Charged Cosmic String Nucleation in de Sitter Space

We investigate the quantum nucleation of pairs of charged circular cosmic strings in de Sitter space. By including self-gravity we obtain the classical potential energy barrier and compute the quantum mechanical tunneling probability in the semiclassical approximation. We also discuss the classical evolution of charged circular strings after their nucleation.Comment: 12 pages Latex + 3 figures (not included), Nordita 94/38

Cosmic String Nucleation near the Inflationary Phase Boundary

We investigate the nucleation of circular cosmic strings in models of generalized inflationary universes with an accelerating scale factor. We consider toy cosmological models of a smooth inflationary exit and transition into a flat Minkowski spacetime. Our results establish that an inflationary expanding phase is necessary but not sufficient for quantum nucleation of circular cosmic strings to occur.Comment: 11 pages Latex + 4 figures (not included), NBI-HE-94-2

Charged Open Membrane Solutions On A Manifold With Boundary

Explicit open single and multi-membrane solutions of the low energy limit of M-theory on the orbifold $R^{10}\times S^1/Z_2$ are presented. This low energy action is described by an 11-dimensional supergravity action coupled to two $E_8$ super Yang-Mills fields, which propagate only on the 10-dimensional boundaries of the target space. The membrane solutions we construct preserve half the supersymmetries. They carry electric charge and current with respect to the gauge fields, whose generators are in the Cartan subalgebra of the two $E_8$ gauge groups present at the boundaries.Comment: 14 pages, Late

Hawking Temperature and String Scattering off the 2+1 Black Hole

The 2+1 black hole anti de Sitter solution, obtained as a special limit of the conformally exact $SL(2,R)\otimes SO(1,1)/SO(1,1)$ coset WZW model to all orders in 1/k, is investigated with respect to tachyon scattering. We calculate the off-shell reflection and transmission coefficients and we find an expression for the Hawking temperature, which in a certain limit reduces to the statistical result.Comment: 12 pages Latex + 2 figures (not included), NBI-HE-94-1

Null Strings in Schwarzschild Spacetime

The null string equations of motion and constraints in the Schwarzschild spacetime are given. The solutions are those of the null geodesics of General Relativity appended by a null string constraint in which the "constants of motion" depend on the world-sheet spatial coordinate. Because of the extended nature of a string, the physical interpretation of the solutions is completely different from the point particle case. In particular, a null string is generally not propagating in a plane through the origin, although each of its individual points is. Some special solutions are obtained and their physical interpretation is given. Especially, the solution for a null string with a constant radial coordinate $r$ moving vertically from the south pole to the north pole around the photon sphere, is presented. A general discussion of classical null/tensile strings as compared to massless/massive particles is given. For instance, tensile circular solutions with a constant radial coordinate $r$ do not exist at all. The results are discussed in relation to the previous literature on the subject.Comment: 16 pages, REVTEX, no figure

Molecular characterization and temporal expression profiling of presenilins in the developing porcine brain

<p>Abstract</p> <p>Background</p> <p>The transmembrane presenilin (PSEN) proteins, PSEN1 and PSEN2, have been proposed to be the catalytic components of the γ-secretase protein complex, which is an intramembranous multimeric protease involved in development, cell regulatory processes, and neurodegeneration in Alzheimer's disease. Here we describe the sequencing, chromosomal mapping, and polymorphism analysis of PSEN1 and PSEN2 in the domestic pig (<it>Sus scrofa domesticus</it>).</p> <p>Results</p> <p>The porcine presenilin proteins showed a high degree of homology over their entire sequences to the PSENs from mouse, bovine, and human. PSEN1 and PSEN2 transcription was examined during prenatal development of the brain stem, hippocampus, cortex, basal ganglia, and cerebellum at embryonic days 60, 80, 100, and 114, which revealed distinct temporal- and tissue-specific expression profiles. Furthermore, immunohistochemical analysis of PSEN1 and PSEN2 showed similar localization of the proteins predominantly in neuronal cells in all examined brain areas.</p> <p>Conclusion</p> <p>The data provide evidence for structural and functional conservation of PSENs in mammalian lineages, and may suggest that the high sequence similarity and colocalization of PSEN1 and PSEN2 in brain tissue reflect a certain degree of functional redundancy. The data show that pigs may provide a new animal model for detailed analysis of the developmental functions of the PSENs.</p

Chaotic Scattering and Capture of Strings by Black Hole

We consider scattering and capture of circular cosmic strings by a Schwarzschild black hole. Although being a priori a very simple axially symmetric two-body problem, it shows all the features of chaotic scattering. In particular, it contains a fractal set of unstable periodic solutions; a so-called strange repellor. We study the different types of trajectories and obtain the fractal dimension of the basin-boundary separating the space of initial conditions according to the different asymptotic outcomes. We also consider the fractal dimension as a function of energy, and discuss the transition from order to chaos.Comment: RevTeX 3.1, 9 pages, 5 figure