Dynamic analysis of assembled structures with nonlinearity

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Instability of Tachyon Supertube in Type IIA Godel Spacetime

We study the tachyon supertube probes in a type IIA supergravity background which is a stringy-like G\"odel spacetime and contains closed timelike curve. In the case of small value of $f$, which is a parameter of the background, we use the Minahan-Zwiebach tachyon action to obtain a single regular tube solution and argue that the tube is a BPS D2-brane. However, we find that the fluctuation around the tube configuration has a negative-energy mode. This means that the tachyon supertube, despite being a BPS configuration, develops an instability in the pathological spacetime with closed timelike curve which violates the causality.Comment: Latex 12 pages, add more discussions in last sectio

Thermal Tachyon Cosmology

We show that in a multi D\={D} branes system with high temperature, there may exist a thermal cosmological phase before usual tachyon inflation. Though this thermal phase can be very transitory, it may has some interesting applications for early tachyon/brane cosmology.Comment: 5 pages, no figures. new version with 6 pages, part paragraphs were rewritten and title was slightly changed, to publish in PL

Transient temperature distribution in a finite cylinder and an infinite cylinder subjected to some boundary conditions

This thesis is concerned with the theoretical heat transfer analysis of solid cylinders. The first problem considered is the transient temperature distribution in a finite cylinder. This cylinder has a uniform initial temperature and a uniform constant surrounding temperature. This case is solved by the separation of variables. Combining the charts for the infinite cylinder and the charts for the infinite plate one can determine the solution to this case easily. If a uniform constant surface temperature is prescribed instead of a surrounding temperature, the solution can be obtained from the previous one by charging the Nusselt number to infinity. If the surface temperature changes with time, then it can be solved by the Duhamel\u27s theorem. The infinite cylinder with uniform internal heat generation is also included in this thesis. This cylinder has a uniform initial temperature distribution and a uniform constant surface temperature. This case is solved by the Laplace transformation. If surface temperature varies with time, the Duhamel\u27s theorem will again be applied --Abstract, page 2

On Tachyon Condensation of Intersecting Noncommutative Branes in M(atrix) Theory

The interaction between the intersecting noncommutative D-branes (or membranes) is investigated within the M(atrix) theory. We first evaluate the spectrum of the off-diagonal fluctuation and see that there is a tachyon mode, which signals the instability of the intersecting branes. We next explain in detail how the tachyon modes (which are the off-diagonal fluctuations) can be combined with the original branes (which are the diagonal elements) to become a new diagonal matrix, which then represents the new recombined configurations after the tachyon condensation. The tachyon condensation configurations of the noncommutative branes we find are different from those of the commutative cases studied in the previous literatures.Comment: Latex, 11 pages, typos correcte

A fully two-dimensional flux-corrected transport algorithm for hyperbolic partial differential equations

Thesis (Ph.D.) University of Alaska Fairbanks, 1989Numerical solutions of the hyperbolic partial differential equation, $\partial p\over\partial t$ + $\vec\nabla \cdot (p\vec u)$ = 0, will generally encounter the difficulties of large diffusion and oscillations near steep gradients or discontinuities. The method of Flux-Corrected Transport (FCT) developed by Boris and Book has conquered these difficulties for the one-dimensional case. Motivated by this one-dimensional FCT algorithm, a fully two-dimensional FCT algorithm is developed in this present work. This fully two-dimensional FCT algorithm is a two-step procedure: (1) the transport scheme, and (2) the antidiffusion scheme. The second step of the procedure could also be replaced by an application of the one-dimensional antidiffusion algorithm in the x direction and the y direction separately. The stability, phase shift errors and positivity for the fully two-dimensional transport scheme are analyzed. Test results are presented. The possibility of the extension of the FCT method to three dimensions are discussed