The spectral energy distribution(SED) of TeV blazars has a double-humped shape that is usually interpreted as a Synchrotron Self Compton(SSC) model.The one zone SSC model is used broadly but cannot fit the high energy...The spectral energy distribution(SED) of TeV blazars has a double-humped shape that is usually interpreted as a Synchrotron Self Compton(SSC) model.The one zone SSC model is used broadly but cannot fit the high energy tail of SED very well.It needs a bulk Lorentz factor which is in conflict with the observation.Furthermore,a one zone SSC model cannot explain the entire spectrum.We propose a new model where the high energy emission is produced by the accelerated protons in the blob with a small size and high magnetic field,and the low energy radiation comes from the electrons in the expanded blob.Because the high and low energy photons are not produced at the same time,the requirement of a large Doppler factor from pair production is relaxed.We present the fitting results of the SEDs for Mrk 501 during April 1997 and Mrk 421 during March 2001.展开更多
With the Zebiak-Cane model and a parameterized stochastic representation of intraseasonal forcing, the impact of the uncertainties of Madden Jullian Oscillation （MJO） on the ＂Spring Predictability Barrier （SPB）＂...With the Zebiak-Cane model and a parameterized stochastic representation of intraseasonal forcing, the impact of the uncertainties of Madden Jullian Oscillation （MJO） on the ＂Spring Predictability Barrier （SPB）＂ for El Nifio-Southern Oscillation （ENSO） prediction is studied. The parameterized form of MJO forcing is added physically to the Zebiak-Cane model to obtain the so-called Zebiak-Cane-MJO model and then the effects of initial error, stochastic model error, and their joint error mode on the SPB associated with El Nifio prediction are estimated. The results show that the model errors caused by stochastic MJO forcing could hardly lead to a significant SPB while initial errors can do; furthermore, the joint error mode of initial error and model error associated with the stochastic MJO forcing can also lead to a significant SPB. These demonstrate that the initial error is probably the main error source of the SPB, which may provide a theoretical foundation of data assimilation for ENSO forecasts.展开更多
Semiconducting cubic group IV monotellurides,including PbTe and SnTe, have historically led most of the advancements in thermoelectrics. Recently, noncubic ones such as GeTe and MnTe have also shown to be promising,wh...Semiconducting cubic group IV monotellurides,including PbTe and SnTe, have historically led most of the advancements in thermoelectrics. Recently, noncubic ones such as GeTe and MnTe have also shown to be promising,which motivates the current work focusing on the thermoelectric properties of MnGeTe2, a derivative compound of noncubic GeTe and MnTe but crystalizing in a cubic structure.This compound intrinsically comes with a carrier concentration as high as ~3.6×1021 cm-3, indicating the existence of highconcentration cation vacancies due to Ge-precipitation. This intrinsic carrier concentration is much higher than that needed for thermoelectric applications but can be successfully decreased to ~9×1020 cm-3 for MnGe0.9Bi0.1Te2 at room temperature. Such a broad carrier concentration not only offers a full assessment of its electronic transport properties according to a single parabolic band model with acoustic scattering, but also enables an optimization for thermoelectric power factor.The low lattice thermal conductivity of ~1.2 W m-1 K-1 or lower in the entire temperature range, can be understood by the highly disordered cations and cation vacancies. A peak zT approaching 1.0 at 850 K was achieved in materials at an optimal carrier concentration of ~9×1020 cm-3, an isotropic cubic structure as well as a Vickers hardness of >200 HV, strongly indicating MnGeTe2 as a promising thermoelectric material.展开更多
基金National Key Research and Development Program of China(2018YFB0703600)National Natural Science Foundation of China(11474219,51772215)+2 种基金Fok Ying Tung Education Foundation(20170072210001)Fundamental Research Funds for Shanghai Science and Technology Innovation Plan(18JC1414600)Fundamental Research Funds for the Central Universities
基金supported by the National Natural Science Foundation of China (Grant Nos. 10673028 and 10778702)the National Basic Research Program of China (Grant No. 2009CB824800)
文摘The spectral energy distribution(SED) of TeV blazars has a double-humped shape that is usually interpreted as a Synchrotron Self Compton(SSC) model.The one zone SSC model is used broadly but cannot fit the high energy tail of SED very well.It needs a bulk Lorentz factor which is in conflict with the observation.Furthermore,a one zone SSC model cannot explain the entire spectrum.We propose a new model where the high energy emission is produced by the accelerated protons in the blob with a small size and high magnetic field,and the low energy radiation comes from the electrons in the expanded blob.Because the high and low energy photons are not produced at the same time,the requirement of a large Doppler factor from pair production is relaxed.We present the fitting results of the SEDs for Mrk 501 during April 1997 and Mrk 421 during March 2001.
基金Supported by Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-QN203)National Basic Research and Development (973) Program of China (2010CB950400 and 2012CB955202)National Natural Science Foundation of China (41176013)
文摘With the Zebiak-Cane model and a parameterized stochastic representation of intraseasonal forcing, the impact of the uncertainties of Madden Jullian Oscillation （MJO） on the ＂Spring Predictability Barrier （SPB）＂ for El Nifio-Southern Oscillation （ENSO） prediction is studied. The parameterized form of MJO forcing is added physically to the Zebiak-Cane model to obtain the so-called Zebiak-Cane-MJO model and then the effects of initial error, stochastic model error, and their joint error mode on the SPB associated with El Nifio prediction are estimated. The results show that the model errors caused by stochastic MJO forcing could hardly lead to a significant SPB while initial errors can do; furthermore, the joint error mode of initial error and model error associated with the stochastic MJO forcing can also lead to a significant SPB. These demonstrate that the initial error is probably the main error source of the SPB, which may provide a theoretical foundation of data assimilation for ENSO forecasts.
基金supported by the National Natural Science Foundation of China (11474219 and 51772215)the National Key Research and Development Program of China (2018YFB0703600)+3 种基金the Fundamental Research Funds for Science and Technology Innovation Plan of Shanghai (18JC1414600)Fok Ying Tung Education Foundation (20170072210001)"Shu Guang" Project Supported by Shanghai Municipal Education CommissionShanghai Education Development Foundation
文摘Semiconducting cubic group IV monotellurides,including PbTe and SnTe, have historically led most of the advancements in thermoelectrics. Recently, noncubic ones such as GeTe and MnTe have also shown to be promising,which motivates the current work focusing on the thermoelectric properties of MnGeTe2, a derivative compound of noncubic GeTe and MnTe but crystalizing in a cubic structure.This compound intrinsically comes with a carrier concentration as high as ~3.6×1021 cm-3, indicating the existence of highconcentration cation vacancies due to Ge-precipitation. This intrinsic carrier concentration is much higher than that needed for thermoelectric applications but can be successfully decreased to ~9×1020 cm-3 for MnGe0.9Bi0.1Te2 at room temperature. Such a broad carrier concentration not only offers a full assessment of its electronic transport properties according to a single parabolic band model with acoustic scattering, but also enables an optimization for thermoelectric power factor.The low lattice thermal conductivity of ~1.2 W m-1 K-1 or lower in the entire temperature range, can be understood by the highly disordered cations and cation vacancies. A peak zT approaching 1.0 at 850 K was achieved in materials at an optimal carrier concentration of ~9×1020 cm-3, an isotropic cubic structure as well as a Vickers hardness of >200 HV, strongly indicating MnGeTe2 as a promising thermoelectric material.
