A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier-Stokes equation in the liquid r...A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier-Stokes equation in the liquid region is solved by MAC projection algorithm combined with second-order ENO scheme for the advection terms. The moving inter-face is captured by the level set function, and the interface velocity is resolved by ＂one-side＂ velocity extension from the liquid region to the bubble region, complementing the second-order weighted least squares method across the interface and projection inside bubble. The use of non-uniform grid overcomes the difficulty caused by the large computational domain and very small bubble size. The computation is very stable without suffering from large flow-field gradients, and the results are in good agreements with other studies. The bubble interface kinematics, dynamics and its effect on the wall are highlighted, which shows that the code can effectively capture the ＂shock wave＂-like pressure and velocity at jet impact, toroidal bubble, and complicated pressure structure with peak, plateau and valley in the later stage of bubble oscillating.展开更多
A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this proble...A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.展开更多
There are a lot of personal information stored in our smartphones, for instance, contacts, messages, photos, banking credentials and social network access. Therefore, ensuring personal data safety is a critical resear...There are a lot of personal information stored in our smartphones, for instance, contacts, messages, photos, banking credentials and social network access. Therefore, ensuring personal data safety is a critical research and practical issue. The objective of this paper is to evaluate the influence of personal data sect,rity and decrease the privacy risks in the Android system. We apply the concept of privacy impact assessment （PIA） to design a system, which identifies permission requirements of apps, detects the potential activities from the logger and analyses the configuration settings. The system provides a user-friendly interface for users to get in-depth knowledge of the impact of privacy risk, and it could run on Android devices without USB teleport and network connection to avoid other problems. Our research finds that many apps announce numerous unnecessary permissions, and the application installing confirmation dialog does not show all requirement permissions when apps are installed first time.展开更多
The impact of rotavirus (RV) vaccination in reducing severe rotavirus gastroenteritis (RVGE) in outpatient settings was prospectively surveyed in three pediatric clinics in Shibata City. In children younger than 3 yea...The impact of rotavirus (RV) vaccination in reducing severe rotavirus gastroenteritis (RVGE) in outpatient settings was prospectively surveyed in three pediatric clinics in Shibata City. In children younger than 3 years of age, the occurrence of severe RVGE among all acute gastroenteritis (AGE) was found to be significantly lower in three seasons after introduction of RV vaccines, compared to that in 2011, before introduction of RV vaccines. The incidence rates of severe RVGE among children younger than 3 years of age were found to be reduced by 71.2%, 47.7%, and 81.1% for 2012, 2013, and 2014, respectively, compared to that in 2011. These results suggest that the RV vaccination is effective for the prevention of severe RVGE in Japanese voluntary RV vaccination settings with estimated coverage rates of 32.5%, 40.5% and 47.1% for 2012, 2013 and 2014, respectively. It is expected that the reducing effect on severe RVGE would be persistently established by increasing the vaccine coverage rates.展开更多
基金the National Natural Science Foundation of China(10272032 and 10672043).
文摘A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier-Stokes equation in the liquid region is solved by MAC projection algorithm combined with second-order ENO scheme for the advection terms. The moving inter-face is captured by the level set function, and the interface velocity is resolved by ＂one-side＂ velocity extension from the liquid region to the bubble region, complementing the second-order weighted least squares method across the interface and projection inside bubble. The use of non-uniform grid overcomes the difficulty caused by the large computational domain and very small bubble size. The computation is very stable without suffering from large flow-field gradients, and the results are in good agreements with other studies. The bubble interface kinematics, dynamics and its effect on the wall are highlighted, which shows that the code can effectively capture the ＂shock wave＂-like pressure and velocity at jet impact, toroidal bubble, and complicated pressure structure with peak, plateau and valley in the later stage of bubble oscillating.
基金Project supported by the National Natural Science Foundation of China(Nos.11672310 and 11372326)the National Basic Research Program of China(No.2014CB04680202)
文摘A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.
基金supported in part by the Ministry of Science and Technology of Taiwan,China under Grant No.MOST 102-2221-E-017-003-MY3
文摘There are a lot of personal information stored in our smartphones, for instance, contacts, messages, photos, banking credentials and social network access. Therefore, ensuring personal data safety is a critical research and practical issue. The objective of this paper is to evaluate the influence of personal data sect,rity and decrease the privacy risks in the Android system. We apply the concept of privacy impact assessment （PIA） to design a system, which identifies permission requirements of apps, detects the potential activities from the logger and analyses the configuration settings. The system provides a user-friendly interface for users to get in-depth knowledge of the impact of privacy risk, and it could run on Android devices without USB teleport and network connection to avoid other problems. Our research finds that many apps announce numerous unnecessary permissions, and the application installing confirmation dialog does not show all requirement permissions when apps are installed first time.
文摘The impact of rotavirus (RV) vaccination in reducing severe rotavirus gastroenteritis (RVGE) in outpatient settings was prospectively surveyed in three pediatric clinics in Shibata City. In children younger than 3 years of age, the occurrence of severe RVGE among all acute gastroenteritis (AGE) was found to be significantly lower in three seasons after introduction of RV vaccines, compared to that in 2011, before introduction of RV vaccines. The incidence rates of severe RVGE among children younger than 3 years of age were found to be reduced by 71.2%, 47.7%, and 81.1% for 2012, 2013, and 2014, respectively, compared to that in 2011. These results suggest that the RV vaccination is effective for the prevention of severe RVGE in Japanese voluntary RV vaccination settings with estimated coverage rates of 32.5%, 40.5% and 47.1% for 2012, 2013 and 2014, respectively. It is expected that the reducing effect on severe RVGE would be persistently established by increasing the vaccine coverage rates.
