Out-of-hospital cardiac arrest is a life threatening situation where the first person performing car-diopulmonary resuscitation (CPR) most often is a bystander without medical training. Some existing smart phone apps ...Out-of-hospital cardiac arrest is a life threatening situation where the first person performing car-diopulmonary resuscitation (CPR) most often is a bystander without medical training. Some existing smart phone apps can call the emergency number and provide for example global positioning system (GPS) loca-tion by the Norwegian air ambulance. To extend functionality of such apps by using the built in camera in a smart phone to capture video of the CPR performed, primarily to estimate the duration and rate of the chest compression executed.展开更多
Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dyna...Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.展开更多
Effects of strain rate and water-to-cement ratio on the dynamic compressive mechanical behavior of cement mortar are investigated by split Hopkinson pressure bar(SHPB) tests. 124 specimens are subjected to dynamic uni...Effects of strain rate and water-to-cement ratio on the dynamic compressive mechanical behavior of cement mortar are investigated by split Hopkinson pressure bar(SHPB) tests. 124 specimens are subjected to dynamic uniaxial compressive loadings.Strain rate sensitivity of the materials is measured in terms of failure modes, stress-strain curves, compressive strength, dynamic increase factor(DIF) and critical strain at peak stress. A significant change in the stress-strain response of the materials with each order of magnitude increase in strain rate is clearly seen from test results. The slope of the stress-strain curve after peak value for low water-to-cement ratio is steeper than that of high water-to-cement ratio mortar. The compressive strength increases with increasing strain rate. With increase in strain rate, the dynamic increase factor(DIF) increases. However, this increase in DIF with increase in strain rate does not appear to be a function of the water-to-cement ratio. The critical compressive strain increases with the strain rate.展开更多
The effect of fly ash and silica fume on hydration rate and strength of cement in the early stage was studied. Contrast test was applied to the complex cementitious system to investigate the hydration rate. Combined w...The effect of fly ash and silica fume on hydration rate and strength of cement in the early stage was studied. Contrast test was applied to the complex cementitious system to investigate the hydration rate. Combined with mechanical strength, the influence of fly ash and silica fume during the hydration process of complex binder was researched. The peak of the rate of hydration heat evolution and the mechanical strength decreased as the ratio of fly ash increased, however, as the ratio of silica fume increased, the peak of the rate of hydration heat evolution and the mechanical strength increased obviously. When the ratios of fly ash and silica fume are 10% and 5%, the peak of the rate of hydration heat evolution is the highest. At the same time 7 days of flexural and compressive strength are the highest as 8.89 MPa and 46.52 MPa, respectively. Fly ash and silica fume are the main factors affecting the hydration rate and the mechanical property.展开更多
The cold-work tool steels T10A and GCr15 have been studied with regard to the influence of austenitization temperature, tempering temperature and the residual stress on the crack propagation rate and the critical crac...The cold-work tool steels T10A and GCr15 have been studied with regard to the influence of austenitization temperature, tempering temperature and the residual stress on the crack propagation rate and the critical crack length. The kinds of fracture morphology have been studied too. The crack propagation rate is dependent strongly on the austenitization temperature, the tempering temperature and the surface compressional residual stress in specimens.展开更多
Bearing the large moment that is generated by the wind load that acts on the upper structure of offshore wind turbines is an important feature of their foundations that is different from other offshore structures.A co...Bearing the large moment that is generated by the wind load that acts on the upper structure of offshore wind turbines is an important feature of their foundations that is different from other offshore structures.A composite bucket shallow foundation(CBSF)has been proposed by Tianjin University to address the soft geological conditions in the offshore regions of China for wind turbines.The CBSF is a new type of foundation and is effective against large moments.The soil deformation test of a CBSF and the numerical simulation study under the same working conditions are carried out to determine the failure mechanism of a CBSF under moment loading.The resisting soil compression rateηm is defined as a new empirical parameter that indicates the ability of the soil inside the bucket to resist moment loading.The upper limit of the resisting moment bearing capacity of the bucket foundation is derived through the upper bound theorem of classical plasticity theory based on the failure mechanism.The calculation method is validated by tests of bucket models with different height-diameter ratios in sand under moment loading.展开更多
In the process of image transmission, the famous JPEG and JPEG-2000 compression methods need more transmission time as it is difficult for them to compress the image with a low compression rate. Recently the compresse...In the process of image transmission, the famous JPEG and JPEG-2000 compression methods need more transmission time as it is difficult for them to compress the image with a low compression rate. Recently the compressed sensing（CS） theory was proposed, which has earned great concern as it can compress an image with a low compression rate, meanwhile the original image can be perfectly reconstructed from only a few compressed data. The CS theory is used to transmit the high resolution astronomical image and build the simulation environment where there is communication between the satellite and the Earth. Number experimental results show that the CS theory can effectively reduce the image transmission and reconstruction time. Even with a very low compression rate, it still can recover a higher quality astronomical image than JPEG and JPEG-2000 compression methods.展开更多
The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were exe...The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture content.Furthermore, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.展开更多
The antifreeze critical strength and the pre-curing time of low-temperature concrete were studied by means of guaranteed rate of compressive strength and antifreeze performance for the structural safety requirement of...The antifreeze critical strength and the pre-curing time of low-temperature concrete were studied by means of guaranteed rate of compressive strength and antifreeze performance for the structural safety requirement of concrete engineering,suffering once freeze damage under air environment.It is shown that the antifreeze critical strength is 3.7-4.4MPa,pre-curing time is 18-32 h by guaranteed rate of compressive strength,and the antifreeze critical strength is 3.7-4.4MPa,pre-curing time is 18-32 h by guaranteed rate of antifreeze performance.It can be found that the method of guaranteed rate of compressive strength is sensitive to the defect which generated by freeze damage in the concrete interior.The method is fit to evaluate the antifreeze critical strength of low-temperature concrete.展开更多
The start point in this paper is dynamic load damage caused by hydrodynamic pressure to the inside void of cement stabilized macadam base considering the affect of gradation type,testing time and cracking simulation.T...The start point in this paper is dynamic load damage caused by hydrodynamic pressure to the inside void of cement stabilized macadam base considering the affect of gradation type,testing time and cracking simulation.Then the moisture damage rule of cement stabilized macadam was investigated in the lab by using the hydrodynamic pressure simulation device and testing system.Test results shows that the cement stabilized macadam with dense framework structure has better moisture-resistant performance than mixtures with suspend-dense structure.And the strength deterioration is just one-third of origin one when crack in base is loaded by hydrodynamic pressure.展开更多
Semi-periodic structures namely inclined wavy structures （IWS） are experimentally observed in compressible mixing layers at two convective Mach numbers （Mc = 0.11 and 0.47）. Flow structures are visualized by the l...Semi-periodic structures namely inclined wavy structures （IWS） are experimentally observed in compressible mixing layers at two convective Mach numbers （Mc = 0.11 and 0.47）. Flow structures are visualized by the laserinduced planar laser Mie scattering （PLMS） technique. Two methods are developed to investigate the spatial distribu- tion and geometry of IWS： （1） the dominant mode extrac- tion （DME） method, to extract the dominant modes of IWS from the streamwise gray-level fluctuation, and （2） the phase tracking （PT） method, to identify the shape of IWS. The re- sults suggest that pressure perturbations account for the for- marion of IWS in the initial mixing region and the joint effect of dilatation and coherent vortices enhances IWS in the well- developed region. The large transverse （cross-flow） scale of the IWS and their relation to coherent vortices （CV） indicate that the disturbance originated from CV in the mixing center propagates far into the free streams. The DME and the PT method are shown to be the effective tools to study the geometrical features of wavy structures in compressible shear flows.展开更多
The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y（wt%） alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing（SDAS） of Mg–6Zn–1Y a...The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y（wt%） alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing（SDAS） of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates（Rc） from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0：45：45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction（Vf） of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.展开更多
For quantum fluids governed by the compressible quantum Navier-Stokes equations in R;with viscosity and heat conduction, we prove the optimal L;- L;decay rates for the classical solutions near constant states. The pro...For quantum fluids governed by the compressible quantum Navier-Stokes equations in R;with viscosity and heat conduction, we prove the optimal L;- L;decay rates for the classical solutions near constant states. The proof is based on the detailed linearized decay estimates by Fourier analysis of the operators, which is drastically different from the case when quantum effects are absent.展开更多
文摘Out-of-hospital cardiac arrest is a life threatening situation where the first person performing car-diopulmonary resuscitation (CPR) most often is a bystander without medical training. Some existing smart phone apps can call the emergency number and provide for example global positioning system (GPS) loca-tion by the Norwegian air ambulance. To extend functionality of such apps by using the built in camera in a smart phone to capture video of the CPR performed, primarily to estimate the duration and rate of the chest compression executed.
基金Project (14JJ6047) supported by the Natural Science Foundation of Hunan Province,ChinaProject (51274092) supported by the National Natural Science Foundation of ChinaProject (20120161110040) supported by the Doctoral Program of Higher Education ofChina
文摘Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.
基金Project(51479048) supported by National Natural Science Foundation of China
文摘Effects of strain rate and water-to-cement ratio on the dynamic compressive mechanical behavior of cement mortar are investigated by split Hopkinson pressure bar(SHPB) tests. 124 specimens are subjected to dynamic uniaxial compressive loadings.Strain rate sensitivity of the materials is measured in terms of failure modes, stress-strain curves, compressive strength, dynamic increase factor(DIF) and critical strain at peak stress. A significant change in the stress-strain response of the materials with each order of magnitude increase in strain rate is clearly seen from test results. The slope of the stress-strain curve after peak value for low water-to-cement ratio is steeper than that of high water-to-cement ratio mortar. The compressive strength increases with increasing strain rate. With increase in strain rate, the dynamic increase factor(DIF) increases. However, this increase in DIF with increase in strain rate does not appear to be a function of the water-to-cement ratio. The critical compressive strain increases with the strain rate.
基金Funded by the National Natural Science Foundation of China(No.51472168)
文摘The effect of fly ash and silica fume on hydration rate and strength of cement in the early stage was studied. Contrast test was applied to the complex cementitious system to investigate the hydration rate. Combined with mechanical strength, the influence of fly ash and silica fume during the hydration process of complex binder was researched. The peak of the rate of hydration heat evolution and the mechanical strength decreased as the ratio of fly ash increased, however, as the ratio of silica fume increased, the peak of the rate of hydration heat evolution and the mechanical strength increased obviously. When the ratios of fly ash and silica fume are 10% and 5%, the peak of the rate of hydration heat evolution is the highest. At the same time 7 days of flexural and compressive strength are the highest as 8.89 MPa and 46.52 MPa, respectively. Fly ash and silica fume are the main factors affecting the hydration rate and the mechanical property.
文摘The cold-work tool steels T10A and GCr15 have been studied with regard to the influence of austenitization temperature, tempering temperature and the residual stress on the crack propagation rate and the critical crack length. The kinds of fracture morphology have been studied too. The crack propagation rate is dependent strongly on the austenitization temperature, the tempering temperature and the surface compressional residual stress in specimens.
基金supported by the National Natural Science Foundation of China(Grant Nos.51709199 and 51322904).
文摘Bearing the large moment that is generated by the wind load that acts on the upper structure of offshore wind turbines is an important feature of their foundations that is different from other offshore structures.A composite bucket shallow foundation(CBSF)has been proposed by Tianjin University to address the soft geological conditions in the offshore regions of China for wind turbines.The CBSF is a new type of foundation and is effective against large moments.The soil deformation test of a CBSF and the numerical simulation study under the same working conditions are carried out to determine the failure mechanism of a CBSF under moment loading.The resisting soil compression rateηm is defined as a new empirical parameter that indicates the ability of the soil inside the bucket to resist moment loading.The upper limit of the resisting moment bearing capacity of the bucket foundation is derived through the upper bound theorem of classical plasticity theory based on the failure mechanism.The calculation method is validated by tests of bucket models with different height-diameter ratios in sand under moment loading.
文摘In the process of image transmission, the famous JPEG and JPEG-2000 compression methods need more transmission time as it is difficult for them to compress the image with a low compression rate. Recently the compressed sensing（CS） theory was proposed, which has earned great concern as it can compress an image with a low compression rate, meanwhile the original image can be perfectly reconstructed from only a few compressed data. The CS theory is used to transmit the high resolution astronomical image and build the simulation environment where there is communication between the satellite and the Earth. Number experimental results show that the CS theory can effectively reduce the image transmission and reconstruction time. Even with a very low compression rate, it still can recover a higher quality astronomical image than JPEG and JPEG-2000 compression methods.
基金Project(50979032)supported by the National Natural Science Foundation of China
文摘The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture content.Furthermore, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.
基金Funded by the National Key Technology R&D Program of China for the 11th Five-Year Plan(2006BAJ04A04)the Natural Science Foundation Project of Liaoning Province(20082008)the Nationd Natural Science Foundation of China(51072122)
文摘The antifreeze critical strength and the pre-curing time of low-temperature concrete were studied by means of guaranteed rate of compressive strength and antifreeze performance for the structural safety requirement of concrete engineering,suffering once freeze damage under air environment.It is shown that the antifreeze critical strength is 3.7-4.4MPa,pre-curing time is 18-32 h by guaranteed rate of compressive strength,and the antifreeze critical strength is 3.7-4.4MPa,pre-curing time is 18-32 h by guaranteed rate of antifreeze performance.It can be found that the method of guaranteed rate of compressive strength is sensitive to the defect which generated by freeze damage in the concrete interior.The method is fit to evaluate the antifreeze critical strength of low-temperature concrete.
基金Sponsored by the Guangdong Provincial Department of Transportation Science and Technology Project (Grant No. 2010-04-003)Ministry of Transportation Western Transportation Construction Science and Technology Project (Grant No. 200631881216)
文摘The start point in this paper is dynamic load damage caused by hydrodynamic pressure to the inside void of cement stabilized macadam base considering the affect of gradation type,testing time and cracking simulation.Then the moisture damage rule of cement stabilized macadam was investigated in the lab by using the hydrodynamic pressure simulation device and testing system.Test results shows that the cement stabilized macadam with dense framework structure has better moisture-resistant performance than mixtures with suspend-dense structure.And the strength deterioration is just one-third of origin one when crack in base is loaded by hydrodynamic pressure.
基金supported by National Nature Science Foundation of China(90716008,10572004,and 11172006)by MOST 973 Project(2009CB724100)
文摘Semi-periodic structures namely inclined wavy structures （IWS） are experimentally observed in compressible mixing layers at two convective Mach numbers （Mc = 0.11 and 0.47）. Flow structures are visualized by the laserinduced planar laser Mie scattering （PLMS） technique. Two methods are developed to investigate the spatial distribu- tion and geometry of IWS： （1） the dominant mode extrac- tion （DME） method, to extract the dominant modes of IWS from the streamwise gray-level fluctuation, and （2） the phase tracking （PT） method, to identify the shape of IWS. The re- sults suggest that pressure perturbations account for the for- marion of IWS in the initial mixing region and the joint effect of dilatation and coherent vortices enhances IWS in the well- developed region. The large transverse （cross-flow） scale of the IWS and their relation to coherent vortices （CV） indicate that the disturbance originated from CV in the mixing center propagates far into the free streams. The DME and the PT method are shown to be the effective tools to study the geometrical features of wavy structures in compressible shear flows.
基金financially supported by the National Natural Science Foundation of China (NO. 51464034)the Cooperation and Exchanges of Nanchang City (2012DWHZXCL@JDYTH-001)+5 种基金the Educational Commission of Jiangxi Province (No. GJJ13069)the Innovation Fund Designated for Graduate Students of Jiangxi Province (No. YC2013-S027)the Hong Kong Scholars Program (No. XJ2012025)the China Post-doctoral Science Foundation funded project (No. 2012T50594, 2014M551866)the Jiangxi Post-doctoral Science Foundation (No. 2014KY11)Doctoral Fund of Ministry of Education of China (No. 20113601110008)
文摘The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y（wt%） alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing（SDAS） of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates（Rc） from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0：45：45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction（Vf） of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.
基金supported in part by NSFC(11471057)Natural Science Foundation Project of CQ CSTC(cstc2014jcyjA50020)the Fundamental Research Funds for the Central Universities(Project No.106112016CDJZR105501)
文摘For quantum fluids governed by the compressible quantum Navier-Stokes equations in R;with viscosity and heat conduction, we prove the optimal L;- L;decay rates for the classical solutions near constant states. The proof is based on the detailed linearized decay estimates by Fourier analysis of the operators, which is drastically different from the case when quantum effects are absent.
