541 research outputs found
Method for rating power cables buried in surface troughs
An alternative method is detailed by which the ambient temperature parameter as applied to the calculation of ratings of cables buried in surface trough installations can be determined. Improvement in the accuracy of cable rating calculations will allow greater utilisation of the cable asset and assist for example in the planning of system outages for maintenance work. The proposed model calculates the temperature at the cable burial depth based on measurements of solar radiation, windspeed and air temperature. The model is based on physical laws rather than empirical approaches that have been shown to be generally conservative in application. Results based on weather data monitored over a two-year period show that the ambient temperature of the soil at cable depth can be accurately determined and the model provides a significant improvement on existing methods
The boundary layer of Mars: Fluxes, stability, turbulent spectra and growth of the mixed layer
Comment on "Long-range electrostatic interactions between like-charged colloids: Steric and confinement effects"
In a recent study [Phys. Rev. E 60, 6530 (1999)], Trizac and Raimbault showed
that the effective pair interaction between like charged colloids immersed in a
cylindrically confined electrolyte remains repulsive even when the size of the
micro-ions or the finite longitudinal extension of the confining cylinder are
taken into account. Contrary to their claim, we argue that the case of finite
longitudinal confinement doesn't always generate repulsive interactions and to
illustrate this point we also provide a simple example.Comment: 3 pages, 1 figure. Accepted for publication in Phys. Rev. E 200
Two-dimensional negative donors in magnetic fields
A finite-difference solution of the Schroedinger equation for negative donor
centers D^- in two dimensions is presented. Our approach is of exact nature and
allows us to resolve a discrepancy in the literature on the ground state of a
negative donor. Detailed calculations of the energies for a number of states
show that for field strengths less than \gamma=0.117 a.u. the donor possesses
one bound state, for 0.117<\gamma<1.68 a.u. there exist two bound states and
for field strengths \gamma>1.68 a.u. the system possesses three bound states.
Further relevant characteristics of negative donors in magnetic fields are
provided.Comment: 7 pages, 1 figur
Non-Standard Intersections of S-Branes in D=11 Supergravity
We construct new intersecting S-brane solutions in 11-dimensional
supergravity which do not have supersymmetric analogs. They are obtained by
letting brane charges to be proportional to each other. Solutions fall into two
categories with respect to whether there is a non-diagonal term to be cancelled
in the field equations or not. In each case we show that they can be
constructed by using a simple set of rules which is similar to the harmonic
function rule of the usual static p-branes. Furthermore, we study an
intersection where the Chern-Simons term makes a non-zero contribution to the
field equations. We show that this configuration has a singularity like other
S-branes.Comment: 13 pages, 2 figures;v2 Section 2.2 is improved with new examples,
references added;v3 typos correcte
The Final Fate of the Rolling Tachyon
We propose an alternative interpretation of the boundary state for the
rolling tachyon, which may depict the time evolution of unstable D-branes in
string theory. Splitting the string variable in the temporal direction into the
classical part, which we may call "time" and the quantum one, we observe the
time dependent behaviour of the boundary. Using the fermion representation of
the rolling tachyon boundary state, we show that the boundary state correctly
describes the time-dependent decay process of the unstable D-brane into a
S-brane at the classical level.Comment: 9 pages, revte
Thermodynamics of Black Holes in Two (and Higher) Dimensions
A comprehensive treatment of black hole thermodynamics in two-dimensional
dilaton gravity is presented. We derive an improved action for these theories
and construct the Euclidean path integral. An essentially unique boundary
counterterm renders the improved action finite on-shell, and its variational
properties guarantee that the path integral has a well-defined semi-classical
limit. We give a detailed discussion of the canonical ensemble described by the
Euclidean partition function, and examine various issues related to stability.
Numerous examples are provided, including black hole backgrounds that appear in
two dimensional solutions of string theory. We show that the Exact String Black
Hole is one of the rare cases that admits a consistent thermodynamics without
the need for an external thermal reservoir. Our approach can also be applied to
certain higher-dimensional black holes, such as Schwarzschild-AdS,
Reissner-Nordstrom, and BTZ.Comment: 63 pages, 3 pdf figures, v2: added reference
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