The use of composite materials in aerospace engineering is ever increasing. Properties such as low weight, high performance, high stiffness and the ability for it to be tailored specifically for different structural u...The use of composite materials in aerospace engineering is ever increasing. Properties such as low weight, high performance, high stiffness and the ability for it to be tailored specifically for different structural uses has increased its importance in recent years. Specific experimental/numerical activities were developed in the last decade at the aerospace department of Polito and are under consideration in recent years regarding the analysis of fatigue behavior of composite/metallic structural samples under cyclic loading condition. A review of the main significant results connected to three case-studies is presented in the paper. The first is related to the definition and analysis of innovative joint for composite high aspect ratio aircraft structures. The modular design oriented to limit component dimensions for transportability requires the presence of a removable joints able to overcome the typical low bearing failure level of composite pin-loaded joint under static and fatigue loading distribution according to airworthiness requirements. The static experiments demonstrate the consistency of the proposed advanced joint configuration that postpones the joint failure to high load level according to the structural requirements. The cyclic loading phase takes as reference point the failure load of the initial configuration and defines a loading cycle with a maximum higher than the failure load of the initial configuration. The fatigue behavior of the advanced joint also demonstrates a substantial consistency with expected duration of 1 e6 cycles as required by the structural design for operating reasons. Specific indication on fatigue limit with respect to critical amplitude is reported. The second is related to the presence of specific damaged situation in thin-walled fiat/stiffened composite plate. Stiffened configurations are frequently used to increase buckling load level. Unexpected events on solid/stiffened composite panels can introduce a certain level of damage, typically delamination, that can cause reduction in buckling design level and reduction in global strength. The presence of cyclic load and fatigue effect can have an important consequence on damage propagation and structural integrity. The damaged area determined by the skin-stiffener de-bonding of a certain dimension is investigated under static compression and cyclic compression. Local buckling of damaged area is determined and pointed out by tests in uniaxial compression. The experimental static behavior points out the presence of a snap-effect during loading and un-loading. Fatigue loading configuration is applied in the range of post-critical local configuration considered as the most effective situation. Preliminary fatigue results are presented and discussed. The third is related to preliminary investigation on the effect of fatigue life reduction of 2024 AI alloy in corrosive （exfoliation） environment. The effect of corrosion is taken into consideration introducing specific concentration factors into the life estimation relationship. Differences between fatigue in prior corroded specimens and fatigue in presence of corrosive environment are emphasized. No crack propagation is considered. Related concentration factors are derived and compared by the few experimental results in order to define some guidelines for design process and to improve aircraft better evaluation of component structural integrity in operative situations. A preliminary approach is presented in the paper in order to correctly identify the contribution of corrosive environment in coupled fatigue loading phase. The results are discussed and future improvements are suggested.展开更多
Experimenial studies on active acoustic fiutter control are carried out successfully in wind-tunnel after the theoretical study The experdrients verify the theory presented in the reference[1] and give valuable experi...Experimenial studies on active acoustic fiutter control are carried out successfully in wind-tunnel after the theoretical study The experdrients verify the theory presented in the reference[1] and give valuable experimeotal results which predict a prondsing future of applying new techology and new ideas to the area of vibration induced by flow.展开更多
Underground lifeline engineering (ULE for short) in modern city demands the appreciation of an active fault in buried bedrock . Generally speaking , a large number of urban geological textures of a basement may all be...Underground lifeline engineering (ULE for short) in modern city demands the appreciation of an active fault in buried bedrock . Generally speaking , a large number of urban geological textures of a basement may all be simplified into a dual geological texture model , i. e., the upper part of the basement consists of loose covering layer and the lower part consists of bedrock . The study of an active fault should include three parts of contents , i . e ., to determine the lower time limit of activity of the fault , and the time limit must be recognized by both of designing engineers and geologists ; on the basis of the studies of repetition periods of earthquake occurrence to deter mine whether the fault moves or not during the allowed time of efficacy of buildings and constructions ; for the sake of engineering practice , the active rate of the fault must be given . The fault with different active mechanism has different effects on the ULE . The authors studied the effect of lateral non-uniform overburden site on the ULE by means of the supersonic earthquake modelling . Owing to the lateral non - uniformity of the covering sediments , there occurs an obvious jump of amplitude of the seismic wave propagation near the contact surface between two different sedi ments . In addition , from the modelling experiment curves it may be seen that the different focus mechanisms and different medium characters may also exert an effect in different degrees .展开更多
In recent years, tumor-nfiltrating lymphocytes (TILs) have been reported to be effective for tumors in experimental and clinical research. In order to increase the therapeutical effect, we modified some steps of Rosen...In recent years, tumor-nfiltrating lymphocytes (TILs) have been reported to be effective for tumors in experimental and clinical research. In order to increase the therapeutical effect, we modified some steps of Rosenberg's approach a. cold digestion with collagenase at 4C for 24 hours; b. sedimentation instead of centrifugation; c. elimination of tumor cells before the cultivation procedure. Compared with the original approach, the proliferation, activity and cytotoxicity of TILs obtained by the modified procedure were much improved. TILs' expansion-old was greater than that with the original approach. Cytotoxicity against rumor cells was more potent. Increased TILs' subsets were CD3 and CD8 cells. Meanwhile, we took tumor cells from tumor tissues to test their in vitro chemosensitivities to different drugs in order to select highly sensitive antitumor drugs for treatment of cases with advanced tumors. According to the design of using highly active TILs and highly sensitive drugs (H & H therapy), preliminary clinical results of 50 cases showed higher response rates than those in treatment with TIL / IL2, LAK / 1L2 and TIL+IL2+CTX. Less toxic side effects were observed in 14 patients.展开更多
Barium release experiment is an effective way to study the near-earth environment, in which artificial plasma cloud is created via ionization of neutral gases released from a rocket or a satellite. The first barium re...Barium release experiment is an effective way to study the near-earth environment, in which artificial plasma cloud is created via ionization of neutral gases released from a rocket or a satellite. The first barium release experiment in China was success- fully carried out by a sounding rocket at a height of about 190 km on April 5, 2013. The observed barium cloud images show that the neutral cloud follows a damping motion, whose velocity decreases exponentially and finally tends towards the wind velocity of the background. But for the ion cloud, the motion is controlled mainly by the Lorentz force and a ExB drift happens This work is devoted to calculating the wind and electric field of the background by analyzing the observed images from dif- ferent stations. It turns out that the wind has a magnitude of 51.28 m/s, which is mainly in the northeast direction but also has an appreciable vertical component; the ion cloud has a drift velocity of 71.38 m/s, with a large vertical velocity component be- sides the horizontal components, then the electric field is obtained from the drift velocity as 2.49 mV/m. It is interesting that the wind field shows a better agreement with GITM model than the other empirical or theoretical models, and the GITM model can also give a good prediction for the ion velocity observed by us, which is consistent with the ISR observation at Jicamarca as well.展开更多
Based on diagnostic results,a numerical study is made of the processes of Australian cold air activity affecting East Asian summer monsoon by using Kuo-Qian P-σ incorporated coordinate five-layer primitive equation s...Based on diagnostic results,a numerical study is made of the processes of Australian cold air activity affecting East Asian summer monsoon by using Kuo-Qian P-σ incorporated coordinate five-layer primitive equation spherical band model.Analysis is done of the response to the Southern Hemisphere circulation with and without cold air activity in Australia of the flow,rainfall and diabatic heating fields in the monsoon area of Asia,especially,East Asia,with special attention to the intensification and northward march of the monsoon due to the activity.It is found that the processes for the effect transmission are very analogous to the meridional propagation of quasi-40-day oscillation,together with the meridional wind disturbance showing south-north travel and the flow/rainfall fields exhibitirg corresponding movement in this direction,only with a 12-day lag.展开更多
This article reports a study using a self-reporting questionnaire adapted from Reid (1987) toexamine the preferred learning styles of the students majoring in English in Hubei Three Gorges Univer-sity Humanities’ Col...This article reports a study using a self-reporting questionnaire adapted from Reid (1987) toexamine the preferred learning styles of the students majoring in English in Hubei Three Gorges Univer-sity Humanities’ College,Hubei,China.Based on the results the study generated,activities were createdthat could reflect the students’ learning style preferences.These activities were effective in motivatingour students and developing productive language skills.展开更多
The present paper investigates the asymmetrical variability of the location of the north and the south equatorial ionization anomaly(EIA) crests in the East-Asian sector,along with their association with simultaneous ...The present paper investigates the asymmetrical variability of the location of the north and the south equatorial ionization anomaly(EIA) crests in the East-Asian sector,along with their association with simultaneous observations of equatorial electrojet(EEJ) strength,geomagnetic activity index,and solar flux index during the 2002-2003 sudden stratospheric wanning(SSW) event.Analysis of these observations indicates the existence of a large-scale quasi 16-day periodic meridional movement in both EIA crests,and also reveals a strong correlation between the quasi 16-day oscillation in geomagnetic latitudes of the EIA crest and EEJ strength.The latitude of the northern/southern EIA crest and the EEJ strength indicate that obvious synchronous periodic oscillations were in-phase in the northern and southern hemisphere when the SSW occurred.In addition,it is also found that both the EIA crest location and amplitude of the periodic movement of the EIA locations exhibit hemispheric asymmetry.The amplitude of the periodic movement of the EIA location in the southern hemisphere is larger than that of the northern hemisphere,and the southern EIA crest is further off from the equator than the north one.Understanding these asymmetries requires a combination of mechanisms that involve at least trans-equator meridional winds and the position of a sub-solar point;however,potential disturbances in neutral winds associated with the SSW may additionally complicate the equatorial ionospheric dynamics.展开更多
Ionospheric irregularities can adversely affect the performance of Global Navigation Satellite System (GNSS). How-ever, this opens the possibility of using GNSS as an effective ionospheric remote sensing tool. Despite...Ionospheric irregularities can adversely affect the performance of Global Navigation Satellite System (GNSS). How-ever, this opens the possibility of using GNSS as an effective ionospheric remote sensing tool. Despite ionospheric monitoring has been undertaken for decades, these irregularities in multiple spatial and temporal scales are still not fully understood. This paper reviews Virginia Tech’s recent studies on multi-scale ionospheric irregularities using ground-based and space-based GNSS observations. First, the relevant background of ionospheric irregularities and their impact on GNSS signals is reviewed. Next, three topics of ground-based observations of ionospheric irregulari-ties for which GNSS and other ground-based techniques are used simultaneously are reviewed. Both passive and active measurements in high-latitude regions are covered. Modelling and observations in mid-latitude regions are considered as well. Emphasis is placed on the increased capability of assessing the multi-scale nature of ionospheric irregularities using other traditional techniques (e.g., radar, magnetometer, high frequency receivers) as well as GNSS observations (e.g., Total-Electron-Content or TEC, scintillation). Besides ground-based observations, recent advances in GNSS space-based ionospheric measurements are briefly reviewed. Finally, a new space-based ionospheric observa-tion technique using GNSS-based spacecraft formation flying and a differential TEC method is demonstrated using the newly developed Virginia Tech Formation Flying Testbed (VTFFTB). Based on multi-constellation multi-band GNSS, the VTFFTB has been developed into a hardware-in-the-loop simulation testbed with external high-fidelity global ionospheric model(s) for 3-satellite formation flying, which can potentially be used for new multi-scale ionospheric measurement mission design.展开更多
文摘The use of composite materials in aerospace engineering is ever increasing. Properties such as low weight, high performance, high stiffness and the ability for it to be tailored specifically for different structural uses has increased its importance in recent years. Specific experimental/numerical activities were developed in the last decade at the aerospace department of Polito and are under consideration in recent years regarding the analysis of fatigue behavior of composite/metallic structural samples under cyclic loading condition. A review of the main significant results connected to three case-studies is presented in the paper. The first is related to the definition and analysis of innovative joint for composite high aspect ratio aircraft structures. The modular design oriented to limit component dimensions for transportability requires the presence of a removable joints able to overcome the typical low bearing failure level of composite pin-loaded joint under static and fatigue loading distribution according to airworthiness requirements. The static experiments demonstrate the consistency of the proposed advanced joint configuration that postpones the joint failure to high load level according to the structural requirements. The cyclic loading phase takes as reference point the failure load of the initial configuration and defines a loading cycle with a maximum higher than the failure load of the initial configuration. The fatigue behavior of the advanced joint also demonstrates a substantial consistency with expected duration of 1 e6 cycles as required by the structural design for operating reasons. Specific indication on fatigue limit with respect to critical amplitude is reported. The second is related to the presence of specific damaged situation in thin-walled fiat/stiffened composite plate. Stiffened configurations are frequently used to increase buckling load level. Unexpected events on solid/stiffened composite panels can introduce a certain level of damage, typically delamination, that can cause reduction in buckling design level and reduction in global strength. The presence of cyclic load and fatigue effect can have an important consequence on damage propagation and structural integrity. The damaged area determined by the skin-stiffener de-bonding of a certain dimension is investigated under static compression and cyclic compression. Local buckling of damaged area is determined and pointed out by tests in uniaxial compression. The experimental static behavior points out the presence of a snap-effect during loading and un-loading. Fatigue loading configuration is applied in the range of post-critical local configuration considered as the most effective situation. Preliminary fatigue results are presented and discussed. The third is related to preliminary investigation on the effect of fatigue life reduction of 2024 AI alloy in corrosive （exfoliation） environment. The effect of corrosion is taken into consideration introducing specific concentration factors into the life estimation relationship. Differences between fatigue in prior corroded specimens and fatigue in presence of corrosive environment are emphasized. No crack propagation is considered. Related concentration factors are derived and compared by the few experimental results in order to define some guidelines for design process and to improve aircraft better evaluation of component structural integrity in operative situations. A preliminary approach is presented in the paper in order to correctly identify the contribution of corrosive environment in coupled fatigue loading phase. The results are discussed and future improvements are suggested.
文摘Experimenial studies on active acoustic fiutter control are carried out successfully in wind-tunnel after the theoretical study The experdrients verify the theory presented in the reference[1] and give valuable experimeotal results which predict a prondsing future of applying new techology and new ideas to the area of vibration induced by flow.
基金The paper is one Part of a project supported by National Education Commitce Funds for Doctoral Faculty
文摘Underground lifeline engineering (ULE for short) in modern city demands the appreciation of an active fault in buried bedrock . Generally speaking , a large number of urban geological textures of a basement may all be simplified into a dual geological texture model , i. e., the upper part of the basement consists of loose covering layer and the lower part consists of bedrock . The study of an active fault should include three parts of contents , i . e ., to determine the lower time limit of activity of the fault , and the time limit must be recognized by both of designing engineers and geologists ; on the basis of the studies of repetition periods of earthquake occurrence to deter mine whether the fault moves or not during the allowed time of efficacy of buildings and constructions ; for the sake of engineering practice , the active rate of the fault must be given . The fault with different active mechanism has different effects on the ULE . The authors studied the effect of lateral non-uniform overburden site on the ULE by means of the supersonic earthquake modelling . Owing to the lateral non - uniformity of the covering sediments , there occurs an obvious jump of amplitude of the seismic wave propagation near the contact surface between two different sedi ments . In addition , from the modelling experiment curves it may be seen that the different focus mechanisms and different medium characters may also exert an effect in different degrees .
文摘In recent years, tumor-nfiltrating lymphocytes (TILs) have been reported to be effective for tumors in experimental and clinical research. In order to increase the therapeutical effect, we modified some steps of Rosenberg's approach a. cold digestion with collagenase at 4C for 24 hours; b. sedimentation instead of centrifugation; c. elimination of tumor cells before the cultivation procedure. Compared with the original approach, the proliferation, activity and cytotoxicity of TILs obtained by the modified procedure were much improved. TILs' expansion-old was greater than that with the original approach. Cytotoxicity against rumor cells was more potent. Increased TILs' subsets were CD3 and CD8 cells. Meanwhile, we took tumor cells from tumor tissues to test their in vitro chemosensitivities to different drugs in order to select highly sensitive antitumor drugs for treatment of cases with advanced tumors. According to the design of using highly active TILs and highly sensitive drugs (H & H therapy), preliminary clinical results of 50 cases showed higher response rates than those in treatment with TIL / IL2, LAK / 1L2 and TIL+IL2+CTX. Less toxic side effects were observed in 14 patients.
文摘Barium release experiment is an effective way to study the near-earth environment, in which artificial plasma cloud is created via ionization of neutral gases released from a rocket or a satellite. The first barium release experiment in China was success- fully carried out by a sounding rocket at a height of about 190 km on April 5, 2013. The observed barium cloud images show that the neutral cloud follows a damping motion, whose velocity decreases exponentially and finally tends towards the wind velocity of the background. But for the ion cloud, the motion is controlled mainly by the Lorentz force and a ExB drift happens This work is devoted to calculating the wind and electric field of the background by analyzing the observed images from dif- ferent stations. It turns out that the wind has a magnitude of 51.28 m/s, which is mainly in the northeast direction but also has an appreciable vertical component; the ion cloud has a drift velocity of 71.38 m/s, with a large vertical velocity component be- sides the horizontal components, then the electric field is obtained from the drift velocity as 2.49 mV/m. It is interesting that the wind field shows a better agreement with GITM model than the other empirical or theoretical models, and the GITM model can also give a good prediction for the ion velocity observed by us, which is consistent with the ISR observation at Jicamarca as well.
基金National Natural Science Foundation of ChinaState Meteorological Administration Monsoon Research Funds
文摘Based on diagnostic results,a numerical study is made of the processes of Australian cold air activity affecting East Asian summer monsoon by using Kuo-Qian P-σ incorporated coordinate five-layer primitive equation spherical band model.Analysis is done of the response to the Southern Hemisphere circulation with and without cold air activity in Australia of the flow,rainfall and diabatic heating fields in the monsoon area of Asia,especially,East Asia,with special attention to the intensification and northward march of the monsoon due to the activity.It is found that the processes for the effect transmission are very analogous to the meridional propagation of quasi-40-day oscillation,together with the meridional wind disturbance showing south-north travel and the flow/rainfall fields exhibitirg corresponding movement in this direction,only with a 12-day lag.
文摘This article reports a study using a self-reporting questionnaire adapted from Reid (1987) toexamine the preferred learning styles of the students majoring in English in Hubei Three Gorges Univer-sity Humanities’ College,Hubei,China.Based on the results the study generated,activities were createdthat could reflect the students’ learning style preferences.These activities were effective in motivatingour students and developing productive language skills.
基金supported by the National Natural Science Foundation of China(Grant Nos.41274156, 41464006 & 41674157)Guangxi Natural Science Foundation(Grant No.2014GXNSFAA118282)+1 种基金L.Goncharenko and S R.Zhang have been supported through US National Science Foundation(Grant No. AGS-1132267)the Haystack Observatory was also supported through a cooperative agreement(Grant No.AGS-1242204) between the US National Science Foundation and MIT
文摘The present paper investigates the asymmetrical variability of the location of the north and the south equatorial ionization anomaly(EIA) crests in the East-Asian sector,along with their association with simultaneous observations of equatorial electrojet(EEJ) strength,geomagnetic activity index,and solar flux index during the 2002-2003 sudden stratospheric wanning(SSW) event.Analysis of these observations indicates the existence of a large-scale quasi 16-day periodic meridional movement in both EIA crests,and also reveals a strong correlation between the quasi 16-day oscillation in geomagnetic latitudes of the EIA crest and EEJ strength.The latitude of the northern/southern EIA crest and the EEJ strength indicate that obvious synchronous periodic oscillations were in-phase in the northern and southern hemisphere when the SSW occurred.In addition,it is also found that both the EIA crest location and amplitude of the periodic movement of the EIA locations exhibit hemispheric asymmetry.The amplitude of the periodic movement of the EIA location in the southern hemisphere is larger than that of the northern hemisphere,and the southern EIA crest is further off from the equator than the north one.Understanding these asymmetries requires a combination of mechanisms that involve at least trans-equator meridional winds and the position of a sub-solar point;however,potential disturbances in neutral winds associated with the SSW may additionally complicate the equatorial ionospheric dynamics.
基金the AFOSR(Grant No.13-0658-09)Virginia Tech.Z.Xu and M.D.Hartinger were supported by NSF-1543364(Polar Experiment Network for Geospace Upper-atmosphere Investigations-PENGUIn:Interhemispheric Investigations along the 40-degree Magnetic Meridian)1744828(Collaborative Proposal:A High-Latitude Conjugate Area Array Experiment to Investigate Solar Wind-Magnetosphere-Ionosphere Coupling).
文摘Ionospheric irregularities can adversely affect the performance of Global Navigation Satellite System (GNSS). How-ever, this opens the possibility of using GNSS as an effective ionospheric remote sensing tool. Despite ionospheric monitoring has been undertaken for decades, these irregularities in multiple spatial and temporal scales are still not fully understood. This paper reviews Virginia Tech’s recent studies on multi-scale ionospheric irregularities using ground-based and space-based GNSS observations. First, the relevant background of ionospheric irregularities and their impact on GNSS signals is reviewed. Next, three topics of ground-based observations of ionospheric irregulari-ties for which GNSS and other ground-based techniques are used simultaneously are reviewed. Both passive and active measurements in high-latitude regions are covered. Modelling and observations in mid-latitude regions are considered as well. Emphasis is placed on the increased capability of assessing the multi-scale nature of ionospheric irregularities using other traditional techniques (e.g., radar, magnetometer, high frequency receivers) as well as GNSS observations (e.g., Total-Electron-Content or TEC, scintillation). Besides ground-based observations, recent advances in GNSS space-based ionospheric measurements are briefly reviewed. Finally, a new space-based ionospheric observa-tion technique using GNSS-based spacecraft formation flying and a differential TEC method is demonstrated using the newly developed Virginia Tech Formation Flying Testbed (VTFFTB). Based on multi-constellation multi-band GNSS, the VTFFTB has been developed into a hardware-in-the-loop simulation testbed with external high-fidelity global ionospheric model(s) for 3-satellite formation flying, which can potentially be used for new multi-scale ionospheric measurement mission design.
