21,581 research outputs found
Mitigation of common mode failures at multi-circuit line configurations by application of line arresters against back-flashovers
Due to the limited number of corridors multi circuit line configurations are often applied. These
overhead lines frequently consist of high towers that are subject to lightning strokes. In case of higher
current amplitudes and higher footing resistances due to bad earthing conditions back-flashovers are
caused leading to common mode failures and to severe outages.
The paper describes investigations performed by means of computer simulations to identify the towers
of a multi-circuit line consisting of voltage levels 380 kV, 220 kV and 110 kV that are endangered by
back-flashovers of the 110-kV double-circuit lines. The footing resistance of towers of the targeted
line section has been measured by an instrument at high-frequency. Influence of various factors on the
back-flashover over 110 kV insulator strings has been studied by means of EMTP-ATP simulations.
Different current waveforms of the lightning stroke have been used to represent the first stroke and
subsequent strokes. The towers are represented by the models described in [3], [8]. Available
flashover analysis methods [7], [8], [12], [13] like leader development method by Pigini et al and by
Motoyama, and voltage-time integration method by Kind have been applied.
The towers at which back-flashover is more likely to occur than at other towers are identified by the
time integral of voltage according to Kind. Various factors like tower footing impedance, tower surge
impedance and tower height are considered. Application of line a surge arrester is shown to be a
successful mitigation technique to reduce the back-flashover rate of those 110 kV lines. The lightning
overvoltage performance of surge arresters has been analyzed by means of digital simulations. Based
on the results of investigations line arresters were installed on the towers in question. Since the
installation no further common mode failure has been observed
A Theory of Errors in Quantum Measurement
It is common to model random errors in a classical measurement by the normal
(Gaussian) distribution, because of the central limit theorem. In the quantum
theory, the analogous hypothesis is that the matrix elements of the error in an
observable are distributed normally. We obtain the probability distribution
this implies for the outcome of a measurement, exactly for the case of 2x2
matrices and in the steepest descent approximation in general. Due to the
phenomenon of `level repulsion', the probability distributions obtained are
quite different from the Gaussian.Comment: Based on talk at "Spacetime and Fundamental Interactions: Quantum
Aspects" A conference to honor A. P. Balachandran's 65th Birthda
Abell 3627: A Nearby, X-ray Bright, and Massive Galaxy Cluster
The cluster A3627 was recently recognized to be a very massive, nearby
cluster in a galaxy survey close to the galactic plane. We are reporting on
ROSAT PSPC observations of this object which confirm that the cluster is indeed
very massive. The X-ray emission detected from the cluster extends over almost
1 degree in radius. The X-ray image is not spherically symmetric and shows
indications of an ongoing cluster merger. Due to the strong interstellar
absorption the spectral analysis and the gas temperature determination are
difficult. The data are consistent with an overall gas temperature in the range
5 to 10 keV. There are signs of temperature variations in the merger region. A
mass estimate based on the X-ray data yields values of \msu \ if extrapolated to the virial radius of Mpc. In
the ROSAT energy band (0.1 - 2.4 keV) the cluster emission yields a flux of
about erg s cm which makes A3627 the 6
brightest cluster in the ROSAT All Sky Survey. The cluster was missed in
earlier X-ray surveys because it was confused with a neighbouring X-ray bright,
galactic X-ray binary (1H1556-605). The large X-ray flux makes A3627 an
important target for future studies.Comment: 14 pages, Latex file, including aaspp.sty, 9 postscript figures and 1
table, accepted for publication by the Astrophysical Journa
Single spike solutions for strings on S2 and S3
We study solutions for rigidly rotating strings on a two sphere. Among them
we find two limiting cases that have a particular interest, one is the already
known giant magnon and the other we call the single spike solution. The
limiting behavior of this last solution is a string infinitely wrapped around
the equator. It differs from that solution by the existence of a single spike
of height theta that points toward the north pole.
We study its properties and compute its energy E and angular momentum J as a
function of theta. We further generalize the solution by adding one angular
momentum to obtain a solution on S3. We find a spin chain interpretations of
these results in terms of free fermions and the Hubbard model but the exact
relation with the same models derived from the field theory is not clear.Comment: LaTeX, 20 pages, 3 figures. v2: Refs adde
The δ-Opioid Receptor Affects Epidermal Homeostasis via ERK-Dependent Inhibition of Transcription Factor POU2F3.
Neuropeptides and their receptors are present in human skin, and their importance for cutaneous homeostasis and during wound healing is increasingly appreciated. However, there is currently a lack of understanding of the molecular mechanisms by which their signaling modulates keratinocyte function. Here, we show that δ-opioid receptor (DOPr) activation inhibits proliferation of human keratinocytes, resulting in decreased epidermal thickness in an organotypic skin model. DOPr signaling markedly delayed induction of keratin intermediate filament (KRT10) during in vitro differentiation and abolished its induction in the organotypic skin model. This was accompanied by deregulation of involucrin (IVL), loricrin, and filaggrin. Analysis of the transcription factor POU2F3, which is involved in regulation of KRT10, IVL, and profilaggrin expression, revealed a DOPr-mediated extracellular signal-regulated kinase (ERK)-dependent downregulation of this factor. We propose that DOPr signaling specifically activates the ERK 1/2 mitogen-activated protein kinase pathway to regulate keratinocyte functions. Complementing our earlier studies in DOPr-deficient mice, these data suggest that DOPr activation in human keratinocytes profoundly influences epidermal morphogenesis and homeostasis
3C 295, a cluster and its cooling flow at z=0.46
We present ROSAT HRI data of the distant and X-ray luminous (L_x(bol)=2.6^
{+0.4}_{-0.2} 10^{45}erg/sec) cluster of galaxies 3C 295. We fit both a
one-dimensional and a two-dimensional isothermal beta-model to the data, the
latter one taking into account the effects of the point spread function (PSF).
For the error analysis of the parameters of the two-dimensional model we
introduce a Monte-Carlo technique. Applying a substructure analysis, by
subtracting a cluster model from the data, we find no evidence for a merger,
but we see a decrement in emission South-East of the center of the cluster,
which might be due to absorption. We confirm previous results by Henry &
Henriksen(1986) that 3C 295 hosts a cooling flow. The equations for the simple
and idealized cooling flow analysis presented here are solely based on the
isothermal beta-model, which fits the data very well, including the center of
the cluster. We determine a cooling flow radius of 60-120kpc and mass accretion
rates of dot{M}=400-900 Msun/y, depending on the applied model and temperature
profile. We also investigate the effects of the ROSAT PSF on our estimate of
dot{M}, which tends to lead to a small overestimate of this quantity if not
taken into account. This increase of dot{M} (10-25%) can be explained by a
shallower gravitational potential inferred by the broader overall profile
caused by the PSF, which diminishes the efficiency of mass accretion. We also
determine the total mass of the cluster using the hydrostatic approach. At a
radius of 2.1 Mpc, we estimate the total mass of the cluster (M{tot}) to be
(9.2 +/- 2.7) 10^{14}Msun. For the gas to total mass ratio we get M{gas}/M{tot}
=0.17-0.31, in very good agreement with the results for other clusters of
galaxies, giving strong evidence for a low density universe.Comment: 26 pages, 7 figures, accepted for publication in Ap
An Alternative Parameterization of R-matrix Theory
An alternative parameterization of R-matrix theory is presented which is
mathematically equivalent to the standard approach, but possesses features
which simplify the fitting of experimental data. In particular there are no
level shifts and no boundary-condition constants which allows the positions and
partial widths of an arbitrary number levels to be easily fixed in an analysis.
These alternative parameters can be converted to standard R-matrix parameters
by a straightforward matrix diagonalization procedure. In addition it is
possible to express the collision matrix directly in terms of the alternative
parameters.Comment: 8 pages; accepted for publication in Phys. Rev. C; expanded Sec. IV,
added Sec. VI, added Appendix, corrected typo
Magnetoconductance switching in an array of oval quantum dots
Employing oval shaped quantum billiards connected by quantum wires as the
building blocks of a linear quantum dot array, we calculate the ballistic
magnetoconductance in the linear response regime. Optimizing the geometry of
the billiards, we aim at a maximal finite- over zero-field ratio of the
magnetoconductance. This switching effect arises from a relative phase change
of scattering states in the oval quantum dot through the applied magnetic
field, which lifts a suppression of the transmission characteristic for a
certain range of geometry parameters. It is shown that a sustainable switching
ratio is reached for a very low field strength, which is multiplied by
connecting only a second dot to the single one. The impact of disorder is
addressed in the form of remote impurity scattering, which poses a temperature
dependent lower bound for the switching ratio, showing that this effect should
be readily observable in experiments.Comment: 11 pages, 8 figure
Classical, quantum and total correlations
We discuss the problem of separating consistently the total correlations in a
bipartite quantum state into a quantum and a purely classical part. A measure
of classical correlations is proposed and its properties are explored.Comment: 10 pages, 3 figure
Weak Values and Continuous-Variable Entanglement Concentration
We demonstrate a general weak measurement model which allows Gaussian
preserving entanglement concentration of the two mode squeezed vacuum. The
power of this simple and elegant protocol is through the constraints it places
on possible ancilla states and measurement strategies that will allow
entanglement concentration. In particular, it is shown how previously
discovered protocols of this kind emerge as special examples of the general
model described here. Finally, as evidence of its utility, we use it to provide
another novel example of such a protocol.Comment: 4 pages, 1 figure, Final version to appear in Phys. Rev.
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