32,902 research outputs found
Recent developments in Vorton Theory
This article provides a concise overview of recent theoretical results
concerning the theory of vortons, which are defined to be (centrifugally
supported) equilibrium configurations of (current carrying) cosmic string
loops. Following a presentation of the results of work on the dynamical
evolution of small circular string loops, whose minimum energy states are the
simplest examples of vortons, recent order of magnitude estimates of the
cosmological density of vortons produced in various kinds of theoretical
scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq,
Franc
Cosmic Vortons and Particle Physics Constraints
We investigate the cosmological consequences of particle physics theories
that admit stable loops of superconducting cosmic string - {\it vortons}.
General symmetry breaking schemes are considered, in which strings are formed
at one energy scale and subsequently become superconducting in a secondary
phase transition at what may be a considerably lower energy scale. We estimate
the abundances of the ensuing vortons, and thereby derive constraints on the
relevant particle physics models from cosmological observations. These
constraints significantly restrict the category of admissible Grand Unified
theories, but are quite compatible with recently proposed effects whereby
superconducting strings may have been formed close to the electroweak phase
transition.Comment: 33 pages, 2 figures, RevTe
Renormalisation of gravitational self interaction for wiggly strings
It is shown that for any elastic string model with energy density and
tension , the divergent contribution from gravitational self interaction can
be allowed for by an action renormalisation proportional to . This
formula is applied to the important special case of a bare model of the
transonic type (characterised by a constant value of the product ) that
represents the macroscopically averaged effect of shortwavelength wiggles on an
underlying microscopic model of the Nambu-Goto type (characterised by ).Comment: 11 pages, Latex; original 8 page version extended to include
estimates of relevant orders of magnitude. To be published in Physical
Review,
A single-board preprocessor and pulse generator
The Aeronomy Lab. of NOAA has designed and built a single board, programmable radar controller for use with VHF ST (stratosphere troposphere) radars. The controller consists of a coherent integrator preprocessor and a radar pulse generator, both of which are described, as well as interfaces to an antenna beam switch and a receiver bandwidth switch. The controller occupies a single slot in a Data General Nova of Eclipse computer. The integrator and pulse generator take advantage of high density, dual port FIFO chips such as the 512 x 9 Mostek MK 4501. These FIFOs have separate input and output ports and independent read and write cycles with cycle times of less than 200 ns, making them very fast and easy to interface. A simple block diagram of the coherent integrator is shown. The integrator is designed to handle inputs from one receiver (2 channels) with 1 sec sample spacing. The pulse generator is based on controllers designed by R. F. Woodman for the Arecibo and SOUSY radars us a recirculating memory scheme
Dynamical Stability of Witten Rings
The dynamical stability of cosmic rings, or vortons, is investigated for the
particular equation of state given by the Witten bosonic model. It is found
that there exists a finite range of the state parameter for which the vorton
states are actually stable against dynamical perturbations. Inclusion of the
electromagnetic self action into the equation of state slightly shrinks the
stability region but otherwise yields no qualitative difference. If the Witten
bosonic model represents a good approximation for more realistic string models,
then the cosmological vorton excess problem can only be solved by assuming
either that strings are formed at low energy scales or that some quantum
instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP
R-94/1
Skylab-EREP investigations of wetlands ecology
There are no author-identified significant results in this report
Skylab - EREP investigations of wetlands ecology
There are no author-identified significant results in this report
New concept in brazing metallic honeycomb panels
Aluminum oxide coating provides surface which will not be wetted by brazing alloy and which stops metallic diffusion welding of tooling materials to part being produced. This method eliminates loss of tooling materials and parts from braze wetting and allows fall-apart disassembly of tooling after brazing
Involution products in Coxeter groups
For W a Coxeter group, let
= {w ∈ W | w = xy where x, y ∈ W and x 2 = 1 = y 2}.
It is well known that if W is finite then W = . Suppose that w ∈ . Then the minimum value of ℓ(x) + ℓ(y) – ℓ(w), where x, y ∈ W with w = xy and x 2 = 1 = y 2, is called the excess of w (ℓ is the length function of W). The main result established here is that w is always W-conjugate to an element with excess equal to zero
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