Impact testing is a primary method to evaluate the impact property of resistance spot welding,which is an important quality index in automotive industry.For testing impact properties of spot welds,many customized test...Impact testing is a primary method to evaluate the impact property of resistance spot welding,which is an important quality index in automotive industry.For testing impact properties of spot welds,many customized testers have been developed.This paper summarized some of the impact testers reported in open literatures and the emphasis was placed on the equipment structures,functions,technical parameters,advantages and disadvantage,etc.Some key issues about the development of the testers such as kinematic energy input mode,fixture design,combined load testing,sensor and data acquisition were discussed.Finally,the problems and prospects in the research and development of impact testers for spot welds were pointed out.展开更多
This study gives a comparison between what occurs when braking on a MOT （Ministry of Transport） brake tester. The results from this research and the exhaustive comparative study carried out by the mechanical enginee...This study gives a comparison between what occurs when braking on a MOT （Ministry of Transport） brake tester. The results from this research and the exhaustive comparative study carried out by the mechanical engineering staffs at the mechanical laboratory at MOT stations in cities such as： Elche, Pilar de la Horadada and Orihuela from Alicante region [2] have led to the following main conclusions： this paper demonstrates that MOT brake testing results can vary depending on parameters variation such as： distance between rollers, roller diameter, roughness of rollers and velocity of the brake test.展开更多
With the rapid development of silicon chip tech-nology,web-based instruction(WBI)and computer-ized adaptive testing(CAT)will be the new trends inthe field of language teaching and testing.We assumethat only when teach...With the rapid development of silicon chip tech-nology,web-based instruction(WBI)and computer-ized adaptive testing(CAT)will be the new trends inthe field of language teaching and testing.We assumethat only when teaching and testing share the sameview about the nature of language and language learn-ing can testing exercise a beneficial backwash effect onteaching.However,WBI and CAT prove to be basedon opposite theories of language and language learn-ing.While WBI believes in constructivism,CAT cor-responds to structuralism and behaviorism.This situ-ation places language testers in a dilemma,for if theyfollow the trend,testing will go against teaching.Butif they give up CAT,it is very difficult to substituteanother testing system possessing so many advantages.This paper illustrates in detail why WBI and CAT areto become the new trends in teaching and testing,ex-plains clearly the discrepancy between WBI and CAT intheory and their objectives and finally attempts toprovide a solution to help the language testers out ofthe dilemma.展开更多
In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci poi...In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the ]enike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.展开更多
To determine the fracture characteristics of asphalt mixture a novel fracture test with modified loading modes loading fixtures and the control system of the conventional overlay tester is implemented by the asphalt m...To determine the fracture characteristics of asphalt mixture a novel fracture test with modified loading modes loading fixtures and the control system of the conventional overlay tester is implemented by the asphalt material performance tester AMPT .In order to evaluate the validity of the proposed fracture test four different loading rates including 1 2 3 and 4 mm/min are examined in the AMPT. The results indicate that the fracture behavior is similar to creep at a low loading rate and does not show significant marginal tail extension at a high loading rate.It clearly shows the phase of crack initiation crack propagation and fracture at a loading rate of 3 mm/min. Besides eight fracture parameters such as fracture energy tensile strength and tensile modulus are applied to evaluate the fracture characteristics of asphalt mixture.Development of the overlay tester for the fracture test of asphalt mixture can be considered as a new fracture test of asphalt mixture.展开更多
AIM To describe the characteristics of people diagnosed with acute and chronic hepatitis B virus(HBV) infection in British Columbia(BC).METHODS We used data from the BC Hepatitis Testers Cohort(BCHTC),which includes a...AIM To describe the characteristics of people diagnosed with acute and chronic hepatitis B virus(HBV) infection in British Columbia(BC).METHODS We used data from the BC Hepatitis Testers Cohort(BCHTC),which includes all individuals tested for hepatitis C virus(HCV) or human immunodeficiency virus(HIV) or those diagnosed with HBV or active tuberculosis in BC since 1990.These data were integrated with prescription drug,medical visit,hospitalization and mortality data.HBV cases were classified as acute or chronic according to provincial guidelines.We compared characteristics of individuals by HBV infection group(acute,chronic and negative).Factors associated with acute or chronic HBV infection were assessed with multinomial logistic regression models in comparison to the HBV negative group.RESULTS46498 of the 1058056 eligible BC-HTC participants were diagnosed with HBV infection.4.3% of HBV positive individuals were diagnosed with acute HBV infections while 95.7% had chronic infections.Problematic alcohol use,injection drug use,and HIV or HCV co-infection were more common among individuals diagnosed with acute HBV compared to those with chronic infections and HBV negative individuals.In multivariable multinomial logistic regression models,we observed significant associations between acute or chronic HBV diagnosis and being male,age at HBV diagnosis or birth cohort,South and East Asian ethnicity,HCV or HIV infection,and injection drug use.The odds of acute HBV decreased with increasing age among people who inject drugs,while the opposite was true for chronic HBV.Persons with acute HBV were predominantly White(78%) while those with chronic HBV were mostly East Asian(60%).Relative to Whites,East Asians had 12 times greater odds of being diagnosed with chronic HBV infection.These odds increased with increasing socioeconomic deprivation.CONCLUSION Differences in the profiles of people diagnosed with acute and chronic HBV infection necessitate differentiated screening,prevention,care and treatment programs.展开更多
The purpose of this study was to investigate the diversity of 14 popcorn populations and a broad genetic base tester using molecular RAPD markers and to estimate the correlation between the genetic distances and the p...The purpose of this study was to investigate the diversity of 14 popcorn populations and a broad genetic base tester using molecular RAPD markers and to estimate the correlation between the genetic distances and the performance of top-cross hybrids. For the evaluation of populations and hybrids resulting from topcrosses, the reduced model of Gardner was used. A genetic distance matrix was generated based on RAPD markers by Jaccard coefficient, and a dendrogram was constructed. In general, topcrosses performed better than the populations per se and evidenced heterosis occurrence in topcrosses. The trait grain weight is influenced by additive as much as by dominance effects. Genetic associations separated the populations in three groups, and RAPD showed to be a useful tool to determine the extension of genetic diversity in popcorn populations and to place genotypes in distinct heterotic groups. Correlations between genetic divergences, detected by RAPD, and the means observed in the topcross crosses were positive and non-significant for expansion volume, plant height, and female flowering, and were negative for grain weight.展开更多
Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. On...Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.展开更多
文摘Impact testing is a primary method to evaluate the impact property of resistance spot welding,which is an important quality index in automotive industry.For testing impact properties of spot welds,many customized testers have been developed.This paper summarized some of the impact testers reported in open literatures and the emphasis was placed on the equipment structures,functions,technical parameters,advantages and disadvantage,etc.Some key issues about the development of the testers such as kinematic energy input mode,fixture design,combined load testing,sensor and data acquisition were discussed.Finally,the problems and prospects in the research and development of impact testers for spot welds were pointed out.
文摘This study gives a comparison between what occurs when braking on a MOT （Ministry of Transport） brake tester. The results from this research and the exhaustive comparative study carried out by the mechanical engineering staffs at the mechanical laboratory at MOT stations in cities such as： Elche, Pilar de la Horadada and Orihuela from Alicante region [2] have led to the following main conclusions： this paper demonstrates that MOT brake testing results can vary depending on parameters variation such as： distance between rollers, roller diameter, roughness of rollers and velocity of the brake test.
文摘With the rapid development of silicon chip tech-nology,web-based instruction(WBI)and computer-ized adaptive testing(CAT)will be the new trends inthe field of language teaching and testing.We assumethat only when teaching and testing share the sameview about the nature of language and language learn-ing can testing exercise a beneficial backwash effect onteaching.However,WBI and CAT prove to be basedon opposite theories of language and language learn-ing.While WBI believes in constructivism,CAT cor-responds to structuralism and behaviorism.This situ-ation places language testers in a dilemma,for if theyfollow the trend,testing will go against teaching.Butif they give up CAT,it is very difficult to substituteanother testing system possessing so many advantages.This paper illustrates in detail why WBI and CAT areto become the new trends in teaching and testing,ex-plains clearly the discrepancy between WBI and CAT intheory and their objectives and finally attempts toprovide a solution to help the language testers out ofthe dilemma.
文摘In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the ]enike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.
基金The National Natural Science Foundation of China(No.51178114)the Chinese Western Transportation Construction Technology Project of Transportation Ministry(No.2009318000086)
文摘To determine the fracture characteristics of asphalt mixture a novel fracture test with modified loading modes loading fixtures and the control system of the conventional overlay tester is implemented by the asphalt material performance tester AMPT .In order to evaluate the validity of the proposed fracture test four different loading rates including 1 2 3 and 4 mm/min are examined in the AMPT. The results indicate that the fracture behavior is similar to creep at a low loading rate and does not show significant marginal tail extension at a high loading rate.It clearly shows the phase of crack initiation crack propagation and fracture at a loading rate of 3 mm/min. Besides eight fracture parameters such as fracture energy tensile strength and tensile modulus are applied to evaluate the fracture characteristics of asphalt mixture.Development of the overlay tester for the fracture test of asphalt mixture can be considered as a new fracture test of asphalt mixture.
基金Supported by the BC Centre for Disease Control and the Canadian Institutes of Health Research,No.NHC–142832 and No.PHE-141773
文摘AIM To describe the characteristics of people diagnosed with acute and chronic hepatitis B virus(HBV) infection in British Columbia(BC).METHODS We used data from the BC Hepatitis Testers Cohort(BCHTC),which includes all individuals tested for hepatitis C virus(HCV) or human immunodeficiency virus(HIV) or those diagnosed with HBV or active tuberculosis in BC since 1990.These data were integrated with prescription drug,medical visit,hospitalization and mortality data.HBV cases were classified as acute or chronic according to provincial guidelines.We compared characteristics of individuals by HBV infection group(acute,chronic and negative).Factors associated with acute or chronic HBV infection were assessed with multinomial logistic regression models in comparison to the HBV negative group.RESULTS46498 of the 1058056 eligible BC-HTC participants were diagnosed with HBV infection.4.3% of HBV positive individuals were diagnosed with acute HBV infections while 95.7% had chronic infections.Problematic alcohol use,injection drug use,and HIV or HCV co-infection were more common among individuals diagnosed with acute HBV compared to those with chronic infections and HBV negative individuals.In multivariable multinomial logistic regression models,we observed significant associations between acute or chronic HBV diagnosis and being male,age at HBV diagnosis or birth cohort,South and East Asian ethnicity,HCV or HIV infection,and injection drug use.The odds of acute HBV decreased with increasing age among people who inject drugs,while the opposite was true for chronic HBV.Persons with acute HBV were predominantly White(78%) while those with chronic HBV were mostly East Asian(60%).Relative to Whites,East Asians had 12 times greater odds of being diagnosed with chronic HBV infection.These odds increased with increasing socioeconomic deprivation.CONCLUSION Differences in the profiles of people diagnosed with acute and chronic HBV infection necessitate differentiated screening,prevention,care and treatment programs.
文摘The purpose of this study was to investigate the diversity of 14 popcorn populations and a broad genetic base tester using molecular RAPD markers and to estimate the correlation between the genetic distances and the performance of top-cross hybrids. For the evaluation of populations and hybrids resulting from topcrosses, the reduced model of Gardner was used. A genetic distance matrix was generated based on RAPD markers by Jaccard coefficient, and a dendrogram was constructed. In general, topcrosses performed better than the populations per se and evidenced heterosis occurrence in topcrosses. The trait grain weight is influenced by additive as much as by dominance effects. Genetic associations separated the populations in three groups, and RAPD showed to be a useful tool to determine the extension of genetic diversity in popcorn populations and to place genotypes in distinct heterotic groups. Correlations between genetic divergences, detected by RAPD, and the means observed in the topcross crosses were positive and non-significant for expansion volume, plant height, and female flowering, and were negative for grain weight.
基金supported by National Basic Research Program of China(973 Program,Grant No. 2009CB724304)Key Research Program of the State Key Laboratory of Tribology of Tsinghua University,China (Grant No. SKLT08A06)National Natural Science Foundation of China(Grant No. 50975157)
文摘Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.
