Solar flare emission is detected in all EM bands and variations in flux density of solar energetic particles. Often the EM radiation generated in solar and stellar flares shows a pronounced oscillatory pattern, with characteristic periods ranging from a fraction of a second to several minutes. These oscillations are referred to as quasi-periodic pulsations (QPPs), to emphasise that they often contain apparent amplitude and period modulation. We review the current understanding of quasi-periodic pulsations in solar and stellar flares. In particular, we focus on the possible physical mechanisms, with an emphasis on the underlying physics that generates the resultant range of periodicities. These physical mechanisms include MHD oscillations, self-oscillatory mechanisms, oscillatory reconnection/reconnection reversal, wave-driven reconnection, two loop coalescence, MHD flow over-stability, the equivalent LCR-contour mechanism, and thermal-dynamical cycles. We also provide a histogram of all QPP events published in the literature at this time. The occurrence of QPPs puts additional constraints on the interpretation and understanding of the fundamental processes operating in flares, e.g. magnetic energy liberation and particle acceleration. Therefore, a full understanding of QPPs is essential in order to work towards an integrated model of solar and stellar flares.

中文翻译：

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模拟太阳耀斑和恒星耀斑中的准周期性脉动

在所有 EM 波段和太阳高能粒子通量密度的变化中都检测到太阳耀斑发射。太阳耀斑和恒星耀斑中产生的电磁辐射通常显示出明显的振荡模式，其特征周期从几分之一秒到几分钟不等。这些振荡被称为准周期脉动 (QPP)，以强调它们通常包含明显的幅度和周期调制。我们回顾了目前对太阳和恒星耀斑中准周期性脉动的理解。特别是，我们关注可能的物理机制，重点是产生周期性结果范围的基础物理。这些物理机制包括 MHD 振荡、自振荡机制、振荡重联/重联反转、波驱动重联、两个回路合并、MHD 流动过稳定性、等效的 LCR 轮廓机制和热动力循环。我们还提供了此时在文献中发表的所有 QPP 事件的直方图。QPP 的出现对解释和理解耀斑中运行的基本过程（例如磁能释放和粒子加速）提出了额外的限制。因此，为了建立太阳和恒星耀斑的综合模型，全面了解 QPP 是必不可少的。QPP 的出现对解释和理解耀斑中运行的基本过程（例如磁能释放和粒子加速）提出了额外的限制。因此，为了建立太阳和恒星耀斑的综合模型，全面了解 QPP 是必不可少的。QPP 的出现对解释和理解耀斑中运行的基本过程（例如磁能释放和粒子加速）提出了额外的限制。因此，为了建立太阳和恒星耀斑的综合模型，全面了解 QPP 是必不可少的。