315,605 research outputs found
Impact of mechanical deformation on space charge in XLPE
In this paper we report the effect of mechanical deformation on space charge dynamics in crosslinked polyethylene. Thin films were peeled from a 66 kV commercial XLPE cable. Space charge measurements under dc electric fields have been monitored using the pulsed electroacoustic (PEA) technique. It has been found that charge dynamics in deformed XLPE are different from that from undeformed XLPE at lower voltages. At low applied electric field, space charge is dominated by heterocharge in the deformed XLPE while homocharge governs charge formation in undeformed XLPE. However, at high electric field, there is no significant difference between them. Space charge is dominated by homocharge in both deformed and undeformed XLPE. The results indicated that through deformation, molecular chains rearrange so small molecules such as crosslinking by-products, initially being trapped, can be released. Under the influence of the applied electric field they can be ionised to form heterocharge in the sample
Supercurrent conservation in the lattice Wess-Zumino model with Ginsparg-Wilson fermions
We study supercurrent conservation for the four-dimensional Wess-Zumino model
formulated on the lattice. The formulation is one that has been discussed
several times, and uses Ginsparg-Wilson fermions of the overlap (Neuberger)
variety, together with an auxiliary fermion (plus superpartners), such that a
lattice version of U(1)_R symmetry is exactly preserved in the limit of
vanishing bare mass. We show that the almost naive supercurrent is conserved at
one loop. By contrast we find that this is not true for Wilson fermions and a
canonical scalar action. We provide nonperturbative evidence for the
nonconservation of the supercurrent in Monte Carlo simulations.Comment: 19 pages, 5 figure
Convergence of the largest eigenvalue of normalized sample covariance matrices when p and n both tend to infinity with their ratio converging to zero
Let
where 's are independent and identically distributed (i.i.d.) random
variables with and . It is showed
that the largest eigenvalue of the random matrix
tends to 1 almost surely as with
.Comment: Published in at http://dx.doi.org/10.3150/11-BEJ381 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
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"Mirror Image" space charge distribution in XLPE power cable under opposite stressing voltage polarity
The paper presents the research on space charge distribution under different polarities in full size cross-linked polyethylene power cables using the pulsed electro-acoustic technique. Under both positive and negative voltage space charge distributions possess about the same profiles but opposite polarities. Similar phenomenon had been reported previously in plaque samples and was termed as “mirror image effect”. By comparing the results among the cables treated (degassing) under different conditions, the paper concludes that the “mirror image” charge distribution is mainly attributed to bulk effect within the volume of the insulation, whilst the electron transfer by tunnelling through an electrode/insulator interface contribute to the generation of homo “mirror image” at the vicinity of the electrode
Effect of high resistive barrier on earthing system
Substation earthing provides a low impedance path and carries current into ground under normal and fault conditions without adversely affecting continuity of service. Under a fault condition, the ground voltage may rise to a level that may endanger the public outside the vicinity of the substation. In such a case a high resistive barrier can be inserted around the vicinity of the substation to reduce the surface potentials immediately beyond the barrier. In this paper the effect of barrier on the overall performance of the earthing system has been investigated experimentally and computationally based on an earthing system consisted of combined grid and rods in a water tank. The effect of the position and depth of the barrier to the resistance of the earthing system and surface potentials in and around the substation have been examined
Bound states of the Klein-Gordon equation for vector and scalar general Hulthen-type potentials in D-dimension
We solve the Klein-Gordon equation in any -dimension for the scalar and
vector general Hulth\'{e}n-type potentials with any by using an
approximation scheme for the centrifugal potential. Nikiforov-Uvarov method is
used in the calculations. We obtain the bound state energy eigenvalues and the
corresponding eigenfunctions of spin-zero particles in terms of Jacobi
polynomials. The eigenfunctions are physical and the energy eigenvalues are in
good agreement with those results obtained by other methods for D=1 and 3
dimensions. Our results are valid for value when and for any
value when and D=1 or 3. The % -wave () binding energies for
a particle of rest mass are calculated for the three lower-lying
states using pure vector and pure scalar potentials.Comment: 25 page
Laboratory photo-chemistry of pyrene clusters: an efficient way to form large PAHs
In this work, we study the photodissociation processes of small PAH clusters
(e.g., pyrene clusters). The experiments are carried out using a quadrupole ion
trap in combination with time-of-flight (QIT-TOF) mass spectrometry. The
results show that pyrene clusters are converted into larger PAHs under the
influence of a strong radiation field. Specifically, pyrene dimer cations
(e.g., [CHCH] or CH), will
photo-dehydrogenate and photo-isomerize to fully aromatic cations (PAHs) (e.g.,
CH) with laser irradiation. The structure of new formed PAHs
and the dissociation energy for these reaction pathways are investigated with
quantum chemical calculations. These studies provide a novel efficient
evolution routes for the formation of large PAHs in the interstellar medium
(ISM) in a bottom-up process that will counteract the top-down conversion of
large PAHs into rings and chains, and provide a reservoir of large PAHs that
can be converted into C and other fullerenes and large carbon cages
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