Previous studies have showed clinical characteristics of patients with the 2019 novel coronavirus disease(COVID-19)and the evidence of person-to-person transmission.Limited data are available for asymptomatic infectio...Previous studies have showed clinical characteristics of patients with the 2019 novel coronavirus disease(COVID-19)and the evidence of person-to-person transmission.Limited data are available for asymptomatic infections.This study aims to present the clinical characteristics of 24 cases with asymptomatic infection screened from close contacts and to show the transmission potential of asymptomatic COVID-19 virus carriers.Epidemiological investigations were conducted among all close contacts of COVID-19 patients(or suspected patients)in Nanjing,Jiangsu Province,China,from Jan 28 to Feb 9,2020,both in clinic and in community.Asymptomatic carriers were laboratory-confirmed positive for the COVID-19 virus by testing the nucleic acid of the pharyngeal swab samples.Their clinical records,laboratory assessments,and chest CT scans were reviewed.As a result,none of the 24 asymptomatic cases presented any obvious symptoms while nucleic acid screening.Five cases(20.8%)developed symptoms(fever,cough,fatigue,etc.)during hospitalization.Twelve(50.0%)cases showed typical CT images of ground-glass chest and 5(20.8%)presented stripe shadowing in the lungs.The remaining 7(29.2%)cases showed normal CT image and had no symptoms during hospitalization.These 7 cases were younger(median age:14.0 years;P=0.012)than the rest.None of the 24 cases developed severe COVID-19 pneumonia or died.The median communicable period,defined as the interval from the first day of positive nucleic acid tests to the first day of continuous negative tests,was 9.5 days(up to 21 days among the 24 asymptomatic cases).Through epidemiological investigation,we observed a typical asymptomatic transmission to the cohabiting family members,which even caused severe COVID-19 pneumonia.Overall,the asymptomatic carriers identified from close contacts were prone to be mildly ill during hospitalization.However,the communicable period could be up to three weeks and the communicated patients could develop severe illness.These results highlighted the importance of close cont展开更多
Al2O3f/Al2O3 ceramic matrix composites(CMC)are promising candidate materials of blades and combustor liners of future gas turbines in light of their higher temperature capability,higher environmental stability and oxi...Al2O3f/Al2O3 ceramic matrix composites(CMC)are promising candidate materials of blades and combustor liners of future gas turbines in light of their higher temperature capability,higher environmental stability and oxidizing-free capacity[1–3].Nevertheless,grain growth,sintering and creep deformation at high operation temperatures are still serious problems for Al2O3f/Al2O3 ceramic matrix composites,which can lead to a reduction in the strength and damage tolerance[2].Moreover,Al2O3 can be corroded by the high temperature water vapor in combustion environments and yields volatile products,such as Al(OH)3[4].Consequently,environmental barrier coatings(EBCs)are necessary for Al2O3f/Al2O3 ceramic matrix composites,which can protect Al2O3f/Al2O3 CMC from high temperature and flowing combustion gas corrosion and thus increase the high temperature capability and the service life of components.展开更多
The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have bee...The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a minimum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 us, which is much larger than the usual result. The peak current of stroke I_p(kA) and the neutralized charge Q(C) has a relationship of I_p = 18.5Q^(0.65). The radiation field of return stroke is 5.9 kV ? m^(-1) and 0.39 kV ? m^(-1) at 60 m and 550 m, respectively. The radiation field decreases as r^(-1.119) with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4 × 10~8m·s^(-1), with a variation range of (1.1-1.6)×10~8m·s^(-1). Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.展开更多
This paper studies the close-contact melting around a moving, horizontal elliptical heat source thatmelts its way through a phase change material under its own weight. The heat source velocity andthe volume of the mat...This paper studies the close-contact melting around a moving, horizontal elliptical heat source thatmelts its way through a phase change material under its own weight. The heat source velocity andthe volume of the material melted are obtained by analysis. The effects of compression coefficient andtemperature distribution in the melt are investigated. The results include that for melting around amoving cylindrical heat source.展开更多
A high-precision shape detecting system of cold rolling strip is developed to meet industrial application, which mainly consists of the shape detecting roller, the collecting ring, the digital signal processing （DSP...A high-precision shape detecting system of cold rolling strip is developed to meet industrial application, which mainly consists of the shape detecting roller, the collecting ring, the digital signal processing （DSP） shape signal processing board and the shape control model. Based on the shape detecting principle, the shape detecting roller is designed with a new integral structure for improving the precision of shape detecting and avoiding scratching strip surface. Based on the DSP technology, the DSP shape signal processing circuit board is designed and embedded in the shape detecting system for the reliability and stability of shape signal processing. The shape detecting system was successfully used in Angang 1 250 mm HC 6-high reversible cold rolling mill. The precision of shape detecting is 0.2 I and the shape deviation is controlled within 6 1 after the close loop shape control is input.展开更多
This paper analyzed the fundamental limitations of previous work and developed a new method to optimally locate actuators and sensors for structures with close modes. Optimization criteria were defined based on the di...This paper analyzed the fundamental limitations of previous work and developed a new method to optimally locate actuators and sensors for structures with close modes. Optimization criteria were defined based on the distinguishing modal controllability and observability measures of close modes. An appropriate genetic algorism was adopted as the optimization algorism. Solving the high order Lyapunov functions was avoided by means of the closed-form expressions for controllability and observability Grammians. Since structure with widely separated natural frequencies is approximately balanced, computational efficiency was improved by grouping close modes together and dealing with the resulting subsystems independently. Finally, the effectiveness and optimality of the novel placement scheme were verified on a model structure with close modes.展开更多
In multi-seam mining,the interlayer rock strata between the upper coal seam(UCS)and the lower coal seam(LCS)appear damage and strength weakening after mining the UCS.Ground stability control of the gob-side entry reta...In multi-seam mining,the interlayer rock strata between the upper coal seam(UCS)and the lower coal seam(LCS)appear damage and strength weakening after mining the UCS.Ground stability control of the gob-side entry retaining(GER)under the gob with close distance coal seams(CDCS)is faced with difficulties due to little attention to GER under this condition.This paper focuses on surrounding rock stability control and technical parameters design for GER under the gob with CDCS.The floor rock strata damage characteristics after mining the UCS is first evaluated and the damage factor of the interlayer rock strata below the UCS is also determined.Then,a structural mechanics model of GER surrounding rock is set up to obtain the main design parameters of the side-roadway backfill body(SBB)including the maximum and minimum SBB width calculation formula.The optimal SBB width and the water-to-cement ratio of high water quick-setting material(HWQM)to construct the SBB are determined as 1.2 m and 1.5:1.0,respectively.Finally,engineering trial tests of GER are successfully carried out at#5210 track transportation roadway of Xingwu Colliery.Research results can guide GER design under similar mining and geological conditions.展开更多
基金supported by the project of Jiangsu province medical youth talent(QNRC2016059)Nanjing medical science and technique development foundation(ZKX17040 and YKK18153)+1 种基金the National Natural Science Foundation of China(81903382)Cheung Kong Scholars Program of China。
文摘Previous studies have showed clinical characteristics of patients with the 2019 novel coronavirus disease(COVID-19)and the evidence of person-to-person transmission.Limited data are available for asymptomatic infections.This study aims to present the clinical characteristics of 24 cases with asymptomatic infection screened from close contacts and to show the transmission potential of asymptomatic COVID-19 virus carriers.Epidemiological investigations were conducted among all close contacts of COVID-19 patients(or suspected patients)in Nanjing,Jiangsu Province,China,from Jan 28 to Feb 9,2020,both in clinic and in community.Asymptomatic carriers were laboratory-confirmed positive for the COVID-19 virus by testing the nucleic acid of the pharyngeal swab samples.Their clinical records,laboratory assessments,and chest CT scans were reviewed.As a result,none of the 24 asymptomatic cases presented any obvious symptoms while nucleic acid screening.Five cases(20.8%)developed symptoms(fever,cough,fatigue,etc.)during hospitalization.Twelve(50.0%)cases showed typical CT images of ground-glass chest and 5(20.8%)presented stripe shadowing in the lungs.The remaining 7(29.2%)cases showed normal CT image and had no symptoms during hospitalization.These 7 cases were younger(median age:14.0 years;P=0.012)than the rest.None of the 24 cases developed severe COVID-19 pneumonia or died.The median communicable period,defined as the interval from the first day of positive nucleic acid tests to the first day of continuous negative tests,was 9.5 days(up to 21 days among the 24 asymptomatic cases).Through epidemiological investigation,we observed a typical asymptomatic transmission to the cohabiting family members,which even caused severe COVID-19 pneumonia.Overall,the asymptomatic carriers identified from close contacts were prone to be mildly ill during hospitalization.However,the communicable period could be up to three weeks and the communicated patients could develop severe illness.These results highlighted the importance of close cont
基金financial supported by the National Natural Science Foundation of China(Nos.51672064 and U1435206).
文摘Al2O3f/Al2O3 ceramic matrix composites(CMC)are promising candidate materials of blades and combustor liners of future gas turbines in light of their higher temperature capability,higher environmental stability and oxidizing-free capacity[1–3].Nevertheless,grain growth,sintering and creep deformation at high operation temperatures are still serious problems for Al2O3f/Al2O3 ceramic matrix composites,which can lead to a reduction in the strength and damage tolerance[2].Moreover,Al2O3 can be corroded by the high temperature water vapor in combustion environments and yields volatile products,such as Al(OH)3[4].Consequently,environmental barrier coatings(EBCs)are necessary for Al2O3f/Al2O3 ceramic matrix composites,which can protect Al2O3f/Al2O3 CMC from high temperature and flowing combustion gas corrosion and thus increase the high temperature capability and the service life of components.
基金the National Natural Science Foundation of China (Grant Nos. 40135010 and 40325013) the Ministry of Science and Technology of China (Grant No. 2004DEA71070)
文摘The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a minimum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 us, which is much larger than the usual result. The peak current of stroke I_p(kA) and the neutralized charge Q(C) has a relationship of I_p = 18.5Q^(0.65). The radiation field of return stroke is 5.9 kV ? m^(-1) and 0.39 kV ? m^(-1) at 60 m and 550 m, respectively. The radiation field decreases as r^(-1.119) with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4 × 10~8m·s^(-1), with a variation range of (1.1-1.6)×10~8m·s^(-1). Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.
文摘This paper studies the close-contact melting around a moving, horizontal elliptical heat source thatmelts its way through a phase change material under its own weight. The heat source velocity andthe volume of the material melted are obtained by analysis. The effects of compression coefficient andtemperature distribution in the melt are investigated. The results include that for melting around amoving cylindrical heat source.
基金Foundation item: Project(2009AA04Z143) supported by the National High Technology Research and Development Program of ChinaProject (E2011203004) supported by Natural Science Foundation of Hebei Province, ChinaProjects(2011BAF15B03, 2011BAF15B02) supported by the National Science Plan of China
文摘A high-precision shape detecting system of cold rolling strip is developed to meet industrial application, which mainly consists of the shape detecting roller, the collecting ring, the digital signal processing （DSP） shape signal processing board and the shape control model. Based on the shape detecting principle, the shape detecting roller is designed with a new integral structure for improving the precision of shape detecting and avoiding scratching strip surface. Based on the DSP technology, the DSP shape signal processing circuit board is designed and embedded in the shape detecting system for the reliability and stability of shape signal processing. The shape detecting system was successfully used in Angang 1 250 mm HC 6-high reversible cold rolling mill. The precision of shape detecting is 0.2 I and the shape deviation is controlled within 6 1 after the close loop shape control is input.
基金supported by the National Natural Science Foundation of China (Grant No. 10872028)
文摘This paper analyzed the fundamental limitations of previous work and developed a new method to optimally locate actuators and sensors for structures with close modes. Optimization criteria were defined based on the distinguishing modal controllability and observability measures of close modes. An appropriate genetic algorism was adopted as the optimization algorism. Solving the high order Lyapunov functions was avoided by means of the closed-form expressions for controllability and observability Grammians. Since structure with widely separated natural frequencies is approximately balanced, computational efficiency was improved by grouping close modes together and dealing with the resulting subsystems independently. Finally, the effectiveness and optimality of the novel placement scheme were verified on a model structure with close modes.
基金financial support from the National Natural Science Foundation of China(Nos.51804111,51974117,51904102,and 52074117)Natural Science Foundation of Hunan Province(No.2020JJ5194)the Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20200991)。
文摘In multi-seam mining,the interlayer rock strata between the upper coal seam(UCS)and the lower coal seam(LCS)appear damage and strength weakening after mining the UCS.Ground stability control of the gob-side entry retaining(GER)under the gob with close distance coal seams(CDCS)is faced with difficulties due to little attention to GER under this condition.This paper focuses on surrounding rock stability control and technical parameters design for GER under the gob with CDCS.The floor rock strata damage characteristics after mining the UCS is first evaluated and the damage factor of the interlayer rock strata below the UCS is also determined.Then,a structural mechanics model of GER surrounding rock is set up to obtain the main design parameters of the side-roadway backfill body(SBB)including the maximum and minimum SBB width calculation formula.The optimal SBB width and the water-to-cement ratio of high water quick-setting material(HWQM)to construct the SBB are determined as 1.2 m and 1.5:1.0,respectively.Finally,engineering trial tests of GER are successfully carried out at#5210 track transportation roadway of Xingwu Colliery.Research results can guide GER design under similar mining and geological conditions.
