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
We rederive from first principles and generalize the theoretical framework of the nonlinear Gaussian noise model to the case of coherent optical systems with multiple fiber types per span and ideal Nyquist spectra.We ...We rederive from first principles and generalize the theoretical framework of the nonlinear Gaussian noise model to the case of coherent optical systems with multiple fiber types per span and ideal Nyquist spectra.We focus on the accurate numerical evaluation of the integral for the nonlinear noise variance for hybrid fiber spans.This task consists in addressing four computational aspects:(1)Adopting a novel transformation of variables(other than using hyperbolic coordinates)that changes the integrand to a more appropriate form for numerical quadrature;(2)Evaluating analytically the integral at its lower limit,where the integrand presents a singularity;(3)Dividing the interval of integration into subintervals of size and approximating the integral over each subinterval by using various algorithms;and(4)Deriving an upper bound for the relative error when the interval of integration is truncated in order to accelerate computation.We apply the proposed analytical model to the performance evaluation of coherent optical communications systems with hybrid fiber spans composed of quasi-single-mode and single-mode fiber segments.More specifically,the model is used to optimize the lengths of the optical fiber segments that compose each span in order to maximize the system performance.We check the validity of the optimal fiber segment lengths per span provided by the analytical model by using Monte Carlo simulation,where the Manakov equation is solved numerically using the split-step Fourier method.We show that the analytical model predicts the lengths of the optical fiber segments per span with satisfactory accuracy so that the system performance,in terms of the Q-factor,is within 0.1 dB from the maximum given by Monte Carlo simulation.展开更多
基金Supported by National High Technology Research and Development Program of China （863 Program） （2006AA01Z197, 2007AA01Z172） and National Natural Science Foundation of China （60673019, 60435020）
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.
文摘We rederive from first principles and generalize the theoretical framework of the nonlinear Gaussian noise model to the case of coherent optical systems with multiple fiber types per span and ideal Nyquist spectra.We focus on the accurate numerical evaluation of the integral for the nonlinear noise variance for hybrid fiber spans.This task consists in addressing four computational aspects:(1)Adopting a novel transformation of variables(other than using hyperbolic coordinates)that changes the integrand to a more appropriate form for numerical quadrature;(2)Evaluating analytically the integral at its lower limit,where the integrand presents a singularity;(3)Dividing the interval of integration into subintervals of size and approximating the integral over each subinterval by using various algorithms;and(4)Deriving an upper bound for the relative error when the interval of integration is truncated in order to accelerate computation.We apply the proposed analytical model to the performance evaluation of coherent optical communications systems with hybrid fiber spans composed of quasi-single-mode and single-mode fiber segments.More specifically,the model is used to optimize the lengths of the optical fiber segments that compose each span in order to maximize the system performance.We check the validity of the optimal fiber segment lengths per span provided by the analytical model by using Monte Carlo simulation,where the Manakov equation is solved numerically using the split-step Fourier method.We show that the analytical model predicts the lengths of the optical fiber segments per span with satisfactory accuracy so that the system performance,in terms of the Q-factor,is within 0.1 dB from the maximum given by Monte Carlo simulation.
