It is shown that the recently claimed two new Brans-Dicke wormhole solutions [F. He and S-W. Kim, Phys. Rev. D65, 084022 (2002) There has been a revival of interest in the Brans-Dicke theory (BDT) in recent times, particularly in the context of traversable Lorentzian wormholes. Now a days, BDT is no longer regarded merely as a Machian competitor to Einstein's General Relativity Theory (GRT) but a little more. There are several reasons. The principal reason is of course that BDT describes weak field tests of gravity reasonably well. Apart from this, it is known that the BD scalar field φ plays the role of classical exotic matter required for the construction of traversable Lorentzian wormholes [1].In a recent paper, He and Kim [2] have found two new classes of solutions of BDT and showed that the solutions represent massive Lorentzian traversable wormholes. The purpose of this short Comment is to demonstrate that these solutions can be alternatively derived by exploiting the conformal invariance of the vacuum BDT action. That is, we show that the claimed solutions are merely the Class I and II solutions of BDT in a different gauge and thus are not essentially new.We start from the BD action given by (we take units G = c = 1):

No abstract

The present paper aims to complete an earlier paper where the acoustic world was introduced. This is accomplished by analyzing the interactions which occur between the inhomogeneities of the acoustic medium, which are induced by the acoustic vibrations travelling in the medium. When a wave packet travels in a medium, the medium becomes inhomogeneous. The spherical wave packet behaves like an acoustic spherical lens for the acoustic plane waves. According to the principle of causality, there is an interaction between the wave and plane wave packet. In specific conditions, the wave packet behaves as an acoustic black hole.

No abstract

The aim of this paper is to investigate the coupled oscillations of multiple bubbles within a cluster. The interaction between a bubble and the other bubbles in a cluster produces an additional mass. For a fixed number of bubbles and uniformly distributed (N ---gt------gt--- 1), in case of a certain value of the bubbles number density, we deduce the relations analogous to the Eddington relation (between the cluster radius and the bubble radius) and the Sciama relation (between the cluster radius and the gravitoacoustic radius) according to Mach’s Principle.