Oscillating instanton solutions and classification of vacuum bubbles

We discuss the nucleation process of an oscillating instanton solution and a vacuum bubble in this presentation. We show that there exist the O(4)- symmetric oscillating instanton solution and the vacuum bubbles with arbitrary energies. The nontrivial solution corresponding to the tunneling is possible only when gravity is switched on. The geometry of these solutions is finite and preserves the Z2 symmetry. The action for the solutions are integrable both in de Sitter and in flat background. The instatons do not have any singularity. Our solutions can be interpreted as solutions describing an instanton-induced domain wall or braneworldlike object rather than a kink-induced domain wall or braneworld. The oscillating instanton solutions have a thick wall and the solutions can be interpreted as a mechanism providing nucleation of the thick wall for topological inflation

Instanton solutions mediating tunneling between the degenerate vacua in curved space

We investigate the instanton solution between the degenerate vacua in curved space. We show that there exist $O(4)$-symmetric solutions not only in de Sitter but also in both flat and anti-de Sitter space. The geometry of the new type of solutions is finite and preserves the $Z_2$ symmetry. The nontrivial solution corresponding to the tunneling is possible only if gravity is taken into account. The numerical solutions as well as the analytic computations using the thin-wall approximation are presented. We expect that these solutions do not have any negative mode as in the instanton solution.Comment: Some typos are corrected and references are added with respect to the published version. 17pages, 11fi

Oscillating instanton solutions in curved space

We investigate oscillating instanton solutions of a self-gravitating scalar field between degenerate vacua. We show that there exist O(4)-symmetric oscillating solutions in a de Sitter background. The geometry of this solution is finite and preserves the $Z_{2}$ symmetry. The nontrivial solution corresponding to tunneling is possible only if the effect of gravity is taken into account. We present numerical solutions of this instanton, including the phase diagram of solutions in terms of the parameters of the present work and the variation of energy densities. Our solutions can be interpreted as solutions describing an instanton-induced domain wall or braneworld-like object rather than a kink-induced domain wall or braneworld. The oscillating instanton solutions have a thick wall and the solutions can be interpreted as a mechanism providing nucleation of the thick wall for topological inflation. We remark that $Z_{2}$ invariant solutions also exist in a flat and anti-de Sitter background, though the physical significance is not clear.Comment: 25 pages, 11 figues. Some typos corrected, references added, and Ch3. modified according to referee's comment

Prediction Model of Drilling Performance for Percussive Rock Drilling Tool

This study suggests a method for quantitatively estimating the drilling performance of the down-the-hole (DTH) hammer during percussive drilling of rock surfaces. A pneumatic dynamic model of the DTH hammer was developed that considers the mass flow rate relations representing the orifice opening areas of the air tube, the piston, and bit flushing channels. A drill bit motion model was developed to represent the dynamics of a drill bit impacted by a dropped piston and explain the impact stress propagation and rock-crushing mechanism. The rock-crushing effect of the drill button bit was measured through a piston drop test. The pneumatic hammer model and drill bit motion model were then combined in a prediction model to determine the impact efficiency according to different rock types (i.e., soft, medium-hard, and very hard). The drilling efficiency was defined as the input value of the prediction model, which was used to simulate the drilling performance of DTH hammers considering the rock type and dynamic effect of the drill bit. Finally, the simulation results were compared with the results of in situ drilling tests for verification