Treating the universe as a quantum system, we investigate impact of non-trivial sound speed circuit complexity on inflationary period, in which is within type resonant characterized by parameter ξ. The vacuum state curvature perturbation could be treated squeezed states with two modes, most essential parameters: angle ϕk and squeezing rk. Through Schrödinger equation, more deviation will lead t...

To provide constraints on the inversion of ocean sound speed profiles (SSPs), SSPs are often modeled using empirical orthogonal functions (EOFs). However, this regularization, which uses the leading order EOFs with a minimum-energy constraint on the coefficients, often yields low resolution SSP estimates. In this paper, it is shown that dictionary learning, a form of unsupervised machine learni...

A usual causal requirement on a viable theory of matter is that the speed of sound be at most the speed of light. In view of various recent papers querying this limit, the question is revisited here. We point to various issues confronting theories that violate the usual constraint.

We calculate the speed of sound cs in an ideal gas of resonances, whose mass spectrum is assumed to have the Hagedorn form ρ(m) ∼ m exp{bm}, which leads to singular behavior at the critical temperature Tc = 1/b. With a = 4 the pressure and the energy density remain finite at Tc, while the specific heat diverges there. As a function of the temperature, the corresponding speed of sound initially ...