Increased voltage blocking capability and the development of packaging technology for IGBTs can enhance the local electric field that may become large enough to increase partial discharges(PDs)within the module.The st...Increased voltage blocking capability and the development of packaging technology for IGBTs can enhance the local electric field that may become large enough to increase partial discharges(PDs)within the module.The study presents a survey on(i)simulation the electric field within an IGBT module;(ii)current standards for evaluation of the insulation systems of IGBTs;(iii)PD detection and localisation methods as well as other diagnostic and quality control test methods about IGBTs;and(iv)various methods for PD control in an IGBT module.The survey shows remarkable technical gaps in all four areas.More sophisticated numerical and theoretical techniques are needed to model complicated geometries,e.g.extremely sharp edges of the copper metallisation and protrusions in the substrate,and composite non-linear field grading materials.There is no model to take into account defects in the gel and on the ceramic substrate.IEC 61287-1 cannot sufficiently assess the behaviour of PDs on IGBT module under the actual operating conditions exposing fast rise pulse-width modulation-like voltages.There is no agreement on the exact origin and location of PDs in the module with relying on measured phase-resolved PD patterns.PD control methods using non-linear grading materials are not mature enough.展开更多
Although discovered more than 100 years ago, X-ray source technology has evolved rather slowly. The recent invention of the carbon nanotube （CNT） X-ray source technology holds great promise to revolutionize the fiel...Although discovered more than 100 years ago, X-ray source technology has evolved rather slowly. The recent invention of the carbon nanotube （CNT） X-ray source technology holds great promise to revolutionize the field of biomedical X-ray imaging. CNT X-ray sources have been successfully adapted to several biomedical imaging applications including dynamic rnicro-CT of small animals and stationary breast tomosynthesis of breast cancers. Yet their more irnportant biomedical imaging applications still lie ahead in the future, with the devel- oprnent of stationary rnulti-source CT as a noteworthy exarnple.展开更多
Recently the Journal of Mountain Science published three papers（Lumbres et al.2014;Jung et al.2015;Lumbres et al.2016）that compared selected taper models for bias and precision when estimating upper stem diameters f...Recently the Journal of Mountain Science published three papers（Lumbres et al.2014;Jung et al.2015;Lumbres et al.2016）that compared selected taper models for bias and precision when estimating upper stem diameters for various tree species.展开更多
In the 1950s,shortly after the founding of the People’s Republic of China(PRC),the central government created the Patriotic Health Campaign(PHC)in order to standardize and disseminate healthfocused educational materi...In the 1950s,shortly after the founding of the People’s Republic of China(PRC),the central government created the Patriotic Health Campaign(PHC)in order to standardize and disseminate healthfocused educational materials intended to control and prevent infectious diseases(1).“Water improvement”,meaning measures aimed at providing safe drinking water for households in China,was an important part of the PHC.After 60 years of water improvement policies.展开更多
文摘Increased voltage blocking capability and the development of packaging technology for IGBTs can enhance the local electric field that may become large enough to increase partial discharges(PDs)within the module.The study presents a survey on(i)simulation the electric field within an IGBT module;(ii)current standards for evaluation of the insulation systems of IGBTs;(iii)PD detection and localisation methods as well as other diagnostic and quality control test methods about IGBTs;and(iv)various methods for PD control in an IGBT module.The survey shows remarkable technical gaps in all four areas.More sophisticated numerical and theoretical techniques are needed to model complicated geometries,e.g.extremely sharp edges of the copper metallisation and protrusions in the substrate,and composite non-linear field grading materials.There is no model to take into account defects in the gel and on the ceramic substrate.IEC 61287-1 cannot sufficiently assess the behaviour of PDs on IGBT module under the actual operating conditions exposing fast rise pulse-width modulation-like voltages.There is no agreement on the exact origin and location of PDs in the module with relying on measured phase-resolved PD patterns.PD control methods using non-linear grading materials are not mature enough.
基金supported by Dr.Guohua Cao’s CAREER award from the U.S.National Science Foundation(CBET 1351936)
文摘Although discovered more than 100 years ago, X-ray source technology has evolved rather slowly. The recent invention of the carbon nanotube （CNT） X-ray source technology holds great promise to revolutionize the field of biomedical X-ray imaging. CNT X-ray sources have been successfully adapted to several biomedical imaging applications including dynamic rnicro-CT of small animals and stationary breast tomosynthesis of breast cancers. Yet their more irnportant biomedical imaging applications still lie ahead in the future, with the devel- oprnent of stationary rnulti-source CT as a noteworthy exarnple.
文摘Recently the Journal of Mountain Science published three papers（Lumbres et al.2014;Jung et al.2015;Lumbres et al.2016）that compared selected taper models for bias and precision when estimating upper stem diameters for various tree species.
文摘In the 1950s,shortly after the founding of the People’s Republic of China(PRC),the central government created the Patriotic Health Campaign(PHC)in order to standardize and disseminate healthfocused educational materials intended to control and prevent infectious diseases(1).“Water improvement”,meaning measures aimed at providing safe drinking water for households in China,was an important part of the PHC.After 60 years of water improvement policies.
