This book on power-law attenuation also covers the topic in more detail. Pandey and Holm gave a physical meaning to fractional differential equations by deriving them from physical principles and interpreting the fractional-order in terms of the parameters of the acoustical media, example in fluid-saturated granular unconsolidated marine sediments. Interestingly, Pandey and Holm derived Lomnitz's law in seismology and Nutting's law in non-Newotnian rheology using the framework of fractional calculus. Nutting's law was used to model the wave propagation in marine sediments using fractional derivatives. The fractional Schrödinger equation, a fundamental equation of fractional quantum mechanics, has the following form:  where the solution of the equation is the wavefunction – the quantum mechanical probability amplitude for the particle to have a given position vector at any given time , and is the reduced Planck constant. The potential energy function depends on the system. Further, is the Laplace operator, and is a scale constant with physical dimension , (at , for a particle of mass ), and the operator is the 3-dimensional fractional quantum Riesz derivative defined by  The index in the fractional Schrödinger equation is the Lévy index, . As a natural generalization of the fractional Schrödinger equation, the variable-order fractional Schrödinger equation has been exploited to study fractional quantum phenomena:  where is the Laplace operator and the operator is the variable-order fractional quantum Riesz derivative.