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  2. Crossing (physics) - Wikipedia

    en.wikipedia.org/wiki/Crossing_(physics)

    In quantum field theory, a branch of theoretical physics, crossing is the property of scattering amplitudes that allows antiparticles to be interpreted as particles going backwards in time. Crossing states that the same formula that determines the S-matrix elements and scattering amplitudes for particle to scatter with and produce particle and ...

  3. Category:Level crossings - Wikipedia

    en.wikipedia.org/wiki/Category:Level_crossings

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  4. Level crossing signals - Wikipedia

    en.wikipedia.org/wiki/Level_crossing_signals

    Level crossing signals are electronic warning devices for road vehicles at railroad level crossings. Level crossings can be operated in various ways. In some countries such as the UK, the warning devices are more often than not activated by remote control, I.e. an operator pressing buttons. However, the majority of countries have automated systems.

  5. Subatomic particle - Wikipedia

    en.wikipedia.org/wiki/Subatomic_particle

    The subatomic particles considered important in the understanding of chemistry are the electron, the proton, and the neutron. Nuclear physics deals with how protons and neutrons arrange themselves in nuclei. The study of subatomic particles, atoms and molecules, and their structure and interactions, requires quantum mechanics.

  6. Neutrino - Wikipedia

    en.wikipedia.org/wiki/Neutrino

    The neutrino [a] was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and angular momentum ().In contrast to Niels Bohr, who proposed a statistical version of the conservation laws to explain the observed continuous energy spectra in beta decay, Pauli hypothesized an undetected particle that he called a "neutron", using the same -on ending ...

  7. Polariton - Wikipedia

    en.wikipedia.org/wiki/Polariton

    They are an expression of level repulsion (quantum phenomenon), also known as the avoided crossing principle. To this extent polaritons can be thought of as the new normal modes of a given material or structure arising from the strong coupling of the bare modes, which are the photon and the dipolar oscillation.

  8. Nucleosynthesis - Wikipedia

    en.wikipedia.org/wiki/Nucleosynthesis

    Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium (called 'metals' by astrophysicists) remains small (few percent), so that the universe still has approximately ...

  9. Intersystem crossing - Wikipedia

    en.wikipedia.org/wiki/Intersystem_crossing

    Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity. [ 1 ] Excited electrons can undergo intersystem crossing to a degenerate state with a different spin multiplicity.