December 3rd, 2019

лошадь, диаграмма, Фейнман

Квантовая и классическая динамика в фазовом пространстве лазера на свободных электронах

Quantum and classical phase-space dynamics of a free-electron laser:

In a quantum mechanical description of the free-electron laser (FEL) the electrons jump on discrete momentum ladders, while they follow continuous trajectories according to the classical description. In order to observe the transition from quantum to classical dynamics, it is not sufficient that many momentum levels are involved. Only if additionally the initial momentum spread of the electron beam is larger than the quantum mechanical recoil, caused by the emission and absorption of photons, the quantum dynamics in phase space resembles the classical one. Beyond these criteria, quantum signatures of averaged quantities like the FEL gain might be washed out.
лошадь, диаграмма, Фейнман

Исследование резонанса при ручном вздрючивании игрушечной пружины

Manually driven harmonic oscillator:

Oscillations and resonance are essential topics in physics that can be explored theoretically and experimentally in the classroom or teaching laboratory environments. However, one of the main challenges concerning the experimental study of resonance phenomena via forced oscillations is the control of the oscillation frequency, which demands an electronic circuit or a fine tuned coupled mechanical system. In this work, we demonstrate that, in what concerns the physics teaching, such demanding accessories are not necessary. The forced oscillations can be implemented by the teacher's hand guided by an oscillating circle displayed in a web application loaded in a smartphone. The oscillations are applied to an ordinary spiral toy. Qualitative, as well quantitative, proposals are explored in this work with excellent results.