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Charge distribution and electroluminescence in cross-linked polyethylene under dc field
The intent of this paper is to cross-correlate the information obtained by space charge distribution analysis and electroluminescence (EL) detection in cross-linked polyethylene samples submitted to dc fields, with the objective to make a link between space charge phenomena and energy release as revealed by the detection of visible photons. Space charge measurements carried out at different field levels by the pulsed electro-acoustic method show the presence of a low-field threshold, close to 15-20 kV mm-1, above which considerable space charge begins to accumulate in the insulation. Charges are seen to cross the insulation thickness through a packet-like behaviour at higher fields, starting at about 60-70 kV mm-1. EL measurements show the existence of two distinct thresholds, one related to the continuous excitation of EL under voltage, the other being transient EL detected upon specimen short circuit. The former occurs at values of field corresponding to charge packet formation and the latter to the onset of space charge accumulation. The correspondence between pertinent values of the electric field obtained through space charge and EL analyses provides support for the existence of degradation thresholds in insulating materials. Special emphasis is given to the relationship between charge packet formation and propagation, and EL. Although the two phenomena are observed in the same field range, it is found that the onset of continuous EL follows the formation at the electrodes of positive and negative space charge regions that extend into the bulk prior to the propagation of charge packets. Charge recombination appears to be the excitation process of EL since oppositely charged domains meet in the material bulk. To gain an insight into specific light-excitation processes associated with charge packet propagation, EL has been recorded for several hours under fields at which charge packet dynamics were evidenced. It is shown that current and luminescence oscillations are detected during charge packet propagation, and that they are in phase. The mechanisms underlying EL and charge packets are further considered on the basis of these results
Trafficking
In cities the world over we are able to determine stability in daily existence, to identify with our social spaces, because modes of transport have become essential components of subjective autonomy. But would it not be just as accurate to say that in transit modern life puts the self in abeyance? I argue that the ways we allow ourselves to be moved around in ‘traffic space’ creates a passivity that renders almost invisible the complex mechanics of movement, which we only become alert to at the moment of breakdown, precisely when they become a threat to autonomy. Our trafficking, I conclude, has an almost narcotic effect, rendering us immobile against the continual movements that constitute urban life, one that also magnifies out of all proportion the accidents or aberrations that sometimes disturb our traffic space, making it seem as if we may easily descend into an uncontrollable chaos
Radioscience simulations in General Relativity and in alternative theories of gravity
In this communication, we focus on the possibility to test GR with
radioscience experiments. We present a new software that in a first step
simulates the Range/Doppler signals directly from the space time metric (thus
in GR and in alternative theories of gravity). In a second step, a
least-squares fit of the involved parameters is performed in GR. This software
allows one to get the order of magnitude and the signature of the modifications
induced by an alternative theory of gravity on radioscience signals. As
examples, we present some simulations for the Cassini mission in
Post-Einsteinian gravity and with the MOND External Field Effect.Comment: 4 pages; Proceedings of "Les Rencontres de Moriond 2011 - Gravitation
session
Heavy ion irradiation of crystalline water ice
Under cosmic irradiation, the interstellar water ice mantles evolve towards a
compact amorphous state. Crystalline ice amorphisation was previously monitored
mainly in the keV to hundreds of keV ion energies. We experimentally
investigate heavy ion irradiation amorphisation of crystalline ice, at high
energies closer to true cosmic rays, and explore the water-ice sputtering
yield. We irradiated thin crystalline ice films with MeV to GeV swift ion
beams, produced at the GANIL accelerator. The ice infrared spectral evolution
as a function of fluence is monitored with in-situ infrared spectroscopy
(induced amorphisation of the initial crystalline state into a compact
amorphous phase). The crystalline ice amorphisation cross-section is measured
in the high electronic stopping-power range for different temperatures. At
large fluence, the ice sputtering is measured on the infrared spectra, and the
fitted sputtering-yield dependence, combined with previous measurements, is
quadratic over three decades of electronic stopping power. The final state of
cosmic ray irradiation for porous amorphous and crystalline ice, as monitored
by infrared spectroscopy, is the same, but with a large difference in
cross-section, hence in time scale in an astrophysical context. The cosmic ray
water-ice sputtering rates compete with the UV photodesorption yields reported
in the literature. The prevalence of direct cosmic ray sputtering over
cosmic-ray induced photons photodesorption may be particularly true for ices
strongly bonded to the ice mantles surfaces, such as hydrogen-bonded ice
structures or more generally the so-called polar ices.Comment: 22pages, 11 figures, accepted in A&
Determination of the branching ratios and
Improved branching ratios were measured for the decay in a
neutral beam at the CERN SPS with the NA31 detector: and .
From the first number an upper limit for and transitions in neutral kaon decay is derived. Using older results for the
Ke3/K3 fraction, the 3 branching ratio is found to be , about a factor three more
precise than from previous experiments
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