smooth lower dimensional edges on the boundary of the domain.
基金The first author in supported by National Natural Science Foundation of China (Grant No. 10571135).
文摘Rational proper holomorphic maps from the unit ball in C2 into the unit ball CN with degree 2 are studied. Any such map must be equivalent to one of the four types of maps.
基金supported by the Chinese Tian Yuan Mathematical Foundation the Doctoral Discipline Foundation of State Education Commission of China.
文摘<正> The distributions of the sojourn time of a ball and hitting time for a sphere for Brownian motion starting at any point in space, as well as the joint distributions of the maximum excursion before last exit sphere and first instance of attaining such a maximum for Brownian motion starting at the inside of a ball are given.
基金This work was financially supported by the Beijing Foundation of Natural Science, China(No. Z012013).
文摘Ordered macroporous titania photonic crystals （PCs） and photonic balls were fabricated by functional modified polymer colloidal crystals. The TiO2 PCs and balls formed through this method exhibit no cracks and lacunae in large areas on their surface and their inner structures.
文摘BACKGROUND The incidence of ingestion of magnetic foreign bodies in the gastrointestinal tract has been increasing year by year.Due to their strong magnetic attraction,if multiple gastrointestinal foreign bodies enter the small intestine,it can lead to serious complications such as intestinal perforation,necrosis,torsion,and bleeding.Severe cases require surgical intervention.CASE SUMMARY We report a 6-year-old child who accidentally swallowed multiple magnetic balls.Under timely and safe anesthesia,the magnetic balls were quickly removed through gastroscopy before entering the small intestine.CONCLUSION General anesthesia with endotracheal intubation can ensure full anesthesia under the condition of fasting for less than 6 h.In order to prevent magnetic foreign bodies from entering the small intestine,timely and effective measures must be taken to remove the foreign bodies.
文摘In Euclidean geometry, for a real submanifold M in E n+a , M is a piece of E n if and only if its second fundamental form is identically zero. In projective geometry, for a complex submanifold M in CP n+a , M is a piece of CP n if and only if its projective second fundamental form is identically zero. In CR geometry, we prove the CR analogue of this fact in this paper.
文摘Biliary obstructions can lead to infections of the biliary system, particularly in patients with occluded biliary stents. Fungal organisms are frequently found in bili-ary aspirates of patients who have been on antibiotics and have stents; however, fungal masses, or "balls", that fully obstruct the biliary system are uncommon and exceedingly diff icult to eradicate. We present 4 cases of obstructing fungal cholangitis in patients who had metal biliary stents placed for pancreatic malignancies, and subsequently required aggressive antifungal administration along with endoscopic and radiologic interventions. This report also reviews approaches previously undertaken to manage severe obstructing fungal cholangitis.
文摘The shaping quality of green ceramic balls is directly related to the efficiency and cost of later machining for the ceramic balls. Until now the shaping for green ceramic balls is still conducted by handwork. In this paper, a new shaping model for green ceramic balls was designed. In the new model, two grinding wheels with the same generator line as circular arc are mounted on symmetry, and their axes are parallel. The green ball can be put in the enveloping space formed by the two grinding wheels. The radius of generator line must be equal to or slightly greater than the final radius of the green balls, which can ensure that an ideal sphere can be enveloped by the generator of grinding wheel as grinding the green body surface with the wheels. One of the two wheels rotates in upward direction at high speed v 1, conversely, the other wheel rotates in downward direction at low speed v 2, and a cluster of compressed air is exerted on the green ball above for canceling out the force acting upon the green ball created by the action of the grinding wheel revolving at high speed and avoiding that the green ball jumps off its station. Because of the randomness of the distributions of abrasive grains on the surface of grinding wheels, the size and shape of the abrasive grains, and the posture of green body when falling into the grinding space, the values and directions of the resultant forces and torques exerted on the body, caused by the tow wheels, are random, the rotation of green body is irregular under the actions of the compressed air and the wheels. The irregularity of rotation can ensure an ideal sphere in theory. Experiment researches indicate that the new shaping model can improve the spherical deviations and the size distribution of the green ceramic balls, raise the production, and reduce the costs. The spherical deviations can be improved to 0.04 mm easily. It can be observed by SEM that there is no crack in the surface of sintered ceramic balls shaped with the new model in green blank.
