11,095 research outputs found
Space Charge Behaviour in Oil-Paper Insulation with Different Aging Condition
Oil-paper insulation system is widely used in power transformers and cables. The dielectric properties of oilpaper insulation play an important role in the reliable operation of power equipment. Oil-paper insulation degrades under a combined stress of thermal (the most important factor), electrical, mechanical, and chemical stresses during routine operations, which has great effect on the dielectric properties of oil-paper insulation [1]. Space charge in oil-paper insulation has a close relation to its electrical performance [1]. In this paper, space charge behaviour of oil-paper insulation sample with three different ageing conditions (aged for 0, 35 and 77 days) was investigated using the pulsed electroacoustic (PEA) technique. The influence of aging on the space charge dynamics behaviour was analysed. Results show that aging has great effect on the space charge dynamics of oil-paper insulation. The homocharge injection takes place under all three aging conditions above. Positive charges tend to accumulate in the sample, and increase with the oil-paper insulation sample deterioration. The time to achieve the maximum injection charge density is 30s, 2min and 10min for oil-paper insulation sample aged for 0, 35 and 77 days, respectively. The maximum charge density injected in the sample aged for 77 days is more than two times larger than the initial sample. In addition, the charge decay speed becomes much slower with the aging time increase. There is an exponential relationship between the total charge amount and the decay time. The decay time constant ? increases with the increasing deterioration condition of the oil-paper insulation sample. The ? value may be used to reflect the aging status of oil-paper insulation
Scaling Relations for Galaxies Prior to Reionization
The first galaxies in the Universe are the building blocks of all observed
galaxies. We present scaling relations for galaxies forming at redshifts when reionization is just beginning. We utilize the ``Rarepeak'
cosmological radiation hydrodynamics simulation that captures the complete star
formation history in over 3,300 galaxies, starting with massive Population III
stars that form in dark matter halos as small as ~. We make
various correlations between the bulk halo quantities, such as virial, gas, and
stellar masses and metallicities and their respective accretion rates,
quantifying a variety of properties of the first galaxies up to halo masses of
. Galaxy formation is not solely relegated to atomic cooling
halos with virial temperatures greater than K, where we find a dichotomy
in galaxy properties between halos above and below this critical mass scale.
Halos below the atomic cooling limit have a stellar mass -- halo mass
relationship .
We find a non-monotonic relationship between metallicity and halo mass for the
smallest galaxies. Their initial star formation events enrich the interstellar
medium and subsequent star formation to a median of and
, respectively, in halos of total mass that
is then diluted by metal-poor inflows, well beyond Population III
pre-enrichment levels of . The scaling relations presented
here can be employed in models of reionization, galaxy formation and chemical
evolution in order to consider these galaxies forming prior to reionization.Comment: 10 pages, 10 figures. Accepted to Ap
Suspension of the fiber mode-cleaner launcher and measurement of the high extinction-ratio (10^{-9}) ellipsometer for the Q & A experiment
The Q & A experiment, first proposed and started in 1994, provides a feasible
way of exploring the quantum vacuum through the detection of vacuum
birefringence effect generated by QED loop diagram and the detection of the
polarization rotation effect generated by photon-interacting (pseudo-)scalar
particles. Three main parts of the experiment are: (1) Optics System (including
associated Electronic System) based on a suspended 3.5-m high finesse
Fabry-Perot cavity, (2) Ellipsometer using ultra-high extinction-ratio
polarizer and analyzer, and (3) Magnetic Field Modulation System for generating
the birefringence and the polarization rotation effect. In 2002, the Q & A
experiment achieved the Phase I sensitivity goal. During Phase II, we set (i)
to improve the control system of the cavity mirrors for suppressing the
relative motion noise, (ii) to enhance the birefringence signal by setting-up a
60-cm long 2.3 T transverse permanent magnet rotatable to 10 rev/s, (iii) to
reduce geometrical noise by inserting a polarization-maintaining optical fiber
(PM fiber) as a mode cleaner, and (iv) to use ultra-high extinction-ratio
(10^{-9}) polarizer and analyzer for ellipsometry. Here we report on (iii) &
(iv); specifically, we present the properties of the PM-fiber mode-cleaner, the
transfer function of its suspension system, and the result of our measurement
of high extinction-ratio polarizer and analyzer.Comment: 8 pages, 6 figures, presented in the 6th Edoardo Amaldi Conference on
Gravitational Waves, Okinawa, Japan, June 2005, and accepted by "Journal of
Physics: Conference Series". Modifications from version 2 were made based on
the referees' comments on figures. Ref. [31] were update
A Systematic Analysis of Fe II Emission in Quasars: Evidence for Inflow to the Central Black Hole
Broad Fe II emission is a prominent feature of the optical and ultraviolet
spectra of quasars. We report on a systematical investigation of optical Fe II
emission in a large sample of 4037 z < 0.8 quasars selected from the Sloan
Digital Sky Survey. We have developed and tested a detailed line-fitting
technique, taking into account the complex continuum and narrow and broad
emission-line spectrum. Our primary goal is to quantify the velocity broadening
and velocity shift of the Fe II spectrum in order to constrain the location of
the Fe II-emitting region and its relation to the broad-line region. We find
that the majority of quasars show Fe II emission that is redshifted, typically
by ~ 400 km/s but up to 2000 km/s, with respect to the systemic velocity of the
narrow-line region or of the conventional broad-line region as traced by the
Hbeta line. Moreover, the line width of Fe II is significantly narrower than
that of the broad component of Hbeta. We show that the magnitude of the Fe II
redshift correlates inversely with the Eddington ratio, and that there is a
tendency for sources with redshifted Fe II emission to show red asymmetry in
the Hbeta line. These characteristics strongly suggest that Fe II originates
from a location different from, and most likely exterior to, the region that
produces most of Hbeta. The Fe II-emitting zone traces a portion of the
broad-line region of intermediate velocities whose dynamics may be dominated by
infall.Comment: 20 pages, 14 figures, accepted for publication in Ap
Density distributions for trapped one-dimensional spinor gases
We numerically evaluate the density distribution of a spin-1 bosonic
condensate in its ground state within a modifed Gross-Pitaevskii theory, which
is obtained by the combination of the exact solution of the corresponding
integrable model with the local density approximation. Our study reveals that
atoms in the m_F = 0 state are almost completely suppressed for the
anti-ferromagnetic interactions in both weakly and strongly interacting
regimes, whereas all three components remain non-vanishing for ferromagnetic
interactions. Specially, when the system is in the Tonks-Girardeau (TG) regime,
obvious Fermi-like distribution emerges for each component. We also discuss the
possible deviation of the spatial distribution from the Fermi-like distribution
when the spin-spin interaction is strong enough.Comment: 6 pages, 3 figures, version to be published in Phys. Rev.
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