9,709 research outputs found
Scaling of the Thue-Morse diffraction measure
We revisit the well-known and much studied Riesz product representation of the Thue-Morse diffraction measure, which is also the maximal spectral measure for the corresponding dynamical spectrum in the complement of the pure point part. The known scaling relations are summarised, and some new findings are explained
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Influence of semicon shields on the dielectric loss of XLPE cables
Dielectric response measurement techniques in both time and frequency domains are studied in order to measure the dielectric loss of XLPE cables, which have very low losses. A high sensitivity transformer ratio bridge system, which can measure loss tangents as low as 10-5, has been developed with the ability to measure these cables. A tuned amplifier was designed to help to extend the frequency range from 200Hz to 20kHz. Different model cables from Borealis AB with different semiconducting materials have been measured in the temperature range 15⁰C to 120⁰C. It is found that the semiconducting layers dominate the dielectric loss in the insulation system of the XLPE cables, when the outer semicon is treated as measuring electrode. In this case, steadily increasing dielectric loss has been measured at higher frequencies. The resistivity of the semiconducting materials was measured, which confirmed that the increasing slope is due to the semiconducting layers. After using conductive tapes to wrap the cable samples, monotonically decreasing losses were measured, corresponding to the actual dielectric frequency response of the XLPE cables. It is concluded that the axial resistance of semiconducting shields have a substantial influence on the dielectric loss of XLPE cables, especially for dielectric response in high frequency range. A device on measuring the loss of such cables is presented
Mass-metallicity relation from z=5 to the present: Evidence for a transition in the mode of galaxy growth at z=2.6 due to the end of sustained primordial gas infall
We analyze the redshift evolution of the mass-metallicity relation in a
sample of 110 Damped Ly absorbers spanning the redshift range
and find that the zero-point of the correlation changes
significantly with redshift. The evolution is such that the zero-point is
constant at the early phases of galaxy growth (i.e. no evolution) but then
features a sharp break at with a rapid incline towards lower
redshifts such that damped absorbers of identical masses are more metal rich at
later times than earlier. The slope of this mass metallicity correlation
evolution is dex per unit redshift.
We compare this result to similar studies of the redshift evolution of
emission selected galaxy samples and find a remarkable agreement with the slope
of the evolution of galaxies of stellar mass log.
This allows us to form an observational tie between damped absorbers and
galaxies seen in emission.
We use results from simulations to infer the virial mass of the dark matter
halo of a typical DLA galaxy and find a ratio .
We compare our results to those of several other studies that have reported
strong transition-like events at redshifts around and argue that
all those observations can be understood as the consequence of a transition
from a situation where galaxies were fed more unprocessed infalling gas than
they could easily consume to one where they suddenly become infall starved and
turn to mainly processing, or re-processing, of previously acquired gas.Comment: 8 pages, 5 figures, accepted for publication in MNRA
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The measurement of very low conductivity and dielectric loss in XLPE cables: A possible method to detect degradation due to thermal aging
The dielectric response of crosslinked polyethylene (XLPE) insulated, miniature power cables, extruded with inner and outer semicons, was measured over the frequency range 10-4 to 104 Hz at temperatures from 20 to 100 °C. A dielectric spectrometer was used for the frequency range 10-4 to 10-2 Hz. A bespoke noise-free power supply was constructed and used to measure the dc conductivity and, using a Fourier transform technique, it was also used to measure the very low dielectric tanδ losses encountered at frequencies of 1 to 100 Hz. Tanδ measurements of <;10-5 were found in this frequency range and attributed to a β-mode dielectric relaxation lying above 100 Hz due to motion of chain segments in the amorphous region and an β-mode relaxation lying below 1 Hz window due to twists of chains in the crystal lamellae. The dc conductivity measurements were consistent with those of the dielectric spectrometer and indicate lower dc conductivities in vacuum degassed cables than have been previously reported for XLPE (less than 10-17 S.m-1). The conduction process is thermally activated with an activation energy of approximately 1.1 eV. Higher conductivities were found for non-degassed cables. A transformer ratio bridge was used for measurements in the range 1 to 10 kHz; loss in this region was shown to be due to the series resistance of the semicon layers. Thermal ageing of the cables at 135 °C for 60 days caused significant increases in the conductivity and tanδ and it is considered that such measurements may be a sensitive way of measuring electrical degradation due to thermal aging
Timelike self-similar spherically symmetric perfect-fluid models
Einstein's field equations for timelike self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure
Three-dimensional N=8 conformal supergravity and its coupling to BLG M2-branes
This paper is concerned with the problem of coupling the N=8 superconformal
Bagger-Lambert-Gustavsson (BLG) theory to N=8 conformal supergravity in three
dimensions. We start by constructing the on-shell N=8 conformal supergravity in
three dimensions consisting of a Chern-Simons type term for each of the gauge
fields: the spin connection, the SO(8) R-symmetry gauge field and the spin 3/2
Rarita-Schwinger (gravitino) field. We then proceed to couple this theory to
the BLG theory. The final theory should have the same physical content, i.e.,
degrees of freedom, as the ordinary BLG theory. We discuss briefly the
properties of this "topologically gauged" BLG theory and why this theory may be
useful.Comment: 20 pages, v2: references and comments added, presentation in section
3.2 extended. v3: misprints and a sign error corrected, version published in
JHE
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