On singularity formation in three-dimensional vortex sheet evolution

It is shown that if a doubly-infinite vortex sheet has cylindrical shape and strength distributions at some initial time, then this property is retained in its subsequent evolution. It is also shown that in planes normal to the generator of the cylindrical sheet geometry, the nonlinear evolution of the sheet is the same as that of an equivalent strictly two-dimensional sheet motion. These properties are used to show that when an initially flat vortex sheet is subject to a finite-amplitude, three-dimensional normal mode perturbation, weak singularities develop along lines which are oblique to the undisturbed velocity jump vector at a time that can be inferred from an extension of Moore's [Proc. R. Soc. A 365, 105 (1979)] result for two-dimensional motion

Black hole singularities: a numerical approach

The singularity structure of charged spherical collapse is studied by considering the evolution of the gravity-scalar field system. A detailed examination of the geometry at late times strongly suggests the validity of the mass-inflation scenario~\cite{PI:90}. Although the area of the two-spheres remains finite at the Cauchy horizon, its generators are eventually focused to zero radius. Thus the null, mass-inflation singularity {\em generally}\/ precedes a crushing $r=0$ singularity deep inside the black hole core. This central singularity is spacelike.Comment: 4 pages Phys. Rev. style including five figures, provided as compressed postscript files. To appear in Physical Review Letter

Damping of vertical coronal loop kink oscillations through wave tunneling

The decay rate of vertical kink waves in a curved flux tube is modeled numerically. The full MHD equations are solved for a curved equilibrium flux tube in an arcade geometry and the decay of ψ, the integral over the flux tube of the modulus of the velocity perpendicular to the local magnetic field, is measured. These simulations are 2D and are thus restricted to kink oscillations in the loop plane. The decay rate is found to increase with increasing wavelength, increasing β and decreasing density contrast ratio. The wave tunneling effect is shown to be a possible mechanism for the high decay rate of the recent observed kink oscillation reported by Wang & Solanki (2004)

Unchartered Territory for the Bluegrass State : Lessons to be learned from over a Quarter-century of State Charter School Legislation

Charter school success or failure is not simply a matter of chance. Both the existence and aggregate quality of charter schools in a state depend on the provisions of state charter school laws. These laws address a wide range of issues and vary from state to state. But the experiences of states with significant charter sectors, as well as those with innovative charter policies, provide important lessons for the charter school movement as a whole

Sterilizable Liquid Propulsion System, Part 1 Final Report, 5 Oct. 1966 - 31 Mar. 1968

Exposure of assembled and fueled bipropellant liquid propulsion system to ethylene oxid

Intelligent Data Reduction (IDARE)

A description of the Intelligent Data Reduction (IDARE) expert system and an IDARE user's manual are given. IDARE is a data reduction system with the addition of a user profile infrastructure. The system was tested on a nickel-cadmium battery testbed. Information is given on installing, loading, maintaining the IDARE system

Functorial properties of Putnam's homology theory for Smale spaces

We investigate functorial properties of Putnam's homology theory for Smale spaces. Our analysis shows that the addition of a conjugacy condition is necessary to ensure functoriality. Several examples are discussed that elucidate the need for our additional hypotheses. Our second main result is a natural generalization of Putnam's Pullback Lemma from shifts of finite type to non-wandering Smale spaces.Comment: Updated to agree with published versio