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Simulating the Peculiar Periphery of the Cygnus Loop

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Research in Astronomy and Astrophysics 2024年第12期24卷 192-206页

作者： Jun-Yu Shen Bi-Wen Bao Li Zhang Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan ProvinceYunnan UniversityKunming 650091China Key Laboratory of Statistical Modeling and Data Analysis of Yunnan Province Yunnan UniversityKunming 650091China

The middle-aged Galactic supernova remnant (SNR)-the Cygnus Loop (CL)-displays a peculiar morphology in X-rays,featuring a blowout in the southern *** underlying process accounting for the formation of the peculiar periphery remains a *** this end,we conduct hydrodynamical simulations to investigate the SNR evolution coupled with a tailored stellar-wind model:a bipolar stellar wind emanating from a runaway red supergiant progenitor,excavating a wind-blown cavity elongated along *** simulation results reveal that the forward shock of the consequent SNR sweeps up the modified ambient media,shaping the overall morphology with a blowout comparable to that of ***,a series of simulation runs are performed to assess the impacts of different model parameters and the projection effect (observational angle θobs) on the final SNR *** physical quantities are extracted from simulation results to characterize the simulated SNR and make a direct comparison with the X-ray observations of *** find that the final SNR morphology is sensitive to both stellar-wind properties and θ_(obs).A Cygnus-Loop-like SNR could be reproduced under appropriate parameter combinations at θ_(obs)=0°.While for θ_(obs)■30°,the projected morphology akin to CL could be also generated under specific conditions.

关键词： hydrodynamics-methods numerical-ISM supernova remnants

Feedback of Efficient Shock Acceleration on Magnetic-field Structure Inside Young Type Ia Supernova Remnants

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Research in Astronomy and Astrophysics 2024年第6期24卷 234-244页

Using an effective adiabatic index γ_(eff) to mimic the feedback of efficient shock acceleration,we simulate the temporal evolution of a young type Ia supernova remnant (SNR) with two different background magnetic field(BMF) topologies:a uniform and a turbulent *** density distribution and magnetic-field characteristics of our benchmark SNR are studied with two-dimensional cylindrical magnetohydrodynamic *** γ_(eff)is considered,we find that:(1) the two-shock structure shrinks and the downstream magnetic-field orientation is dominated by the Rayleigh–Taylor instability structures;(2) there exists more quasi-radial magnetic fields inside the shocked region;and (3) inside the intershock region,both the quasi-radial magnetic energy density and the total magnetic energy density are enhanced:in the radial direction,with γ_(eff)=1.1,they are amplified about 10–26 times more than those with γ_(eff)=5/*** in the angular direction,the total magnetic energy densities could be amplified about 350 times more than those with γ_(eff)=5/3,and there are more grid cells within the intershock region where the magnetic energy density is amplified by a factor greater than 100.

关键词： methods:numerical ISM:magnetic fields ISM:supernova remnants magnetohydrodynamics(MHD)

Evidence for Magneto-gravitational Processes in Supermassive Black Hole Binary PG 1553+113

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arXiv 2025年

作者： Haiyun, Zhang Dahai, Yan Li, Zhang Niansheng, Tang Yunnan Key Laboratory of Statistical Modeling and Data Analysis Yunnan University Kunming650091 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China

PG 1553+113 has drawn significant attention for its quasi-periodic oscillation (QPO) in Υ-ray variability, though the origin of its variability remains uncertain. In this study, we propose a physical mechanism to explain the observed Υ-ray variability within the framework of a supermassive black hole binary (SMBHB) system, supported by a newly identified component hidden in the light curve. A detailed analysis for its ∼16-year light curve obtained from Fermi-LAT observations is performed by Gaussian process (GP). As anticipated, the QPO of 2.1 years (771 ± 8 days) is effectively captured by the stochastically-driven damped simple harmonic oscillator (SHO) kernel within the under-damped regime, and the overall stochastic nature of the variability is described by the damped random walk (DRW) kernel albeit with an unconstrained damping timescale. Additionally, our results reveal a previously unrecognized component in active galactic nuclei variability, characterized by the Matérn−3/2 kernel, which is typically associated with systems undergoing abrupt energy release. These findings can be consistently interpreted within the SMBHB framework. The QPO of ∼2.1 years is likely attributed to the orbital motion in a SMBHB system. The Matérn−3/2 component is interpreted as resulting from magnetic reconnection events triggered by gravitational perturbations of the magnetic field within the jet, occurring as one black hole approaches the other. Meanwhile, in this case, the damping timescale of the common DRW kernel remains unconstrained due to the influence of new perturbations within the system. Copyright © 2025, The Authors. All rights reserved.

关键词： Stochastic systems

Application of statistical shape models in orthopedics: a narrative review

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Intelligent Medicine 2024年第4期4卷 249-255页

作者： Xingbo Cai Ying Wu Junshen Huang Long Wang Yongqing Xu Sheng Lu Postgraduate College of Kunming Medical University KunmingYunnan 650500China Department of Orthopedics The First People’s Hospital of Yunnan ProvinceKunmingYunnan 650032China Key Lab of Statistical Modeling and Data Analysis of Yunnan Yunnan UniversityKunmingYunnan 650091China Yunnan Provincial Key Laboratory of Digital Orthopedics KunmingYunnan 662299China Lvweijia Expert Workstation KunmingYunnanChina Department of Orthopedics 920 Hospital of Chinese People’s Liberation Army Joint Logistic Support ForceKunmingYunnan 650032China

statistical shape models(SSMs)are effective for image processing and analysis and have been used in various medical fields,including face recognition and cranial bone *** orthopedics,SSMs are being used in numerous applications,such as automated segmentation of medical images,preoperative planning,intraoper-ative navigation combined with robotics,simulation reconstruction of defects,human biomechanics research,description of anatomical shape changes,and prosthesis *** review highlighted the wide range of ap-plications while acknowledging the diversity of methodologies and techniques encompassed by SSMs,including Gaussian process models and nonlinear *** addition,the available software packages for constructing shape models,such as Scalismo,ShapeWorks,and Deformetrica,were discussed.

关键词： statistical shape analysis Orthopedics Automated diagnosis support data reconstruction Segmentation

Robust Variable Selection and Estimation in Threshold Regression Model

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Acta Mathematicae Applicatae Sinica 2020年第2期36卷 332-346页

作者： Bo-wen LI Yun-qi ZHANG Nian-sheng TANG School of Management University of Science and Technology of ChinaHefei 230026China Key Lab of Statistical Modeling and Data Analysis of Yunnan Province Yunnan UniversityKunming 650091China

We combine the robust criterion with the lasso penalty together for the high-dimensional threshold *** estimates regression coefficients as well as the threshold parameter robustly that can be resistant to outliers or heavy-tailed noises and perform variable selection *** illustrate our approach with the absolute loss,the Huber’s loss,and the Tukey’s loss,it can also be extended to any other robust *** studies are conducted to demonstrate the usefulness of our robust ***,we use our estimators to investigate the presence of a shift in the effect of debt on future GDP growth.

关键词： Threshold regression Robust estimation Lasso

Pattern and Origin for the Extreme γ-ray Flares of 3C 454.3 and 3C 279: An Astrophysical Critical Damper?

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arXiv 2025年

作者： Zhang, Haiyun Yan, Dahai Zhou, Jianeng Zhang, Li Tang, Niansheng Yunnan Key Laboratory of Statistical Modeling and Data Analysis Yunnan University Kunming650091 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Shanghai Astronomical Observatory Chinese Academy of Sciences 80 Nandan Road Shanghai200030 China

We apply a Gaussian process method to the extreme γ-ray flares of 3C 454.3 and 3C 279 to discover the variable patterns and then to investigate the physical origins of the giant flares. The kernels of stochastically driven damped simple harmonic oscillator (SHO), the damped random-walk (DRW), and Matérn−3/2 are respectively used to describe the adaptive-binning γ-ray light curves of the two flares. Our findings show that both the extreme γ-ray flares of 3C 454.3 and 3C 279 clearly prefer the SHO kernel in the over-damped mode and the Matérn−3/2 kernel over the DRW kernel. The resulted SHO and Matérn−3/2 power spectral densities (PSDs) are the same for each object, with the index changing from -4 at high frequencies to 0 at low frequencies. The patterns of the two flares are both approaching the critical damping mode with the quality factor Q ≈ 0.4 (i.e., the damping ratio η ≈ 1.25), but with slightly different damping timescales. The characteristic timescale (corresponding to the broken frequency in the PSD) for 3C 454.3 is 2-3 days and 3-5 days for 3C 279. The variable patterns found here suggest that once the system responds to the energy injection disturbance, the release of the energy in the system is finished abruptly. The obtained timescale provides a constraint on the size of energy dissipation region for each source. Copyright © 2025, The Authors. All rights reserved.

关键词： Gamma rays

The Gamma/Weibull Customer Lifetime Model

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Communications in Mathematics and Statistics 2019年第1期7卷 33-59页

作者： Gen Ye Songjian Wang Key Lab of Statistical Modeling and Data Analysis of Yunnan Province Yunnan UniversityKunming 650091People’s Republic of China

This paper proposes a new customer lifetime model:the Gamma/Weibull distribution(G/W).Similar to the Pareto/NBD model,we propose a G/W/NBD model by combining the G/W distribution with a negative binomial distribution(NBD)and study its properties such as(i)the probability that a customer to be alive at a time point;(ii)the expectation and variance of the number of transactions for a customer during a fixed time period;(iii)the conditional expectation and conditional variance of the number of future transactions for a customer during a fixed time *** simulation studies are conducted to investigate the forecasting accuracy and flexibility of the proposed model.A CDNOW data set is analyzed by the proposed model.

关键词： Customer lifetime Gamma distribution Negative binomial distribution Purchase history Weibull distribution

Multi-band Emission up to PeV Energy from the Crab Nebula in a Spatially Dependent Lepto-hadronic Model

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arXiv 2021年

作者： Peng, Qi-Yong Bao, Bi-Wen Lu, Fang-Wu Zhang, Li Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory of Statistical Modeling and Data Analysis of Yunnan Province Yunnan University Kunming650091 China Department of Physics Yuxi Normal University Yuxi653100 China

Multi-band emission from radio to ultra-high energy gamma-rays in the Crab Nebula has been detected. To explain the observed results, non-thermal photon production in the Crab Nebula is carefully studied in a spatially dependent lepto-hadronic model. In our model, the dynamical evolution of the PWN is simulated in a spherically symmetric system. Both electrons and protons are accelerated at the termination shock. The relevant particle propagation equations as well as the photon evolving equation are simultaneously solved. For the Crab Nebula, our results reveal that the observed multi-band photon spectra can be well reproduced with reasonable model parameters. In particular, the photons with energy 200 TeV are mainly contributed by the hadronic component via proton-proton interaction. The contribution of the hadronic component depends on both proton spectral index αp and number density nH of medium within the PWN. Besides, high energy neutrino fluxes are predicted with variable proton spectral indices. The predicted fluxes are not only far below the sensitivities of current neutrino observatories, but also beneath the atmospheric neutrino background with energy less than ∼ 40 TeV. Moreover, the calculated radial profiles of surface brightness and spectral index are presented. © 2021, CC BY.

关键词： Photons

Possible hadronic origin of TeV photon emission from SNR G106.3+2.7

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arXiv 2021年

作者： Yang, Chuyuan Zeng, Houdun Bao, Biwen Zhang, Li Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory of Dark Matter and Space Astronomy Purple Mountain Observatory Chinese Academy of Sciences Nanjing210034 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory of Statistical Modeling and Data Analysis of Yunnan Province Yunnan University Kunming650091 China

Context. Recently, HAWC, ASγ, and LHAASO experiments have reported the gamma-ray spectrum of supernova remnant (SNR) G106.3+2.7 above 40 TeV, indicating that SNR G106.3+2.7 is a promising PeVatron candidate. However, the origin of the gamma-ray spectrum is still debated. Thus, a dedicated theoretical model with self-consistent descriptions is required to decipher the properties of the gamma-ray spectrum for this specific source. Aims. We construct a theoretical model to explain the multiband photon emission from the PeVatron SNR G106.3+2.7. Methods. In our model, the acceleration and propagation of particles from the Bohm-like diffusion region inside the SNR to the Galactic diffusion region outside the SNR are described through nonlinear diffusive shock acceleration (NLDSA). The main content of our NLDSA model is solving the hydrodynamic equations numerically for gas density, gas velocity, and gas pressure and the equation for the quasi-isotropic particle momentum distribution. The consequent multiband nonthermal emission stems from two different regions, namely the acceleration region and the escaping region. Results. Our model is capable of explaining the multiband photon emission via the dominant synchrotron radiation of the electrons accelerated inside the SNR. The photons with energy of GeV are naturally produced by the protons inside and outside the SNR. Moreover, photons in the energy range of ∼ 1- ∼ 100 TeV are due to the interaction of escaped protons with dense molecular clouds. Conclusions. For photons with energy Eγ 1 GeV from SNR G106.3+2.7, our results here favor a hadronic origin, where the photons in the energy range of ∼ 1 GeV to ∼ 1 TeV are produced inside the SNR through proton-proton interaction, while photons with Eγ 1 TeV originate from the interaction of escaped protons with a dense molecular cloud. Copyright © 2021, The Authors. All rights reserved.

关键词： Ultraviolet spectroscopy