Dilaton thin-shell wormholes supported by a generalized Chaplygin gas

In this article, we construct spherical thin-shell wormholes with charge in dilaton gravity. The exotic matter required for the construction is provided by a generalized Chaplygin gas. We study the stability under perturbations preserving the symmetry. We find that the increase of the coupling between the dilaton and the electromagnetic fields reduces the range of the parameters for which stable configurations are possible.Comment: 14 pages, 6 figures. v3: typos correcte

Thin-shell wormholes with a generalized Chaplygin gas

In this article, spherically symmetric thin-shell wormholes supported by a generalized Chaplygin gas are constructed and their stability under perturbations preserving the symmetry is studied. Wormholes with charge and with a cosmological constant are analyzed and the results are compared with those obtained for the original Chaplygin gas, which was considered in a previous work. For some values of the parameters, one stable configuration is also present and a new extra unstable solution is found.Comment: 14 pages, 6 figures; v2: typos corrected and minor rewordin

Gravitationally Collapsing Shells in (2+1) Dimensions

We study gravitationally collapsing models of pressureless dust, fluids with pressure, and the generalized Chaplygin gas (GCG) shell in (2+1)-dimensional spacetimes. Various collapse scenarios are investigated under a variety of the background configurations such as anti-de Sitter(AdS) black hole, de Sitter (dS) space, flat and AdS space with a conical deficit. As with the case of a disk of dust, we find that the collapse of a dust shell coincides with the Oppenheimer-Snyder type collapse to a black hole provided the initial density is sufficiently large. We also find -- for all types of shell -- that collapse to a naked singularity is possible under a broad variety of initial conditions. For shells with pressure this singularity can occur for a finite radius of the shell. We also find that GCG shells exhibit diverse collapse scenarios, which can be easily demonstrated by an effective potential analysis.Comment: 27 pages, Latex, 11 figures, typos corrected, references added, minor amendments in introduction and conclusion introd

Stress condensation in crushed elastic manifolds

We discuss an M-dimensional phantom elastic manifold of linear size L crushed into a small sphere of radius R << L in N-dimensional space. We investigate the low elastic energy states of 2-sheets (M=2) and 3-sheets (M=3) using analytic methods and lattice simulations. When N \geq 2M the curvature energy is uniformly distributed in the sheet and the strain energy is negligible. But when N=M+1 and M>1, both energies appear to be condensed into a network of narrow M-1 dimensional ridges. The ridges appear straight over distances comparable to the confining radius R.Comment: 4 pages, RevTeX + epsf, 4 figures, Submitted to Phys. Rev. Let

Progress towards a rapid method for conceptual aerodynamic design for transonic cruise

Results are presented from a study aimed at demonstrating the accuracy and efficiency of a lower order aerodynamic prediction method for transonic cruise flows around aircraft configurations, including conventional swept wing-body and also blended wing-body designs. The Viscous Full Potential (VFP) method, coupling the solution of the full potential equations with the integral boundary layer equations can yield data of almost equivalent accuracy as Navier-Stokes based CFD methods but at 0.5% - 2% of the physical time. In addition it is shown, using both the VFP approach and Delayed Detached Eddy Simulation (DDES) that the flow physics of the stall mechanism associated with blended wing-body configurations is far more complex than that experienced on more conventional swept-tapered wings. The mechanism appears to involve an initial tip stall but also involves highly 3D vortical flows inboard on the upper surface of the wing which significantly distorts the transonic shock wave

Vortical Patterns in the Wake of an Oscillating Airfoil

The vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes are studied in a low speed water channel. it is shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude and also the shape of the oscillation waveform. An important observation in this study has been the existence of an axial flow along the cores of the wake vortices. Estimates of the magnitude of the axial flow suggest a linear dependence on the oscillation frequency and amplitude

Stability of Chaplygin gas thin-shell wormholes

In this paper we construct spherical thin-shell wormholes supported by a Chaplygin gas. For a rather general class of geometries we introduce a new approach for the stability analysis of static solutions under perturbations preserving the symmetry. We apply this to wormholes constructed from Schwarzschild, Schwarzschild-de Sitter, Schwarzschild-anti de Sitter and Reissner-Nordstrom metrics. In the last two cases, we find that there are values of the parameters for which stable static solutions exist.Comment: 14 pages, 5 figures; v2: minor changes and new references added. Accepted for publication in Physical Review

Isolated Gust Generation for the Investigation of Airfoil-Gust Interaction

As part of an effort to examine the impact of vortical gusts on airfoils, a simple gust generator has been built and investigated. This consists of a heaving at plate capable of following a specifed transverse trajectory across a water tunnel. The relationship between the trajectory and the properties of the gusts that are shed downstream is characterized for non-periodic heaving motion described by Eldredge's smooth motion equation. PIV experiments show that the circulation of the vortical gust is proportional to the heaving speed of the plate. Tests with a downstream NACA 0018 airfoil demonstrate repeatable forces in response to the produced gusts

Mechanism of Deep-focus Earthquakes Anomalous Statistics

Analyzing the NEIC-data we have shown that the spatial deep-focus earthquake distribution in the Earth interior over the 1993-2006 is characterized by the clearly defined periodical fine discrete structure with period L=50 km, which is solely generated by earthquakes with magnitude M 3.9 to 5.3 and only on the convergent boundary of plates. To describe the formation of this structure we used the model of complex systems by A. Volynskii and S. Bazhenov. The key property of this model consists in the presence of a rigid coating on a soft substratum. It is shown that in subduction processes the role of a rigid coating plays the slab substance (lithosphere) and the upper mantle acts as a soft substratum. Within the framework of this model we have obtained the estimation of average values of stress in the upper mantle and Young's modulus for the oceanic slab (lithosphere) and upper mantle.Comment: 9 pages, 7 figure