9,770 research outputs found
3D Simulation of Partial Discharge in High Voltage Power Networks
Open accessPartial discharge (PD) events arise inside power cables due to defects of cableâs insulation material, characterized by a lower electrical breakdown strength than the surrounding dielectric material. These electrical discharges cause signals to propagate along the cable, manifesting as noise phenomena. More significantly, they contribute to insulation degradation and can produce a disruptive effect with a consequent interruption of power network operation. PD events are, therefore, one of the best âearly warningâ indicators of insulation degradation and, for this reason, the modeling and studying of such phenomena, together with the development of on-line PDs location methods, are important topics for network integrity assessment, and to define methods to improve the power networksâ Electricity Security. This paper presents a 3D model of PD events inside a void in epoxy-resin insulation cables for High Voltage (HV) power networks. The 3D model has been developed using the High Frequency (HF) Solver of CST Studio SuiteÂź software. PD events of a few ”s duration have been modelled and analyzed. The PD behavior has been investigated using varying electrical stress. A first study of the PD signal propagation in a power network is described
Selection of Dominant Characteristic Modes
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The theory of characteristic modes is a popular
physics based deterministic approach which has found several recent
applications in the fields of radiator design, electromagnetic
interference modelling and radiated emission analysis. The modal
theory is based on the approximation of the total induced current
in an electromagnetic structure in terms of a weighted sum of
multiple characteristic current modes. The resultant outgoing
field is also a weighted summation of the characteristic field
patterns. Henceforth, a proper modal measure is an essential
requirement to identify the modes which play a dominant role
for a frequency of interest. The existing literature of significance
measures restricts itself for ideal lossless structures only. This
paper explores the pros and cons of the existing measures and
correspondingly suggests suitable alternatives for both radiating
and scattering applications. An example is presented in order
to illustrate the proposed modal method for approximating the
shielding response of a slotted geometry
The Caustic Ring Model of the Milky Way Halo
We present a proposal for the full phase space distribution of the Milky Way
halo. The model is axially and reflection symmetric and its time evolution is
self-similar. It describes the halo as a set of discrete dark matter flows with
stated densities and velocity vectors everywhere. We first discuss the general
conditions under which the time evolution of a cold collisionless
self-gravitating fluid is self-similar, and show that symmetry is not necessary
for self-similarity. When spherical symmetry is imposed, the model is the same
as described by Fillmore and Goldreich, and by Bertschinger, twenty-three years
ago. The spherically symmetric model depends on one dimensionless parameter
and two dimensionful parameters. We set = 0.3, a value
consistent with the slope of the power spectrum of density perturbations on
galactic scales. The dimensionful parameters are determined by the Galactic
rotation velocity (220 km/s) at the position of the Sun and by the age of the
Galaxy (13.7 Gyr). The properties of the outer caustics are derived in the
spherically symmetric model. The structure of the inner halo depends on the
angular momentum distribution of the dark matter particles. We assume that
distribution to be axial and reflection symmetric, and dominated by net overall
rotation. The inner caustics are rings whose radii are determined in terms of a
single additional parameter . We summarize the observational
evidence in support of the model. The evidence is consistent with
= 0.18 in Concordance Cosmology, equivalent to = 0.26 in
Einstein - de Sitter cosmology. We give formulas to estimate the flow densities
and velocity vectors anywhere in the Milky Way halo. The properties of the
first forty flows at the location of the Earth are listed.Comment: 35 pages, 6 figure
Yukawa Scalar Self-Mass on a Conformally Flat Background
We compute the one loop self-mass-squared of a massless, minimally coupled
scalar which is Yukawa-coupled to a massless Dirac fermion in a general
conformally flat background. Dimensional regularization is employed and a fully
renormalized result is obtained. For the special case of a locally de Sitter
background our result is manifestly de Sitter invariant. By solving the
effective field equations we show that the scalar mode functions acquire no
significant one loop corrections. In particular, the phenomenon of
super-adiabatic amplification is not affected. One consequence is that the
scalar-catalyzed production of fermions during inflation should not be reduced
by changes in the scalar sector before it has time to go to completion.Comment: 23 pages, LaTeX 2epsilon, 3 figures (uses axodraw
Large deviations for a damped telegraph process
In this paper we consider a slight generalization of the damped telegraph
process in Di Crescenzo and Martinucci (2010). We prove a large deviation
principle for this process and an asymptotic result for its level crossing
probabilities (as the level goes to infinity). Finally we compare our results
with the analogous well-known results for the standard telegraph process
What role can growth curves play in forecasting with particular reference technology strategy?
This paper is the output from a collaborative research project with the Department of EngineeringPreviously, papers have been presented to the IWCS which have looked at the use of a limited set of equations to help predict the path of technology. The results were promising and indicated that a set of biologically inspired equations providing analogies for technology push, consumer pull and âme tooâ type self fuelling growth had potential in predicting (a) the maximum speed etc. of a technology or maximum size of a market (b) the point at which a replacement technology should be invested in (c) understanding the market dynamics driving a technology. Currently an interview-based survey is underway to further investigate this hypothesis. This paper will present the preliminary results of this survey
Fully automated segmentation and tracking of the intima media thickness in ultrasound video sequences of the common carotid artery
AbstractâThe robust identification and measurement of the intima media thickness (IMT) has a high clinical relevance because it represents one of the most precise predictors used in the assessment of potential future cardiovascular events. To facilitate the analysis of arterial wall thickening in serial clinical investigations, in this paper we have developed a novel fully automatic algorithm for the segmentation, measurement, and tracking of the intima media complex (IMC) in B-mode ultrasound video sequences. The proposed algorithm entails a two-stage image analysis process that initially addresses the segmentation of the IMC in the first frame of the ultrasound video sequence using a model-based approach; in the second step, a novel customized tracking procedure is applied to robustly detect the IMC in the subsequent frames. For the video tracking procedure, we introduce a spatially coherent algorithm called adaptive normalized correlation that prevents the tracking process from converging to wrong arterial interfaces. This represents the main contribution of this paper and was developed to deal with inconsistencies in the appearance of the IMC over the cardiac cycle. The quantitative evaluation has been carried out on 40 ultrasound video sequences of the common carotid artery (CCA) by comparing the results returned by the developed algorithm with respect to ground truth data that has been manually annotated by clinical experts. The measured IMTmean ± standard deviation recorded by the proposed algorithm is 0.60 mm ± 0.10, with a mean coefficient of variation (CV) of 2.05%, whereas the corresponding result obtained for the manually annotated ground truth data is 0.60 mm ± 0.11 with a mean CV equal to 5.60%. The numerical results reported in this paper indicate that the proposed algorithm is able to correctly segment and track the IMC in ultrasound CCA video sequences, and we were encouraged by the stability of our technique when applied to data captured under different imaging conditions. Future clinical studies will focus on the evaluation of patients that are affected by advanced cardiovascular conditions such as focal thickening and arterial plaques
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