Constant velocity experiment description

Physically this description corresponds to putting an atom (mass M) in an external time-dependent harmonic potential (frequency co0). The potential relaxes exponentially in time (time constant l/x0) so that eventually the atom experiences only a frictional force. Compared with other models2 which have been proposed for neutron scattering calculation, the present model treats oscillatory and diffusive motions of an atom in terms of a single equation. Both types of motion are governed by the shape of the potential and the manner in which it decays. The model yields the same velocity auto-correlation function v /(r) as that obtained by Berne, Boon, and Rice2 using the memory function approach. 

The parameters measured in an ultrasonic experiment are the amplimde and phase of the signal. They are determined by attenuation and phase velocity of a wave. In turn, the attenuation and phase velocity are associated with material constants. In our case they are elastic coefficients (or elastic moduli). These constants can be calculated using quanmm-mechanical approach. Finally, we will obtain the expressions for the measured (phenomenological) parameters in terms of the microscopic ones. In the present section we will discuss the basics of the phenomenological elasticity theory and the microscopic description of the Jahn-Teller contribution to the elastic moduli will be discussed later. 

The description of the secondary reactions in the gas phase is further complicated by the fact that electron concentration and average electron velocity or energy do not remain constant for the entire experiment because... 

Experience has shown that a quantitative description of the properties of atomic systems is not possible on the basis of the laws of classical physics. Quantum physics represents an attempt at a generalisation of these laws in the sense that a certain constant, Planck s constant, has a finite value A== 6 55.10 erg sec in contrast to classical physics, corresponding to the limit A=0, just as relativistic physics is a generalisation of non-relativistic physics, the latter arising from the former by passing from a finite value of the velocity of light c to an infinite value. Quantum physics in its present form appears adequate for dealing with all questions in which the internal constitution of the electron and the atomic nuclei as well as the theory of relativity need not be taken into ac-... 

There are, of course, other situations in science. We cannot understand magnetic and electric phenomena on the basis of mechanics without introducing new postulates, which are the generalization of experiments and could not be derived logically from the laws of mechanics. The introduction of new postulates is always connected to the appearance of universal constants (for electrical and magnetic phenomena, i.e., the velocity of light propagation, c). An adequate description of the laws of the microworld requires the introduction of quantum mechanical postulates and the universal constant "h" (Planck s constant). 

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